Reptilia: Cordylidae) in the South-Western Cape, South Africa

s. Afr. J. Zool. 1990,25(1) 31 Taxonomic status of the melanistic forms of the Cordylus cordylus complex (Reptilia: Cordylidae) in the south-western Cape, South Africa P. Ie F.N. Mouton· and J.H. van Wyk John Ellennan Museum, Department of Zoology, University of Stellenbosch, Stellenbosch, 7600 Republic of South Africa Received 4 October 1988; accepted 29 June 1989 The taxonomic status of the two melanistic morphotypes belonging to the Cordy/us cordy/us complex in the south-westem Cape, South Africa, is considered. It is proposed that the coastal melanistic fonn, previously described as subspecies of C. cordy/us, be considered a separate species, while the previously unknown montane melanistic fonn is also described as a new species. Areas of uncertainty, which may affect the status of the two melanistic species in the future, are discussed. Die taksonomiese status van die twee melanistiese morfotipes behorende tot die Cordy/us cordy/us kompleks in die suidwes-Kaap, Suid-Afrika, word bespreek. Daar word voorgestel dat die kus-melanistiese vonn, wat voorheen as 'n subspesie van C. cordyfus beskryf is, as 'n aparte spesie beskou moat word. Die voorheen onbekende berg-melanistiese vonn word ook as 'n nuwe spesie beskryf. Gebiede van onsekerheid wat moontlik die status van die twee melanistiese spesies in die toekoms kan be"invloed, word bespreek. 'To whom correspondence should be addressed The melanistic girdled lizard, Cordylus cordylus niger. Piketberg Mountains in the north (Figure 1), and the Cuvier, occurring in the Cape Peninsula and the Saldan typical form (= C. c. cordylus) extensively distributed ha-Langebaan areas, has for many years presented a along the south-western coastal lowlands, but also, at taxonomic problem (Branch 1981; Mouton 1987). Initially described as a distinct species by Cuvier (1829), subsequent workers (Rose 1926; Essex 1927; Power Mlddelberg Paaa 1930; Loveridge 1944) saw it as a subspecies. FitzSimons o . ) (1943) points out the overlap in distinguishing character 0 1 states between the melanistic and nominate forms and 0 2 holds the opinion that C. c. niger is simply an ecological d colour variant not worthy of subspecific status. Visser e t a (1971) mentions the possibility that C. c. niger and the d ( nominate form do not constitute a monophyletic group, r e pointing out similarities between C. c. niger and another h s i melanistic taxon, Cordylus peersi from Little Namaqua l b land. More recently opinions seem to favour the view of u P FitzSimons (1943) that the melanistic form is an ecologi e h cal colour variant and the name C. c. niger has gradually t y started to disappear from checklists and everyday b discussions (Branch 1981). d e t Unfortunately most of the above opinions on the n a taxonomic status of the melanistic form lack a sound Robben laland r g factual basis. Recently, however, Mouton (1987) con e c ducted an in-depth analysis of geographic character n e c variation among populations of the Cordylus cordylus i l complex in the south-western Cape in order to elucidate r Cape Penlnaula e the taxonomic status of C. c. niger. Results obtained d n from this analysis highlighted a unique pattern of u y geographic character variation which constitutes the a w basis of this discussion. ~ TYPICAL '0,." e t Mouton (1987) described the C. cordylus complex in a ~ MONTANI M'LAN'IYle FO,. .. G the south-western Cape as consisting of three morpho COASTAL MELANIIYIC '0 .... t ID e types, namely a melanistic coastal form (= C. c. niger) INTE .... EDIATE POPULATIONS n o i b occurring in insular and peninsular situations along the a S south-western coast (Figure 1), a second, previously y unknown melanistic montane form occurring at isolated Figure 1 Goegraphic distribution of the three morphotypes b d localities along the extreme western borders of the Cape belonging to the Cordylus cordylus complex in the south e c Fold Mountains, from Landdroskop in the south to the western Cape. u d o r p e R 32 S.-Afr. Tydskr. Dierk. 1990,25(1) places, occurring high up in mountains and also on bearing in mind the impact that knowledge of this Robben Island (Figure 1). The typical form also has a pattern could have on future physiological and ecological wide distribution outside the south-western Cape, main studies as well as on our understanding of lizard ly along the southern coastal regions, but also reaching speciation in the south-western Cape. The problem thus further inland in the eastern Cape as far as the southern boils down to whether the coastal melanistic form should Orange Free State (De Waal 1978). receive specific or subspecific status. Apart from the three well-defined morphotypes, a few The nature of the contact zone between the coastal intermediate populations have also been described by melanistic and typical forms at Jacobs