Evolutionary history

Reconstruction of the evolutionary history of the M. lutreola taxon is a very difficult task, due to the limited availability of fossil data, the phenomenon of natural hybridization with the European polecat and the associated ambiguity of phylogenetic analyzes, as well as because of very sparse written historical sources and archaeological sources concerning the species.
Small amounts of fossils of the European mink were found in the Upper Holocene layers. The remnants from late Pleistocene, found among others in Ukraine are much rarer. The Holocene bone remnants, dated 4,300-4,100 years ago, were described for the Vlaardingen site in the Netherlands. The remains of the M. lutreola from Poland were found in the sites from the early Iron Age and the period of Roman influence, including Biskupin. The bone remnants found in the “La Adam” cave in south-eastern Romania also come from the Holocene. In total, only 14 sites of bone remnants of the European mink were described in Europe, including Neolithic, four from the Iron Age and the period of Roman influence, and two from Middle Ages. For comparison, for the comparable period come reports about 900 finds of the M. meles, 472 of the Lutra lutra, 383 of the M. martes, 156 of the M. putorius, 117 of the M. Nivalis, 63 of the M. erminea and M. foina. Comparable amounts of bone remnants of the Gulo gulo (18) and the M. eversmanni (16) were found, while the figures were lower only for the M. zibellina (2) and the Vormela peregusna (6).
A small number of archaeological osteological sources in the sites of ancient human settlements is attributed to the assumption that meat of the European mink was not eaten by humans, and the animals were skinned directly in the hunting grounds or the flesh and bone remnants were eaten by dogs. Moreover, verification of reports of findings of bone fragments attributed to the European mink frequently proves that they belong to other species, mainly the European polecat.

Until recently there were two hypotheses explaining the evolutionary origins of the European mink. The former was based on the conviction – quite commonly held in the past – of phylogenetic closeness of the M. lutreola and the N. vison, supposedly manifested by a high morphological and ecological similarity of both species. This similarity was supposed to be original while the existing differences supposedly resulted from evolutionary divergence. Novikov believed that the American mink had evolved from the evolutionary line of the European mink, and the spatial separation of both species was due to the continental drift. On the other hand, Kurtén argued that both mink species originated in North America, and the European mink emigrated to Eurasia in the late Pleistocene. Hoffmann claims that this migration could begin in the middle Pleistocene, via a land bridge linking north-eastern Siberia with Alaska. Today both these hypotheses are outdated, primarily because of proven secondary nature of the phenotypic similarity between the European mink and American mink.

The latter hypothesis assumes European origins of the M. lutreola and is based on phylogenetic implantation of the European polecat, the steppe polecat and the Siberian weasel. In the context of scarcity of fossil evidence, Youngman stated that the European mink and the American mink had evolved independently in the periglacial fluvial environments of Europe and North America. Similar opinion was pronounced by Saint Girons who points out that the similarity between the two species resulted from evolutionary divergence, which, in turn, is the effect of their evolution in similar quaternary environments located south of areas covered with glacier. Validity of this hypothesis, which already has the status of theory, is firmly confirmed by the above-mentioned results of phylogenetic studies, which unambiguously place the M. lutreola taxon in the monophyletic clade, also including M. putorius, M. eversmanii, M. sibirica and M. itasi. This group corresponds to one of the group of species that evolved in the Asian taiga proposed by Hoffmann. The results of analyses of Flynn et al., as well as the results of the comparison of the complete mtDNA sequence allow to classify the M. nigripes as a member of the same group.

The close phylogenetic relationships between the European mink and the European polecat are also proved by the complete lack of the inter-species reproductive barrier between these taxa, expressed by spontaneous hybridization in nature. The common evolutionary history of the European mink and the European polecat is longer than the common evolutionary history of those two taxa and the American mink, which may also be confirmed by the already mentioned example of the insertion of short interspersed nuclear elements (SINE) in the flanking region of the microsatellite sequence Mel08. The sequence elements of SINE are classified as retrotransposons – their transposition is considered the unique evolutionary event, and their identification in orthologous loci in different species provide the huge amount of phylogenetic information. In the present case, the presence of the SINE element in the Mel08 loci proves that its transposition in the N. vison took place after separation of this species from the common evolutionary line of the M. putorius and the M. lutreola.

