Predaceous diving beetles (Coleoptera: Dytiscidae) of Jordan

The first account of the predaceous diving beetles or Dytiscidae of Jordan is presented. Altogether 25 species are listed, although the occurrence of two of them remains doubtful. Nine species are recorded from the territory of Jordan for the first time, and the first precise locality data are provided for an additional seven species. Bidessus anatolicus Wewalka, 1972 and Nebrioporus stearinus (Kolenati, 1845) recorded recently from Jordan based on misidentification are removed from the list. If available, habitat information is provided for recently collected species. The zoogeographical patterns of the region are briefly summarised.     

New mesozoic Ithyceridae beetles (Coleoptera)

A new subfamily, Mongolocarinae subfam. nov. of the family Ithyceridae, from the Middle-Upper Jurassic and Lower Cretaceous of Asia is described. It includes five genera with five species: Palaeocar gen. nov. (with P. princeps sp. nov.), Mongolocar gen. nov. (M. orcinus sp. nov.), Praecar gen. nov. (P. stolidus sp. nov.), Karacar gen. nov. (M. contractus sp. nov.), and Baissacar gen. nov. (B. passarius sp. nov.).     

Phylogeny and diversification of diving beetles (Coleoptera: Dytiscidae)

Dytiscidae is the most diverse family of beetles in which both adults and larvae are aquatic, with examples of extreme morphological and ecological adaptations. Despite continuous attention from systematists and ecologists, existing phylogenetic hypotheses remain unsatisfactory because of limited taxon sampling or low node support. Here we provide a phylogenetic tree inferred from four gene fragments (cox1, rrnL, H3 and SSU, ≈ 4000 aligned base pairs), including 222 species in 116 of 174 known genera and 25 of 26 tribes. We aligned ribosomal genes prior to tree building with parsimony and Bayesian methods using three approaches: progressive pair‐wise alignment with refinement, progressive alignment modeling the evolution of indels, and deletion of hypervariable sites. Results were generally congruent across alignment and tree inference methods. Basal relationships were not well defined, although we identified 28 well supported lineages corresponding to recognized tribes or groups of genera, among which the most prominent novel results were the polyphyly of Dytiscinae; the grouping of Pachydrini with Bidessini, Peschetius with Methlini and Coptotomus within Copelatinae; the monophyly of all Australian Hydroporini (Necterosoma group), and their relationship with the Graptodytes and Deronectes groups plus Hygrotini. We found support for a clade formed by Hydroporinae plus Laccophilini, and their sister relationship with Cybistrini and Copelatinae. The tree provided a framework for the analysis of species diversification in Dytiscidae. We found a positive correlation between the number of species in a lineage and the age of the crown group as estimated through a molecular clock approach, but the correlation with the stem age was non‐significant. Imbalances between sister clades were significant for several nodes, but the residuals of the regression of species numbers with the crown age of the group identified only Bidessini and the Coptotomus + Agaporomorphus clade as lineages with, respectively, above and below expected levels of species diversity. © The Willi Hennig Society 2008.     

Speciation of Iberian diving beetles in Pleistocene refugia (Coleoptera, Dytiscidae)

The Mediterranean basin is an area of high diversity and endemicity, but the age and origin of its fauna are still largely unknown. Here we use species-level phylogenies based on approximately 1300 base pairs of the genes 16S rRNA and cytochrome oxidase I to establish the relationships of 27 of the 34 endemic Iberian species of diving beetles in the family Dytiscidae, and to investigate their level of divergence. Using a molecular clock approach, 18-19 of these species were estimated to be of Pleistocene origin, with four to six of them from the Late Pleistocene ( approximately 100 000 years). A second, lower speciation frequency peak was assigned to Late Miocene or Early Pliocene. Analysis of the distributional ranges showed that endemic species placed in the tip nodes of the trees are significantly more likely to be allopatric with their sisters than endemic species at lower node levels. Allopatric sister species are also significantly younger than sympatric clades, in agreement with an allopatric mode of speciation and limited subsequent range movement. These results strongly suggest that for some taxa Iberian populations were isolated during the Pleistocene long enough to speciate, and apparently did not expand their ranges to recolonize areas north of the Pyrenees. This is in contradiction to observations from fossil beetles in areas further north, which document large range movements associated with the Pleistocene glacial cycles hypothesized to suppress population isolation and allopatric speciation.     

