GERP'S MOUSE LEMUR

Microcebus gerpi

Geographic Distribution and Habitat
​​The Gerp’s mouse lemur is only found in the Sahafina forest and surrounding secondary forests in eastern Madagascar. The region is a mix of dense lowland forest and formerly logged woodlands now in recovery. This area of the island nation is particularly humid due to its placement in between the Indian Ocean and the Central Highlands of central Madagascar. The natural barriers of the regions have led to the evolution of several unique species such as the Gerp’s mouse lemur.

The Gerp's mouse lemur range is so small, it is barely perceptible even in this zoomed-in map. We circled it to make it more visible. Map, IUCN 2020.

Size, Weight, and Lifespan
The 24 species of mouse lemur found in Madagascar are the smallest primates in the world. The Gerp’s mouse lemur is one of the biggest species within the genus, weighing in at a whopping 2.4 ounces (68 g). These mouse lemurs are about 10.6 in (27 cm) in length from head to tail. Females have been measured to be very slightly larger than males, but this is most likely due to the small sample size of the species. Only 7 fully grown adults have been officially measured.

Mouse lemurs can live to be around 18 years old.

Appearance
Other than their small size, mouse lemurs can be characterized by their long, furry tails, large eyes, long fingers, and round body and head. All mouse lemurs have a white strip between their eyes. Mouse lemurs are physically adapted to nocturnal life with large eyes and protruding, flexible ears. Gerp’s mouse lemurs can be differentiated from their relatives through their small ears, long snouts and tails, and larger overall size. The Gerp’s mouse lemur has a white belly and red dorsal fur that fades to gray. The lemur’s pink skin is visible on his hands, feet, and snout.

All lemuriforms, the suborder including lemurs, galagos, and lorises, possess a toothcomb. A toothcomb is a set of about six lower-front teeth use for grooming.

Photo credit: Blanchard Randrianambinina/Creative Commons

What Does It Mean?

Allomothering:
Individuals other than the biological mother of an offspring perform the functions of a mother (as by caring for an infant temporarily).

Arboreal:
Physically adapted to living primarily or exclusively in trees.

Dominance hierarchy:
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social living groups, member are likely to compete for access to limited resources and mating opportunities. 

Dorsal: 
Of, on, or relating to the upper side or back of an animal, plant, or organ.

Lowland forest:
An equatorial evergreen rainforest, commonly known as a tropical rainforest, which receives high rainfall (80 in, or 2 m) throughout the year.

Nocturnal: 
Active at night.

Omnivorous:
Having a diet that consists of food of both plant and animal origin.

Secondary forest:
A forest that has regrown after a major disturbance, such as fire or timber harvest, but has not yet reached the mature state of primary forest.

Toothcomb:
The incisors on the lower front jaw of some animals are grouped as if to form a comb. The toothcomb is used by these animals to groom and clean their fur.

Torpor:
A sleep-like state in which the body decreases physiological activity. 

​​Trill:
The sound of going quickly back and forth many times between two musical notes that are close to each other.

Visit the Glossary for more definitions

Diet
Little is known about the Gerp’s mouse lemur’s diet. Better studied mouse lemurs are omnivores who have been observed to eat everything from fruits to flowers, leaves, gum, insects, nectar, and small vertebrates. While it is a safe assumption that the Gerp’s mouse lemur eats at least some of these food items, it should be noted that the most well-studied mouse lemurs are only found on the west and north coasts of Madagascar. It is entirely possible that the Gerp’s mouse lemur and their adjacent relatives who live in the wet eastern forests may have several distinct items in their diet.

Behavior and Lifestyle
The Gerp’s mouse lemur is nocturnal and arboreal. They forage for food at night and then return to their sleeping den (usually a hole in a tree or something similar), where they sleep from dawn to dusk.

Mouse lemurs are capable of undergoing torpor and hibernation. The nature of this torpor is different from species to species, and even differs within species. Most mouse lemurs enter a torpor as they sleep during the day. Some species will enter into a torpor period lasting anywhere from one month to as long as six months when food is scarce.

Fun Facts

Weighing in at just 2 grams, mouse lemurs have the smallest brains of any primate in the world.

