| 1. |
- Speakman, John R, et al.
(författare)
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Oxidative stress and life histories: unresolved issues and current needs.
- 2015
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 5:24, s. 745-757
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Tidskriftsartikel (refereegranskat)abstract
- Life-history theory concerns the trade-offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life-history trade-offs, but the details remain obscure. As life-history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life-history trade-offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life-history information is available, cannot generally be performed without compromising the aims of the studies that generated the life-history data. There is a need therefore for novel non-invasive measurements of multi-tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life-history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life-history trade-offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life-history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade-offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other.
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| 2. |
- Griffith, Simon C., et al.
(författare)
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Variation in reproductive success across captive populations: Methodological differences, potential biases and opportunities
- 2017
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Ingår i: Ethology. - : Wiley. - 1439-0310 .- 0179-1613. ; 123:1, s. 1-29
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Tidskriftsartikel (refereegranskat)abstract
- Our understanding of fundamental organismal biology has been disproportionately influenced by studies of a relatively small number of ‘model’ species extensively studied in captivity. Laboratory populations of model species are commonly subject to a number of forms of past and current selection that may affect experimental outcomes. Here, we examine these processes and their outcomes in one of the most widely used vertebrate species in the laboratory – the zebra finch (Taeniopygia guttata). This important model species is used for research across a broad range of fields, partly due to the ease with which it can be bred in captivity. However despite this perceived amenability, we demonstrate extensive variation in the success with which different laboratories and studies bred their subjects, and overall only 64% of all females that were given the opportunity, bred successfully in the laboratory. We identify and review several environmental, husbandry, life-history and behavioural factors that potentially contribute to this variation. The variation in reproductive success across individuals could lead to biases in experimental outcomes and drive some of the heterogeneity in research outcomes across studies. The zebra finch remains an excellent captive animal system and our aim is to sharpen the insight that future studies of this species can provide, both to our understanding of this species and also with respect to the reproduction of captive animals more widely. We hope to improve systematic reporting methods and that further investigation of the issues we raise will lead both to advances in our fundamental understanding of avian reproduction as well as to improvements in future welfare and experimental efficiency.
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| 3. |
- Ballen, Cissy, et al.
(författare)
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Net superoxide levels: steeper increase with activity in cooler female and hotter male lizards
- 2012
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 215:16, s. 731-735
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Tidskriftsartikel (refereegranskat)abstract
- Ectotherms increase their body temperature in response to ambient heat, thereby elevating their metabolic rate. An often inferred consequence of this is an overall upregulation of gene expression and energetic expenditure, and a concomitant increased production of reactive oxygen species (e.g. superoxide) and, perhaps, a shortened lifespan. However, recent work shows that this may be a superficial interpretation. For example, sometimes a reduced temperature may in fact trigger up-regulation of gene expression. We studied temperature and associated activity effects in male and female Australian painted dragon lizards (Ctenophorus pictus) by allowing the lizards to bask for 4 h versus 12 h, and scoring their associated activity (inactive versus active basking and foraging). As predicted, long-basking lizards (hereafter ‘hot’) showed heightened activity in both sexes, with a more pronounced effect in females. We then tested for sex-specific effects of basking treatment and activity levels on the increase in net levels of superoxide. In males, short-baskers (hereafter ‘cold’) had significantly more rapidly decreasing levels of superoxide per unit increasing activity than hot males. In females, however, superoxide levels increased faster with increasing activity in the cold than in the hot basking treatment, and females earlier in the ovarian cycle had lower superoxide levels than females closer to ovulation. In short, males and females differ in how their levels of reactive oxygen species change with temperature-triggered activity.
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| 4. |
- Ballen, Cissy, et al.
(författare)
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Predictors of telomere content in dragon lizards
- 2012
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Ingår i: Naturwissenschaften. - : Springer Science and Business Media LLC. - 1432-1904 .- 0028-1042. ; 99:8, s. 661-664
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Tidskriftsartikel (refereegranskat)abstract
- Telomeres shorten as a consequence of DNA replication, in particular in cells with low production of telomerase and perhaps in response to physiological stress from exposure to reactive oxygen species, such as superoxide. This process of telomere attrition is countered by innate antioxidation, such as via the production of superoxide dismutase. We studied the inheritance of telomere length in the Australian painted dragon lizard (Ctenophorus pictus) and the extent to which telomere length covaries with masscorrected maternal reproductive investment, which reflects the level of circulating yolk precursor and antioxidant, vitellogenin. Our predictors of offspring telomere length explained 72 % of telomere variation (including interstitial telomeres if such are present). Maternal telomere length and reproductive investment were positively influencing offspring telomere length in our analyses, whereas flow cytometry-estimated superoxide level was negatively impacting offspring telomere length. We suggest that the effects of superoxide on hatchling telomere shortening may be partly balanced by transgenerational effects of vitellogenin antioxidation.
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| 5. |
- Gómez-Blanco, David, et al.
(författare)
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Why and when should organisms elongate their telomeres? : Elaborations on the 'excess resources elongation' and 'last resort elongation' hypotheses
- 2023
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Ingår i: Ecology and Evolution. - 2045-7758. ; 13:12
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Tidskriftsartikel (refereegranskat)abstract
- Telomere length and telomere shortening are thought to be critical cellular attributes and processes that are related to an individual's life span and fitness. The general pattern across most taxa is that after birth telomere length gradually decreases with age. Telomere protection and restoration mechanisms are usually assumed to reduce the rate of shortening or at most keep telomere length constant. However, here we have compiled a list of 26 articles showing that there is an increasing number of studies reporting apparent elongation of telomeres (i.e., a net increase in TL from time t to time t+1 ) often in a considerable proportion of the individuals studied. Moreover, the few studies which have studied telomere elongation in detail show that increases in telomere length are unlikely to be due to measurement error alone. In this article, we argue that episodes of telomere elongation deserve more attention as they could reflect individual strategies to optimise life histories and maximise fitness, which may not be reflected in the overall telomere dynamics patterns. We propose that patterns of telomere (net) elongation may be partly determined by other factors than those causing telomere shortening, and therefore deserve analyses specifically targeted to investigate the occurrence of telomere elongation. We elaborate on two ecological hypotheses that have been proposed to explain patterns of telomere elongation (the 'excess resources elongation' and the 'last resort elongation' hypothesis) and we discuss the current evidence for (or against) these hypotheses and propose ways to test them.