The inheritance of intrasexual dimorphism in female diving beetles (Coleoptera: Dytiscidae)

Many species of Dytiscus diving beetles exhibit intrasexual dimorphism, e.g., the elytra is smooth in some females and grooved in others. However, the expression of the grooves and whether they are a product of heredity or the environment remain unknown. One Japanese species, Dytiscus sharpi sharpi Wehncke, 1875 , also shows female dimorphism, with grooved and smooth morphs, while D. sharpi validus Régimbart, 1899, only has a single morph (the grooved type). A hybrid of the two species should therefore provide a means of sorting out how the grooves are inherited. We found two independent wetlands of D. sharpi sharpi in Chiba Prefecture, Japan. One was a place where a high proportion of grooved females lived, and the others had high proportions of smooth females. After five to eight generations of beetles from two populations with different proportions of grooved females were reared under aquarium conditions constituting a common garden design, i.e., water temperature, water depth, and presence of a plant for oviposition, the differences remained. We mated smooth virgin females of D. sharpi sharpi with males of D. sharpi validus to obtain hybrid offspring. The elytral traits of the hybrid females produced only grooved forms. These results suggested that the female dimorphism is determined by genetics, and that the grooved morph was dominant over the smooth one, independent of environmental factors. In addition, the hybrid insects did not differ from the two subspecies insects in larval survivorship, pupation success, or sex ratio. They also showed neither morphological abnormality nor reduced survival.     

New species of variegated mud-loving beetles (Coleoptera: Heteroceridae) from mesozoic deposits of China

A new species of variegated mud-loving beetles, Heterocerites magnus, sp. nov., is described from the Late Tithonian-Berriasian of China (Huangbanjigou, Yixian Formation). This is a second known representative of the family in the Mesozoic.     

Phylogeny and classification of diving beetles in the tribe Cybistrini (Coleoptera, Dytiscidae, Dytiscinae)

Phylogenetic relationships among members of the diving beetle tribe Cybistrini (Coleoptera: Dytiscidae) were inferred from analysis of 47 adult and larval morphological characters and sequences from portions of the genes cytochrome oxidase I (COI) and II (COII), histone III (H3) and wingless. Thirty‐three species of Cybistrini were included, representing all genus‐groups except Regimbartina Chatanay and Megadytes (Bifurcitus) Brinck, and most historically recognized species groups and subgenera used in the tribe. Outgroups include six species from other tribes within Dytiscinae and Lancetinae. Analyses included parsimony analysis of the combined data, likelihood analysis of combined molecular data and partitioned Bayesian analysis of the combined data. Results indicate that Cybistrini is well supported as a monophyletic group. Within the tribe, all currently recognized genus groups were found to be monophyletic with the exception of Onychohydrus Schaum, which is paraphyletic with respect to Austrodytes Watts in the parsimony analysis, but monophyletic in the likelihood and Bayesian analyses, and Cybister sensu stricto, which is paraphyletic with respect to C. (Melanectes) Brinck and C. (Scaphinectes) Ádám in the parsimony analysis or only the latter in the likelihood and Bayesian analyses. Results also suggest that some, but not all, historically recognized species groups or subgenera in the large genus Cybister Curtis are monophyletic, and this is discussed and compared. To improve the classification, the name Sternhydrus Brinck is elevated from subgenus to genus rank ( new status ). Four subgenera in the genus Cybister are recognized: C. (Melanectes) Brinck, C. (Megadytoides) Brinck ( resurrected ), C. (Neocybister) Miller, Bergsten and Whiting ( new subgenus ) and C. (Cybister) Curtis. The following new synonyms are established: Trochalus Dejean ( new synonym ), and ScaphinectesÁdám = Cybister (Cybister) ( new synonym ). The Neotropical species Cybister parvus Trémouilles (not examined) apparently does not fit any historical or currently recognized genus‐group diagnosis in Cybistrini, so it is retained in Cybister but incertae sedis with respect to subgenus. In addition to classification, the evolution of the unique character combinations present in cybistrines are discussed. A key to the adults of genera and subgenera is presented.     

Submersion respiration in small diving beetles (Dytiscidae)

Some small diving beetles can survive submerged through weeks and months, because they can extract oxygen, dissolved in the water, through respiratory pores in their integument. An air flux from the outside to the inside through the respiratory pores has been demonstrated. All diving beetles capable of such pore respiration are small, but not all small diving beetles have pore respiration. With increasing size, more and more of the surface must be covered by respiratory pores to meet the increasing demand of oxygen. In running water species the pore-respiration mode is regarded as an adaptation to life in current exposed substrates, thus they avoid the risk of being swept away during frequent surface visits. In stagnant water species the pore respiration mode reduces the risk of falling victim to pelagic predators. The submersion tolerant species can switch to surface respiration, e.g. during low oxygen content. The pore respiratory mechanism is believed to be a specialised plastron. The oxygen flux through the scattered, small respiratory pore area may be enhanced by a functional thinning of the boundary layer.     

