Alloparental care among animal populations, or parents caring for young who are not directly related, is well known in mammal and bird species; however, the role of alloparental behavior on population demographics is largely unknown. Does such care actually allow populations to increase? Or, despite such behavior obviously being appreciated by the youth in need, does this represent a physiological cost to the charitable benefactors of these lost offspring?
In the pursuit of such population-scale questions, researchers have recently observed instances of adoption in California Sea Lions for the first time. Documented in a study published in PLoS ONE, it seems that adoption can potentially help maintain a high survival rate of pups and can even help population growth over time. Biologists working at the San Jorge and Los Islotes Islands in the Gulf of California captured ea lion pups and marked them with haircuts. Genetic analyses were also done in order to determine relatedness between pups and adult females. For the pups, seemingly the easy part, simple toe clips provided genetic material for analysis. For the adult females, presumably for safety reasons, genetic material from the adult females was obtained via crossbow, with the bolts attached to fishing line so they could be reeled back in.
Two adoption events were observed during this study; distinctive female sea lions and marked pups were seen nursing pups suspected to be not their own, and confirmed by genetic tests (the mother and pup genotypes were mismatched). But how could this affect the population? Using known vital rates of this species, the researcher built a model in order to examine the potential impact of adoption, finding that such behavior could actually positively affect population growth, even if adoption meant that the alloparent–the adopted parent–incurred a fitness cost, such as not being able to reproduce as successfully. The workers caution that it is not explicitly known how adoption would affect an individual sea lion (would she have less pups, be more stressed to find food?), but this hypothetical model provides much-needed insight.
Further genetic work indicated sea lion populations showed different rates of potentially adoptive beahavior: less than 6% on San Jorge, and over 17% on Los Islores. More research is needed to unravel what factors play into this.
Want a diver’s eye view of the California Sea Lion? The video below is via Jason Watts, on Vimeo.
Flatz R, & Gerber LR (2010). First evidence for adoption in California sea lions. PloS one, 5 (11) PMID: 21079727