Repeated evolution of cooperative breeding and life history traits in Tanganyikan cichlid fishes

Cooperative breeding is a complex social system in the animal kingdom
where offspring receive care not only from their parents but also from
other group members. However, the life history traits related to the
evolutionary transition toward this complex system are still poorly
understood. This study investigated the evolutionary transition from
non-cooperativeto cooperative breeding in lamprologine cichlid fishes
endemic to Lake Tanganyika using phylogenetic comparative methods.
Ancestral state reconstruction revealed that the evolutionary transition
from non-cooperative to cooperative breeding occurred at least seven times
independently. Comparative analyses using life history data obtained from
field observations and sampling and literature review showed an
evolutionary link between cooperative breeding and clutch size or body
size but not egg size; both clutch and body sizes were smaller in
cooperative breeders. These findings suggested the evolutionary scenario
that cooperative breeding first evolved in smaller species, most likely
because of ecological constraints, such as an increased predation risk,
followed by a reduction in clutch size. These results highlight the impact
of predation risk on life history traits and how it mediates the
transition toward a complex social organization.