Allozyme Characters Research Articles

Systematics of the Etheostoma punctulatum Species Group (Teleostei: Percidae), with Descriptions of Two New Species

The Stippled Darter, Etheostoma punctulatum, has long been recognized as a single species of the subgenus Ozarka, endemic to the clear, high-gradient creeks and rivers of the Arkansas, White, and Missouri river drainages in the Ozark Plateau of the Interior Highlands of North America. Etheostoma punctulatum is redescribed and two new species are described based on morphological and allozyme characters, and phylogenetic analyses. The Stippled Darter, E. punctulatum, is restricted to tributaries of the Missouri River. The Autumn Darter, E. autumnale, new species, is endemic to the White River system, Missouri and Arkansas. The Sunburst Darter, E. mihileze, new species, is known only from the Arkansas River system, Missouri, Arkansas, Oklahoma, and Kansas. The three species are found to be divergent and diagnosable from one another and represent valid species under a variety of species concepts. Phylogenetic analyses indicate that E. punctulatum is sister to E. mihileze, new species, plus E. autumnale, new species.

Two cryptic species of the Hediste diversicolor group (Polychaeta, Nereididae) in the Baltic Sea, with mitochondrial signatures of different population histories

A presence of two cryptic biological species of Hediste diversicolor complex polychaetes was corroborated in a geographical survey of some 30 populations from the eastern and southern coasts of the Baltic Sea, with data from four completely diagnostic allozyme characters. Species A was dominant in the northernmost part of the Baltic Hediste range (Bothnian Sea), whereas Species B alone was found in the south (Poland, Germany, Denmark). In the intervening region, comprising the majority of the sites studied in southern Finland and Estonia, the two species were usually found together, with no evidence of recent hybridisation (i.e., no heterozygote genotypes). While mitochondrial DNA also distinguished the two taxa, it was not similarly completely diagnostic, but there were rare cases (ca 5%) of lineage mismatch indicating that some introgression has occurred in the past. Comparison with published data suggests that species A also inhabits the North Sea–NE Atlantic–Mediterranean coasts, and species B is also present in the North Sea and the NW Atlantic (Canada). Within the Baltic, the two species show distinctly different patterns of mtDNA diversity, plausibly related to different colonisation histories. Species A shows a generally high haplotype and nucleotide diversity, whereas in species B we found only four deeply diverged groups of closely related haplotypes. Hypothetically this could indicate a recent expansion of species B from a small number of colonising individuals. Moreover, species B showed marked intraspecific geographical structuring, with co-incident genetic changes along the N Estonian–S Finnish coasts both in mtDNA and an allozyme marker; this pattern suggests a contact between two genetically distinct invasion waves of different origins. In all, species A and B represent good, reproductively isolated and partly sympatric species which require to be recognised in ecological work. A formal taxonomical description is needed, but awaits better, range-wide distributional and ecological characterisation and working out of morphological differences that enable a practical identification.

ORIGINAL ARTICLE: Cycads in the insular South‐west Pacific: dispersal or vicariance?

AbstractAim Cycads constitute an ancient plant group that is generally believed to disperse poorly. However, one group of cycads (subsection Rumphiae) is thought to have dispersed relatively recently from a Malesian source area westwards to East Africa and eastwards into the Pacific, using a floatation‐facilitating layer in their seeds. We use morphological and allozyme characters to investigate the relationships among the species within this group and to deduce whether the wide distribution was achieved by recent dispersal (as evidenced by high genetic similarity) or more distant vicariance events (high genetic differentiation).Location We examined specimens collected throughout the range of subsection Rumphiae, from East Africa through Southeast Asia to Tonga in the South‐west Pacific.Methods We investigated relationships within subsection Rumphiae of the genus Cycas by analysing 18 variable (11 informative) morphological characters and 22 allozyme loci for seven of the 10 species currently assigned to this taxon.Results Distinctive morphological characters are few and fail to resolve relationships within the group. Allozyme data show that species within this subsection are closely related and suggest that there are two groups within the subsection, one comprising Cycas thouarsii (East Africa) and C. edentata (the Philippines), and the other the remaining species (from Malesia and the Pacific). The Australian species C. silvestris is sister to subsection Rumphiae in the morphological analysis but is closely allied to C. rumphii (nested within the subsection) in the allozyme analysis, suggesting that Rumphiae may be paraphyletic and that characters thought to be taxonomically important may need to be re‐evaluated.Main conclusions Cycads within subsection Rumphiae are closely related, and the wide distribution of this group was probably achieved through relatively recent oceanic dispersal events. Separate events probably account for the dispersal of these cycads into the Pacific and to Africa. The origin and distribution of C. silvestris (Australia) could be explained by a dispersal event from New Guinea or may have resulted from a former land connection between Australia and New Guinea.