Nonlethal sampling of DNA from critically endangered diving beetles (Coleoptera: Dytiscidae) using a single antenna

Nonlethal DNA sampling is highly desirable in molecular genetic studies of protected and endangered species. To develop a demonstrably nonlethal method of obtaining DNA from endangered diving beetles (Dytiscus sharpi sharpi Wehncke, Cybister lewisianus Sharp and Cybister brevis Aubé), we amputated the antennae of these endangered diving beetles and investigated the impact of the amputation on reproductive behaviors, egg‐laying and lifespan. Diving beetles with either one or no antennae copulated without delay and laid eggs, comparable to the pairs of intact beetles under breeding conditions. The lifespan of antennae‐amputated D. sharpi sharpi was the same as that of the intact beetles. A single antenna was sufficient to allow polymerase chain reaction (PCR) detection of a mitochondrial DNA gene, cytochrome‐c oxidase subunit I (COI), and the sequence of the COI gene could be determined directly. The PCR‐ready genomic DNA was available both in fresh antennae isolated from living beetles and in old antennae from whole beetles preserved for at least 5–6 years in pure ethanol. These results suggest that an antenna is a good sampling site for isolating genomic DNA from endangered diving beetles without sacrificing and disturbing reproductive behaviors such as mating and egg‐laying, or lifespan.     

The phylogeny of diving beetles (Coleoptera: Dytiscidae) and the evolution of sexual conflict

A model of evolution based on conflicts of interest between the sexes over mating decisions is examined in relation to diving beetles (Dytiscidae). The model predicts the following evolutionary sequence: (1) cost to females of mating increases, (2) females evolve behavioural resistance to male mating attempts, (3) males evolve devices to overcome female resistance, and (4) females evolve morphological counter-adaptations to the male devices. This model is tested using species of Dytiscidae, in which (1) some species have a very long mating duration while others mate quickly, (2) females of some species resist male mating attempts by swift and erratic swimming when seized by a male, (3) males of some species possess a grasping device in the form of sucker-shaped setae on the legs used to adhere to the pronota or elytra of females prior to mating, and (4) females of some species have a modified dorsal cuticle with irregular sculpturing which appears to interfere with the male adhesive setae. The predicted order of evolution of some of these features was tested in a cladistic analysis of 52 taxa in Dytiscidae and Hygrobiidae using characters from adult and larval morphology and a portion of the gene wingless . The combined analysis resulted in nine most parsimonious cladograms. The consensus cladogram of these indicates that male sucker setae arose a single time in a clade of Dytiscinae. Nested within this clade are five groups with an independently derived, modified dorsal cuticle in females. This pattern of characters in Dytiscinae is consistent with the prediction implied by the model of sexual selection. The utility of wingless as a marker for phylogenetic analysis of diving beetles is discussed, and the resulting phylogeny is compared with previous analyses and current classification.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 359–388.     

New water scavenger beetles (Coleoptera: Hydrophilidae) from the mesozoic of Mongolia

A new genus and two new species of water scavenger beetles, Hydrophilopsia bontsaganica, sp. nov. and Prospercheus cristatus, gen. et sp. nov., are described from the Upper Jurassic and Lower Cretaceous of Mongolia. The systematic position of the new genus is discussed.     

New box trap for large predaceous diving beetles Cybister Curtis, 1827 and Dytiscus Linnaeus, 1758 (Coleoptera: Dytiscidae)

A box trap was developed for effective collection of large predaceous diving beetles. The floating trap, which was fabricated from a plastic box with two funnel mouths equipped with mesh lids, can be opened only when beetles enter the trap. Considerable attention was paid to the trap's performance as it was quantitatively evaluated in laboratory conditions in detail using Cybister and Dytiscus diving beetles. Without the mesh lid on the trap mouth (negative control test), the number of beetles in the trap was the highest at 2–3 hours. However, most beetles escaped from the trap without a mesh lid within six hours of starting the experiment. When eight beetles were put into a trap without a mesh lid, all of them had escaped from it after eight hours. On the contrary, beetles did not escape from a trap with a mesh lid. This result and testing in the field suggest that trap lids have a significant role in averting the escape of beetles from the trap.     

