The ecological and developmental foundations of brood parasitism in a catfish

Interspecific brood parasitism has evolved repeatedly from parental care. However, many non-avian brood-parasitic lineages have ancestors lacking parental care, leaving the foundations of brood parasitism in these lineages enigmatic. We examine ecological, reproductive, and developmental data from the Lake Tanganyika radiation of Synodontis catfishes, where one species, the cuckoo catfish, exhibits brood parasitism of mouthbrooding cichlid fishes. Our comparative analyses, coupled with experimental parasitism, suggest that a combination of ancestral traits (large eggs and rapid embryo development) enabled the origin of brood parasitism. Evolutionary innovations then presumably enhanced the success of brood parasitism after it emerged. Novel traits comprise frequent production of small clutches to effectively utilize host availability, the evolution of egg mimicry to facilitate host egg adoption, and modifications to development to enhance the performance of catfish embryos in the host's buccal cavity. Interestingly, despite the distinct ecological and life history contexts of the origin of catfish brood parasitism, its evolutionary and developmental outcomes align with those of canonical avian brood parasites. This suggests that general patterns are repeated in the evolution of brood parasitism, despite disparate starting conditions.