Sharing the love? – Nonrandom brood mixing and foster parenting in cichlid colony
Will you let a completely unrelated stranger take care of your child while you adopt someone else’s? Probably not. However, parental care of unrelated offspring has been reported in more than 120 mammal and 150 bird species!! (Riedman, 1982) Specifically, the cichlid fish Neolamprologus caudopunctatus is also known to exhibit such behaviour.
From a recent study of 32 broods of cichlid fish from Lake Tanganyika, 59% of them contain fry unrelated to both parents, suggesting strong evidence of brood mixing. (Schaedelin et al., 2013)
Furthermore, the mixing appears to be nonrandom and deliberate. Small fry are fairly immobile and operate at most at a radius of a few metres. Yet observations show that some fry were found around 40 metres away from their parental nest. The reason behind this is because genetic parents transport some of their fry via their mouths and travel to fairly distant foreign nests to ensure that some of their young will survive and carry on the bloodline even if the parental nest and its neighbourhood is predated, a risk management strategy by the parent cichlid.
The question remains, why will other cichlid fish be willing to adopt fry unrelated to them? One of the reasons is because through adoption, brood size increases and hence leads to a lower chance of the brood being predated. More interestingly, foster parents adopt foreign fry selectively, adopting fry smaller or the same size as their own while rejecting bigger size fry. The reason is because smaller fry gets predated more frequently, hence foster parents protect their own young by adopting smaller foreign fry.
In conclusion, foster parenting and adoption in cichlid colony is really not so much about sharing the love, it is rather the interest and survival of its own kind that drives this behaviour.
“Neolamprologus caudopunctatus Kapampa 1837,” by Melanochromis. Wikimedia Commons. URL:http://commons.wikimedia.org/wiki/File:Neolamprologus_caudopunctatus_Kapampa_1837.jpg (accessed 9th Apr 2013).
Riedman M. L., 1982. The Evolution of Alloparental Care and Adoption in Mammals and Birds. The Quarterly Review of Biology, 57(4): 405.
Schaedelin C. F., Wouter F. D. D., Richard H. W., 2013. Nonrandom brood mixing suggests adoption in a colonial cichlid. Behavioral Ecology, 24 (2): 540-546.