State Key Laboratory of Biotherapy, West China Hospital, West China Medical School, Sichuan University, Chengdu, People's Republic of China.
Department of Life Sciences, The Natural History Museum, London, United Kingdom.
PLoS Negl Trop Dis. 2019 Jan 28;13(1):e0007061. doi: 10.1371/journal.pntd.0007061. eCollection 2019 Jan.
Neotricula aperta is the snail-intermediate host of the parasitic blood-fluke Schistosoma mekongi which causes Mekong schistosomiasis in Cambodia and the Lao PDR. Despite numerous phylogenetic studies only one DNA-sequence based population-genetic study of N. aperta had been published, and the origin, structure and persistence of N. aperta were poorly understood. Consequently, a phylogenetic and population genetic study was performed, with addition of new data to pre-existing DNA-sequences for N. aperta from remote and inaccessible habitats, including one new taxon from Laos and 505 bp of additional DNA-sequence for all sampled taxa,.
Spatial Principal Component Analysis revealed the presence of significant spatial-genetic clustering. Genetic-distance-based clustering indicated four populations with near perfect match to a priori defined ecogeographical regions. Spring-dwelling taxa were found to form an ecological isolate relative to other N. aperta. The poor dispersal capabilities suggested by spatial-genetic analyses were confirmed by Bayesian inference of migration rates. Population divergence time estimation implied a mid-Miocene colonisation of the present range, with immediate and rapid radiation in each ecogeographical region. Estimated effective population sizes were large (120-310 thousand).
The strong spatial-genetic structure confirmed the poor dispersal capabilities of N. aperta-suggesting human-mediated reintroduction of disease to controlled areas as the primary reason for control failure. The isolation of the spring-dwelling taxa and ecogeographical structure suggests adaptation of sub-populations to different habitats; the epidemiological significance of this needs investigation. The large effective population sizes indicate that the high population densities observed in surveyed habitats are also present in inaccessible areas; affording great potential for recrudescence driven by animal-reservoir transmission in remote streams. Mid-Miocene colonisation implies heterochronous evolution of these snails and associated schistosomes and suggests against coevolution of snail and parasite. Heterochronicity favours ecological factors as shapers of host-parasite specificity and greater potential for escape from schistosomiasis control through host-switching.
光滑狭口螺是湄公裂体吸虫的中间宿主，这种寄生虫会导致柬埔寨和老挝人民民主共和国的湄公血吸虫病。尽管已经进行了许多系统发育研究，但仅有一项关于光滑狭口螺种群遗传的基于 DNA 序列的研究已经发表，因此对其起源、结构和持续性知之甚少。因此，我们进行了一项系统发育和种群遗传研究，增加了来自偏远和难以到达栖息地的光滑狭口螺的新数据，包括来自老挝的一个新分类群和所有采样分类群的 505bp 额外 DNA 序列。
空间主成分分析显示存在显著的空间遗传聚类。基于遗传距离的聚类表明存在四个种群，与预先定义的生态地理区域几乎完全匹配。研究发现，春季栖息的分类群相对于其他光滑狭口螺形成了一个生态隔离种群。空间遗传分析表明的较差扩散能力通过贝叶斯推断的迁移率得到了证实。种群分歧时间估计表明，中中新世时该物种现生范围发生了殖民化，然后在每个生态地理区域迅速辐射。估计的有效种群数量较大（12 万至 31 万）。
强烈的空间遗传结构证实了光滑狭口螺较差的扩散能力，这表明人类介导的将疾病重新引入控制区域是控制失败的主要原因。春季栖息的分类群和生态地理结构的隔离表明，亚种群已经适应了不同的栖息地；这需要进一步调查其流行病学意义。较大的有效种群数量表明，在调查栖息地中观察到的高种群密度也存在于难以到达的区域；这为远程溪流中动物宿主传播驱动的复发提供了巨大的潜力。中中新世的殖民化意味着这些蜗牛和相关裂体吸虫的异时性进化，并表明蜗牛和寄生虫之间不存在共同进化。异时性有利于生态因素塑造宿主-寄生虫特异性，并通过宿主转换更有可能逃避血吸虫病控制。
