Charline Parenteau

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.

Does short-term fasting lead to stressed-out parents? A study of incubation commitment and the hormonal stress responses and recoveries in snow petrels

The hormonal stress response is flexible and can be modulated by individuals according to its costs and benefits. Therefore, it is predicted that parents in poor body condition should modify their hormonal stress response, and thus, redirect energy allocation processes from parental care to self-maintenance when stressors occur. To test this prediction, most studies on free-living vertebrates have only focused on the stress response while the stress recovery - how quickly hormonal levels return to baseline values - has been neglected. Moreover, most studies have only focused on corticosterone - the primary mediator of allostasis - without paying attention to prolactin despite its major role in mediating parental behaviors. Here, we examined the effect of a short-term fasting event on the corticosterone and prolactin stress responses and recoveries, and we subsequently explored their relationships with parental decision in the snow petrel (Pagodroma nivea). By comparing the hormonal profiles of fasting and non-fasting snow petrels, we showed that parents modulate their corticosterone (but not prolactin) stress response according to their energetic status. We also described for the first time the hormonal stress recoveries in wild birds and found that they did not differ between fasting and non-fasting birds. Importantly, egg neglect was negatively correlated with circulating prolactin but not corticosterone levels in this species, demonstrating therefore a complex link between body condition, parental behavior and circulating corticosterone and prolactin levels. We suggest that both corticosterone and prolactin play a major role in the way parents adjust to stressors. This multiple signaling may allow parents to fine-tune their response to stressors, and especially, to activate specific allostasis-related mechanisms in a timely manner.

Corticosterone levels in relation to trace element contamination along an urbanization gradient in the common blackbird (Turdus merula)

In a rapidly urbanizing world, trace element pollution may represent a threat to human health and wildlife, and it is therefore crucial to assess both exposition levels and associated effects of trace element contamination on urban vertebrates. In this study, we investigated the impact of urbanization on trace element contamination and stress physiology in a wild bird species, the common blackbird (Turdus merula), along an urbanization gradient (from rural to moderately urbanized areas). Specifically, we described the contamination levels of blackbirds by 4 non-essential (Ag, Cd, Hg, Pb) and 9 essential trace elements (As, Co, Cr, Cu, Fe, Mn, Ni, Se, Zn), and explored the putative disrupting effects of the non-essential element contamination on corticosterone levels (a hormonal proxy for environmental challenges). We found that non-essential trace element burden (Cd and Pb specifically) increased with increasing urbanization, indicating a significant trace element contamination even in medium sized cities and suburban areas. Interestingly, the increased feather non-essential trace element concentrations were also associated with elevated feather corticosterone levels, suggesting that urbanization probably constrains birds and that this effect may be mediated by trace element contamination. Future experimental studies are now required to disentangle the influence of multiple urban-related constraints on corticosterone levels and to specifically test the influence of each of these trace elements on corticosterone secretion.

Females Paired with New and Heavy Mates Reduce Intra- Clutch Differences in Resource Allocation

Reproductive investment affects both offspring and parental fitness and influences the evolution of life histories. Females may vary their overall primary reproductive effort in relation to the phenotypic characteristics of their mate. However, the effects of male quality on differential resource allocation within clutches have been largely neglected despite the potential implications for mate choice and population dynamics, especially in species exhibiting biparental care and brood reduction. Female southern rockhopper penguins Eudyptes chrysocome paired with heavy mates reduced intra-clutch variation in egg and albumen masses. Females paired with new mates also reduced intra-clutch variation in yolk androgen levels. Since both an increased mass and increased androgen concentrations positively influence chick survival under sibling competition, the chances of fledging the whole clutch are likely to be higher for newly formed pairs with heavy males than for previously formed pairs with light males. Interestingly, total clutch provisioning did not vary with male quality. We show for the first time that females vary intra-clutch variation in resource allocation according to male quality. In species with brood reduction, it may be more adaptive for females to modulate the distribution of resources within the clutch according to breeding conditions, than to change their total clutch provisioning.

