| 41. |
- Guidetti, R, et al.
(författare)
-
Long-term anhydrobiotic survival in semi-terrestrial micrometazoans
- 2002
-
Ingår i: Journal of Zoology. - 0952-8369. ; 257:2, s. 181-187
-
Tidskriftsartikel (refereegranskat)abstract
- This study represents the first systematic investigation of long-term anhydrobiotic survival in tardigrades, rotifers and nematodes inhabiting mosses and lichens. Sixty-three different samples from public and private collections, kept dry for 9-138 years, were examined. Rotifers of the genus Mniohia and the eutardigrade Ramazzottius oberhaeuseri (hatched from eggs) were found alive from one of the samples (9 years old). These observations represent the longest record for rotifers in the anhydrobiotic state. For tardigrades, our results confirm previous reports on the upper limit of anhydrobiotic survival under atmospheric oxygen conditions. This study suggests the possibility that tardigrade eggs are able to withstand longer periods in anhydrobiosis than animals. Some problems related to the evaluation of long-term anhydrobiotic survival, such as contamination and chemical treatments of samples, are reported. The possible role of the microenvironment in which the anhydrobiotic animals are kept is discussed.
|
|
| 42. |
- Robertson, Stephanie, et al.
(författare)
-
Microstructures of high strength steel welding consumables from directed thermal cycles by shaped laser pulses
- 2020
-
Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 109:9-12, s. 2653-2662
-
Tidskriftsartikel (refereegranskat)abstract
- Filler wire metallurgy was modified through temporally shaped laser pulses, controlling cooling cycles in a recently developed method. Trends were identified through efficient mapping while maintaining representative thermal cycles of welding processes. A primary pulse melted preplaced filler wires while a secondary, linearly ramped-down pulse elevated the nugget to re-austenization temperatures. Ramped-down pulses resulted in linear cooling rates comparable with and exceeding furnace-based methods, between 50 and 300∘C/s. The linear decay of laser output power guided the temperature through a regime to obtain desired microstructures. For three very high-strength steel filler wire chemistries, quenching resulted in smaller plates with cross-hatched microstructures, accompanied by grain boundary ferrite. Finer bainite microstructures started forming for fast linear temperature decay, about 250∘C/s. Slower decay or a weaker third cycle formed coarser microstructures with coalescent sheaves and less cross-hatching.
|
|
| 43. |
- Boyner, Malin
(författare)
-
A flying start : Adapted hatching and post-hatch feeding in broiler chickens
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Conventional hatching practices do not involve provision of feed and water to broiler chickens before placement at the rearing farm. This can pose problems, especially for early hatchlings, which remain feed-restricted for a considerable period due to biological variation in hatch time. The individual requirements of modern fast-growing chickens in order to remain robust and resilient may have changed in recent decades. This thesis studied the effect of hatching time on interval to first feed intake, growth and organ development in chicks hatched on-farm. It also examined the effects of providing hatching chicks with access to feed and water in the hatcher, combined with two different probiotics, on productivity, organ development, immune traits and development of caecal microbiota. Physiological differences between chicks hatched at different times during the hatching window generally levelled out during the production period. Eating-related activities were low immediately post-hatch, and early hatchlings showed compensatory growth as they were lightest at hatch but heaviest at three days of age. Feed deprivation during hatch resulted in depressed feed intake and associated depressed growth, which in some cases was reversed during the growing phase. Supplementation with probiotics had some negative effects on productivity, especially for chicks deprived of feed and water at hatch. There were no long-term differences due to early feeding on microbiota development or immune traits measured. These results suggest that modern broiler chickens are at least partly capable of compensating for setbacks in early life, and that some early effects of feed and water deprivation are transient. However, the studies in this thesis were performed in highly sanitary conditions and at lower stocking densities than in commercial production. Further research is needed to confirm the effects of adapted hatching and post-hatch feeding strategies in conditions that resemble more closely the challenges faced by the modern broiler.
|
|
| 44. |
- Hedlund, Johanna S. U., et al.
