Publications filtered by: Experimental evolution
Theory assumes that postcopulatory sexual selection favours increased investment in testes size because greater numbers of sperm within the ejaculate increase the chance of success in sperm competition, and larger testes are able to produce more sperm. However, changes in the organization of the testes tissue may also affect sperm production rates. Indeed, recent comparative analyses suggest that sperm competition selects for greater proportions of sperm-producing tissue within the testes. Here, we explicitly test this hypothesis using the powerful technique of experimental evolution. We allowed house mice (Mus domesticus) to evolve via monogamy or polygamy in six replicate populations across 24 generations. We then used histology and image analysis to quantify the proportion of sperm-producing tissue (seminiferous tubules) within the testes of males. Our results show that males that had evolved with sperm competition had testes with a higher proportion of seminiferous tubules compared with males that had evolved under monogamy. Previously, it had been shown that males from the polygamous populations produced greater numbers of sperm in the absence of changes in testes size. We thus provide evidence that sperm competition selects for an increase in the density of sperm-producing tissue, and consequently increased testicular efficiency.
Male genital morphology is characterized by two striking and general patterns of morphological variation: rapid evolutionary divergence in shape and complexity, and relatively low scaling relationships with body size. These patterns of variation have been ascribed to the action of sexual selection. Among species, monogamous taxa tend to have relatively less complex male genital morphology than do polygamous taxa. However, although variation in male genital morphology can be associated with variation in mating and fertilization success, there is no direct evidence that sexual selection generates the evolutionary changes in male genital shape that underlie observed macroevolutionary patterns. Moreover, the hypothesis that sexual selection acts to reduce the scaling relationship between body and genital size is based entirely on the theoretical argument that male genitalia should be selected to provide an appropriate mechanical and/or stimulatory fit to the most commonly encountered female genitalia. Here, using the dung beetle Onthophagus taurus, we combine the power of experimental evolution with multivariate selection and quantitative genetic analyses to provide the most comprehensive evidence available of the form and evolutionary consequences of sexual selection acting on male genital morphology.
Los estudios de evolución experimental constituyen una herramienta de extrema utilidad para comprender los procesos evolutivos a nivel intra-específico. Este artículo expone, a grandes rasgos, en qué consiste la evolución experimental y qué información ofrece. Se resalta el caso particular de estudios que utilizan esta aproximación metodológica para avanzar en el conocimiento de la selección sexual y de sus consecuencias evolutivas. Se muestra con algunos ejemplos cómo los estudios de evolución experimental contribuyen de manera significativa a mejorar la comprensión de la evolución de caracteres que determinan el éxito en el apareamiento y la fecundación, o de las diferencias entre los sexos.