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Xenopus longipes
Lake Oku Clawed Frog
family: Pipidae

© 2012 Lars Fehlandt (1 of 20)

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Conservation Status (definitions)
IUCN (Red List) Status Critically Endangered (CR)
See IUCN account.
CITES No CITES Listing
Other International Status None
National Status None
Regional Status None

   

Description
Xenopus longipes, the only known species in the subgroup longipes, was first described by Loumont and Kobel in 1991. It is a polyploid species, one of only two known dodecaploid vertebrate species, 12n; the other known dodecaploid species is Xenopus ruwenzoriensis) with a chromosome number of 108 (Tinsley and Kobel 1996). It is relatively small compared to other Xenopus, with males being about 28-31 mm and females being about 32-36 mm in length. X. longipes are covered with tiny black spots both dorsally and ventrally. In addition to these small black spots, some specimens have larger, irregularly distributed spots dorsally. The dorsal side of the frog tends to be brown or caramel while the ventral side tends to be a bright orange (Loumont and Kobel 1991). X. longipes has large eyes with the lower eyelid covering about 1/3 of the eye length (Tinsley and Kobel 1996). Unlike many of the Xenopus species that have large webbed feet, X. longipes have small webbed feet with thin limbs and very long toes. X. longipes also differs in bone structure from other Xenopus in its laterally displaced parasagittal crests and unique nasal structure (Loumont and Kobel 1991).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Cameroon

View distribution map using BerkeleyMapper.
X. longipes is found only in Lake Oku in the Northwest Province of Cameroon. Lake Oku is situated in the volcanic highlands of Cameroon at 6°12´N, 10°28´E at an altitude of about 2219 m above sea level (Loumont and Kobel 1991). It is a fully aquatic frog. The lake itself is relatively shallow and is surrounded by montane rainforest.

Life History, Abundance, Activity, and Special Behaviors
Life History – X. longipes was described in 1991 and little is known of its life history. The dodecaploidization is thought to have arisen from a combination of hybridization and polyploidization (Loumont and Kobel 1991).

Abundance – X. longipes is only found in Lake Oku but is the most abundant species in the lake.

Special Behaviors - Unlike most frogs of the genus Xenopus, X. longipes do not have large webbed feet and consequently are not very fast swimmers. The evolution of smaller feet in this species may be due to its location in an isolated lake with very little predation (Project Exploration 2006).

Trends and Threats
X. longipes is listed as Critically Endangered because its area occupancy is less than 10 km2 (IUCN Red List 2004). Because the species is located in such a small and concentrated area, there is fear that increased predation by introduced species may lead to a decline.

In addition, there is a chance that new fish species will be introduced to Lake Oku in the future, which will increase competition for nutrients in the lake. Although Critically Endangered, the population of X. longipes has been relatively stable according to the last evaluation of this species' status in 2004 (Tinsley and Measey IUCN Red List 2004).

A mass mortality event was observed for this species in August 2006, and reported recently by Blackburn et al. (2010). Dozens of dead and moribund X. longipes were found in the lake, although no other amphibian species in the vicinity or at nearby watersheds were observed to suffer similar mortality in the same time period. Although all sick animals had mild to moderate epidermal hyperplasia, histopathology and PCR ruled out chytridiomycosis. All living but sick frogs examined had saprolegniasis (skin infections with presumptive water molds, which can indicate skin trauma and/or compromised water quality). Skin and underlying muscles of the feet and legs were filled with hyphae typical of oomycete-type water molds, and two specimens selected for histopathology had visible tufts of soft white-tan material on a hindfoot. Epidermal hyperplasia was observed in body areas away from sites of water mold colonization. No evidence of ranavirus infection was found (such as viral inclusion bodies, multicentric hemorrhaging, or necrosis in kidney, liver, or hematopoietic tissue), although molecular screens for ranaviruses were not carried out.

Although 2006 specimens collected during the mass mortality event appeared considerably emaciated in comparison to those collected in 2004, when no mortality was observed, the 2004 specimens also had signs of body fat depletion. Specimens from 2004 had abundant stomach contents while those from 2006 did not; it is not clear whether this reflects lack of consumption due to systemic illness or to lack of prey items. Loumont and Kobel (1991) also reported that specimens they collected in 1990 looked somewhat emaciated.

Parasites were found in some 2006 specimens (trematodes in the coelomic cavity and pericardial sac, species undetermined; a different trematode species in the cloacal and oral cavity; a third trematode species in the lumen of the small intestine; a myxozoan species (thought to be a new species of Myxidium) in the gallbladder; a nematode species, probably a member of Spirurida, in the stomachs; and a cestode parasite in the lumen of the small intestine).

The cause of the 2006 mortality event is thus not clear. Volcanic degassing (CO2 eruptions) does not appear to have taken place. The lake is a closed hydrological system, reducing the likelihood of aquatic-borne disease introduction. It is possible that agricultural run-off from nearby farms might have contributed to the mortality event, as fish have also been reported to develop epidermal hyperplasia as a result of exposure to inorganic fertilizer. Perhaps fertilizer or local geological processes have contributed to acidified surface waters (Blackburn et al. 2010).

Complicating captive breeding efforts, all males transported from Cameroon to New York in two separate attempts (one in 2003 and one of apparently healthy frogs collected during the 2006 mortality event) died in transport, leaving only four females currently alive in captivity as of August 2010 (Blackburn et al. 2010).

Possible reasons for amphibian decline

General habitat alteration and loss
Predators (natural or introduced)
Introduced competitors

References
 

Arman Zaman (2006). ''Field notes: Project Exploration - Lake Oku.''  

Blackburn, D. C., Evans, B. J., Pessier, A. P., and Vredenburg, V. T. (2010). '' An enigmatic mortality event in the only population of the Critically Endangered Cameroonian frog Xenopus longipes.'' African Journal of Herpetology, 59, 1-12, published ahead of print July 29, 2010. http://www.informaworld.com/smpp/content~db=all~content=a924878413~frm=titlelink.  

Loumont, C., and Kobel, H.R. (1991). ''Xenopus longipes sp. nov., a new polyploid pipid from western Cameroon.'' Revue Suisse de Zoologie, 98, 731-738.  

Tinsley, R. and Measey, J. 2004. Xenopus longipes. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 05 October 2006.  

Tinsley, R.C. and Kobel, H.R. (1996). The Biology of Xenopus. Oxford Scientific Press, Oxford.



Written by Arman Zaman (armansz AT berkeley.edu), UC Berkeley
First submitted 2006-09-21
Edited by Kellie Whittaker (2010-08-13)



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Citation: AmphibiaWeb: Information on amphibian biology and conservation. [web application]. 2014. Berkeley, California: AmphibiaWeb. Available: http://amphibiaweb.org/. (Accessed: Aug 2, 2014).

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