Male approach and female avoidance as mechanisms of population discrimination in sagebrush lizards
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Reproductive isolation and speciation can result from female choice for particular males. Isolation can also result, however, from male mating preferences or from aggressive encounters which then influence mating decisions. In this study, we use laboratory discrimination trials to study the behavioral mechanisms of population discrimination in sagebrush lizards (Sceloporus graciosus). We specifically ask three questions about population-level discrimination: (1) Does it vary in strength in relation to the geographic distance between the populations? (2) Is it more apparent in inter- or intra-sexual interactions? (3) Does it take the form of attraction or avoidance? We ran 890 trials that tested the ability of male and female sagebrush lizards from one population to discriminate their own population from four other populations. In addition, we utilized both sequential and simultaneous-choice designs, which enabled us to distinguish between attraction and avoidance. We found that most population-level discrimination was exhibited by male lizards preferring to associate with particular types of females, as well as female avoidance of particular types of males. The strength and direction of both discriminations depended on the populations compared and on whether the tests were conducted as sequential- or simultaneous-choice tests, producing a complex relationship between geographic distance and behavioral discrimination. Our results suggest that there are roles for male attraction and female avoidance in population discrimination, reproductive isolation, and speciation.
KeywordsMate choice Male choice Sexual selection Reproductive isolation Geographic differences Sceloporus graciosus Population discrimination Choice tests
We would like to thank B. Bowling, J. Campuzano, J. Feit, K. Morgan, G. O’Campo, L. Sheldahl, and D. Zierten for help with running the discrimination trials. We also thank T. Greenfield, M. Hall, M. Halloy, M. Kerr-Valentic, K. Lacy, and D. Rosseto for help with collecting lizards. Further thanks to W. Cooper, L. Fishman, J. Moretz, K. Morgan, J. Thompson, P. Zani, and two anonymous reviewers for comments on earlier drafts of the manuscript. This research was supported by a NSF research training grant in genetic mechanisms of evolution to ANB, an Explorers Club grant awarded to ANB, as well as NSF grant DEB-9720641 to EPM. This research conformed to all laws of the USA, in which the research was done (animal care protocol 98-102A).
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