An analysis of the Pseudocordylus melanotus complex (Sauria: Cordylidae)

[摘要] ENGLISH ABSTRACT: The taxonomic status of southern Africa's rupicolous crag lizards (genus Pseudocordylus) wasinvestigated. As considerable confusion exists in the literature regarding the type specimens andtype localities of the various taxa, resolution of these problems were considered the starting pointof the study. Examination of museum specimens allowed for the designation of lectotypes,alloparalectotypes and/or paralectotypes. Of particular relevance to this study was the rediscoveryof Andrew Smith's type specimens of P. m. melanotus and P. m. subviridis. Restrictionof the type locality of P. m. subviridis, based on entries in Smith's diary and journal, allowed forthe confirmation of previous interpretations and definitions of the two taxa. The geographicaldistribution of the various taxa and populations was determined using an extensive localitydatabase.Two kinds of molecular markers, namely allozymes and mitochondrial DNA, were used in anattempt to resolve taxon boundaries within the P. melanotus species complex. The allozymeanalysis indicated that P. m. melanotus might be polyphyletic and comprised of two unrelatedlineages. Furthermore, fixed allelic differences between parapatric populations of P. m.melanotus and P. m. subviridis, and between sympatric populations of P. m. subviridis and P.langi, suggested that all three forms might be considered full species, with the possibility of morecryptic species present in the complex. Pseudocordylus transvaalensis differed from most otherpopulations by 1-3 fixed allelic differences, but was indistinguishable from the Nkandhla district(central KwaZulu-Natal) population of P. m. melanotus. There were no heterozygous individualsin a sample from Monontsha Pass (Qwa-Qwa), a population reportedly comprising P. m.melanotus and P. m. subviridis, as well as intermediates, and all specimens were assignable to P.m. subviridis. The allozyme study was, however, based on phenetic principles and for furthertaxonomic resolution a cladistic approach was required. An mtDNA analysis (16S rRNA gene)using Maximum Parsimony, Maximum Likelihood and Bayesian analyses was thereforeconducted to determine phylogenetic relationships among species and subspecies and to re-assessthe taxonomic status of forms in the P. melanotus species complex. The mtDNA analysiscorroborated most of the results obtained in the allozyme analysis. Firstly, P. langi was againfound to be basal. With the addition of P. microlepidotus and P. spinosus to the ingroup, it is nowapparent that P. langi is the basal species in the genus. (Recent studies have indicated that P.capensis and P. nebulosus are not congeneric with Pseudocordylus.) Secondly, the 16S rRNAresults confirm that P. m. melanotus, as presently construed, is comprised of two clades that arenot sister groups. The northern populations of P. m. melanotus (Sabie and Lochiel) form a fairlydeeply divergent clade that may represent a separate species. The Nkandla population was, however, found to cluster with the other southern P. m. melanotus populations and not with P.transvaalensis as was the case in the allozyme electrophoretic analysis. However, the mostsurprising result of the 16S rRNA analysis was the finding that both P. microlepidotus and P.spinosus are embedded within P. m. subviridis. This suggests that these two species evolved fromwithin P. m. subviridis and may have been separated only recently, with rapid morphologicaldivergence occurring, but with limited genetic differentiation. It is suggested that all of the abovethree taxa be provisionally treated as full species.There was also morphological support for the uniqueness of all groupings indicated by themtDNA analysis. Pseudocordylus transvaalensis is characterized by its large size, unique dorsaland gular (black) colour patterns, as many as three horizontal rows of lateral temporal scales, aseries of small scales posterior to the interparietal scale, and usually two subocular scales behindthe median subocular on either side of the head. The various populations currently classifiedunder the name P. melanotus are more difficult to separate, but P. m. melanotus and P. m.subviridis usually differ as follows: frontonasal divided in P. m. melanotus, undivided in P. m.subviridis (and most Northern melanotus); lateral temporals in two rows, upper more elongateversus single row of much elongated scales; longitudinal rows of dorsolaterals closely-set versuswidely separated; femoral pores of females pit-like versus deep with secretory plug. Northernmelanotus differs from Southern melanotus in usually having an undivided frontonasal scale andseldom having a small scale present behind the frontonasal. Pseudocordylus langi has uniquedorsal and gular colour patterns (including a series of blue spots on the flanks), granular dorsalswith 6-9 paravertebral rows of enlarged flat scales, high total numbers of femoral pores (25-34)and usually only five (smooth not keeled or ridged) infralabial scales on either side of the head.Pseudocordylus spinosus also has unique dorsal and gular colour patterns, spinose lateral scales,frontonasal longer than wide and excluded from the loreal scales, low total femoral pore counts(6-9), and females (not only males) have differentiated femoral scales. Both PrincipalComponents Analysis (PCA) and Canonical Discriminant Analysis (CDA) distinguished fourgroups, namely P. transvaalensis, P. langi, P. spinosus and a P.melanotus/subviridis/microlepidotus cluster. A separate CDA of all P. melanotus populationspartly distinguished between Southern melanotus and P. m. subviridis, and largely separatedNorthern melanotus; whereas a CDA of P. transvaalensis showed that all three allopatricpopulations are 100% distinguishable in morphological space.A Nested Clade Analysis indicated that fragmentation as well as range expansion played a role inthe distribution of the P. melanotus species complex. This may be explained by climaticoscillations (high-low temperatures and wet-dry cycles) during the Cenozoic that caused habitatexpansion and contraction. Based on the topology of the mtDNA phylogram it is apparent that the genus Pseudocordylus originated along the eastern escarpment. A P. langi-like ancestor mayhave had an extensive range along the eastern escarpment, with the Maloti-Drakensberg formingthe southern limit of its range. During a subsequent rise in global temperatures, range contractionand fragmentation took place, leaving an isolated population in the south and one in the north.The southern population survived unchanged in the Maloti-Drakensberg refugium, but thenorthern population was forced to adapt to the warmer conditions. Thereafter, the northern formexpanded its range again, but during a subsequent cooler period, range contraction occurred,resulting in an isolated north-eastern population in the Sabie-Lochiel area in Mpumulanga(Northern melanotus) and a western population. Relationships in the latter clade are notsufficiently resolved to allow further reconstruction of biogeographic history, but it is clear that aP. m. subviridis-like form became isolated in the south where it eventually came into contact withP. langi at high elevations. Pseudocordylus m. subviridis eventually extended its range southwestwardsinto the inland mountains of the Eastern Cape and Cape Fold Mountains to give rise tothe P. microlepidotus complex. This cycle of range expansion and contraction may also accountfor the isolated populations at Suikerbosrand, Nkandhla district, and in the Amatole-GreatWinterberg mountain region. Furthermore, it is suggested that P. spinosus originated from a P. m.subviridis-like ancestral population that became isolated on the lower slopes of the Drakensbergwhere terrestrial predation pressure resulted in a quick shift in morphology from fairly smoothbody scales to a more spiny morphology.

[发布机构] Stellenbosch University