Climate-driven population divergence in sex-determining systems

Abstract

Sex determination is a fundamental biological process, yet its mechanisms are remarkably diverse. In vertebrates, sex can be determined by inherited genetic factors or by the temperature experienced during embryonic development. However, the evolutionary causes of this diversity remain unknown. Here we show that live-bearing lizards at different climatic extremes of the species' distribution differ in their sex-determining mechanisms, with temperature-dependent sex determination in lowlands and genotypic sex determination in highlands. A theoretical model parameterized with field data accurately predicts this divergence in sex-determining systems and the consequence thereof for variation in cohort sex ratios among years. Furthermore, we show that divergent natural selection on sex determination across altitudes is caused by climatic effects on lizard life history and variation in the magnitude of between-year temperature fluctuations. Our results establish an adaptive explanation for intra-specific divergence in sex-determining systems driven by phenotypic plasticity and ecological selection, thereby providing a unifying framework for integrating the developmental, ecological and evolutionary basis for variation in vertebrate sex determination.

Geographical differences in maternal basking behaviour and offspring growth rate in a climatically widespread viviparous reptile

“…Maternal thermoregulation during gestation is thought to allow the maintenance of stable developmental temperatures (Shine, 1995) and/or to provide a buffer to embryos from unsuitable developmental temperatures (Kearney et al, 2009) as well as potentially provide fitness benefits to females through, for example, reduced basking length and the costs associated with reproduction (Schwarzkopf and Shine, 1991;Schwarzkopf and Andrews, 2012a;Schwarzkopf and Andrews, 2012b;Shine, 2012). Maternal manipulation of the offspring environment may also potentially allow females to 'pre-programme' offspring phenotype to better suit the environment the offspring will encounter (or be born into) (Marshall and Uller, 2007;Cadby et al, 2010a;Pen et al, 2010;Cadby et al, 2011;Uller et al, 2011). Maternal 'pre-programming' to future developmental temperatures could occur through maternal manipulation of offspring phenotype to fit the predicted environment and/or through embryonic acclimation to the thermal conditions experienced during development (Seebacher, 2005).…”

“…At one extreme of the species range, mountain populations experience restricted basking opportunities and short summers, while at the other extreme, coastal populations experience warm conditions with extended basking opportunities and long summers (Atkins et al, 2007;Wapstra et al, 2009;Cadby et al, 2010b;Pen et al, 2010;Uller et al, 2011). This difference in climate has resulted in considerable variation in life-history and reproductive traits between populations, reflecting a combination of phenotypic and genotypic responses to environmental variation (Wapstra et al, 1999;Melville and Swain, 2000;Wapstra et al, 2009;Cadby et al, 2010b;Wapstra et al, 2010;Pen et al, 2010;Uller et al, 2011). For example, females from cold, mountain areas are typically larger, take longer to reach maturity, and give birth 2-4 weeks later than those from warm, coastal areas Pen et al, 2010).…”

“…This difference in climate has resulted in considerable variation in life-history and reproductive traits between populations, reflecting a combination of phenotypic and genotypic responses to environmental variation (Wapstra et al, 1999;Melville and Swain, 2000;Wapstra et al, 2009;Cadby et al, 2010b;Wapstra et al, 2010;Pen et al, 2010;Uller et al, 2011). For example, females from cold, mountain areas are typically larger, take longer to reach maturity, and give birth 2-4 weeks later than those from warm, coastal areas Pen et al, 2010).Using a reciprocal transplant experiment, we tested whether maternal basking behaviour can increase offspring fitness through maternal pre-programming or by buffering differences in basking opportunities. We further tested whether mothers from populations that have evolved in different thermal environments (i.e.…”

The Sex Ratio Influence on the Dynamics of Structured Population

“…Такого рода механизм ведет к росту числа самок, что в критических условиях способствует быстрому восстановлению численности популяции в перспективе. Также вариация вторичного соотношения полов может происходить вследствие влияния факторов среды, например у некоторых видов черепах, ящериц, крокодилов и змей пол потомства зависит от температуры инкубации яиц [25]. Другим примером являются насекомые (пчелы и другие перепончатокрылые, червецы, клещи), у которых вторичное соотношение полов определяется соотношением полов в размножающейся части популяции, так как из оплодотворенных яиц развиваются самки (или самки и самцы), а из неоплодотворенных только самцы.…”

Multi-objective optimization shapes ecological variation

“…For example, it is well known that weather factors modify the outcome of experiments, and they may even shape the genetic composition of populations [8], yet it is rare for experiments to systematically include different weather alternatives. Accordingly, experimental results in ecology usually contain a huge amount of quantitative phenotypic variation among and within species and locations, which often makes the theoretical interpretation of many experimental results difficult.…”