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| 6. |
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| 7. |
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| 8. |
- Hasselquist, Dennis, et al.
(författare)
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The Accumulating Costs Hypothesis—to Better Understand Delayed “Hidden” Costs of Seemingly Mild Disease and Other Moderate Stressors
- 2021
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Mild diseases and moderate stressors are seemingly harmless and are therefore often assumed to have negligible impact on Darwinian fitness. Here we argue that the effects of “benign” parasites and other moderate stressors may have a greater impact on lifespan and other fitness traits than generally thought. We outline the “accumulating costs” hypothesis which proposes that moderate strains on the body caused by mild diseases and other moderate stressors that occur throughout life will result in small irreversible “somatic lesions” that initially are invisible (i.e., induce “hidden” costs). However, over time these somatic lesions accumulate until their summed effect reaches a critical point when cell senescence and malfunction begin to affect organ functionality and lead to the onset of degenerative diseases and aging. We briefly discuss three potential mechanisms through which the effects of moderate strains (e.g., mild diseases) could accumulate: Accelerated telomere shortening, loss of repetitious cell compartments and other uncorrected DNA damage in the genome. We suggest that telomere shortening may be a key candidate for further research with respect to the accumulating costs hypothesis. Telomeres can acquire lesions from moderate strains without immediate negative effects, lesions can be accumulated over time and lead to a critically short telomere length, which may eventually cause severe somatic malfunctioning, including aging. If effects of mild diseases, benign parasites and moderate stressors accrued throughout life can have severe delayed consequences, this might contribute to our understanding of life history strategies and trade-offs, and have important implications for medicine, including consideration of treatment therapies for mild (chronic) infections such as malaria.
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| 9. |
- Kaufman, Darrell, et al.
(författare)
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A global database of Holocene paleotemperature records
- 2020
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions. The data derive from lake sediment (51%), marine sediment (31%), peat (11%), glacier ice (3%), and other natural archives. The database contains 1319 records, including 157 from the Southern Hemisphere. The multi-proxy database comprises paleotemperature time series based on ecological assemblages, as well as biophysical and geochemical indicators that reflect mean annual or seasonal temperatures, as encoded in the database. This database can be used to reconstruct the spatiotemporal evolution of Holocene temperature at global to regional scales, and is publicly available in Linked Paleo Data (LiPD) format.
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| 10. |
- Nilsson, Johan, et al.
(författare)
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Long-lasting consequences of elevated yolk testosterone for metabolism in the zebra finch.
- 2011
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Ingår i: Physiological and Biochemical Zoology. - : University of Chicago Press. - 1522-2152 .- 1537-5293. ; 84:3, s. 287-291
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Resting metabolic rate is a common way of quantifying the cost of living in endothermic animals. The trait often makes up a substantial part of an animal's energy budget and can also be related to sustainable peak work rate as well as to daily energy expenditure. Studies have shown that metabolic rates are often heritable, but much of the variation seems to be caused by other factors (e.g., environmental and maternal effects). In a previous study, in ovo exposure to increased levels of testosterone induced metabolic costs early in life. It is, however, unknown whether in ovo androgens also have long-term effects on individual metabolic rates. In this study, we show that experimentally increased levels of in ovo testosterone in zebra finches (Taeniopygia guttata) result in a 7% higher resting metabolic rate when they are adults. This shows that maternally transferred hormones can induce long-term effects on metabolic demands and potentially influence variation in life-history strategies among offspring. Variation in maternal hormone transfer may also explain some of the large interindividual variation observed in metabolic rates.
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| 11. |
- Olsson, Mats, et al.
(författare)
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A significant component of ageing (DNA damage) is reflected in fading breeding colors: an experimental test using innate antioxidant mimetics in painted dragon lizards
- 2012
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Ingår i: Evolution. - : Wiley. - 1558-5646 .- 0014-3820. ; 66:8, s. 2475-2483
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Tidskriftsartikel (refereegranskat)abstract
- A decade ahead of their time, von Schantz et al. united sexual selection and free radical biology by identifying causal links between deep-rooted physiological processes that dictate resistance to toxic waste from oxidative metabolism (reactive oxygen species, ROS), and phenotypic traits, such as ornaments. Ten years later, these ideas have still only been tested with indirect estimates of free radical levels (oxidative stress) subsequent to the action of innate and dietary antioxidants. Here, we measure net superoxide (a selection pressure for antioxidant production) and experimentally manipulate superoxide antioxidation using a synthetic mimetic of superoxide dismutase (SOD), Eukarion 134 (EUK). We then measure the toxic effect of superoxide in terms of DNA erosion and concomitant loss of male breeding coloration in the lizard, Ctenophorus pictus. Control males suffered more DNA damage than EUK males. Spectroradiometry showed that male coloration is lost in relation to superoxide and covaries with DNA erosion; in control males, these variables explained loss of color, whereas in EUK males, the fading of coloration was unaffected by superoxide and unrelated to DNA damage. Thus, EUK's powerful antioxidation removes the erosion effect of superoxide on coloration and experimentally verifies the prediction that colors reflect innate capacity for antioxidation.
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| 12. |
- Olsson, Mats, et al.
