Morphological variation of introduced species: The case of American mink (Neovison vison) in Spain

We studied the morphology of American mink Neovison vison in five out of the six introduced populations in Spain. The spatial and temporal variation of body weight (BW), body length (BL), tail length, hind-foot length and ear length were analysed. Temporal trends in BW and BL in relation to years since mink introduction were also analyzed. In addition, we tested the effect of sex, age (juvenile, subadult and adult) and age–sex interaction, on each parameter. Morphological parameters differed between populations, illustrating the high variability of body size of American mink in different environments, and the phenotypic plasticity of the species. Annual variations were synchronized between populations, suggesting a large-scale effect on all of them. BW and BL showed a decreasing trend in both males and females in relation to years since introduction. This decrease may be related to mink's diet. Differences in sex and age were found, pointing to sexual dimorphism in adults, subadults and juveniles. The dimorphism in non-adult individuals suggests that subadult males may have a competitive advantage from subadult females in feeding and/or hunting on bigger prey from an early age (resource partitioning hypothesis).     

Inbreeding affects fecundity of American mink (Neovison vison) in Danish farm mink

Inbreeding is an increasing problem in farmed mink, because of limited exchange of individuals between farms. In this study, genetic relatedness within seven American mink (Neovison vison) colour strains originating from 13 different mink farms in Denmark was analysed using 21 polymorphic microsatellite loci. We detected large differences in the level of relatedness (range 0.017-0.520) within colour strains. Moreover, a very strong and highly significant negative correlation between the level of relatedness and fecundity was observed (r = 0.536, P < 0.001) [Correction added after online publication on 9 March 2011: r(2) has been changed to r]. To our knowledge, this is the first time that such a correlation has been demonstrated for commercially farmed mink.     

Hybridization between escaped domestic and wild American mink (Neovison vison)

The release of domesticated organisms into natural populations may adversely affect these populations through predation, resource competition, and the introduction of disease. Additionally, the potential for hybridization between wild and domestic conspecifics is of great concern because it can alter the evolutionary integrity of the affected populations. Wild American mink ( Neovison vison ) populations may be threatened not only by competition for resources with domestic mink originating from farms, but by breeding with such escapees. Using 10 microsatellite loci, we genotyped mink from Ontario, Canada, sampled from two farms, two putatively mixed populations in regions surrounding the mink farms, and two wild populations with no recent history of mink farming. Using individual-based Bayesian population assignment, we identified four population clusters, including one wild, and three domestic populations. The latter were not clustered by farm but rather by distinct line-bred colour phases. Population clustering also identified domestic and hybrid mink in the free-ranging populations. Nearly two-thirds of the mink sampled in the two putatively mixed populations (78% and 43%) were either farm escapees or descendants of escapees. Principal components analysis of allele frequencies supported our Bayesian assignment results. The power of our assignment test was assessed using simulated hybrid genotypes which suggested that our overall correct classification rate was 96.2%. The overwhelming presence of domestic animals and their hybridization with mink in natural populations is of great concern for the future sustainability of wild mink populations.     

Parasitic helminths of free-ranging mink (Neovison vison mink) from southern Florida

Five free-ranging mink, Neovison vison mink, from in or near the Fakahatchee Strand Preserve State Park, Collier County, Florida (26 degrees 00'N, 81 degrees 25'W), were examined for parasitic helminths. Nine species of helminths were identified (2 trematodes, 5 nematodes, and 2 acanthocephalans). The most prevalent parasites were Molineus patens (4 of 5 mink), mean intensity 173 (range, 12-342); Strongyloides sp. (4 of 5), mean intensity 48 (range, 1-170); Macracanthorhynchus ingens (immature) (4 of 5), mean intensity 2.5 (range, 1-4); and Alaria mustelae (3 of 5), mean intensity 59.3 (range, 11-127). Polymorphus brevis and Dirofilaria lutrae are reported from the mink for the first time.     

