Taxonomy and Systematics
Mustelidae (weasels and relatives) is the largest family in the order Carnivora. Mustelids are found on every continent except Antarctica and Australia (although Ermine [Mustela erminea] and Least weasels [Mustela nivalis] were introduced by humans to New Zealand). Larivère and Jennings (2009) recognized 57 mustelid species in 22 genera, but noted that future research could result in this number changing.
There has been considerable uncertainty about the position of the mustelids in the carnivoran tree, as well as about phylogenetic relationships within the Mustelidae. With regard to the first question, although the skunks and stink badgers (family Mephitidae) were long considered a subfamily within the Mustelidae, several independent molecular phylogenetic studies have now established that Mephitidae represents a distinct lineage that is basal to a clade that includes the Ailuridae (Red Panda) basally and the Procyonidae (raccoons and relatives) and Mustelidae as sister taxa (Eizirik et al. 2010; Nyakatura and Bininda-Emonds 2012; Sato et al. 2012). Relationships within the Mustelidae are less well resolved, although there have been quite a few molecular genetic studies attempting to infer these relationships. Some results appear to be quite consistent among these studies, such as the position of the American Badger lineage, subfamily Taxidiinae (which includes just one extant species, Taxidea taxus), as the most basal mustelid lineage, and the relationship of the subfamilies Lutrinae (otters) and Mustelinae (weasels) as sister taxa (for review, see Yu et al. 2011 and references therein). Although the precise relationships among them are not entirely resolved, eight mustelid subfamilies are generally recognized (e.g., Koepfli et al. 2008; Larivère and Jennings 2009; Yu et al. 2011), with the following list of included genera and number of species from Larivère and Jennings (2009):
American Badger (1 species, Taxidea taxus, found from southern Canada and the midwestern United States south [west of the Mississippi River] to central Mexico). In contrast to the group-living European Badgers, American Badgers are solitary.
Honey Badger (1 species, Mellivora capensis, found across much of Africa, with the exception of most of North Africa, and in southwestern Asia).
Eurasian badgers (Meles, 3 species, found in Europe and north-central and southeastern Asia). A 4thMeles species, formerly treated as a southwest Asian subspecies of the European Badger, was recognized by Del Cerro et al. (2010). All mustelids are solitary except for Eurasian badgers and some otter species.
Tayra (1 species, Eira barbara, found from Mexico south through Central America and much of South America north of Patagonia).
Wolverine (1 species, Gulo gulo, found across northern North America and northern Eurasia).
Martens and Fisher (Martes, 8 species; various species are found in North America, Europe, and Asia; in the 1950s, the Stone Marten [M. foina], of central and southern Europe and Asia, was accidentally introduced to Wisconsin in the United States, where it is now established at multiple localities). Larivère and Jennings (2009) noted that, in the context of recent data indicating that the genus Martes as currently formulated is paraphyletic unless the Fisher (M. pennanti) is excluded (Koepfli et al. 2008 and references therein), it has been proposed that the Fisher be placed in its own genus, Pekania.
Ferret-badgers (Melogale, 4 species, found in Southeast Asia).
Grisons (Galictis, 2 species, found in Central and South America). Bornholdt et al. (2013) confirmed and clarified the species delineations and geographic distributions within this genus.
Marbled Polecat (Vormela peregusna, found in southeastern Europe and Central Asia).
African Striped Weasel (Poecilogale albinucha, found in southern Africa). Larivère and Jennings (2009) noted that, given recent data indicating that the African Striped Weasel is the sister taxon to the Zorilla (Ictonyx striatus) (Koepfli et al. 2008), it should probably be placed in the genus Ictonyx as well.
Giant Otter (Pteroneura brasiliensis, found in northern South America).
New World Otters (Lontra, 4 species, found in North, Central, and South America).
Sea Otter (Enhydra lutris, found in the coastal North Pacific Ocean).
Spotted-necked Otter (Hydrictis maculicollis, found across much of sub-Saharan Africa).
Old World Otters (Lutra, 2 species, found across much of Europe and Asia). Larivère and Jennings (2009) noted that the Japanese Otter is sometimes recognized as a distinct species, L. nippon, although they treated it as a subspecies of the Eurasian Otter (L. lutra).
African Clawless Otter and Asian Small-clawed Otter (Aonyx, 2 species, found across much of sub-Saharan Africa and Southeast Asia). Larivère and Jennings (2009) note that a subspecies of the African Clawless Otter (A. capensis) is sometimes recognized as a distinct species, the Congo Clawless Otter (A. congicus). Aonyx otters feed on crabs and shellfish.
