性选择、配偶外父亲身份确认程度、遗传变异性和保护

岛屿动物中的性选择强度不高，其原因可能是由于岛屿种群的遗传变异性水平较低。本文作者检验了鸟类岛屿种群是否具有较低的遗传变异性、性选择强度大的种群是否具有较高的突变输入率（rate of mutational input)，在鸟类岛屿种群中是否具有较低的性选择强度（可以根据配偶外父亲身份的频率来估计）。小卫星共有谱带系数（minisatellite band sharing coefficient)可确定无亲源关系个体之间的遗传变异性，对与遗传变异性有关的雄性个体的父亲（paternity)进行了成对比较以检验如下假说：在具有较多遗传变异的种群中，雌性个体更经常地进行配偶外交配。在小卫星谱带系数较低的鸟类种群中，配偶外父亲的频次较高。对岛屿和大陆鸟类进行的第二个比较分析表明：岛屿种群中的配偶外父亲频次较低，遗传变异性也较低，其部分原因在于突变输入（mutational input)减少。上述发现表明：（1）父亲确认程度（parternity)随遗传变异性的数量而增加；（2）在遗传变异性较大的种群中，突变率较高，性选择的程度更激烈；（3）岛屿种群中性选择的强度一般比大陆种群弱。这对于理解遗传变异性的空间变异、理解岛屿种群和其它隔离种群的保护问题有重要启示。

SEXUAL SELECTION, EXTRA-PAIR PATERNITY, GENETIC VARIABILITY AND CONSERVATION

Sexual selection has been hypothesised to be relaxed on islands, perhaps because island populations often have low levels of genetic variability. I tested whether island population of birds have low genetic variability, whether the rate of mutational input is higher in populations with more intense sexual selection, and whether the intensity of sexual selection as estimated from the frequency of extra-pair paternity is reduced on islands. A pairwise comparison of paternity studies of bird populations in relation to genetic variability as determined by minisatellite band sharing coefficients among unrelated individuals was used to test the prediction that females should engage more frequently in extra-pair copulations in populations with a greater amount of genetic variation. There was a higher frequency of extra-pair paternity in bird populations with a lower band sharing coefficient. A second comparative analysis of pairs of island and mainland populations of birds revealed that extra-pair paternity was consistently lower in island populations, which also had lower genetic variability. This reduced genetic variability was partly due to a reduction in mutational input. These findings suggest that (1) intraspecific variation in paternity increases with the amount of genetic variability, (2) the mutation rate is higher in populations with greater genetic variability and more intense sexual selection, and that (3) the intensity of sexual selection generally is weaker on islands than on the mainland. This has implications for our understanding of spatial variation in genetic variability and for problems of conservation on islands and in other isolated populations.