Animals who fall victim to hosting another species' offspring are in a constant evolutionary battle with their parasitic foster children. While most brood parasitism in vertebrates can be seen in species of birds, The cuckoo catfish (Synodontis Multipunctatus) has also dipped its evolutionary toes into taking advantage of another fish's good parenting.
Female African cichlids (Pseudotropheus) raise and care for their babies in a special pouch in their mouths to protect their offspring from being eaten while they get big enough to eat things for themselves. This form of parenting is a good strategy for ensuring that a large number of the eggs get to become baby fish and eventually big fish. Cuckoo catfish lay their eggs in the same place as the cichlids, causing them to accidentally be picked up with the cichlid eggs. The cuckoo eggs hatch faster than the cichlids and eat the biological eggs, all while the unsuspecting mother lovingly protects them from becoming snacks for other fish.
Researchers at the Institute of Vertebrate Biology aimed to find out how effective the catfish were at infecting the broods of the cichlid species that had experienced this invasion compared to species that had not.
The scientists imported 20 Cuckoo catfish from Lake Tanganyika and let them reproduce until there were 100. A breeder supplied 4 species of cichlid, one of which (S.diagramma) was native to the same lake as the Cuckoo catfish. When the cichlids and catfish were sexually mature, each species of cichlids was partitioned into breeding groups and housed with male-female pairs of cuckoo catfish. The researchers counted the number of cichlid and catfish eggs in the brooding cichlid's mouths and counted the number and type of rejected eggs. The team then recorded how many of each species hatched and survived to determine which species was more immune to brood parasitism.
They found that the Cichlids that had previously experienced catfish parasitism were more likely to reject the broods that had been infected with the catfish eggs within the first day than the Chiclid species that came from surrounding lakes. The inexperienced cichlids were more likely to retain all of the eggs and, in turn, hatch more surviving catfish when infected. When the cichlids reject the imposter Cuckoo Catfish eggs, the Chiclid eggs go with them. Since the experienced cichlids were better at rejecting the infected broods, the number of surviving Chiclid offspring also suffered.
While all cichlids that are taken advantage of by the cuckoo catfish experience losses in their numbers of babies, the S.diagramma cichlid has evolved a strong eject mechanism to rid themselves of parasitic catfish eggs within their brood. While the S.diagramma’s defenses against the cuckoo catfish are strong, they unintendedly neglect their offense, and their babies are lost in the evolutionary fight.