Abstract
Sex determination in Australian agamid lizards shows a complex framework of different mechanisms, varying even among closely related taxa. It is clear that discrete classification of these species as either having genetic (GSD) or environmental sex determination (ESD) does not agree with empirical data. Although many species in this group show temperature‐dependent sex determination (TSD), recent evidence suggests additional genetic or epigenetic effects. A proposed model explaining the adaptive significance and evolution of TSD in short‐lived agamids predicts that selection will favor temperature‐biased sex ratios in species with intense male‐male competition. Here, we use experimental incubation at (near) constant temperatures to test whether the sex of Australian painted dragons (Ctenophorus pictus) is influenced by temperature, building on previous research yet to have reached an agreement regarding the role of temperature in this species. In this study, incubation temperature and parental identity affected hatchling sex suggesting that environment and genetics may work in concert to determine sex in this species. Although our results are consistent with TSD, our data cannot rule out a temperature‐by‐sex effect on egg or hatchling mortality. However, our findings together with the observed differences of sex determination systems in closely related species within this genus may provide novel opportunities to address fundamental questions in the evolution of sex determination systems.
Highlights
The fundamental biological process of sex determination has been under intense scientific research for decades, mainly because of its profound implications on the phenotype of individuals and the formation of sex ratios in natural populations (West, Reece, & Sheldon, 2002)
It is clear that discrete classification of these species as either having genetic (GSD) or environmental sex determination (ESD) does not agree with empirical data
We use experimental incubation at constant temperatures to test whether the sex of Australian painted dragons (Ctenophorus pictus) is influenced by temperature, building on previous research yet to have reached an agreement regarding the role of temperature in this species
Summary
The fundamental biological process of sex determination has been under intense scientific research for decades, mainly because of its profound implications on the phenotype of individuals and the formation of sex ratios in natural populations (West, Reece, & Sheldon, 2002). In contrast to the Charnov- Bull model, this model does not attempt to explain the evolution of ESD in all reptiles, but focuses on a single family (Agamidae) containing many short-lived lizards This model shows that in species with intense male-male competition for mating opportunities, newly hatched sons are likely to achieve little reproductive success in their first year when faced with competition from males of previous cohorts. The Australian dragon lizards (Agamidae) are of particular interest when testing the validity of this model, as these lizards have distinct variation in life-histories, social systems, and sex determination processes (Harlow, 2004) They have shown a complex diversity of species with GSD and TSD, with even closely related species differing in sex determining mechanisms (Harlow, 2004; Harlow & Taylor, 2000; Uller, Odierna, & Olsson, 2008). The life-history of C. pictus is in congruence with the traits listed by Warner et al.’s model, predicting that this species has a temperature-influenced sex determination system
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