(författare)
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Polymorphic male color morphs visualized with steroids in monomorphic females: a tool for designing analysis of sex-limited trait inheritance
- 2012
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 215:4, s. 575-577
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Tidskriftsartikel (refereegranskat)abstract
- In diploid animals, males and females share most of the genome (except sex-specific elements, such as sex chromosome genes), yet despite sharing the underlying genes that hard-wire traits, males and females may differ in their phenotypes when traits are controlled by proximate mechanisms, such as hormones. In color polymorphic species where coloration is only expressed in one sex, the design of studies of the inheritance of color and coevolved morph-specific traits (e.g. territorial vs sneaker strategies, skewed energetic investment in territorial defense vs sperm production, etc.) is compromised as the expression of morph-coding genes is only visualized in one sex. Here, we circumvented this problem by first characterizing oxidative stress traits in both sexes and then using testosterone implants in females to expose their otherwise ‘silent’ coloration. Males of our model species are highly territorial and exhibit morph-specific levels of aggression, whereas females are non-territorial and display very low levels of aggression. Interestingly, reactive oxygen species levels were found to be morph specific regardless of sex, despite considerable differences in lifestyle. Males and females did differ remarkably, however, in superoxide levels depending on whether they sported a colored throat bib or not, a trait also used in male sexual signaling. Females with throat bibs had significantly lower levels of superoxide than females without a bib, which was not the case for males.
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| 13. |
- Olsson, Mats, et al.
(författare)
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Sex-specific SOD levels and DNA damage in painted dragon lizards (Ctenophorus pictus)
- 2012
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 170:4, s. 917-924
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Tidskriftsartikel (refereegranskat)abstract
- When groups of individuals differ in activities that may influence the production of reactive molecules, such as superoxide, we expect selection to result in congruent upregulation of antioxidant production in the group(s) most at risk of suffering concomitant erosion of essential tissue and biomolecules, such as DNA. We investigate this in a (near) annual lizard species, the Australian painted dragon (Ctenophorus pictus), in which males and females have fundamentally different lifestyles, with males being overtly conspicuous and aggressive, whereas females are placid and camouflaged. When kept in identical conditions to females in captivity, males had higher levels of superoxide dismutase (SOD) through the activity season, which is consistent with selection for a higher capacity of superoxide antioxidation and a lower level of DNA damage than females. Males, however, lacked the clear negative, linear relationship between SOD and DNA erosion observed in females, suggesting that female upregulation of SOD results in a more predictable antioxidation and a more immediate target for selection. Lastly, we analysed aspects of female reproduction from a DNA erosion perspective. Females closer to ovulation, hence with less remaining, circulating vitellogenin, had higher superoxide levels. Furthermore, a multiple regression analysis showed that females that produced more clutches over time suffered more DNA erosion, whereas females with higher SOD levels suffered less DNA erosion.
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| 14. |
- Rice, Amber M., et al.
(författare)
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Optimizing the trade-off between offspring number and quality in unpredictable environments: Testing the role of differential androgen transfer to collared flycatcher eggs
- 2013
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Ingår i: Hormones and Behavior. - : Elsevier BV. - 1095-6867 .- 0018-506X. ; 63:5, s. 813-822
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Tidskriftsartikel (refereegranskat)abstract
- According to the brood reduction hypothesis, parents adjust their brood size in response to current environmental conditions. When resources are abundant, parents can successfully raise all hatched offspring, but when resources are scarce, brood reduction, i.e., the sacrifice of some siblings to secure the quality of a subset of offspring, may maximize fitness. Differential transfer of maternal androgens is one potential proximate mechanism through which female birds may facilitate brood reduction because it may alter the relative competitive ability of sibling nestlings. We tested the hypothesis that female collared flycatchers (Ficedula albicollis) manipulate sibling competition by transferring less androgens to eggs late in the laying sequence. We experimentally elevated androgen levels in i) whole clutches and ii) only the two last laid eggs, and compared growth and begging behavior of offspring from these treatments with a control treatment. By using three treatments and video assessment of begging, we examined the effects of within-clutch patterns of yolk androgen transfer on levels of sibling competition in situ. When androgens were elevated in only the two last laid eggs, begging was more even among siblings compared to control nests. We also found that female nestlings receiving additional yolk androgens showed higher mass gain later in the breeding season, while their male counterparts did not. Our results suggest that females may improve reproductive success in unpredictable environments by altering within-clutch patterns of yolk androgen transfer. We discuss the possibility that life-history divergence between the co-occurring collared and pied flycatcher (Ficedula hypoleuca) is amplified by patterns of yolk androgen transfer. (C) 2013 Elsevier Inc. All rights reserved.
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| 15. |
- Sandell, Maria, et al.
(författare)
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Yolk androgens and the development of avian immunity: an experiment in jackdaws (Corvus monedula).
- 2009
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 212:Pt 6, s. 815-822
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Tidskriftsartikel (refereegranskat)abstract
- Maternally derived androgens have been shown to influence offspring phenotype in various ways. In birds, the benefits of prenatal androgen exposure, such as increased competitiveness and accelerated growth in nestlings, have been suggested to be balanced by costs, such as reduced immune function. In this study, we used an integrative approach to examine the influence of yolk androgens on the development of immune function in jackdaw (Corvus monedula) nestlings. Specifically, we tested whether the effects of yolk androgens on offspring immunity may extend over the first few days of life and be detectable even after several weeks. We manipulated yolk androgen concentrations in jackdaw eggs and estimated immune responsiveness by challenging the young with different pathogens at different stages of the nestling period. Six-day-old chicks hatched from eggs with elevated yolk androgen levels had lower pre-challenge antibody titres against lipopolysaccharide (LPS) than control chicks. However, antibody titres against LPS did not differ between treatment groups eight days after a challenge with LPS. During the late nestling phase, both humoral (towards diphtheria/tetanus antigens) and cell-mediated (towards phytohaemagglutinin) immune responsiveness were lower in chicks from yolk androgen-treated eggs compared with control chicks. Our experimental study on jackdaw chicks shows that elevated yolk androgen levels result in a general immunosuppression in offspring; this conclusion was based on results for several immunological tests of both humoral and cell-mediated immunity conducted at 1-2 and 3-4 weeks of age.
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| 16. |
- Scharnweber, Kristin, 1983-, et al.
(författare)
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Dietary niche overlap in sympatric asexual and sexual livebearing fishes Poecilia spp.
