Bradypodion

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Bradypodion
Robertson Dwarf Chameleon, Bradypodion gutturale
Robertson Dwarf Chameleon, Bradypodion gutturale
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Iguania
Family: Chamaeleonidae
Subfamily: Chamaeleoninae
Genus: Bradypodion
Fitzinger, 1843
Species

Some 15-20 (see text)

Bradypodion (meaning "slow-footed") is one of six genera of chameleons within the "true" or "typical" chameleons (subfamily Chamaeleoninae). They are native to southern Africa, and are sometimes collectively called South African dwarf chameleons. Some other small chameleons from eastern and central Africa are occasionally placed herein, but this is probably in error and not followed here. See also "Systematics" below and Kinyongia and Nadzikambia.

Contents

[edit] Alphabetic species list

[edit] Systematics

Delimitation of Bradypodion has been controversial for some time. Most species seem readily distinguishable by morphological characters, but for some time the genus was used as a wastebin taxon for smaller chameleons from sub-Saharan Africa with a plesiomorphic hemipenis (Klaver & Böhme 1986, Branch 1998). Alternatively, many of the present species were reduced to subspecies status (Klaver & Böhme 1997). This has since been refuted (Branch 1998, Tolley et al. 2004) but several more species seem recognizable judging from morphological (Raw 2001) and mitochondrial 16S rRNA and NADH dehydrogenase subunit 2 sequence data (Tolley et al. 2004).

The phylogeny and biogeography of this group is quite consistently resolved (Tolley et al. 2004). The Cape Dwarf Chameleon and the Knysa Dwarf Chameleon (and possibly one new species close to it) are basal lineages with unclear relationships; they seem a bit closer to each other than to any other species but altogether are quite distant. They occur in isolated ranges in coastal Western Cape and western Eastern Cape provinces. Inhabiting a wide range of habitats, they are (for the genus) large, and have brilliant, predominantly green coloration and a long tail - just as in many Chamaeleo. These characters are plesiomorphic, retained from the genus' ancestor.

The remaining species form a well-supported clade, which in turn can be divided into smaller groups. One consists of forms that radiated on the seawards slopes of the Drakensberg mountains: the southern Drakensberg Dwarf Chameleon, the northern Transvaal Dwarf Chameleon, and what appears to be undescribed species from the Ngome Forest on the SE slopes. These are also plesiomorphic in habitus and habits.

Another group of taxa occurs from easternmost Eastern Cape to central KwaZulu-Natal provinces, between Gilboa Forest and the Tugela River. These inhabit a wide range of habitat and contain the plesiomorphic Natal Midlands Dwarf Chameleon from the namesake region, the small Black-headed Dwarf Chameleon which inhabits fynbos and other low forest on slopes of mainly coastal W KwaZulu-Natal, and another probable new species from the Gilboa Forest area. These appear to be a quite recent radiation from a single ancestor and the group requires more research as regards species limits, and geographical demilitation from the Drakensberg Dwarf Chameleon.

There are several largish but short-tailed and cryptic taxa which inhabit more arid habitat such as karoo. The Karroo and Southern Dwarf Chameleons between which there seems to be considerable gene flow range from Northern Cape to coastal Eastern Cape provinces. The small and nearly extinct Smith's Dwarf Chameleon is close to these; it occurs on the escarpment inland from Jeffreys Bay. Less closely related is the Robertson Dwarf Chameleon, another aridland species which is found in Western Cape province inland from the range of the Cape Dwarf Chameleon and may be a cryptic species complex, and an undescribed population from the Swartberg mountains (Branch 1998: plate 1, Tolley et al. 2004). The last species with aridland apomorphies, the Namaqua Dwarf Chameleon, is quite distant to the others; it occurs in coastal regions from north of the Cape species through Namaqualand. This is probably still a part of a single radiation which brought about all the aridland taxa, and eventually Smith's Dwarf Chameleon.

The remaining species are all small inhabitants of forested slopes and fynbos, like the Black-headed and Smith's Dwarf Chameleons. However, as already indicated by the distinctness of these two, their morphology seems to be a convergent adaptation. The Kentani and Transkei Dwarf Chameleons from the E coasts of Eastern Cape may or may not be each other's closest relatives. Setaro's Dwarf Chameleon from northeastern coastal KwaZulu-Natal is not close to these. The Zululand Dwarf Chameleon from western uThungulu apparently consists of 2 or more species, one that may be closer to the preceding, and one that might be an early offshoot of the ancestral Drakensberg stock, and which are distinguishable by morphological (Raw 2001) and mtDNA characteristics.

In conclusion, of the 3 basic morphotypes found in this genus, one (bright, long-tailed, large) is plesiomorphic, another (large, short-tailed, drab) apparently only evolved once, and the third (the small slope-inhabiting forms) are convergent in morphology. The ancestors of Bradypodion thus were mid-sized chameleons with vivid color, which settled the Cape region from roughly north-northwestwards. Due to climate change with fluctuating aridity, the basal lineages inhabiting humid fynbos in the SW became isolated from each other and from the animals living approximately in the border region between Northern and Eastern Cape and Free State , and Lesotho. The aridland habitat fluctuates in extent during climate shifts, and mountaineous habitat becomes fragmented or consolidates accordingly. Consequently, the Drakensberg, the thamnobates-melanocephalum, and the aridland group, as well as several coastal lineages diverged and evolved to their present-day ranges and diversity.(Tolley et al. 2004)

[edit] References

  • Branch, W.R. (1998): Field Guide to Snakes and Other Reptiles of Southern Africa. Struik Publishers Ltd, Cape Town (revised edition).
  • Klaver, C.J.J. & Böhme, W. (1986): Phylogeny and classification of the Chamaeleonidae (Sauria) with special reference to hemipenis morphology. Bonner Zoologische Monographien 22: 1–64.
  • Klaver, C.J.J. & Böhme, W. (1997): Liste der rezenten Amphibien und Reptilien - Chamaeleonidae. Das Tierreich 112: i-xiv, 1-85.
  • Tolley, Krystal A.; Tilbury, Colin R.; Branch, William R. & Matthee, Conrad A. (2004): Phylogenetics of the southern African dwarf chameleons, Bradypodion (Squamata: Chamaeleonidae). Molecular Phylogenetics and Evolution 30: 354–365. doi:10.1016/S1055-7903(03)00211-2 PDF fulltext