Smooth-coated Otter (Lutrogale perspicillata, from Southeast Asia).
Weasels, European Mink, and polecats (Mustela, 17 species, various species found across much of North America, Europe, and Asia; in Africa, the European Polecat [Mustela putorius] is present in Morocco and the Egyptian Weasel [Mustela subpalmata] is found in Egypt; Ermine [M. erminea] have been introduced to New Zealand and Least Weasels [M. nivalis] have been introduced to New Zealand, Malta, Crete, the Azores, and apparently São Tomé Island). The Domestic Ferret is believed to be descended from the European Polecat and is often referred to as M. putorius furo, but Steppe Polecats (M. eversamanii) may also be among the ancestors of the Domestic Ferret.
American Mink (Neovison vison, found across most of North America north of Mexico and introduced in China and Japan and widely in Europe). Based on new molecular phylogenetic studies, Harding and Smith (2009) concluded that the American Mink is closely related to several Mustela species and that together with the American Mink these should be segregated out from Mustela in a genus Vison. Although the American Mink and European Mink are morphologically and ecologically similar, molecular phylogenetic analyses indicate that they are not actually closely related within the subfamily Mustelinae.
Patagonian Weasel (Lyncodon patagonicus, found in western Argentina and central and southern Chile).
Morphology: Most mustelids are small to medium-sized carnivores with long bodies and short limbs (some, such as the Wolverine and badgers, have a stockier body shape). The Least Weasel, which is not only the smallest weasel but also the world's smallest carnivore, may weigh in at as little as 25 g when fully grown. Sexual size dimorphism in mustelids can be striking, with males often twice the size of females. The largest mustelid is the Sea Otter, which can reach 45 kg, and on land, the Wolverine, which can reach 18 kg. Mustelids have five toes on each foot and often strong claws. Their ears can be pointed forward or swiveled to the side, but not folded back.
The Ermine, Least Weasel, and Long-tailed Weasel (Mustela frenata) completely change their coats between summer and winter, with a dramatic change from brown to white in the northern parts of the range and at high elevations (in other areas, the summer coat is dark). Interestingly, Ermine and Long-tailed Weasels retain the black tail tip in the winter, which experiments have suggested may focus the attention of potential predators away from the body as a weasel makes its escape. Japanese Weasels (Mustela itatsi) replace their dark brown summer coat with a much paler yellowish one in the winter.
Habitat: Mustelids can be found in a great diversity of habitats, including marine (Marine Otter [Lontra felina] and Sea Otter), rivers (North American River Otter [Lontra canadensis] and Spotted-necked Otter), temperate forest (European Pine Marten [Martes martes] and American Marten [Martes americana]), dry open woodlands (African Striped Weasel), and grasslands (Black-footed Ferret [Mustela nigripes]). Some mustelids have very broad habitat preferences. For example, Ermine and Least Weasels can be found from grasslands to woodlands and Honey Badgers from forests to deserts.
Although most mustelids are terrestrial, their lifestyles are highly variable, ranging from fossorial (badgers--an American Badger can dig itself out of sight in just a few minutes), semi-fossorial (weasels and polecats), or semi-arboreal (martens) to semi-aquatic (mink and otters) or aquatic (Sea Otter and Marine Otter). River otters must actively swim to stay on the surface, but Sea Otters are so thoroughly aquatic they can drink seawater and can float passively on the surface thanks to their dense fur, which traps air and provides extra buoyancy.
Diet: Many mustelids have diverse diets, but animal prey is generally a major component of the diet—and mustelids must eat a lot to maintain their basal metabolism. If they are able to kill more than they need immediately, they may stash the surplus for later use in a rock crevice or burrow. In addition to killing their own food, some mustelids, such as Wolverines and Fishers, may also feed on carcasses of animals killed by other predators, such as wolves. Across much of their range, European Badgers rely heavily on earthworms, which can make up nearly two thirds of their diet, but at certain times of year and in certain places, fruit can make up the bulk of their diet—and they also feed on small vertebrates, acorns, roots, tubers, grass, and other foods.
During the 18th and 19th centuries Sea Otters were heavily hunted for their fur. Because Sea Otters prey on sea urchins, which in turn feed on algae, such as Giant Kelp, eliminating Sea Otters led to local increases in sea urchin populations and this in turn resulted in the loss of kelp beds as they were consumed by sea urchins. Thus, Sea Otters are a classic example of a "keystone species", i.e., a species whose impact on an ecological community is disproportionately large given its numbers and/or biomass.