Higher‐level phylogeny of diving beetles (Coleoptera: Dytiscidae) based on larval characters

A comprehensive higher‐level phylogeny of diving beetles (Dytiscidae) based on larval characters is presented. Larval morphology and chaetotaxy of a broad range of genera and species was studied, covering all currently recognized subfamilies and tribes except for the small and geographically restricted Hydrodytinae, where the larva is unknown. The results suggest several significant conclusions with respect to the systematics of Dytiscidae including the following: monophyly of all currently recognized subfamilies, although Dytiscinae when considered in a broad context is rendered paraphyletic by Cybistrinae; currently recognized tribes are monophyletic except for Agabini, Hydroporini and Laccornellini; inter‐subfamily and inter‐tribe relationships generally show weak support, except for a few well supported clades; three distinct clades are recognized within Dytiscinae [Dytiscini sensu lato (i.e. including the genera Dytiscus Linnaeus and Hyderodes Hope), Hydaticini sensu lato, and Cybistrini]; and recognition of Pachydrini as a distinct tribe. Other less robust results include: Methlini sister to the rest of Hydroporinae; relative basal position of Laccornini, Hydrovatini and Laccornellini within Hydroporinae; close relationship of Agabinae and Copelatinae; Matinae nested deep within Dytiscidae, as sister to a large clade including Colymbetinae, Coptotominae, Lancetinae and Dytiscinae sensu lato; the sister‐group relationship of Agabetini and Laccophilini is confirmed. The results presented here are discussed and compared with previous phylogenetic hypotheses based on different datasets, and the evolution of some significant morphological features is discussed in light of the proposed phylogeny. All suprageneric taxa are diagnosed, including illustrations of all relevant synapomorphies, and a key to separate subfamilies and tribes is presented, both in traditional (paper) format and as an online Lucid interactive identification key.     

Abundance and species richness patterns of diving beetles (Coleoptera, Dytiscidae) from exposed and protected sites in 98 northern Swedish lakes

Forty species of predaceous diving beetles (Coleoptera, Dytiscidae) were collected in sweepnet samples from 98 boreal lakes in northern Sweden. Samples from protected sites with vegetation had significantly more specimens and species than those from exposed sites without vegetation in the same lakes. No geographically based differences, e.g. latitudinal or in distance from the coast, were found. These gradients were 200 and 150 km long, respectively. Species' distribution in terms of occurence at number of sites was positively correlated with the mean abundance of the species. The relationship between species' abundance and body length was characterized by the lack of large, abundant species. Partial least square regressions on dytiscid abundance and species richness showed low predictive power of lake area, altitude and water chemistry. The seven environmental variables used explained at best 15.3 and 24.4% of the total variance in abundance and species richness, respectively. The results are compared to activity trap catches of dystiscids in lakes in an adjacent region. A majority of the species occured in both materials. However, species occuring in high proportion in one of the materials, were rare in the other material. The mean body length of the species caught more efficiently with traps was not larger than that of those overpresented in net sampling. Based on this study and the available literature data, the regional species pool of boreal lake dytiscids is estimated to 30–40 species. It is still an open question if lake assemblages are markedly poorer than those found in the development of vegetation, whereas the impact of water chemistry is small.     

Intraspecific variation and intersexual correlation in secondary sexual characters of three diving beetles (Coleoptera: Dytiscidae)

Male diving beetles of the subfamily Dytiscinae possess tarsi with adhesive discs that they strike on the female dorsum during mating interactions. Females of many species are dimorphic, being either smooth or structured dorsally. Darwin suggested the female structures were an aid for the male but in this study we investigate these characteristics in the light of sexual conflicts. The intraspecific variation in the numbers and size distribution of male tarsal discs, and in body measurements were recorded for three dytiscine species, all with dimorphic females. The number of protarsal discs in the two Dytiscus species varied much more than previously reported. In addition, only a small part of the variation could be explained by body size. In Graphoderus we found highly significant differences in male secondary sexual characters among populations. A multivariate analysis significantly correlated male secondary sexual characters with the proportion of granulate females in the populations. These observations are consistent with the theory of arms races and female counter adaptations. Covariation between male and female characters is predicted from a framework of sexual conflict over mating rate. At the same time our study gives a new perspective on the function of dytiscine female dorsal irregularities debated ever since Darwin.     

