Gray mouse lemur
The gray mouse lemur, grey mouse lemur or lesser mouse lemur is a small lemur, a type of strepsirrhine primate, found only on the island of Madagascar. Weighing, it is the largest of the mouse lemurs, a group that includes the smallest primates in the world. The species is named for its mouse-like size and coloration and is known locally as tsidy, koitsiky, titilivaha, pondiky, and vakiandry. The gray mouse lemur and all other mouse lemurs are considered cryptic species, as they are nearly indistinguishable from each other by appearance. For this reason, the gray mouse lemur was considered the only mouse lemur species for decades until more recent studies began to distinguish between the species.
Like all mouse lemurs, this species is nocturnal and arboreal. It is very active, and though it forages alone, groups of males and females form sleeping groups and share tree holes during the day. It exhibits a form of dormancy called torpor during the cool, dry winter months, and in some cases undergoes seasonal torpor, which is unusual for primates. The gray mouse lemur can be found in several types of forest throughout western and southern Madagascar. Its diet consists primarily of fruit, insects, flowers, and nectar. In the wild, its natural predators include owls, snakes, and endemic mammalian predators. Predation pressure is higher for this species than among any other primate species, with one out of four individuals taken by a predator each year. This is counterbalanced by its high reproductive rate. Breeding is seasonal, and distinct vocalizations are used to prevent hybridization with species that overlap its range. Gestation lasts approximately 60 days, and typically two young are born. The offspring are usually independent in two months, and can reproduce after one year. The gray mouse lemur has a reproductive lifespan of five years, although captive individuals have been reported to live up to 15 years.
Although threatened by deforestation, habitat degradation, and live capture for the pet trade, it is considered one of Madagascar's most abundant small native mammals. It can tolerate moderate food shortages by experiencing daily torpor to conserve energy, but extended food shortages due to climate change may pose a significant risk to the species.
Etymology
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. In the northern end of its range, it is known as tsidy. Around Morondava, it is referred to as koitsiky, titilivaha , and vakiandry. In many cases, these Malagasy names are also used for other visually indistinguishable mouse lemur species that live within its range.
Taxonomy
As its name implies, the gray mouse lemur is a lemur, a type of primate, and belongs to the suborder Strepsirrhini and infraorder Lemuriformes. Within Lemuriformes, it belongs to the family Cheirogaleidae, which contains the mouse lemurs, dwarf lemurs, giant mouse lemurs, fork-marked lemurs, and hairy-eared dwarf lemur. The mouse lemur genus Microcebus includes the smallest primates in the world. Phylogenetic analyses of D-loop DNA sequences of various lemur species suggest that the gray mouse lemur may be most closely related to the reddish-gray mouse lemur.In 1777, the English illustrator John Frederick Miller included a hand-coloured plate of the gray mouse lemur in his Icones animalium et plantarum and coined the binomial name Lemur murinus. The species was moved to the genus Microcebus by the French naturalist Étienne Geoffroy Saint-Hilaire in 1834. M. murinus remained the only species of its genus, as well as the name used for all mouse lemurs on Madagascar, between the first major taxonomic revision in 1931 and an extensive field study conducted in 1972. The field study distinguished the brown mouse lemur, M. rufus—then considered a subspecies—as a distinct, sympatric species in the southeastern part of the island. Upon this revision, the gray mouse lemur was thought to account for all mouse lemurs that lived in the drier parts of the north, west, and south, while the brown mouse lemur represented the eastern rainforest mouse lemurs. More recently, scientific understanding of the distribution and diversity of the mouse lemurs has become much more complex. Additional field studies, genetic testing, and resulting taxonomic revisions throughout the 1990s and 2000s identified numerous new mouse lemur species, demonstrating that the genus includes at least 17 cryptic species.
Anatomy and physiology
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, with a head-body length of and a tail length of. The average weight for this species is, with ranges of and reported. This is smaller than the world's smallest monkey, the pygmy marmoset, which ranges between. Weight varies by season, with both sexes building fat reserves, up to 35% of their body weight, in the tail and hind legs prior to the dry season and periods of dormancy. The tail of the gray mouse lemur can increase fourfold in volume during the wet season when it is storing fat. Even in captivity when environmental limitations are not an issue, mouse lemurs have shown a seasonal dietary preference with a greater protein intake during what would be their more active season.
Researchers have identified differences in the tooth morphology of the first and second molars between the gray mouse lemur and the reddish-gray mouse lemur. In the reddish-gray mouse lemur, the first lower molar is squared and both the first and second upper molars have slight indentations around the middle of the posterior margin. The gray mouse lemur has a more elongated m1 and lacks the aforementioned indentation on M1 and M2. In terms of its general dentition, the gray mouse lemur shares the same dental formula as all other members of its family, Cheirogaleidae:
This species has 66 chromosomes, closely resembling the karyotype of the dwarf lemurs. Except for the X chromosome, all chromosomes are acrocentric. Its genome size is 3.12 picograms .
Ecology
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 above sea level. The species is more common in secondary forest than in primary forest, particularly bush and scrub habitat, where it occupies a "fine branch" niche, restricting the vertical range to fine branches, fine terminal supports, lianas and dense foliage. These lemurs are usually seen on branches less than in diameter. The gray mouse lemur tends to prefer lower levels of the forest and the understory, where branches and vegetation are dense.In secondary forest, it is generally observed from ground level up to above ground, yet in the canopy of primary forest. Studies have found that the species can spend as much as 40% of its time below, with 70% of its time spent at this level during the end of the dry season, when plant food is limited and insects compose a larger percentage of the diet. The species is more numerous in spiny forest, such as the Andohahela Special Reserve, than in the gallery forest, preferring drier, littoral forest, whereas the brown mouse lemur prefers inland rain forest.
The limits of the distribution are poorly understood. It is believed to range from the Onilahy River or Lake Tsimanampetsotsa in the south to Ankarafantsika National Park in the north. There is also an isolated and disjointed population in the southeastern part of the island, near Tôlanaro and the Andohahela National Park, up to the Mandena Conservation Zone. Individuals tend to occupy small home ranges of. The gray mouse lemur is also sympatric with the reddish-gray mouse lemur, golden-brown mouse lemur, Madame Berthe's mouse lemur, and several other cheirogaleid lemurs. In Ankarafantsika National Park, where it coexists with the golden-brown mouse lemur, the gray mouse lemur's relative population density was highest at higher altitudes and in drier habitat, while the golden-brown mouse lemur preferred the opposite. Another study has looked at the coexistence of the gray mouse lemur and Madame Berthe's mouse lemur and found small, exclusive clusters of each species and a high degree of feeding niche overlap.
The gray mouse lemur can reach high population densities up to several hundred individuals per square kilometer. This abundance is not uniform and tends to concentrate in "population nuclei", suggesting that it is difficult to accurately estimate population densities when extrapolating from a small area to a large area. The difficulty in finding individuals during some times of the year, particularly during the dry periods, can further complicate the problem of estimating population densities.
Mouse lemurs are omnivorous, and favor fruit and insects for the bulk of their diet. The gray mouse lemur may even come down to the ground to catch insect prey, though it quickly returns to the protective cover of the understory to consume its catch. Nectar is also a part of the gray mouse lemur's diet, making it a potential pollinator for local plant species. A single instance of a male cannibalizing an adult female is known.