Overview

Comprehensive Description

Description

Xenopus gilli was first described by Rose and Hewitt (1927). It is a tetraploid species with a chromosome number of 36 (Tinsley and Kobel 1996). The females average 55 mm in length and can be as long as 60 mm, while the males are about 30% the length of females. X. gilli has a pointed head and contains a lower eyelid that covers almost half its eye. Furthermore, X. gilli has no subocular tentacle and has one less toe than most other Xenopus species. X. gilli has a dorsal color that is yellowish-brown and has two or four bands of dark spots behind the eyes. In addition, X. gilli tends to be heavily spotted ventrally, although several specimens have been found to be spotless. The clear and distinct markings on X. gilli make it easily distinguishable from other closely related Xenopus species such as X. laevis (Tinsley and Kobel 1996).

  • Harrison, J., Measey, J., Tinsley, R., and Minter, L. 2004. Xenopus gilli. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 02 November 2006.
  • Tinsley, R.C. and Kobel, H.R. (1996). The Biology of Xenopus. Oxford Scientific Press, Oxford.
  • Aslett, C. “Endangered Clawed Frog: Xenopus gilli.” http://clawedfrogs.tripod.com/index.html Download on: 02 November 2006.
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Distribution

Range Description

This species is endemic to extreme south-western South Africa, occurring on the Cape Peninsula and the south-western Cape coast. It is a low-altitude species occurring at 10-140 m asl; currently known populations occur within 10 km of the coast. Its extent of occurrence (EOO) is estimated to be 1,450 km2, is considered to be declining, and its area of occurrence is estimated to be 1% of the EOO.
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Distribution and Habitat

X. gilli is found in the highly acidic black lakes found in the Cape Floral Kingdom (fynbos biome) of South Africa. Except for a few exceptions, X. gilli is situated in coastal lowlands in the Cape Peninsula and Cape Agulhas. Geographically, it is restricted to acidic black-waters that facilitate the breakdown of phenolic-rich plant matter to organic acids such as hubic, fulvic, hymenomelanic, and humin, which are vital for the species (Tinsley and Kobel, 1996)[2307]. Biome/Ecosystem: Freshwater, Terrestrial Habitat: Mediterranean-type Shrubby Vegetation Wetland - Permanent Freshwater Marshes/Pools Wetland - Seasonal/intermittent Freshwater Marshes/Pools Artificial/Aquatic - Ponds (below 8 ha). [3722]

  • Harrison, J., Measey, J., Tinsley, R., and Minter, L. 2004. Xenopus gilli. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 02 November 2006.
  • Tinsley, R.C. and Kobel, H.R. (1996). The Biology of Xenopus. Oxford Scientific Press, Oxford.
  • Aslett, C. “Endangered Clawed Frog: Xenopus gilli.” http://clawedfrogs.tripod.com/index.html Download on: 02 November 2006.
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This species is endemic to the winter rainfall region of the Western Cape, generally occurring in relatively low lying areas (10–140 m a.s.l.) within 10 km of the coastline. Its distribution is correlated with the presence of nearby mountain ranges and an annual rainfall exceeding 500 mm p.a. (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Physical Description

Morphology

The upper body is light to yellow-brown with elongated, dark brown patches, sometimes paired, that begin between the eyes and extend backwards, breaking up into smaller patches on the lower back and upper surfaces of the hind limbs. The underside usually has clear blackish and yellow mottling, but this may be pale and indistinct in some individuals (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

X. gilli can be distinguished from X. laevis by the following morphological features: its smaller size (<60 mm in body length); a narrower, more acutely pointed head; the absence of a subocular tentacle (present but inconspicuous in laevis); a poorly developed inner metatarsal tubercle (a distinct ridge in laevis); and less conspicuous lateral line sense organs (Poynton, 1964; Picker and De Villiers, 1988; Passmore and Carruthers, 1995; Kobel et al., 1996; Channing 2001; Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
It is found only in black, acid water in Cape fynbos heathland. It is a winter breeder (July to October). It aestivates if waterbodies dry up. It does not tolerate alteration of its habitat, and the larvae are very sensitive to changes in water quality.