Exclusion of candidate genes for coat colour phenotypes of the American mink (Neovison vison)

In a previous project, we screened the American mink Bacterial Artificial Chromosome library, CHORI‐231, for genes potentially involved in various coat colour phenotypes in the American mink. Subsequently, we 454 sequenced the inserts containing these genes and developed microsatellite markers for each of these genes. Here, we describe a lack of association between three different ‘roan‐type' phenotypes represented by Cross, Stardust and Cinnamon in American mink and six different genes that we considered to be potentially linked to these phenotypes. Thus, c‐KIT (HUGO‐approved symbol KIT), ATOH‐1 (HUGO‐approved symbol ATOH1) and POMC were excluded as potential candidates for these three phenotypes. In addition, MITF and SLC24A5 were excluded for Cross and Cinnamon, and KITL (HUGO‐approved symbol KITLG) for Cross and Stardust. Although most of these genes have been implicated as the cause of similar phenotypes in other mammals, including horses, pigs, cows, dogs, cats, mice and humans, they do not appear to be responsible for comparable phenotypes found in American mink.     

Muskrat (Ondatra zibethicus) decline after the expansion of American mink (Neovison vison) in Poland

Field survey data in Central Poland revealed that the proportion of sites inhabited by muskrats decreased from 44% to 7% over one decade. This corresponded to the decline in hunting bags of muskrat over the whole of Poland. The largest hunting harvest of muskrat was recorded in 1987/1988 (66,416 individuals), the smallest in 2007/2008 (4,567 individuals). The decline in hunting bags occurred in all regions analysed; however, it was most rapid in the north and north-east. Before the expansion of mink, which started in northern Poland at the beginning of the 1980s, muskrat densities in particular regions depended on the availability of aquatic habitats. A comparison of hunting bags of muskrat and American mink in years 2002–2008 indicated a significant negative correlation between the numbers of these two species harvested in seven regions of Poland. The negative correlation between numbers of muskrat and mink suggests that mink predation is one of the most important factors in the decline of the muskrat population in Poland.     

Albinism in the American mink (Neovison vison) is associated with a tyrosinase nonsense mutation

Albino phenotypes are documented in various species including the American mink. In other species the albino phenotypes are associated with tyrosinase (TYR) gene mutations; therefore TYR was considered the candidate gene for albinism in mink. Four microsatellite markers were chosen in the predicted region of the TYR gene. Genotypes at the markers Mvi6025 and Mvi6034 were found to be associated with the albino phenotype within an extended half-sib family. A BAC clone containing Mvi6034 was mapped to chromosome 7q1.1-q1.3 by fluorescent in situ hybridization. Subsequent analysis of genomic TYR sequences from wild-type and albino mink samples identified a nonsense mutation in exon 1, which converts a TGT codon encoding cysteine to a TGA stop codon (c.138T>A, p.C46X; EU627590). The mutation truncates more than 90% of the normal gene product including the putative catalytic domains. The results indicate that the nonsense mutation is responsible for the albino phenotype in the American mink.     

Wild mink (Neovison vison) as sentinels in environmental monitoring

Superficial inguinal lymph nodes from 72 wild boars examined in a previous immunohistochemical (IHC) study on porcine circovirus type 2 (PCV2) were selected for a PCV2 polymerase chain reaction (PCR) analysis. Four of these lymph nodes were PCV2-IHC strongly positive with PMWS histological lesions (outcome 1), 6 weak to mild PCV2-IHC positive without PMWS histological lesions (outcome 2) and 62 PCV2-IHC negative. Considering IHC the gold standard for diagnosis, the aims of the study were to evaluate the suitability of the PCV2-DNA extraction from formalin-fixed and paraffin-embedded (FFPE) tissue and the sensitivity and specificity of PCR under two IHC interpretations criteria: (A) the sample was considered positive if the result was outcome 1; (B) the sample was considered positive if the result was outcome 1 or 2. Under (A) criteria, sensitivity and specificity of PCR were 100% and 89.7%, respectively; the Cohen's Kappa coefficient was 0.49. Under (B) criteria, sensitivity and specificity of PCR were 80.0% and 95.2%, respectively; the Cohen's Kappa coefficient was 0.72. The high Cohen's Kappa coefficient under the (B) interpretative criteria indicates good agreement between the two methods. In conclusion, 1) DNA extracted from FFPE specimens of wild boar is suitable for PCR and further represents a screening test for PCV2/PCVD (PCV2 Diseases) investigations in wild boar as well; 2) routine histological sampling can also be useful for PCV2 virological studies in wild boar.     

