Civetta Alberto, Singh Rama S
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada.
Evolution. 1998 Aug;52(4):1080-1092. doi: 10.1111/j.1558-5646.1998.tb01835.x.
Phenotypic divergence in the male reproductive system (genitalia and gonads) between species of the Drosophila melanogaster complex and their hybrids was quantified to decipher the role of these traits in species differentiation and speciation. Internal as well as external, sexual and nonsexual traits were analyzed with respect to genetic variation and trait asymmetry between strains within species, genetic divergence between species, and dominance and asymmetry in species and hybrids. The variation between strains within species was significant among sexual traits, and only external traits were less asymmetric than internal ones, which suggests that sexual traits are not strongly constrained within species. Three main findings show that sexual traits are most divergent between species: (1) testis length and area, and the area of the posterior lobe of the genital arch (sexual traits) showed the highest proportion of variation between species; (2) linear discriminant functions with the highest components associated to sexual traits were better predictors of species membership; and (3) testis length and area revealed a departure from a linear relationship between members of the species group. Examination of interspecific hybrids showed that sexual traits had higher asymmetry in species hybrids than in the parental species and that sexual traits showed additivity or dominance whereas nonsexual traits showed overdominance (with the exception of malpighian tubules length). These results suggest that sexual traits have undergone more genetic changes and, as a result, tend to show higher divergence and stronger hybrid breakdown between species than nonsexual traits. We propose that sexual selection in the broad sense, affecting all aspects of sexuality, may be responsible for the diversified appearance of sexual traits among closely related species and that the genetic architecture underlying sexual traits may be more prone to disruption during the early stages of speciation.
对黑腹果蝇复合体物种及其杂种雄性生殖系统（生殖器和性腺）的表型差异进行了量化，以解读这些性状在物种分化和物种形成中的作用。分析了内部和外部、有性和无性性状在种内品系间的遗传变异和性状不对称性、物种间的遗传差异以及物种和杂种中的显性和不对称性。种内品系间的差异在有性性状中很显著，只有外部性状比内部性状的不对称性小，这表明有性性状在种内没有受到强烈限制。三项主要发现表明，有性性状在物种间差异最大：（1）睾丸长度和面积以及生殖弓后叶面积（有性性状）在物种间的变异比例最高；（2）与有性性状相关成分最高的线性判别函数是物种归属的更好预测指标；（3）睾丸长度和面积显示出物种组内成员之间的线性关系出现偏离。对种间杂种的研究表明，有性性状在物种杂种中的不对称性高于亲本物种，有性性状表现为加性或显性，而无性性状表现为超显性（马尔皮基氏小管长度除外）。这些结果表明，与无性性状相比，有性性状经历了更多的遗传变化，因此在物种间往往表现出更高的差异和更强的杂种衰败。我们提出，广义的性选择影响性的各个方面，可能是近缘物种间有性性状多样化外观的原因，并且有性性状的遗传结构在物种形成早期可能更容易受到破坏。
