Novel evolutionary pathways of sex-determining mechanisms

Evolutionary transitions between sex-determining mechanisms (SDMs) are an enigma. Among vertebrates, individual sex (male or female) is primarily determined by either genes (genotypic sex determination, GSD) or embryonic incubation temperature (temperature-dependent sex determination, TSD), and these mechanisms have undergone repeated evolutionary transitions. Despite this evolutionary lability, transitions from GSD (i.e. from male heterogamety, XX/XY, or female heterogamety, ZZ/ZW) to TSD are an evolutionary conundrum, as they appear to require crossing a fitness valley arising from the production of genotypes with reduced viability owing to being homogametic for degenerated sex chromosomes (YY or WW individuals). Moreover, it is unclear whether alternative (e.g. mixed) forms of sex-determination can persist across evolutionary time. It has previously been suggested that transitions would be easy if temperature-dependent sex-reversal (e.g. XX male or XY female) were asymmetrical, occur...

性别决定机制（sex-determining mechanisms，SDMs）之间的进化转变长期以来都是学界未解的谜题。在脊椎动物类群中，个体性别（雄性或雌性）主要由两类核心机制决定：一是基因决定性别（genotypic sex determination，GSD），二是胚胎孵化温度依赖型性别决定（temperature-dependent sex determination，TSD），且这两类性别决定机制均已发生过多次独立的进化转变。尽管这类机制具备进化可塑性，但从GSD（即雄性异配性别（male heterogamety）系统XX/XY或雌性异配性别（female heterogamety）系统ZZ/ZW）向TSD的进化转变却仍是一道进化难题：该转变似乎需要跨越一道适合度低谷——即由于个体携带退化性染色体并呈现纯合配子状态（YY或WW个体），其所产生的基因型存活力会显著下降。此外，学界仍不清楚其他形式的性别决定机制（例如混合型性别决定）是否能够在漫长的进化历程中持续存续。此前有研究提出，若温度诱导的性反转（如XX雄性或XY雌性）呈现不对称性且发生……