Involving alloparental care, cooperative breeding provides a unique opportunity to study alternative selection mechanisms underlying altruistic behaviour, as it generates higher immediate direct fitness costs than direct fitness benefits. This can be compensated by indirect fitness benefits if brood care helpers are related to the recipients of their investment, but in many cooperative breeders at least some helpers are not related to their beneficiaries. What compensates for the negative cost/benefit balance of unrelated helpers?
Trading of commodities in Neolamprologus pulcher: Dominant breeders defend the territory against predators (here: Lepidiolamprologus elongatus) thereby protecting their brood care helpers, which in return care for the dominants' brood.
To answer this question we study the behavioural ecology of cooperative breeding in lamprologine cichlid fishes from Lake Tanganyika. These cichlids live in extended family groups: in Neolamprologus pulcher, for instance, both male and female offspring remain in their natal territory and help to defend and maintain the territory, and to raise broods produced by the territory owners. Due to frequent replacements of breeders and helper exchanges between territories, large, sexually mature helpers are often unrelated to the breeders' offspring they care for. In laboratory and field experiments we can manipulate various aspects of these families (e.g. helper size and behaviour, group size and composition, relatedness) and the environment (e.g. the densities of conspecifics, predators and breeding sites), and we record the effects of these manipulations on helping behaviour, dispersal and reproductive skew (the reproductive share of group members). DNA-microsatellite analyses help to unravel the composition of natural families, and parentage. We use individual-based models and dynamic game theory to find optimal and evolutionarily stable solutions to reproductive competition and alternative life history options of breeders and helpers. Our experiments and analyses revealed that helpers and breeders trade commodities against each other, whereby breeders - being dominant - can demand alloparental effort from helpers, but the latter can decide to leave when the costs of fulfilling the breeders' claims are exceeding the benefits of staying in a safe territory. In other words, the helpers pay-to-stay by alloparental care in order to enhance their survival chances through protection by breeders.
Principal investigator: Michael Taborsky
Naef, J., Taborsky, M. 2020. Commodity-specific punishment for experimentally induced defection in cooperatively breeding fish. R. Soc. Open Sci. 7: 191808 [PDF]
Groenewoud, F., Frommen, J.G., Josi, D., Tanaka, H., Jungwirth, A. and Taborsky, M. (2016): Predation risk drives social complexity in cooperative breeders. Proc. Nat. Acad. Sci. USA, 113(15): 4104-4019 [PDF]
Jungwirth, A., Taborsky, M. (2015): First- and second-order sociality determine survival and reproduction in cooperative cichlids. Proc. R. Soc. B 282: 20151971 [PDF]
Zöttl M., Heg D., Chervet N. & Taborsky M. (2013): Kinship reduces alloparental care in cooperative cichlids where helpers pay-to-stay. Nature Commun. 4:1341 [PDF]
Heg D., Bachar Z., Brouwer L. & Taborsky M. (2004): Predation risk is an ecological constraint for helper dispersal in a cooperatively breeding cichlid. Proc. Roy. Soc. Lond. B 271:2367-2374 [PDF]