The development, evaluation, and illustration of a timeline procedure for testing the role of sperm competition in the evolution of sexual traits using paternity data

The empirical study of the role of sperm competition in the evolution of sexual traits has historically been problematic through the inability either to measure sperm competition levels directly in the present or to reconstruct changes in the evolutionary past. Here, we develop and test a procedure based on paternity data that potentially permits both. For our pilot study, we use the rate of change of the seminal protein gene SEMG2 for catarrhine primates published by Dorus et al. (Nat Genet 36:1326–1329, 2004). From their data, Dorus et al. proposed a two-part hypothesis: (1) sperm competition plays a role in the evolution of the SEMG2 gene and (2) higher levels of sperm competition generate more positive selection for change in SEMG2 than lower levels. Dorus et al. were limited, however, by being able to use only proxy measures of sperm competition and only seven “recent” segments of catarrhine primate phylogeny. Here, we develop a “timeline procedure” that permits the Dorus hypothesis to be tested using data from across the whole of catarrhine phylogeny. Our analysis supports part (1) of the Dorus hypothesis but questions part (2), suggesting instead that changes in level of sperm competition have a more powerful influence on the rate of evolution of traits than the level of sperm competition itself. We conclude that the timeline procedure developed here could be a valuable investigative tool in the role of sperm competition in the evolution of sexual traits measured over evolutionary time such as SEMG2. The empirical study of the role of sperm competition in the evolution of sexual traits has historically been problematic through the inability to measure sperm competition levels directly in the present and to reconstruct changes in the evolutionary past. Here, we test a “timeline procedure” based on paternity data that potentially permits both. For our pilot study, we use the rate of change of the seminal protein gene SEMG2 for catarrhine primates published by Dorus et al. (Nat Genet 36:1326–1329, 2004). Whereas Dorus et al. were limited to using proxy measures for only “recent” segments of catarrhine primate phylogeny, our method permits direct measures of sperm competition to be applied across the whole of Catarrhine phylogeny. We conclude that this new procedure could be valuable for investigation of the role of sperm competition in the evolution of a wide range of sexual traits.