Egg investment in response to helper presence in cooperatively breeding Tibetan ground tits

Abstract

Life‐history theory predicts a trade‐off between current and future reproduction to maximize lifetime fitness. In cooperatively breeding species, where offspring care is shared between breeders and helpers, helper presence may influence the female breeders’ egg investment, and consequently, survival and future reproductive success. For example, female breeders may reduce egg investment in response to helper presence if this reduction is compensated by helpers during provisioning. Alternatively, female breeders may increase egg investment in response to helper presence if helpers allow the breeders to raise more or higher quality offspring successfully. In the facultatively cooperative‐breeding Tibetan ground tit Pseudopodoces humilis, previous studies found that helpers improve total nestling provisioning rates and fledgling recruitment, but have no apparent effects on the number and body mass of fledglings produced, while breeders with helpers show reduced provisioning rates and higher survival. Here, we investigated whether some of these effects may be explained by female breeders reducing their investment in eggs in response to helper presence. In addition, we investigated whether egg investment is associated with the female breeder's future fitness. Our results showed that helper presence had no effect on the female breeders’ egg investment, and that egg investment was not associated with breeder survival and reproductive success. Our findings suggest that the responses of breeders to helping should be investigated throughout the breeding cycle, because the conclusions regarding the breeders’ adjustment of reproductive investment in response to being helped may depend on which stage of the breeding cycle is considered.

Maternal allocation in relation to weather, predation and social factors in a colonial cooperative bird

“…'s (2017) analysis with the effect obtained here, we found no general tendency of load lightening at the egg stage in cooperative breeders (estimate = −0.1320, CI = [−0.2921, 0.0281]; p = 0.1061; Figure S7; details in Supporting Information section F). Moreover, three additional studies have recently reported no evidence of prenatal load lightening in other cooperative breeders (Cusick et al., 2018; Van de Loock, 2019; Zhao et al., 2019). The meta‐analysis on prenatal load lightening in cooperative breeders should therefore be revisited in a future investigation.…”

How do helpers slow senescence in a Tibetan cooperatively breeding bird?

“…Second, additional evidence is available from previous studies. Clutch size and egg size (Zhao et al, 2019) as well as level of brood reduction (Lu et al, 2011) did not differ between helped and unhelped nests. Helped ground tit parents improved their survival largely because they adopted a “load‐lightening” strategy (Crick, 1992): reducing efforts of feeding young without compromising annual reproductive output (Lu et al, 2011).…”