Stable isotopes document the winter foraging ecology of king penguins and highlight connectivity between subantarctic and Antarctic ecosystems

International audienceThe poorly known winter foraging ecology of the king penguin, a major Southern Ocean consumer, was investigated at the subantarctic Crozet Islands where the largest global population breeds. Blood δ13C and δ15N values were used as proxies of the birds’ foraging habitat and diet, respectively, and circulating prolactin levels helped in determining the birds’ reproductive status. Plasma prolactin concentrations showed that king penguin adults of unknown breeding status (n = 52) that were present at the colony in winter were in fact breeders and failed breeders, but were not non -breeders. Circulating prolactin was neither related to δ13C nor δ15N values, thus suggesting that both breeders and failed breeders used the same foraging habitats and fed on the same prey. Plasma and blood cell isotopic values depicted four new relevant biological features on the feeding strategies of king penguins during the critical winter period: (1) 42% of the birds foraged in the distant Antarctic Zone, but 58% fed primarily in subantarctic waters (δ13C), (2) they preyed upon myctophids in both zones (δ15N), (3) individuals were consistent in their foraging strategies over the winter months (δ13C and δ15N), and (4) a higher proportion of females (77%–80%) than males (27%–31%) favored feeding in distant Antarctic waters (δ13C). This study highlights trophic connectivity between subantarctic and Antarctic ecosystems and hence the key role of energy export from Antarctic waters to sustain breeding populations of subantarctic predators, including during the Austral winter

Intra-Clutch Ratio of Yolk Progesterone Level Changes with Laying Date in Rockhopper Penguins: A Strategy to Influence Brood Reduction?

Hatching asynchrony in avian species generally leads to a size hierarchy among siblings, favouring the first-hatched chicks. Maternally deposited hormones affect the embryo and chick's physiology and behaviour. It has been observed that progesterone, a hormone present at higher levels than other steroid hormones in egg yolks, is negatively related to body mass in embryos, chicks and adults. A differential within-clutch progesterone deposition could therefore be linked to the size hierarchy between siblings and to the resulting brood reduction. We tested whether yolk progesterone levels differed between eggs according to future parental ability to feed the entire clutch in wild rockhopper penguins Eudyptes chrysocome. This species presents a unique reversed egg-size dimorphism and hatching asynchrony, with the larger second-laid egg (B-egg) hatching before the smaller first-laid egg (A-egg). Yolk progesterone levels increased only slightly with female body mass at laying. However, intra-clutch ratios were not related to female body mass. On the other hand, yolk progesterone levels increased significantly with the date of laying onset for A-eggs while they decreased for B-eggs. Early clutches therefore had proportionally more progesterone in the B-egg compared to the A-egg while late clutches had proportionally less progesterone in the B-egg. We propose that females could strategically regulate yolk progesterone deposition within clutches according to the expected food availability during chick growth, an adaptive strategy to adjust brood reduction to conditions. We also discuss these results, relating to yolk progesterone, in the broader context of other yolk steroids

Influence of urbanization on body size, condition, and physiology in an urban exploiter: a multi-component approach

Consistent expanding urbanization dramatically transforms natural habitats and exposes organisms to novel environmental challenges, often leading to reduced species richness and diversity in cities. However, it remains unclear how individuals are affected by the urban environment and how they can or cannot adjust to the specific characteristics of urban life (e.g. food availability). In this study, we used an integrative multi-component approach to investigate the effects of urbanization on the nutritional status of house sparrows (Passer domesticus). We assessed several morphological and physiological indices of body condition in both juveniles (early post-fledging) and breeding adults from four sites with different levels of urbanization in France, Western Europe. We found that sparrows in more urbanized habitats have reduced body size and body mass compared to their rural conspecifics. However, we did not find any consistent differences in a number of complementary indices of condition (scaled mass index, muscle score, hematocrit, baseline and stress-induced corticosterone levels) between urban and rural birds, indicating that urban sparrows may not be suffering nutritional stress. Our results suggest that the urban environment is unlikely to energetically constrain adult sparrows, although other urban-related variables may constrain them. On the other hand, we found significant difference in juvenile fat scores, suggesting that food types provided to young sparrows differed highly between habitats. In addition to the observed smaller size of urban sparrows, these results suggest that the urban environment is inadequate to satisfy early-life sparrows' nutritional requirements, growth, and development. The urban environment may therefore have life-long consequences for developing birds

Maternal effects in relation to helper presence in the cooperatively breeding sociable weaver

In egg laying species, breeding females may adjust the allocation of nutrients or other substances into eggs in order to maximise offspring or maternal fitness. Cooperatively breeding species offer a particularly interesting context in which to study maternal allocation because helpers create predictably improved conditions during offspring development. Some recent studies on cooperative species showed that females assisted by helpers produced smaller eggs, as the additional food brought by the helpers appeared to compensate for this reduction in egg size. However, it remains unclear how common this effect might be. Also currently unknown is whether females change egg composition when assisted by helpers. This effect is predicted by current maternal allocation theory, but has not been previously investigated. We studied egg mass and contents in sociable weavers ( Philetairus socius ). We found that egg mass decreased with group size, while fledgling mass did not vary, suggesting that helpers may compensate for the reduced investment in eggs. We found no differences in eggs’ carotenoid contents, but females assisted by helpers produced eggs with lower hormonal content, specifically testosterone, androstenedione (A4) and corticosterone levels. Taken together, these results suggest that the environment created by helpers can influence maternal allocation and potentially offspring phenotypes

