Carryover effects of winter mercury contamination on summer concentrations and reproductive performance in little auks.

Many animals migrate after reproduction to respond to seasonal environmental changes. Environmental conditions experienced on non-breeding sites can have carryover effects on fitness. Exposure to harmful chemicals can vary widely between breeding and non-breeding grounds, but its carryover effects are poorly studied. Mercury (Hg) contamination is a major concern in the Arctic. Here, we quantified winter Hg contamination and its carryover effects in the most abundant Arctic seabird, the little auk Alle alle. Winter Hg contamination of birds from an East Greenland population was inferred from head feather concentrations. Birds tracked with Global Location Sensors (GLS, N = 28 of the total 92) spent the winter in western and central North Atlantic waters and had increasing head feather Hg concentrations with increasing longitude (i.e., eastward). This spatial pattern was not predicted by environmental variables such as bathymetry, sea-surface temperature or productivity, and needs further investigation. Hg concentrations in head feathers and blood were strongly correlated, suggesting a carryover effect of adult winter contamination on the consequent summer concentrations. Head feather Hg concentrations had no clear association with telomere length, a robust fitness indicator. In contrast, carryover negative effects were detected on chick health, as parental Hg contamination in winter was associated with decreasing growth rate of chicks in summer. Head feather Hg concentrations of females were not associated with egg membrane Hg concentrations, or with egg volume. In addition, parental winter Hg contamination was not related to Hg burdens in chicks' body feathers. Therefore, we hypothesise that the association between parental winter Hg exposure and the growth of their chick results from an Hg-related decrease in parental care, and needs further empirical evidence. Our results stress the need of considering parental contamination on non-breeding sites to understand Hg trans-generational effects in migrating seabirds, even at low concentrations.

Transgenerational epigenetic sex determination: Environment experienced by female fish affects offspring sex ratio.

Sex determination is a complex process that can be influenced by environment in various taxa. Disturbed environments can affect population sex ratios and thus threaten their viability. Emerging evidences support a role of epigenetic mechanisms, notably DNA methylation, in environmental sex determination (ESD). In this work, using zebrafish as model and a transgenerational experiment comprising 4 successive generations, we report a strength link between the promotor methylation level of three genes in female gonads and population sex ratio. One generation of zebrafish was exposed throughout its lifetime to cadmium (Cd), a non-essential metal, at an environmentally relevant concentration. The subsequent generations were not exposed. At the first and the third generation a subset of individuals was exposed to an elevated temperature, a well-known masculinizing factor in zebrafish. While heat was associated to an increase in the methylation level of cyp19a1a gene and population masculinization, foxl2a/dmrt1 methylation levels appeared to be influenced by Cd and fish density leading to offspring feminization. Ancestral Cd exposure indeed led to a progressive feminization of the population over generations and affected the sex plastic response of zebrafish in response to heat. The effect of Cd on the methylation level of foxl2a was observed until the third generation, supporting potential transgenerational inheritance. Our results support (i) a key role of cyp19a1a methylation in SD in zebrafish in response to environmental cues and (ii) the fact that the environment experienced by parents, namely mothers in the present case, can affect their offspring sex ratio via environment-induced DNA methylation changes in gonads.

Are glucocorticoids good indicators of pregnancy constraints in a capital breeder?

Pregnancy imposes a substantial energetic demand on the mother (i.e. metabolic costs of pregnancy) and is often associated with modified maternal behavior and increased physical burdens that make females more vulnerable to predation. The Hypothalamic-Pituitary-Adrenal axis plays a fundamental role in reproduction through hormonal control of energy regulation and parental care. Therefore, evaluating the changes in baseline and stress-induced glucocorticoid levels in response to pregnancy may provide a robust tool to assess not only the constraints of gestation but also the way females may adjust to these constraints. In this study, we measured baseline and stress-induced corticosterone (CORT) concentrations in pregnant and non-pregnant aspic vipers (Vipera aspis), which are capital breeders. We also measured muscle condition (tail width) and locomotion performance (traction force) because these are robust proxies of protein mobilization associated with fasting. Baseline CORT concentration increased significantly over time in pregnant females, while they were lower and stable in non-reproductive females. Pregnant females had lower muscle condition at the onset of the study and tail width was negatively correlated with CORT concentration in this group. Contrary to our prediction, the stress response was not attenuated in pregnant females, but was proportional to baseline CORT concentration. Our results suggest that baseline CORT variations are closely related to energy constraints and structural protein mobilization in this capital breeder.

Embryonic water uptake during pregnancy is stage- and fecundity-dependent in the snake Vipera aspis.

Water is a crucial resource that can profoundly impact the biology of terrestrial organisms. Early life stages are particularly sensitive to hydric constraints because water uptake is an important component of embryonic development. While amniotic eggs constitute a key innovation to terrestrial life, many vertebrates are viviparous wherein the mother must be the source of water for her developing embryos. Since most viviparous squamates are lecithotrophic (i.e., energy is supplied to the offspring as yolk deposited into pre-ovulated follicles), water is the predominant resource allocated from the mother to the offspring during development. Contrary to energy that can be stored (e.g., as fat reserves), water typically cannot be acquired in advance. Therefore, the embryos' need for water can impose significant constraints on the pregnant female. We detailed water flux during pregnancy in a viviparous snake, the aspic viper (Vipera aspis). We found that embryonic water uptake occurred mostly during the second half of pregnancy-a period dominated by somatic growth. We also found that, somewhat unexpectedly, changes in female plasma osmolality were negatively related to fecundity. This latter result suggests that water consumption by the female is especially important for large litter sizes, and thus may suggest an important sensitivity of reproductive females to environmental water availability.

Stage dependence of phenotypical and phenological maternal effects: insight into squamate reptile reproductive strategies.

