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

Abstract

Sociality is known to be capable of slowing individual senescence, but it is unclear whether the effect differs for reproduction versus survival in a sex-specific manner. Here we predict that social benefits are directed toward (1) somatic maintenance in harsh environments where high survival prospects of adults over young intensify the trade-off between current and future reproduction, and (2) females that invest more in reproduction and have a greater marginal effect if their survival is improved by reducing the cost of reproduction. These two predictions are tested with cooperatively breeding Tibetan ground tits (Pseudopodoces humilis). Across the lifetime, both mothers and fathers with helpers did not differ in brood size at fledging from their counterparts without helpers. The presence of helpers reduced survival senescence of both parents, but mothers benefited more than fathers from receiving help. Consequently, the inherent sex difference in life span and along with lifetime reproductive success, as expressed in breeders of never-receiving help, became no longer obvious. The model of social modulation for senescence should facilitate the persistence of cooperative breeding in challenging environments.

Should sons breed independently or help? Local relatedness matters

“…Helpers usually help for one breeding year and if they survive, breed themselves (90%), with a few continuing to help (10%). Helping involves burrow construction, territory defence and provisioning of young, which improve breeders' survival but not annual reproductive output (Fan et al, 2022; Li et al, 2015). Helpers hardly share paternity in the brood even though helping their stepmother (Tang et al, 2017).…”

“…Social status of banded individuals associated with each nest was determined through observations of behaviours, including copulations and mate guarding in which breeding males followed their mates closely (helpers did not do so). Since breeders of both sexes, helpers and yearling males do not disperse or only move into territories nearby home, such individuals can be reliably assumed to have died if they were missed from resighting records (Fan et al, 2022).…”