The Comal River, a spring-fed system in central Texas, was invaded in the 1960s by two Asian aquatic snails (Thiaridae: red-rimmed melania Melanoides tuberculata and quilted melania Tarebia granifera) and subsequently by three of their trematode parasites (the avian eye-fluke Philophthalmus gralli in the 1960s; the gill trematode Centrocestus formosanus in the 1990s; and the intestinal fluke Haplorchis pumilio in the 2000s). Previous snail collections (2001-2002) established that habitat conditions significantly affect the distribution of both snail species. However, the effects of snail size (known to influence infection prevalence) and habitat conditions (known to influence snail size) on trematode infection patterns in this system were not evaluated. In a re-evaluation of this data set, logistic regression analyses with individual snails showed that for both M. tuberculata and T. granifera populations, large snails were more likely to be infected than small snails, and habitat conditions were significantly related to infection in T. granifera. However, only snail size was significant in explaining the probability of infection in M. tuberculata. This result was confirmed by linear regression models, which showed that both infected and noninfected M. tuberculata used similar habitats, as large individuals in both infection categories were found in patches dominated by fine substrates and high levels of aquatic vegetation and detritus. For the large size-class of T. granifera, noninfected individuals were found primarily in habitats with silt/sand substrates and high vegetation and detritus cover, while infected individuals occurred among all available habitats. Using these results, we suggest that targeted sampling of large individuals of M. tuberculata in habitats with high detritus and vegetation and large individuals of T. granifera in any habitat can be used to efficiently ascertain parasite "hot spots" and to evaluate changes in parasite prevalence or detect the invasion of new parasites in these thiarid snails.

中文翻译：

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寄生虫感染和宿主体型对入侵水生蜗牛栖息地关联的影响：对环境监测的影响

Comal 河是德克萨斯州中部的一个泉水系统，在 1960 年代被两种亚洲水生蜗牛（Thiaridae：红边黑圈螺和绗缝黑圈螺）入侵，随后它们的三种吸虫寄生虫（鸟眼-1960 年代的 Philophthalmus gralli；1990 年代的鳃吸虫 Centrocestus formosanus；以及 2000 年代的肠吸虫 Haplorchis pumilio）。以前的蜗牛收藏（2001-2002）确定栖息地条件显着影响两种蜗牛物种的分布。然而，没有评估蜗牛大小（已知会影响感染流行）和栖息地条件（已知会影响蜗牛大小）对这个系统中吸虫感染模式的影响。在重新评估这个数据集时，对单个蜗牛的逻辑回归分析表明，对于 M. tuberculata 和 T. granifera 种群，大蜗牛比小蜗牛更容易被感染，栖息地条件与 T. granifera 的感染显着相关。然而，只有蜗牛大小在解释结核分枝杆菌感染的可能性方面具有重要意义。这一结果得到了线性回归模型的证实，该模型表明受感染和未受感染的结核分枝杆菌使用相似的栖息地，因为两种感染类别中的大个体都被发现在以精细基质和高水平水生植被和碎屑为主的斑块中。对于大规格的 T. granifera，未感染的个体主要在淤泥/沙质基质和高植被和碎屑覆盖的栖息地中发现，而受感染的个体出现在所有可用的栖息地中。使用这些结果，我们建议对具有高碎屑和植被的栖息地中的大块结核菌和任何栖息地中的大粒棘球虫进行有针对性的采样，可用于有效确定寄生虫“热点”并评估寄生虫的变化流行或检测新寄生虫在这些 thiarid 蜗牛中的入侵。