Characterisation of the Complete Mitochondrial Genome of Critically Endangered Mustela lutreola (Carnivora: Mustelidae) and Its Phylogenetic and Conservation Implications

In this paper, a complete mitochondrial genome of the critically endangered European mink Mustela lutreola L., 1761 is reported. The mitogenome was 16,504 bp in length and encoded the typical 13 protein-coding genes, two ribosomal RNA genes and 22 transfer RNA genes, and harboured a putative control region. The A+T content of the entire genome was 60.06% (A > T > C > G), and the AT-skew and GC-skew were 0.093 and −0.308, respectively. The encoding-strand identity of genes and their order were consistent with a collinear gene order characteristic for vertebrate mitogenomes. The start codons of all protein-coding genes were the typical ATN. In eight cases, they were ended by complete stop codons, while five had incomplete termination codons (TA or T). All tRNAs had a typical cloverleaf secondary structure, except tRNASer(AGC) and tRNALys, which lacked the DHU stem and had reduced DHU loop, respectively. Both rRNAs were capable of folding into complex secondary structures, containing unmatched base pairs. Eighty-one single nucleotide variants (substitutions and indels) were identified. Comparative interspecies analyses confirmed the close phylogenetic relationship of the European mink to the so-called ferret group, clustering the European polecat, the steppe polecat and the black-footed ferret. The obtained results are expected to provide useful molecular data, informing and supporting effective conservation measures to save M. lutreola.

Effect of intensity and duration of anthropic noises on European mink locomotor activity and faecal cortisol metabolite levels

Human activities involving noise emission can affect wild animals. European mink was exposed to road noise and human voice playbacks to analyse how sound intensity level and duration of both noises altered the time that individuals were active and if their faecal cortisol metabolite (FCM) levels varied. A Hierarchical Analysis Cluster was performed to established two mink groups with respect to both noise source type: short duration/low intensity (SL) and long duration/high intensity (LH). We performed General Linear Mixed Models to evaluate the variation in locomotor activity duration (s) and FCM (ng/g) levels, respectively. The results showed both road noise and human voices decreased locomotor activity duration in SL more sharply compared to LH, and human voices were the triggers that induced the most pronounced response to both exposure conditions. FCM levels increased in SL compared to LH during road noise while the opposite happened during human voices. Differences based on sex and age of individuals were observed. In conclusion, noise characteristics given by the sound type determined the variations in locomotor activity duration while noise exposure level determined the variations in FCM levels. Attention should be paid to noisy activities (e.g. recreational activities for visitors in protected natural areas) and loud groups of people to conserve wildlife, especially noise sensitive species.

Conservation Genetics and Gut Microbial Communities’ Variability of the Critically Endangered European Mink Mustela Lutreola: Implications for Captive Breeding Programs

Host’s fitness can be affected by its genotype and gut microbiota, defined as the microbes living in the host’s intestinal tract. This study explored how the genetic diversity of the host influences its bacterial communities in the context of captive breeding programs, for the critically endangered European mink (Mustela lutreola). As stated by the ecosystem on a leash model, loss of host genetic diversity may lead to changes in immunomodulation and will therefore induce modifications of the gut microbiota. We investigated variation in the gut bacteria through 16S rRNA metabarcoding, related to the genetic diversity of European mink held in captivity in two breeding centers representing separate breeding stocks originating from the western and eastern populations. The genetic diversity of the host was assessed through diversity analysis of the adaptive MHC class I and II genes as well as neutral microsatellite markers. Results indicate lower diversity in neutral and MHC class I genes for the western population, and the opposite for MHC class II. A lower MHC class II gene variability led to an increase in microbial phylogenetic diversity and in abundance depending on the presence of specific MHC-II motifs. Those results seem to be linked to management practices that differs between the two programs, especially the number of generations in captivity. Long term Ex situ conservation practices can thus modulate gut microbial communities, that might potentially have consequences on the survival of reintroduced animals. We suggest strategies to foster genetic diversity in captive breeding program to mitigate the effects of genetic drift on those small, isolated populations.

A Microbial Tale of Farming, Invasion and Conservation: On the Gut Bacteria of European and American Mink in Western Europe

One of the threats that the critically endangered European mink (Mustela lutreola) faces throughout its relict range, including the occidental population, is the impact of the American mink (Mustela vison) invasion in its natural habitat. We aimed to explore the differences in microbiota and genetic diversity between European and American mink to test phylosymbiosis theory. We investigated the gut microbiota composition of European and American mink in a controlled environment (captive breeding compounds and fur farms respectively) to account for the impact of the environment on gut bacterial composition. We compared them to the gut microbiota of both mink species in the natural environment across multiple habitats. Our exploratory results showed differences between free-ranging and captive individuals, with more extreme changes in American mink compared to European mink. However, feral American mink from a long-established population exhibited gut bacterial composition closer to the free-ranging native species compared to more recently established feral populations. This result could be explained by dietary shifts in the area sampled based on prey availability through different landscape, but also to a lesser extent due to greater genetic differentiation. This exploratory work contributes to the scarce literature currently available on the dynamics between gut microbiota and mammal invasion.