Systematics and evolution of the subfamily Gerbillinae (Mammalia, Rodentia, Muridae)

Although they represent a quarter of the mammalian species, the evolutionary relationships among as well as within, the main murid lineages are still controversial. The subfamily Gerbillinae is no exception as previous studies based on morphological, karyotypical, and allozyme characters are highly incongruent. Here, we present the first molecular phylogeny for gerbils based on cytochrome b and 12S rRNA mitochondrial genes. Results are largely congruent between the two genes as well as with the concatenated data set with most of the nodes being well-supported. Based on the topologies retrieved here, we (1) propose the identification of three main clades, (2) support the split of Tatera genus into an Asian and an African group, the latter including Gerbillurus species, and (3) provide some evidence towards the inaccuracy of subgeneric divisions within both Gerbillus and Meriones. In addition, the sharp contrast between the genetic characters and morphological data sets suggest high levels of convergence, probably as a result of strong environmental constraints imposed on these rodents adapted to arid and semi-arid regions. Finally, molecular datings for the various cladogenetic events are in good agreement with the known gerbilline fossil record and support an African origin with subsequent migrations to Asia.

Phylogeny of the African murid tribe Otomyini (Rodentia), based on morphological and allozyme evidence

Based on a cladistic analysis of 45 morphological (craniodental) and 46 binary allozyme characters, previous systematic treatments of the African murid tribe, Otomyini (laminate‐toothed rats), are reviewed. Cladistic analysis of the craniodental data, involving eight outgroup taxa, confirmed the monophyly of the Otomyini, and suggested Pelomys to represent the sister genus of the Otomyini. Craniodental synapomorphies provided strong support for certain basal relationships among Otomyini rodents, reinforcing available palaeontological evidence. However, poor statistical (Bremer decay index) support was obtained for terminal relationships. The data presented revealed a ‘mesic clade’ of southern and eastern African species, with Otomys sloggetti basal to this group. The arid‐adapted, southern Africa‐endemic species, Parotomys littledalei, P. brantsii and O. unisulcatus, were all placed basal to the ‘mesic clade’, but did not form a separate ‘arid clade’, as suggested by earlier biochemical studies. Two allozyme synapomorphies supported the existence of the ‘mesic clade’, separate from arid‐adapted southern African species. A strict cladistic interpretation of the present data did not support the existence of two genera in the tribe, and the two species of Parotomys (whistling rats) should be transferred to Otomys. At the species level, specific identity of O. lacustris and O. barbouri, distinct from O. anchietae, was supported by several autapomorphies, and O. tropicalis burtoni was shown to be included in O. angoniensis rather than O. tropicalis, extending the range of the former species into West Africa.

Systematics of sphagnum frogs of the genus Philoria (Anura: Myobatrachidae) in eastern Australia, with the description of two new species

Analyses of allozyme and mitochondrial nucleotide sequence variation in Philoria from northeastern NSW and southeastern Queensland revealed that there are more species than the three that are currently recognized. In addition to the three species presently recognized P. kundagungan, P. loveridgei, and P. sphagnicolus, another two species P. pughi n.sp. and P. richmondensis n.sp. were recognized under the evolutionary species concept. All species are allopatric. Each of the five species had two or more fixed genetic differences with all other species. Additionally, each species possessed two or more unique allozyme characters (apomorphies). Each species had strongly supported reciprocally monophyletic mitochondrial haplotypes in comparison with each of the other species. Multivariate morphometric analysis was able to distinguish P. sphagnicolus from the remaining four northern taxa but was unsuccessful in reliably distinguishing the two new species. Mating call analysis identified two distinct call groups: P. sphagnicolus and the remaining species, the latter showing little discrimination between species. The distribution of Philoria in NSW and Queensland shows a strong association with high rainfall rainforest at mid to high altitudes (above 600 m elevation). The habitat of all species is remarkably similar, all are found predominantly in the headwaters of rainforest streams or soaks on the forest floor. All species lay their eggs in nests in the ground, where the larvae remain throughout their entire development until they emerge post metamorphosis. It was confirmed that nests where the embryos were at an early stage of development were of two types: foaming egg masses, and nests containing a non-foaming jelly substance. All species are limited in their distribution. In particular P. richmondensis is in need of special conservation consideration, as it is known from only three localities within a very small range. A number of populations in southeastern Queensland and northern NSW await molecular analysis to be identified with certainty.

