| 1. |
- Bauerfeind, Stephanie S., et al.
(författare)
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Geographic variation in responses of European yellow dung flies to thermal stress
- 2018
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Ingår i: Journal of Thermal Biology. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0306-4565 .- 1879-0992. ; 73, s. 41-49
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Tidskriftsartikel (refereegranskat)abstract
- Climatic conditions can be very heterogeneous even over small geographic scales, and are believed to be major determinants of the abundance and distribution of species and populations. Organisms are expected to evolve in response to the frequency and magnitude of local thermal extremes, resulting in local adaptation. Using replicate yellow dung fly (Scathophaga stercoraria; Diptera: Scathophagidae) populations from cold (northern Europe) and warm climates (southern Europe), we compared 1) responses to short-term heat and cold shocks in both sexes, 2) heat shock protein (Hsp70) expression in adults and eggs, and 3) female reproductive traits when facing short-term heat stress during egg maturation. Contrary to expectations, thermal traits showed minor geographic differentiation, with weak evidence for greater heat resistance of southern flies but no differentiation in cold resistance. Hsp70 protein expression was little affected by heat stress, indicating systemic rather than induced regulation of the heat stress response, possibly related to this fly group's preference for cold climes. In contrast, sex differences were pronounced: males (which are larger) endured hot temperatures longer, while females featured higher Hsp70 expression. Heat stress negatively affected various female reproductive traits, reducing first clutch size, overall reproductive investment, egg lipid content, and subsequent larval hatching. These responses varied little across latitude but somewhat among populations in terms of egg size, protein content, and larval hatching success. Several reproductive parameters, but not Hsp70 expression, exhibited heritable variation among full-sib families. Rather than large-scale clinal geographic variation, our study suggests some local geographic population differentiation in the ability of yellow dung flies to buffer the impact of heat stress on reproductive performance.
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| 2. |
- Bauerfeind, Stephanie S., et al.
(författare)
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Replicated latitudinal clines in reproductive traits of European and North American yellow dung flies
- 2018
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 127:11, s. 1619-1632
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Tidskriftsartikel (refereegranskat)abstract
- Geographic variation in phenotypic traits is commonly correlated with spatial variation in the environment, e.g. seasonality and mean temperature, providing evidence that natural selection generates such patterns. In particular, both body size and egg size of ectothermic animals are commonly larger in northern climates, and temperature induces plastic responses in both traits. Size-independent egg quality can also vary with latitude, though this is rarely investigated. For the widespread yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) we investigated whether there are latitudinal clines in reproductive traits (clutch size, egg size and egg composition), whether these clines are due to variation in body and/or egg size, and whether such clines replicate across independent experiments performed on different continents (North America and Europe). Egg size generally increased with latitude (especially in Europe), an effect largely explained by body size of the mother, while clutch size did not; overall reproductive effort thus increased with latitude. Both the absolute and relative (correcting for egg size) amount of egg protein increased with latitude, egg glycogen decreased with latitude, while latitudinal trends for egg lipids and total egg energy content were complex and non-linear. Altitude sometimes showed relationships analogous to those of latitude (egg proteins and glycogen) but occasionally opposite (egg size), possibly because latitude and altitude are negatively related among populations of this cold-adapted species. There was no evidence of a tradeoff between egg size and number across latitudinal populations; if anything, the relationship was positive. All traits, including body and egg size, varied with rearing temperature (12 degrees C, 18 degrees C, 24 degrees C), generally following the temperature-size rule. Clines based on common garden rearing, thus reflecting genetic differentiation, were qualitatively but not always quantitatively consistent between continents, and were similar across rearing temperatures, suggesting they evolved due to natural selection, although the concrete selective mechanisms involved require further study.
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| 3. |
- Baur, Julian, et al.
