Is gene expression totally thermoinsensitive in GSD taxa?
An additional evolutionary question that this comparative approach helps elucidate is whether GSD species derived from TSD ancestors have lost all thermal sensitivity in the regulation of the gene network underlying sexual differentiation. Data from A. mutica indicate that this is not always the case, as this GSD turtle has retained its ancestral sensitivity in the expression of a gene involved in gonadogenesis, the first such case ever to be reported (Valenzuela 2008). This result has paramount implications as it reveals that GSD taxa can harbor thermal sensitivity even when it is non-functional for sexual differentiation (temperature does not bias sex ratios in A. mutica). This is a critical finding because theoretical models for the evolution of TSD rely on the premise that GSD taxa posses an ubiquitous thermal sensitivity that can be co-opted during the evolution of phenotypic plasticity (TSD), and our data provide the first empirical evidence for its existence at the level of gene
