Research article

Frequency-dependent selection by wild birds promotes polymorphism in model salamanders

Benjamin M Fitzpatrick¹ , Kim Shook^2,3 and Reuben Izally^2,3

¹Ecology & Evolutionary Biology, University of Tennessee, Knoxville TN 37996, USA

²Pre-collegiate Research Scholars Program, University of Tennessee, Knoxville TN 37996, USA

³Farragut High School, Knoxville TN 37934, USA

author email corresponding author email

BMC Ecology 2009, 9:12doi:10.1186/1472-6785-9-12

Published:	8 May 2009

Abstract

Background

Co-occurrence of distinct colour forms is a classic paradox in evolutionary ecology because both selection and drift tend to remove variation from populations. Apostatic selection, the primary hypothesis for maintenance of colour polymorphism in cryptic animals, proposes that visual predators focus on common forms of prey, resulting in higher survival of rare forms. Empirical tests of this frequency-dependent foraging hypothesis are rare, and the link between predator behaviour and maintenance of variation in prey has been difficult to confirm. Here, we show that predatory birds can act as agents of frequency-dependent selection on terrestrial salamanders. Polymorphism for presence/absence of a dorsal stripe is widespread in many salamander species and its maintenance is a long-standing mystery.

Results

We used realistic food-bearing model salamanders to test whether selection by wild birds maintains a stripe/no-stripe polymorphism. In experimental manipulations, whichever form was most common was most likely to be attacked by ground-foraging birds, resulting in a survival advantage for the rare form.

Conclusion

This experiment demonstrates that frequency-dependent foraging by wild birds can maintain colour polymorphism in cryptic prey.