(författare)
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Exaggerated male forelegs are not more differentiated than wing morphology in two widespread sister species of black scavenger flies
- 2020
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Ingår i: Journal of Zoological Systematics and Evolutionary Research. - : Hindawi Limited. - 0947-5745 .- 1439-0469. ; 58:1, s. 159-173
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Tidskriftsartikel (refereegranskat)abstract
- Sexual selection represents a potent force that can drive rapid population differentiation in traits related to reproductive success. Hence, sexual traits are expected to show greater population divergence than non‐sexual traits. We test this prediction by exploring patterns of morphological differentiation of the exaggerated fore femur (a male‐specific sexual trait) and the wing (a non‐sexual trait) among allopatric and sympatric populations of the widespread sister dung fly species Sepsis neocynipsea and Sepsis cynipsea (Diptera: Sepsidae). While both species occur in Eurasia, S. neocynipsea also abounds in North America, albeit previous studies suggest strong differentiation in morphology, behavior, and mating systems. To evaluate the degree of differentiation expected under neutrality between S. cynipsea, European S. neocynipsea, and North American S. neocynipsea, we genotyped 30 populations at nine microsatellite markers, revealing almost equal differentiation between and minor differentiation among geographic populations within the three lineages. Landmark‐based analysis of 18 populations reared at constant 18 and 24°C in a laboratory common garden revealed moderate temperature‐dependent phenotypic plasticity and significant heritable differentiation in size and shape of male forelegs and wings among iso‐female lines of the three lineages. Following the biological species concept, there was weaker differentiation between cross‐continental populations of S. neocynipsea relative to S. cynipsea, and more fore femur differentiation between the two species in sympatry versus allopatry (presumably due to character displacement). Contrary to expectation, wing morphology showed as much shape differentiation between evolutionary independent lineages as fore femora, providing no evidence for faster diversification of traits primarily engaged in mating.
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| 4. |
- Baur, Julian, et al.
(författare)
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Intraspecific mating system evolution and its effect on complex male secondary sexual traits : Does male-male competition increase selection on size or shape?
- 2020
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Ingår i: Journal of Evolutionary Biology. - : WILEY. - 1010-061X .- 1420-9101. ; 33:3, s. 297-308
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Tidskriftsartikel (refereegranskat)abstract
- Sexual selection is generally held responsible for the exceptional diversity in secondary sexual traits in animals. Mating system evolution is therefore expected to profoundly affect the covariation between secondary sexual traits and mating success. Whereas there is such evidence at the interspecific level, data within species remain scarce. We here investigate sexual selection acting on the exaggerated male fore femur and the male wing in the common and widespread dung flies Sepsis punctum and S. neocynipsea (Diptera: Sepsidae). Both species exhibit intraspecific differences in mating systems and variation in sexual size dimorphism (SSD) across continents that correlates with the extent of male-male competition. We predicted that populations subject to increased male-male competition will experience stronger directional selection on the sexually dimorphic male foreleg. Our results suggest that fore femur size, width and shape were indeed positively associated with mating success in populations with male-biased SSD in both species, which was not evident in conspecific populations with female-biased SSD. However, this was also the case for wing size and shape, a trait often assumed to be primarily under natural selection. After correcting for selection on overall body size by accounting for allometric scaling, we found little evidence for independent selection on any of these size or shape traits in legs or wings, irrespective of the mating system. Sexual dimorphism and (foreleg) trait exaggeration is therefore unlikely to be driven by direct precopulatory sexual selection, but more so by selection on overall size or possibly selection on allometric scaling.
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| 5. |
- Berger, David, et al.
(författare)
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Quantitative genetic divergence and standing genetic (CO)variance in thermal reaction norms along latitude
- 2013
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 67:8, s. 2385-2399
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Tidskriftsartikel (refereegranskat)abstract
- Although the potential to adapt to warmer climate is constrained by genetic trade-offs, our understanding of how selection and mutation shape genetic (co)variances in thermal reaction norms is poor. Using 71 isofemale lines of the fly Sepsis punctum, originating from northern, central, and southern European climates, we tested for divergence in juvenile development rate across latitude at five experimental temperatures. To investigate effects of evolutionary history in different climates on standing genetic variation in reaction norms, we further compared genetic (co) variances between regions. Flies were reared on either high or low food resources to explore the role of energy acquisition in determining genetic trade-offs between different temperatures. Although the latter had only weak effects on the strength and sign of genetic correlations, genetic architecture differed significantly between climatic regions, implying that evolution of reaction norms proceeds via different trajectories at high latitude versus low latitude in this system. Accordingly, regional genetic architecture was correlated to region-specific differentiation. Moreover, hot development temperatures were associated with low genetic variance and stronger genetic correlations compared to cooler temperatures. We discuss the evolutionary potential of thermal reaction norms in light of their underlying genetic architectures, evolutionary histories, and the materialization of trade-offs in natural environments.
