Evanno Guillaume, Madec Luc, Arnaud Jean-François
Département d'Ecologie et Evolution, Bâtiment de Biologie, Université de Lausanne, CH-1015 Lausanne, Switzerland.
Mol Ecol. 2005 Mar;14(3):805-12. doi: 10.1111/j.1365-294X.2005.02449.x.
Sperm competition has been studied in many gonochoric animals but little is known about its occurrence in simultaneous hermaphrodites, especially in land snails. The reproductive behaviour of the land snail Helix aspersa involves several features, like multiple mating, long-term sperm storage and dart-shooting behaviour, which may promote sperm competition. Cryptic female choice may also occur through a spermatheca subdivided into tubules, which potentially allows compartmentalized sperm storage of successive mates. In order to determine the outcome of postcopulatory sexual selection in this species, we designed a cross-breeding experiment where a recipient ('female') mated with two sperm donors ('males'). Mates came from either the same population as the recipient or from a distinct one. To test for the influence a recipient can have on the paternity of its offspring, we excluded the effects of dart shooting by using only virgin snails as sperm donors because they do not shoot any dart before their first copulation. We measured the effects of size of mates as well as time to first and second mating on second mate sperm precedence (P2; established using microsatellite markers). Multiple paternity was detected in 62.5% of clutches and overall there was first-mate sperm precedence with a mean P2 of 0.24. Generalized linear modelling revealed that the best predictors of paternity were the time between matings and the time before first mating. Overall, both first and second mates that copulated quickly got greater parentage, which may suggest that postcopulatory events influence patterns of sperm precedence in the garden snail.
精子竞争在许多雌雄异体动物中都有研究，但对于其在同时具有雌雄两性生殖器官的动物中发生的情况却知之甚少，尤其是在陆地蜗牛中。陆地蜗牛（Helix aspersa）的生殖行为具有多个特点，如多次交配、长期储存精子以及射弹行为，这些可能会促进精子竞争。隐秘的雌性选择也可能通过一个被细分为小管的受精囊发生，这可能允许对连续配偶的精子进行分区储存。为了确定该物种交配后性选择的结果，我们设计了一个杂交实验，让一个接受者（“雌性”）与两个精子供体（“雄性”）交配。配偶要么与接受者来自同一群体，要么来自不同群体。为了测试接受者对其后代父系的影响，我们仅使用未交配过的蜗牛作为精子供体，以排除射弹的影响，因为它们在首次交配前不会射弹。我们测量了配偶大小以及首次和第二次交配时间对第二次交配精子优先性（P2；使用微卫星标记确定）的影响。在62.5%的卵块中检测到多重父系，总体上存在首次交配精子优先性，平均P2为0.24。广义线性模型显示，父系的最佳预测因素是两次交配之间的时间以及首次交配前的时间。总体而言，快速交配的首次和第二次配偶都获得了更大的父系份额，这可能表明交配后的事件会影响花园蜗牛中精子优先性的模式。
