A test of Rensch’s rule in dwarf chameleons (Bradypodion spp.), a group with female-biased sexual size dimorphism
- 300 Downloads
Rensch’s rule describes a pattern of allometry in sexual size dimorphism (SSD): when males are the larger sex (male-biased SSD), SSD increases with increasing body size, and when females are the larger sex (female-biased SSD), SSD decreases with increasing body size. While this expectation generally holds for taxa with male-biased or mixed SSD, examples of allometry for SSD consistent with Rensch’s rule in groups with primarily female-biased SSD are remarkably rare. Here, I show that the majority of dwarf chameleons (Bradypodion spp.) have female-biased SSD. In accordance with Rensch’s rule, the group exhibits an allometric slope of log(female size) on log(male size) less than one, although statistical significance is dependent on the phylogenetic comparative method used. In this system, this pattern is likely due to natural selection on both male and female body size, combined with fecundity selection on female body size. In addition to quantifying SSD and testing Rensch’s rule in dwarf chameleons, I discuss reasons why Rensch’s rule may only rarely apply to taxa with female-biased SSD.
KeywordsAllometry Allometric scaling Body size Comparative method Fecundity selection Natural selection Phylogenetic Sexual selection
I am grateful to Adnan Moussalli for field assistance and critical comments on the manuscript and to Martin Whiting for facilitating this research. Funding was from a National Research Foundation (NRF) grant to DSF. Permits: MPB.5104 (Mpumalanga), 005-00001 (Limpopo), 1721/2003 and 4390/2005 (KZN), 234/2003 (Western Cape), WRO 11/03 WR (Eastern Cape).
- Blanckenhorn WU, Dixon AFG, Fairbairn DJ, Foellmer MW, Gibert P, van der Linde K, Meier R, Nylin S, Pitnick S, Schoff C, Signorelli M, Teder T, Wiklund C (2007) Proximate causes of Rensch’s rule: does sexual size dimorphism in arthropods result from sex differences in development time? Am Nat 169:245–257PubMedCrossRefGoogle Scholar
- Branch WR (1998) A field guide to snakes and other reptiles of southern Africa 3rd edn. Struik Publishers, Cape TownGoogle Scholar
- Burrage BR (1973) Comparative ecology and behaviour of Chamaeleo pumilis pumilis (Gmelin) and C. namaquensis A. Smith (Sauria: Chamaeleonidae). Ann S Afr Mus 61:1–158Google Scholar
- Garland TJ, Harvey PH, Ives AR (1992) Procedures for the analysis of comparative data using phylogenetically independent contrasts. Syst Biol 41:18–32Google Scholar
- Jacobsen NHG (1989) A herpetological survey of the Transvaal. School of Life and Environmental Sciences, University of Natal, DurbanGoogle Scholar
- Martins EP (2004) COMPARE 4.6: statistical analysis of comparative data. pp. Available free from http://compare.bio.indiana.edu/. Dept. of Biology, Indiana University, Bloomington
- Nečas P (2001) Chameleons: Nature’s Hidden Jewels. Krieger Publishing, MalabarGoogle Scholar
- Rensch B (1960) Evolution above the species level. Columbia University Press, New YorkGoogle Scholar