Measuring corticosterone in seabird egg yolk and the presence of high yolk gestagen concentrations

Large inter-species differences have been found in yolk corticosterone amounts in avian eggs. While some studies have failed to detect significant amounts of corticosterone, in other species high amounts have been recorded, such as in a recent study of southern rockhopper penguins Eudyptes chrysocome chrysocome. However, attention has been drawn recently to the fact that many antibodies for corticosterone measurement cross-react with other steroids present in the yolk. In particular, progesterone and related substances can occur in yolk in high concentrations, such that also low cross-reactions of corticosterone assays may lead to measurement errors. We thus performed high-performance liquid chromatographic (HPLC) analyses of yolk extracts and determined the concentration of immunoreactive corticosterone, as well as cross-reacting progesterone and cortisol in egg yolks of southern rockhopper penguins and imperial shags Phalacrocorax atriceps albiventer. We found that high gestagen concentrations in the yolk result in large measurement errors for yolk corticosterone, even when the cross-reactivity seems small. This was observed for both species. We further found species-specific differences in the actual corticosterone amounts present in the egg yolks.

Feather and faecal corticosterone concentrations predict future reproductive decisions in harlequin ducks (Histrionicus histrionicus)

Understanding sources of reproductive variation can inform management and conservation decisions, population ecology and life-history theory. Annual reproductive variation can drive population growth rate and can be influenced by factors from across the annual cycle (known as carry-over effects). The majority of studies, however, focus solely on the role of current environmental events. Past events often influence future reproductive decisions and success but can be logistically difficult to collect and quantify, especially in migratory species. Recent work indicates that glucocorticoids may prove good indicators to evaluate carry-over effects across life-history transitions. Here, we evaluated three different measures of glucocorticoid physiology (feathers, faeces and plasma) to evaluate the predictability of future breeding decision in the harlequin duck (Histrionicus histrionicus). We collected tail and back feathers, plasma and faeces for glucocorticoid analysis, and fitted female harlequin ducks with very high-frequency transmitters to track their breeding decisions. Both back feathers (moulted immediately before the current season) and faecal glucocorticoid metabolites were identified as important predictive factors of reproductive decisions; high concentrations of glucocorticoid metabolites in back feathers and faeces predicted a higher likelihood of reproductive deferral for the year. Although back and tail feather corticosterone concentrations were correlated, tail feathers (moulted at the end of the previous breeding season) did not predict breeding decisions. Plasma corticosterone concentrations were collected over too broad a time range after capture to be useful in this study. This study demonstrates the utility of non-invasive corticosterone metrics in predicting breeding decisions and supports the use of feathers to measure carry-over effects in migratory birds. With this technique, we identified the prenuptial moult as an important life-history phase that contributes to reproductive decisions. Identification of critical life-history phases is paramount to efficient management of species.

Contaminants and energy expenditure in an Arctic seabird: Organochlorine pesticides and perfluoroalkyl substances are associated with metabolic rate in a contrasted manner