Reproduction: Many mustelid species appear to be induced ovulators, with females shedding eggs from their ovaries only when stimulated by copulation. Some authors have speculated that the large baculum in the penis of the males of many mustelid species may serve to ensure sufficient stimulation of the cervix, triggering the release of a sequence of hormones that results in ovulation. Least weasels, the smallest mustelids, reach sexual maturity at three months; larger species such as Sea Otters, Giant Otters, and Wolverines reach sexual maturity at two years. Mustelid lifespans range from one to two years for the small weasels to up to 20 years for the largest mustelids.
A close relative of the American Mink, the Sea Mink (Neovison macrodon), reportedly lived among rocks along ocean shores in the northeastern United States and southeastern Canada, feeding mainly on fish, but little is known about this species since it was hunted heavily for its fur and was apparently extinct by the late 1800s, leaving no complete specimens behind. This is the only mustelid known to have been driven to extinction by humans, but a number of others are in trouble.
At the time of the review of the family Mustelidae by Larivère and Jennings (2009), the IUCN listed seven mustelid species as Endangered (Giant Otter, Marine Otter, Southern River Otter [Lontra provocax], Sea Otter, Hairy-nosed Otter [Lutra sumatrana], European Mink, and Black-footed Ferret); five as Vulnerable (Nilgiri Marten [Martes gwatkinsii], Marbled Polecat, Asian Small-clawed Otter [Aonyx cinereus], Smooth-coated Otter, and Colombian Weasel [Mustela felipei]); and four as Near Threatened (Hog Badger, Wolverine, Eurasian Otter, and Mountain Weasel [Mustela altaica]). Of the remaining species, 35 were listed as Least Concern and six as Data Deficient. In fact, so little is known about most mustelid species that reliable status assessments are difficult. The Colombian Weasel (Mustela felipei) was described only in 1978 (Izor and de la Torre 1978) and may be the rarest carnivore in South America (Ramírez-Chaves et al. 2012).
The Black-footed Ferret is a mustelid that came extremely close to extinction. Black-footed Ferrets were once common on the North American Great Plains, where they fed almost exclusively on prairie dogs. Unfortunately, the widespread destruction of prairie dog colonies led to a dramatic Black-footed Ferret decline to the point that the species was believed to be extinct, although unconfirmed sightings persisted. A tiny remnant population was rediscovered in Wyoming in 1981 when a dead individual was brought back by a dog. All wild individuals were brought into captivity for breeding and the species was listed as Extinct in the Wild for many years. Fortunately, intensive captive breeding and reintroduction efforts over many years have met with some limited success. Although the status of the species remains very precarious, the reintroductions have been sufficiently successful that in 2008 the IUCN changed the status of the species from Extinct in the Wild to Endangered.
Intensive trapping has seriously impacted populations of some mustelid species, such as the Fisher and American Marten, whose populations were severely reduced in many parts of their range in North America by the early 20th century. Fur trapping brought the Sea Otter to the brink of extinction by the early 20th century, but conservation efforts resulted in significant population rebounds in the latter part of the century.
Some other mustelids, such as the Sable (Martes zibellina) and American Mink, are still highly valued for their fur commercially and African Striped Weasel skins are used in traditional ceremonies in Africa. Although American Mink are still trapped in the wild, many millions are also bred on farms in the United States, Europe, and, more recently, China. The escape of American Mink from fur farms has resulted in the establishment of wild populations in Europe and Asia, which are believed to have negative consequences for competitors, such as European Mink, as well as for native prey, such as Water Voles in Britain. In New Zealand, Ermine and Least Weasels were introduced deliberately in the 1880s in an effort to reduce populations of introduced European Rabbits. Ermine have thrived, not only feeding on rabbits but also devastating local fauna, especially flightless birds. Today, Ermine are present in virtually all forested areas in New Zealand, although Least weasels are rare, presumably due to the scarcity of the smaller prey on which they specialize (voles are absent and feral House Mice are the only rodents smaller than 50 g).
Mustelids are hunted for food in some parts of the world, although they are more often taken incidentally (antelopes, deer, pigs, and primates being the most sought after targets). In Guinea, for example, where there is significant sale and consumption of bushmeat, Honey Badger and Spotted-necked Otter are among the species sold. Some mustelids, such as otters, are captured for the illegal international pet trade or for body parts for use in traditional medicine in China and elsewhere.
