Sex Determination in the garden lizard, Calotes versicolor: Is Environment a Factor?

Abstract

The Indian garden lizard, C. versicolor, is known to lack sex chromosomes (Singh, 1974, Ganesh et al 1997). A report from the tropical southern India (Inamdar et al., 2012), claims a TSD (FMFM) mechanism in this species in which the male/female ratio in embryos oscillates within a range of 3-4{degrees}C. The present study presents results of experiments done in 4 consecutive breeding seasons of C. versicolor belonging to the subtropical/temperate climate of northern region of India. Eggs were grown at different temperatures (at 24.5/28/31.5{degrees}C) or under seminatural conditions. Another set of eggs was exposed to fadrozol, an aromatase inhibitor (AI), or Lithium Chloride (inhibitor of GSK3 enzyme inducing Wnt4-dependent Beta-Catenin). Results confirm our earlier finding that in this subtropical population of C. versicolor, temperature does not regulate gonadal differentiation but AI-induces sex reversal to the male sex (Ganesh and Raman, 1995, Ganesh et al 1999). We also report lack of any effect of Sox9 inhibitor on sexual differentiation which may be due to inadequate quantity or mode of application. Importantly, we report the serendipitous observation that in each year almost all the embryos/hatchlings were of the same sex ( females in 2013, 15, 16 and males in 2014) regardless of the rearing condition and duration of incubation. Obviously, parthenogenesis is not the cause of it. In the absence of an obvious reason to explain this pattern, we surmise that in this north Indian population of C. versicolor, female is the default sex, and certain epigenetic regulators could modulate the sexual differentiation of the individual.