Widespread disruptive selection in the wild is associated with intense resource competition

Abstract

Background: Disruptive selection has been documented in a growing number of natural populations. Yet, its prevalence within individual systems remains unclear. Furthermore, few studies have sought to identify the ecological factors that promote disruptive selection in the wild. To address these issues, we surveyed 15 populations of Mexican spadefoot toad tadpoles, Spea multiplicata, and measured the prevalence of disruptive selection acting on resource-use phenotypes. We also evaluated the relationship between the strength of disruptive selection and the intensity of intraspecific competitionan ecological agent hypothesized to be an important driver of disruptive selection. Results: Disruptive selection was the predominant mode of quadratic selection across all populations. However, a directional component of selection favoring an extreme ecomorpha distinctive carnivore morphwas also common. Disruptive selection was strongest in populations experiencing the most intense intraspecific competition, whereas stabilizing selection was only found in populations experiencing relatively weak intraspecific competition. Conclusions: Disruptive selection can be common in natural populations. Intraspecific competition for resources may be a key driver of such selection. © 2012 Martin and Pfennig; licensee BioMed Central Ltd.