The impact of helping on helper life-history and fitness in a cooperatively breeding bird

Abstract

Cooperative breeding occurs when helpers provide alloparental care to the offspring of a breeding pair. One hypothesis of why helping occurs is that helpers gain valuable experience (skills) that may increase their own future reproductive success. However, research typically focuses on the effect of helping on short-term measures of reproductive success. Fewer studies have considered how helping affects long-term fitness measures. Here, we analyse how helping experience affects key breeding and fitness-related parameters in the Seychelles warbler (Acrocephalus sechellensis). Importantly, we control for females that have co-bred, as they have experience with direct reproduction. Helping experience alone had no impact on any of the metrics considered, except that helpers had an older age at first dominance. Females that had co-bred had longer dominant tenures, produced more recruits as dominant breeders and had a higher lifetime reproductive success than females that had never co-bred. Our results suggest that helping experience alone does not increase direct fitness in Seychelles warblers and highlights the importance of separating the effects of helping from co-breeding. Our findings also emphasise the importance of analysing the effect of helping at various life-history stages, as higher short-term fitness may not translate to an overall increase in lifetime fitness.

Evolution of sex differences in cooperation: the role of trade-offs with dispersal

“…This hypothesis could be relevant to sparrow-weavers as dominant females feed offspring at higher rates than dominant males (Walker et al 2021). However, compelling evidence that helping improves parenting skills remains elusive (Chesterton et al 2023;Cockburn 1998), and as immigrant subordinate sparrow-weavers rarely help at all (Walker et al 2021), it seems unlikely that direct benefits arising via skills acquisition are a major driver of helping in this system. It has also been suggested that the sex that shows higher variance in lifetime reproductive success (LRS) may invest more in helping given its lower chance of securing direct fitness by breeding (Cockburn 1998;Koenig et al 1983).…”

“…2021). However, compelling evidence that helping improves parenting skills remains elusive (Chesterton et al . 2023; Cockburn 1998), and as immigrant subordinate sparrow-weavers rarely help at all (Walker et al .…”

“…However, compelling evidence that helping improves parenting skills remains elusive [2,30], and as immigrant subordinate sparrow-weavers rarely help at all [27], it seems unlikely that direct benefits arising via skills acquisition are a major driver of helping in this system. It has also been suggested that the sex that shows higher variance in lifetime reproductive success (LRS) may invest more in helping given its lower chance of securing direct fitness by breeding [2,31].…”