Phylogeography and demographic dynamics of Rhipicephalus microplus from North India.

Abstract

Rhipicephalus microplus, a hematophagous vector prevalent in the tropics and subtropics, is responsible for huge economic losses throughout the globe. However, the taxonomy of the tick species, especially prevalent in north India and south China has been challenged in the recent past. The present study attempted to assess the cryptic status of R. microplus ticks of north India based on two mitochondrial markers; the 16S rRNA and cox1 gene sequences. The phylogenetic tree corresponding to both markers demonstrated the presence of three distinct genetic assemblages/ clades of R. microplus. The present study isolates (n=five and seven for the cox1 and 16S rRNA gene sequences, respectively) from north India along with other isolates from India assorted in the R. microplus clade C sensu. Based on the median joining network analysis corresponding to the 16S rRNA gene sequence, 18 haplotypes were recorded, exhibiting a stellate shape, which was indicative of rapid population expansion. For the cox1 gene, the haplotypes corresponding to clades A, B and C were distantly placed with two exceptions. While performing the population structure analysis, low nucleotide (0.04745±0.00416 and 0.01021±0.00146) and high haplotype diversities (0.913±0.032 and 0.794±0.058) were recorded for the different clades of R. microplus based on the cox1 and 16S rRNA mitochondrial markers, respectively. Eventually, high genetic differentiation and low gene flow were recorded among the different clades. A negative value for the neutrality indices (Tajima's D=-1.44125, Fu's Fs=-4.879, Fu and Li's D=-2.78031 and Fu and Li's F=-2.75229) corresponding to the 16S rRNA gene for the overall dataset evinced an expansion of population size. Based on the detailed studies, it was inferred that the R. microplus tick species circulating in north India belonged to clade C sensu, similar to that of the species prevalent in the other parts of the country as well as in the Indian subcontinent.