Do dwarf chameleons (Bradypodion) show developmental plasticity?

Abstract

Developmental plasticity results from environmental influences on the phenotype of an organism during its development, and its effects are irreversible. The  phenomenon of phenotype–genotype uncoupling (plasticity) causes problems in species delineations, and has been suggested as a cause underlying a mismatch between morphology and genetics between the Natal Midlands dwarf chameleon (Bradypodion thamnobates) and the KwaZulu dwarf chameleon (Bradypodion melanocephalum). The two species are morphologically distinct, but are very poorly distinguished genetically. It has been hypothesized that B. melanocephalum and B. thamnobates may be phenotypically plastic populations of the same species, since environmental conditions, the driving force behind developmental plasticity, varies between the distributions of these two allopatric taxa.We raised juveniles of both species under identical controlled laboratory conditions. Two treatments were used. These varied in both habitat structure and temperature, each approximating conditions that one of the species would encounter naturally. Although not specifically controlled or monitored, all other environmental factors (e.g. humidity, light and wind) were standardized since chameleons were raised in the artificial  conditions created in environmental chambers. If taxa are developmentally plastic, phenotypes would reflect treatment conditions, irrespective of specific associations. Neither B. thamnobates nor B. melanocephalum were phenotypically plastic over the environmental differences tested; species developed into the expected phenotypes, irrespective of treatment conditions. The low genetic difference between B.  thamnobates and B. melanocephalum may indicate their recent divergence from a common ancestor or the mitochondrial gene fragments (ND2 and 16S) used in previously published phylogenetic analyses of the genus may not be representative of divergence for the genome as a whole.

Key words: developmental plasticity, phenotypic plasticity, phylogenetic mismatch, Bradypodion.