Department of Zoology, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand.
Parasitol Res. 2011 Sep;109(3):865-70. doi: 10.1007/s00436-011-2313-8. Epub 2011 Mar 11.
The growth, and thus to some extent the fitness, of parasites may vary among individuals based on a range of factors including which host species they infect or how many other parasites share the host with them. Here, we investigate the determinants of the size attained by metacercariae of an opecoelid trematode within two species of intertidal polychaetes serving as second intermediate host, Heteromastus filiformis and Abarenicola affinis. Metacercarial cysts were found predominantly in the anterior region of H. filiformis, particularly in segments 3-6, whereas no apparent pattern of encystment was observed in A. affinis. No relationship was found between the volume achieved by an individual metacercarial cyst and either host body volume, total number of cysts per host, the segment number in which a cyst was located, or the number of other cysts sharing a distinct segment; this was true for parasites in either polychaete species. However, cysts were found to be significantly larger, on average, within A. affinis than within H. filiformis. It remains to be determined whether the polychaete species in which larger sizes are achieved is also the one in which transmission to fish hosts is maximized.
寄生虫的生长，在某种程度上也会影响其适应性，可能会因宿主物种的感染情况或与它们共享宿主的其他寄生虫数量等一系列因素而有所不同。在这里，我们研究了两种潮间带多毛类蠕虫作为第二中间宿主时，片形吸虫的后生尾蚴达到的大小的决定因素，这两种多毛类蠕虫分别是长吻沙蚕和阿费尼科尔蚓。后生尾蚴包囊主要存在于长吻沙蚕的前体区域，特别是在 3-6 节，而在阿费尼科尔蚓中没有明显的包囊形成模式。个体后生尾蚴包囊的体积与宿主的体积、每个宿主的包囊总数、包囊所在的节数或共享特定节的其他包囊数量之间没有关系；这对两种多毛类蠕虫中的寄生虫都是如此。然而，阿费尼科尔蚓中的包囊平均比长吻沙蚕中的包囊大。目前尚不清楚是否是在体型较大的多毛类蠕虫中，寄生虫向鱼类宿主的传播效率达到最大化。