Enhanced thermal conditions have been credited as a driving force for the evolution of viviparity, particularly in squamate reptiles, among which it has independently evolved more than 100 times. However, maternal thermoregulation is also a critical component of reproduction in oviparous squamates, for which considerable embryonic development occurs prior to oviposition. When carrying eggs, oviparous mothers modify thermoregulation in a manner similar to that of pregnant females. To further understand the role of temperature in influencing reproductive strategies, it is critical that we elucidate the degree to which thermal sensitivity varies across developmental stages. We studied stage-dependent embryonic sensitivity in a viviparous snake, the aspic viper (Vipera aspis). We manipulated female body temperature at different stages of pregnancy-early development, early embryonic growth, and late embryonic growth-by imposing two contrasting daily thermal cycles that mimicked reproductive (warm) and nonreproductive (cool) female temperature profiles. Thermal sensitivity of offspring phenotype was stage dependent, with offspring quality more negatively affected when exposure to cool temperatures occurred early in development. In contrast, developmental rate was slowed by the cooler cycle, independent of the timing of the exposure. Given the more persistent effect on phenology, phenological effects likely provide a greater driving force for complete embryonic retention (i.e., viviparity).

Morphological and physiological changes during reproduction and their relationships to reproductive performance in a capital breeder.

Current reproductive effort typically comes at a cost to future reproductive value by altering somatic function (e.g., growth or self-maintenance). Furthermore, effects of reproduction often depend on both fecundity and stage of reproduction, wherein allocation of resources into additional offspring and/or stages of reproduction results in increased costs. Despite these widely accepted generalities, interindividual variation in the effects of reproduction is common-yet the proximate basis that allows some individuals to mitigate these detrimental effects is unclear. We serially measured several variables of morphology (e.g., musculature) and physiology (e.g., antioxidant defenses) in female Children's pythons (Antaresia childreni) throughout reproduction to examine how these traits change over the course of reproduction and whether certain physiological traits are associated with reduced effects of reproduction in some individuals. Reproduction in this capital breeder was associated with changes in both morphology and physiology, but only morphological changes varied with fecundity and among specific reproductive stages. During reproduction, we detected negative relationships between morphology and self-maintenance (e.g., increased muscle allocation to reproduction was related to reduced immune function). Additionally, females that allocated resources more heavily into current reproduction also did so during future reproduction, and these females assimilated resources more efficiently, experienced reduced detriments to self-maintenance (e.g., lower levels of oxidative damage and glucocorticoids) during reproduction, and produced clutches with greater hatching success. Our results suggest that interindividual variation in specific aspects of physiology (assimilation efficiency and oxidative status) may drive variation in reproductive performance.

Structural and performance costs of reproduction in a pure capital breeder, the Children's python Antaresia childreni.

Females often manage the high energy demands associated with reproduction by accumulating and storing energy in the form of fat before initiating their reproductive effort. However, fat stores cannot satisfy all reproductive resource demands, which include considerable investment of amino acids (e.g., for the production of yolk proteins or gluconeogenesis). Because capital breeders generally do not eat during reproduction, these amino acids must come from internal resources, typically muscle proteins. Although the energetic costs of reproduction have been fairly well studied, there are limited data on structural and performance costs associated with the muscle degradation required to meet amino acid demands. Thus, we examined structural changes (epaxial muscle width) and performance costs (constriction and strength) over the course of reproduction in a pure capital breeder, the children's python (Antaresia childreni). We found that both egg production (i.e., direct resource allocation) and maternal care (egg brooding) induce muscle catabolism and affect performance of the female. Although epaxial muscle loss was minimal in nonreproductive females, it reached up to 22% (in females after oviposition) and 34% (in females after brooding) of initial muscle width. Interestingly, we found that individuals with higher initial muscular condition allocated more of their muscle into reproduction. The amount of muscle loss was significantly linked to clutch mass, underscoring the role of structural protein in egg production. Egg brooding significantly increased proteolysis and epaxial loss despite no direct allocation to the offspring. Muscle loss was linked to a significant reduction in performance in postreproductive females. Overall, these results demonstrate that capital-breeding females experience dramatic costs that consume structural resources and jeopardize performance.

Maternal influences on early development: preferred temperature prior to oviposition hastens embryogenesis and enhances offspring traits in the Children's python, Antaresia childreni.

Embryonic life is particularly sensitive to its surroundings, and the developmental environment can have long-lasting effects on offspring. In oviparous species, the impacts of the developmental environment on offspring traits are mostly examined during development within the egg. However, as more than 25% of the development of squamate reptiles can occur prior to oviposition, we explored the effect of thermal conditions on development prior to oviposition in an oviparous snake species, the Children's python (Antaresia childreni). We housed gravid female pythons under three thermal cycles: an optimal regime that reflected maternal preference in a non-constrained environment (constant preferred body temperature of gravid females, T(set)=31.5°C) and two mildly suboptimal regimes that shared the same mean temperature of 27.7°C, but differed in the duration at T(set). In one of the constraining regimes, females had access to T(set) for 4 h daily whereas in the other regime, females never reached T(set) (maximal temperature of 29.0°C). Thermal treatments were maintained throughout gravidity in all three groups, but, after oviposition, all eggs were incubated at T(set) until hatching. Compared with the optimal regime, the two suboptimal regimes had a longer duration of gravidity, which resulted in delayed hatching. Between the two suboptimal regimes, gravidity was significantly shorter in the treatment that included time at T(set). Furthermore, suboptimal regimes influenced offspring traits at hatching, including body morphology, antipredator behavior, strength and metabolism. However, partial access to maternal T(set) significantly enhanced several offspring traits, including performance. Our results demonstrate the importance of time at T(set) on early development and suggest an adaptive significance of maternal thermoregulation prior to oviposition.