- 2011
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 79:7, s. 1760-1773
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the spatiotemporal patterns in trophic resource use in a system of a gynogenetic poeciliid fish, the Amazon molly Poecilia formosa, and its sexual congeners the sailfin molly Poecilia latipinna and the Atlantic molly Poecilia mexicana using gut contents analysis. No statistically significant differences in trophic resource use were found between sexual and gynogenetic species, but gut contents varied significantly across sites and over time. In addition, variation in trophic morphology (i.e. gut length) was significant across sites but not species, and laboratory experiments indicated that gut length is phenotypically plastic. Overall, trophic differentiation between coexisting asexual and sexual Poecilia appears to be minimal, and it is unlikely that niche differentiation contributes to a stable coexistence of the two reproductive forms.
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| 17. |
- Scharnweber, Kristin, 1983-, et al.
(författare)
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Examination of boldness traits in sexual and asexual mollies (Poecilia latipinna, P. formosa)
- 2011
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Ingår i: Acta Ethologica. - : Springer Science and Business Media LLC. - 0873-9749 .- 1437-9546. ; 14:2, s. 77-83
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Tidskriftsartikel (refereegranskat)abstract
- Considering the high costs of sexual reproduction (e.g., the production of males), its maintenance and predominance throughout the Animal Kingdom remain elusive. Especially the mechanisms allowing for a stable coexistence of closely related sexual and asexual species are still subject to a lively debate. Asexuals should rapidly outnumber sexuals due to higher population growth rates, unless they face some disadvantages. Here, we investigate potential differences in feeding behavior in a system of sexual (sailfin mollies, Poecilia latipinna) and coexisting gynogenetic fishes (Amazon mollies, Poecilia formosa). In two different experiments, we tested for differences in behavioral traits associated with boldness. Bold individuals take higher risks for gains in resources, so shyer individuals should be less competitive. Our study was motivated by the recent finding that P. formosa are less likely to be preyed upon by piscine predators than P. latipinna. We asked whether this result is indicative of low boldness in P. formosa. However, no differences between the two species were detectible in our behavioral experiments measuring (a) time to emerge from shelter to explore a novel environment, (b) latency time until feeding in a novel environment, and (c) recovery time until feeding restarted after a simulated predator attack. Furthermore, different boldness measures were not correlated with each other within individuals.
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| 18. |
- Scharnweber, Kristin, 1983-, et al.
(författare)
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Feeding efficiency and food competition in coexisting sexual and asexual livebearing fishes of the genus Poecilia
- 2011
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Ingår i: Environmental Biology of Fishes. - : Springer Science and Business Media LLC. - 0378-1909 .- 1573-5133. ; 90:2, s. 197-205
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Tidskriftsartikel (refereegranskat)abstract
- Considering its immediate costs of producing dispensable males, the maintenance of sexual reproduction is a major paradox in evolutionary biology. Asexual lineages that do not face such costs theoretically should replace sexuals over time. Nonetheless, several systems are known in which closely related sexual and asexual lineages stably coexist. In the present study, we studied a sexual/asexual mating complex of a sperm-dependent parthenogenetic fish (amazon molly, Poecilia formosa) and its sexual congeners, the sailfin molly P. latipinna and the Atlantic molly P. mexicana. We asked whether differences in feeding behavior could contribute to their stable coexistence. We conducted a laboratory experiment to compare feeding efficiencies and also measured the competitive abilities between the two reproductive forms. Additionally, we measured gut fullness of fishes caught in natural habitats. Contrary to our predictions, we could not find P. formosa to be less efficient in feeding. We argue that food competition in mollies plays a minor role in mediating coexistence between closely related asexual and sexual mollies.
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| 19. |
- Scharnweber, Kristin, 1983-, et al.
(författare)
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Trophic niche segregation between the sexes in two species of livebearing fishes (Poeciliidae)
- 2011
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Ingår i: Bulletin of Fish Biology. - 1867-5417. ; 13:1-2, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- Fishes of the genus Poecilia are highly sexually dimorphic. In the two species investigated here (P. latipinna and P. mexicana) males are, on average, of smaller body size and more colorful than females. Males also differ from females in time allocated to feeding as they engage in mating behavior almost dayround. We hypothesized that, due to different time allocations and energy requirements, the sexes might forage on different food items and thus could occupy different trophic niches. We investigated gut content compositions, intestinal tract length and gut fullness in multiple populations of P. latipinna and P. mexicana. Our fi nding of females having fuller guts than males corroborated sex differences in time allocation for foraging. A major difference between sexes was also found in intestinal tract length, with males consistently having shorter guts, likely refl ecting spatial constraints due to sexually dimorphic traits (like a more anterior anal porus). Contrary to prediction, however, gut content composition indicated no clear-cut pattern of sex-specifi c trophic niches across study sites. Niche widths, on the other hand, differed between sexes with males having narrower trophic niches than females. Overall, we found sex-specifi c differences in some aspects of feeding ecology, but no clear trophic niche segregation was detected.
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| 20. |
- Sköld Chiriac, Sandra, et al.
(författare)
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Body temperature changes during simulated bacterial infection in a songbird: fever at night and hypothermia during the day
- 2015
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 218:18, s. 2961-2969
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Tidskriftsartikel (refereegranskat)abstract
- Although fever (a closely regulated increase in body temperature in response to infection) typically is beneficial, it is energetically costly and may induce detrimentally high body temperatures. This can increase the susceptibility to energetic bottlenecks and risks of overheating in some organisms. Accordingly, it could be particularly interesting to study fever in small birds, which have comparatively high metabolic rates and high, variable body temperatures. We therefore investigated two aspects of fever and other sickness behaviours (circadian variation, dose dependence) in a small songbird, the zebra finch. We injected lipopolysaccharide (LPS) at the beginning of either the day or the night, and subsequently monitored body temperature, body mass change and food intake for the duration of the response. We found pronounced circadian variation in the body temperature response to LPS injection, manifested by (dose-dependent) hypothermia during the day but fever at night. This resulted in body temperature during the peak response being relatively similar during the day and night. Day-to-night differences might be explained in the context of circadian variation in body temperature: songbirds have a high daytime body temperature that is augmented by substantial heat production peaks during activity. This might require a trade-off between the benefit of fever and the risk of overheating. In contrast, at night, when body temperature is typically lower and less variable, fever can be used to mitigate infection. We suggest that the change in body temperature during infection in small songbirds is context dependent and regulated to promote survival according to individual demands at the time of infection.
