Introducing the Lake Oku Clawed Frog

This is the first blog from Thomas Doherty-Bone, who is carryng out conservation research on amphibians unique to Cameroon. Thomas is being supported by a grant from ZSL‘s Erasmus Darwin Barlow Conservation Expeditions fund. See the previous post for more information.

In the misty hills of Cameroon….

Lake Oku

If you were to go to the North West Province of Cameroon, and wanted to see a scenic lake with a difference, then Lake Oku is the one for you. This lake is hailed as sacred by the local Oku community, and its banks are surrounded by thick evergreen forest. It is a small lake, with an average depth of 32 m, and a shoreline of approximately 5 km. In the mountains at an elevation of about 2,392 meters above sea level, this lake is apparently without fish. However in the place of fish exists a special species of frog, the Lake Oku Clawed Frog, Xenopus longipes

Lake Oku clawed frog

The Family (….of genetic freaks!)

This frog belongs to the family pipidae, a group of highly aquatic frogs, including the common laboratory subject: the African Clawed Frog (X. laevis), used in the past for pregnancy tests. Pipid frogs are thought to have emerged around the Jurassic period, and presently occur in South America and Africa, with the majority of species concentrated in Africa. These frogs are special because of their more established evolutionary history compared to other, more familiar anuran lineages, and because of the variation of chromosome number between species. Some species have two copies of each chromosome, while others have four copies (polyploidy – additional chromosomes). If you are X. longipes, you will have a staggering six copies of each chromosome, matched only by the Ugandan endemic, X. ruwenzoriensis. It has been postulated that such genetic characteristics evolved millions of years ago, through the hybridization of Xenopus species with differing chromosome number. Reasons for such a characteristic to evolve has been linked to parasites (such as helminths), with polyploidy suggested as a way to increase a selective advantage by shedding a long co-evolved parasite that otherwise impinges on the host’s survival and breeding potential. The potential biomedical value of these frogs has barely been addressed.

Most Pipid frogs will commonly be found submerged in water somewhere, eating any bite-size object that moves in front of their grappling arms and snappy jaws (said to be one of the most lethal mastication tools in amphibia, if not the animal kingdom).  Breeding season will typically coincide with the start rainy season for many species. Unlike other Xenopus, considerably little is known about the life history, reproduction or eco-physiology of X. longipes, which was not described by science until 1991. 

Lake Oku clawed frogs

Setting the standard of a biodiversity hotspot

Many members of Pipidae can move about on land, colonising new ponds, rivers, streams, but X. longipes is found to be very inept on land. Based on this, and the absence of fish in the Lake, it makes sense that this frog is unable to make anywhere else its home, apart from Lake Oku. No other lake in Cameroon has been found to hold this species, despite other lakes being examined in past expeditions. There is a second endemic pipid frog in this region, the Volcano Clawed Frog, X. amieti (named after Jean-Claude Amiet, who has significantly contributed to knowledge on the amphibians of Cameroon), which has a broader range and has even been found living in fish ponds on people’s farms. This species of pipid frog has four copies of each chromosome, so not quite as strange as our Lake Oku counterpart. This is testament to the biodiversity generated in the highlands of West Africa: in much the same way that species have evolved in island archipelagos, so have the mountains in Africa nurtured a variety of different species. Instead of oceanic water, it is the receding and recurring grassland (driven by dynamics in precipitation over millennia), isolating and reconnecting these forested mountain “islands”. In this case, the archipelago is the Biafran Highlands, which extend from Bioko Island (in the Bight of Biafra) through Cameroon to southern Nigeria.

On the Edge?

The Lake Oku Clawed Frog has been listed as Critically Endangered following the IUCN’s Global Amphibian Assessment. This is because of the hugely restricted range (to within 243 hectares). There is also the concern that Lake Oku could be one of the many lakes in Africa that have succumbed to well meaning but ill thought-out development projects to improve protein availability to communities – the introduction of fish (e.g. as in Lake Victoria). For these reasons, along with its amazing genetic characteristics, this frog has also been placed in the top 100 of the EDGE programme (at #34), highlighting its evolutionary significance and vulnerability to extinction. The remnants of the montane forests of this region have so far been safe guarded by forest management groups, devolved from the government to the community, a project implemented by Birdlife International. This has partly protected the Lake from degradation through deforestation, but does leave a gap for the specific conservation of amphibians through other factors.

