Abstract
Population structure and biogeography of marine organisms are formed by different drivers than in terrestrial organisms. Yet, very little information is available even for common marine organisms and even less for their associated parasites. Here we report the first analysis of population structure of both a cephalopod host (Sepia officinalis) and its dicyemid parasite, based on a homologous molecular marker (cytochrome oxidase I). We show that the population of common cuttlefish in the Mediterranean area is fragmented into subpopulations, with some areas featuring restricted level of gene flow. Amongst the studied areas, Sardinia was genetically the most diverse and Cyprus the most isolated. At a larger scale, across the Mediterranean, the population structure of the parasite shows co-diversification pattern with its host, but a slower rate of diversification. Differences between the two counterparts are more obvious at a finer scale, where parasite populations show increased level of fragmentation and lower local diversities. This discrepancy can be caused by local extinctions and replacements taking place more frequently in the dicyemid populations, due to their parasitic lifestyle.
Highlights
In marine organisms, genetic structure is usually supposed to be determined by various extrinsic factors unique to this environment
Comparative studies of single-host-parasite associations provide a more straightforward approach, with the capacity to address such questions as: Is the overall population structure of a parasite mirroring that of its host due to their shared dispersal? May the structure of parasite’s local subpopulation differ from the host due to local extinctions and reinfections? Would such extinctions result in a decrease of genetic diversities within local populations of the parasites? Here, we address these questions using a model of host-parasite pair, Common cuttlefish (Sepia officinalis) and its parasites from a rarely studied group Dicyemida
Two cuttlefish specimens from Sicily (Accession numbers MN069250 and MN069251) were found to be genetically distinct from the rest of the S. officinalis specimens in this study and from available S. officinalis sequences in public databases
Summary
Genetic structure is usually supposed to be determined by various extrinsic factors unique to this environment. In a recent meta-analysis Pascual et al.[12] showed that the relationship between population structure and oceanographic features in Mediterranean Sea varies considerably across different species and is largely determined by the life history of the given organism. A slightly different view was presented by Maze-Guilmo et al.[18] Based on their meta-analysis of a broader spectrum of parasites, they demonstrated that the outcome of such parasite-host comparison is dependent on various biological traits (i.e. reproduction mode, presence/absence of a larval stage). We address these questions using a model of host-parasite pair, Common cuttlefish (Sepia officinalis) and its parasites from a rarely studied group Dicyemida This model allows for addressing the general issues of genetic diversification in marine environment and the relationship between diversities of the host and parasite. This study introduces the first single-host model entirely bound to the marine environment and involving a free-living host
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