(författare)
-
Long-term phenological shifts and intra-specific differences in migratory change in the willow warbler Phylloscopus trochilus
- 2015
-
Ingår i: Journal of Avian Biology. - : Wiley. - 0908-8857 .- 1600-048X. ; 46:1, s. 97-106
-
Tidskriftsartikel (refereegranskat)abstract
- Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life-cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long-term study on the willow warbler Phylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22-yr of ringing records and two temporally separated data sets of egg-laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg-laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra-specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg-laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.
|
|
| 45. |
- Smith, Henrik G., et al.
(författare)
-
Intrasexual competition among polygynously mated female starlings (Sturnus vulgaris)
- 1994
-
Ingår i: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 5, s. 57-63
-
Tidskriftsartikel (refereegranskat)abstract
- In southern Sweden, the starling (Sturnus vulgaris) has a variable mating system with some males mating monogamously and others attracting several females. Mating status affected the reproductive success of females: monogamous and primary females laid larger clutches and fledged more and heavier young than secondary females. This pattern was explained by female competition for male help, with the male primarily helping the offspring of highest value (i.e., the oldest brood). However, when the nesting attempt of the primary female failed, the success of the secondary female increased to the same level as that for primary and monogamous females. The success of the secondary female in terms of fledging success and fledgling size was higher when the secondary female hatched her eggs soon after the primary female. This was due to the fact that a male divided his effort between his broods when the age difference between broods was small
|
|
| 46. |
- Filipsson, Karl, et al.
(författare)
-
Do predator odours and warmer winters affect growth of salmonid embryos?
- 2023
-
Ingår i: Ecology of Freshwater Fish. - : John Wiley & Sons. - 0906-6691 .- 1600-0633. ; :1
-
Tidskriftsartikel (refereegranskat)abstract
- Conditions early in ontogeny can have considerable effects later on in life. Many salmonids spawn during the autumn, and temperature during subsequent embryogenesis may have far-reaching effects on life-history traits, especially when considering ongoing climate change. Even biotic conditions during embryogenesis, such as predation threat, may affect later life stages. Here, we examined how predator odours and increased temperatures affect embryonic growth and development of a fish (brown trout Salmo trutta). We found that embryos had lower body mass and greater yolk volume close to hatching when subjected to predator odours. Trout embryos incubated at temperatures representing natural winter conditions were larger than embryos incubated at higher temperatures, although the latter hatched earlier. Fry sizes at emergence did not differ between treatments, perhaps because of compensatory growth during spring. This study shows that predator presence can have similar effects on embryonic growth of salmonids as warming winters, with possible impact later in ontogeny.
|
|
| 47. |
- Loman, Jon
(författare)
-
Microevolution and maternal effects on tadpole Rana temporaria growth and development rate
- 2002
-
Ingår i: Journal of Zoology. - 0952-8369. ; 257:1, s. 93-99
-
Tidskriftsartikel (refereegranskat)abstract
- Can variation in egg size explain the local variation in tadpole growth and development of the common frog Rana temporaria or are other mechanisms, e.g. microevolution, involved? To study this, tadpoles were raised in outdoor tanks. Each tank housed tadpoles from one clutch. Eggs were collected during 2 years from six different ponds and their sizes were measured. Large eggs gave rise to tadpoles that grew and developed faster than those hatched from small eggs. Tadpoles from large eggs thus metamorphosed earlier but, because they grew for a shorter time, size at metamorphosis was not affected by initial egg size. Tadpoles from different ponds differed in strategy; after correcting for egg size effects, tadpoles from some ponds tended to metamorphose earlier and at a larger size than those from others. These ponds occasionally dry out during or before the tadpoles period of metamorphosis. I argue that the detected pond differences are genetically based and represent a case of microevolution.
|
|
| 48. |
- Tobler, Michael
(författare)
-
Maternal programming: costs, benefits and constraints of maternal hormone transfer
- 2007
-
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.