A foe in woe: American mink (Neovison vison) diet changes during a population decrease

The invasive American mink has been a component of Iceland's fauna since the 1930s. Hunting statistics indicate that until 2003 the population size was increasing, but thereafter decreased rapidly. The Icelandic marine environment has experienced various changes in recent years, including rising sea temperature and sand-eel collapse followed by seabird recruitment failure and population declines. Furthermore the arctic fox population has increased at least six-fold in the last three decades. Mink stomach content analysis in the period 2001–2009 revealed diet changes, and signs of reduced prey availability for this generalist predator, that were most significant in males. The most marked shift in composition was a decrease in consumption of birds. Our findings suggest that climate events, together with competition with increasing numbers of arctic foxes over terrestrial food, contributed to the sharp reduction in the mink population from 2004 and onwards. Despite their generalist behaviour, mink have apparently failed to respond fully to these environmental changes, and this susceptibility may benefit attempts to control their numbers. The results are relevant to the ability of top predators in general to cope with diverse ecosystem alterations triggered by climate change.     

Dynamics in space use of American mink (Neovison vison) in a fishpond area in Northern Germany

Telemetry of American mink Neovison vison revealed seasonal and sexual variations in home-range size, intersexual- and partially intrasexual range overlaps and spatial dynamic of territorial system. From 2003 to 2006, 14 mink (nine males and five females) were radio-tracked in a fishpond area in northern Germany. We observed comparatively large home ranges. Both sexes reduced their large summer home ranges to smaller ones in the winter period. In both seasons, male mink used significantly larger areas than female mink. During the mating season, males considerably enlarged their home ranges and roamed nearly through the entire study area. These variations and diversity of range size were discussed in connection with thermoregulatory behaviour, prey availability and distribution, population density and stability of the social system. Analysing intraspecific static interactions, we observed high intersexual overlapping rates in both the summer and winter periods. But there were no or rather very low levels of intrasexual overlapping. However, in the summer period, large home ranges of neighbouring males also overlapped to some extent, but temporal avoidance of adjacent territory holders was observed. Consequently, our results reveal intrasexual territoriality, with males having larger territories, overlapping those of females. The shifting of stable temporary home ranges observed within one season or between the same seasons of consecutive years demonstrates the highly dynamic nature of spatial behaviour among American mink. All these recorded characteristic features of spatial behaviour should be considered when planning mink control projects and measures for the management of this invasive carnivore.     

The effects of estradiol and catecholestrogens on uterine glycogen metabolism in mink (Neovison vison)