The role of parasitism in the energy management of a free-ranging bird

Parasites often prompt sub-lethal costs to their hosts by eliciting immune responses. These costs can be hard to quantify but are crucial to our understanding of the host's ecology. Energy is a fundamental currency to quantify these costs, as energetic trade-offs often exist between key fitness-related processes. Daily energy expenditure (DEE) comprises of resting metabolic rate (RMR) and energy available for activity, which are linked via the energy management strategy of an organism. Parasitism may play a role in the balance between self-maintenance and activity, as immune costs can be expressed in elevated RMR. Therefore, understanding energy use in the presence of parasitism enables mechanistic elucidation of potential parasite costs. Using a gradient of natural parasite load and proxies for RMR and DEE in a wild population of breeding European shags (Phalacrocorax aristotelis), we tested the effect of parasitism on maintenance costs as well as the relationship between proxies for RMR and DEE. We found a positive relationship between parasite load and our RMR proxy in females but not males, and no relationship between proxies for RMR and DEE. This provides evidence for increased maintenance costs in individuals with higher parasite loads and suggests the use of an allocation energy management strategy, whereby an increase to RMR creates restrictions on energy allocation to other activities. This is likely to have fitness consequences as energy allocated to immunity is traded off against reproduction. Our findings demonstrate that understanding energy management strategies alongside fitness drivers is central to understanding the mechanisms by which these drivers influence individual fitness

Post-natal glucocorticoid elevation affects GnRH-induced luteinizing hormone concentration in female house sparrows

International audienceMost non-mammalian studies investigating the long-term effects of early-life stressor exposure on endocrineregulation have focused on the hypothalamic-pituitaryadrenal (HPA) axis. However, the hypothalamic-pituitarygonadal(HPG) axis may more directly affect fitness by regulating reproduction. Changes in HPG axis regulationcould allow vertebrates to adaptively mitigate negative effects of early-life stressor exposure. However, only afew studies have examined long-term effects of early-life stressor experience on the HPG axis, and these havefound mixed results. Here, we evaluate long-term effects of post-natal corticosterone exposure on the HPG axis inadult female house sparrows (Passer domesticus). We elevated circulating corticosterone non-invasively in wildnestling house sparrows between 8 and 11 days post-hatching, and then brought birds into captivity at fledging.Early in their first breeding season (ages 285-353d post-hatching), females were given a gonadotropin releasinghormone (GnRH) challenge. We found that early-life corticosterone exposure interacted with current conditionsuch that females exposed to elevated post-natal corticosterone had higher baseline and GnRH-induced luteinizinghormone (LH) concentration than control females, but only if they had a high mass. Our results suggestthat female house sparrows may mitigate negative impacts of early-life corticosterone exposure by investing inearly reproduction, but only when current energetic condition allows

Endocrine consequences of an acute stress under different thermal conditions: a study of corticosterone, prolactin, and thyroid hormones in the pigeon (Columbia livia)

International audienceIn the context of global change, the physiological and hormonal stress responses have received much attentionbecause of their implications in terms of allostasis. However, most studies have focused on glucocorticoidsonly as the “common” response to stressorswhile neglecting other endocrine axes and hormones (e.g. prolactin,thyroid hormones) that play a crucial role in metabolic adjustments. Interestingly, the responsiveness of all theseendocrine axes to stress may depend on the energetic context and this context-dependent stress response hasbeen overlooked so far. In the wild, temperature can vary to a large extent within a short time window and ambienttemperature may affect these metabolic-related endocrine axes, and potentially, their responsiveness to anacute stressor. Here,we explicitly tested this hypothesis by examining the effect of a standardized stress protocolon multiple hormonal responses in the rock pigeon (Columbia livia). We tested the effect of an acute restraintstress on (1) corticosterone levels, (2) prolactin levels, and (3) thyroid hormone levels (triiodothyronine,thyroxine) in pigeons that were held either at cool temperature (experimental birds) or at room temperature(control birds) during the stress protocol. Although we found a significant influence of restraint stress on mosthormone levels (corticosterone, prolactin, and thyroxine), triiodothyronine levels were not affected by the restraintstress. This demonstrates that stressors can have significant impact on multiple endocrine mechanisms.Importantly, all of these hormonal responses to stress were not affected by temperature, demonstrating thatthe exposure to cold temperature does not affect the way these hormone levels change in response to handlingstress. This suggests that some endocrine responses to temperature decreases may be overridden by the endocrineresponses to an acute restraint stress

The behavioural and physiological stress responses are linked to plumage coloration in the rock pigeon ( Columbia livia )

International audienceIn wild vertebrates, conspicuousness often signals a high phenotypic quality and is therefore associated with fitness benefits (“the handicap principle hypothesis”). However, conspicuous individuals usually face a higher risk of predation because they are easier to detect. Therefore, conspicuous individuals are expected to modify their behavioural and their physio logical stress responses to limit the negative effect of their conspicuousness on survival. We examined the link between plumage coloration and the stress response in a bird species (the rock pigeon, Columbia livia) by comparing two groups of pigeons with different plumage characteristics: ‘blue-bar’ birds (lighter birds) and ‘checker’ birds (darker birds). Specifically, we measured several behavioural and physiological components of the stress response (breath rate, corticosterone, and tonic immobility). Although breath rate did not differ between ‘checker’ and ‘blue bar’ birds, the corticosterone stress response of ‘blue-bar’ birds was greater relative to that of ‘checker’ birds. Moreover, ‘checker’ birds were more likely to initiate tonic immobility relative to ‘blue bar’ birds. Therefore, this study suggests that the behavioural and physiological stress responses of wild birds may differ according to their plumage coloration. To conclude, our results suggest that plumage colorations may be functionally linked to specific behavioral and physiological sensitivities to stressors

Short-term dehydration influences baseline but not stress-induced corticosterone levels in the house sparrow ( Passer domesticus )

International audienc