Washington, May 29 : Laysan albatross employ a strategy to make up for the shortage of males in their specie-reciprocity, a process in which unrelated females pair together and take turns raising offspring.
On Hawaiian island of Oahu, 31 percent of nests are found to be female-female pairs, who raise fewer chicks than male-female pairs. And owing to their limitation to raise only one chick each year, females stay together for multiple years for each to reproduce.
The discovery of this unusual strategy by University of Hawaii at Manoa zoology doctoral candidate Lindsay Young, and her co-authors, may explain why Laysan Albatross are successfully re-colonizing islands.
Such unrelated same-sex individuals pairing together and cooperating to raise offspring over many years is not a common sight in the animal kingdom. Usually, cooperative breeding, in which animals help raise offspring that are not their own, is linked to kin selection when individuals are related, or altruism when individuals are unrelated.
Here, the researchers have observed long-term pairing of unrelated female Laysan albatross (Phoebastria immutabilis) and have shown how cooperation may have arisen as a result of a skewed sex ratio in this species. It was found that 31 percent of Laysan albatross pairs on Oahu were female-female, and the overall sex ratio was 59 percent females as a result of female-biased immigration.
While female-female pairs raised fewer offspring than male-female pairs, but this was considered to be a better alternative than not breeding at all. Majority of female-female pairs that raised a chick in more than 1 year, were found to have at least one offspring that was genetically related to each female, suggesting that both females had opportunities to reproduce.
The results indicate how changes in the sex ratio of a population can modify the social structure and leads to cooperative behaviour in a monogamous species. They even highlighted the importance of genetically sexing monomorphic species.
The findings of the study are published in the Royal Society journal Biology Letters in a paper entitled, "Successful same-sex pairing in Laysan albatross."