Stigge Heather A, Bolek Matthew G
Department of Integrative Biology, Oklahoma State University, Stillwater, Oklahoma, 74078.
J Parasitol. 2015 Dec;101(6):658-65. doi: 10.1645/15-793. Epub 2015 Aug 24.
Complex life cycles are a hallmark characteristic of many parasites; however, little is known about the process by which life cycles become more complex through the addition of hosts. Paratenic hosts are present in the life cycles of several phylogenetically distinct groups of helminths; this suggests that they may play a key role during this process. This study examined the development of metacercariae of Halipegus eccentricus within intermediate microcrustacean and odonate paratenic hosts. Then a comparative approach was used to evaluate how life history traits of H. eccentricus within the anuran definitive hosts differ between metacercariae of the same age that developed within an intermediate ostracod host or a paratenic odonate host. The results of this study indicate that metacercariae of H. eccentricus do not grow at the same rate in different intermediate hosts, and significant differences exist in growth within intermediate and paratenic hosts. Individuals from odonate paratenic hosts always had larger bodies and suckers than those of metacercariae of the same age that develop within microcrustacean intermediate hosts. Furthermore, metacercariae from odonates were more successful in establishing and migrating in definitive anuran hosts. Last, individuals from paratenic hosts began reproducing earlier within anuran definitive hosts than age-matched worms that develop within the intermediate hosts. Collectively these results suggest that the variation in body and sucker sizes within odonate and microcrustacean hosts may carry over to the definitive host and in the case of H. eccentricus using the paratenic host increases transmission and alters other life history traits within definitive hosts. These results indicate that using a paratenic host can affect the success of parasites in subsequent hosts, and therefore these hosts may provide benefits other than just increasing transmission by bridging an ecological gap.
复杂的生命周期是许多寄生虫的一个标志性特征；然而，对于生命周期如何通过增加宿主而变得更加复杂的过程，我们知之甚少。在几种系统发育上不同的蠕虫类群的生命周期中存在转续宿主；这表明它们可能在此过程中发挥关键作用。本研究考察了奇异哈氏吸虫后尾蚴在中间微甲壳动物和蜻蜓目转续宿主中的发育情况。然后采用比较方法来评估奇异哈氏吸虫在无尾目终末宿主中的生活史特征在同一年龄、分别在中间介形虫宿主或转续蜻蜓目宿主中发育的后尾蚴之间有何差异。本研究结果表明，奇异哈氏吸虫的后尾蚴在不同的中间宿主中生长速度不同，并且在中间宿主和转续宿主中的生长存在显著差异。来自蜻蜓目转续宿主的个体的身体和吸盘总是比在微甲壳动物中间宿主中发育的同龄后尾蚴更大。此外，来自蜻蜓目的后尾蚴在无尾目终末宿主中更易定殖并迁移。最后，来自转续宿主的个体在无尾目终末宿主中比在中间宿主中发育的年龄匹配的虫体更早开始繁殖。总体而言，这些结果表明，蜻蜓目和微甲壳动物宿主内身体和吸盘大小的差异可能延续到终末宿主，就奇异哈氏吸虫而言，使用转续宿主会增加传播并改变终末宿主内的其他生活史特征。这些结果表明，使用转续宿主会影响寄生虫在后续宿主中的成功，因此这些宿主可能提供的益处不仅仅是通过弥合生态差距来增加传播。
