Results
The Tshr gene of the common vole is 113,629 bp long and consists
of 8 introns and 9 exons (Fig. 2A). In this study we sequenced a
~1700 bp region around the beginning of exon 9,
comprising 829 bp of intronic and 849 bp of exonic sequences (Fig. 2B).
The predicted TSHR protein structure, based on the Microtus
arvalis genome (NCBI: txid47230, GCA_007455615.1), comprises seven
leucine-rich repeats, a hinge region and seven transmembrane domains
(Fig. 2C, D).
Forty-nine single nucleotide polymorphisms (SNPs) were detected (Table
S4, S5). Twenty-two intronic SNPs and 27 exonic SNPs were found, from
which 23 were synonymous. These SNPs were used to calculate the genetic
differentiation of the sampled populations. Pairwise multilocus
FST estimates ranged from FST = 0.000 to
0.978 (mean FST = 0.366, with 0 denoting no difference
and 1 referring to completely different populations), and reveal high
genetic differentiation between the populations sampled (Fig. 3). The
high FST values in this species are in agreement with
previous studies(Heckel, Burri, Fink, Desmet, & Excoffier, 2005;
MartĂnková et al., 2013). The structure of the observed population
differentiation suggests that not only population subdivision but also
natural selection may be an explanatory factor. Therefore, it was tested
whether the observed SNPs are associated with geographical location.
Genetic differentiation between Eastern and Western European populations
was larger (FST = 0.247 to 0.978, mean: 0.640) than
differentiation among Western European populations (FST= 0.016 to 0.467, mean: 0.234) and among Eastern European populations
(FST = 0.000 to 0.648, mean: 0.132), and strongly
depends on geographical distance and longitude (Figs. 3, S2, Table S5).
The constructed distance tree based on Tshr haplotypes (Fig. S2)
together with pairwise multilocus FST analysis (Fig. 3),
confirmed that the Western and Eastern European populations belong to
different genetic lineages. Given the genetic separation of these
lineages, it is appropriate to analyze Western and Eastern European
samples separately. To reveal possible patterns of association between
SNPs, heatmaps of pairwise linkage disequilibrium (LD) measurements were
generated (Fig. S3).