Systems
  • Terrestrial
  • Freshwater
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Habitat and Ecology

X. gilli inhabits blackwater wetlands in low-lying coastal areas. These are permanent and seasonal seepages, marshes, ponds, pans, vleis and coastal lakelets, in a variety of fynbos vegetation types and, in places, a mixture of fynbos and dune thicket. The vegetation types include mostly Mountain Fynbos, Sand Plain Fynbos (on the Cape Flats), or Mountain Fynbos mixed with either Limestone Fynbos or Dune Thicket. The substrate has a predominantly sandy base and varies, depending on the humic content, from white or grey to a dark brown or blackish soil (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

The water is humic and dark in colour, low in nutrients, high in dissolved solids, and typically has a low pH at a minimum 3.4 (Picker 1985). It has been demonstrated that the tadpoles of X. gilli can tolerate pH as low as 3.6, whereas X. laevis tadpoles have a reduced rate of survival below pH 5–6. Picker (1985) as well as Picker and De Villiers (1989) reported that X. gilli avoids habitats that have been disturbed by urban development or agriculture, or that contain invasive plants and animals (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Associations

Xenopus gilli tested positive for Batrachochytrium dendrobatidis (fungus that causes chytridiomycosis) in the Western Cape of South Africa in 1943 and 1976 (Weldon et al., 2004).

Disturbances of X. gilli water bodies which alter the humic content and nutrient levels, cause an increase in pH levels and often result in the colonisation of these water bodies by X. laevis, providing an opportunity for hybridization between the species (Simmonds 1985; Picker et al. 1996). Rau (1978) and Picker et al. (1996) found that the breeding season of X. gilli overlaps with that of X. laevis, which increases the opportunity for hybridization (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

Picker and De Villiers (1988) describe the prey of adult frogs as both living and dead animal material in their wetland habitat, including aquatic invertebrates and their eggs, tadpoles and smaller frogs of their own kind and other species (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Life History and Behavior

Behavior

Activity and Special Behaviors

When its wetland habitat dries up during the summer months, X. gilli survives by aestivating below the surface (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Life Cycle

Metamorphosis

The nektonic tadpoles feed on phytoplankton in the water and complete their metamorphosis by the end of summer. Rau (1978) recorded spawning activity over a four-month period and found metamorphosis to take about 120 days (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Reproduction

Advertisement Call

The advertisement call consists of a series of short, rapidly pulsed, metallic buzzes emitted under water at a rate of about two per second (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Channing (2001) found that breeding commences during the wet winter months (July), and continues until late October (Rau 1978). Three to four hundred dark brown eggs are laid over a period of a day, each surrounded by a jelly capsule 1.3 mm in diameter (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Xenopus gilli

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 3
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
B1ab(i,iii)+2ab(i,iii)

Version
3.1

Year Assessed
2010

Assessor/s
South African Frog Re-assessment Group (SA-FRoG), IUCN SSC Amphibian Specialist Group

Reviewer/s
Angulo, A. & von May, R.

Contributor/s
Channing, A., Turner, A., de Villiers, A., Harvey, J., Tarrant, J., Measey, J., Tolley, K., Minter, L., du Preez, L., Burger, M., Cunningham, M. & Davies, S.

Justification
Listed as Endangered in view of its declining extent of occurrence currently being 1,450 km2, and area of occupancy of 14.5 km2, with all individuals in four locations, and a continuing decline in the extent and quality of its habitat.

History
  • 2004
    Endangered
  • 1996
    Vulnerable
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Vulnerable
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Vulnerable
    (IUCN Conservation Monitoring Centre 1986)
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IUCN Red List Category and Justification of Conservation Status

X. gilli was included in the first South African Red Data book for amphibians, in the Rare category (McLachlan 1978). In the revision (Branch 1988), it was classified Endangered. Endangered status was retained in Harrison et al. (2001), based on an extent of occurrence <5000 km2, an area of occupancy <500 km2, a severely fragmented habitat, continuing decline in the extent of occurrence, area of occupancy, extent and quality of habitat and the number of locations/subpopulations and mature individuals. The species is legally protected by Nature Conservation Ordinance 19 of 1974, but is not listed by CITES (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Population

Population

The spatial distribution of this species is not considered to be severely fragmented as one subpopulation/location holds >50% of individuals, however the distances between subpopulations of around 100 km is considered to be too great for dispersal within one generation. It appears to be relatively abundant in some of the known localities.


