Abstract
The social environment can have profound effects on an individual’s physiology and behaviour and on the transfer of resources to the next generation, with potential consequences for fecundity and reproduction. However, few studies investigate all of these aspects at once. The present study housed female Japanese quail (Coturnix japonica) in pairs or groups to examine the effects on hormone concentrations in plasma and yolk and on reproductive performance. Circulating levels of androgens (testosterone and 5-α-dihydrotestosterone) and corticosterone were measured in baseline samples and after standardised challenges to assess the responsiveness of the females’ endocrine axes. Effects of the social environment on female fecundity were analysed by measuring egg production, egg mass, fertilization rates, and number of hatched offspring. Counter to expectation, females housed in pairs had higher plasma androgen concentrations and slightly higher corticosterone concentrations than females housed in groups, although the latter was not statistically significant. Pair vs. group housing did not affect the females’ hormonal response to standardised challenges or yolk testosterone levels. In contrast to previous studies, the females’ androgen response to a gonadotropin-releasing hormone challenge was not related to yolk testosterone levels. Non-significant trends emerged for pair-housed females to have higher egg-laying rates and higher fertility, but no differences arose in egg weight or in the number, weight or size of hatchlings. We propose that our unexpected findings are due to differences in the adult sex ratio in our social treatments. In pairs, the male may stimulate female circulating hormone levels more strongly than in groups where effects are diluted due to the presence of several females. Future studies should vary both group size and sex composition to disentangle the significance of sexual, competitive and affiliative social interactions for circulating and yolk hormone levels, and their consequences for subsequent generations.
Highlights
The social environment of an individual can profoundly affect its behaviour, morphology and physiology
Individual baseline plasma CORT concentrations were not significantly correlated with baseline plasma androgen concentrations (r(28) = 0.23, p = 0.22; S1A Fig) and post-challenge plasma CORT concentrations did not correlate with post-challenge androgen levels (r(27) = 0.21, p = 0.26; S1B Fig)
Baldness and baseline plasma hormones. In both pairs and groups, the proportion of time a female spent sitting with the male did not predict baseline plasma androgen or CORT concentrations, nor did the proportion of time a female spent sitting with at least one other female in her group (All F-values < 1.32, all corresponding p-values > 0.26; S2A–S2D Fig)
Summary
The social environment of an individual can profoundly affect its behaviour, morphology and physiology. Steroid hormones can act as mediators between the social environment and behaviour [1, 6], which can affect survival and reproduction [7, 8]. The social environment affects the individual itself, and the amount of resources and other substances transferred to the generation, potentially affecting offspring fitness [9, 10]. Such socially induced maternal effects enable parents to prepare offspring for their future social conditions, potentially resulting in adaptive transgenerational plasticity [11,12,13,14]; but see [15]. The mechanisms underlying the effects of the social environment on female physiology and behaviour and the consequences for fecundity and offspring quality are not yet well understood and deserve further research
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