Circumpolar phylogeography of the northern pike (Esox lucius) and its relationship to the Amur pike (E. reichertii)

Abstract

Background: Freshwater fishes of the genus Esox are found throughout the Holarctic region. The northern pike (E. lucius) has a circumpolar distribution whereas the assumed sister species the Amur pike (E. reichertii) is only found in the Amur region. The genetic structure and post-glacial dispersal of these species are not well known. Here, we use sequence variation at two mitochondrial DNA regions (cytb and D-loop) to investigate the phylogeography, infer location of glacial refugia and investigate the time of divergence and potential demographic expansion of the various clades detected. Results: The two species did not share haplotypes implying long-term isolation with no gene flow, and divergence of the taxa were estimated at 4.55 Myr. The northern pike mtDNA haplotypes revealed three main lineages. One of the northern pike mtDNA lineages was found throughout the entire Holarctic region suggesting transcontinental dispersal from a single refugium. The three lineages exhibited a star phylogeny, indicating population expansion following isolation in separate glacial refugia. Estimated time of divergence of these lineages was 0.18 -0.26 Myr.Conclusions: The precise location of the glacial refugia is uncertain, but our data suggests an Asian origin. The expansion of the circumpolar lineage is estimated to be around the end of the second glacial, implying that the current distribution is due to a recent recolonization from an east-Asian refugium. All three northern pike mtDNA lineages occurred sympatrically in Europe, possibly due to secondary contact. Two of the lineages probably originated from different European refugia, one in the Danube-region and one in Western Europe, the latter seems to be the primary source for recolonization of northern Europe.

Post-glacial dispersal patterns of Northern pike inferred from an 8800 year old pike (Esox cf. lucius) skull from interior Alaska

“…3) and is clearly referred to this species genetically, consistent with the morphological analyses. The D-loop sequence of the newly described specimen matches haplotype 'B' of Skog et al (2014) found across the Holarctic including a modern Alaskan sample and haplotype Eld7 (Maes et al, 2003) from Ontario, Canada. The Maes et al (2003) sequences were not included in the network analysis, as their inclusion led to too many sites with missing information.…”

“…In contrast, the timing and genetic affinity of the specimen documented here combined with documented distribution patterns of genetic diversity in modern populations of Northern pike (Skog et al, 2014;Lopez, unpublished data) suggest that Northern pike populations expanded rapidly following glacial retreat. There is no evidence reported to date that indicates the survival of Northern pike in Beringia through the habitat changes associated with Pleistocene glaciations.…”

“…However, available genetic data from across North America are sparse. Northern pike have consistently shown low within-population variation (Miller and Senanan, 2003;Skog et al, 2014). Low genetic variation within populations may result from compounding factors of low effective population size and bottlenecks (Miller and Senanan, 2003).…”

“…This could be explained by contact and gene flow between E. lucius from various refugia during Pleistocene glaciations (Raat, 1988;Miller and Senanan, 2003). Modern E. lucius samples have been placed into three mitochondrial DNA haplogroups, two of which are largely restricted to Europe and one that is found across the Holartic (Skog et al, 2014). These clades became separated~200,000 yrs BP and underwent a post-glacial expansion~100,000 yrs BP (Skog et al, 2014), although the location of the refugia for the late-middle Pleistocene glaciations for the Holarctic clade remain unclear.…”

“…Modern E. lucius samples have been placed into three mitochondrial DNA haplogroups, two of which are largely restricted to Europe and one that is found across the Holartic (Skog et al, 2014). These clades became separated~200,000 yrs BP and underwent a post-glacial expansion~100,000 yrs BP (Skog et al, 2014), although the location of the refugia for the late-middle Pleistocene glaciations for the Holarctic clade remain unclear. Drastic population declines on a time scale of several thousand years within European populations of E. lucius have been ascribed to either glacial bottlenecks or postglacial founder events (Jacobsen et al, 2005).…”