Intrinsic timing of brood care in shell-dwelling cichlids

Brood care relies on interactions between parents and offspring. Emergence of nestlings from their nest has been hypothesized to rely on the readout by the parent of the maturational state of the young. Theoretical considerations predict a conflict: parents should push for early emergence, if possible, to reduce care demands and maximize the number of reproductive cycles, whereas offspring should delay leaving to maximize resource allocation and protection by the parents. We tested this prediction in Lamprologus ocellatus, a shell-dwelling cichlid from Lake Tanganyika. We developed a laboratory paradigm to investigate the factors influencing emergence from the shell and found that mothers ensure their young stay inside the nest until 9 days after egg laying. Emergence coincides with an inversion of larval phototactic tendency from dark-seeking to light-seeking behavior on day 9. When we experimentally created a timing conflict by introducing older larvae to a foster mother, the mother resisted the (subjectively) premature emergence of her adopted fry. Removing the mother did not alter the larval intrinsic schedule, provided fresh water was supplied inside the shell. These findings suggest that, in L. ocellatus brood care, maternal and offspring behavior is normally synchronized by independent timing mechanisms. Our findings highlight the intricate coordination of parental and offspring behavior, offering insights into the evolutionary pressures shaping brood care in cichlids and challenging the traditional view of parent-offspring conflict over emergence timing.