Is biparental defence driven by territory protection, offspring protection or both?

Holger Zimmermann,Aneesh P.H Bose,Angelika Ziegelbecker,Florian Richter,Sandra Bračun,Helgit Eisner,Cyprian Katongo,Taylor Banda,Lawrence Makasa,Jonathan M Henshaw,Karoline Fritzsche,Kristina M Sefc

doi:10.1016/j.anbehav.2021.03.012

Abstract

In many animal systems, the defence of a territory or nest coincides with the defence of offspring, and it is often unclear whether the defence behaviour exists for the purpose of offspring protection, territory protection or a combination of both. In species with biparental care, the drivers of defence behaviours in males may differ from those in females, particularly if there are sex-specific fitness benefits from the current brood or territory. In this study, we present field experiments aimed at elucidating sex differences in the drivers behind nest defence in a fish species (Variabilichromis moorii, Cichlidae) with biparental care. High rates of cuckoldry in this species create asymmetries in brood value between mates, suggesting that increased brood survival may be a weaker driver of male than of female defence effort. We conducted parent and offspring removal experiments and found that following the removal of their mates, single males lost significantly more fry than single females. Some single males lost their territories, while others constricted their space use, suggesting that experimental divorce decreased their success in territory defence. Removal of fry from territories guarded by both parents caused the defence behaviour to become more male biased, that is, males contributed relatively more to defence without any fry present. Our results suggest that, relative to that of females, male defence behaviour is more strongly driven by territory retention than by brood protection. Nevertheless, the presence of males improves parents’ abilities to keep territory intruders at bay, and thus probably confers benefits to broods. We conclude that the drivers of defence behaviours differ between the sexes in this species, with defence behaviours aligning well with the traditional definition of parental care for females, but less so for males.

Highlights

In many animal systems, the defence of a territory or nest coincides with the defence of offspring, and it is often unclear whether the defence behaviour exists for the purpose of offspring protection, territory protection or a combination of both
When parents attack intruders encroaching on a nesting site or a territory, their behaviour is often ascribed to offspring protection, and considered a form of parental care
We developed the following predictions for the case that male and female defence behaviours are driven by brood survival: males and females should be successful in uniparental brood defence and division of defence labour between males and females of a pair should be independent of the presence of the brood

Summary

Introduction

The defence of a territory or nest coincides with the defence of offspring, and it is often unclear whether the defence behaviour exists for the purpose of offspring protection, territory protection or a combination of both. Further complexity arises in biparental species in which both parents cooperate to raise their offspring and to defend a territory or nesting site In these systems, the evolutionary drivers of defence behaviours may differ between the sexes, and it is often not obvious to what extent each parent's defence is driven by the benefits of offspring protection, territory protection or both. The evolutionary drivers of defence behaviours may differ between the sexes, and it is often not obvious to what extent each parent's defence is driven by the benefits of offspring protection, territory protection or both This is especially true when the fitness value of the same brood of offspring differs between the two parents, which occurs frequently in species with extrapair copulations. As with other potentially pleiotropic behaviours, careful experiments are required to tease apart the drivers of defence behaviours, because evidence for one mechanism (e.g. offspring protection) does not preclude the importance of the other (e.g. territory protection)

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Conclusion