Supplementary Material for: Environmental (and random?) sex determination in endangered and invasive Phelsuma geckos

Introduction: Sex is a fundamental characteristic of an individual. It is therefore puzzling why in some systems sex is precisely determined by a genotype, while in others it is influenced by the environment or even subtle, not to say random, factors. Some stochasticity in sex determination would be expected if environmental conditions did not have a large sex-specific effect on fitness. Although data are only available for a small fraction of species, geckos show exceptional variability in sex determination. Methods: We tested the effects of three incubation temperatures on sex ratio and adult body size in the invasive gecko Phelsuma laticauda and the vulnerable gecko Phelsuma nigristriata. Results: We document temperature-dependent sex determination (TSD) in both species. Only females hatched at a low temperature (24 °C), whereas male production peaked at an intermediate temperature (29 °C) and declined, at least in P. laticauda, again at the highest temperature (31 °C). Interestingly, full siblings hatched from eggs glued together during the incubation at temperatures producing both sexes are often of the opposite sex. We found no significant effect of incubation temperature on adult body length. Conclusions: Documentation of TSD in the day geckos has implications for conservation practice in environmental management of endangered species or eradication of invasive species. However, it appears that a very subtle (random?) factor may also be involved in their sex determination. In line with this, we found no significant effect of incubation temperature on adult body length, suggesting that, at least in this trait, there is no strong selection against producing females at “male” temperatures.

引言：性别是个体的核心特征之一。因此，为何部分生物的性别由基因型精准决定，而另一些类群的性别却受环境影响，甚至由微妙乃至近乎随机的因素调控，这一问题始终令人困惑。倘若环境条件对适合度不存在显著的性别特异性影响，那么性别决定过程中理应存在一定的随机性。尽管目前仅对极少部分物种开展了相关研究，但壁虎类的性别决定方式却展现出极高的变异性。
方法：本研究针对入侵性壁虎宽尾日行守宫（Phelsuma laticauda）与易危壁虎黑纹日行守宫（Phelsuma nigristriata），设置三种孵化温度，探究其对种群性比与成体体型的影响。
结果：本研究在两个物种中均证实了温度依赖型性别决定（temperature-dependent sex determination, TSD）现象的存在。在低温（24℃）条件下仅能孵化出雌性个体；而在中等温度（29℃）下雄性孵化率达到峰值，当温度升至最高的31℃时，雄性孵化率再次下降，这一现象在宽尾日行守宫（Phelsuma laticauda）中尤为明显。值得注意的是，在可同时孵化出雌雄个体的温度条件下，一同孵化的粘连卵所产出的全同胞后代，其性别往往互为异性。本研究未发现孵化温度对成体体长存在显著影响。
结论：日行守宫类温度依赖型性别决定现象的证实，对于濒危物种的环境管理保育实践，以及入侵物种的根除防控工作均具有指导意义。然而，研究结果同时表明，极细微的（甚至可能是随机的）因素同样参与了该类群的性别决定过程。与此相一致，本研究再次证实孵化温度对成体体长无显著影响，这提示至少在体长这一性状上，在"雄性偏好温度"下产生雌性个体并未受到强烈的选择压力。