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| 21. |
- Tobler, Michael, et al.
(författare)
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Basal superoxide as a sex-specific immune constraint
- 2011
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Ingår i: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 7:6, s. 906-908
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Tidskriftsartikel (refereegranskat)abstract
- There is increasing evidence that reactive oxygen species (ROS), a group of unstable and highly reactive chemical molecules, play a key role in regulating and maintaining life-history trade-offs. Upregulation of ROS in association with immune activation is costly because it may result in an imbalance between pro- and antioxidants and, hence, oxidative damage. Previous research aimed at quantifying this cost has mostly focused on changes in the pro-/antioxidant balance subsequent to an immune response. Here, we test the hypothesis that systemic ROS may constrain immune activation. We show that systemic, pre-challenge superoxide (SO) levels are negatively related to the strength of the subsequent immune response towards the mitogen phytohaemagglutinin in male, but not female painted dragon lizards (Ctenophorus pictus). We therefore suggest that systemic SO constrains immune activation in painted dragon males. We speculate that this may be due to sex-specific selection pressures on immune investment.
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| 22. |
- Tobler, Michael, et al.
(författare)
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Convergent changes in the trophic ecology of extremophile fish occurring along replicated environmental gradients
- 2015
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 60:4, s. 768-780
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Tidskriftsartikel (refereegranskat)abstract
- Divergent selection along environmental gradients connecting locally restricted extreme habitats and adjacent benign habitats can shape convergent evolution of traits involved in coping with physiochemical stressors and can drive speciation. At the same time, the presence of such stressors alters aspects of the biotic environment, including resource availability and competitive regimes. However, it remains unclear whether and how the ecology of populations occurring in both extreme and benign environments varies in a predictable fashion. We investigated the trophic ecology of live-bearing fishes of the genus Poecilia that have independently colonised multiple springs containing toxic hydrogen sulphide in southern Mexico. Sulphide spring fish are adapted to the unique environmental conditions and are reproductively isolated from ancestral populations in adjacent non-sulphidic habitats. We used gut content analyses to test whether colonisation of extreme habitats was accompanied by shifts of trophic resource use and expansions of trophic niche width. Furthermore, we tested whether dietary shifts were reflected in trophic morphology by comparing intestinal tract lengths among populations using both wild-caught and common garden-raised individuals. Gut content analyses revealed that fish inhabiting toxic springs expanded their trophic niche width and changed their dietary resource use from detritus and algae to sulphide bacteria and invertebrates. This dietary shift was paralleled by changes in intestinal tract morphology, whereby sulphide spring fish had shorter intestines than fish from adjacent non-sulphidic habitats. Analysis of common garden-raised fish indicated that morphological differences between sulphidic and non-sulphidic populations are at least in part due to genetic differentiation. Both patterns of trophic resource use and differentiation in trophic morphology were consistent across replicated pairs of sulphidic and non-sulphidic populations, although the magnitude of differentiation varied among river drainages. Our results suggest that colonisation of and adaptation to sulphide springs in southern Mexico was paralleled by convergent changes in trophic ecology. This highlights the complexity of environmental gradients and the necessity of considering multiple sources of selection when studying the evolution of complex phenotypes.
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| 23. |
- Tobler, Michael, et al.
(författare)
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Costly steroids: egg testosterone modulates nestling metabolic rate in the zebra finch
- 2007
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Ingår i: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 3:4, s. 408-410
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Tidskriftsartikel (refereegranskat)abstract
- The transfer of non-genetic resources from mother to the offspring often has considerable consequences for offspring performance. In birds, maternally derived hormones are known to influence a variety of morphological, physiological and behavioural traits in the chick. So far, the range of these hormonal effects involves benefits in terms of enhanced growth and competitive ability as well as costs in terms of immunosuppression. However, since yolk hormones can enhance growth and begging activity, high levels of these hormones may also involve energetic costs. Here, we show experimentally that elevated levels of prenatal testosterone increase resting metabolic rate in nestling zebra finches (Taeniopygia guttata). Surprisingly, however, elevation of prenatal testosterone did not result in higher growth rates and, thus, differences in resting metabolism do not seem to be linked to nestling growth. We conclude that apart from immunosuppressive effects, high levels of egg steroids may also entail costs in terms of increased energy expenditure.
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| 24. |
- Tobler, Michael, et al.
(författare)
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Digit ratio, color polymorphism and egg testosterone in the Australian painted dragon.
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Variation in exposure to sex hormones during early development contributes to phenotypic plasticity in vertebrate offspring. As a proposed marker for prenatal sex hormone exposure and because of their association with various physiological and behavioral characteristics, digit ratio and/or digit length have received notable interest within the field of evolutionary ecology. However, the validity of digit measures as a proxy of prenatal sex hormone exposure is controversial and only few studies have provided direct evidence for the link between digit development and prenatal sex hormones. Here, we report morph- and sex-specific variation in digit ratio in wild painted dragon lizards (Ctenophorus pictus). Lizards expressing a yellow bib have significantly larger third-to-fourth toe ratios (3D:4D) than lizards without a bib. Males have significantly smaller 3D:4D than females. Furthermore, we show that experimental elevation of yolk testosterone significantly increases 3D:4D in hatchling painted dragon lizards, but has no influence on hatchling size. Our results provide direct and indirect evidence for the involvement of prenatal sex steroids in digit development and it is suggested that digit ratio may be used as a biomarker for prenatal steroid exposure in this reptilian species. As such, digit ratio may provide a useful tool to study temporal or spatial differences in the proximate hormonal mechanisms modulating physiological and behavioural phenotypes.
