Lifetime reproductive benefits of cooperative polygamy vary for males and females in the acorn woodpecker (Melanerpes formicivorus).

Sahas Barve,Christina Riehl,Walter D Koenig,Joseph Haydock,Eric L Walters,Hannah L Dugdale

doi:10.1098/rspb.2021.0579

Abstract

Cooperative breeding strategies lead to short-term direct fitness losses when individuals forfeit or share reproduction. The direct fitness benefits of cooperative strategies are often delayed and difficult to quantify, requiring data on lifetime reproduction. Here, we use a longitudinal dataset to examine the lifetime reproductive success of cooperative polygamy in acorn woodpeckers (Melanerpes formicivorus), which nest as lone pairs or share reproduction with same-sex cobreeders. We found that males and females produced fewer young per successful nesting attempt when sharing reproduction. However, males nesting in duos and trios had longer reproductive lifespans, more lifetime nesting attempts and higher lifetime reproductive success than those breeding alone. For females, cobreeding in duos increased reproductive lifespan so the lifetime reproductive success of females nesting in duos was comparable to those nesting alone and higher than those nesting in trios. These results suggest that for male duos and trios, reproductive success alone may provide sufficient fitness benefits to explain the presence of cooperative polygamy, and the benefits of cobreeding as a duo in females are higher than previously assumed. Lifetime individual fitness data are crucial to reveal the full costs and benefits of cooperative polygamy.

Highlights

Cooperative breeding, in which more than two adults cooperate to raise a single brood of young, is a widespread reproductive strategy in both vertebrates [1] and invertebrates [2]
In red wolves (Canis rufus) [8], red-cockaded woodpeckers (Dryobates borealis) [9] and green woodhoopoes (Phoeniculus purpureus) [10], for example, offspring that remain as helpers on their natal territory have higher survival than those that disperse, leading to equal lifetime reproductive success for offspring that cooperate relative to those that disperse
We examined the effects of cobreeding on several demographic parameters that could contribute to observed differences in lifetime reproductive output, including age at first reproduction, the number of offspring produced per successful breeding attempt, reproductive lifespan and number of lifetime reproductive attempts

Summary

Introduction

Cooperative breeding, in which more than two adults cooperate to raise a single brood of young, is a widespread reproductive strategy in both vertebrates [1] and invertebrates [2]. Kin selection provides a powerful explanation for the evolutionary persistence of cooperation among relatives, since the indirect fitness gained from raising non-descendant kin can mitigate the direct fitness costs of cooperation [3,6] Cooperative strategies such as helping or cobreeding may yield delayed direct fitness benefits, such as increased survival or reproductive output later in life, which may compensate for the reproductive costs suffered by a cooperator for a given breeding attempt [7]. In red wolves (Canis rufus) [8], red-cockaded woodpeckers (Dryobates borealis) [9] and green woodhoopoes (Phoeniculus purpureus) [10], for example, offspring that remain as helpers on their natal territory have higher survival than those that disperse, leading to equal (or greater) lifetime reproductive success for offspring that cooperate relative to those that disperse In such species, reproductive gains later in life may partly explain the evolution of helping behaviour [11]

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