Tinsley R C, Jackson J A
School of Biological Sciences, University of Bristol, U.K.
Int J Parasitol. 1998 Oct;28(10):1573-82. doi: 10.1016/s0020-7519(98)00085-x.
Protopolystoma (Monogenea, Polystomatidae) is strictly specific to the anuran amphibian genus Xenopus. The host group is characterised by a polyploid series in which chromosome numbers reflect diploid, tetraploid, octoploid and dodecaploid constitutions; the series is considered to have evolved through interspecies hybridisation and genome duplication. This study correlates information on host evolutionary relationships with patterns of parasite speciation and host specificity. Protopolystoma is restricted to one subgenus (Xenopus) with multiples of 36 chromosomes, and is absent from the subgenus Silurana (with multiples of 20 chromosomes). Molecular, biochemical and karyotype evidence distinguishes three subgroups within Xenopus. Representative species from each subgroup, Xenopus muelleri, Xenopus fraseri and Xenopus laevis, have been examined for polystomatid infection. Two species of Protopolystoma occur in each of these host species. In X. muelleri, the two Protopolystoma species reflect parasite co-speciation corresponding with the divergence of two sibling host species. Xenopus fraseri and X. laevis (both with 2n = 36 chromosomes) are implicated in the hybrid origin of two octoploid species, Xenopus wittei and Xenopus vestitus (both 2n = 72). The relationships of the Protopolystoma species in these Xenopus taxa reflect this presumed ancestry. Xenopus wittei carries two species of Protopolystoma, one shared with X. fraseri and the other shared with X. laevis. Xenopus vestitus carries a single species of Protopolystoma which is shared with X. laevis but there is no "heirloom" which reflects its hybrid origin involving X. fraseri. In addition to these shared parasite species which may reflect shared host genes, X. fraseri and X. laevis each carry separate species-specific Protopolystoma which do not occur in other Xenopus species even where there is evidence of common genetic information (as in the allopolyploid wittei and vestitus). This case study may be interpreted as indicating a powerful influence of host genetic factors on susceptibility to infection, host-specificity, and parasite speciation.
原多盘虫属（单殖吸虫纲，多盘科）严格寄生于非洲爪蟾属的无尾两栖动物。该宿主群体的特征是一个多倍体系列，其中染色体数目反映了二倍体、四倍体、八倍体和十二倍体的组成；这个系列被认为是通过种间杂交和基因组复制进化而来的。本研究将宿主进化关系的信息与寄生虫物种形成模式和宿主特异性联系起来。原多盘虫属局限于一个具有36条染色体倍数的亚属（非洲爪蟾属），而在具有20条染色体倍数的希氏蟾亚属中不存在。分子、生化和核型证据区分了非洲爪蟾属内的三个亚组。对每个亚组的代表性物种，即穆氏非洲爪蟾、弗雷泽非洲爪蟾和光滑爪蟾，进行了多盘虫感染检测。这些宿主物种中的每一种都有两种原多盘虫。在穆氏非洲爪蟾中，这两种原多盘虫物种反映了与两个姐妹宿主物种分化相对应的寄生虫共同物种形成。弗雷泽非洲爪蟾和光滑爪蟾（均为2n = 36条染色体）与两种八倍体物种，即威特非洲爪蟾和韦氏非洲爪蟾（均为2n = 72）的杂交起源有关。这些非洲爪蟾类群中原多盘虫属物种的关系反映了这种推测的祖先关系。威特非洲爪蟾携带两种原多盘虫，一种与弗雷泽非洲爪蟾共有，另一种与光滑爪蟾共有。韦氏非洲爪蟾携带一种与光滑爪蟾共有的原多盘虫，但没有反映其涉及弗雷泽非洲爪蟾的杂交起源的“祖传物种”。除了这些可能反映共享宿主基因的共享寄生虫物种外，弗雷泽非洲爪蟾和光滑爪蟾各自还携带单独的物种特异性原多盘虫，即使在有共同遗传信息证据的情况下（如在异源多倍体的威特非洲爪蟾和韦氏非洲爪蟾中），这些原多盘虫也不会出现在其他非洲爪蟾物种中。这个案例研究可以解释为表明宿主遗传因素对感染易感性、宿主特异性和寄生虫物种形成有强大影响。
