Cuckolding fish breaks the model

The theory of evolution predicts that males will not take care of offspring other than their own. But the ocellated wrasse, a fish found in the Mediterranean Sea, will often act as a father to offspring which are not his, a recent study by a pair of Yale researchers concluded.

The study, published online on Oct. 7 in the Proceedings of the Royal Society of London, found that male ocellated wrasses were as likely to provide care for non-related offspring as they were for their own offspring. In fact, the study reported that males were more likely to provide care to young ocellated wrasses if they were surrounded by “sneaker males” who deposit sperm but do not raise their possible offspring.

“The basic expectation is that when males are more closely related to offspring, they are more likely to invest in them,” Suzanne Alonzo, one of the authors of the study, said. “But here, there was no relationship between the two.”

To determine the relationship between paternity and paternal care, Suzanne Alonzo, an assistant professor of ecology and evolutionary biology, and Kellie Heckman, a postdoctoral fellow at the University, performed genetic testing on eggs from 11 nests from the wild. They found that all of the nesting males studied were caring for some offspring that were not their own.

Alonzo and Heckman also observed 727 ocellated wrasse nests in the Mediterranean Sea during the fish’s mating seasons, which lasts from May to June, in 1996, 1997, 2000 and 2005. For each nest, the two researchers recorded parental activity, the number of sneaker males and the presence of females. They found that the probability of male care increased with the number of sneaker males.

Alonzo said that this result defied long-held evolutionary predictions about male behavior. Although her conclusions were surprising on the surface, Alonzo said, the results could be explained by the complex interactions between males and females. Females will deposit more eggs in nests where there are large numbers of offspring, which indicate a successful male, the study found. These nests, however, tend to be ones surrounded by sneaker males, Alonzo said. By increasing the number of eggs in a nest, a male can increase the number of offspring that are his even if not all are fathered by the same male.

Alonzo and Heckman suggested in the study that scientists will need to look more closely at male-female relationships to determine offspring patterns.

“The social interactions within and between the sexes determine patterns of mating and care in ways that cannot be predicted or understood by a more traditional and static view of the interactions between mating and parental care,” the study found.

In light of human male behavior, five students interviewed said they were surprised by the behavior of the ocellated wrasse.

“If an average human male found out that his baby may not be biologically related to him, you would think that he would be less likely to invest in that child, not more,” Sunny Chung ’13 said.

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