Within-host distributions of parasites can have relevance to parasite competition, parasite mating, transmission, and host health. We examined the within-host distribution of the adult trematode Alloglossidium renale infecting the paired antennal glands of grass shrimp. There are 4 possible parasite distributions for infections of paired organs: random, uniform, biased aggregation to 1 particular organ (e.g., left vs. right), or inconsistently biased (aggregated, but does not favor 1 side). Previous work has shown that morphological asymmetries in hosts can lead to biased infections of paired organs. Apparent symmetry between the antennal glands of grass shrimp leads to the prediction that there would be no bias for 1 particular organ. However, an alternative prediction stems from the fact that A. renale is hermaphroditic: aggregation between glands would increase outcrossing opportunities and thus, avoid inbreeding via self-mating. Existing methods to test for an overall pattern did not apply to the A. renale system because of low-intensity infections as well as many 0 values for abundance per unit of the antennal gland. Hence, we used Monte Carlo simulations to determine if the observed overall patterns differed from those expected by randomly allocating parasites into groups of 2. We found that in 3 of 4 data sets, A. renale infections did not deviate from random distributions. The fourth data set had a more uniform pattern than expected by chance. As there was no aggregation between glands and the proportion of worms in single gland infections did not differ from that expected by chance alone, we found no evidence of inbreeding avoidance as might be manifested via a within-host distribution. Given the large proportion of worms in single infections, we predict as a major evolutionary outcome that populations of A. renale will be largely inbred.

寄生虫的宿主内分布可能与寄生虫竞争、寄生虫交配、传播和宿主健康有关。我们检查了感染草虾成对触角腺的成年吸虫Alloglossidium的宿主内分布。成对器官的感染有 4 种可能的寄生虫分布：随机、均匀、偏向于 1 个特定器官的聚集（例如，左对右），或不一致的偏向（聚集，但不利于一侧）。以前的工作表明，宿主的形态不对称会导致成对器官的偏向感染。草虾触角腺之间的明显对称性导致预测不会对 1 个特定器官产生偏差。然而，另一种预测源于以下事实：A.renene是雌雄同体的：腺体之间的聚集会增加异交机会，从而避免通过自我交配进行近亲繁殖。现有的测试整体模式的方法不适用于A.renale系统，因为低强度感染以及每单位触角腺的丰度为 0 值。因此，我们使用蒙特卡罗模拟来确定观察到的整体模式是否与通过将寄生虫随机分配到 2 个组中所预期的不同。我们发现在 4 个数据集中的 3 个数据集中，A.renale感染并没有偏离随机分布。第四个数据集的模式比偶然预期的更统一。由于腺体之间没有聚集，并且单腺体感染中的蠕虫比例与偶然预期的没有差异，我们没有发现近交避免的证据，这可能通过宿主内分布表现出来。鉴于单次感染中有很大比例的蠕虫，我们预测作为主要进化结果的A.renale 种群将在很大程度上是近交系。