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| 25. |
- Tobler, Michael, et al.
(författare)
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Digit ratio, polychromatism and associations with endurance and antipredator behaviour in male painted dragon lizards
- 2012
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Ingår i: Animal Behaviour. - : Elsevier BV. - 1095-8282 .- 0003-3472. ; 84:5, s. 1261-1269
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Tidskriftsartikel (refereegranskat)abstract
- Variation in sex hormone exposure during early embryonic development contributes to individual differences in behaviour and cognitive abilities later in life. Digit ratio has gained considerable interest as a putative marker for early androgen/oestrogen exposure in behavioural ecology research. Studying digit ratio in nonhuman laboratory as well as wild vertebrate species may be useful to assess whether different traits may be influenced by a common (e. g. endocrine-related) mechanism and whether digit ratio might be used as a phenotypic indicator for behavioural or fitness-related traits. We examined whether digit ratio (third-to-fourth toe ratio; 3D:4D) may indicate a common mechanism underlying endurance and antipredator behaviour in male painted dragon lizards, Ctenophorus pictus. We have previously shown that 3D:4D is associated with the presence/absence of a yellow throat patch (bib), with males with bibs having higher 3D:4D than those without bibs. In this study we found that 3D: 4D predicted antipredator behaviour with individuals with higher 3D:4D having shorter escape response times; however, 3D:4D was not associated with endurance. Endurance and antipredator behaviour were also associated with male coloration. Males expressing a bib had shorter escape response times and lower endurance than those without a bib. Moreover, males with orange head colour had lower endurance compared to yellow-headed and uncoloured males. On the basis of these results, we speculate that the associations between antipredator behaviour, endurance, 3D:4D and male sexual coloration are caused, at least partly, by different underlying mechanisms. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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| 26. |
- Tobler, Michael, et al.
(författare)
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Effects of prenatal testosterone exposure on antioxidant status and bill color in adult zebra finches.
- 2013
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Ingår i: Physiological and Biochemical Zoology. - : University of Chicago Press. - 1522-2152 .- 1537-5293. ; 86:3, s. 333-345
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Tidskriftsartikel (refereegranskat)abstract
- Permanent offspring modification through maternal hormone transfer is thought to be a tool for mothers to influence life-history trajectories of individual offspring. In birds, yolk hormones influence numerous aspects of the offspring's physiology, including antioxidant status, an important physiological measure that is linked to growth, reproductive effort, and survival. While it is evident that yolk hormones can affect antioxidant status of nestlings, it is not known whether their effect extends beyond the nestling stage. In this study, we use the zebra finch (Taeniopygia guttata) to test experimentally whether exposure to elevated yolk testosterone (T) levels can result in long-term effects on antioxidant status and traits likely to be associated with this measure. Our data show a significant but sex-specific effect with respect to a period from fledging to the age of 7 mo; T males had higher antioxidant status than control males, whereas antioxidant levels did not differ among females and were intermediate compared with the two male groups. Bill color, a trait associated with carotenoids (a specific group of antioxidants) and known to be under the control of circulating levels of T, was not affected by our yolk T manipulation. Bill color (alone or in covariation with egg treatment or sex) did not predict immune responsiveness or antioxidant status. Moreover, there was only weak evidence that antioxidant status predicted the strength of different immune responses. Antioxidant status (in covariation with egg treatment and sex) predicted levels of circulating total antibody levels but did not predict the strength of cell-mediated and humoral immune responses. Our results suggest that yolk T affects antioxidant status independently of these other traits.
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| 27. |
- Tobler, Michael, et al.
(författare)
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Maternal androgens in the pied flycatcher; timing of breeding and within-female consistency
- 2007
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 1432-1939 .- 0029-8549. ; 151:4, s. 731-740
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Tidskriftsartikel (refereegranskat)abstract
- Maternal hormones can have substantial phenotypic effects in the progeny of many vertebrates. It has been proposed that mothers adaptively adjust hormone levels experienced by particular young to optimize their reproductive output. In birds, systematic variation in egg hormone levels has been related to different female reproductive strategies. Because in many bird species prospects of the offspring change seasonally and with brood number, strategic adjustment of yolk androgen levels would be expected. To test this idea, we induced pied flycatcher (Ficedula hypoleuca) females to nest twice during the same season by removing their first clutches shortly after clutch completion. We collected eggs of first and replacement clutches to measure yolk concentrations of androstenedione (A4) and testosterone (T) and captured the females that laid these clutches for phenotypic measurements. Although average egg androgen levels were remarkably consistent within females, hormone patterns differed considerably between first and replacement clutches. Eggs of replacement clutches were heavier with larger yolks compared to first clutches, but they contained on average lower levels of androgens. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Mean yolk T, but not A4 levels, were negatively associated with laying date for both breeding attempts. Moreover, females in good body condition produced eggs containing lower levels of androgens than females in poor condition. Our results are consistent with the idea that differences in yolk androgen levels may be one mechanism underlying seasonal variation in reproductive success and it is possible that changes in egg androgen patterns may reflect a change in female reproductive strategy. High within-female consistency also highlights the possibility that there may be some underlying genetic variation in yolk androgen levels
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| 28. |
- Tobler, Michael
(författare)
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Maternal programming: costs, benefits and constraints of maternal hormone transfer
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Avian mothers convey significant quantities of androgens (i.e. ?male? steroids) to their eggs, which are known to positively influence embryonic development, post-natal growth and competitive behaviour of the offspring. However, there is large inter-female variation in the amount of androgens transferred to the eggs. Recent studies suggest that this variation may be maintained because the positive effects on growth and behaviour are counterbalanced by negative effects on the immune function of the offspring. This thesis deals with the causal and functional aspects of maternal androgen transfer in birds. In a study on a wild pied flycatcher (Ficedula hypoleuca) population, I investigated female plasticity in androgen transfer with respect to the timing of breeding. Eggs of replacement clutches produced late in the season contained on average lower levels of androgens compared to first clutches produced early in the season. Within clutches, androgen concentration increased over the laying sequence in the first clutch, but decreased or remained more constant over the laying sequence in the replacement clutch. Differential androgen transfer with respect to timing of breeding is discussed as an adaptive female tactic to optimize reproductive output. To examine the effects of egg androgens on offspring phenotype, I compared offspring hatched from eggs with experimentally elevated androgen levels with offspring hatched from eggs with sham-manipulated androgen levels (controls). I found that exposure to elevated egg levels of testosterone (T) increased metabolism in zebra finch (Taeniopygia guttata) chicks. Extra egg T also enhanced growth in male zebra finch chicks, but at the same time reduced their ability to resist oxidative stress during the early growth phase. These results are the first to demonstrate that high levels of egg androgens can entail costs in terms of increased energy expenditure and increased susceptibility to oxidative stress. To evaluate whether there are any long-term effects of egg T on offspring physiology and behaviour, I followed a cohort of zebra finches hatched from manipulated eggs. Although no effects of egg T on adult immunity were found, there appeared to be a positive effect of high levels of egg T on oxidative stress resistance in adult males when they were subjected to an immunization with a pathogen. Furthermore, egg T influenced adult behaviour in males and females. High levels of egg T facilitated the ability of adult zebra finches to habituate to a novel situation. The effects of egg androgens on growth and immunity were also investigated in a study on wild jackdaws (Corvus monedula). In this study, there was a clear negative effect of high egg androgen levels on nestling immunity. The study shows that the effect is present during different developmental periods of the nestlings, and most interestingly, still present just before fledging. The results from these experimental studies add to our understanding of how transgenerational transmission of hormones affect the formation of the offspring phenotype.
