Postcopulatory sexual selection is very important in species with reproductive strategies that involve multiple mating and prolonged sperm storage. The sperm storage organ has been hypothesized to evolve in response to different levels of sperm competition in several species while population density has been considered as a factor that approximates sperm competition risk and intensity in the field. Apart from population density, local microclimatic conditions may also play a role in determining sperm competition levels in natural populations of land snails by affecting their chances of encountering mates. The goal of this study was to investigate the variation of the structure of the sperm storage organ in the simultaneously hermaphroditic land snails Helix lucorum and Cepaea vindobonensis occurring sympatrically in two sites which differed in habitat humidity. The populations of both species from the two sites, also differed in density and in duration of reproductive period. Multiple samples were taken from each population in order to test for temporal variation. In both species, the spermatheca consisted of a simple fertilization chamber and a variable number of lateral tubules. The length of the spermatheca showed no temporal or spatial differentiation nor did it show any correlation with snail size. The number of tubules in Helix lucorum ranged from five to sixteen and in Cepaea vindobonensis from one to eight and in both species a significant difference of this trait between the two study sites was detected. In Cepaea vindobonensis, the difference in tubule number led to difference of the total tubule length which reflects sperm storage capacity of the spermatheca but this was not the case with H. lucorum in which no increase in total tubule length was detected. Intraspecific variation in the spermatheca was observed in both snail species studied. The variation observed was independent of snail size, and reproduction status, while the two species responded differently to higher sperm competition levels.

中文翻译：

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两种雌雄同体田螺物种精子贮藏器官的种内形态变异

交配后的性选择在繁殖策略涉及多重交配和精子储存时间长的物种中非常重要。据推测，精子贮藏器官会在几种物种中响应不同水平的精子竞争而进化，而种群密度已被认为是近似于该领域中精子竞争风险和强度的因素。除了人口密度以外，当地的微气候条件还可能通过影响蜗牛的自然相遇机会来决定其自然种群中精子的竞争水平。这项研究的目的是调查同时在两个栖息地湿度不同的地方同时发生的雌雄同体螺Helco lucorum和Cepaea vindobonensis的精子贮藏器官结构的变化。来自两个地点的两个物种的种群密度和繁殖期也不同。从每个人群中采集多个样本以测试时间变化。在这两个物种中，精子都由一个简单的受精腔和数量不等的侧小管组成。精囊的长度没有时间或空间上的差异，也没有与蜗牛的大小相关。lucorum lucorum中的小管数量为5至16，而Cepaea vindobonensis中的小管数量为1至8，并且在两个物种中，两个研究地点之间均检测到该性状的显着差异。在Cepaea vindobonensis中，肾小管数目的差异导致总肾小管长度的差异，这反映了精子的精子储存能力，但对于H. lucorum则没有发现总肾小管总长度的增加。在所研究的两种蜗牛中都观察到了精囊内的种内变异。观察到的变异与蜗牛的大小和繁殖状态无关，而两个物种对更高的精子竞争水平的反应却不同。肾小管数目的差异导致总肾小管长度的差异，反映了精子的精子储存能力，但对于不存在总肾小管长度增加的H. lucorum则不是这样。在所研究的两种蜗牛中都观察到了精囊中的种内变异。观察到的变异与蜗牛的大小和繁殖状态无关，而两个物种对更高的精子竞争水平的反应却不同。肾小管数目的差异导致总肾小管长度的差异，反映了精子的精子储存能力，但对于不存在总肾小管长度增加的H. lucorum则不是这样。在所研究的两种蜗牛中都观察到了精囊中的种内变异。观察到的变异与蜗牛的大小和繁殖状态无关，而两个物种对更高的精子竞争水平的反应却不同。