CIBIO, InBIO - Research Network in Biodiversity and Evolutionary Biology, Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, 4485-661, Vairão, Portugal.
Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 4169-007, Porto, Portugal.
Parasit Vectors. 2018 Mar 19;11(1):190. doi: 10.1186/s13071-018-2760-5.
Host-parasite relationships are expected to be strongly shaped by host specificity, a crucial factor in parasite adaptability and diversification. Because whole host communities have to be considered to assess host specificity, oceanic islands are ideal study systems given their simplified biotic assemblages. Previous studies on insular parasites suggest host range broadening during colonization. Here, we investigate the association between one parasite group (haemogregarines) and multiple sympatric hosts (of three lizard genera: Gallotia, Chalcides and Tarentola) in the Canary Islands. Given haemogregarine characteristics and insular conditions, we hypothesized low host specificity and/or occurrence of host-switching events.
A total of 825 samples were collected from the three host taxa inhabiting the seven main islands of the Canarian Archipelago, including locations where the different lizards occurred in sympatry. Blood slides were screened to assess prevalence and parasitaemia, while parasite genetic diversity and phylogenetic relationships were inferred from 18S rRNA gene sequences.
Infection levels and diversity of haplotypes varied geographically and across host groups. Infections were found in all species of Gallotia across the seven islands, in Tarentola from Tenerife, La Gomera and La Palma, and in Chalcides from Tenerife, La Gomera and El Hierro. Gallotia lizards presented the highest parasite prevalence, parasitaemia and diversity (seven haplotypes), while the other two host groups (Chalcides and Tarentola) harbored one haplotype each, with low prevalence and parasitaemia levels, and very restricted geographical ranges. Host-sharing of the same haemogregarine haplotype was only detected twice, but these rare instances likely represent occasional cross-infections.
Our results suggest that: (i) Canarian haemogregarine haplotypes are highly host-specific, which might have restricted parasite host expansion; (ii) haemogregarines most probably reached the Canary Islands in three colonization events with each host genus; and (iii) the high number of parasite haplotypes infecting Gallotia hosts and their restricted geographical distribution suggest co-diversification. These findings contrast with our expectations derived from results on other insular parasites, highlighting how host specificity depends on parasite characteristics and evolutionary history.
宿主-寄生虫关系预计会受到宿主特异性的强烈影响，宿主特异性是寄生虫适应性和多样化的关键因素。由于要评估宿主特异性，必须考虑整个宿主群落，因此海洋岛屿是理想的研究系统，因为它们的生物组合比较简单。以前关于岛屿寄生虫的研究表明，在殖民过程中宿主范围会扩大。在这里，我们研究了加那利群岛（Canary Islands）的一组寄生虫（血孢子虫）和三种蜥蜴属（Gallotia、Chalcides 和 Tarentola）的多个共生宿主之间的联系。鉴于血孢子虫的特征和岛屿条件，我们假设宿主特异性低和/或存在宿主转换事件。
从栖息在加那利群岛七个主要岛屿上的三个宿主类群中采集了 825 个样本，包括不同蜥蜴共生的地点。通过血涂片筛查来评估感染率和寄生虫血症，同时从 18S rRNA 基因序列推断寄生虫的遗传多样性和系统发育关系。
感染水平和单倍型的遗传多样性在地理和宿主群体上都有所不同。在七个岛屿上的所有 Gallotia 物种中都发现了感染，在特内里费岛、拉戈梅拉岛和拉帕尔马岛的 Tarentola 中也发现了感染，在特内里费岛、拉戈梅拉岛和埃尔埃希罗岛的 Chalcides 中也发现了感染。Gallotia 蜥蜴的寄生虫感染率最高，寄生虫血症和多样性最高（七个单倍型），而其他两个宿主群体（Chalcides 和 Tarentola）各携带一个单倍型，感染率和寄生虫血症水平较低，地理分布范围非常有限。仅检测到两次同一血孢子虫单倍型的宿主共享，但这些罕见的情况可能代表偶尔的交叉感染。
我们的研究结果表明：（i）加那利群岛的血孢子虫单倍型高度宿主特异性，这可能限制了寄生虫宿主的扩张；（ii）血孢子虫很可能通过与每个宿主属的三次殖民事件到达加那利群岛；（iii）感染 Gallotia 宿主的大量寄生虫单倍型及其有限的地理分布表明共同多样化。这些发现与我们从其他岛屿寄生虫研究中得出的预期结果形成对比，突出了宿主特异性如何取决于寄生虫特征和进化历史。
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