Genetic discontinuities in a continuously distributed and highly mobile ungulate, the Norwegian moose

Abstract

Many species with currently continuously distributed populations have histories of geographic range shifts and successive shifts between decline or fragmentation, growth and spatial expansion. The moose (Alces alces) colonised Scandinavia after the last ice age. Historic records document a high abundance and a wide distribution across Norway in the middle ages, but major decline and fragmentation in the eighteenth and nineteenth centuries. After growth and expansion during the twentieth century, the Norwegian population is currently abundant and continuously distributed. We examined the distribution of genetic variation, differentiation and admixture in Norwegian moose, using 15 microsatellites. We assessed whether admixture has homogenised the population or if there are any genetic structures or discontinuities that can be related to recent or ancient shifts in demography or distribution. The Bayesian clustering algorithm STRUCTURE without any spatial information showed that there is currently a genetic dichotomy dividing the population into one southern and one northern subpopulation. Including spatial information, the Bayesian clustering algorithm TESS, which considers gradients of genetic variation and spatial autocorrelation, suggests that the population is divided into three subpopulations along a latitudinal axis, the southern one identical to the one identified with STRUCTURE. Present convergence zones of high admixture separate the identified subpopulations, which are delimited by genetic discontinuities corresponding to geographic barriers against dispersal, e.g. wide fiords and mountain ranges. The distribution of the subpopulations is supported by spatial autocorrelation analysis. However, some loci are not in Hardy-Weinberg equilibrium and the STRUCTURE analysis suggests that a lower hierarchical structure may exist within the southernmost subpopulation. No bottlenecks or founder events are indicated by the levels of genetic variation, rather a high degree of private alleles in the northern subpopulations indicates introgression. Coalescent-based Approximate Bayesian Computation estimates unambiguously suggest that the genetic structure is a result of an ancient divergence event and a more recent admixture event a few centuries ago. This indicates that the central Scandinavian subpopulation constitutes a relatively recent convergence zone of secondary contact.

Diverse rates of gene flow and long-distance migration in two moose Alces alces subpopulations in Europe

“…A significant migration barrier was also detected within the Scandinavian Peninsula, and this could be a consequence of the Scandinavian Mountain range (the Scandes), which has a maximum elevation of 2469 m a.s.l. Significant genetic substructuring of the Scandinavian moose subpopulation was also reported earlier by Haanes et al (2011) and Niedziałkowska et al (2016).…”

Admixture promotes genetic variation in bottlenecked moose populations in eastern Poland

“…For the total sample, the observed heterozygosity (H O ) ranged from 0.594 (locus McM58) to 0.770 (locus MAF46), averaging 0.769 across loci, while expected heterozygosity (H E ) ranged from 0.688 (MAF70) to 0.874 (BM1225; Table 2). Among all the moose populations studied so far, average H E across loci was highest in eastern Poland (0.781; Table 2): slightly higher than in the moose population from Finland (Kangas et al 2013) and considerably higher than in other moose populations from Sweden (Charlier et al 2008), Norway (Haanes et al 2011), Alaska (Schmidt et al 2009), and Canada ; Table 2). Although we examined about three times fewer individuals than in the Norwegian study and despite our samples represented a much smaller area, the H E value we obtained for eastern Poland was somewhat higher than for the population in Norway (0.630-0.650; Haanes et al 2011).…”

“…Among all the moose populations studied so far, average H E across loci was highest in eastern Poland (0.781; Table 2): slightly higher than in the moose population from Finland (Kangas et al 2013) and considerably higher than in other moose populations from Sweden (Charlier et al 2008), Norway (Haanes et al 2011), Alaska (Schmidt et al 2009), and Canada ; Table 2). Although we examined about three times fewer individuals than in the Norwegian study and despite our samples represented a much smaller area, the H E value we obtained for eastern Poland was somewhat higher than for the population in Norway (0.630-0.650; Haanes et al 2011). In moose populations from eastern Poland, we also identified one of the highest value of allelic richness (A R =6.363; Table 2), being smaller that in Norway only (Haanes et al 2011).…”

“…Knowledge of genetic structure is an essential element of wildlife management and conservation (Haanes et al 2011). The population genetics and evolutionary history of ungulates, a group of ecologically, socially, and economically important species, have received much attention (e.g., Hundertmark et al 2002;Świsłocka et al 2013;Queiros et al 2014).…”

“…Despite the biological and socioeconomic importance of moose, only a few studies have used microsatellite loci to examine population genetic structure and diversity for European moose populations (Charlier et al 2008;Haanes et al 2011;Kangas et al 2013). Microsatellites have been considered the markers of choice because they are highly polymorphic, codominant, and amenable to PCR technique (e.g., Kohler et al 2011).…”