Conditional cooperation as potential resolution for sexual conflict between caring blue tit parents

Biparental care requires that two unrelated individuals raise their offspring together, which increases offspring survival and therefore parental fitness. However, each parent has to invest in care which comes with an individual cost and thus both parents benefit by investing as little as possible to retain resource for future reproductive events. Thus, parents are in a sexual conflict about investment and they have to agree upon the level of investment into the current reproductive event. Recently, conditional cooperation as a parental strategy has been proposed that could provide a resolution for this conflict between parents. It implies that parents will follow up on each other’s provisioning visit and that a visit of the partner motivates the other to increase its own provisioning rate. This indicates that parents will have an equal and higher visit rate when they use conditional cooperation. However, some important aspects are still unknown, while vital for our understanding of the adaptive significance of this strategy. Therefore, the main aim of this thesis is to investigate whether conditional cooperation, via turn taking of provisioning visits, indeed bears the potential for conflict resolution. In particular, I aim to study (a) whether turn taking is an honest, stable strategy; (b) how such a resolution of conflict between parents affects the offspring, as turn taking is thought to increase nest visit rates and thus possibly offspring growth; (c) how turn taking can last, if parents may have to invest more heavily in another parental task besides provisioning. To answer these questions, I studied a wild population of blue tits, a species with biparental care, on which I performed multiple manipulation experiments in the field. Blue tit pairs had stable alternation levels which they maintained regardless of any disturbance (chapter 2 and 3). Yet, parents were expected to change their alternation level in accordance with the amount of conflict. Furthermore, the parents were not responding as predicted by changing their provisioning rate to the rate of their partner (chapter 4 and 5). However, parents were not using prey to exploit their partner by investing less into bigger profitable prey items (chapter 2 and 4). Blue tit parents, therefore, seem to be honest in their investment in terms of prey sizes, considering these experiments. Regardless of the honesty in prey sizes, the offspring did not benefit but also were not limited by the conditional cooperation strategy (chapter 2 and 4). From the experiment in which females’ brooding duration was manipulated, females were not restricted by this other care task in their potential to take turns (chapter 5). Taken all together, blue tit parents did not seem to be using the turn taking rules as predicted by the initial theoretical concept. Yet, they seem to maintain a fixed level of alternated visits. A specific fraction of monitoring the partner’s feeding behaviour might provide a sufficient estimate of its investment and could serve as a signal to avoid substantial exploitation. Hence, it seems that the coordination of parental care within pairs is not exclusively related to visit rates, but that partners may use different information streams to co-adjust their behaviour.

Jaar van publicatie:2021

Trefwoorden:Doctoral thesis

Toegankelijkheid:Open