Evolution of subterranean diving beetles (Coleoptera: Dytiscidae: Hydroporini, Bidessini) in the arid zone of Australia

Calcrete aquifers in arid inland Australia have recently been found to contain the world's most diverse assemblage of subterranean diving beetles (Coleoptera: Dytiscidae). In this study we test whether the adaptive shift hypothesis (ASH) or the climatic relict hypothesis (CRH) is the most likely mode of evolution for the Australian subterranean diving beetles by using a phylogeny based on two sequenced fragments of mitochondrial genes (CO1 and 16S-tRNA-ND1) and linearized using a relaxed molecular clock method. Most individual calcrete aquifers contain an assemblage of diving beetle species of distantly related lineages and/or a single pair of sister species that significantly differ in size and morphology. Evolutionary transitions from surface to subterranean life took place in a relatively small time frame between nine and four million years ago. Most of the variation in divergence times of the sympatric sister species is explained by the variation in latitude of the localities, which correlates with the onset of aridity from the north to the south and with an aridity maximum in the Early Pliocene (five mya). We conclude that individual calcrete aquifers were colonized by several distantly related diving beetle lineages. Several lines of evidence from molecular clock analyses support the CRH, indicating that all evolutionary transitions took place during the Late Miocene and Early Pliocene as a result of aridification.     

Evidence for speciation underground in diving beetles (Dytiscidae) from a subterranean archipelago

Most subterranean animals are assumed to have evolved from surface ancestors following colonization of a cave system; however, very few studies have raised the possibility of “subterranean speciation” in underground habitats (i.e., obligate cave‐dwelling organisms [troglobionts] descended from troglobiotic ancestors). Numerous endemic subterranean diving beetle species from spatially discrete calcrete aquifers in Western Australia (stygobionts) have evolved independently from surface ancestors; however, several cases of sympatric sister species raise the possibility of subterranean speciation. We tested this hypothesis using vision (phototransduction) genes that are evolving under neutral processes in subterranean species and purifying selection in surface species. Using sequence data from 32 subterranean and five surface species in the genus Paroster (Dytiscidae), we identified deleterious mutations in long wavelength opsin (lwop), arrestin 1 (arr1), and arrestin 2 (arr2) shared by a sympatric sister‐species triplet, arr1 shared by a sympatric sister‐species pair, and lwop and arr2 shared among closely related species in adjacent calcrete aquifers. In all cases, a common ancestor possessed the function‐altering mutations, implying they were already adapted to aphotic environments. Our study represents one of the first confirmed cases of subterranean speciation in cave insects. The assessment of genes undergoing pseudogenization provides a novel way of testing modes of speciation and the history of diversification in blind cave animals.     

Convergence, recurrence and diversification of complex sperm traits in diving beetles (Dytiscidae)

Sperm display remarkable morphological diversity among even closely related species, a pattern that is widely attributed to postcopulatory sexual selection. Surprisingly few studies have used phylogenetic analyses to discern the details of evolutionary diversification in ornaments and armaments subject to sexual selection, and the origins of novel sperm traits and their subsequent modification are particularly poorly understood. Here we investigate sperm evolution in diving beetles (Dytiscidae), revealing dramatic diversification in flagellum length, head shape, presence of sperm heteromorphism, and the presence/type of sperm conjugation, an unusual trait where two or more sperm unite for motility or transport. Sperm conjugation was found to be the ancestral condition in diving beetles, with subsequent diversification into three forms, each exhibiting varying degrees of evolutionary loss, convergence, and recurrence. Sperm head shape, but not length or heteromorphism, was found to evolve in a significantly correlated manner with conjugation, consistent with the different mechanisms of head alignment and binding required for the different forms of conjugation. Our study reveals that sperm morphological evolution is channeled along particular evolutionary pathways (i.e., conjugate form), yet subject to considerable diversification within those pathways through modification in sperm length, head shape, and heteromorphism.     

Structure in temperate predaceous diving beetle communities (Coleoptera: Dytiscidae)

