Wisenden Brian D, Martinez-Marquez Jorge Y, Gracia Emilia S, McEwen Daniel C
College of Biological Sciences, University of Minnesota, St. Paul, MN 55108, USA.
J Parasitol. 2012 Aug;98(4):722-7. doi: 10.1645/GE-2454.1. Epub 2012 Apr 3.
Opportunity for parasites to manipulate host behavioral phenotype may be influenced by several factors, including the host ecology and the presence of cohabiting parasites in the same host. Metacercariae of Ornithodiplostomum ptychocheilus and "black spot" Crassiphiala bulboglossa have similar life cycles. Each parasite uses a littoral snail as a first intermediate host, fathead minnows as a second intermediate host, and a piscivorous bird as a final host. Metacercariae of black spot encyst in the dermal and epidermal tissues, while metacercariae of O. ptychocheilus encyst on the brain over a region that coordinates optomotor responses. Because of site differences within the host, we predicted that O. ptychocheilus metacercariae might manipulate the behavioral phenotype of minnows to facilitate transmission to the final host, but metacercariae of black spot would not. In our study population, prevalence was 100% for O. ptychocheilus , with an overall median intensity of 105 metacercariae per minnow. Prevalence of black spot was 60%, with a median abundance and intensity of 12 and 20 metacercariae per minnow for the overall sample and for infected fish, respectively. Minnows accumulated both parasites over time, producing significant correlations between intensity and minnow body length and between intensities of the 2 parasites. Minnows infected with black spot had on average twice as many O. ptychocheilus metacercariae as similar-sized minnows without any black spot cercariae. We found no correlation between body condition of minnows and intensity for either parasite. We measured 2 aspects of anti-predator competence to test for effects linked to parasite intensity. We found no correlation between intensity of either species of parasite and latency to behavioral response to attack from a mechanical model heron, nor was there any effect of parasite intensity on a measure of shoaling affinity. The absence of any detectable effect of metacercariae on anti-predator competence in minnows may reflect selection against parasite pathology from predation by non-hosts of the parasites and overwinter mortality due to low dissolved oxygen.
寄生虫操纵宿主行为表型的机会可能受到多种因素的影响，包括宿主生态以及同一宿主中共存寄生虫的存在情况。褶盘双口吸虫和“黑点”博氏并殖吸虫的后尾蚴具有相似的生命周期。每种寄生虫都以滨螺作为第一中间宿主，黑头呆鱼作为第二中间宿主，食鱼鸟类作为终末宿主。“黑点”的后尾蚴在真皮和表皮组织中形成囊蚴，而褶盘双口吸虫的后尾蚴在协调视动反应的脑区上形成囊蚴。由于宿主体内的寄生部位不同，我们预测褶盘双口吸虫的后尾蚴可能会操纵呆鱼的行为表型，以促进向终末宿主的传播，但“黑点”的后尾蚴则不会。在我们的研究群体中，褶盘双口吸虫的感染率为100%，每条呆鱼体内后尾蚴的总体中位强度为105个。“黑点病”的感染率为60%，总体样本和感染鱼中每条呆鱼的囊蚴中位丰度和强度分别为12个和20个。随着时间的推移，呆鱼会累积这两种寄生虫，导致强度与呆鱼体长之间以及两种寄生虫的强度之间产生显著的相关性。感染“黑点病”的呆鱼体内褶盘双口吸虫后尾蚴的数量平均是未感染任何“黑点”尾蚴的同等大小呆鱼的两倍。我们发现呆鱼的身体状况与这两种寄生虫的强度之间均无相关性。我们测量了反捕食能力的两个方面，以测试与寄生虫强度相关的影响。我们发现，两种寄生虫的强度与对机械模型苍鹭攻击的行为反应潜伏期之间均无相关性，寄生虫强度对集群亲和力的测量也没有任何影响。后尾蚴对呆鱼反捕食能力没有任何可检测到的影响，这可能反映出针对寄生虫病理学的选择，这种选择来自寄生虫非宿主的捕食以及低溶解氧导致的越冬死亡率。
