The pine marten (Martes martes) is a medium-sized carnivore from the weasel family (Mustelidae); It is somewhat smaller than a house cat, normally weighing around one kilogram, with a slim, flexible body, strong springy limbs and long tail. It is generally brownish – anywhere from chocolate to tan – with a large contrasting yellowish patch on its neck. In winter, it grows thick, soft fur, which is why it has been among the most important furbearing species for centuries. It has an extensive range, stretching from Western Europe, including some of the British Isles, to the east across the Urals, reaching the Siberian rivers Irtysh and upper Ob; beyond that, it is replaced by its close relative, the sable (Martes zibellina), which occupies a very similar ecological niche. It is critically endangered in England and Wales, but is generally treated as Least Concern by IUCN. The pine marten is a fast and tenacious predator, targeting a variety of animals, from frogs, rodents and shrews to large birds, such as the capercaillie (Tetrao urogallus) – a strong, turkey-sized grouse. It also eats fruits, nuts, insects – and it is a notorious nest robber.
The pine marten has likely co-evolved with its main prey, the red squirrel (Sciurus vulgaris) – its excellent vestibular apparatus, semi-retractable claws, and long, bushy tail with longer guard hair than in any other marten are adaptations to fast-paced arboreal hunts. However, in one part of its range, it has become the savior of the squiggly reds. In Scotland, the red squirrel was pushed away from its original habitats by the larger, more aggressive grey squirrels (Sciurus carolinensis) – an introduced North American species. The tables turned when the pine marten, previously nearly eradicated by local gamekeepers for the sake of grouse hunters, made a comeback to its former range after the species was granted full protection in 1988. Since red squirrels are generally on a par with their nemesis in terms of tree top acrobatics, martens opted for easier prey and feast on the heavier, slower greys, clearing out the living space for the reds.
We present the chromosome-length assembly for yet another – but not the final – species in the genus Martes. All C-scaffolds (Lewin et al. 2019) of the pine marten were assigned to the corresponding chromosomes via a Zoo-FISH experiment with the stone marten chromosomes used as probes. Both the stone and pine marten have the same diploid number of chromosomes (2n=38) with no detected translocations, so we arranged the pine marten chromosomes in the same order as in the stone marten karyotype. Among other types of rearrangements only several inversions were found (Fig. 1).
We thank Dr. Rogell Powell (North Carolina State University) for funding 10x Genomics linked-read sequencing for the draft assembly and Dr. Klaus Koepfli for organizing this sequencing and bringing all of the collaborators together. Also we thank Sergei Pisarev, Pavel Reznichenko and Ksenia Koniaeva from the zoo “Lesnaya skazka” (eng. “Forest tale”) in Barnaul, Russia, who provided samples for a cell line. These cells were used for both DNA extraction for linked read sequencing and for HiC experiments. DNA extraction and Zoo-FISH experiments were performed by Natalia Serdyukova and Dr. Violetta Beklemisheva. The initial assembly was performed by Sergei Kliver. Hi-C experiments and scaffolding to chromosomes were done by Polina Perelman, Ruqayya Khan, David Weisz and Olga Dudchenko. The genome annotation and a paper describing this research is in progress.