Glycogen is a uterine histotroph nutrient synthesized by endometrial glands in response to estradiol. The effects of estradiol may be mediated, in part, through the catecholestrogens, 2-hydroxycatecholestradiol (2-OHE2) and 4-hydroxycatecholestradiol (4-OHE2), produced by hydroxylation of estradiol within the endometrium. Using ovariectomized mink, our objectives were to determine the effects of estradiol, 4-OHE2, and 2-OHE2 on uterine: 1) glycogen concentrations and tissue localization; 2) gene expression levels for glycogen synthase, glycogen phosphorylase, and glycogen synthase kinase-3B; and 3) protein expression levels for glycogen synthase kinase-3B (total) and phospho-glycogen synthase kinase-3B (inactive). Whole uterine glycogen concentrations (mean ± SEM, mg/g dry wt) were increased by estradiol (43.79 ± 5.35), 4-OHE2 (48.64 ± 4.02), and 2-OHE2 (41.36 ± 3.23) compared to controls (4.58 ± 1.16; P ≤ 0.05). Percent glycogen content of the glandular epithelia was three-fold greater than the luminal epithelia in response to estradiol and 4-OHE2 (P ≤ 0.05). Expression of glycogen synthase mRNA, the rate limiting enzyme in glycogen synthesis, was increased by 4-OHE2 and 2-OHE2 (P ≤ 0.05), but interestingly, was unaffected by estradiol. Expression of glycogen phosphorylase and glycogen synthase kinase-3B mRNAs were reduced by estradiol, 2-OHE2, and 4-OHE2 (P ≤ 0.05). Uterine phospho-glycogen synthase kinase-3B protein was barely detectable in control mink, whereas all three steroids increased phosphorylation and inactivation of the enzyme (P ≤ 0.05). We concluded that the effects of estradiol on uterine glycogen metabolism were mediated in part through catecholestrogens; perhaps the combined actions of these hormones are required for optimal uterine glycogen synthesis in mink.     

Odontologic anomaly in the American mink Neovison vison (Carnivora, Mustelidae) and possible reasons for its appearance

The paper describes the phenomenon of substitution of the reduced M₂ with a tooth of a complex structure in the American mink Neovison vison Schreber. The anomaly is observed on three skulls out of the 574 examined (0.52%) and is characterized by a clear localization, identical structure, and symmetrical manifestation. Atypical molars have two roots, equally well-developed paraconid, eokonid, hypoconid, and a less pronounced metaconid. Some possible hypotheses for the anomaly that are considered include disruption in the development of the dental germ, mutation, and phenotypic expression of genes that are characteristic of plesiomorphic species of mustelids. The substantiated viewpoint is that the cause of this phenomenon may be the “awakening of dormant genes” as a result of destabilizing selection and hybrid dysgenesis in the area of contact of farm and feral American minks.     

A comparative, BAC end sequence enabled map of the genome of the American mink (Neovison vison)

In this report we present the results of the analysis of approximately 2.7 Mb of genomic information for the American mink (Neovison vison) derived through BAC end sequencing. Our study, which encompasses approximately 1/1000^th of the mink genome, suggests that simple sequence repeats (SSRs) are less common in the mink than in the human genome, whereas the average GC content of the mink genome is slightly higher than that of its human counterpart. The 2.7 Mb mink genomic dataset also contained 2,416 repeat elements (retroids and DNA transposons) occupying almost 31% of the sequence space. Among repeat elements, LINEs were over-represented and endogenous viruses (aka LTRs) under-represented in comparison to the human genome. Finally, we present a virtual map of the mink genome constructed with reference to the human and canine genome assemblies using a comparative genomics approach and incorporating over 200 mink BESs with unique hits to the human genome.     

Reproductive aspects of American minks (Neovison vison) in central Spain: Testing the effects of prey availability

Some reproductive components of fitness (breeding times, litter size and the proportion of breeding females per year) of two feral populations of American minks in central Spain were investigated by means of direct observation from 2006 to 2010. The effects of prey availability were explored. Mating season was from February to March. Parturition dates did not differ between the two sites and pooled births took place between April (33.3%) and July (2.8%), peaking in May (40.3%). Mean litter size (the number of small cubs following their mother) was 3.43 ± 1.01 cubs (±SD; n = 30) with statistical significant differences between the two study sites. The strong seasonality in births and differences in litter size were related to prey availability (i.e. these are food-limited life-history traits), but in a complex non-linear fashion. A minimum value of prey abundance is necessary to breed. While litter size rises with prey abundance, there is a point where increasing prey did not result in an increase in litter size. Up to 75% of the females in the breeding pool reared cubs each year in both areas, which represents a somewhat high pool of breeding females. Delayed implantation is shorter than a month or does not exist in these populations. Such a short time-span seems to emerge because longer delays would have an important fitness cost to females. The breeding calendar and the litter size were similar to that reported previously from other areas.