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| 29. |
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| 30. |
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| 31. |
- Tobler, Michael, et al.
(författare)
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Oxidant trade-offs in immunity: an experimental test in a lizard.
- 2015
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Immune system functioning and maintenance entails costs which may limit investment into other processes such as reproduction. Yet, the proximate mechanisms and 'currencies' mediating the costs of immune responses remain elusive. In vertebrates, up-regulation of the innate immune system is associated with rapid phagocytic production of pro-oxidant molecules (so-called 'oxidative burst' responses). Oxidative burst responses are intended to eliminate pathogens but may also constitute an immunopathological risk as they may induce oxidative damage to self cells. To minimize the risk of infection and, at the same time, damage to self, oxidative burst activity must be carefully balanced. The current levels of pro- and antioxidants (i.e. the individual oxidative state) is likely to be a critical factor affecting this balance, but this has not yet been evaluated. Here, we perform an experiment on wild-caught painted dragon lizards (Ctenophorus pictus) to examine how the strength of immune-stimulated oxidative burst responses of phagocytes in whole blood relates to individual oxidative status under control conditions and during an in vivo immune challenge with Escherichia coli lipopolysaccharide (LPS). Under control conditions, oxidative burst responses were not predicted by the oxidative status of the lizards. LPS-injected individuals showed a strong increase in pro-oxidant levels and a strong decrease in antioxidant levels compared to control individuals demonstrating a shift in the pro-/antioxidant balance. Oxidative burst responses in LPS-injected lizards were positively related to post-challenge extracellular pro-oxidants (reflecting the level of cell activation) and negatively related to pre-challenge levels of mitochondrial superoxide (suggesting an immunoregulatory effect of this pro-oxidant). LPS-challenged males had higher oxidative burst responses than females, and in females oxidative burst responses seemed to depend more strongly on antioxidant status than in males. Our results confirm the idea that oxidative state may constrain the activity of the innate immune system. These constraints may have important consequences for the way selection acts on pro-oxidant generating processes.
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| 32. |
- Tobler, Michael, et al.
(författare)
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Sex-specific effects of prenatal testosterone on nestling plasma antioxidant capacity in the zebra finch.
- 2009
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Ingår i: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 212:1, s. 89-94
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Tidskriftsartikel (refereegranskat)abstract
- Trans-generational transfer of non-genetic, maternal resources such as hormones can have a substantial influence on offspring phenotype in many vertebrate species. In birds, maternal androgens enhance both growth and competitive behaviour, but also suppress the immune system. It has been hypothesised that high levels of egg androgens could also influence the prooxidant-antioxidant balance through their positive effect on growth and metabolism. We tested this hypothesis in the zebra finch (Taeniopygia guttata). Eggs were injected with testosterone dissolved in sesame oil or sesame oil only (control). We subsequently assessed the effect of the egg hormone manipulation on nestling growth and nestling plasma total antioxidant capacity (TAC). Growth rates of zebra finch nestlings were not significantly affected by egg hormone treatment. However, male offspring hatched from eggs with experimentally elevated testosterone had reduced plasma TAC at 10 days of age compared with male offspring hatching from control eggs. At the age of 34 days, males had similar plasma TAC irrespective of egg treatment. No effects of egg testosterone manipulation on nestling plasma TAC were found in females. Our results demonstrate that embryonic exposure to elevated levels of testosterone modulates chick antioxidant status, but this seems to be independent of chick growth. Sex-specific effects of prenatal testosterone on plasma TAC of zebra finch nestlings may have important consequences for sex allocation.
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| 33. |
- Tobler, Michael, et al.
