Blais Jonatan, Rico Ciro, Bernatchez Louis
Départment de biologie, Québec-Océan, Université Laval, Ste-Foy, Québec GIK 7P4, Canada.
Evolution. 2004 Nov;58(11):2498-510. doi: 10.1111/j.0014-3820.2004.tb00879.x.
Sexual selection by mate choice represents a very important selective pressure in many animal species and might have evolutionary impacts beyond exaggeration of secondary sexual traits. Describing the shape and strength of the relationships linking mating success and nonsexual traits in natural conditions represents a challenging step in our understanding of adaptive evolution. We studied the effect of behavioral (nest site choice), immunological (trematode level of infection), genetic diversity (measured by mean d2) and morphological (standard length and pectoral fin size) traits on male mating success in a natural population of threespine sticklebacks Gasterosteaus aculeatus. Male mating success was measured by microsatellite genotyping of embryos used to infer female genotypes. First, we analyzed all territorial males (full analysis) but also considered independently only males with a nonzero mating success (reduced analysis) because some of the males with no eggs could have been part of a later breeding cycle. Multiple linear regressions identified a significant negative effect of parasite load in the full analysis, whereas no linear effect was found in the reduced analysis. The quadratic analyses revealed that nest location and parasite load were significantly related to mating success by positive (concave selection) and negative (convex selection) quadratic coefficients respectively, resulting in a saddle-shaped fitness surface. Moreover, there were significant interactions between nest location, mean d2 and parasite load in the reduced analysis. The subsequent canonical rotation of the matrix of quadratic and cross-product terms identified two major axes of the response surface: a vector representing mostly nest site choice and a vector representing parasite load. These results imply that there exists more than one way for a male threespine stickleback to maximize its mating success and that such nonlinear relationships between male mating success induced by female mate choice and male characteristics might have been overlooked in many studies.
通过配偶选择进行的性选择在许多动物物种中是一种非常重要的选择压力，其进化影响可能远不止于夸张的第二性征。描述在自然条件下将交配成功与非性特征联系起来的关系的形式和强度，是我们理解适应性进化过程中具有挑战性的一步。我们研究了行为（筑巢地点选择）、免疫（吸虫感染水平）、遗传多样性（通过平均d2测量）和形态（标准长度和胸鳍大小）特征对三刺鱼自然种群中雄性交配成功率的影响。通过对用于推断雌性基因型的胚胎进行微卫星基因分型来衡量雄性交配成功率。首先，我们分析了所有具有领地意识的雄性（完整分析），但也单独考虑了交配成功率非零的雄性（简化分析），因为一些没有卵的雄性可能参与了后续的繁殖周期。多元线性回归在完整分析中发现寄生虫负荷有显著的负面影响，而在简化分析中未发现线性影响。二次分析表明，筑巢位置和寄生虫负荷分别通过正（凹形选择）和负（凸形选择）二次系数与交配成功率显著相关，从而形成一个鞍形的适应度表面。此外，在简化分析中，筑巢位置、平均d2和寄生虫负荷之间存在显著的相互作用。随后对二次项和交叉乘积项矩阵进行的典型旋转确定了响应面的两个主轴：一个主要代表筑巢地点选择的向量和一个代表寄生虫负荷的向量。这些结果意味着，雄性三刺鱼有不止一种方式来最大化其交配成功率，而且在许多研究中，雌性配偶选择所诱导的雄性交配成功率与雄性特征之间的这种非线性关系可能被忽视了。