Bay, just north of Mouton (1987). Noteworthy is the fact that these Saldanha Bay (Figure 1), probably holds the key to populations without exception occur in the immediate solving this problem. Mouton (1987) describes the vicinity of melanistic populations (Figure 1). Further Jacobs Bay locality as representing an abrupt change more, a contact zone between the coastal melanistic from the one morphotype to the other. A subsequent form and the typical form has been identified at Jacobs visit to Jacobs Bay revealed that the two morphotypes Bay (Figure 1) where, in terms of external morphologi occur sympatrically at this locality along a narrow zone cal characters, there is an abrupt change from the one of 100--200 m. The melanistic form occurs abundantly form to the other. among the rocks above the high-water mark, but In their proposed model for the evolution of the three towards the interior, at ± 100--200 m from the shore is morphotypes Mouton & Oelofsen (1988) argue that the replaced abruptly by individuals of the typical form. melanistic populations are not simply ecological variants Moving northwards along the shoreline there is likewise of the typical form, but that the observed pattern is an abrupt transition from the melanistic to the typical historical in origin, only preserved by present environ form and from there on northwards individuals of the mental conditions. They interpret the available informa typical form occur from among the rocks along the shore tion as indicating that the melanistic populations are to well into the interior. Along the narrow transition relict populations, which resulted from the contraction zone individuals of both morphotypes are found as well and fragmentation of formerly large melanistic popula as an occasional odd individual seemingly representing tions along the south-western coast and along the Cape hybridization between the two forms. Fold Mountains. The typical form on the other hand, is It stands to reason that a major analysis of this contact seen as a newcomer to the south-western Cape through zone is necessary for a clear perspective of the amount of the expansion in range of a south-eastern population. introgression taking place, of possible competitive exclusion, and of other eco-physiological factors that The Last Glacial period and subsequent amelioration of . ) might be involved. The relevant picture emerging, how 0 the climate are seen as instrumental in the evolution of 1 ever, is that of two distinct morpho types predominating 0 the melanistic forms. The intermediate populations are 2 interpreted as products of the swamping of small remain outside the contact zone, with limited introgression d e occurring only along a very narrow sympatric zone. t ing melanistic populations by the inmoving typical form. a Wiley (1981) is of the opinion that under such circum d Mouton & Oelofsen (1988) concluded that the three ( stances the parental morpho types could be considered as r morphotypes recognized by Mouton (1987), form a e h monophyletic group, having originated from an ancestral separate species. If more pronounced introgression over s i l a broader zone had been observed, the decision would b form through a sequence of events from about 40000 BP u to about 11 000 BP. In their proposed model no state probably have been in favour of one species, thus P subspecific status. In the case under discussion it seems e ment, however, has been made regarding the taxonomic h t as if species-distinct characters are being selected for status of the three morphotypes. The purpose of this y outside the zone of sympatry and that both morpho types b report is to consider the taxonomic status of the two d show independent species cohesion. e melanistic forms. t Mouton (1987) pointed out that a subocular reaching n a the lip, a diagnostic character of the melanistic form, is r Taxonomic status of the coastal melanistic form g also found to be widely occurring among populations of e c The view of FitzSimons that the Cape Peninsula and the typical form (Figure 2), although at a much lower n e Saldanha melanistic populations represent local adapta c intra-population frequency. The presence of this charac i l tions to similar environmental conditions cannot be ter in populations of the typical form to the north of r e accepted without serious reservations. All indications Jacobs Bay (Figure 2) could therefore not be considered d n are that these two coastal melanistic populations are as prima facie evidence for introgression. Furthermore, u y genealogically related, although geographically separa no signs of introgression outside the contact zone are a ted by the typical form (Figure 1), and that they resulted w observable in any of the other diagnostic characters of e t from the contraction and fragmentation of a former large the melanistic form.

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