Orlofske Sarah A, Belden Lisa K, Hopkins William A
Department of Fisheries and Wildlife, Virginia Tech, Blacksburg, Virginia 24061, USA.
J Parasitol. 2009 Aug;95(4):787-92. doi: 10.1645/GE-1840.1.
High intensity infections of Echinostoma trivolvis metacercariae decrease survival and growth of young amphibian larvae. However, in nature, parasites are highly aggregated, which results in a large proportion of the amphibian population being only moderately infected. Survival and growth responses at these more-common, low-infection levels remain poorly studied. Thus, we investigated the effects of moderate Echinostoma trivolvis metacercariae infection (following exposure to 0, 10, 30, or 90 cercariae) on the growth and development of pickerel frog (Rana palustris) tadpoles. We measured metabolism to determine whether increased energy expenditure is a potential physiological mechanism underlying previously documented reduced growth. Furthermore, we quantified tadpole intestine size, which can exhibit plasticity in response to changing metabolic demands, and we characterized metacercariae distribution in tadpole kidneys. Metacercariae encysted in the pronephros significantly more than in the mesonephros, but tended to occur equally in right and left kidneys. Two mo post-infection (PI), there were no changes in tadpole survival, development, intestine size, or growth related to metacercariae infection. Similarly, metacercariae did not significantly increase metabolic rates during encystment or at 1 mo PI. Our study demonstrated that modest E. trivolvis infections, representative of a large proportion of the host population, had no detectable effects on fitness-related traits in laboratory isolation from other ecological variables.
棘口吸虫（Echinostoma trivolvis）囊蚴的高强度感染会降低幼年两栖类幼虫的存活率和生长速度。然而，在自然环境中，寄生虫高度聚集，这导致很大一部分两栖动物种群仅受到中度感染。对于这些更常见的低感染水平下的存活和生长反应，目前仍研究不足。因此，我们研究了中度棘口吸虫囊蚴感染（暴露于0、10、30或90尾尾蚴后）对北美豹蛙（Rana palustris）蝌蚪生长和发育的影响。我们测量了新陈代谢，以确定能量消耗增加是否是先前记录的生长减缓的潜在生理机制。此外，我们对蝌蚪肠道大小进行了量化，肠道大小可因代谢需求变化而表现出可塑性，并且我们对蝌蚪肾脏中囊蚴的分布进行了特征描述。囊蚴在蝌蚪前肾中的包囊化明显多于中肾，但在左右肾脏中的分布趋于相同。感染后两个月（PI），蝌蚪的存活、发育、肠道大小或生长与囊蚴感染无关。同样，囊蚴在包囊化期间或感染后1个月时也没有显著提高代谢率。我们的研究表明，代表大部分宿主种群的适度棘口吸虫感染，在与其他生态变量隔离的实验室环境中，对与适应性相关的性状没有可检测到的影响。
