Sexual size dimorphism in a Tunisian population of Bosk's fringe-toed lizards Acanthodactylus boskianus asper

Abstract

Investigating how patterns of sexual size dimorphism vary among local populations may be useful for understanding size evolution in lizards. We investigated patterns of sexual size dimorphism in a Tunisian population of Bosk's fringe-toed lizards Acanthodactylus boskianus asper, in relation to a Middle-eastern population of the same subspecies. Our results showed an overall male-biased size dimorphism, consistent with general sexual size dimorphism trends in lacertids, and provide support for both the fecundity advantage hypothesis and the intra-sexual selection hypothesis. Indeed, for similarly-sized heads, females had longer trunks than males, and for similarly-sized trunks, males showed larger heads than females. Using the discriminant function approach, we investigated whether the power of discrimination between sexes varied when morphometric measures were expressed relative to head length vs. trunk length. We found that the two methods agreed in the classification of individuals as males or females, although the discrimination power was slightly higher when data were expressed relative to head length. Our results also showed that when using trunk length-adjusted data the power of discriminating the sexes was higher when the analysis was restricted to the largest individuals, which gives support to the idea that for morphological investigations small subsamples of the largest individuals should be used. Overall, the results of our work support the conclusions of a recent study on sexual size dimorphism in a Middle-eastern population of the same subspecies, suggesting that patterns of sexual size dimorphism are geographically stable in this widely distributed subspecies.

Key words:

• discriminant function
• lacertids
• morphometric data
• North Africa
• sexes

Acknowledgments

Permits for working at the study sites and for lizard sampling were obtained from the forest service in the Tunisian Ministry of Agriculture (permit reference: 910-15/03/2012). We thank Sarra Ouled Ali and Khaoula Sellami for their helpful assistance in the field. We also thank two anonymous reviewers and the Associate Editor for their comments on earlier versions of the manuscript.