Impact of number of isoenzyme loci on the robustness of intraspecific phylogenies using multilocus enzyme electrophoresis: consequences for typing of Trypanosoma cruzi.

Thirty-one stocks of Trypanosoma cruzi, the agent of Chagas disease, representative of the genetic variability of the 2 principal lineages, that subdivide T. cruzi, were selected on the basis of previous multilocus enzyme electrophoresis analysis using 21 loci. Analyses were performed with lower numbers of loci to explore the impact of the number of loci on the robustness of the phylogenies obtained, and to identify the loci that have more impact on the phylogeny. Analyses were performed with numerical (UPGMA) and cladistical (Wagner parsimony analysis) methods for all sets of loci. Robustness of the phylogenies obtained was estimated by bootstrap analysis. Low numbers of randomly selected loci (6) were sufficient to demonstrate genetic heterogeneity among the stocks studied. However, they were unable to give reliable phylogenetic information. A higher number of randomly selected loci (15 and more) were required to reach this goal. All loci did not convey equivalent information. The more variable loci detected a greater genetic heterogeneity among the stocks, whereas the least variable loci were better for robust clustering. Finally, analysis was performed with only 5 and 9 loci bearing synapomorphic allozyme characters previously identified among larger samples of stocks. A set of 9 such loci was able to uncover both genetic heterogeneity among the stocks and to build robust phylogenies. It can therefore be recommended as a minimum set of isoenzyme loci that bring maximal information for all studies aiming to explore the phylogenetic diversity of a new set of T. cruzi stocks and for any preliminary genetic typing. Moreover, our results show that bootstrap analysis, like any statistics, is highly dependent upon the information available and that absolute bootstrap figures should be cautiously interpreted.

SPECIES BOUNDARIES AMONG THE TELMATOBIUS (ANURA: LEPTODACTYLIDAE) OF THE LAKE TITICACA BASIN: ALLOZYME AND MORPHOLOGICAL EVIDENCE

The frog genus Telmatobius represents the radiation of 49 recognized species confined to high elevation aquatic habitats in the Andes Mountains of South America. The genus has not been shown to be monophyletic, and issues of species boundaries and relationships are poorly resolved. In this study, we sampled the four recognized subspecies of T. albiventris from Lake Titicaca, and other species (T. crawfordi, T. culeus, and T. marmoratus) from within the lake and the greater Titicaca Basin. We used allozyme characters and multivariate assessments of morphometric variation to test species boundaries in this complex. Our results suggest that four evolutionary species can be recognized: T. culeus (which includes T. albiventris and T. crawfordi), T. marmoratus, T. affinis halli, and T. sp. nov. Unique combinations of allozyme and morphometric variables can distinguish these, but only the sample of T. culeus is large enough, relative to the proportion of fixed characters, to evaluate distinctness of diagnostic c...

Phylogeny and Character Evolution in the Empidonax Group of Tyrant Flycatchers (Aves: Tyrannidae): A Test of W. E. Lanyon's Hypothesis Using mtDNA Sequences

We sequenced mitochondrial DNA from four protein-coding genes for 26 taxa to test W. E. Lanyon's hypothesis of intergeneric relationships and character evolution in the Empidonax group of tyrant flycatchers. Three genera in this group (Empidonax, Contopus, and Sayornis) successfully occupy north temperate habitats for breeding, while the remaining genera (Mitrephanes, Cnemotriccus, Aphanotriccus, Lathrotriccus, and Xenotriccus) are restricted to neotropical latitudes. Lanyon hypothesized two major clades in the group based on differences in syringeal morphology and proposed relationships among genera using a combination of morphologic, behavioral, and allozymic characters. The mtDNA data strongly support Lanyon's division of genera into two clades. In addition, the molecular and nonmolecular data sets agree in uniting Aphanotriccus and Lathrotriccus as sister taxa, with Cnemotriccus as basal to these genera. Species of Aphanotriccus, Lathrotriccus, and Cnemotriccus form a clade that exploits a distinctive nesting niche relative to other members of the Empidonax group. Within the second major clade, mtDNA sequences support a reconstruction based on allozymes that places Contopus and Empidonax as sister taxa. This hypothesis contradicts that of Lanyon, who allied Contopus with Mitrephanes on the basis of similarity in foraging mode. Genera in the Empidonax group are members of a larger assemblage that radiated in South America. Occupancy of temperate habitats by certain genera in this group is coincident with their evolution of migratory behavior and with independent diversification in foraging modes that reduces potential competition in sympatry.