As with most species, the greatest threat faced by mustelids is generally habitat degradation, fragmentation, and destruction, although hunting poses a major threat to some species, such as the Neotropical Otter (Lontra longicaudis), which is heavily hunted for its pelts, and other threats may be important for particular species.
(Larivère and Jennings 2009 and references therein)
- Bornholdt, R., K. Helgen, K.-P. Koepfli, et al. 2013. Taxonomic revision of the genus Galictis (Carnivora: Mustelidae): species delimitation, morphological diagnosis, and refined mapping of geographical distribution. Zoological Journal of the Linnean Society 167: 449-472.
- Del Cerro, I., J. Marmi, A. Ferrando, et al. 2010. Nuclear and mitochondrial phylogenies provide evidence for four species of Eurasian badgers (Carnivora). Zoologica Scripta 39: 415-425.
- Eizirik, E., W.J. Murphy, K.P. Koepfli, W.E. Johnson, J.W. Dragoo, and S.J. O'Brien. 2010. Pattern and timing of the diversification of the mammalian order Carnivora inferred from multiple nuclear gene sequences. Molecular Phylogenetics and Evolution 56: 49-63.
- Harding, L.E. and F.A. Smith. 2009. Mustela or Vison? Evidence for the taxonomic status of the American mink and a distinct biogeographic radiation of American weasels. Molecular Phylogenetics and Evolution 52: 632-642.
- Helgen, K.M., N.T-L Lim, and L.E. Helgen. 2008. The hog-badger is not an edentate: systematics and evolution of the genus Arctonyx (Mammalia: Mustelidae). Zoological Journal of the Linnean Society: 154: 353-385.
- Izor, R.J. and L. de la Torre. 1978. A new species of weasel (Mustela) from the highlands of Colombia, with comments on the evolution and distribution of South American weasels. Journal of Mammalogy 50: 92-102.
- Koepfli, K.P., K.A. Deere, G.J. Slater et al. 2008. Multigene phylogeny of the Mustelidae: Resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation. BMC Biology 2008, 6:10.
- Larivère, S. and A.P. Jennings. 2009. Family Mustelidae (Weasels and Relatives). Pp. 564-656 in: Wilson, D.E. & Mittermeier, R.A., eds. Handbook of the Mammals of the World. Volume 1. Carnivores. Lynx Edicions, Barcelona.
- Nyakatura, K. and O.R.P. Bininda-Emonds. 2012. Updating the evolutionary history of Carnivora (Mammalia): a new species-level supertree complete with divergence time estimates. BMC Biology 10:12. doi:10.1186/1741-7007-10-12
- Ramírez-Chaves, H.E., K.P. Mulder, D. Marin, et al. 2012. Has Colombian Weasel Mustela felipei been overlooked in collections? Small Carnivore Conservation 47: 30-34.
- Sato, J.J., M. Wolsan, F.J. Prevosti, et al. 2012. Evolutionary and biogeographic history of weasel-like carnivorans (Musteloidea). Molecular Phylogenetics and Evolution 63: 745-757.
- Yu, L., D. Peng, J. Liu, et al. 2011. On the phylogeny of Mustelidae subfamilies: analysis of seventeen nuclear non-coding loci and mitochondrial complete genomes. BMC Evolutionary Biology 2011, 11:92.
Mustelidae is the largest family within Carnivora and is comprised of 56 species in 22 genera. Members of this family include weasels, stoats, polecats, mink, marten, fishers, wolverines, otters, badgers and others. While many authors have traditionally considered skunks a subfamily within Mustelidae, recent molecular evidence indicates that skunks do not lie within the mustelid group and instead are recognized as a single family, Mephitidae, a systematic understanding which is accepted here (Dragoo and Honeycutt, 1997; Flynn et al., 2005; Marmi et. al., 2004; Sato et. al., 2003; Sato et. al., 2004).
Mustelids inhabit all continents except Australia and Antarctica, and do not occur on Madagascar or oceanic islands. Members of this group can be found in diverse habitats, which include both terrestrial, aquatic and marine environments. Mustelids are mainly carnivorous, with various members of the family exploiting a great diversity of both vertebrate and invertebrate prey. Mustelids are generally proficient hunters; some weasels can take prey larger than themselves. Members of this family often hunt in burrows and crevices, and some species have evolved to become adept at climbing trees (e.g., marten) or swimming (e.g., sea otters, mink) in search of prey.