A Meta-Analytical Investigation of the Gap between Measured and Predicted Inter-Population Genetic Diversity in Species of High Conservation Concern—The Case of the Critically Endangered European Mink Mustela lutreola L., 1761

Although properly designed sampling in population genetic studies is of key importance for planning evidence-informed conservation measures, sampling strategies are rarely discussed. This is the case for the European mink Mustela lutreola, a critically endangered species. In order to address this problem, a meta-analysis aiming to examine the completeness of mtDNA haplotype sampling in recent studies of M. lutreola inter-population genetic diversity was conducted. The analysis was performed using the sample-size-based rarefaction and extrapolation sampling curve method for three populations—the Northeastern (Russia, Belarus and Estonia), the Western (France and Spain), and the Southeastern (Romania). The extrapolated values of the Shannon–Wiener index were determined, assuming full sample coverage. The gap between the measured and predicted inter-population genetic diversity was estimated, indicating that the identified level of sample coverage was the lowest for the NE population (87%), followed by the SE population (96%) and the W population (99%). A guide for sampling design and accounting for sampling uncertainty in future population genetic studies on European mink is provided. The relatively low sample coverage for the Russian population clearly indicates an urgent need to take conservation measures for European mink in this country.

Behavioral responses of the European mink in the face of different threats: conspecific competitors, predators, and anthropic disturbances

Prey species assess the risk of threat using visual, olfactory, and acoustic cues from their habitat. Thus, they modify their behavior in order to avoid encounters with competitors, predators, and human disturbances that endanger their fitness. European mink (Mustela lutreola) is a critically endangered species that can be preyed upon by larger carnivores and displaced by dominant conspecifics to areas of lower quality, e.g., near to more anthropized localities which may be noisier. In this study, the behavioral responses of 24 European mink were evaluated by conducting an experiment in which the presence of a conspecific competitor was simulated with a visual cue (mirror) and the presence of predators (terrestrial and aerial) with odorous cues. Additionally, they were also exposed to potential sources of anthropic disturbance with acoustic cues (road traffic noise and human voices). Our results showed that European mink were hidden for longer periods of time due to the presence of conspecifics and being exposed to the fecal odors of a terrestrial predator such as dog, but especially when they were exposed to anthropic noises. In the presence of a conspecific, the females and the subadults were the ones who remained hidden for the longest time. As well, they were hidden for longer periods of time due to the presence of conspecifics but in combination with dog feces and anthropic sounds did not induce variations in the response, as both by themselves already triggered an increase in the time they spent hiding. The vigilance model showed the effects of the same factors as the hiding model, but with antagonistic effects in the case of vigilance time which decreased during anthropic noises exposition. Finally, we want to highlight that European mink showed an innate response favorable to all three types of threats, but attention should be focused on human disturbances—as they trigger the most extreme responses—which may affect the rate of survival of this threatened species.

Fifty Years of Research on European Mink Mustela lutreola L., 1761 Genetics: Where Are We Now in Studies on One of the Most Endangered Mammals?

The purpose of this review is to present the current state of knowledge about the genetics of European mink Mustela lutreola L., 1761, which is one of the most endangered mammalian species in the world. This article provides a comprehensive description of the studies undertaken over the last 50 years in terms of cytogenetics, molecular genetics, genomics (including mitogenomics), population genetics of wild populations and captive stocks, phylogenetics, phylogeography, and applied genetics (including identification by genetic methods, molecular ecology, and conservation genetics). An extensive and up-to-date review and critical analysis of the available specialist literature on the topic is provided, with special reference to conservation genetics. Unresolved issues are also described, such as the standard karyotype, systematic position, and whole-genome sequencing, and hotly debated issues are addressed, like the origin of the Southwestern population of the European mink and management approaches of the most distinct populations of the species. Finally, the most urgent directions of future research, based on the research questions arising from completed studies and the implementation of conservation measures to save and restore M. lutreola populations, are outlined. The importance of the popularization of research topics related to European mink genetics among scientists is highlighted.

High Trophic Niche Overlap between a Native and Invasive Mink Does Not Drive Trophic Displacement of the Native Mink during an Invasion Process

The pressure elicited by invasive species on native species significantly increases with the increase of the overlap of their ecological niches. Still, the specific mechanisms of the trophic displacement of native species during the invasion process are unclear. The effects of the invasive American mink (Neovison vison) on the critically endangered European mink (Mustela lutreola) was assessed by analyses of diet and niche overlap during the invasion process. To do this, the isotopic composition (δ13C and δ15N) of both species of mink and their four main types of prey was analysed. Significant trophic overlap between the native European mink and invasive American mink was found when they coexisted in sympatry. Furthermore, both mink species were characterised by significant individual variation in diet and no obvious change in diet of the native species in response to the arrival of the introduced species was observed. High niche overlap registered between both species in sympatry with no displacement in diet of the native mink in response to the arrival of the invasive mink is expected to have important consequences for the viability and conservation of the native mink populations, as it suggests high competitive pressure.