Mitochondrial Phylogeny of Namib Day Geckos (Rhoptropus) Based on Cytochromeband 16S rRNA Sequences

Abstract We examined phylogenetic relationships among the Namib day geckos (genus Rhoptropus) using DNA sequence data from the mitochondrial cytochrome b (cytb) and 16S ribosomal RNA genes. Maximum-parsimony analysis of the cytb, 16S, and combined (cytb/16S) datasets each recovered an identical single most-parsimonious tree, revealing two well-supported clades: (1) Rhoptropus afer + Rhoptropus bradfieldi ssp and (2) Rhoptropus boultoni + (Rhoptropus barnardi + Rhoptropus biporosus). Maximum-likelihood analysis identified the same two species groups and corroborated patterns of relationship within respective parsimony clades. Moreover, the mitochondrial DNA trees were congruent with parsimony trees derived from morphological and allozymic characters. Congruence observed among these different data offers strong evidence for our molecular phylogeny of Rhoptropus, bringing taxonomic stability to a genus whose species-level relationships were widely debated throughout the last century.

Reconstructing phylogenies from allozyme data: comparing method performance with congruence

Allozyme data are widely used to infer the phylogenies of populations and closely-related species. Numerous parsimony, distance, and likelihood methods have been proposed for phylogenetic analysis of these data; the relative merits of these methods have been debated vigorously, but their accuracy has not been well explored. In this study, I compare the performance of 13 phylogenetic methods (six parsimony, six distance, and continuous maximum likelihood) by applying a congruence approach to eight allozyme data sets from the literature. Clades are identified that are supported by multiple data sets other than allozymes (e.g. morphology, DNA sequences), and the ability of different methods to recover these «known» clades is compared. The results suggest that (1) distance and likelihood methods generally outperform parsimony methods, (2) methods that utilize frequency data tend to perform well, and (3) continuous maximum likelihood is among the most accurate methods, and appears to be robust to violations of its assumptions. These results are in agreement with those from recent simulation studies, and help provide a basis for empirical workers to choose among the many methods available for analysing allozyme characters.

Reconstructing phylogenies from allozyme data: comparing method performance with congruence

Abstract Allozyme data are widely used to infer the phylogenies of populations and closely-related species. Numerous parsimony, distance, and likelihood methods have been proposed for phylogenetic analysis of these data; the relative merits of these methods have been debated vigorously, but their accuracy has not been well explored. In this study, I compare the performance of 13 phylogenetic methods (six parsimony, six distance, and continuous maximum likelihood) by applying a congruence approach to eight allozyme data sets from the literature. Clades are identified that are supported by multiple data sets other than allozymes (e.g. morphology, DNA sequences), and the ability of different methods to recover these «known» clades is compared. The results suggest that (1) distance and likelihood methods generally outperform parsimony methods, (2) methods that utilize frequency data tend to perform well, and (3) continuous maximum likelihood is among the most accurate methods, and appears to be robust to violations of its assumptions. These results are in agreement with those from recent simulation studies, and help provide a basis for empirical workers to choose among the many methods available for analysing allozyme characters.

Phylogeny and biogeographic history of hake (genus Merluccius ), inferred from mitochondrial DNA control-region sequences

Phylogenetic analyses of the left domain of the mitochondrial DNA control-region sequence have been used to examine the relationships among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypotheses based on morphological, meristic and allozyme characters. Analysis of aligned sequences revealed that transition bias was much lower than in mammalian mtDNA, and that nucleotide composition of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for the genus, based on the rise of the Isthmus of Panama, which is believed to have created a barrier to dispersal between marine species of the Atlantic and Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allozyme-based phylogenies, but poorly so with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-supported principal clades, one of American (west Atlantic and east Pacific) species and the other of Euro–African (east Atlantic) species. This suggests an evolutionary history during which the ancestral lineage of Merluccius was divided between two geographic regions, with subsequent dispersal and vicariant events resulting in the evolution and distribution of extant taxa. However, the relationships between some taxa within the American clade could not be resolved. We suggest that this is consistent with an hypothesis of a rapid origin and radiation of these taxa.

