Hybridization in natural sympatric populations of Dermacentor ticks in northwestern North America

Abstract

Hybridization in ticks has been described in a handful of species and mostly as a result of laboratory experiments. We used 148 AFLP loci to describe putative hybridization events between D. andersoni and D. variabilis in sympatric populations from northwestern North America. Recently, D. variabilis has expanded its range westward into the natural range of D. andersoni. Using a sample of 235 D. andersoni and 62 D. variabilis, we identified 31 individuals as putative hybrids: four F2 individuals and 27 backcrosses to D. andersoni (as defined by NewHybrids). We found no evidence of hybrids backcrossing into D. variabilis. Furthermore, all hybrids presented 16S mtDNA signatures characteristic of D. andersoni, which indicates the directionality of the hybrid crosses: female D. andersoni × male D. variabilis. We also discovered 13 species-specific AFLP fragments for D. andersoni. These loci were found to have a decreased occurrence in the putative hybrids and were absent altogether in D. variabilis samples. AFLP profiles were also used to determine the levels of genetic population structure and gene flow among nine populations of D. andersoni and three of D. variabilis. Genetic structure exists in both species (D. andersoni, ΦST = 0.110; D. variabilis, ΦST = 0.304) as well as significant estimates of isolation by distance (D. andersoni, ρ = 0.066, P = 0.001; D. variabilis, ρ = 0.729, P = 0.001).

Range-wide genetic analysis of Dermacentor variabilis and its Francisella-like endosymbionts demonstrates phylogeographic concordance between both taxa

“…(causing anaplasmosis) [3]. Dermacentor variabilis is abundant in the eastern USA and southeastern Canada, with a more restricted western population that occurs in the Pacific coast states of the USA; additional disjunct populations have also become established in restricted localities in the intermountain USA and Canada (Alberta, British Columbia, Idaho and Montana) [2, 4–7]. Overall, regional climatic and geographical differences (e.g.…”

“…temperature and elevation) appear to be the prevailing factors that affect the distributional limits of D. variabilis and it has been hypothesized that these factors, along with associated physiological limitations of the tick, could result in genetic divergence of populations [8]. Interestingly, a westward expansion of D. variabilis has been documented in recent decades, highlighting the potential for range expansion due to climatic shifts across this region [6, 7, 9]. …”

“…This important disease vector boasts an extensive and expanding range, which emphasizes the need for comprehensive phylogeographic studies to better understand its distributional patterns and characterize the relationship between these ticks and their microbiota. Multiple population genetic studies of D. variabilis have identified important phylogeographic trends for this species [5, 7, 21–23] and the bacterial pathogens that they vector; however, the breadth of these studies has been limited by geographical scope (1 to 3 states or provinces).…”

Occurrence and County-Level Distribution of Ticks (Acari: Ixodoidea) in Nebraska Using Passive Surveillance

“…However, the low number of submissions, coupled with our Þeld observations in Sioux and Dawes Co. (R. C. and S. M. S., unpublished data), suggest that either the distribution or abundance of the tick is restricted. In addition, American dog ticks and Rocky Mountain wood ticks occur sympatrically in northwest Nebraska, with potential for hybridization (Araya-Anchetta et al 2013). Further studies should address the presence and stability of hybridization zones and the possible ramiÞcations for disease pathogen transmission risk.…”

Natural hybridization of the ticks Ixodes persulcatus and Ixodes pavlovskyi in their sympatric populations in Western Siberia

“…Moreover, distribution ranges of closely related tick species often overlap, resulting in large sympatric zones. However, little data confirming interspecific hybridization in nature are available (Araya-Anchetta et al, 2013;Rees et al, 2003). This can be explained mostly by the difficulties in identifying hybrids, assuming that the first generation tick hybrids and backcrosses are often morphologically indistinguishable from one of the parental species (Barton, 2001;Rees et al, 2003).…”