Low incidence of cannibalism among brood parasitic cuckoo catfish embryos

Offspring of brood parasites vigorously compete for host resources. Cuckoo catfish embryos feed on host offspring but only rarely resort to cannibalism, despite the ensuing benefits of decreased competition and direct energy provisions. Cannibalism among cuckoo catfish embryos emerges to mitigate starvation and not to eliminate competition. Abstarct Brood parasites have demanding needs of host resources. Brood parasitic offspring are highly competitive and frequently cause the failure of host broods and the survival of a single parasitic offspring. Accordingly, virulent brood parasites lay a single egg in the same host nest to avoid sibling competition. In the cuckoo catfish (Synodontis multipunctatus), which parasitize mouthbrooding cichlid fishes in Lake Tanganyika, the modes of host and parasite oviposition lead to frequent cases of multiple parasitism. We experimentally tested the prediction that multiple parasitism leads to frequent cannibalism among offspring. Cuckoo catfish embryos prey upon host offspring to obtain nourishment during their 3-week development in the host buccal cavity and may also consume conspecific embryos. The potential benefits of cannibalism in the system are, therefore, twofold; to decrease competition for limited resources (i.e., host brood with rich yolk sacs) and to directly obtain nourishment by consuming rivals. We found that cannibalism indeed provided measurable benefits in terms of increased growth of the cannibals, but cannibalism was rare and typically occurred once all host offspring had been consumed. This implies that cannibalism among cuckoo catfish embryos emerges to mitigate starvation rather than eliminate competition.

Automated summary

Offspring of brood parasites compete for resources, but rarely resort to cannibalism. Cannibalism is used to mitigate starvation, not eliminate competition.