Gray mouse lemur

Appearance

The gray mouse lemur shares many traits with other mouse lemurs, including soft fur, a long tail, long hind limbs, a dorsal stripe down the back , a short snout, rounded skull, prominent eyes, and large, membranous, protruding ears. It has large eyes and a ''tapetum lucidum'' to enhance its vision at night.

The dorsal coat is brownish-gray with various reddish tones, the flanks are light gray to beige, and the ventral fur has discrete dull beige or whitish-beige patches along portions of the belly. On the rounded face, there is a pale white patch above the nose and between the eyes; some individuals have dark orbital markings. The furred portions of the hands and feet are off-white.

The gray mouse lemur is one of the smallest primates in the world, yet it is also the largest mouse lemur. Its total length is 25 to 28 cm, with a head-body length of 12 to 14 cm and a tail length of 13 to 14.5 cm. The average weight for this species is 60 g, with ranges of 58 and 67 g and 40 and 70 g reported.

Naming

The gray or lesser mouse lemur is named for its brownish-gray fur and mouse-like size and appearance. The genus name, ''Microcebus'', derives from the Greek words ''mikros'', meaning "small", and ''kebos'', meaning "monkey". The Latin version of ''kebos'', ''cebus'', is a common suffix used for primate names, despite the fact that the gray mouse lemur is a lemur, and not a monkey. The species name, ''murinus'', means "mouse-like" and derives from the Latin word ''mus'', or "mouse", and the Latin suffix ''-inus'', which means "like".

The lemur is known locally by several names in Malagasy, depending upon the region. Around Tôlanaro, it is called ''pondiky'' [punˈdikʲ]. In the northern end of its range, it is known as ''tsidy'' [ˈtʃidʲ]. Around Morondava, it is referred to as ''koitsiky'' [kuiˈtʃikʲ], ''titilivaha'' [ti̥tiliˈva], and ''vakiandry'' [vakiˈaɳɖʐʲ]. In many cases, these Malagasy names are also used for other visually indistinguishable mouse lemur species that live within its range.

Status

The gray mouse lemur was listed in Appendix 1 by the Convention on International Trade in Endangered Species in 1975, declaring it as threatened with extinction and prohibiting international trade of specimens except for non-commercial use, such as scientific research. As of 2009, the species was no longer listed under Appendix 1. The 2008 International Union for Conservation of Nature Red List assessment lists it as a species of Least Concern with a decreasing population trend.

Its greatest threats are habitat loss from slash-and-burn agriculture and cattle-grazing, as well as live capture for the local pet trade in the northern and southern parts of its range.

Behavior

The gray mouse lemur is nocturnal, sleeping during the day in tree holes lined with leaf litter or purpose-built spherical nests constructed from dead leaves, moss and twigs. It usually forages alone at night, but may sleep in groups during the day, the composition of which depends on gender and season. Tree holes can be shared with up to 15 other individuals, although males tend to sleep alone while females tend to share nests.

All mouse lemurs are highly active at night, often scurrying like mice and leaping over 3 m, using the tail as a balancing organ. When moving among the terminal branches of bushes and trees, they grip using all four feet and move with four legs. When on the ground, either to catch insects or cross short open areas, mouse lemurs hop like a frog. When hunting, the grey mouse lemur is known to catch invertebrates and small vertebrates with quick hand grasps.

In the dry season, the gray mouse lemur faces the challenge of exploiting sparsely distributed feeding resources efficiently. Results of a recent study on this showed that the gray mouse lemur does not move around randomly, but rather use spatial cues to find food resources in the absence of sensory cues, and that they seem to reuse common, highly efficient routes with regard to travel distance. It is believed that rather than using a route-based network, the gray mouse lemur has some sense of mental representation of their spatial environment, which they use to find and exploit food resources.

Foraging behavior is often slow, with height and direction changing continuously. Predation of insects occurs primarily on the ground. Before descending, the ear pinnae move alternately to help pinpoint the precise location of their prey. Insects are captured during a rapid dash across the leaf litter and are transported by mouth up into the relative safety of the branches. Studies with captive gray mouse lemurs have shown that vision is primarily used for prey detection, although the other senses certainly play a role in foraging.

The gray mouse lemur is omnivorous, feeding primarily on fruit and invertebrates. Local populations appear to specialize on locally available fruit.

Habitat

Like all other members of the family Cheirogaleidae, the gray mouse lemur is nocturnal and arboreal. It inhabits lowland tropical dry forest, sub-arid thorn scrub, gallery forest, spiny forest, eastern littoral forest, dry deciduous forests, semi-humid deciduous, moist lowland forest, transitional forest, and secondary forests or degraded forests all ranging up to 800 m above sea level.

Reproduction

The mating system is described as multi-male and multi-female. Males establish dominance hierarchies prior to the mating season, however, some studies in the wild have shown no male aggression or visible competition for receptive females.

The gray mouse lemur is sexually dimorphic in terms of body mass, which fluctuates annually with the breeding season. Male body mass increases prior to the mating season, which is believed advantageous in searching for receptive females in estrus, and enabling them to maintain shorter periods of torpor. The study found that this is because males exhibit continued activity during the dry season while females hibernate. Thus, sexual dimorphism in terms of body size is dependent on environmental conditions and can therefore vary by season, location, population, and individuals' specific behavior.

The females are receptive for 45 to 55 days between September and October, with estrus lasting 1 to 5 days. Females advertise estrus by distinctive high-frequency calls and scent-marking. Gestation lasts 54 to 68 days, averaging 60 days, typically resulting in 2 or 3 offspring weighing 5 g each.

Infants are born in a leaf nest or tree hole in November prior to the onset of the rainy season. Weaning occurs after 25 days, and the infants are either left in the nest or carried in the mother's mouth and deposited on a branch while she forages. Infant mouse lemurs do not cling to the mother's fur. Independence is attained in 2 months, while sexual maturity is reached at 10 to 29 months in females and 7 to 19 months in males. Closely related females remain loosely associated after maturation , whereas males disperse from their natal area. In the wild, the gray mouse lemur's reproductive lifespan is no more than 5 years, although captive specimens have reportedly lived as long as 15 years and 5 months.

The gray mouse lemur uses cooperative breeding as a form of family insurance. The female regularly transfers her offspring to other females' nests—and likewise grooms and cares for offspring other than her own. While this can have a high physiological cost on a lactating female that is already expending a lot of energy, it can be beneficial overall to insuring survival among closely related groups with high mortality risk. A study that took place over three breeding seasons showed that closely related females form breeding groups mainly when there is a shortage of suitable roosts; when there is an advantage of a communal nest for defense, or when there are thermoregulatory benefits. In the event of offspring adoption, when a parent dies and a closely related female takes over care, it is believed that this is beneficial to groups with high mortality risk.