Factors affecting sex-ratio variation and sex-determining mechanisms in the apple snail Pomacea canaliculata

淡水螺Pomacea canaliculata在后代性别比上表现出较大的差异。我们研究了这种变异是否由少数性别决定基因引起，通过两个系列的实验。首先，我们从几个同父异母的姐妹与同一雄性杂交中培养了F2个后代，并确定了F2的性别比例。F2的性别比例趋近于几个值，说明F1全同胞姐妹的性别决定基因型也比较少。这表明这种蜗牛的性别是由少数基因而不是多基因决定的。其次，我们开发了遗传标记来研究与假定的性别决定基因的联系。我们发现了4040个微卫星位点，并开发了4个有用的标记。这些标记在PCR中可重复，具有多态性，并遵循孟德尔分离。我们用这些标记对熊本和奈良两个种群进行了片段分析。其中一种频率在两种人群中男性和女性之间存在显著差异；它可能与性别决定位点在同一连锁群中。

The freshwater snail Pomacea canaliculata shows a large variation in offspring sex ratio. We investigated whether this variation is caused by a small number of sex-determining genes, with two series of experiments. First, we reared F2 offspring from several crosses involving full-sib sisters with the same male, and determined sex ratios of F2. The sex ratios of F2 converged into a few values, indicating that the sex-determining genotypes of the F1 full-sib sisters were also a few. This suggests that the sex in this snail is determined by a few genes rather than polygenes. Secondly, we developed genetic markers to study linkage with the putative sex-determining genes. We found >40 microsatellite loci, and developed four useful markers. These markers were repeatable in PCR, polymorphic and followed Mendelian segregation. We conducted fragment analyses in two populations (Kumamoto and Nara) with these markers. One of them showed significantly different frequencies between males and females in both populations ; it may be in the same linkage group as a sex-determining locus.