Abstract
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.
Highlights
Maximising reproductive success over an individual’s lifetime involves a series of trade-offs between current reproductive effort and survival between breeding events [1]
It varied in a negative quadratic way with the number of helpers, this remained below significance (Table 3; Fig. 2; controlling for egg mass)
Yolk mass was not affected by group type (F1,22 = 0.84, P = 0.37), clutch size, the number of clutches attempted before, colony size or rainfall, but increased with egg mass in a linear manner when taking into account the effect of the number of helpers (F1,21 = 4.428, P = 0.048, estimate = 0.13860.066) (Table 3)
Summary
Maximising reproductive success over an individual’s lifetime involves a series of trade-offs between current reproductive effort and survival between breeding events [1]. An important way to adjust the costs of reproduction and influence offspring fitness is the possibility of varying maternal allocation during embryonic development in terms of nutrients, hormones or antibodies [2,3]. This differential allocation according to early, current or expected environment (e.g. temperature, food availability or mate quality) has been shown in several species [2,4,5,6]. Differential allocation in reproduction can occur first through the production of eggs of different sizes [7,8]. Carotenoids are expected to play a central role during embryo development and at hatching [20,21,22], but are important for the breeding female’s own immunity
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