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The Mouse Lemur

Microcebus

Suborder: Strepsirrhini

Infraorder: Lemuriformes

Superfamily and family: Cheirogaleoidea

Genus: Microcebus

Species of mouse lemurs: M. berthae, M. bongolavensis, M. danfossi, M. griseorufus, M. jollyae, M. lehilahytsara, M. mamiratra, M. mittermeieri, M. murinus, M. myoxinus, M. ravelobensis, M. rufus, M. sambiranensis, M. simmonsi, M. tavaratra

 

The taxonomy of the genus Microcebus is extremely fluid, with ten new species described since 2000 (Rylands 2007). Generally, the best researched species to date are M. murinus, M. rufus and M. ravelobensis and less or little is known about the other species.

 

Morphology

 

Mouse lemurs have a combined head, body and tail length of less than 27 cm (10.6 in) making them the most diminutive of the primates. Among the mouse lemurs, the superlative goes to M. berthae, which is the world's smallest primate. Mouse lemurs can be divided up into two groups based on their general overall fur coloration. M. murinus and M. griseorufus are generally grayish, while M. rufus, M. ravelobensis, M. myoxinus, M. berthae, M. sambiranensis, M. tavaratra, M. lehilahytsara, M mittermeieri, M. jollyae, and M. simmonsi are overall generally reddish. However, it is difficult to distinguish certain species apart purely by observation, and such species are discriminated from one another based on genetic differences and/or body measurements.

 

All mouse lemurs have a white strip between the eyes. M. lehilahytsara is bright maroon, with a whitish ventrum and an orangeish back, head, and tail. M. rufus has a grayish brown back with a black stripe, reddish arms, grayish-white ventrum and a red-brown head. M. mittermeieri is red-brown or rust coloured on its head and back with some orange on its limbs with a white-brown ventrum. M. jollyae is reddish-brown on its back and head and has a grey ventrum. M. simmonsi has dark reddish or orange brown fur on its back, arms, and head and has a grayish white ventrum. The colour of the head of M. bongolavensis and M. danfossi varies with the individual but the back is orangish maroon, and the ventrum is creamy-white. M. mamiratra has a light reddish-brown back and tail, with a white or cream colored ventrum. M. tavaratra has a reddish head, dark brownish back, and a whitish-beige ventrum. M. sambiranensis has a reddish back with a vaguely defined stripe and a whitish-beige ventrum. M. ravelobensis has a golden-brown or mottled-red back, with a yellow to white ventrum and a brown tail. M. murinus has a grayish-brown to brownish-gray back, a beige or gray ventrum, and a stripe down the back. M. myoxinus has a red-brown back with a dorsal stripe and red-brown head markings. M. berthae is reddish, with a dorsal line and a head that is brighter than the rest of its coloration. M. griseorufus has a gray back with a cinnamon-brown stripe, reddish markings on its head, and a white ventrum.

 

The body mass of mouse lemurs is seasonally variable, but published body weight averages range from 39.6-48 g (1.4-1.7 oz) 

 

M. myoxinus is not sexually dimorphic in body size but shows a seasonal swap of dimorphism between males and females, with males consistently heavier than females during the reproductive season with the opposite true the rest of the year. A similar seasonal shift in sexual dimorphism of mass is seen in M. murinus. Body mass is seasonally variable in M. murinus as well. M. rufus do not show significant differences in body mass between the sexes.

 

Neither M. berthae nor M. murinus show sexual dimorphism of body size. M. myoxinus are not sexually dimorphic in body size but show a seasonal swap of dimorphism between males and females, with males consistently heavier than during the reproductive season with the opposite true the rest of the year (Schwab 2000). A similar seasonal shift in sexual dimorphism of mass is seen in M. murinus.

 

All mouse lemurs generally move quadrupedally; including running, but also leaping short distances, and some movement on the ground. However, the usual mode of travel is quadrupedally on branches. Some locomotor differences between mouse lemur species have been discovered. M. ravelobensis, for example, moves through its environment by leaping although M. murinus is predominantly quadrupedal; the differences are probably due to different body morphology, as well as different preferred forest strata.

