Shostak A W, Walsh J G, Wong Y C
Department of Biological Sciences, CW405 Biological Sciences Building, University of Alberta, Edmonton, Alberta, Canada.
Parasitology. 2008 Jul;135(8):1019-33. doi: 10.1017/S0031182008004459. Epub 2008 May 12.
We studied the 'crowding effect' in Tribolium confusum infected with Hymenolepis diminuta. Manipulations included age and number of parasites, and diet, sex, age and number of exposures of hosts. Volume per parasite was unaffected until an intensity of at least 5-10 parasites per host, then declined approximately inversely as intensities increased. Parasite size was affected by host sex but not age or reproductive status. Host diet affected parasite size and the impact of crowding. Daily gain in parasite volume peaked partway through the developmental period and preceded the first evidence of a crowding effect. Parasites that established during a second exposure had a transient developmental delay but eventually grew as large or larger than parasites from a single exposure with the same total intensity. Parasites responded to crowding by differential allocation of resources. Cercomer volume decreased even with slight crowding, the capsule surrounding the scolex was not reduced until crowding became more severe, and scolex width was reduced only in the most extreme conditions. The data support the hypothesis that the crowding effect in this system is driven primarily by nutrient, rather than space limitations.
我们研究了感染微小膜壳绦虫的杂拟谷盗中的“拥挤效应”。实验操作包括寄生虫的年龄和数量，以及宿主的饮食、性别、年龄和接触次数。每个寄生虫的体积在宿主感染强度至少达到每只宿主5 - 10只寄生虫之前不受影响，然后随着感染强度增加大致呈反比下降。寄生虫大小受宿主性别影响，但不受宿主年龄或生殖状态影响。宿主饮食影响寄生虫大小和拥挤效应。寄生虫体积的每日增长在发育中期达到峰值，且早于首次出现拥挤效应的迹象。在第二次接触时感染的寄生虫有短暂的发育延迟，但最终生长得与相同总感染强度下单次接触感染的寄生虫一样大或更大。寄生虫通过资源的差异分配对拥挤做出反应。即使轻度拥挤，尾器体积也会减小，直到拥挤变得更严重时，围绕头节的囊才会减小，且只有在最极端的情况下头节宽度才会减小。数据支持了这一假设，即该系统中的拥挤效应主要由营养物质限制而非空间限制驱动。