Generally, mustelids have elongate bodies with short legs and a short rostrum, as typified by weasels, ferrets, mink, and otters. Wolverines and badgers have broader bodies. An order of magnitude difference in size exists between the smallest and largest mustelid species. The smallest species is the least weasel (Mustela nivalis), weighing between 35 and 250 grams. Wolverines (Gulo gulo) and sea otters (Enhydra lutris) reach 32 kg and 45 kg, respectively. All mustelids have well developed anal scent glands, which serve various functions, including territorial marking and defense.
- Flynn, J., J. Finarelli, S. Zehr, J. Hsu, M. Nedbal. 2005. Molecular phylogeny of the Carnivora (Mammalia): Assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology, 54: 317-337.
- Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th Edition. Toronto: Brooks Cole.
- Dragoo, J., R. Honeycutt. 1997. Systematics of mustelid-like carnivores. Journal of Mammalogy, 78: 426-443.
- Whitaker, J., W. Hamilton. 1998. Mammals of the Eastern United States. Ithaca: Comstock Publishing.
- Sato, J., T. Hosada, M. Wolsan, H. Suzuki. 2004. Molecular phylogeny of arctoids (Mammalia: Carnivora) with emphasis on phylogenetic and taxonomic positions of the ferret-badgers and skunks. Zoologial Science, 21: 111-118.
- Hutchings, M., P. White. 2000. Mustelid scent-marking in managed ecosystems: implications for population management. Mammal Review, 30: 157-169.
- Marmi, J., J. Lopez-Giraldez, X. Domingo-Roura. 2004. Phylogeny, evolutionary history and taxonomy of the Mustelidae based on sequences of the cytochrome b gene and a complex repetitive flanking region. Zoologica Scripta, 33: 481-499.
- Sato, J., T. Hosada, W. Mieczyslaw, K. Tsuchiya, Y. Yamamoto, H. Suzuki. 2003. Phylogenetic relationships and divergence times among mustelids (Mammalia: Carnivora) based on nucleotide sequences of the nuclear interphotoreceptor retinoid binding protein and mitochondrial cytochrome b genes. Zoologial Science, 20: 243-264.
- Nowak, R. 1991. Carnivora: family Mustelidae. Pp. 1104-1105 in Walker's Mammals of the World, Vol. 2, 5th Edition. Baltimore: Johns Hopkins University Press.
Members of the family Mustelidae inhabit all continents except Antarctica and Australia. They do not occur on Madagascar or oceanic islands, but have been introduced to New Zealand.
Biogeographic Regions: nearctic ; palearctic ; oriental ; ethiopian ; neotropical ; australian (Introduced )
Other Geographic Terms: cosmopolitan
Adult mustelids range in size from 114 mm and 25 g (least weasel) to over 1 m and 45 kg (sea otters). These animals are generally long-bodied with short legs. Most species have slender bodies, but some, like badgers (Mustelinae, Mustelinae) and wolverines have much broader bodies. The skull is elongate with a relatively short rostrum. Adult males are generally about 25 percent larger than females of the same species. The ears are short, as are the legs, each of which bears five digits. The claws do not retract and, in digging species, are especially robust. Mustelids are digitigrade or plantigrade. The dental formula varies among species: 3/3, 1/1, 2-4/2-4, 1/1-2 = 28-38. The canines are long, and the carnassials are well-developed. The upper molars are often narrow in the middle, giving them an hourglass shape. Mustelids have a powerful bite; in many species, the large postglenoid process locks the lower jaw into the upper, causing the lower jaw to only move in the vertical plane, without any rotary motion.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Mustelidae are distributed from the arctic to the tropics and occupy nearly all terrestrial habitats. Several species are semi- or nearly fully aquatic and inhabit freshwater rivers and streams, as well as coastal marine waters.
Habitat Regions: temperate ; tropical ; polar ; terrestrial ; saltwater or marine ; freshwater
Terrestrial Biomes: tundra ; taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Aquatic Biomes: lakes and ponds; rivers and streams; coastal ; brackish water
Wetlands: marsh ; swamp ; bog
Other Habitat Features: suburban ; agricultural ; riparian ; estuarine ; intertidal or littoral
Mustelids are primarily carnivorous, but some species may at times eat plant material. A wide range of animal taxa are preyed upon by various members of this family; many mustelids are opportunistic feeders rather than specialists. However, many mustelids are especially adept at capturing small, mammalian prey. Weasels, for example, are capable of chasing and capturing rodents in their burrows. Otters are well-adapted to chasing and capturing aquatic prey, including fish, crustaceans, and other aquatic invertebrates. Mustelids hunt in a variety of terrestrial, aquatic, and arboreal habitats. Some species regularly prey on animals larger than themselves. Some species have been known to store food (e.g., Mustela, Gulo).