 

Range

 

Mouse lemurs, like all other lemurs, are restricted to the island-nation of Madagascar off of the eastern shores of Africa. Between the reddish forms and grayish forms, reddish species (M. rufus, M. ravelobensis, M. myoxinus, M. berthae, M. sambiranensis, M. tavaratra, M. lehilahytsara, M. mittermeieri, M. jollyae, and M. simmonsi) tend toward small spatial distributions while grayish forms (M. murinus and M. griseorufus) have larger distributions.

M. bongolavensis is found between the Sofia River in the north and the Mahajamba River in the south in the northwestern part of Madagascar. The distribution of this species is delimited by the central Malagasy plateau in the east and by the Mozambique Channel in the west. M. danfossi can be found just north of M. bongolavensis, delimited by the Sofia River in the south and the Maevarano River in the north. The eastern and western limits are as in M. bongolavensis. M. rufus is reported from Ranomafana National Park and Mantadia National Parks in southeastern and eastern Madagascar respectively. M. mittermeieri has only been found at the Anjanaharibe-Sud Special Reserve in northern Madagascar, whereas M. jollyae as only be found at the Mananjary and Kianjavato localities in eastern Madagascar. M. simmonsi has only been found in the Betampona Special Reserve and in the Zahamena National Park in northeastern Madagascar.

 

M. mamiratra is known only from the island of Nosy Be, off the northwest coast of Madagascar, M. ravelobensis is only found in the Ankarafantiska Nature Reserve in northwest Madagascar. M. tavaratra is only known from the Ankarana Special Reserve in far northern Madagascar, M. sambiranensis is only known from Manongarivo Special Reserve in northern Madagascar.

While not well defined, the M. murinus distribution is wide, roughly stretching in the west of Madagascar from Ankarafantsika National Park south to the Onilahy River, with another pocket of inhabitance in the southeastern tip of the island in the Mandena Conservation Zone. M. myoxinus is found between the Tsiribihina River and the Soalala Peninsula in northwestern Madagascar. M. berthae is found around the Kirindy/CFPF Forest and perhaps further north in western Madagascar. M. griseorufus inhabits the area around Toliara in southwestern Madagascar north to Lamboharana and may range further south and southeast. M. lehilahytsara has only been found at Andasibe and Mantadia National Park in eastern Madagascar (Kappeler et al. 2005). Finally, M. simmonsi has been found only at the Betampona Special Reserve and in the Zahamena National Park in eastern Madagascar (Louis et al. 2006).

 

Habit

 

In general, all types of forest habitat on Madagascar are called home by mouse lemurs, including forests altered by humans (Kappeler & Rasoloarison 2003; Radespiel 2006). Types of forest in which different species of mouse lemur are found include evergreen littoral, dry deciduous, transitional, gallery, arid spiny, sub-arid thorn scrub, thick scrub, spiny, mangrove, sub-humid, partially evergreen, lowland, lowland and montane tropical humid, and mosaic. They have also been found in old eucalyptus plantations with undergrowth. Some species are found in several habitat types, whereas others are found in only one type, although data on restricted habitat use can sometimes be the result of a lack of research, for habitat use by species. Mouse lemurs can be found from sea level up to almost 2000 m.

 

Ecology

 

Omnivorous food choice is characteristic of all species of mouse lemur and generally, diets are diverse and change depending on the season. For example, foods that are consumed by M. murinus include insect secretions, arthropods, small vertebrates, gum, fruit, flowers, nectar, and also leaves and buds. Gums, but also sugary secretions of insects, are extremely important in mouse lemur diets, especially the diets of mouse lemurs living in dry forests. The diets of M. rufus and M. ravelobensis are both similar to the diet of M. murinus. At the only long-term study site of M. rufus diet at the Ranomafana National Park, the species was highly frugivorous, consuming an estimated minimum of 64 kinds of fruit but also members of 9 different orders of insect. In the same study of mouse lemur diet (M. rufus) to date, fruit of the mistletoe (Bakerella) was found to be a diet staple for the species, and was a keystone food used to get through times of resource scarcity. At this study site, a seasonal change in diet is seen at the end of the rainy season and the early ensuing dry season when there is a significant increase in the number of types and quantities of fruits eaten. Data on the diet of M. berthae is limited, but preliminary data indicates that the species eats mostly animal matter and insect secretions. Also, where more than one species of mouse lemur are sympatric, diets can be considerably different between the species.