Genetic introgression between tetraploidDactylis glomerata subspp.reichenbachii andglomerata in the French Alps. Insight from morphological and allozyme variation

The morphology, phenology and allozyme polymorphism in seven tetraploidDactylis glomerata populations growing in the French Alps were studied. Based on habitat and morphological characteristics, two of the populations could be classified asD. glomerata subsp.reichenbachii, which is known to comprise diploid and tetraploid plants growing exclusively on dolomite, on south-facing meadows. This subspecies has been previously recorded in the Italian and Swiss Alps but not in the French Alps. The remaining five populations were morphologically intermediate but more similar to the cosmopolitanD. glomerata subsp.glomerata. On the basis of allozyme variation, all populations were more related to subsp.reichenbachii than to the cosmopolitan subsp.glomerata, suggesting that gene flow has occurred between the two tetraploid subspecies. The possibility that selection has acted differently on morphological and allozyme characters is discussed.

Allozyme Variation among Disjunct Populations of the Florida Green Watersnake (Nerodia floridana)

necessary before future listing considerations (e.g., candidacy for Endangered Species status). The objective of this study was to examine allozyme variation between the two disjunct populations of N. floridana. The null hypothesis is that the two populations are homogeneous in allozyme distribution; the alternative is that they differ. The possible implications of the study are as follows: (1) if the population in South Carolina is diagnosed as a species [following the phylogenetic species concept as the operational form of the evolutionary species concept (Frost and Kluge, 1994)], it should warrant careful consideration for protection under the Endangered Species Act; and (2) if the null is not rejected, that is, no differences in allozyme characters are found, the special status of the species in South Carolina might require reconsideration.

Systematic Relationships among the Emberizid Sparrows

We developed a phylogeny for 34 taxa (species, species groups, or genera) in the Emberizidae, including all of those placed in the first group of the Emberizidae by Paynter and Storer (1970). Structural, plumage-related, behavioral, oological, and allozymic characters were employed. The lateroventral process of the laterosphenoid, a skeletal feature not previously used in comparative anatomy among passerines, also was included. Majority- rule, strict-consensus, and bootstrapped maximum-parsimony trees were constructed. Phy- logenies uncovered were in fairly close agreement with previously published work that used molecular data, although the Old World bunting clade (Emberiza, Melophus, Plectrophenax, Calcarius, etc.) was basal to all other emberizid sparrows examined. The majority-rule and strict-consensus phylogenies supported the monophyly of all currently accepted genera (e.g. Aimophila, Ammodramus, Spizella, and Zonotrichia), provided that Amphispiza quinquestriata is placed in the genus Aimophila. In some cases, however, the monophyly was weak (e.g. Melospiza, especially M. melodia vs. Passerella), and for others (e.g. Ammodramus) more work is needed to establish fully the intrageneric relationships. Received 11 March 1997, accepted 3

Evidence of a reproductive barrier between two forms of the marine periwinkle Littorina fabalis (Gastropoda)

Studies of allozyme variation may reveal unexpected patterns of genetic variation which challenge earlier conclusions of species delimitations based on morphological data. However, allozyme variation alone may not be sufficient to resolve this kind of problem. For example, populations of the marine intertidal snailLittorina fabalis(=Littorina mariae) from wave exposed parts and from protected parts of the same shores are distinguished by different alleles of arginine kinase (Ark) while indifferent, or very nearly so, in another 29 loci. Intermediate populations have large deficiencies of exposed/sheltered heterozygote classes ofArkand we have earlier suggested habitat-related selection in this locus as the explanation. In this study we estimated growth rate of individual snails of differentArk-genotypes in three different habitats (exposed, sheltered and intermediate). In all habitats the snails homozygous for alleles of ‘exposed’ type grew faster and matured at a larger size than did snails homozygous for alleles of ‘sheltered’ types. This relationship was indirectly confirmed in three additional sites of intermediate exposure where exposedArk-genotypes dominated among large (>8 mm) snails while the sheltered genotypes dominated among small (<5 mm) snails of truly sympatric samples. We furthermore found small differences in allele frequencies of two other loci (PgiandPgm-2) and in shell colour frequencies, comparing sympatric snails of exposed and shelteredArk-homozygotes. Although we found no signs of habitat-related selection among snails of differentArk-genotype, or selection against heterozygotes, we cannot reject selection inArk, as our experiments only covered one island, one season and grown-up snails. The coupling between allozyme and phenotypic characters in strictly sympatric samples of snails suggests the presence of two gene pools. Perhaps the large and small forms ofL. fabalisrepresent very closely related cryptic taxa. However, introgression between them seems a possible explanation for the striking similarities in the vast majority of morphological and allozyme characters.