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Insectivore , Eats non-insect arthropods, Molluscivore )
Mustelids mainly impact their communities through their effects on prey populations. Many species limit rodent and bird populations. In some cases, mustelids limit rodents that are considered pests, in other cases, mustelids threaten rare bird species. Some species, such as sea otters (Enhydra lutra) are keystone predators, enhancing the diversity of their community by keeping highly competitive prey species in check. Honey badgers (or ratels, Mellivora capensis) have developed commensal relationships with both humans and honey guides (Indicator indicator), using both to aid in the location of bee colonies.
Ecosystem Impact: keystone species
- Indicator indicator
- Homo sapiens
- Macdonald, R., C. King. 2000. Biology of mustelids: reviews and future directions. Mammal Review, 30/3-4: 145.
Mustelids are generally small carnivores, and are therefore subject to predation by larger carnivores such as canids with which they co-occur. They may also fall prey to large snakes (Serpentes), raptors (Falconiformes), and owls (Strigiformes). Some mustelids secrete noxious chemicals to discourage predators. In some of these species, aposematic color patterns can help ward off predators.
Anti-predator Adaptations: aposematic
- Bright, P. 2000. Lessons from lean beasts: conservation biology of the mustelids. Mammal Review, 30: 217-226.
Known prey organisms
This list may not be complete but is based on published studies.
Life History and Behavior
Communication and Perception
Vision and hearing are important in Mustelidae, but olfaction is particularly well developed. In addition to using scent cues to find food, scent-marking is the main form of communication in this family. Secretions from well-developed scent glands function in territorial interactions, indicate reproductive state, and are used in other social contexts. The degree and function of scent marking varies among species, and according to social and environmental conditions within species.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: scent marks
Perception Channels: visual ; acoustic
Mustelids typically live between 5 and 20 years in the wild.
Mating systems vary both within and among species. Many species are polygynous and/or promiscuous. Some species are social, while others are solitary. Social organization can vary within species as well. Mustelids require prolonged periods of copulation to induce ovulation of an unfertilzed egg. As a result, copulation may last for several hours before fertilization can be successful.
Mating System: polygynous ; polygynandrous (promiscuous)
Most mustelids breed seasonally, but the length of the reproductive period varies among species. Day length often dictates the onset of the breeding season, which usually lasts 3 to 4 months. Many mustelids undergo delayed implantation, with the fertilized embryo taking up to 10 months (e.g. Meles meles) to implant in the uterus in some species. Environmental conditions such as temperature and day length determine when implantation occurs. Mustelids that live in more seasonal climates are more likely to exhibit delayed implantation. Following implantation, gestation typically lasts 30 to 65 days. Females give birth to a single litter each season, the size of which varies within and among species. For example, sables have an average litter size of 2.2, but can give birth to anywhere from 1 to 7 pups. The mountain weasel averages 8.7 pups per litter, but can have between 3 and 14 young in a single bout of reproduction. Generally, mustelids are altricial, being born small and blind. They reach sexual maturity between 8 months and two years following birth.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; delayed implantation
Young are generally born in an alricial state, requiring extenisive care and protection from their mother. Young mustelids typically are able to care for themselves when they are about two months old. Females defend territories in order to acquire enough resources to care for their young and most often nurse and protect them in a burrow or den.
Parental Investment: altricial ; precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)
- Vaughan, T., J. Ryan, N. Czaplewski. 2000. Mammalogy, 4th Edition. Toronto: Brooks Cole.
- Amstislavsky, S., Y. Ternovskaya. 2000. Reproduction in Mustelids. Animal Reproduction Science, 60-61: 571-581.
- Johnson, D., D. MacDonald, A. Dickman. 2000. An analysis and review of models of the sociobiology of the Mustelidae. Mammal Review, 30: 171-196.
- Nowak, R. 1991. Carnivora: family Mustelidae. Pp. 1104-1105 in Walker's Mammals of the World, Vol. 2, 5th Edition. Baltimore: Johns Hopkins University Press.
