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.

Linking microhabitat structure, morphology and locomotor performance traits in a recent radiation of dwarf chameleons

“…Asplund ; Fleming ), which might also be the case here. Moreover, each form reaches different absolute body sizes (da Silva & Tolley ), which is not a consequence of phenotypic plasticity, as demonstrated by a common garden experiment on B. thamnobates and B. melanocephalum (Miller & Alexander ). Accordingly, the differences in absolute performance are likely indicative of ecological differences between them.…”

Diversification through ecological opportunity in dwarf chameleons

“…The climatic and associated vegetation shifts ultimately would have shaped the present ecomorphological and genetic structure (da Silva & Tolley, ; da Silva et al ., ,b). Indeed, the discrepancies between the different lines of evidence indicate a dynamic system, with habitat shifts and concomitant local ecomorphological adaptation and strong selection on functional traits associated with habitat (Alexander, ; Miller & Alexander, ). The fluctuating nature of this system is also reflected in the presence of bottlenecks for each of the population clusters, as well as some admixture (Fig.…”

“…They also have functional adaptations corresponding to microhabitats, which can be broadly classified as either open‐ or closed‐canopy (da Silva & Tolley, ; da Silva et al ., ,b). They are not developmentally plastic, further suggesting that strong selection has resulted in rapid morphological diversification despite lack of strong genetic differentiation (Tolley et al., ; Tolley et al ., ; Miller & Alexander, ). The lack of strong genetic differences is attributed to recent divergence (Tolley et al ., , ) and incomplete lineage sorting and/or low levels of hybridization from periods of secondary contact.…”

Morphological variation in the Cape Dwarf Chameleon (Bradypodion pumilum) as a consequence of spatially explicit habitat structure differences

“…These two morphs relate strongly to habitat structure, and it is unlikely that phenotypic plasticity can be invoked as a parsimonious explanation, given that common garden experiments show no evidence for plasticity in this genus (Miller & Alexander, 2009). The most reasonable explanation is that phenotypic divergence is partly driven by habitat specific selection pressures (Tolley et al ., 2006, 2008; Cox & Calsbeek, 2010).…”