Young Lindsay C, Zaun Brenda J, Vanderwerf Eric A
Ecology, Evolution and Conservation Biology Program, Department of Zoology, University of Hawaii, Honolulu, HI 96822, USA.
Biol Lett. 2008 Aug 23;4(4):323-5. doi: 10.1098/rsbl.2008.0191.
Unrelated same-sex individuals pairing together and cooperating to raise offspring over many years is a rare occurrence in the animal kingdom. Cooperative breeding, in which animals help raise offspring that are not their own, is often attributed to kin selection when individuals are related, or altruism when individuals are unrelated. Here we document long-term pairing of unrelated female Laysan albatross (Phoebastria immutabilis) and show how cooperation may have arisen as a result of a skewed sex ratio in this species. Thirty-one per cent of Laysan albatross pairs on Oahu were female-female, and the overall sex ratio was 59% females as a result of female-biased immigration. Female-female pairs fledged fewer offspring than male-female pairs, but this was a better alternative than not breeding. In most female-female pairs that raised a chick in more than 1 year, at least one offspring was genetically related to each female, indicating that both females had opportunities to reproduce. These results demonstrate how changes in the sex ratio of a population can shift the social structure and cause cooperative behaviour to arise in a monogamous species, and they also underscore the importance of genetically sexing monomorphic species.
在动物王国中，无亲缘关系的同性个体多年来配对并合作养育后代是一种罕见的现象。合作繁殖，即动物帮助养育非自己亲生的后代，当个体有亲缘关系时通常归因于亲缘选择，当个体无亲缘关系时则归因于利他行为。在此，我们记录了无亲缘关系的雌性黑背信天翁（Phoebastria immutabilis）的长期配对情况，并展示了合作行为可能是如何因该物种性别比例失衡而产生的。瓦胡岛上31%的黑背信天翁配对是雌性与雌性，由于雌性偏向性的迁入，总体性别比例为59%为雌性。雌性与雌性配对育出的后代比雄性与雌性配对育出的少，但这比不繁殖要好。在大多数养育雏鸟超过一年的雌性与雌性配对中，至少有一个后代与每个雌性有基因关联，这表明两个雌性都有繁殖机会。这些结果证明了种群性别比例的变化如何能够改变社会结构并导致一夫一妻制物种中出现合作行为，同时也强调了对单态性物种进行基因性别鉴定的重要性。
