Center for Genomics Sciences, UNAM, CP62210, Cuernavaca, Mexico.
Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.
BMC Evol Biol. 2020 Aug 17;20(1):103. doi: 10.1186/s12862-020-01671-y.
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.
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.
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.
脊椎动物表现出多样化的性别决定系统，而爬行动物则以高度可变的性别决定系统为特点，包括温度依赖性性别决定（TSD）和基因型性别决定（GSD）。理论预测，生活在高度可变或寒冷气候条件下的种群应该进化出基因型性别决定，以缓冲种群免受极端性别比例的影响，但这些基本预测尚未在广泛的分类群中得到检验。
在这里，我们使用了 213 种爬行动物物种的系统发育分析，代表了 38 个科（TSD=101 种，GSD=112 种）和气候数据，比较了具有 GSD 和 TSD 的爬行动物的繁殖环境。我们表明，GSD 和 TSD 在繁殖季节都面临着相同水平的气候波动。然而，TSD 爬行动物与温暖的气候显著相关。我们发现了对繁殖季节长度的强烈选择，以最小化对寒冷和波动气候的暴露。比较竞争进化假说的系统发育路径分析支持性别决定系统的转变影响了物种繁殖和筑巢的环境温度。反过来，这种相互作用又影响了其他变量，如繁殖季节的持续时间和生活史特征。
综上所述，我们的研究结果挑战了关于性别决定与气候变异性之间关联的长期假设。我们还表明，环境温度在繁殖季节很重要，它有助于解释性别决定系统对现存爬行动物物种地理分布的影响。