Abstract Basal metabolic rate (BMR), the minimal energetic cost of living in endotherms, is known to be influenced by thyroid hormones (THs) which are known to stimulate in vitro oxygen consumption of tissues in birds and mammals. Several environmental contaminants may act on energy expenditure through their thyroid hormone‐disrupting properties. However, the effect of contaminants on BMR is still poorly documented for wildlife. Here, we investigated the relationships between three groups of contaminants (organochlorines (OCs), perfluoroalkyl substances (PFASs), and mercury) with metabolic rate (MR), considered here as a proxy of BMR and also with circulating total THs (thyroxine (TT4) and triiodothyronine (TT3)) in Arctic breeding adult black‐legged kittiwakes (Rissa tridactyla) from Svalbard, during the chick rearing period. Our results indicate a negative relationship between the sum of all detected chlordanes (&Sgr;CHLs) and MR in both sexes whereas perfluorotridecanoate (PFTrA) and MR were positively related in females only. MR was not associated with mercury. Additionally, levels of TT3 were negatively related to &Sgr;CHLs but not to PFTrA. The findings from the present study indicate that some OCs (in both sexes) and some PFASs (only in females) could disrupt fine adjustment of BMR during reproduction in adult kittiwakes. Importantly, highly lipophilic OCs and highly proteinophilic PFASs appear, at least in females, to have the ability to disrupt the metabolic rate in an opposite way. Therefore, our study highlights the need for ecotoxicological studies to include a large variety of contaminants which can act in an antagonistic manner. Graphical abstract Figure. No Caption available. HighlightsContaminant effects on MR and plasma total THs are studied in an Arctic seabird.MR and TT3 are negatively related to blood chlordane concentrations in both sexes.Plasma PFTrA concentration is positively associated with MR in females only.Mercury concentration in red blood cells is not related to MR nor plasma total THs.

Water deprivation increases maternal corticosterone levels and enhances offspring growth in the snake Vipera aspis.

ABSTRACT Circulating glucocorticoid (GC) levels may increase as a result of reproductive effort or in response to unpredictable events. However, GC secretion can vary with the availability of vital trophic resources such as energy. While water represents another critical resource, the impact of water deprivation on GC secretion during reproduction has not yet been thoroughly investigated. Here, we examined the effects of water deprivation on plasma corticosterone (CORT) concentrations of female aspic vipers (Vipera aspis), and determined the impacts of water deprivation on offspring traits. We exposed both pregnant and non-reproductive females to a 20-day water deprivation and compared their pre- and post-deprivation CORT levels with those of control females. At the end of the treatment, only water-deprived pregnant females showed a significant increase in CORT levels. In pregnant females, changes in baseline CORT level were correlated with changes in female hydration state. Changes in baseline CORT levels were also negatively influenced by maternal reproductive effort in pregnant control females, while such a relationship was not apparent in pregnant water-deprived females. Finally, we found that offspring from water-deprived females had higher growth rates than offspring from control females. Offspring growth was also positively correlated with changes in both maternal osmolality and baseline CORT levels. Together, our results suggest that dehydration increases maternal CORT levels, which may subsequently influence offspring development. Further long-term field studies are therefore required to assess whether there is an adaptive significance of this response. Summary: Water deprivation induces an increase in baseline corticosterone level in pregnant aspic vipers, which may subsequently influence offspring growth.

Does the stress response predict the ability of wild birds to adjust to short-term captivity? A study of the rock pigeon (Columbia livia)

Although the transfer of wild animals to captivity is crucial for conservation purposes, this process is often challenging because some species or individuals do not adjust well to captive conditions. Chronic stress has been identified as a major concern for animals held on long-term captivity. Surprisingly, the first hours or days of captivity have been relatively overlooked. However, they are certainly very stressful, because individuals are being transferred to a totally novel and confined environment. To ensure the success of conservation programmes, it appears crucial to better understand the proximate causes of interspecific and interindividual variability in the sensitivity to these first hours of captivity. In that respect, the study of stress hormones is relevant, because the hormonal stress response may help to assess whether specific individuals or species adjust, or not, to such captive conditions (‘the stress response-adjustment to captivity hypothesis’). We tested this hypothesis in rock pigeons by measuring their corticosterone stress response and their ability to adjust to short-term captivity (body mass loss and circulating corticosterone levels after a day of captivity). We showed that an increased corticosterone stress response is associated with a lower ability to adjust to short-term captivity (i.e. higher body mass loss and circulating corticosterone levels). Our study suggests, therefore, that a low physiological sensitivity to stress may be beneficial for adjusting to captivity. Future studies should now explore whether the stress response can be useful to predict the ability of individuals from different populations or species to not only adjust to short-term but also long-term captivity.