 

All mouse lemurs are strictly nocturnal. In general, mouse lemur activity levels, metabolism, body temperature, and body mass all vary throughout the year and are perhaps viewed best through the lens of an annual cycle which is driven by changes in day length. Mouse lemur seasonal weight fluctuations are also related to changes in daylight duration. Two types of torpor are seen in mouse lemurs; daily and seasonal. Daily torpor functions in energy management, while seasonal torpor functions to help mouse lemurs survive yearly periods of resource scarcity. However, not all mouse lemurs hibernate, and in fact, there appears to be no clear pattern at all. Some individuals of the same species and even the same population hibernate while others do not, and different populations of the same and different species at different locations show varying patterns of torpor. During torpor and hibernation, metabolic rate as well as body temperature decline, and can reduce the metabolism of the mouse lemur by up to 90% and the body temperature to nearly that of the environment around it.

 

At one study site in western Madagascar, two different types of torpor are practiced by M. murinus; daily torpor averaging 9.3 hours punctuated by activity, and long-term torpor, which may last for weeks.. Long-term torpor in M. rufus has lasted between 6-24 weeks (Atsalis 2008). There are also seasonal changes in body weight, with all species gaining weight during the rainy season and losing weight during the dry season. For example, during the austral winter (May-June) M. murinus and M. rufus begin fattening themselves, gaining body weight as well as increasing the volume of the tail. Individuals who enter seasonal torpor lose more weight than those that do not. After a period of long-term torpor, mouse lemurs will have lost all of the preceding weight gain (Atsalis 2008).

 

Mouse lemurs are often found living sympatrically with other primates. For example, at Ranomafana National Park in southeastern Madagascar, M. rufus is a member of a primate community that also includes Avahi laniger, Cheirogaleus major, Daubentonia madagascariensis, Eulemur fulvus, Eulemur rubriventer, Hapalemur aureus, Hapalemur griseus, Prolemur simus, Varecia variegata, Lepilemur sp., and Propithecus diadema. In a given habitat, more than one species of mouse lemur can live in sympatry, as is the case with M. murinus and M. ravelobensis in northwestern Madagascar, M. murinus and M. berthae in western Madagascar and M. murinus and M. griseorufus in southern Madagascar and M. murinus and M. myoxinus in western Madagascar as examples. Aggression has been seen between sympatric mouse lemurs and dwarf lemurs.

 

M. murinus prefers to sleep in holes in trees while the other species of mouse lemur use tree holes as well as a variety of other sleeping site options. When living in sympatry, M. murinus prefers tree holes while M. ravelobensis sleeps on branches, lianas, and leaves; a difference that is attributable to inter-species competition. M. berthae sleeps alone in thick vegetation. In the dry season, over a dozen individuals of M. murinus have been found in a single tree hole sleeping site.

 

Possible and potential predators of mouse lemurs include a variety of nocturnal viverrids, mongooses, and domestic dogs as well as several different types of raptor. Snakes are also predators of mouse lemurs and have been seen attacking M. murinus. In wild M. murinus, several individuals were observed to mob and even bite a Malagasy tree boa (Sanzinia madagascariensis) that was attacking an adult male, permitting its escape. The Madagascar long-eared owl and the Madagascar harrier-hawk both prey on mouse lemurs. The red owl (Tyto soumagnei) is a predator of the northern rufous mouse lemur (M. tavaratra). In fact, predation can be quite severe, with estimates at Beza Mahafaly, southern Madagascar assigning a 25% loss each year in the entire M. murinus population exclusively to owl predation.



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