Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom.
Evolution. 2010 Jul;64(7):1926-34. doi: 10.1111/j.1558-5646.2010.00958.x. Epub 2010 Jan 21.
Studies of experimental sexual selection have tested the effect of variation in the intensity of sexual selection on male investment in reproduction, particularly sperm. However, in several species, including Drosophila pseudoobscura, no sperm response to experimental evolution has occurred. Here, we take a quantitative genetics approach to examine whether genetic constraints explain the limited evolutionary response. We quantified direct and indirect genetic variation, and genetic correlations within and between the sexes, in experimental populations of D. pseudoobscura. We found that sperm number may be limited by low heritability and evolvability whereas sperm quality (length) has moderate V(A) and CV(A) but does not evolve. Likewise, the female reproductive tract, suggested to drive the evolution of sperm, did not respond to experimental sexual selection even though there was sufficient genetic variation. The lack of genetic correlations between the sexes supports the opportunity for sexual conflict over investment in sperm by males and their storage by females. Our results suggest no absolute constraint arising from a lack of direct or indirect genetic variation or patterns of genetic covariation. These patterns show why responses to experimental evolution are hard to predict, and why research on genetic variation underlying interacting reproductive traits is needed.
实验性性选择的研究检验了性选择强度变化对雄性生殖投资（尤其是精子）的影响。然而，在包括黑腹果蝇在内的一些物种中，实验进化并没有引起精子的反应。在这里，我们采用数量遗传学的方法来检验遗传限制是否解释了有限的进化反应。我们量化了实验种群中黑腹果蝇的直接和间接遗传变异以及雌雄之间的遗传相关性。我们发现，精子数量可能受到低遗传力和可进化性的限制，而精子质量（长度）则具有中等的 V(A)和 CV(A)，但不会进化。同样，雌性生殖道被认为是推动精子进化的因素，但即使存在足够的遗传变异，它也没有对实验性性选择做出反应。雌雄之间缺乏遗传相关性支持了雄性在精子投资和雌性储存方面存在性冲突的机会。我们的结果表明，不存在由于直接或间接遗传变异或遗传协变模式缺乏而导致的绝对限制。这些模式解释了为什么对实验进化的反应难以预测，以及为什么需要研究相互作用的生殖特征的遗传变异。
