Levri E P, Dillard J, Martin T
Division of Math and Sciences, 3000 Ivyside Park, Penn State-Altoona, Altoona, PA 16601, USA.
Parasitology. 2005 Jun;130(Pt 6):699-708. doi: 10.1017/s0031182005007286.
Parasitism often influences the phenotype of individuals. Many of the resulting changes are due to changes in resource allocation that come with infection. Here we examine the effect of a trematode parasite on the shape and defence morphology of a New Zealand freshwater snail, Potamopyrgus antipodarum. The trematode Microphallus sp. asexually produces hundreds of metacercarial cysts in the snail. The length, width and 2-dimensional area of each snail were measured. Snails were also assessed for their degree of spininess. Snails were dissected to determine gender, brooding condition and parasitism. Snails infected with Microphallus sp. were found to be significantly less spiny than uninfected snails. Microphallus-infected snails were also found to have a significantly greater width to length ratio at larger sizes than their uninfected counterparts. These trends could be explained in at least 3 ways. (1) Infection causes the snails to not produce spines and to become wider. (2) Spiny and narrower snails are more likely to die when they become infected. (3) Spiny and narrower snails are more resistant to infection. The changes in phenotype observed are unlikely to be adaptive for either the host or parasite and probably represent physiological by-products of the host-parasite relationship.
寄生现象常常会影响个体的表型。许多由此产生的变化是由于感染带来的资源分配变化所致。在此，我们研究了一种吸虫寄生虫对新西兰淡水螺——新西兰泥蜗（Potamopyrgus antipodarum）的外形和防御形态的影响。吸虫Microphallus sp.会在螺体内无性繁殖出数百个尾蚴囊肿。测量了每只螺的长度、宽度和二维面积。还评估了螺的多刺程度。解剖螺以确定其性别、育幼状况和是否被寄生。结果发现，感染了Microphallus sp.的螺的多刺程度明显低于未感染的螺。还发现，在体型较大时，感染Microphallus的螺的宽长比显著大于未感染的同类螺。这些趋势至少可以通过三种方式来解释。（1）感染导致螺不产生刺且变宽。（2）多刺且较窄的螺在感染时更易死亡。（3）多刺且较窄的螺对感染更具抵抗力。观察到的表型变化对宿主或寄生虫而言都不太可能具有适应性，可能代表了宿主 - 寄生虫关系的生理副产物。
