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Differential Allocation (differential + allocation)
Selected AbstractsSex-related effects of maternal egg investment on offspring in relation to carotenoid availability in the great titJOURNAL OF ANIMAL ECOLOGY, Issue 1 2008Anne Berthouly Summary 1Maternal carotenoids in the egg yolk have been hypothesized to promote maturation of the immune system and protect against free radical damages. Depending on availability, mothers may thus influence offspring quality by depositing variable amounts of carotenoids into the eggs. Sex allocation theory predicts that in good quality environments, females should invest into offspring of the sex that will provide larger fitness return, generally males. 2In a field experiment we tested whether female great tits bias their investment towards males when carotenoid availability is increased, and whether male offspring of carotenoid-supplemented mothers show higher body condition. We partially cross-fostered hatchlings to disentangle maternal effects from post-hatching effects, and manipulated hen flea Ceratophyllus gallinae infestation to investigate the relationship between carotenoid availability and resistance to ectoparasites. 3As predicted, we found that carotenoid-supplemented mothers produced males that were heavier than their sisters at hatching, while the reverse was true for control mothers. This suggests that carotenoid availability during egg production affects male and female hatchlings differentially, possibly via a differential allocation to male and female eggs. 4A main effect of maternal supplementation became visible 14 days after hatching when nestlings hatched from eggs laid by carotenoid-supplemented mothers had gained significantly more mass than control nestlings. Independently of the carotenoid treatment, fleas impaired mass gain of nestlings during the first 9 days in large broods only and reduced tarsus length of male nestlings at an age of 14 days, suggesting a cost to mount a defence against parasites. 5Overall, our results suggest that pre-laying availability of carotenoids affects nestling condition in a sex-specific way with potentially longer-lasting effects on offspring fitness. [source] Maternal yolk testosterone does not modulate parasite susceptibility or immune function in great tit nestlingsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2005BARBARA TSCHIRREN Summary 1Maternal yolk hormones can enhance the development and phenotypic quality of nestling birds. Nevertheless, within species large differences in yolk androgen concentrations among clutches are observed. This differential allocation of maternal yolk hormones might be explained by a trade-off between beneficial effects of yolk androgens and their associated costs. 2Potential costs include an increased susceptibility to parasites in nestlings exposed to high concentrations of yolk androgens during embryonic development, weaker immune response or increased levels of circulating corticosterone that indirectly reduce immune function. 3In a field study, we manipulated yolk testosterone in great tit (Parus major) eggs and tested the nestling's susceptibility to ectoparasites as measured by the parasites' effect on growth, the cellular immune response, and the levels of circulating corticosterone. 4At the end of the nestling period, nestlings originating from testosterone-injected eggs were heavier than control nestlings. This effect was strongest in nestlings at the end of the size hierarchy, as shown by a significant interaction between hormone treatment and the nestlings' size rank within nests. 5High levels of yolk testosterone promoted growth of the nestling's body mass similarly in parasite-infested and parasite-free nests, and neither affected the levels of plasma corticosterone, nor the nestling's cell-mediated immune response. 6In summary, our results do not show negative short-term effects of high concentrations of yolk testosterone on immune function or parasite susceptibility, but emphasize that maternal investment via deposition of yolk testosterone can promote fitness-related growth and development of nestlings. [source] Seasonal growth patterns of wild juvenile fish: partitioning variation among explanatory variables, based on individual growth trajectories of Atlantic salmon (Salmo salar) parrJOURNAL OF ANIMAL ECOLOGY, Issue 1 2005P. J. BACON Summary 1We present an empirical, analytical model that estimates both temperature and seasonal response functions for the growth of wild juvenile fish without the need for costly tank experiments in less realistic conditions. 2Analysis of monthly recapture data on the lengths and weights of individual wild juvenile fish demonstrates that simple temperature-driven models of growth can be less informative than more realistic, empirical, models. 3A case study of wild Atlantic salmon parr (Salmo salar) showed that: most growth took place in a 10-week period in spring, at temperatures below those that previous published models report as necessary for rapid growth and at faster rates than the maximum that previous models predicted. 4Temperature and fish size allometry explained 45% of growth variation, but the effects of temperature were significantly and markedly different at different seasons. 5Seasonal effects explained an additional 18% of the variation and were strongly associated with the abundance of potential ,drift' food. 6The seasonal patterns for growth in length and weight were different, implying differential allocation of resources to structural and reserve tissues. 7The growth patterns of sexually maturing male parr and emigrants also differed in comparison to other parr. 8Condition factor, length at first capture and seasonal interactions with both early maturity and smolting explained another 7% of the variation. 9However, individual fish did not grow consistently better, or worse, than the ,average' fish. 10This study emphasizes the necessity to test the adequacy of laboratory-based physiological models with suitably detailed field data and to focus model refinement by identifying processes which otherwise confound interpretation. [source] Egg-yolk androgen and carotenoid deposition as a function of maternal social environment in barn swallows Hirundo rusticaJOURNAL OF AVIAN BIOLOGY, Issue 4 2010Rebecca J. Safran Evidence is mounting that female animals use egg-yolk compounds (e.g. steroids, antioxidants) to adaptively engineer the quality of their offspring as a function of several maternal and environmental factors. Though adjustments to yolk allocation have been well-characterized as a function of parental phenotypes, we know very little about how an individual's social environment influences yolk composition. Here, we consider how two types of yolk compounds, androgens and carotenoids, relate to the maternal social environment during the egg-laying period, controlling statistically for known correlations between various aspects of parental quality and egg yolk compounds. Barn swallows Hirundo rustica erythrogaster breed in groups of highly variable size and spacing, allowing us to test whether or not the social environment is correlated with these maternal effects. We found no relationship between carotenoid levels in eggs as a function of colony size, colony density, or nearest-neighbor distance. However, eggs from females in larger groups had lower concentrations and total amounts of yolk androgens than those from females in smaller, less dense social settings. Our results counter previous predictions and literature, showing that females breeding in large groups deposit more androgen in eggs, mechanistically, because they compete more with conspecifics and have higher circulating androgen levels themselves and, functionally, because it could be advantageous for their offspring to show high androgen-mediated competitive abilities early in life. Instead, because group size in this species is governed largely by site fidelity and the availability of old nests for re-use, and because reproductive output does not differ as a function of group size, it may be that competition is greater for limited nests in small groups, thus elevating androgen levels. Further, yolk androgens were previously shown to be affected by male quality, and the greater concentrations and amounts of yolk androgens in smaller sites may reflect differential allocation to darker males found at these sites. [source] | ||||||||||