Small-toothed Sportive Lemur - Taxonomy and Phylogeny

Taxonomy and Phylogeny

The small-toothed sportive lemur or small-toothed weasel lemur, a member of the sportive lemur genus (Lepilemur), was first described in 1894 by Charles Immanuel Forsyth Major, based on a specimen found in the Ankafana Forest in the eastern districts of the former Betsileo province in central Madagascar. Although Forsyth Major did not explicitly state the origins of either the scientific name or the vernacular name, he did note that it had smaller molar teeth relative to other sportive lemurs. The species name microdon is derived from the Ancient Greek micro-, meaning "small" and -odon, meaning "tooth."

Until the 1990s, there was some dispute over the taxonomic status of the species. For much of the 20th century, the small-toothed sportive lemur was considered a subspecies of the weasel sportive lemur (Lepilemur mustelinus). In his book The Primates of Madagascar from 1982, primatologist Ian Tattersall deviated from the traditional view by considering L. microdon a synonym of the weasel sportive lemur, while also recognizing only a single species of sportive lemur. Tattersall based his decision on what he considered to be a lack of detailed anatomical studies and field surveys, while also factoring in the difficulty in observing the animals in the wild, the presence of only subtle variations among museum specimens, and his own unwillingness to consider differences in karyotypes as grounds for defining distinct species. However, primatologist Russell Mittermeier, et al. in Lemurs of Madagascar (1994), taxonomist Colin Groves in Mammal Species of the World (2005), and others favored recognizing the small-toothed sportive lemur as a species while also recognizing a total of seven sportive lemur species.

A cytogenetic (chromosome) study by Nicole Andriaholinirina, et al. published in 2005 added strong support to the species status of the small-toothed sportive lemur by demonstrating that its karyotype was distinct from all other sport lemur species. The species has 24 chromosomes (2n=24); the autosomal pairs (not sex chromosomes) include eight that are meta- or submetacentric (where chromosome arms are equal or unequal in length, respectively) and three smaller acrocentric pairs (with the shorter chromosome arm difficult to observe). Both the X and Y chromosomes are acrocentric. The study also showed that the small-toothed sportive lemur was the sportive lemur species most genetically distinct from the weasel sportive lemur, despite their similar appearance. A total of 18 chromosomal rearrangements distinguished the two species, indicating that if the two shared the same range, hybrids would be either completely sterile or suffer greatly reduced fertility.

In September 2006, Edward E. Louis, Jr., et al. announced the discovery of 11 new species of sportive lemur based on mitochondrial DNA (mtDNA) data. Each new species resulted from the splitting of existing species. In the case of the small-toothed sportive lemur, the population at Kalambatritra Reserve became known as Wright's sportive lemur (Lepilemur wrightae), the population as Andohahela National Park became Fleurete's sportive lemur (L. fleuretae), the population in Fandriana became Betsileo sportive lemur (L. betsileo), and the population at Manombo Reserve became James' sportive lemur (L. jamesorum). The small-toothed sportive lemur remains a distinct species, while even more species have since been described, though none within its range.

Between 2006 and 2009, three studies were published to resolve the phylogenetic relationships between the sportive lemurs. Cytogenetic and molecular studies in 2006 and 2008 concluded that the small-toothed sportive lemur is most closely related to the Milne-Edwards' sportive lemur (Lepilemur edwardsi). In 2009, a study examined every known species, including the species most recently described, using two pieces of mtDNA: the D-loop and an array of genes known as the PAST fragment. The resulting data placed the sportive lemurs into four groups: Section A from northern and northwestern Madagascar, section B from northwestern Madagascar, section C from west central and southern Madagascar, and section D from eastern Madagascar. Only the small-toothed sportive lemur generated conflicting results when comparing the results between the mtDNA and D-loop data. The PAST data placed it in section B, while the D-loop data placed it in section C. The relationship between the small-toothed sportive lemur, an eastern Malagasy species, and a group of species from the west coast of Madagascar suggests that the ancestral population of the small-toothed sportive lemur dispersed to its current range from western Madagascar using river corridors. However, the conflicting data about the relationship of the small-toothed sportive lemur to either section B or section C render the precise dispersal route uncertain.