Daily Life and Group Dynamics 
The level of social activity can vary greatly among the mouse lemur genus. For instance, the gray mouse lemur spends around 96% of the day around others, while the brown mouse lemur spends less than 10% of its time with others. Although the amount of research available is limited, the Gerp’s mouse lemur is believed to be a solitary animal.

Still, it is common for even the most solitary of mouse lemurs to gather in communal sleeping sites. Given our knowledge of the Gerp’s mouse lemur’s closest relatives, our safest assumption is that closely related females gather in sleeping dens of 2-5 individuals every night while males sleep alone. It is also possible that males and females sleep together.

There is a subtle dominance hierarchy in most species of mouse lemurs, with females often having dominance over males. This social organization becomes more pronounced in captivity

Communication
Mouse lemurs are capable of making several different vocalizations mostly made up of trills and whistles. These calls include mating calls, predator warnings, trills for their morning reunion at the sleeping site, and calls possibly meant to signal dominance over a territory. Babies possess their own repertoire of calls to stay in contact with their mothers. Some species of mouse lemurs also make ultrasonic calls that cannot be heard by humans without special equipment.

Mouse lemurs use their urine for scent-marking, marking territory, alerting others to their presence, and advertising their reproductive state.

Reproduction and Family
There is no data available regarding the reproduction of Gerp’s mouse lemurs. Most mouse lemurs develop quickly compared to other primates, with some species mating in their first year of life. Females’ gestation period lasts an average of 55–60 days. Infants do not tend to ride on their mothers, as is common in primates; instead, the mother will carry her baby with her mouth. Females that live with family practice allomothering and may even nurse babies that are not their own.

Mouse lemurs are weaned off of nursing at around a month of age and are fully independent at just two months. Mouse lemurs in captivity reach sexual maturity after about six months. Mating occurs sometime between September and January. Most species of mouse lemur practice scramble competition reproduction, meaning that instead of defending a territory from rivals, males essentially race each other to mate with as many females as possible.

Ecological Role
There is not enough research to accurately state the ecological role of the Gerp’s mouse lemurs. Since ancestral lemurs arrived in Madagascar between 50 and 60 million years ago, lemurs and their close cousins have evolved to undertake a wide variety of niches.

Conservation Status and Threats
The International Union for Conservation of Nature classifies the Gerp’s mouse lemur as Critically Endangered (IUCN, 2012) and list the species as one of the 25 most endangered primates on Earth. The IUCN justifies this assessment by noting that the population is severely fragmented and is in decline, the species only occurs in a single, unprotected area, and there are no signs of human encroachment slowing down.

As is the case with most primates in Madagascar, the greatest threat to the Gerp’s mouse lemur is habitat destruction. Much of their territory has been destroyed for agricultural purposes. Over-logging has also limited the Gerp’s mouse lemurs habitat. There is also opportunistic hunting of mouse lemurs by locals.

Conservation Efforts
The IUCN has called for an increase in research on the Gerp’s mouse lemur and the Sahafina forest. The forest was not studied in depth until 2008, which is why the Gerp’s mouse lemur was not officially described until 2012. One notable group studying the region is Groupe d’Étude et de Recherche sur les Primates de Madagascar (GERP). This Malagasy-German research team, for whom the animal is named, discovered the Gerp’s mouse lemur when they began their study of the forest in 2008. GERP works to enforce environmental protection laws, reforest degraded areas, educate locals, and provide opportunities to Malagasy college students.

​References:

  • Rasoloarison RM, Weisrock DW, Yoder AD, Rakotondravony D, Kappeler PM. (2013) Two new species of mouse lemurs (Cheirogaleidae: Microcebus) from eastern Madagascar. International Journal Primatology. 34(3):455–469.
  • https://www.iucnredlist.org/species/16971461/16971464
  • https://portals.iucn.org/library/sites/library/files/documents/2017-059.pdf
  • http://pin.primate.wisc.edu/factsheets/entry/mouse_lemur/cons
  • https://phys.org/news/2012-01-primate-species-madagascar/
  • https://www.alltheworldsprimates.org/Members/Home/MasterPrimate.aspx?tid=1144
  • http://www.edgeofexistence.org/species/gerps-mouse-lemur/#overview
  • https://www.lemurconservationnetwork.org/organization/gerp/
  • https://www.nature.com/articles/289583a0

Written by Eric Starr, January 2019