Nest site choice compensates for climate effects on sex ratios in a lizard with environmental sex determination

Abstract

Theoretical models suggest that in changing environments natural selection on two traits, maternal nesting behaviour and pivotal temperatures (those that divide the sexes) is important for maintaining viable offspring sex ratios in species with environmental sex determination (ESD). Empirical evidence, however, is lacking. In this paper, we provide such evidence from a study of clinal variation in four sex-determining traits (maternal nesting behaviour, pivotal temperatures, nesting phenology, and nest depth) in Physignathus lesueurii, a wide-ranging ESD lizard inhabiting eastern Australia. Despite marked differences in air and soil temperatures across our five study sites spanning 19°latitude and 1200 m in elevation, nest temperatures did not differ significantly among sites. Lizards compensated for climatic differences chiefly by selecting more open nest sites with higher incident radiation at cooler sites. Clinal variation in the onset of nesting also compensated for climatic differences, but to a lesser extent. There was no evidence of compensation through pivotal temperatures or nest depth. More broadly, our results extend to the egg stage the life history prediction that behaviour is the chief compensatory mechanism for climatic differences experienced by species spanning environmental extremes. Furthermore, our study was unique in revealing that nest site choice influenced mainly the daily range in nest temperatures, rather than mean temperatures, in a shallow-nesting reptile. Finally, indirect evidence suggests that the cue used by nesting lizards was radiation or temperature (through basking or assessing substrate temperatures), not visual detection of canopy openness. We conclude that maternal nesting behaviour and nesting phenology are traits subject to sex ratio selection in P. lesueurii, and thus, must be considered among the repertoire of ESD species for responding to climate change.

Turtle mating patterns buffer against disruptive effects of climate change

“…Although maternal nest-site choice has been shown to compensate for geographical differences in nest temperature in a lizard [11], and marine turtles have shown climate-related phenological nesting responses [12] (but see [13]), evidence suggests that these mechanisms may not be adequate to compensate for climate effects on sex ratio, especially in long-lived and late-maturing reptiles [10]. For example, the evolution of nest-site choice and threshold temperature (above which female offspring are produced) are predicted to be slow in response to climate warming in a freshwater turtle, and unlikely to effectively offset sex ratio bias resulting from rapid climate change [10].…”

Climate and predation dominate juvenile and adult recruitment in a turtle with temperature‐dependent sex determination

“…In fluctuating environments or under directional environmental change, production of extreme offspring sex ratios is predicted to lead to one of several ecological or evolutionary responses: (1) reduce the temperature dependence of sex determination (Bull and Bulmer 1989, Van Dooren and Leimar 2003, Schwanz and Proulx 2008, (2) alter maternal oviposition behavior or pivotal temperatures of sex determination (Morjan 2003a, b, Ewert et al 2004, Doody et al 2006a, Schwanz and Janzen 2008, McGaugh et al 2010, or (3) result in geographic range change or extinction. Appreciation of the impact of offspring sex ratios on evolutionary and ecological processes has led to substantial empirical research on species with environmentally sensitive sex determination (e.g., Conover et al 1992, Godfrey et al 1996, Girondot et al 2004, Wapstra et al 2009).…”

Extension, single-locus conversion and physical mapping of sex chromosome sequences identify the Z microchromosome and pseudo-autosomal region in a dragon lizard, Pogona vitticeps

“…This is true even within the family of dragon lizards (Agamidae), which are emerging as a model group for the study of sex determination evolution, sex ratio evolution and sex allocation (Harlow, 2004;Ezaz et al, 2005;Warner and Shine, 2005;Doody et al, 2006;Janzen and Phillips, 2006;Quinn et al, 2007;Shine, 2007, 2008;Ezaz et al, 2009). They present an excellent opportunity to understand better the molecular and chromosomal basis of evolutionary transitions between the two fundamental mechanisms of vertebrate sex determination, TSD and GSD.…”