Institute of Biology, University of Graz, Universitätsplatz 2, 8010, Graz, Austria.
BMC Biol. 2019 Jan 31;17(1):2. doi: 10.1186/s12915-018-0620-6.
In socially monogamous species, reproduction is not always confined to paired males and females. Extra-pair males commonly also reproduce with paired females, which is traditionally thought to be costly to the females' social partners. However, we suggest that when the relatedness between reproducing individuals is considered, cuckolded males can suffer lower fitness losses than otherwise expected, especially when the rate of cuckoldry is high. We combine theoretical modeling with a detailed genetic study on a socially monogamous wild fish, Variabilichromis moorii, which displays biparental care despite exceptionally high rates of extra-pair paternity.
We measured the relatedness between all parties involved in V. moorii spawning events (i.e. between males and females in social pairs, females and their extra-pair partners, and paired males and their cuckolders), and we reveal that males are on average more related to their cuckolders than expected by chance. Queller-Goodnight estimates of relatedness between males and their cuckolders are on average r = 0.038 but can range up to r = 0.64. This also increases the relatedness between males and the extra-pair offspring under their care. These intriguing results are consistent with the predictions of our mathematical model, which shows that elevated relatedness between paired males and their cuckolders can be adaptive for both parties when competition for fertilizations is strong.
Our results show how cuckoldry by relatives can offset males' direct fitness losses with inclusive fitness gains, which can be substantial in systems where males face almost certain paternity losses.
在社会一夫一妻制的物种中，繁殖并不总是局限于配对的雄性和雌性。额外的雄性通常也与配对的雌性繁殖，这传统上被认为对雌性的社交伙伴代价高昂。然而，我们认为，当考虑到繁殖个体之间的亲缘关系时，被戴绿帽子的雄性可能会遭受比预期更低的适应度损失，尤其是当被戴绿帽子的频率很高时。我们将理论建模与对一种社会一夫一妻制的野生鱼类 Variabilichromis moorii 的详细遗传研究相结合，该鱼类尽管存在异常高的额外配对父权率，但仍表现出双亲养育。
我们测量了 V. moorii 产卵事件中所有涉及方之间的亲缘关系（即社会对中雄性和雌性之间、雌性与其额外配对伙伴之间以及配对雄性与其戴绿帽子者之间），并揭示了雄性平均与他们的戴绿帽子者比随机情况下更具亲缘关系。雄性与其戴绿帽子者之间的 Queller-Goodnight 估计的亲缘关系平均 r = 0.038，但范围可以高达 r = 0.64。这也增加了雄性与其照顾的额外配对后代之间的亲缘关系。这些有趣的结果与我们的数学模型的预测一致，该模型表明，当受精竞争激烈时，配对雄性与其戴绿帽子者之间升高的亲缘关系对双方都是适应性的。
我们的研究结果表明，亲属的戴绿帽子行为可以通过包容性适应度收益来抵消雄性的直接适应度损失，在雄性面临几乎确定的父权损失的系统中，这种收益可能是巨大的。
