Sex determination systems in reptiles are related to ambient temperature but not to the level of climatic fluctuation

Abstract

Background: Vertebrates exhibit diverse sex determination systems and reptiles stand out by having highly variable sex determinations that include temperature-dependent and genotypic sex determination (TSD and GSD, respectively). Theory predicts that populations living in either highly variable or cold climatic conditions should evolve genotypic sex determination to buffer the populations from extreme sex ratios, yet these fundamental predictions have not been tested across a wide range of taxa. Results: Here, we use phylogenetic analyses of 213 reptile species representing 38 families (TSD = 101 species, GSD = 112 species) and climatic data to compare breeding environments between reptiles with GSD versus TSD. We show that GSD and TSD are confronted with the same level of climatic fluctuation during breeding seasons. However, TSD reptiles are significantly associated with warmer climates. We found a strong selection on the breeding season length that minimises exposure to cold and fluctuating climate. Phylogenetic path analyses comparing competing evolutionary hypotheses support that transitions in sex determination systems influenced the ambient temperature at which the species reproduces and nests. In turn, this interaction affects other variables such as the duration of the breeding season and life-history traits. Conclusions: Taken together, our results challenge long-standing hypotheses about the association between sex determination and climate variability. We also show that ambient temperature is important during breeding seasons and it helps explain the effects of sex determination systems on the geographic distribution of extant reptile species.

Are evolutionary transitions in sexual size dimorphism related to sex determination in reptiles?

“…Variation in sex determination systems has been linked to a multitude of extrinsic and intrinsic factors, for example ecological patterns such as variation in ambient temperature (Cornejo‐Páramo et al. 2020; Pen et al. 2010), life‐history parameters such as longevity (Janzen & Paukstis, 1991a,b; Sabath et al.…”

“…Variation in sex determination systems has been linked to a multitude of extrinsic and intrinsic factors, for example ecological patterns such as variation in ambient temperature (Cornejo-Páramo et al 2020;Pen et al 2010), life-history parameters such as longevity (Janzen & Paukstis, 1991a,b;Sabath et al 2016), reproductive mode (Organ et al, 2009) and demographic composition of the populations expressed as adult sex ratio (Pipoly et al 2015). A link between sex determination and sexual size dimorphism is also suggested, either by direct physiological causation or indirectly, acting through the above-mentioned mediators (Adkins-Regan & Reeve, 2014;Ewert et al 1994;Ewert & Nelson, 1991;Janzen & Paukstis, 1991a,b;Kraak, 1994;Schwanz et al 2016;Viets et al 1994).…”

A study of thermally-induced sex reversal in casque-headed lizards

“…Thus, B. vittatus does not appear to show temperature-dependent sex reversal within the 26-32°C temperature range. We selected these incubation temperatures because they are common male-producing or female-producing temperatures in non-avian reptiles and because they represent average temperatures during the reproductive season of B. vittatus [31].…”

Genotypic Sex Determination Systems could be Adaptations to Extreme Temperature Environments in Reptiles and to Endothermy in Mammals and Birds

“…Recently, [11] it has been suggested that the evolution of SDS systems in reptiles is related to temperature environment rather than to environmental temperature fluctuations. In particular, the authors reported that TSD species were more frequent in warmer climates cand GSD more frequent in cooler ones.…”