Limnogale mergulusaquatic tenrec

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Geographic Range

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' (Benstead and Olson, 2004; Benstead, et al., 2001)

Habitat

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). (Benstead and Olson, 2004; Benstead, et al., 2001)

  • Aquatic Biomes
  • rivers and streams
  • Range elevation
    450 to 2000 m
    1476.38 to 6561.68 ft

Physical Description

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). (Benstead and Olson, 2004; Eisenberg and Gould, 1970; Endo, et al., 2006; Major, 1896)

  • Range mass
    60 to 107 g
    2.11 to 3.77 oz
  • Range length
    250 to 325 mm
    9.84 to 12.80 in

Reproduction

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). (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

No information is available on parental investment of aquatic tenrecs.

Lifespan/Longevity

There is little available information on lifespan of aquatic tenrecs.

Behavior

Aquatic tenrecs begin foraging after sunset and end just before sunrise. Most of their time outside of the burrow is spent foraging. During the night, aquatic tenrecs remain active, though resting periods of inactivity have also been reported (Benstead et al. 2001). These inactive periods are spent either in the burrow or in the home range. Temporary streamside burrows may be used during these rest periods. When foraging, aquatic tenrecs move both up and downstream from the main burrow. Stream flow may influence the direction of travel. The approximate distance traveled each night is 1000 m and ranges from 200 to 1550 m (Benstead et al. 2001). The distance traveled is correlated with the width of the stream channel. Individuals living in narrower streams tend to travel further than those living in wider streams. Regardless of stream width, the total home range size tends to be very similar (Benstead and Olson 2004). Only one burrow has been investigated (Malzy 1965). It was situated approximately 0.5 m high on a high-gradient bank. The dimensions of the burrow were 10 cm in diameter and 17 cm deep. It was lined with twigs and grass. Males and females maintain separate burrows, though they share a territory. The home range for the female is smaller and lies within the home range of resident males (Benstead et al. 2001). Aquatic tenrecs groom extensively after emerging from the water (Benstead and Olson 2004). (Benstead and Olson, 2004; Benstead, et al., 2001)

Home Range

There is little available information on the home range of aquatic tenrecs.

Communication and Perception

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). (Benstead and Olson, 2004)

Food Habits

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). (Benstead, et al., 2001)

  • Animal Foods
  • amphibians
  • insects
  • aquatic crustaceans

Predation

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. (Durbin, et al., 2010)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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
  • Aelurostrongylus minimus
  • Madangiostrongylus limnogali
  • Molineus malzyi

Economic Importance for Humans: Positive

There is no known positive economic importance for humans.

Economic Importance for Humans: Negative

Aquatic tenrecs are occasionally caught in eel and crayfish traps (Benstead and Olson 2004). (Benstead and Olson, 2004)

Conservation Status

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). (Benstead, et al., 2001; Olson and Goodman, 2004; Olson and Goodman, 2008)

Other Comments

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). (Major, 1896; 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). (Benstead and Olson, 2004; Gotch, 1995)

Contributors

Travis LaPointe (author), University of Alaska Fairbanks, Link Olson (editor), University of Alaska Fairbanks, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

freshwater

mainly lives in water that is not salty.

insectivore

An animal that eats mainly insects or spiders.

island endemic

animals that live only on an island or set of islands.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Benstead, J., K. Barnes, C. Pringle. 2001. Diet, activity patterns, foraging movement and responses to deforestation of the aquatic tenrec Limnogale mergulus (Lipotyphla : Tenrecidae) in eastern Madagascar. Journal of Zoology, 254: 119-129.

Benstead, J., L. Olson. 2004. Limnogale mergulus, web-footed tenrec or aquatic tenrec. Pp. 1267-1273 in J Benstead, S Goodman, eds. The Natural History of Madagascar. Chicago: University of Chicago Press.

Durbin, J., S. Funk, F. Hawkins, D. Hills, C. Jenkins, C. Moncrieff, F. Ralainasolo. 2010. Investigations into the status of a new taxon of Salanoia (Mammalia: Carnivora: Eupleridae) from the marshes of Lac Alaotra, Madagascar. Systematics and Biodiversity, 8/3: 341-355.

Eisenberg, J., E. Gould. 1970. The Tenrecs: A study in mammalian behavior and evolution.. Smithsonian Contributions to Zoology, 27: 1-138.

Endo, H., T. Yonezawa, F. Rakotondraparany, M. Sasaki, M. Hasagawa. 2006. The adaptational strategies of the hindlimb muscles in the Tenrecidae species including the aquatic web-footed tenrec (Limnogale mergulus). Annals of Anatomy, 188/4: 383-390.

Gotch, A. 1995. Latin Names Explained. A guide to the scientific classification of reptiles, birds, and mammals. London: Blandford Press.

Major, C. 1896. Diagnoses of new mammals from Madagascar. Annals and Magazine of Natural History, 6/18: 318-325.

Malzy, P. 1965. Un mammifere aquatique de Madagascar: le Limnogale. Mammalia, 29: 399-411.

Olson, L., S. Goodman. 2008. "Limnogale mergulus" (On-line). IUCN Red List of Threatened Species. Accessed November 26, 2011 at www.iucnredlist.org.

Olson, L., S. Goodman. 2004. Phylogeny and biogeography of tenrecs. Pp. 1235-1242 in J Benstead, S Goodman, eds. The Natural History of Madagascar. Chicago: University of Chicago Press.