Genetic analysis has revealed the existence of two new species of Madagascan mouse lemur, bringing the total number of recognised species to 20.

Weighing less than 100 g and rarely stretching more than 28 cm, tail included, mouse lemurs are the smallest primate in the world. Native to the forests of Madagascar, these strictly nocturnal omnivores come in either grey or a rich, rusty brown, and each one has a distinctive white splash running between the eyes and down the snout. Eighteen new mouse lemur species have been discovered since 1993, and their genus, Microcebus, boasts one of the highest species numbers of all primate groups. But because mouse lemur species all look so similar, distinguishing them can now only be done through genetic analysis.

During a field trip in December 2003, Rodin Rasoloarison from the University of Antananarivo in Madagascar caught two female mouse lemurs and one male in the Forêt de Marohita of the Toamasina province in eastern Madagascar. Four years later, in the Anosy region of south-eastern Madagascar, Rasoloarison caught six individuals in the Forêt de Manantantely and four more in the Forêt d’Ivorona. He performed a morphological analysis on the individuals, including weighing and measuring various external and internal parts, and fur colours were identified using colour charts. Tissue samples were then extracted and sent to Anne Yoder and Dave Weisrock at Duke University in Durham, North Carolina, for analysis.

Two mitochondrial and four nuclear loci were sequenced from the two new species, and then analysed alongside 279 mitochondrial and 209 nuclear sequences from different mouse lemur species found in 78 sites across Madagascar. The team used a technique called a Bayesian phylogenetic analysis for both the mitochondrial and nuclear loci, and a STRUCTURE analysis to infer the presence of distinct populations using multi-locus nuclear genotype data.

“I would say that in general, it is highly unusual to describe new species of primates in this age of global travel and consequent access to remote areas of the planet,” says Yoder, a Professor of Biology and Evolutionary Anthropology and Director of the Duke Lemur Centre. “That said, the number of described lemur species has more than tripled in the last 10 years. A large number of these new species have been mouse lemurs.

“I suspect that there are even more mouse lemur species out there to be found (indeed, there are hints of that in some of our genetic data). Mouse lemurs are morphologically cryptic, they are tiny, they are nocturnal, and they occur in remote places. It therefore makes a lot of sense that the harder we look, the more species we will find.”

The team named the new species from the Forêt de Marohita (Marohita meaning “many views") the Marohita mouse lemur (Microcebus marohita). It turned out to be a very large species, stretching 275–286 mm from nose to tail, with a considerable body mass of up to 89 g. "The large body mass of M. marohita is remarkable," the team report in today's issue of the International Journal of Primatology. "The single male M. marohita, which we judge to be a subadult, is as heavy as M. gerpi males, which until the new species described here, were the largest known mouse lemur males." The females were found to be 20% heavier than all other known females.

The colouring of the Marohita mouse lemur's long, dense fur ranges from a gorgeous ginger to a dusty umber with a coat of blackish grey underfur. Its undersides and the upper surfaces of its paws are a whitish beige and it has long, pink little fingers.

The second new species, found in the Anosy region in 2007, was called the Anosy mouse lemur (Microcebus tanosi). It has a total body length of 275 mm and weighs 49 g, which still makes it relatively large by mouse lemur standards. Like the Marohita mouse lemur, the Anosy mouse lemur has a rusty-coloured coat, but has a slightly darker colouring on its undersides.

Due to continuous habitat destruction threatening the survival of the Marohita mouse lemur, the researchers have classified it as endangered. "As revealed by a recent visit (in 2012), the forest of Marohita is highly degraded and has been substantially damaged since the initial collecting trip from 2003," they report. "Thus, despite its species’ name, this mouse lemur is threatened by ongoing habitat destruction, and “many views” of its members are unlikely.”

The Tanosi mouse lemur's status is so far unknown, but the researchers say it will likely also been classified as endangered due to similar environmental concerns. "The forest at Manantantely was already heavily degraded at the time of our field survey, whereas the forest at Ivorona was only slightly degraded, but the current state of these forests and the mouse lemur populations therein is not known," they report.

“Public awareness in Madagascar is very important,” adds Yoder. “I have found that the Malagasy people take great pride in their lemurs, as soon as they understand that Madagascar is unique in having lemurs, and also, that certain lemurs are specific only to a particular area. Also, and obviously, the government needs to participate in protecting the forests, and in providing economic alternatives to slash and burn agriculture to the Malagasy people.”

Here's a video of mouse lemurs at the Duke Lemur Centre. Their eyes are so big, blinking looks like an enormous effort for them:


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