Marmi et al. formulated the extreme view on the systematic position of the European mink based on the similarity of the gene sequence for the mitochondrial cytochrome b and the microsatellite nuclear sequence Mel08. According to this view, the evolutionary divergence of the European polecat, the steppe polecat and the European mink is so low that these taxa should be ranked as subspecies within the species M. putorius.

It is assumed that the evolution of the genome of the European mink from the hypothetical Ancestral Carnivore Karyotype (ACK, 2n= 42), proposed by Murphy et al., included five centric fusions (Robertsonian translocations), three centric divisions and one pericentric chromosome inversion.

Separation of the evolutionary line of the European mink with the line of the M. itasi occurred about 2.4-2.8 million years ago, with the M. sibirica about 1.7-2.0 million years ago, with the M. nigripes about 1.1-1.3 million years ago, with the M. putorius and the M. eversmanni about 0.5-0.6 million years ago. Slightly different figures are given by Koepfli et al., who estimated the time of separation of the evolutionary line of the M. lutreola with the M. sibirica as about 1.6 million years ago, while with the M. nigripes, the M. putorius and the M. eversmanni as about 1.2 million years ago. Marmi et al. prove that the M. itatsi and the M. sibirica separated from the evolutionary line of polecats, including the European mink (the M. putroius, the M. eversmannii, the M. lutreola), about 0.7-0.4 million years ago, while the M. lutreola evolved from the evolutionary trunk common to the M. putorius and the M. eversmannii only about 150 thousand years ago. In the three mentioned reports, the separation of the M. sibirica, the M. nigripes, the M. putorius, the M. eversmanni and the M. lutreola is located in the Pleistocene. On the other hand, the separation of the evolutionary lines of genera Neovison and Mustela is dated back, based on molecular phylogenetics, about 14.0-6.0 million years ago. The study of Koepfli et al. clearly indicates the Eurasian origins of the European mink and its closest evolutionary relatives – the European polecat, the steppe polecat, the black-footed ferret, and the Siberian weasel. On the basis of molecular phylogenetics this is an additional argument against the first of the described hypotheses of the M. lutreola species. Hosoda et al. reached the similar conclusions and speculated that separation isolation of the M. lutreola and the M. eversmanii from the evolutionary line of the M. putorius was a speciation that occurred in Eurasia in a very recent evolutionary past (the Pleistocene) and which has just ended or is still ongoing. All the abovementioned evidences (the phylogenetic analysis, the possibility of hybridization with the European polecat, the absence of bone fragments in sediments older than the late Pleistocene) indicate that in an evolutionary sense the European mink is a young species. While phylogenetic analyzes make it possible to reconstruct the evolutionary history of the species at its inception, its subsequent phylogeographic history in the postglacial period (the Holocene) is much more difficult to trace.

The hitherto studies on the phylogenetics of the M. lutreola have been based on two research strategies: (1) genotyping based on the fragmentary sequence of nuDNA or mtDNA, or (2) the simultaneous analysis of nuclear genes and mitochondrial sequences. In order to obtain more information from the molecular data, and hence for greater appropriateness and credibility of the results of the phylogenetic analyzes based on these data it is postulated to conduct multigene analyses – or, more broadly, multilocus analyses – based on a large number of nucleotide sequences or single nucleotide polymorphisms (SNPs). Multilocus genotyping is also used in phylogeographic analyzes. The RAD-Seq (restriction site-associated DNA sequencing) technique, which allows for genotyping-by-sequencing, seems especially promising for phylogenetic and phylogeographic studies of the European mink.