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The European mink (Mustela lutreola) is one of the most threatened small carnivores, listed as Critically Endangered on the IUCN Red List. Tallinn Zoo started a conservation breeding operation in 1980, which in 1992 was shaped into the European mink EEP Program to maintain a demographically and genetically healthy population in captivity. Since 2000, mink have been translocated on a yearly basis from the breeding facility in the zoo to Hiiumaa Island (Estonia) until the formation of the wild island population in 2016. Maintaining a healthy genetic structure in a captive population was a priority, so genetically the least valuable animals, according to calculations made by a population management program, were used for translocation. This study aims to assess the amount of genetic diversity passed from an ex situ population on to the island population. Comparisons of the genetic diversity were made by mitochondrial, microsatellite and nuclear markers. In addition, our results were combined with the pedigree data from the European mink EEP Studbook to further evaluate the flow of genetic diversity from the founder population to the established wild population. According to the findings, the island population's allelic richness was comparable to that of the founder population, and no evidence was found that its genetic structure had diverged from that of the founder population. It seems that the formation of the island population has been a gradual process of no more than the last seven yearly translocations., (© 2023 Wiley Periodicals LLC.)

Founding captive populations is often the last chance for saving endangered species from extinction. Ensuring successful reproduction is typically most critical for the maintenance of captive populations, with purposeful selection of individuals for breeding being one of the crucial aspects. Comparable cross-species data on the determinants of reproduction success are most useful for solving problems in captive species programs. In the present study, we provide an overview of a 20-year captive breeding program of the critically endangered European mink. The mating season starts in March, reaching its peak in the middle of April. The average gestation length was 43.8days (mode 43), the mean litter size being 4.4 (mode 4). Litter size and cub survival were negatively correlated with maternal age but this effect was entirely due to the lower performance of the females over 4 years of age. Female body weight also showed a positive correlation with litter size, with the weight itself having increased by 10% during the 20- year period. We did not find any signs of a cost of reproduction: the number of litters the female had delivered earlier in her life did not have an effect on her litter size in the focal year. Beyond the effect of age and size, individual females did not differ in litter sizes. Consistently, we found the heritability of litter size to be low. We conclude that, when selecting females for breeding, there is little need to consider aspects other than genetic relatedness crucial for avoiding progressive inbreeding., (Copyright © 2017 Elsevier B.V. All rights reserved.)

This study examined the reproductive physiology of female European mink (Mustela lutreola) to augment the available information on estrus, ovulation, and pregnancy with the long-term goal of supporting ex situ breeding management of this highly endangered species. Fecal reproductive hormone metabolites were measured using EIAs for estrogen and 20-oxo-pregnane metabolites. Seasonal hormone profiles were established. A comparison of hormone fluctuations in pregnant and nonpregnant females showed that both estrogen and 20-oxo-pregnane metabolites were significantly elevated during gestation, which is 42 days in length. Delayed implantation or embryonic diapause does not occur in this species. Litter size was correlated with 20-oxo-pregnane levels but not with estrogen concentrations. During lactation, 20-oxo-pregnane metabolite levels remained higher than in nonpregnant females. The breeding season was characterized by peaks in vaginal cornified cells and fecal estrogen metabolite levels. Up to four peaks in estrogen levels were identified and confirmed that European mink are seasonally polyestrous. The results of 20-oxo-pregnane measurements indicated that hCG can be applied to induce ovulation. With the establishment of this noninvasive method, we present a new tool to support population management of this species., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Non-human animal personality is defined as consistent behavioural differences across time and situations/contexts. Behaviours are, however, often plastic and to explain how plasticity and personality may coexist an adaptive framework has been developed. Still, there is little information on how personality is impacted by situations and contexts on an individual level. We investigated this in the European mink (Mustela lutreola) by performing a set of five experiments in two situations consisting of non-breeding and breeding season, and by using different test contexts. Three personality trait domains were identified; boldness, exploration and sociability. The levels of boldness and exploration changed between seasons but remained repeatable, which implies behavioural reaction norms and supports that the concept of personality remained applicable despite plasticity. Whilst males became bolder and more explorative in the breeding season females became shyer, which reflects European mink breeding behaviour. Furthermore, behaviours performed in mirror stimulus tests fell into different domains depending on whether, the test was conducted in the own territory or not, suggesting plasticity in the response towards conspecifics. To conclude, our results highlight the importance of situation and context for the expression of personality, and the significance of measuring multiple personality trait domains with several methods., (Copyright © 2013 Elsevier B.V. All rights reserved.)

High among-individual variation in mating success often causes problems in conservation breeding programs. This is also the case for critically endangered European mink and may jeopardize the long-term maintenance of the species' genetic diversity under the European mink EEP Program. In this study, breeding success of wild and captive born European minks at Tallinn Zoological Garden are compared, and the mating behavior of the males is analyzed. Results show that wild born males successfully mate significantly more often than captive born males (89% and 35%, respectively). On the basis of an extensive record of mating attempts, both male aggressiveness and passivity are identified as primary causes of the observed mating failures. All other potential determinants have only a minor role. Mating success as well as a male's aggressiveness and passivity are shown to depend more strongly on the male than the female partner. We did not find any evidence that the behavior of an individual is dependent on the identity of its partner. We suggest that aggressiveness and passivity are two expressions of abnormal behavior brought about by growing up in captivity: the same individuals are likely to display both aggressive and passive behavior. The results point to the need to study and modify maintenance conditions and management procedures of mink to reduce the negative impact of the captive environment on the long-term goals of the program., (© 2013 Wiley Periodicals, Inc.)

Human-mediated global change will probably increase the rates of natural hybridization and genetic introgression between closely related species, and this will have major implications for conservation of the taxa involved. In this study, we analyse both mitochondrial and nuclear data to characterize ongoing hybridization and genetic introgression between two sympatric sister species of mustelids, the endangered European mink (Mustela lutreola) and the more abundant polecat (M. putorius). A total of 317 European mink, 114 polecats and 15 putative hybrid individuals were collected from different localities in Europe and genotyped with 13 microsatellite nuclear markers. Recently developed Bayesian methods for assigning individuals to populations and identifying admixture proportions were applied to the genetic data. To identify the direction of hybridization, we additionally sequenced mtDNA and Y chromosomes from 78 individuals and 29 males respectively. We found that both hybridization and genetic introgression occurred at low levels (3% and 0.9% respectively) and indicated that hybridization is asymmetric, as only pure polecat males mate with pure European mink females. Furthermore, backcrossing and genetic introgression was detected only from female first-generation (F1) hybrids of European mink to polecats. This latter result implies that Haldane's rule may apply. Our results suggest that hybridization and genetic introgression between the two species should be considered a rather uncommon event. However, the current low densities of European mink might be changing this trend., (© 2011 Blackwell Publishing Ltd.)