In 2006, an expedition lead by myself to North West Province, observed many Xenopus longipes either dead or dying and sporting lesions on their body. There were many healthy looking frogs also, and we made a preliminary survey over a month to see how many frogs we could count and how many were moribund. Working under biosecurity (disinfected boots and equipment), we captured, marked and released 737 frogs, 28 of which displayed illness (about 4% of population). Tissue samples were collected and taken to the Institue of Zoology, Zoological Society of London, where they were screened for chytrid fungus and ranavirus. Chytrid was found to be absent, while ranavirus results were inconclusive. Meanwhile, the current status of the Lake Oku Clawed Frog is unclear – is this species in decline, or was this a natural phenomena? 

Dead X. longipes

Very little information is available on this lake and its inhabitants, so conclusions cannot be made with any confidence. We must assume the worst, however. Work is being planned to gain more information on this species to help determine the causes and implications of these deaths and morbidities. To learn about this, see the next blog in this series.

Comments

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  1. Matthew said,

    on November 12th, 2008 at 7:38 pm

    Very interesting article Thomas, I hope you are able to make some conclusions. I’m sure you have thought about any angles I could give, keep up the work over there. I’m looking forward to the update.

  2. Immanuel Jenling said,

    on May 23rd, 2009 at 12:00 pm

    can we send you more fotos of OKU and what one sees there_

  3. NCCHSNF said,

    on January 14th, 2010 at 7:21 pm

    Sirs,
    We will feel much obliged by your furnishing our organization through our postal mailing address with handbooks, handouts, publications and other educational materials that might be of help to our organization.
    Thanks.
    NCCHSNF
    P.O.BOX 90. CITY OF KUMBA.
    SOUTH WEST REGION.
    CAMEROON.
    Please take note, for our organization has no access to the Internet facilities.

  4. Peter Tatah said,

    on April 26th, 2011 at 2:47 pm

    What conclusion can be given about fears that the absence of fish in this Lake might be a bad omen? Really what explains the absence of fish in this Lake considering that Lake Awing at the same altitude has fish? How stable is the lake volume considering that it is one of Cameroon’s shallow Lakes? And if the volume is not stable, what consequences has it got on the survival of the clawed frog?

  5. Thomas Doherty-Bone said,

    on June 14th, 2011 at 9:26 pm

    Dear Peter,

    To say it is a “bad omen” for there to be no fish in Lake Oku depends more on your point of view. It might be considered to be a good omen that a species of frog lives in that lake and nowhere else in the world, not even anywhere else in Cameroon. That is something special, something to celebrate.

    It is however very interesting to consider why fish have not colonized this lake naturally. There has certainly been enough time for a frog to evolve to become endemic! I do not know Lake Awing (I have seen no studies and have not been myself), but I would put money on those fish being introduced by well meaning but perhaps misguided people. Whether those fish will survive in that lake is therefore uncertain. If those fish have indeed been introduced, what lived in that lake before? The ecology of that lake will certainly be undergoing detrimental changes as in other African lakes where exotic species have been introduced (think of Lake Victoria and the Nile Perch).

    If fish cannot survive, is that a bad omen for people to linger around the lake? Given the traditional stories in Oku about the lake and other lakes in the region erupting gas, this could be the bad omen you talk of.

    As for lake volume, this has not been measured scientifically by our team, though it has been observed to undergo fluctuations that are clearly attributed to rainfall. These fluctuations are however not significant, and seem to have no effect on the Lake Oku Clawed Frog.

    Thanks for your comments, hope this helps.

    Best wishes,

    Thomas Doherty-Bone
    Principle Researcher on the ecology of Lake Oku

  6. Tatah Peter said,

    on June 15th, 2011 at 11:45 am

    I am satisfied with your answer. The fear was based on explanations that the absence of fish might be due to gas explosions in the past. As for the clawed frog which is the only living creature of the Lake known and documented, I pray that it should always be there. The good thing about this is its uniqueness. I am personally against the introduction of any fish in this Lake.

    The introduction of fish into the Nyong River in the Centre and East regions of Cameroon has left indescribable damages to the river. The fish locally known as “kanga” is very large as compared to other species. Unfortunately, it is carnivorous and has eliminating other fish species in the river. It equally multiplies by building nests with weeds at the shores of the river. This weed multiplies very fast and the surface of the river has been completely covered, thereby reducing sun light and oxygen into the river. Mud is gradually accumulating on the bed of the river due to the weeds and flooding is the order of the day in the rainy season. The river is thinning up in the dry season. If the river bed is not drained, one does not know what will happen to the river in some years to come. Strange diseases (Bururi ulcer for example) are now developing along the course of the river.

    As a native of Oku, I will exhaust all my strength to resist the introduction of fish into Lake Oku. If fish is introduced into the Lake, it therefore means that fishing camps will be constructed there. What of pollution from human waste? What about desecration? What about other creatures and plants that might consequently emerge?

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