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| 6. |
- Blanckenhorn, Wolf U., et al.
(författare)
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Comparative sexual selection in field and laboratory in a guild of sepsid dung flies
- 2021
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Ingår i: Animal Behaviour. - : Elsevier. - 0003-3472 .- 1095-8282. ; 175, s. 219-230
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Tidskriftsartikel (refereegranskat)abstract
- Phenomenological and behavioural studies have greatly advanced the study of natural selection. Field studies of selection well appraise the natural situation, but is this also true for laboratory studies, which are typically more mechanistic? We compared precopulatory sexual selection (mating differential based on pairing success) in field and laboratory of several closely related, ecologically similar black scavenger dung flies (Diptera: Sepsidae). Selection on fore femur (sexual trait) and wing size (nonsexual trait) and shape varied considerably among seven species and continental populations in agreement with variation in their mating system and sexual size dimorphism. Selection on trait size was mostly positive or nil, but never significantly negative, implying mating advantages of large males in most species. Strongest selection was found in species/populations with male-biased size dimorphism, associating evolutionary shifts from female- to male-biased dimorphism with intensified sexual selection for large male size by adding male -male competition to a mating system previously driven primarily by female choice. Although sexual selection on shape was closely aligned with allometric shape variation, selection on fore femur shape was more consistent than selection on wing shape, which was absent in most species. Sexual selection intensities, but not necessarily the underlying behavioural mechanisms, were overall similar in field and laboratory, suggesting that laboratory assessments well represent the natural situation. If this conclusion can be generalized, it would lend credence to the strategy of using controlled laboratory mating studies to better understand natural selection, behaviour and ecology, at least for smaller animals that can be held in captivity. ? 2021 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
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| 7. |
- Blanckenhorn, Wolf U., et al.
(författare)
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Comprehensive thermal performance curves for yellow dung fly life history traits and the temperature-size-rule
- 2021
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Ingår i: Journal of Thermal Biology. - : Elsevier BV. - 0306-4565 .- 1879-0992. ; 100
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Tidskriftsartikel (refereegranskat)abstract
- Ambient temperature strongly determines the behaviour, physiology, and life history of all organisms. The technical assessment of organismal thermal niches in form of now so-called thermal performance curves (TPC) thus has a long tradition in biological research. Nevertheless, several traits do not display the idealized, intuitive dome-shaped TPC, and in practice assessments often do not cover the entire realistic or natural temperature range of an organism. We here illustrate this by presenting comprehensive sex-specific TPCs for the major (juvenile) life history traits of yellow dung flies (Scathophaga stercoraria; Diptera: Scathophagidae). This concerns estimation of prominent biogeographic rules, such as the temperature-size-rule (TSR), the common phenomenon in ectothermic organisms that body size decreases as temperature increases. S. stercoraria shows an untypical asymptotic TPC of continuous body size increase with decreasing temperature without a peak (optimum), thus following the TSR throughout their entire thermal range (unlike several other insects presented here). Egg-to-adult mortality (our best fitness estimator) also shows no intermediate maximum. Both may relate to this fly entering pupal winter diapause below 12 °C. While development time presents a negative exponential relationship with temperature, development rate and growth rate typify the classic TPC form for this fly. The hitherto largely unexplored close relative S. suilla with an even more arctic distribution showed very similar responses, demonstrating large overlap among two ecologically similar, coexisting dung fly species, thus implying limited utility of even complete TPCs for predicting species distribution and coexistence.
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| 8. |
- Blanckenhorn, Wolf U., et al.
