Aquatic tenrecs are considered descended from shrew tenrec ancestors (Microgale species) but are different enough that they were placed in a separate monotypic genus. Like all tenrecs, aquatic tenrecs have incomplete zygomatic arches, no postorbital processes, unique crowns on the molar teeth, and ring-shaped tympanic bones (Major 1896). The strong relationship to shrew tenrecs has not always been so clear. In the past the specialization for an aquatic lifestyle caused Limnogale mergulus to be associated with other aquatic tenrecs known as otter shrews (Potamogalinae) that inhabit mainland tropical Africa. Recent evidence says that this is not the case. Morphological and molecular evidence show that the terrestrial shrew tenrecs, genus Microgale, are the closest relatives to Limnogale (Olson and Goodman 2004). This evidence illustrates that aquatic tenrecs belong to the subfamily of tenrecs known as Oryzorictinae. Oryzorictinae consists of three genera: Limnogale, Microgale, and Oryzorictes (mole tenrecs) (Olson and Goodman 2004).
The name Limnogale is derived from the Greek words "limne", meaning marshy lake, and "gale," meaning marten-cat or weasel. The name mergulus is derived from the Latin words "mergo", meaning I dip or I plunge, and "ulus", an adjective denoting tendency (Gotch 1995). In other words, Limnogale mergulus can be translated as “lake weasel who plunges.” This is a slight misnomer because they are not weasels and because they are usually found in more turbulent waters such as rivers and streams. Similar to other semiaquatic small mammals, aquatic tenrecs have several adaptations that can be attributed to their semiaquatic, carnivorous lifestyles. These include an enlarged body size relative to their close relatives, countershaded coloration, elongated lateral metatarsals, webbed feet, dense lateral fringe hair on the feet, reduced and densely furred ears, and stiffened mystacial vibrissae supported by enlarged mystacial pads (Benstead and Olson 2004).
The muzzles of aquatic tenrecs are well adapted, presumably for aquatic predation. Enlarged mystacial pads support stiffened mystacial vibrissae that are thought to be used for tactile scanning of the riverbed for prey (Benstead and Olson 2004).
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
Aquatic tenrecs are listed as Vulnerable on the IUCN Red List. Reasons for their status as vulnerable include habitat degradation and sparse distribution within their range. Forest fragmentation, river siltation, and soil erosion are believed to be major threats. Aquatic tenrecs rely heavily on benthic prey sources, such as Ephemeroptera, which are especially vulnerable to changes in river sedimentation (Olson and Goodman 2008). Conservation of aquatic tenrecs depends on habitat protection. Even in sites where forests have been cleared, this species has proliferated as long as riparian areas remain intact. Maintaining a mosaic of natural habitat and developed land should ensure both species survival and the needs of local human populations. Preserving natural catchment areas and restructuring agricultural fields to include effective terracing will limit soil erosion and prevent sedimentation (Benstead et al. 2001).
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: vulnerable
Aquatic tenrecs are occasionally caught in eel and crayfish traps (Benstead and Olson 2004).
There is no known positive economic importance for humans.
Based on the diet information of aquatic tenrecs, some ecosystem roles can be considered. Aquatic tenrecs likely compete with fish, frogs, and other small mammals for invertebrate prey in the area. Aquatic insects such as mayfly, dragonfly, and stonefly nymphs, which are important prey items are also likely to be important food sources for others. Another small role may be that coprophagous insects use latrine sites as food sources.
Commensal/Parasitic Species:
Due to the rarity of observations in the wild, studies on feeding behavior have only been conducted on captive animals. Aquatic tenrecs dive to the bottom of a stream for 10 to 15 seconds and search for food using a sweeping motion with their sensitive vibrissae (Benstead et al. 2001). Once detected, prey is seized in the mouth and brought to the surface. On the surface, aquatic tenrecs roll on their backs and kick prey using their hind feet until the prey is subdued. At this point, prey is brought to an emergent rock where it is consumed while being held with the forefeet. The claws are removed from crayfish prior to eating (Benstead et al. 2001). Analysis of fecal pellets collected from several sites reveal that insects, both larval and adult, are the dominant prey. These include species of Ephemeroptera, Odonata, and Trichoptera. Larval anurans and crayfish are also common prey items. There is no evidence in fecal pellet analysis of predation on adult amphibians or fish (Benstead et al. 2001).
