Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, Western Australia 6009, Australia.
Evolution. 2018 Apr;72(4):893-905. doi: 10.1111/evo.13455. Epub 2018 Mar 12.
When females mate with more than one male, sexual selection acts both before and after mating. The interaction between pre- and postmating episodes of selection is expected to be context dependent, but few studies have investigated how total sexual selection changes under different ecological conditions. We examined how population density mediates the interaction between pre- and postmating sexual selection by establishing replicate populations of the horned dung beetle Onthophagus taurus at low, medium, and high densities, and then using microsatellite-based parentage analyses to measure male fitness. We found that mating success and fertilization success were positively correlated at all three densities, but the strength of the correlation decreased with increasing density. We also found a shift from negative to positive linear selection on testes mass as density increased, and opposing selection on weapons and testes at high densities. These patterns suggest that the importance of postmating processes increases with increasing population density, which reduces the selective advantage of weapons for premating contest competition, and increases the selective advantage of large ejaculates for postmating sperm competition. We expect that density-dependent selection on testes mass has contributed to the phenotypic variation observed between natural populations of O. taurus that differ in density.
当雌性与多个雄性交配时，性选择会在交配前后同时发生。选择的交配前和交配后事件之间的相互作用预计是依赖于环境的，但很少有研究调查总性选择在不同生态条件下如何变化。我们通过在低、中、高三种密度下建立角粪金龟 Onthophagus taurus 的重复种群，并使用基于微卫星的亲子分析来衡量雄性适合度，来研究种群密度如何调节交配前和交配后性选择之间的相互作用。我们发现，在所有三种密度下，交配成功率和受精成功率呈正相关，但随着密度的增加，相关性的强度会降低。我们还发现，随着密度的增加，睾丸质量的线性选择从负向转为正向，而在高密度下，武器和睾丸的选择则相反。这些模式表明，随着种群密度的增加，交配后过程的重要性增加，这降低了武器在交配前竞争中的选择优势，并增加了大精液在交配后精子竞争中的选择优势。我们预计，睾丸质量的密度依赖选择促成了在密度不同的 O. taurus 自然种群中观察到的表型变异。
