Abstract
BackgroundHost-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.MethodsA 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.ResultsInfection 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.ConclusionsOur 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.
Highlights
Host-parasite relationships are expected to be strongly shaped by host specificity, a crucial factor in parasite adaptability and diversification
The three lizard groups can be found inhabiting the same locations, though they differ in their ecology: Gallotia lacertids are diurnal and ground-dwelling; Chalcides skinks are diurnal but semifossorial; and Tarentola geckos are crepuscular/nocturnal and saxicolous [55]
Our results seem to suggest a high level of host specificity for haemogregarine parasites infecting lizards of the Canary Islands, with no evidence of host-switching events
Summary
Host-parasite relationships are expected to be strongly shaped by host specificity, a crucial factor in parasite adaptability and diversification. One of the most decisive factors shaping parasite distribution is host specificity [5, 6] This trait determines the range of hosts a parasite can successfully infect and its ability to establish in new environments. Ideally the whole community of potential hosts of a parasite has to be considered In this context, oceanic islands present a naturally simplified version of ecological interactions, being characterized by a depauperate and dis-harmonic fauna with high levels of endemics, which resulted from the non-random arrival of a small subset of the mainland pool followed by diversification processes [16, 17]. Colonizers face different selective pressures, which promote loss of genetic variability, increase in densities, niche broadening, among others [18] These features are collectively referred to as the Island Syndrome. In the case of parasites, studies suggest that in insular systems they exhibit reduced diversity, higher prevalence values and an enlargement of the ecological niche, which is reflected in more frequent host-switching and more generalist parasites, in comparison to the mainland [19, 20]
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