Assessment of population genetic structure in the arbovirus vector midge, Culicoides brevitarsis (Diptera: Ceratopogonidae), using multi-locus DNA microsatellites

Abstract

Bluetongue virus (BTV) is a major pathogen of ruminants that is transmitted by biting midges (Culicoides spp.). Australian BTV serotypes have origins in Asia and are distributed across the continent into two distinct episystems, one in the north and another in the east. Culicoides brevitarsis is the major vector of BTV in Australia and is distributed across the entire geographic range of the virus. Here, we describe the isolation and use of DNA microsatellites and gauge their ability to determine population genetic connectivity of C. brevitarsis within Australia and with countries to the north. Eleven DNA microsatellite markers were isolated using a novel genomic enrichment method and identified as useful for genetic analyses of sampled populations in Australia, northern Papua New Guinea (PNG) and Timor-Leste. Significant (P < 0.05) population genetic subdivision was observed between all paired regions, though the highest levels of genetic sub-division involved pair-wise tests with PNG (PNG vs. Australia (FST = 0.120) and PNG vs. Timor-Leste (FST = 0.095)). Analysis of multi-locus allelic distributions using STRUCTURE identified a most probable two-cluster population model, which separated PNG specimens from a cluster containing specimens from Timor-Leste and Australia. The source of incursions of this species in Australia is more likely to be Timor-Leste than PNG. Future incursions of BTV positive C. brevitarsis into Australia may be genetically identified to their source populations using these microsatellite loci. The vector’s panmictic genetic structure within Australia cannot explain the differential geographic distribution of BTV serotypes.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0250-8) contains supplementary material, which is available to authorized users.

Delineation of the population genetic structure of Culicoides imicola in East and South Africa

“…A phylogenetic study of C. brevitarsis, another member of the Imicola Complex, in the Australasian region showed no evidence of genetic separation or structure between populations sampled from northern and eastern Australia, approximately 3000 km apart, suggesting a panmictic population in the continent [ 30 ]. The breeding habitat of C. brevitarsis is restricted to fresh dung of wild and domesticated bovids [ 52 ].…”

“…Its distribution in Australia, within its climatic niche, coincides with the distribution of cattle [ 53 ] suggesting that this species of biting midge could not have existed in Australia before the introduction of cattle to the continent in the late 19th Century [ 54 ]. Therefore, the genetic connectivity that is evident among the populations of C. brevitarsis within Australia could be an indication of a recent colonization and expansion into this region [ 30 ]; this is in contrast to probably longer past history of C. imicola in South Africa and Kenya.…”

“…De novo isolation of microsatellite DNA was carried out using a recently-developed workflow [ 30 ]. In brief, genomic DNA was obtained from four pools of midges (each pool consisting of 15 samples) from Kenya, Madagascar, Balearic Islands and South Africa using the DNeasy blood and tissue kit (QIAgen) according to the manufacturer’s protocol and was quantified using a Qubit fluorometer (Life Technologies, Invitrogen).…”

“…It has considered the potential geographical and physical factors, acting as barriers or motors to gene flow and dispersal. Technically, the first aim of this study was to develop de novo DNA microsatellite markers for C. imicola using a recently described experimental workflow [ 30 ]. The second aim of the study was to employ both the developed microsatellite markers and DNA sequences of the COI gene to test genetic diversity amongst geographically different populations from Balearic Islands, Kenya, South Africa, Madagascar and Mauritius.…”

Important Dispersal Capacity of One Main Species Vector of Bluetongue and Schmallenberg Viruses Culicoides Obsoletus (Diptera: Ceratopogonidae) Revealed by Landscape Genetic Analyses&nbsp;

“…The low overall inter-individual genetic dissimilarity highlighted by our study re ected the important level of gene ow for C. obsoletus and comes to reinforce what has been described previously for other Culicoides species. In particular, important level of gene ows have already been observed in France for C. imicola [29] and in Australia for C. brevitarsis [82]. Genetic studies on C. imicola in Europe revealed an important gene ow as re ected by the inference of two large genetic clusters: a "Central Mediterranean cluster" including Algeria, Sardinia, Corsica, Pyrénées-Orientales and Var French departments of France, and a "Western Mediterranean cluster" including Morocco, Spain, Portugal and Majorca [26].…”