Microsatellite loci support recent speciation of Ambylomma maculatum s.l., Koch, 1944 (Acari: Ixodidae) morphotypes II and III

In the United States, the Amblyomma maculatum sensu lato (s.l.) group is represented by two, distinct allopatric clusters of hard ticks identified as morphotype II in the eastern US and morphotype III in the southwestern states. Previous studies have shown that the two entities have evolved very recently from a common ancestor, are morphologically distinguishable in the adult stage, and are reproductively incompatible. Because of the recent divergence of the two morphotypes, gene sequences usually analyzed for a phylogenetic species definition are insufficiently informative to assign them to separate species. Microsatellite loci are predominantly non-coding sequences, selectively neutral, and usually have higher mutation rates than mitochondrial and coding nuclear gene sequences. An estimate of their divergence time based on the analysis of 8 previously developed microsatellite loci confirmed the recent speciation hypothesis, dating the radiation to approx. 230-460 years ago. A strong bottleneck signature suggests the establishment of these populations after a 1000-fold reduction in the population size of origin.