[Show abstract][Hide abstract] ABSTRACT: Summary • Carotenoids are fat-soluble pigments that stimulate the immune system and can act as antioxidants. Carotenoids are thus expected to buffer the effects of environmental stressors on health. As carotenoids are a limited resource, the ability of an individual to use and metabolize carotenoids is assumed to influence its stress-resistance. Accordingly, it has been found that nestlings hatched from eggs with increased carotenoid concentration, show an enhanced ability to use carotenoids and a lower susceptibility of tissues to lipid peroxidation. • We tested the prediction that nestling great tits (Parus major), hatched from eggs laid by carotenoid-supplemented mothers, cope better with a transient stressor encountered after hatching. We supplemented half of the breeders with carotenoids during egg production (C+), used the other half as a control (C–), and cross-fostered the eggs between nests after clutch completion. Three days after hatching, we applied a stressor in two-third of the nests either by increasing brood size, or by infesting nests with hen fleas (Ceratophyllus gallinae) during five consecutive days. A third group was kept as a control. We then assessed the responses of C+ and C– nestlings to each stressor by measuring mass gain, body condition, plumage coloration, humoral immune response and fever response to a lipopolysaccharide injection. • In control nests, C+ and C– nestlings showed similar body condition but C+ nestlings had a higher increase in body temperature and tended to have a higher wing web swelling in response to lipopolysaccharide injection. Under stress, however, there were no differences in overall condition between C+ and C– nestlings. The two stressors led to different responses: when sibling competition was increased, C– nestlings favoured immune development, whereas C+ nestlings favoured mass gain and body condition, while under parasite exposure C+ and C– nestlings seemed to invest in immune development and body growth similarly. • Our results support the hypothesis that carotenoid-induced maternal effects provide developmental benefits under natural conditions without additional stressors. Additionally, we show that the response to sudden environmental changes depends on the environment during the initial phases of development, which thus shape phenotype and individual variation.
[Show abstract][Hide abstract] ABSTRACT: Experimental studies provide evidence that, in spatially and temporally heterogeneous environments, individuals track variation in breeding habitat quality to adjust breeding decisions to local conditions. However, most experiments consider environmental variation at one spatial scale only, while the ability to detect the influence of a factor depends on the scale of analysis. We show that different breeding decisions by adults are based on information about habitat quality at different spatial scales. We manipulated (increased or decreased) local breeding habitat quality through food availability and parasite prevalence at a small (territory) and a large (patch) scale simultaneously in a wild population of Great Tits (Parus major). Females laid earlier in high-quality large-scale patches, but laying date did not depend on small-scale territory quality. Conversely, offspring sex ratio was higher (i.e., biased toward males) in high-quality, small-scale territories but did not depend on large-scale patch quality. Clutch size and territory occupancy probability did not depend on our experimental manipulation of habitat quality, but territories located at the edge of patches were more likely to be occupied than central territories. These results suggest that integrating different decisions taken by breeders according to environmental variation at different spatial scales is required to understand patterns of breeding strategy adjustment.
[Show abstract][Hide abstract] ABSTRACT: 1. Maternal 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. 2. In 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. 3. As 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. 4. A 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. 5. Overall, 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.
[Show abstract][Hide abstract] ABSTRACT: Carotenoids are antioxidants playing major roles in physiological functions at various stages of an animal's life. Female birds deposit large amounts of carotenoids into their eggs. Carotenoids are, however, a limiting resource, and females are expected to balance carotenoid deposition into the eggs with their utilization for themselves. Carotenoid availability is thus likely to determine both the levels of yolk carotenoids and maternal care during rearing. Carotenoids have been shown to benefit the embryo and the growing nestling, and it can be hypothesized that an increase in carotenoid availability during laying leads to higher nestling condition and competitive ability. We manipulated carotenoid availability to great tit pairs prior to and during egg laying and later partially cross-fostered chicks at hatching. During the rearing period, we measured how carotenoid availability affected nestlings begging behavior and male and female feeding effort. We also manipulated the ectoparasite load, predicting that carotenoid supplementation would help adults and nestling to cope with parasites. Nestlings hatched from eggs laid by carotenoid-supplemented females and raised in small broods begged more intensely. Nestlings in small deparasitized broods also begged more actively. The feeding effort of control females increased with brood size, whereas the feeding effort of carotenoid-supplemented females was high whatever the brood size. Male feeding effort was unaffected by our treatment. Our results support the hypothesis that maternally derived carotenoids increase nestling begging behavior and hence competitive ability. They further suggest that carotenoid availability determines the level of parental investment and can mediate trade-offs between life-history traits. Copyright 2008, Oxford University Press.
[Show abstract][Hide abstract] ABSTRACT: 1Egg yolks contain carotenoids that protect biological molecules against free-radical damage and promote maturation of the immune system. Availability of carotenoids to birds is often limited. Trade-offs can thus arise in the allocation of carotenoids to different physiological functions, and mothers may influence the immunocompetence of nestlings by modulating the transfer of carotenoid to the yolk.2In the great tit Parus major, we experimentally manipulated the dietary supply of carotenoid to mothers, and partially cross-fostered hatchlings to investigate the effect of an increased availability of carotenoids during egg laying on immunocompetence of nestlings.3In addition, we infested half of the nests with hen fleas Ceratophyllus gallinae to investigate the relationship between carotenoid availability, resistance to ectoparasites and immunocompetence.4We found that the procedure of cross-fostering can reduce the immune response of nestlings, but this effect can be compensated by the maternally transferred carotenoids. Cross-fostered nestlings of carotenoid-supplemented females show a similar immune response to non-cross-fostered nestlings, while cross-fostered nestlings of control females mounted a weaker cell-mediated immune response. This suggests that yolk carotenoids may help nestlings to cope with stress, for example the one generated by cross-fostering and/or they may enhance nestling competitiveness.5There was no statistically significant interaction between parasite and carotenoid treatments, as would be expected if carotenoids helped nestlings to fight parasites. Under parasite pressure, however, lighter nestlings raised a lower immune response, while the immune response was only weakly correlated with body mass in uninfested nests.