Population Trend
Unknown
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Life History, Abundance, Activity, and Special Behaviors

Life History/Abundance - X. gilli is a very rare species that was only known in eight locations in South Africa before 1970. Later in 1985, it was found in locations farther east and was believed to span 35 localities. Although X. gilli’s distribution is restricted by the necessity of an acidic environment, it was believed to once have occupied as 75 different localities in South Africa (Tinsley and Kobel 1996). However, by 2004, X. gilli was believed to occupy less than 5 locations in South Africa (ICUN Red List 2006). Special Behaviors - X. gilli has a call that resembles short trill that occur at a rate of 1-3 per second (Tinsley and Kobel 1996). X. gilli also interbreeds with X. laevis. The two species interbreed when X. laevis gains access to the ponds inhabited by X. gilli due to disturbances in the ponds. X. gilli and X. laevis are physically different in many ways including size, coloration, and morphological features. Based on these differences, the hybrids fall into two categories: X. gilli-like or X. laevis-like (Tinsley and Kobel 1996). X. laevis tend to greatly outnumber of X. gilli, which often leads to mismating. This interbreeding is contributing further to the decline of X. gilli.

  • Harrison, J., Measey, J., Tinsley, R., and Minter, L. 2004. Xenopus gilli. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 02 November 2006.
  • Tinsley, R.C. and Kobel, H.R. (1996). The Biology of Xenopus. Oxford Scientific Press, Oxford.
  • Aslett, C. “Endangered Clawed Frog: Xenopus gilli.” http://clawedfrogs.tripod.com/index.html Download on: 02 November 2006.
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Threats

Major Threats
The main threats are habitat loss due to urbanization, agricultural run-off, and the effects of spreading alien plants. It may be threatened by hybridization with X. laevis, and there have been concerns about how many populations of this species represent pure X. gilli. X. laevis does not favour the acid water that X. gilli requires.
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Life History, Abundance, Activity, and Special Behaviors

X. gilli is listed as endangered because its area occupancy is less than 500 km and because there is a continuing decline in its habitats as well as the number of mature individuals (IUCN Red List 2006). X. gilli has been the victim of land development. Various farming practices and the construction of dams destroyed the specie’s natural habitats. The Cape of Good Hope Natural Reserve decided to introduce new fauna into the area, which further altered X. gilli’s surroundings. Once X. gilli and X. laevis began to interbreed, sterile male hybrids led to even greater risk of X. gilli going extinct (Aslett 2004).

  • Harrison, J., Measey, J., Tinsley, R., and Minter, L. 2004. Xenopus gilli. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 02 November 2006.
  • Tinsley, R.C. and Kobel, H.R. (1996). The Biology of Xenopus. Oxford Scientific Press, Oxford.
  • Aslett, C. “Endangered Clawed Frog: Xenopus gilli.” http://clawedfrogs.tripod.com/index.html Download on: 02 November 2006.
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Management

Conservation Actions

Conservation Actions
Research priorities for this species include estimating dispersal capabilities, identification of management units and monitoring population size. The threat of hybridisation needs to be clarified, as Xenopus laevis now occurs throughout the range. Habitat management and restoration are needed. It occurs in Cape Peninsula National Park and Agulhas National Park, both of which are relatively well managed, although there is a need to control the spread of invasive plants within these areas.
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Relevance to Humans and Ecosystems

Risks

Relation to Humans

When concern was raised about the future of the species, scientists began to take action, proposing to drive out the X. laevis species in order to protect the future of X. gilli. However, scientists realized that X. laevis had been too deeply rooted in the habitat but are still making efforts to remove other introduced fauna and alien vegetation from the area. Scientists also pushed for new legislations to conserve the status of the area and in 1998, the area was proclaimed Cape Peninsula National Park. In hopes of preserving the rare and unique species X. gilli, humans are slowly making progress to undo the damage that was inflicted on the habitat of X. gilli (Aslett, 2004)[3723].

  • Harrison, J., Measey, J., Tinsley, R., and Minter, L. 2004. Xenopus gilli. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 02 November 2006.
  • Tinsley, R.C. and Kobel, H.R. (1996). The Biology of Xenopus. Oxford Scientific Press, Oxford.
  • Aslett, C. “Endangered Clawed Frog: Xenopus gilli.” http://clawedfrogs.tripod.com/index.html Download on: 02 November 2006.
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Wikipedia

Cape clawed toad

The Cape platanna or Gill's platanna (Xenopus gilli) is a species of frog in the Pipidae family endemic to South Africa. Its natural habitats are Mediterranean-type shrubby vegetation, freshwater marshes, intermittent freshwater marshes, and ponds. It is threatened by habitat loss.[1]

References[edit]

  1. ^ Harrison, J., Measey, J., Tinsley, R. & Minter, L. 2004. Xenopus gilli. 2006 IUCN Red List of Threatened Species. Downloaded on 23 July 2007.
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