(författare)
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Life history traits, but not body size, vary systematically along latitudinal gradients on three continents in the widespread yellow dung fly
- 2018
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Ingår i: Ecography. - : Wiley. - 0906-7590 .- 1600-0587. ; 41:12, s. 2080-2091
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale clinal variation in body size and other life-history traits is common enough to have stimulated the postulation of several eco-geographical rules. Whereas some clinal patterns are clearly adaptive, the causes of others remain unclear. We present a comprehensive intraspecific population comparison for the cosmopolitan yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae) to check for consistent world-wide patterns. Common garden assessment of various life history traits permitted continental comparison of (clinal) quantitative genetic differentiation (Qst) with putatively neutral genetic differentiation (Fst) derived from field-caught flies. Latitudinal clines in fly development time, growth rate, and overwintering propensity were consistent among North American, European and Japanese populations. Increased winter dormancy incidence and duration at higher latitude, combined with a faster growth rate and shorter development time, suggest that flies are adaptated to season length more than to temperature. The resulting body size clines, in contrast, were not very consistent; importantly, they were not negative, as expected under seasonal constraints, but flat or even positive clines. Quantitative genetic differentiation Q(ST) exceeded neutral molecular variation F-ST for most traits, suggesting that natural selection plays a consistent role in mediating global dung fly life histories. We conclude that faster growth and development in response to shorter growing seasons at higher latitudes may indirectly counteract expected direct effects of temperature on body-size, potentially resulting in flat or inconsistent body size clines in nature.
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| 9. |
- Blanckenhorn, Wolf U, et al.
(författare)
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Proximate causes of Rensch's rule : Does sexual size dimorphism in arthropods result from sex differences in development time?
- 2007
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Ingår i: American Naturalist. ; 169:2, s. 245-257
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Tidskriftsartikel (refereegranskat)abstract
- A prominent interspecific pattern of sexual size dimorphism (SSD) is Rensch's rule, according to which male body size is more variable or evolutionarily divergent than female body size. Assuming equal growth rates of males and females, SSD would be entirely mediated, and Rensch's rule proximately caused, by sexual differences in development times, or sexual bimaturism (SBM), with the larger sex developing for a proportionately longer time. Only a subset of the seven arthropod groups investigated in this study exhibits Rensch's rule. Furthermore, we found only a weak positive relationship between SSD and SBM overall, suggesting that growth rate differences between the sexes are more important than development time differences in proximately mediating SSD in a wide but by no means comprehensive range of arthropod taxa. Except when protandry is of selective advantage ( as in many butterflies, Hymenoptera, and spiders), male development time was equal to ( in water striders and beetles) or even longer than ( in drosophilid and sepsid flies) that of females. Because all taxa show female-biased SSD, this implies faster growth of females in general, a pattern markedly different from that of primates and birds (analyzed here for comparison). We discuss three potential explanations for this pattern based on life-history trade-offs and sexual selection.
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| 10. |
- Blanckenhorn, Wolf U, et al.
(författare)
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Sexual size dimorphism is associated with reproductive life history trait differentiation in coexisting sepsid flies
- 2020
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 129:8
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Tidskriftsartikel (refereegranskat)abstract
- Organismal life histories evolve as syndromes, resulting in correlated evolutionary differentiation of key traits that ultimately aid in discerning species. Reproductive success depends both on the absolute body size of an individual and its size relative to the opposite sex: sexual size dimorphism. In an attempt to further elucidate their coexistence and ecological diversification, we compared standard life history (first reproduction, clutch size, egg size) and associated reproductive trait differentiation of 15 widespread European sepsid fly species (Diptera: Sepsidae) under laboratory common garden conditions. Despite relatively uniform body sizes, sexual dimorphism ranged from female‐ to male‐biased, and development time varied twofold across species. We expected, and found, the abundant and relatively large species (Sepsis cynipsea, punctum, thoracica) with often male‐biased SSD to lay larger but fewer eggs and show fast‐developing, fast‐reproducing life histories with aggressive (coercive) mating behavior characterized by short mating latencies and male conflict. In contrast, the smaller and more dispersed species with female‐biased SSD (S. flavimana, orthocnemis, violacea) laid smaller but more eggs, showing a generally slower life history with long and delayed copulation and oviposition, high mating reluctance fostering extensive inter‐sexual conflict, and more elaborate male (pre‐)copulatory courtship. Two Saltella species were exceptional, being large, developing slowly, nevertheless copulating soon after adult emergence, profusely and briefly. The documented life history differentiation seems partly driven by sexual selection leading to male‐biased dimorphism, rather than undetermined ecological selection, but regardless appears insufficient to explain the coexistence and diversification of these sepsid species in European pastoral landscapes.
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