McCormick Aaron L, Nickol Brent B
School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0118, USA.
J Parasitol. 2004 Feb;90(1):103-7. doi: 10.1645/GE-3170.
The relationship of fish age class to parasitism by Paulisentis missouriensis was determined by sampling at least 29 creek chubs, Semotilus atromaculatus, from Easly Creek, Richardson County, Nebraska, every month from February 1996 to March 1997. In general, mean abundance and prevalence of the acanthocephalans increased with the age or length of chubs. It is unlikely that this distribution is explained by increased consumption of intermediate hosts by older, larger fish or by predatory fish acquiring parasites from paratenic hosts. The intermediate host for P. missouriensis is the cyclopoid copepod Acanthocyclops robustus, and creek chubs do not consume more microscopic crustaceans as they age or grow. Instead, the percentage of fish in the diet of creek chubs increases. Furthermore, P. missouriensis apparently does not use paratenic hosts. In laboratory infections, P. missouriensis survived predation of its original definitive host and transferred to the predator. Postcyclically transmitted P. missouriensis survived at least 14 days in the intestine of creek chubs, where they localized around the first flexure beyond the stomach. All stages of development of both sexes were transferred successfully. Postcyclic transmission is a plausible explanation, in some cases, for the greater worm burden frequently observed in older, larger hosts and for the occurrence in top carnivores of parasites not known to have paratenic hosts. This method of transmission appears to result in distribution of acanthocephalans to groups of animals that otherwise would be inaccessible.
1996年2月至1997年3月期间，每月从内布拉斯加州理查森县伊兹利溪采集至少29条溪鲈（Semotilus atromaculatus）样本，以确定鱼类年龄组与密苏里保罗棘头虫（Paulisentis missouriensis）寄生之间的关系。总体而言，棘头虫的平均丰度和感染率随溪鲈的年龄或体长增加而上升。这种分布不太可能是由于年龄较大、体型较大的鱼类对中间宿主的摄食量增加，或者是掠食性鱼类从转续宿主获取寄生虫所致。密苏里保罗棘头虫的中间宿主是剑水蚤类桡足动物粗壮棘剑水蚤（Acanthocyclops robustus），溪鲈并不会随着年龄增长或体型增大而摄食更多的小型甲壳类动物。相反，溪鲈食谱中鱼类的比例增加。此外，密苏里保罗棘头虫显然不利用转续宿主。在实验室感染实验中，密苏里保罗棘头虫在其原始终末宿主被捕食后存活下来，并转移到捕食者体内。经后循环传播的密苏里保罗棘头虫在溪鲈肠道中至少存活了14天，它们聚集在胃后第一个弯曲处周围。两性的所有发育阶段都成功转移。在某些情况下，后循环传播是一个合理的解释，可说明在年龄较大、体型较大的宿主中经常观察到的蠕虫负荷较高，以及在顶级食肉动物中出现没有已知转续宿主的寄生虫的现象。这种传播方式似乎导致棘头虫分布到其他情况下无法感染的动物群体中。
