Vertebrate host or tick vector? Which is to blame for Borrelia lusitaniae population structure?

Borrelia lusitaniae is a lizard-associated spirochaete which shows highly genetically structured populations in western Europe. Our objective was to assess whether selective forces acting on the Ixodes tick vector or the reservoir lizard, Psammodromus algirus, shaped its population structure.

We collected ticks feeding on P. algirus in the Iberian Peninsula and north Africa, and genetically characterized B. lusitaniae, the infected ticks, and the vertebrate host.

The goeBURST analysis on seven MLST B. lusitaniae genes identified two main clusters: one from central Europe and other from north Africa and Portugal (south of Tagus river), with some connections between the north Tagus populations in central Spain and north African ones. The Ixodes sp. nuclear gene trospA did not entirely correspond with the B. lusitaniae population structure. The P. algirus's phylogeny based on the ND4 mitochondrial gene also did not show lineage distinctions between north and south Tagus.

Both the clustering of B. lusitaniae lineages from this region together with those of south Portugal and north Africa, and the presence of ticks belonging to different trospA clades, suggests Central Spain, a contact area between lineages of P. algirus, as pivotal in the phylogeography of the host, its ticks and Borrelia.