Steinauer Michelle L, Hanelt Ben, Mwangi Ibrahim N, Maina Geoffrey M, Agola Lelo E, Kinuthia Joseph M, Mutuku Martin W, Mungai Ben N, Wilson Wade D, Mkoji Gerald M, Loker Eric S
Department of Biology, University of New Mexico, MSC03 2020, 1 University of New Mexico, Albuquerque, NM 87131-0001, USA.
Mol Ecol. 2008 Dec;17(23):5062-74. doi: 10.1111/j.1365-294X.2008.03957.x. Epub 2008 Nov 3.
Hybridization and introgression can have important consequences for the evolution, ecology and epidemiology of pathogenic organisms. We examined the dynamics of hybridization between a trematode parasite of humans, Schistosoma mansoni, and its sister species, S. rodhaini, a rodent parasite, in a natural hybrid zone in western Kenya. Using microsatellite markers, rDNA and mtDNA, we showed that hybrids between the two species occur in nature, are fertile and produce viable offspring through backcrosses with S. mansoni. Averaged across collection sites, individuals of hybrid ancestry comprised 7.2% of all schistosomes collected, which is a large proportion given that one of the parental species, S. rodhaini, comprised only 9.1% of the specimens. No F1 individuals were collected and all hybrids represented backcrosses with S. mansoni that were of the first or successive generations. The direction of introgression appears highly asymmetric, causing unidirectional gene flow from the rodent parasite, S. rodhaini, to the human parasite, S. mansoni. Hybrid occurrence was seasonal and most hybrids were collected during the month of September over a 2-year period, a time when S. rodhaini was also abundant. We also examined the sex ratios and phenotypic differences between the hybrids and parental species, including the number of infective stages produced in the snail host and the time of day the infective stages emerge. No statistical differences were found in any of these characteristics, and most of the hybrids showed an emergence pattern similar to that of S. mansoni. One individual, however, showed a bimodal emergence pattern that was characteristic of both parental species. In conclusion, these species maintain their identity despite hybridization, although introgression may cause important alterations of the biology and epidemiology of schistosomiasis in this region.
杂交和基因渗入对致病生物的进化、生态和流行病学可能产生重要影响。我们在肯尼亚西部的一个自然杂交区域，研究了人类血吸虫曼氏血吸虫与其姐妹物种、啮齿动物寄生虫罗氏血吸虫之间的杂交动态。利用微卫星标记、核糖体DNA和线粒体DNA，我们发现这两个物种之间的杂交种在自然环境中存在，具有生育能力，并通过与曼氏血吸虫回交产生可存活的后代。在所有采集地点进行平均后，杂交血统的个体占所有采集到的血吸虫的7.2%，鉴于亲本物种之一罗氏血吸虫仅占标本的9.1%，这一比例相当高。未采集到F1个体，所有杂交种均代表与曼氏血吸虫的第一代或连续几代回交。基因渗入的方向似乎高度不对称，导致基因从啮齿动物寄生虫罗氏血吸虫单向流入人类寄生虫曼氏血吸虫。杂交现象具有季节性，在两年期间，大多数杂交种是在9月份采集到的，此时罗氏血吸虫也大量出现。我们还研究了杂交种与亲本物种之间的性别比例和表型差异，包括在蜗牛宿主中产生的感染阶段数量以及感染阶段出现的时间。在这些特征中未发现统计学差异，大多数杂交种表现出与曼氏血吸虫相似的出现模式。然而，有一个个体表现出双亲物种特有的双峰出现模式。总之，尽管存在杂交现象，但这些物种仍保持其特性，不过基因渗入可能会导致该地区血吸虫病生物学和流行病学的重要改变。