- Thom, M., D. Johnson, D. Macdonald. 2004. Evolution and delayed implantation in the Mustelidae (Mammalia: Carnivora). Evolution, 58/1: 175-183.
Evolution and Systematics
The ears of otters protect from water via ear-flaps.
"Among aquatic mammals such as the otter, the ear-flap can be pressed down to close the ear to water." (Foy and Oxford Scientific Films 1982:167)
Learn more about this functional adaptation.
- Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimen Records: 466
Specimens with Sequences: 509
Specimens with Barcodes: 308
Species With Barcodes: 35
Public Records: 188
Public Species: 31
Public BINs: 29
Some mustelid species are considered highly threatened by the IUCN, while other species are so abundant that they are considered pests. Approximately 38% of all species of Mustelidae are considered threatened,which is a much higher proportion than mammals in general (15%). Habitat destruction is a serious risk to species with restricted habitat requirements such as otters and martens. Smaller carnivores that are restricted to small habitat fragments may also be at risk to predation by larger carnivores that can more easily move among fragments. Hunting has been a problem for some species, while others, particularly tropical mustelids, do not seem to be declining as a result. Endangered mustelids include: Colombian weasels (Mustela felipei), European mink (Mustela lutreola), Indonesian mountain weasels (Mustela lutreolina), marine otters (Lontra felina), southern river otters (Lontra provocax), sea otters (Enhydra lutris), and giant Brazilian otters (Pteronura brasiliensis). Sea mink (Neovison macrodon) became extinct in recent times.
Numerous re-introduction programs for various mustelid species have met with mixed success. Generally, "soft" re-introductions, those that allow the animals to acclimate to their new surroundings while in a temporary enclosure, are more successful than "hard" re-introductions, in which captive-bred animals are released directly into the wild. Black-footed ferrets (Mustela nigripes) are considered extinct in the wild, although several re-introduction programs are underway.
Relevance to Humans and Ecosystems
Economic Importance for Humans: Negative
Some mustelids are considered pests, either for harming poultry livestock, for threatening other species in the wild, or for transmitting diseases. European badgers have been implicated in the transmission of bovine tuberculosis. Cattle may become infected from grazing on land where badgers have defecated. Up to 20% of badgers carry the disease in areas where bovine tuberculosis is a problem. Since 1975, badgers have been culled in the United Kingdom, but there is no conlcusive evidence that it has helped control bovine TB. As mammalian carnivores, mustelids can also be infected by, and transmit, rabies.
Negative Impacts: causes or carries domestic animal disease
- Gough, M., S. Rushton. 2000. The application of GIS-modelling to mustelid landscape ecology. Mammal Review, 30: 197-216.
Economic Importance for Humans: Positive
Many mustelids help control rodent populations that are considered to be pests. In addition, many are hunted and/or raised for their pelts, which are often considered highly valuable (e.g., the pelts of mink and sable). Some species have been domesticated and are traded as pets (e.g., ferrets).
Positive Impacts: pet trade ; body parts are source of valuable material; controls pest population
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The Mustelidae (from Latin mustela, weasel) are a family of carnivorous mammals, including the otters, badgers, weasels, martens, ferrets, minks and wolverines. Mustelids are diverse and the largest family in the order Carnivora. The internal classification still seems to be rather unsettled, with rival proposals containing between two and eight subfamilies. One study, published in 2008, questions the long-accepted Mustelinae subfamily, and suggests that Mustelidae consist of four major clades and three much smaller lineages.
Mustelids vary greatly in size and behaviour. The least weasel is not much larger than a mouse, while the giant otter can measure up to 2.4 m (7.9 ft) in length and sea otters can exceed 45 kg (99 lb) in weight. The wolverine can crush bones as thick as the femur of a moose to get at the marrow, and has been seen attempting to drive bears away from their kills. The sea otter uses rocks to break open shellfish to eat. The marten is largely arboreal, while the badger digs extensive networks of tunnels, called setts. Some mustelids have been domesticated: the ferret and the tayra are kept as pets (although the tayra requires a Dangerous Wild Animals licence in the UK), or as working animals for hunting or vermin control. Others have been important in the fur trade—the mink is often raised for its fur.
As well as being one of the most species-rich families in the order Carnivora, the family Mustelidae is one of the oldest. Mustelid-like forms first appeared about 40 million years ago, roughly coinciding with the appearance of rodents. The direct ancestors of the modern mustelids first appeared about 15 million years ago.
