Back in September, the discovery of a new monkey – the Lesula (Cercopithecus lomamiensis) – was announced in PLoS ONE. How did science completely ignore a monkey?!? Well, these monkeys are only found in a small, isolated part of the vast, mostly unknown-to-science, rainforests of the Democratic Republic of Congo. Researchers were in the “TL2″ forest (in the river basins of the Tshuapa, Lomami and Lualaba Rivers) searching for bonobos in habitat that hadn’t yet been censused. John Hart, one of the researchers responsible for the discovery, explained, “This area is so remote that we are the first binocular sporting biologist to venture into the depth of the TL2,” and it is likely that any primate that made it out of the forest “arrived as heavily smoked and unrecognizable bushmeat in centers like Kisangani.” It wasn’t until someone brought back a photograph of a little girl and her pet monkey that they realized a monkey previously unknown to science was waiting for them.

Photograph by Terese B. Hart

Lesula: A New Species of Cercopithecus Monkey Endemic to the Democratic Republic of Congo and Implications for Conservation of Congo’s Central Basin

John A. Hart, Christopher C. Gilbert, Andrew S. Burrell, James L. Fuller, Maurice Emetshu, Terese B. Hart, Ashley Vosper, Eric Sargis, and Anthony J. Tosi. Published 2012 in PLoS ONE. doi:10.1371/journal.pone.0044271.

In June 2007, a previously undescribed monkey known locally as “lesula” was found in the forests of the middle Lomami Basin in central Democratic Republic of Congo (DRC). We describe this new species as Cercopithecus lomamiensis sp. nov., and provide data on its distribution, morphology, genetics, ecology and behavior. C. lomamiensis is restricted to the lowland rain forests of central DRC between the middle Lomami and the upper Tshuapa Rivers. Morphological and molecular data confirm that C. lomamiensis is distinct from its nearest congener, C. hamlyni, from which it is separated geographically by both the Congo (Lualaba) and the Lomami Rivers. C. lomamiensis, like C. hamlyni, is semi-terrestrial with a diet containing terrestrial herbaceous vegetation. The discovery of C. lomamiensis highlights the biogeographic significance and importance for conservation of central Congo’s interfluvial TL2 region, defined from the upper Tshuapa River through the Lomami Basin to the Congo (Lualaba) River. The TL2 region has been found to contain a high diversity of anthropoid primates including three forms, in addition to C. lomamiensis, that are endemic to the area. We recommend the common name, lesula, for this new species, as it is the vernacular name used over most of its known range.

What Determines a New Species?

Hart and colleagues were lucky to have access to several specimens of lesula and their close relatives, Owl-faced monkeys (frankly, I think owl-faced monkeys, C. hamlyni, are even odder looking than the lesula!). They took a number of cranial measurements which have previously been shown to distinguish between species, as well as comparisons of pelage color. They also sequenced genetics from these samples and determined that C. lomamiensis and C. hamlyni likely shared their most recent common ancestor 1.7 millions years ago (95% confidence interval 3.0-0.5 million years). The figure below shows a lesula cranium (left) and owl-faced monkey cranium (right), and the resulst of a principle components analysis which accurately separated the species based on morphological characteristics.

From Hart et al. 2012

Lesula are distinct from their probable closest relatives based on morphology and genetics.

Lesula Behavior

Lesula were the least frequently seen primate during transects, though analyses of their vocalizations suggest that they were more numerous than visual sightings suggested. Like many guenons across Africa, the lesula were often in polyspecific associations with other primates. Polyspecific associations, when multiple species travel together, are probably an anti-predator adaptation. Primates in polyspecific associations generally make use of different levels of the forest and are better at picking up on particular predators, so being in a group with a number of species allows them to take advantage of the predator detection of all the other species in the association.

Lesula seem to take the low road relative to the other primates they associate with: when they were seen, 35% of individuals (17 of 48) were on the ground and several others descended to the group for an escape. Being cryptic may be an anti-predator adaptation for the lesula. However, the researchers actually observed a crowned eagle attack on a subadult female lesula; she later died (the eagle never returned for her, so the researchers collected her for analysis).

Lesula post-predation. From Hart et al 2012.

Lesula are sexually dimorphic: males are larger both in body and canine size than females. Sexual dimorphism is often associated with increased aggression between males in relation to access to females for mating. Excitingly, male lesula have brightly colored genitalia. This irridescent blue coloration is suspected to make the genitals stand out more in the dim light of the rainforest understory. Females are “choosy” about who they mate with – they want to choose the best, healthiest male – and conspicuous genitalia, colored in an energetically expensive way, might be a good mechanism for signalling to females that these genes are awesome. Male mandrills have similar coloration,though some primates take genital colors to extremes.

Adult male perinea and scrota. From Hart et al. 2012.

Implications for Conservation

The researchers write:

At present, TL2 remains remote from human expansion, and there is no logging or mining. Hunting is the immediate threat to the faunas of TL2. We provide a provisional IUCN Red List Assessment of Vulnerable  for C. lomamiensis based on the inferred population decline from uncontrolled bushmeat hunting. This has expanded into the species’ range over the last decade driven by the urban bushmeat markets of Kindu and Kisangani . For species with restricted ranges and reliance on primary forest, such as C. lomamiensis, uncontrolled hunting can lead to catastrophic declines over a short period.

The conservation of C. lomamiensis urgently requires controls on hunting along with the creation of a protected area. A core zone of 9000 km2 in the TL2 region is proposed as the Lomami National Park. The proposed protected area, along with the existing Réserve Naturelle de Sankuru, will cover most of the known range of C. lomamiensis. While the establishment of the new protected area is a necessary first step, active protection and monitoring are required to ensure the conservation of the lesula and other unique biodiversity of the eastern rim of Congo’s central basin.

The discovery of the lesula – very charismatic megafauna - will hopefully have umbrella effects as efforts to conserve its habitat also conserve the habitats of less charismatic species who also live in this part of the Democratic Republic of Congo.

Ethics of Research

Researchers were (sadly) lucky to have access to a number of captive and dead specimens of lesula for their analysis. The ethics of using these primates is complicated, but Hart and colleagues explain:

We obtained approval from the hunters to use these samples and no animal was hunted for the purpose of research. We acquired specimens only opportunistically in villages outside of the forest and we did not request samples from all lesula available to avoid targeting this species. When we encountered captive monkeys in villages, we photographed them with permission from the owner. We advised owners on the monkeys’ care and discouraged owners to acquire wild animals as captives.