Department of Epidemiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
Biodiversity Institute and Natural History Museum, University of Kansas, Lawrence, Kansas, USA.
Genome Biol Evol. 2023 Oct 6;15(10). doi: 10.1093/gbe/evad190.
Theory predicts relaxed host specificity and high host vagility should contribute to reduced genetic structure in parasites while strict host specificity and low host vagility should increase genetic structure. Though these predictions are intuitive, they have never been explicitly tested in a population genomic framework. Trypanorhynch tapeworms, which parasitize sharks and rays (elasmobranchs) as definitive hosts, are the only order of elasmobranch tapeworms that exhibit considerable variability in their definitive host specificity. This allows for unique combinations of host use and geographic range, making trypanorhynchs ideal candidates for studying how these traits influence population-level structure and genetic diversity. Multiplexed shotgun genotyping (MSG) data sets were generated to characterize component population structure and infrapopulation diversity for a representative of each trypanorhynch suborder: the ray-hosted Rhinoptericola megacantha (Trypanobatoida) and the shark-hosted Callitetrarhynchus gracilis (Trypanoselachoida). Adults of R. megacantha are more host-specific and less broadly distributed than adults of C. gracilis, allowing correlation between these factors and genetic structure. Replicate tapeworm specimens were sequenced from the same host individual, from multiple conspecific hosts within and across geographic regions, and from multiple definitive host species. For R. megacantha, population structure coincided with geography rather than host species. For C. gracilis, limited population structure was found, suggesting a potential link between degree of host specificity and structure. Conspecific trypanorhynchs from the same host individual were found to be as, or more, genetically divergent from one another as from conspecifics from different host individuals. For both species, high levels of homozygosity and positive FIS values were documented.
理论预测，宿主特异性放松和宿主迁移性高应该会降低寄生虫的遗传结构，而宿主特异性严格和宿主迁移性低则会增加遗传结构。尽管这些预测直观合理，但它们从未在种群基因组框架中得到明确验证。寄生在鲨鱼和鳐鱼（软骨鱼）身上的旋盘尾线虫绦虫是唯一一类在其终末宿主特异性方面表现出相当大变异性的软骨鱼绦虫目。这使得宿主利用和地理范围的独特组合成为可能，使旋盘尾线虫成为研究这些特征如何影响种群水平结构和遗传多样性的理想候选者。为了描述每个旋盘尾亚目代表的种群结构和亚种群多样性，我们生成了多重鸟枪法基因分型（MSG）数据集：射线宿主 Rhinoptericola megacantha（旋盘尾虫目）和鲨鱼宿主 Callitetrarhynchus gracilis（旋吻目）。R. megacantha 的成虫比 C. gracilis 的成虫更具宿主特异性和分布范围更广，这使得这些因素与遗传结构相关。从同一宿主个体、同一地理区域内和跨地理区域的多个同种宿主以及多个终末宿主物种中重复采集绦虫样本进行测序。对于 R. megacantha，种群结构与地理分布而非宿主物种相关。对于 C. gracilis，发现种群结构有限，这表明宿主特异性和结构之间可能存在潜在联系。来自同一宿主个体的同种旋盘尾线虫被发现彼此之间的遗传差异与来自不同宿主个体的同种旋盘尾线虫相同或更大。对于这两个物种，都记录到了高度的同质性和正的 FIS 值。