Evidence of a reproductive barrier between two forms of the marine periwinkleLittorina fabalis(Gastropoda)

Studies of allozyme variation may reveal unexpected patterns of genetic variation which challenge earlier conclusions of species delimitations based on morphological data. However, allozyme variation alone may not be sufficient to resolve this kind of problem. For example, populations of the marine intertidal snailLittorina fabalis(=Littorina mariae) from wave exposed parts and from protected parts of the same shores are distinguished by different alleles of arginine kinase (Ark) while indifferent, or very nearly so, in another 29 loci. Intermediate populations have large deficiencies of exposed/sheltered heterozygote classes ofArkand we have earlier suggested habitat-related selection in this locus as the explanation. In this study we estimated growth rate of individual snails of differentArk-genotypes in three different habitats (exposed, sheltered and intermediate). In all habitats the snails homozygous for alleles of ‘exposed’ type grew faster and matured at a larger size than did snails homozygous for alleles of ‘sheltered’ types. This relationship was indirectly confirmed in three additional sites of intermediate exposure where exposedArk-genotypes dominated among large (>8 mm) snails while the sheltered genotypes dominated among small (<5 mm) snails of truly sympatric samples. We furthermore found small differences in allele frequencies of two other loci (PgiandPgm-2) and in shell colour frequencies, comparing sympatric snails of exposed and shelteredArk-homozygotes. Although we found no signs of habitat-related selection among snails of differentArk-genotype, or selection against heterozygotes, we cannot reject selection inArk, as our experiments only covered one island, one season and grown-up snails. The coupling between allozyme and phenotypic characters in strictly sympatric samples of snails suggests the presence of two gene pools. Perhaps the large and small forms ofL. fabalisrepresent very closely related cryptic taxa. However, introgression between them seems a possible explanation for the striking similarities in the vast majority of morphological and allozyme characters.

Allozyme Evidence for the Phylogeny of Giant New Caledonian Geckos (Squamata: Diplodactylidae: Rhacodactylus), with Comments on the Status of R. leachianus henkeli

The phylogenetic analysis of allozyme characters within the New Caledonian giant geckos, genus Rhacodactylus, yields a pattern of relationships that is largely congruent with that derived from morphological data. A ‘total evidence’ approach, incorporating 13 allozyme and 29 morphological characters, yields a single most-parsimonious tree with the pattern: R. auriculatus ((R. leachainus (R. ciliatus, R. chahoua)) (R. sarasinorum, R. trachyrhynchus)). A phenetic analysis based on Nei’s genetic distance data results in a similar branching pattern. The genus Pseudothecadactylus is tentatively regarded as valid because allozyme data conflict strongly with morphological data that suggest that these geckos evolved from within Rhacodactylus. Allozymes and available morphological data do not support the recognition of the recently described subspecies R. leachianus henkeli.

Phylogenetic systematics of the day geckos, genus, Rhoptropus (Reptilia: Gekkonidae), of south‐western Africa

The genus Rhoptropus consists of six species of diurnal, chiefly rupicolous, geckos that are endemic to the arid and semi‐arid zones of Namibia and southern Angola. Sixteen skeletal and scalation characters and six allozyme characters analysed cladistically yield a single most parsimonious pattern of relationships: ((R. afer, R. bradfieldi) (R. taeniostictus (R. boultoni (R. barnardi, R. biporosus)))). Support for the placement of R. taeniostictus is tenuous because of missing allozyme data, but the remainder of the topology, especially the basal dichotomy, is well supported. Morphological and allozyme data are congruent and a phenetic analysis of genetic distances among the taxa is consistent with the phylogeny. The diversification of the genus probably took place in the Mid‐ to Late Tertiary and both basal and distal cladogenic events may be related to the evolution of the Namib Desert and movement of the Namib sands. Rates of evolution among the lineages of Rhoptropus appear to be unequal and R. afer, a species largely restricted to horizontal sheet rock habitats, has accumulated a large number of autapomorphic traits.