Animal Foods: amphibians; insects; aquatic crustaceans
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)
Limnogale mergulus, known as the aquatic or web-footed tenrec, is endemic to Madagascar, where it is known from only ten sites. All sites are in the highlands and escarpment region of eastern Madagascar's rainforests and extend from the Andringitra Massiff in the south to the upper Iantatra River to the east and the Sihanaka Forest to the north (Benstead et al. 2001). Ranomafana National Park appears to support a large population and was the location of a recent radio-tracking study of two specimens (Benstead et al. 2001). It is unknown if all ten historical sites where aquatic tenrecs have been found still hold viable populations. Populations have been documented on both sides of Madagascar’s continental divide (Benstead and Olson 2004). Limnogale mergulus is the only member of its genus.
'The IUCN Red List of Threatened Species range map http://mapservices.iucnredlist.org/IUCN/mapper/index.html?ID_NO=11979'
Biogeographic Regions: ethiopian (Native )
Other Geographic Terms: island endemic
Aquatic tenrecs nest along fast-flowing streams and rivers in Madagascar's premontane tropical rainforest. These streams may either be in forested or zero-canopy areas (Bentead et al. 2001). Like other aquatic foraging mammals, they travel strictly by means of water corridors (Bentead et al. 2001). Habitat reduction is an ongoing concern due to destruction caused by “tavy” (slash and burn agriculture) (Bentead et al. 2001). For most of the 20th century, an association was suspected between L. mergulus and lace plants (Aponogeton fenestralis). Scientists believed the association was due to an abundant food source found at the root of these plants. However, lack of a correlated distribution has ruled out such an association (Benstead and Olson 2004).
Range elevation: 450 to 2000 m.
Habitat Regions: tropical ; terrestrial ; freshwater
Terrestrial Biomes: rainforest
Aquatic Biomes: rivers and streams
Other Habitat Features: riparian
There is little available information on lifespan of aquatic tenrecs.
Aquatic tenrecs are similar in size and shape to small rats. In comparison to their closest relatives in the genus Microgale (shrew tenrecs), they have large body mass, which may be because of the greater thermal inertia required for an aquatic lifestyle (Benstead and Olson 2004). Aquatic tenrecs are dark brown to almost black with red/black dorsal and yellowish-gray ventral undertones (Benstead and Olson 2004). When wet, the fur clumps together to form small matted points. They have a combined head and body length of 122 to 170 mm plus a tail length of 119 to 161 mm (Eisenberg and Gould 1970). Dental formula is 3/3 1/1 3/3 3/3 = 40 (Major 1896). Both hind and forefeet are webbed to the base of the claws and have five digits each. Aquatic tenrecs have relatively large hindlimb muscles, visible to the naked eye, which aid in aquatic locomotion (Endo et al. 2006). The pinnae (external ears) and eyes are both reduced. Protruding from the rostrum are stout mystacial vibrissae supported by large mystacial pads, presumably allowing for a highly-developed sense of touch needed for aquatic predation (Benstead and Olson 2004).
Range mass: 60 to 107 g.
Range length: 250 to 325 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Aquatic tenrecs have several adaptations for predator avoidance. They are strictly nocturnal, leaving their burrows in the evening and returning just before dawn. Countershaded coloration provides camouflage for an aquatic lifestyle. Viewed from above, aquatic tenrecs blend in with the darkness of the water. Viewed from below, they blend in with the light backdrop of the sky.
There are no known predators of aquatic tenrecs. Recently though, a new species of mongoose-like carnivore was found in Madagascar that may prey on these tenrecs. Durrell’s vontsira, Salanoia durrelli, described in 2010 (Durbin et al. 2010), shares a similar habitat and has dentition that suggests it feeds on small invertebrates and possibly small vertebrates. Very little research has been conducted on this new species, so it is unknown if there is any interaction between the two species. Though their habitats are similar, Durrell’s vontsira was discovered in a marshy wetland, while aquatic tenreca are associated with fast-moving streams.
Anti-predator Adaptations: cryptic
Nothing is known about the mating system of aquatic tenrecs.
There is limited information on reproduction in aquatic tenrecs. Females have six mammae (three per side) including two ventral, two pectoral, and two inguinal mammae. An average litter size of three is presumed (Eisenberg and Gould 1970). The breeding season is thought to be between December and January based on the fact that a lactating female was discovered in December and a nest discovered in January occupied by two juveniles (Eisenberg and Gould 1970).
Breeding interval: Breeding intervals in aquatic tenrecs are unknown.
Breeding season: The breeding season is thought to be between December and January, based on two observations.
Average number of offspring: 3.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
No information is available on parental investment of aquatic tenrecs.
The web-footed or aquatic tenrec is restricted to streams and rivers within natural forests in the eastern humid forests and central highlands of Madagascar at altitudes of 450–2,000 m.
It grows to 25-39 cm long and weighs 40-60 g. It is nocturnal, spending most of its time swimming and diving in fast-moving streams for food. It sleeps during the day in small streamside burrows.
