Polymorphism in the couch potato gene clines in eastern Australia but is not associated with ovarian dormancy in Drosophila melanogaster

Natural selection can generate parallel latitudinal clines in traits and gene frequencies across continents but these have rarely been linked. An amino acid (isoleucine to lysine, or I462K) polymorphism of the couch potato (cpo) gene in Drosophila melanogaster is thought to control female reproductive diapause cline in North America (Schmidt et al. 2008). Here, we show that under standard diapause inducing conditions (12 °C and short photoperiod) (Saunders et al. 1989), egg maturation in Australian flies is delayed but not arrested at previtellogenic stages. At 12°C, the phenotypic distribution in egg development was bimodal at stages 8 and 14, and showed a strong non-linear pattern on the east coast of Australia, with incidence of egg maturation delay (ovarian dormancy) increasing both toward tropical and temperate climates. Furthermore, we found no evidence for an association between the cpo I462K polymorphism and ovarian dormancy at either 12 or 10 °C (when egg maturation was often d...

自然选择可在不同大陆间催生性状与基因频率的平行纬度梯度（latitudinal clines），但此类梯度间的关联却鲜有报道。此前研究认为，黑腹果蝇（Drosophila melanogaster）的couch potato（cpo）基因存在一处异亮氨酸向赖氨酸突变的氨基酸多态性（amino acid polymorphism）位点（I462K），该位点可调控北美地区的雌性生殖滞育（female reproductive diapause）纬度梯度（Schmidt等，2008）。本研究在标准滞育诱导条件（12℃、短日照光周期（photoperiod），Saunders等，1989）下开展实验，结果显示澳大利亚果蝇的卵子成熟（egg maturation）过程会出现延迟，但并未停滞于卵黄发生前期阶段（previtellogenic stages）。在12℃条件下，卵子发育的表型分布在第8和14期呈现双峰特征；在澳大利亚东海岸，该分布呈现显著的非线性模式，卵子成熟延迟（卵巢休眠，ovarian dormancy）的发生率随向热带与温带区域过渡而升高。此外，我们未发现cpo基因I462K多态性与卵巢休眠存在关联的证据，无论在12℃还是10℃条件下（此时卵子成熟过程常出现...）