Cuckolder kids stick together

Why do animals help each other? At first glance, helping behavior seems to stand in stark contrast to the notion that evolution is driven by the 'survival of the fittest'. This paradox can be resolved by considering relatedness: individuals may enhance the transmission of their own genes by helping individuals who possess many of the same genes (termed 'inclusive fitness'). Celebrated examples of individuals helping others, with no apparent benefit to themselves, include: (1) birds that help feed young at relatives' nests, and (2) ground squirrels that warn of impending danger when relatives are nearby. In both, inclusive fitness has been invoked to explain the evolution of this otherwise perplexing behavior.

From this begs is the question: How do animals know who to help? For sexually monogamous species, the answer comes easily; they should help nestmates. In sexually promiscuous species, however, individuals cannot reliably assume nestmates are siblings, and so require a more direct mechanism for differentiating kin from non-kin. This could be accomplished by evaluating the phenotype of potential kin relative to one's own phenotype, a technique known as self-referent kin recognition.

Bluegill sunfish are an ideal model organism with which to test for an association between promiscuity and the evolution of self-referent kin recognition. Males are either parentals or cuckolders (left and right, respectively, in above photo); the former tend nests and secure most of the paternity, while the latter forgo parental duties and instead sneak sperm into parental nests during spawning. Bluegills may gain inclusive fitness benefits by cooperating with shoal-mates that are kin. During such interactions, parental offspring can reliably assume a certain degree of relatedness with most individuals that originated from the same nest. Cuckolder offspring cannot, so they would benefit more from actively discriminating kin from non-kin using phenotypic cues.

Tim Hain - a graduate student from the University of Western Ontario, renowned for his prowess on the dance floor - and his supervisor, Bryan Neff, embarked on a series of elegant experiments to test kin recognition mechanisms in Bluegills from Lake Opinicon. Larvae of known parentage were presented with a choice between two odors originating from broods of varying degrees of relatedness. As predicted, cuckolder offspring were more likely to associate with the odors of relatives, while parental offspring showed no such association. This study was therefore able to show that, even within a species, promiscuity can be a driving force behind the evolution of self-referent kin recognition.

If you find yourself intrigued and eager to learn more, don't go looking for Tim at Western. He is currently doing fieldwork on guppies/establishing himself on dance floors in Trinidad. Though if you pay QUBS a visit next summer, keep an eye out for Tim’s distinctive 'dominance markings' (see photo) and you can’t go wrong.

Hain TJA, Neff BD (2006) Promiscuity drives self-referent kin recognition. Current Biology 16: 1807-1811 [Full Text]