Collection records of adult dytiscid beetles (Coleoptera, Dytiscidae) from 312 sites within the province of Alberta, Canada, were analyzed for patterns of similarity in species distribution. Sites compared on the basis of species occurrence (Jaccard coefficient of similarity and group average cluster analysis) separated into 12 principal clusters, interpreted as communities. However, cluster inclusion occurred at very low levels of similarity and 30% of sites were unclustered outliers. Ecological charade us tics of sites that were recognized as varying between dusters were salinity, productivity, stability, water temperature, substrate type, flow and vegetation. An index relating these qualitatively defined variables to species numbers is presented. An analysis of co-occurrence patterns of species was conducted as an alternative approach to definition of multispecies associations. Each possible combination of co-occurrence between pairs of species occurring in more than 5 collections each was tested for significance (p = 0.005) by means of Yates corrected χ² tests. Results of tests were expressed in binary terms, blank – no significance, x - significant. Species were then clustered on the basis of patterns of significant co-occurrences as above. This analysis was used as the basis for ordination of species in a symmetrical matrix with species ordered so as to maximize density of points of significant co-occurrence (x) around the principal diagonal. Areas in the matrix showing high densities of co-occurrence were interpreted as representing communities. The cluster analysis of species produced a better cluster pattern than obtained for sites but while generally similar, the species clustering pattern was less fine. The principal species groups consisted of those of saline water, alpine/subalpine lotic sites, other lotic habitats, and lentic habitats with two subgroups, species in forest areas and grassland species. The ordination, while reflecting this grouping of species, demonstrated that each group graded into others through loss of certain species and acquisition of others and thus showed the continuum nature of these communities. Restricting ordination to congeneric species indicated that these do not usually show identical patterns of co-occurrence but neither are patterns coincident with mutual exclusion. Within genera, considerable overlap in occurrence between species is the norm but species tend to occupy slightly different positions relative to one another along qualitatively defined ecological gradients. Relative position of species in these ordinations shows good correlation with patterns of geographical distribution lending support to the interpretation of ordination patterns reflecting relative ecological segregation. The dytiscid beetle fauna of north temperate regions is especially rich. Also, the large number of significant co-occurrences observed between species shows that species packing in many habitats of this region is dense. It is speculated that this species richness is possible because of the seasonality of habitats at these latitudes which reduces competition and predation from other groups and produces seasonal pulses of high productivity permitting a species rich fauna to develop because of abundant resources. It is likely that factors other than interspecific competition for resources are important in shaping dytiscid communities in habitats with strong nutrient pulses.     

Recognition of a species-poor, geographically restricted but morphologically diverse Cape lineage of diving beetles (Coleoptera: Dytiscidae: Hyphydrini)

Aim To establish the phylogeny and geographical origin of the genera of the diving beetle tribe Hyphydrini in order to investigate the origin of differences in geographical range size, intrageneric species‐richness and morphological disparity. In particular, we tested the hypothesis that the geographically restricted, species‐poor and morphologically deviating genera found in the Cape Region of South Africa are a paraphyletic pool of ‘primitive’ Hyphydrini, from which the morphologically more uniform, species‐rich and geographically widespread genera have originated. Location Worldwide, with special reference to the Cape Region of South Africa. Methods We constructed a genus‐level molecular phylogeny of 10 of the 14 known genera of Hyphydrini, including the five endemic to the Cape Region, using sequences from four gene fragments (two mitochondrial, rrnL and cox1; and two nuclear, 18S rRNA and histone 3, c. 2200 bp). Phylogenies were built with Bayesian methods, and linearized using penalized likelihood. Morphological disparity was characterized by correspondence analysis of a data matrix of 21 binary characters. We compare morphological disparity among groups using distance to the global and local centroids and the total range of morphospace occupied. Geographical range was estimated using the number of 6° longitude × 8° latitude Universal Transverse Mercator squares known to contain any species of each genus. Results Hyphydrini is made up of four well supported clades of similar relative genetic divergence: (1) Hyphydrus (Old World plus Australasia, 133 species), (2) the five endemic genera of the Cape Region, sister to Hovahydrus (Madagascar) (10 species), (3) Desmopachria (America, 92 species), and (4) two Oriental genera (Microdytes and Allopachria, 68 species). The morphological disparity within the Cape Region lineage has apparently increased with time, with the two genera closest to the global centroid paraphyletic and basal with respect to the three more recent, morphologically deviating genera. Differences in the number of species between each of the four lineages were not significant. The correlation between the number of species in each lineage and geographical range extent was highly significant, with the low species number of the Cape Region (six) well within the 95% confidence interval of the regression. Main conclusions Contrary to expectations, the species‐poor, morphologically deviating endemic genera of the Cape Region are not a ‘primitive’ relictual pool from which the widespread, species‐rich and morphologically uniform genera have originated. The morphological disparity within the Cape lineage has increased with time, and the apparent lack of species‐level diversification disappears when species–area relationships are considered. A major unanswered question is why one of the four main lineages of Hyphydrini has remained restricted to a very reduced area (the Cape Region), but despite this evolved the highest degree of morphological diversity seen in the tribe.