|
|
| 49. |
- Bergström, Ulf
(författare)
-
Spatio-temporal dynamics of cod nursery areas in the Baltic Sea
- 2017
-
Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 155, s. 28-40
-
Tidskriftsartikel (refereegranskat)abstract
- In this study the drift of eastern Baltic cod larvae and juveniles spawned within the historical eastern Baltic cod spawning grounds was investigated by detailed drift model simulations for the years 1971-2010, to examine the spatio-temporal dynamics of environmental suitability in the nursery areas of juvenile cod settlement. The results of the long-term model scenario runs, where juvenile cod were treated as simulated passively drifting particles, enabled us to find strong indications for long-term variations of settlement and potentially the reproduction success of the historically important eastern Baltic cod nursery grounds. Only low proportions of juveniles hatched in the Arkona Basin and in the Gotland Basin were able to settle in their respective spawning ground. Ocean currents were either unfavorable for the juveniles to reach suitable habitats or transported the juveniles to nursery grounds of neighboring subdivisions. Juveniles which hatched in the Bornholm Basin were most widely dispersed and showed the highest settlement probability, while the second highest settlement probability and horizontal dispersal was observed for juveniles originating from the Gdansk Deep. In a long-term perspective, wind-driven transport of larvae/juveniles positively affected the settlement success predominately in the Bornholm Basin and in the Bay of Gdansk. The Bornholm Basin has the potential to contribute on average 54% and the Bay of Gdansk 11% to the production of juveniles in the Baltic Sea. Furthermore, transport of juveniles surviving to the age of settlement with origin in the Bornholm Basin contributed on average 13 and 11% to the total settlement in the Arkona Basin and in the Gdansk Deep, respectively. The time-series of the simulated occupied juvenile cod habitat in the Bornholm Basin and in the Gdansk Deep showed a similar declining trend as the Fulton's K condition factor of demersal 1-group cod, which may confirm the importance of oxygen-dependent habitat availability and its effect on density dependence as a process relevant for recruitment success. (C) 2017 Elsevier Ltd. All rights reserved.
|
|
| 50. |
- Cuello, C., et al.
(författare)
-
Vitrification of in vitro cultured porcine two-to-four cell embryos
- 2007
-
Ingår i: Theriogenology. - : Elsevier. - 0093-691X .- 1879-3231. ; 68:2, s. 258-264
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this experiment was to evaluate the effect of a 5-day period of in vitro culture of two-to-four cell porcine embryos up to the blastocyst stage on their ability to survive vitrification and warming. In order to increase the cooling rate, superfine open pulled straws and Vit-Master (R) technology were used for vitrification. Two-to-four cell embryos were collected from weaned sows (n = 11) on day 2 (DO = onset of estrus). Some embryos (N = 63) were vitrified within 3 It after collection, warmed and cultured for 120 h (Group V2). Additionally, 81 two-to-four cell embryos were cultured for 96 It in order to obtain blastocysts; these were then vitrified, warmed and cultured for 24 h (Group VB; N = 65). The remaining two-to-four cell embryos were used as controls and thus not vitrified (control embryos; N = 70) but were cultured in vitro for 120 h. The V2, VB and control embryos were evaluated for their developmental progression and morphology during culture. All embryos (V2, VB and controls) were fixed on the same day of development in order to assess the total number of blastomeres. The survival and blastocyst formation rates obtained from V2 embryos were very poor (9.6 +/- 0.7% and 3.2 +/- 0.5%, respectively). The survival and hatching rates of VB embryos (75.0 +/- 0.69% and 33.6 +/- 0.13%) were lower (p less than 0.001) than those obtained with control embryos (89.1 +/- 0.8% and 47.5 +/- 0.12%). Hatched VB embryos had a lower (p less than 0.01) total cell number than hatched control embryos (70.3 +/- 4.5 versus 90.6 +/- 3.2, respectively). There was no difference between expanded VB and control blastocysts. In conclusion, blastocysts derived from in vitro culture of two-to-four cell pig embryos could be successfully vitrified using SOPS straws and Vit-Master (R). (c) 2007 Elsevier Inc. All rights reserved.
|
|
