QTL linkage mapping of zebra finch beak color shows an oligogenic control of a sexually selected trait

Mate choice based on sexual ornaments can impose strong selection, which raises the question of how genetic variation in ornaments is maintained. One mechanism that has been proposed is genic capture. If ornament expression is influenced by general condition and condition is under polygenic control, selection will be inefficient in removing genetic variation. Here we analyze whether the genetic architecture of beak color in a population of zebra finches supports this hypothesis. Zebra finch beak color is commonly assumed to be under strong selection by mate choice, although some of the evidence is ambiguous. We show that beak redness has a heritability of 34% in our population and that it is strongly genetically correlated between the sexes, suggesting that it is largely controlled by the same genes in males and females. We mapped variation in beak redness based on 1,404 SNP markers genotyped in a large pedigree. We find evidence for linkage on four chromosomes (Tgu1, Tgu5, Tgu13, Tgu21), which together explain a large part of the additive genetic variance. Our finding of genomic regions with major additive effects is not consistent with directional selection and genic capture, but rather suggests a role of antagonistic pleiotropy in maintaining genetic variation.

基于性装饰性状的配偶选择可施加强烈选择压力，这一现象引出了一个核心科学问题：装饰性状的遗传变异是如何得以维持的。此前学界提出的一种维持机制为基因捕获（genic capture）假说。若装饰性状的表达受个体一般条件的调控，且该条件由多基因控制，则自然选择在清除群体遗传变异方面效率将较为低下。本研究以斑胸草雀（zebra finch）种群的喙色遗传架构为研究对象，旨在检验该假说是否成立。通常认为，配偶选择会对斑胸草雀的喙色施加强烈选择压力，但相关实证证据存在一定模糊性。我们的分析结果显示，该种群中喙部红色程度的遗传力为34%，且雌雄个体间存在极强的遗传相关，提示该性状在两性间大体由同一套基因调控。我们基于大型家系中分型的1404个单核苷酸多态性（Single Nucleotide Polymorphism, SNP）标记，对喙部红色程度的变异开展了定位分析。研究在四条染色体（Tgu1、Tgu5、Tgu13、Tgu21）上检测到连锁信号，这些区域共同解释了该性状大部分的加性遗传方差。本研究发现存在具有显著加性效应的基因组区域，这一结果与定向选择及基因捕获假说并不一致，反而表明拮抗多效性在维持该种群的遗传变异中发挥了关键作用。