Spatio-temporal genetic variation of the biting midge vector species Culicoides imicola (Ceratopogonidae) Kieffer in France

Abstract

Background: Introduction of vector species into new areas represents a main driver for the emergence and worldwide spread of vector-borne diseases. This poses a substantial threat to livestock economies and public health. Culicoides imicola Kieffer, a major vector species of economically important animal viruses, is described with an apparent range expansion in Europe where it has been recorded in south-eastern continental France, its known northern distribution edge. This questioned on further C. imicola population extension and establishment into new territories. Studying the spatio-temporal genetic variation of expanding populations can provide valuable information for the design of reliable models of future spread.

Methods: Entomological surveys and population genetic approaches were used to assess the spatio-temporal population dynamics of C. imicola in France. Entomological surveys (2-3 consecutive years) were used to evaluate population abundances and local spread in continental France (28 sites in the Var department) and in Corsica (4 sites). We also genotyped at nine microsatellite loci insects from 3 locations in the Var department over 3 years (2008, 2010 and 2012) and from 6 locations in Corsica over 4 years (2002, 2008, 2010 and 2012).

Results: Entomological surveys confirmed the establishment of C. imicola populations in Var department, but indicated low abundances and no apparent expansion there within the studied period. Higher population abundances were recorded in Corsica. Our genetic data suggested the absence of spatio-temporal genetic changes within each region but a significant increase of the genetic differentiation between Corsican and Var populations through time. The lack of intra-region population structure may result from strong gene flow among populations. We discussed the observed temporal variation between Corsica and Var as being the result of genetic drift following introduction, and/or the genetic characteristics of populations at their range edge.

Conclusions: Our results suggest that local range expansion of C. imicola in continental France may be slowed by the low population abundances and unsuitable climatic and environmental conditions.

Keywords: Culicoides; Distribution range; Entomological survey; Mediterranean basin; Population genetics; Spatio-temporal.

Fig. 1

Distribution area of C. imicola in the Var department in 2011 and 2012. Presence/absence maps from 2003 to 2010 were previously published in [9]

Fig. 2

Collection sites in Corsica with maximum catches of Culicoides imicola per year in 2010 and 2012. Population abundance maps from 2003 to 2009 were previously published in [9]

Fig. 3

Sampled sites of C. imicola used for population genetic analyses

Fig. 4

Maximum catch per year of C. imicola in the Var department from 2003 to 2014

Fig. 5

Population genetic structure results of Culicoides imicola. a Genetic clustering of C. imicola samples. Each vertical line represents an individual and each colour represents a cluster. b Microsatellite neighbor-joining tree based on genetic distance of Cavalli-Sforza & Edwards (1967). Bootstrap values are calculated over 1,000 replicates (only values > 50 % are shown). c Principal Component Analysis based on microsatellite allelic frequencies

Fig. 6

Results of the Mantel tests for isolation by distance (IBD)