Höglund J, Thulin J
Department of Zoology, Uppsala, Sweden.
J Helminthol. 1990 Jun;64(2):139-50. doi: 10.1017/s0022149x00012050.
Thermal effects on the dynamics of infection with metacercariae of Diplostomum baeri and D. spathaceum were monitored between May and September, in a year-class of perch Perca fluviatilis, in an artificial lake receiving warm water discharges from a nuclear power station and in an unheated reference site, for a two year period. In the heated area the prevalence of infection of the retinal form, D. baeri, was always 100%, whereas in the unheated site there was an increase from 93% in May to 100% in June 1986. The relative density of D. baeri was found to increase gradually during the first summer in both areas, although the accumulation rate of metacercariae was significantly increased in the heated area. In August of the first year the relative density of D. baeri peaked in the heated area, whereas it continued to increase in the unheated control. However, in September of the following year, the relative densities were at the same level in both thermal regimes. A concomitant decline in the degree of overdispersion of metacercariae within the host population was observed in the heated area as the population density of metacercariae decreased, whereas the index of dispersion remained at the same level throughout the study in the unheated area. However, it was not possible to sample perch in the unheated area between October 1986 and May 1987 and changes in the parasite population could have occurred during this period. The prevalence and relative density of D. spathaceum, the lens form, was on the contrary low, especially in the unheated site where it was recorded only occasionally. The infection of D. baeri exhibited a convex pattern in both thermal regimens, although the peak infection was noticed earlier in the heated area. Regulation of the parasite infrapopulation may have been achieved by the combined effects of a decreased transmission rate of cercariae with increasing age of the host, the mortality of metacercariae as a natural termination of the life span and to selective predation of heavily infected hosts. However, regardless of an increased accumulation rate of metacercariae in the heated area, the relative densities of D. baeri became equal in both thermal regimes at the end of the study. The mortality rate of metacercariae in the heated area was therefore presumably increased as compared with the unheated reference site.
在两年时间里，于5月至9月期间，对一年龄的河鲈（Perca fluviatilis）感染巴氏双腔吸虫（Diplostomum baeri）和匙形双腔吸虫（D. spathaceum）囊蚴的动态热效应进行了监测，监测地点在一个接收核电站温排水的人工湖以及一个未加热的对照地点。在加热区域，视网膜型的巴氏双腔吸虫感染率始终为100%，而在未加热地点，感染率从1986年5月的93%上升至6月的100%。发现巴氏双腔吸虫的相对密度在两个区域的第一个夏季均逐渐增加，尽管加热区域囊蚴的积累速率显著提高。在第一年的8月，巴氏双腔吸虫的相对密度在加热区域达到峰值，而在未加热的对照区域则持续增加。然而，在次年9月，两个热环境下的相对密度处于同一水平。随着加热区域囊蚴种群密度的降低，观察到宿主种群中囊蚴的过度分散程度随之下降，而在未加热区域，整个研究期间分散指数保持在同一水平。然而，在1986年10月至1987年5月期间无法在未加热区域采集河鲈样本，在此期间寄生虫种群可能发生了变化。相反，晶状体型的匙形双腔吸虫的感染率较低，尤其是在未加热地点，仅偶尔有记录。巴氏双腔吸虫的感染在两种热环境下均呈现出凸形模式，尽管在加热区域感染高峰出现得更早。寄生虫种群的调节可能是由于随着宿主年龄增长尾蚴传播率降低、囊蚴作为自然寿命终结的死亡率以及对重度感染宿主的选择性捕食等综合作用实现的。然而，尽管加热区域囊蚴的积累速率有所增加，但在研究结束时，两个热环境下巴氏双腔吸虫的相对密度变得相等。因此，与未加热的对照地点相比，加热区域囊蚴的死亡率可能有所增加。