(författare)
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Short- and long-term consequences of prenatal testosterone for immune function: an experimental study in the zebra finch
- 2010
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 1432-0762 .- 0340-5443. ; 64:5, s. 717-727
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Tidskriftsartikel (refereegranskat)abstract
- Hormone-mediated maternal effects play an important role in the formation of a differentiated phenotype. They have been shown to influence a wide array of offspring traits, both early in life and in adulthood. One important offspring trait that is under the influence of maternal androgens is the immune system. In birds, a growing number of studies show that yolk androgens modulate immune function during the chick stage. However, there is a lack of knowledge regarding long-term effects of prenatal androgens on offspring immunity. In this study, we therefore investigated the influence of prenatal testosterone (T) on several measures of immunity in fledgling and adult zebra finches (Taeniopygia guttata). Cell-mediated immune response (towards phytohaemagglutinin, PHA) of fledglings hatching from control eggs was negatively related to brood size, whereas there was no such association for fledglings hatching from eggs with experimentally elevated T levels (T fledglings). Male control fledglings showed reduced mass gain compared to female control fledglings within 24 h after the PHA injection. This pattern was reversed in T fledglings. Total antibody levels in fledglings were not affected by egg treatment. Neither cell-mediated immunity nor total antibody levels in sexually mature zebra finches were influenced by egg treatment. However, there was an immuno-enhancing effect of elevated egg T on both primary and secondary humoral immune responses toward diphtheria and tetanus antigens in ca 5 and 7 month old zebra finches. In addition, the covariation between different immune components differed between T and control offspring, suggesting that egg treatment may have altered the potential trade-offs between different parts of the immune system. Our results suggest that prenatal androgens could be an important factor contributing to individual variation in immune function even in adulthood.
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| 34. |
- Tobler, Michael, et al.
(författare)
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Specific floater home ranges and prospective behaviour in the European starling, Sturnus vulgaris
- 2004
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Ingår i: Naturwissenschaften. - : Springer Science and Business Media LLC. - 1432-1904 .- 0028-1042. ; 91:2, s. 85-89
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Tidskriftsartikel (refereegranskat)abstract
- In many bird species, floaters are present on the breeding grounds in one or more years before they breed. There is increasing evidence that they have specific home ranges in which they search for information about current and future breeding opportunities. We investigated the role of prospecting in a migratory European starling (Sturnus vulgaris) population. Radio-tracking showed that male starling floaters use specific home range areas during the breeding period. Nest-box observations demonstrated that non-parental nest intrusion is common in the starling and that it is significantly more frequent during the nestling than during the incubation period. In addition, small groups of nest boxes were more likely to be occupied by starlings if they had been put up during the preceding breeding season. The results suggest that floaters try to acquire information about local breeding communities. One specific type of information may be the location of potential breeding sites.
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| 35. |
- Tobler, Michael, et al.
(författare)
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Telomeres in ecology and evolution : A review and classification of hypotheses
- 2022
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 31:23, s. 5946-5965
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Forskningsöversikt (refereegranskat)abstract
- Research on telomeres in the fields of ecology and evolution has been rapidly expanding over the last two decades. This has resulted in the formulation of a multitude of, often name-given, hypotheses related to the associations between telomeres and life-history traits or fitness-facilitating processes (and the mechanisms underlying them). However, the differences (or similarities) between the various hypotheses, which can originate from different research fields, are often not obvious. Our aim here is therefore to give an overview of the hypotheses that are of interest in ecology and evolution and to provide two frameworks that help discriminate among them. We group the hypotheses (i) based on their association with different research questions, and (ii) using a hierarchical approach that builds on the assumptions they make, such as about causality of telomere length/shortening and/or the proposed functional consequences of telomere shortening on organism performance. Both our frameworks show that there exist parallel lines of thoughts in different research fields. Moreover, they also clearly illustrate that there are in many cases competing hypotheses within clusters, and that some of these even have contradictory assumptions and/or predictions. We also touch upon two topics in telomere research that would benefit from further conceptualization. This review should help researchers, both those familiar with and those new to the subject, to identify future avenues of research.
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| 36. |
- Tobler, Michael, et al.
(författare)
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Yolk testosterone modulates persistence of neophobic responses in adult zebra finches, Taeniopygia guttata
- 2007
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Ingår i: Hormones and Behavior. - : Elsevier BV. - 1095-6867 .- 0018-506X. ; 52:5, s. 640-645
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Tidskriftsartikel (refereegranskat)abstract
- Individual differences in animal behavior can be attributed to genetic as well as non-genetic influences. One mechanism by which the behavioral phenotype of an individual can be shaped is via transmission of maternal sex steroids. In this study, we examined the role of yolk testosterone (T) in controlling neophobia in 9-month-old, sexually mature zebra finches (Taeniopygia guttata). Offspring hatched from either T-treated or control eggs were subjected to a sequential series of behavioral tests in which we measured the neophobic response and its persistence towards two unfamiliar stimuli. Birds from T-treated and control eggs did not differ in their latencies to approach and eat a novel food source during their first encounter. However, egg treatment affected subsequent habituation. Latencies decreased in both groups over a habituation period of 5 days, but considerably more so in T-offspring. Although males appeared to approach novel food faster than females, there was no overall sex effect during the habituation period. When a novel object was added in combination with the previously learned food stimulus, this caused an behavioral shift in approach latencies. In males, control offspring had significantly shorter latencies than T-offspring, whereas there was no difference among females. The latency to eat in the same test was not significantly affected by sex or egg treatment. Our results demonstrate long-term effects of prenatal T on neophobic responses in adult zebra finches. We hypothesize that prenatal T may be one underlying mechanism for individual differences routine formation. (C) 2007 Elsevier Inc. All rights reserved.
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| 37. |
- Trachsel, Mathias, et al.
(författare)
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Multi-archive summer temperature reconstruction for the European Alps, AD 1053-1996
- 2012
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Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 46, s. 66-79
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Tidskriftsartikel (refereegranskat)abstract
- We present a multi-archive, multi-proxy summer temperature reconstruction for the European Alpscovering the period AD 1053-1996 using tree-ring and lake sediment data. The new reconstruction isbased on nine different calibration approaches and errors were estimated conservatively. Summertemperatures of the last millennium are characterised by two warm (AD 1053-1171 and 1823-1996) andtwo cold phases (AD 1172-1379 and 1573-1822). Highest pre-industrial summer temperatures of the12th century were 0.3 degC warmer than the 20th century mean but 0.35 degC colder than proxy derivedtemperatures at the end of the 20th century. The lowest temperatures at the end of the 16th centurywere ~1 degC lower than the 20th century mean.
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