Within a large range of variation, the mustelids exhibit some common characteristics. They are typically small animals with short legs, short, round ears, and thick fur. Most mustelids are solitary, nocturnal animals, and are active year-round.
Most mustelid reproduction involves embryonic diapause. The embryo does not immediately implant in the uterus, but remains dormant for a period of time. No development takes place as long as the embryo remains unattached to the uterine lining. As a result, the normal gestation period is extended, sometimes up to a year. This allows the young to be born under more favorable environmental conditions. Reproduction has a large energy cost and it is to a female's benefit to have available food and mild weather. The young are more likely to survive if birth occurs after previous offspring have been weaned.
Mustelids are predominantly carnivorous, although some will sometimes eat vegetable matter. While not all mustelids share an identical dentition, they all possess teeth adapted for eating flesh, including the presence of shearing carnassials. With variation between species, the most common dental formula is:
Several members of the family are aquatic to varying degrees, ranging from the semiaquatic mink, to the river otters, and to the highly aquatic sea otter. The sea otter is one of the few nonprimate mammals known to use a tool while foraging. It uses "anvil" stones to crack open the shellfish that form a significant part of its diet. It is a "keystone species", keeping its prey populations in balance so some do not outcompete the others and destroy the kelp in which they live.
The black-footed ferret is entirely dependent on another keystone species, the prairie dog. A family of four ferrets will eat 250 prairie dogs in a year; this requires a stable population of prairie dogs from an area of some 500 acres (2.0 km2).
The mongoose and the meerkat bear a striking resemblance to many mustelids, but belong to a distinctly different suborder—the Feliformia (all those carnivores sharing more recent origins with the Felidae) and not the Caniformia (those sharing more recent origins with the Canidae). Because the mongooses and the mustelids occupy similar ecological niches, convergent evolution has led to some similarity in form and behavior.
Several mustelids, including the mink, the sable (a type of marten) and the stoat (ermine), boast exquisite and valuable furs, and have been accordingly hunted since prehistoric times. Since the early Middle Ages, the trade in furs was of great economic importance for northern and eastern European nations with large native populations of fur-bearing mustelids, and was a major economic impetus behind Russian expansion into Siberia and French and English expansion in North America. In recent centuries, fur farming, notably of mink, has also become widespread and provides the majority of the fur brought to market.
One species, the sea mink (Neovison macrodon) of New England and Canada, was driven to extinction by fur trappers. Its appearance and habits are almost unknown today because no complete specimens can be found and no systematic contemporary studies were conducted.
The sea otter, which has the densest fur of any animal, narrowly escaped the fate of the sea mink. The discovery of large populations in the North Pacific was the major economic driving force behind Russian expansion into Kamchatka, the Aleutian Islands and Alaska, as well as a cause for conflict with Japan and foreign hunters in the Kuril Islands. Together with widespread hunting in California and British Columbia, the species was brought to the brink of extinction until an international moratorium came into effect in 1911.
Today, some mustelids are threatened for other reasons. Sea otters are vulnerable to oil spills and the indirect effects of overfishing; the black-footed ferret, a relative of the European polecat, suffers from the loss of American prairie; and wolverine populations are slowly declining because of habitat destruction and persecution. The rare European mink Mustela lutreola is one of the most endangered mustelid species.
The traditional classification of the Family has recently been questioned. The genetic studies on which the modern scheme was based did not include the genus Lyncodon, which is therefore unplaced, but probably allied with Mustela and Neovison. Older reference works generally suggest that Mustelidae should be divided into just two extant subfamilies, denoted Lutrinae and Mustelinae, although the latter now appears paraphyletic as originally described. Instead, Mustelidae is now thought to be divided into four major clades and three, much smaller, lineages. The early mustelids appear to have undergone two rapid bursts of diversification in Eurasia, with the resulting species only spreading to other continents later.
Examination of the mitochondrial DNA suggests that Taxidiinae diverged first, followed by Melinae. Lutrinae and Mustelinae are sister clades. The position of Helictidinae is unclear because the mitochondrial evidence suggests the sub-family is related to the Lutrinae-Mustelinae clade, while the intron data suggest a relationship to Martinae.
According to the older theory proposing two subfamilies, the 57 living species of mustelid are classified as:
- Extant mustelidae species
(2 subfamilies and 57 living species in 22 genera)
Extinct genera of the Mustelidae family include:
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