title: Mechanisms that shape the evolution of cooperative breeding
Creators: name: García Ruiz, Irene
Publisher: name: Universität Bern
Year: 2025
Subjects: subject: 570 Life sciences; biology
subject: 590 Animals (Zoology)

description: The evolution of cooperation is an area of intensive theoretical and empirical research not only in biology but also in anthropology, political sciences and economics. Cooperative breeding, a form of cooperation in which helpers provide alloparental care to increasing the productivity of dominant individuals in the group has received considerable interest among behavioural ecologists. This behaviour poses a striking problem because helpers forego their own reproduction well after reaching sexual maturity, while investing in costly forms of help. Evolutionary mechanisms selecting for this form of cooperation are to this day not well understood.
Cooperative breeding is spread among a wide range of different taxa (i.e. mammals, birds, fish and social insects), across different ecological environments ranging from benign and stable to harsh and unpredictable, and groups range from family groups to groups with very low relatedness. Therefore, finding general evolutionary forces selecting for alloparental care has proven challenging. Kin selection can be a strong selective force in some instances, particularly when groups are formed by offspring that delay dispersal due to challenges in independent breeding. But neither all family groups provide help, nor all cooperative breeders have high within-group relatedness. Alternatively, direct fitness benefits could select for cooperative breeding, but evidence on the relevance of distinct mechanisms is limited in nature. In addition, research on the interplay of direct and indirect fitness benefits is scarce, but mixed groups of related and unrelated helpers are not uncommon. This thesis explores from a theoretical and empirical approach different evolutionary mechanisms based on direct fitness benefits and their interplay with kin selection.
In Chapter 1 we investigated whether direct fitness benefits derived from living in large groups are an important selective force for cooperative breeding to evolve. We modelled the coevolution of delayed dispersal and alloparental care across different ecological scenarios. We assumed that helping increased the fecundity of the breeder at a survival cost to the helper. Individuals could adjust philopatry and helping levels to their resource holding potential or show fixed evolutionary strategies. We allowed relatedness to arise from population dynamics, and blocked relatedness to build-up to contrast your results. We found that direct fitness benefits from grouping are the main driver for the evolution of philopatry while kin selection is mainly responsible for the emergence of alloparental care. Direct benefits of increasing group size also selected for alloparental care to evolve in harsh environments. Although philopatry is a prerequisite for alloparental care to evolve, both philopatry and help were subjected to positive feedback. Moreover, behavioural plasticity in their decision to disperse allowed individuals to maximise group living benefits while reducing competition with kin for the breeding position.
In Chapter 2, we further explore in an empirical study the evolution of alloparental care driven by direct fitness benefits of living in larger groups (as predicted by the group augmentation hypothesis). For this we use the cooperative breeding cichlid Neolamprologus pulcher as a model species. After controlling for alternative mechanisms like kin selection, coercion and load-lightening, we found that subordinates provided more help in the form of defence against an egg predator when in small compared to large groups. This difference was only evident in large helpers due to size-specific task specialization. These results confirm predictions for the group augmentation hypothesis, as in small groups there is a greater need to increase group size.
In Chapter 3 we studied the negotiation process between dominant and subordinate group members, in which helpers may trade alloparental brood care against safety and resource access in the dominants’ territory (as predicted by the pay-to-stay hypothesis). We investigated how unequal partners in bargaining power solve the conflict of fitness interests, and whether indirect fitness benefits alleviate this conflict in N. pulcher. To test this, in a full factorial design we experimentally disturbed the equilibrium in the negotiation process between dominant breeders and related or unrelated subordinates by simulating transgression from the helpers while allowing or preventing breeders the possibility to promote helping by coercion. Our results show that coercion by breeders is crucial for the performance of alloparental egg care by subordinate helpers, but that kinship reduces the importance of coercion as predicted by theoretical models.