It is a semi-aquatic carnivore and probably eats freshwater crayfish, tadpoles, aquatic insects and their larvae and small crustaceans.
It needs permanent, clean and fast flowing water, but many of the streams where it lives are threatened by siltation. Deforestation is causing soil erosion and agricultural expansion is fragmenting the upland forests, which isolates fast-flowing riverine habitat. The tenrec is listed as Vulnerable, but was thought to be extinct.
The web-footed tenrec, Malagasy otter shrew, or aquatic tenrec (Microgale mergulus) is the only known semiaquatic tenrec (the related African otter shrews have similar habits), and is found in eastern Madagascar, especially in and around Ranomafana National Park. It grows to between 25 and 39 cm (9.8 and 15.4 in), and was once thought to be extinct. It feeds on crabs, aquatic insects, and crayfish. The population is considered vulnerable. It was formerly placed in the monotypic genus Limnogale,[2] but has been moved to Microgale based on molecular data showing it to be deeply nested within the latter.[3]
Microgale mergulus is strictly nocturnal, spending the day in stream side burrows, only emerging at night to hunt. Nocturnal movements appear to be restricted to waterways but include movements away from burrows and diving. Radio collar tracking has shown that some individuals are known to utilize stream channels as much as 1160 meters in length, while others may only patrol 500 meters. In one night a web-footed tenrec may travel 1550 meters along channels in search of food.[4]
M. mergulus is only known to inhabit stream habitats in eastern Madagascar. While it is no longer classified in the obsolete order of Insectivora, M. mergulus could very well be designated an insectivore.[4] The bulk of its diet consists of aquatic insects and larvae, with crustaceans and small fish making up the rest. The larvae of insects in the orders Ephemeroptera, Odonata and Trichoptera are favored. Diets of individuals inhabiting zero-canopy steams appear to be the same as those living in forested streams.[4][1]
The aquatic or web-footed tenrec, Microgale mergulus, and other tenrecs are endemic to Madagascar. They are part of the monophyletic clade Afrotheria, which includes placental mammals of diverse anatomies including hyraxes, elephants and mammoths, manatees and dugong, tenrecs, golden moles, elephant shrews, and aardvarks. Genetic sequencing and other methods have confirmed the accuracy and relatedness of this grouping.[5]
The web-footed tenrec is one of 22 members of the genus Microgale. Molecular studies have led to its placement in the subfamily Oryzorictinae, along with two species each of the genera Nesogale and Oryzorictes.[3][6] It is the largest member of this subfamily and likely evolved this increased size in response to its aquatic lifestyle.[1] Ancestral tenrecs are thought to have rafted from mainland Africa to Madagascar in a single event.[7] All tenrecs are thought to descend from a common ancestor that lived 29–37 million years (Ma) ago[3][8][9] They include members of subfamilies Tenrecinae and Geogalinae as well as Oryzorictinae.[6]
While it is similar in habits to the related equatorial African otter shrews of family Potamogalidae, their aquatic lifestyles evolved independently from one another.[6][9] The split between tenrecs and otter shrews has been dated to about 47–53 Ma ago.[3][8][9]
The aquatic tenrec is currently ranked by the IUCN as Vulnerable on the Red List. Due to their specialized habitat requirements and restriction to the island of Madagascar, it is estimated that less than 2,000 km2 of suitable habitat remains. Degradation of riparian ecosystems and siltation of streams are the leading threat to the species’.[1] Deforestation is also recognized as a potential cause of decline. However, recent studies have shown healthy populations of M. mergulus in streams where forest has been cleared or otherwise degraded, as well as non-native plantations.[5] Areas of its habitat which are currently protected include Ranomafana National Park and the Andringitra National Park (1989) and it is also reported in the new Nosy Volo Reserve in the east (2014).[6]
Within afrotherian mammals, Microgale mergulus is typically considered for highest priority conservation priority along with the giant otter shrew, giant golden mole, northern shrew tenrec and Nimba otter shrew, as well as some better-known conservation symbols like the dugong, Asian elephant, and three species of manatees. This priority has been analyzed using two different methods, including phylogenetic diversity (PD) and evolutionary distinctiveness (ED).[5]
The web-footed tenrec, Malagasy otter shrew, or aquatic tenrec (Microgale mergulus) is the only known semiaquatic tenrec (the related African otter shrews have similar habits), and is found in eastern Madagascar, especially in and around Ranomafana National Park. It grows to between 25 and 39 cm (9.8 and 15.4 in), and was once thought to be extinct. It feeds on crabs, aquatic insects, and crayfish. The population is considered vulnerable. It was formerly placed in the monotypic genus Limnogale, but has been moved to Microgale based on molecular data showing it to be deeply nested within the latter.
