Taxonomic review of the genus Copelatus Erichson (Coleoptera: Dytiscidae) in Korea

A taxonomic review of the genus Copelatus Erichson (Coleoptera: Dytiscidae) in Korea is presented. In the present study, five species of Copelatus are recognized from Korea, including one unrecorded species, C. kammuriensis. We provide a key to the Korean species of Copelatus, diagnosis of one unrecorded species, habitus photographs, scanning electron micrographs of the elytron, and illustrations of the aedeagus.     

Range expansion and ancestral niche reconstruction in the Mediterranean diving beetle genus Meladema (Coleoptera,Dytiscidae)

Species of the genus Meladema (Dytiscidae, Colymbetinae) are some of the largest macroinvertebrates in the western Palearctic region, being top predators in fishless streams. Two of the three described species, Meladema imbricata (Wollaston, 1871) and Meladema lanio (Fabricius, 1775) are Macaronesian endemics from the Canary Islands and Madeira, respectively, while the third, Meladema coriacea Laporte, 1835, is widely distributed from Morocco and the Iberian Peninsula to Turkey, including the Canary Islands. Previous phylogenetic analysis using only mitochondrial markers revealed the existence of two cryptic lineages within M. coriacea, one restricted to Corsica and the other including the rest of sampled populations. We reconstruct here the evolutionary history of the species of Meladema using a more comprehensive sampling covering its whole geographical range, adding nuclear markers and Bayesian molecular dating. Using environmental niche modelling, we test for possible differences in climatic preferences among lineages and reconstruct their ancestral climatic niche. Our results strongly supported the existence of four monophyletic lineages represented by the three recognized species plus a fourth cryptic lineage with populations of M. coriacea from the Tyrrhenian islands (Corsica, Sardinia and Montecristo). This pattern is not likely to be the result of mitochondrial artefacts due to Wolbachia infection, as all 11 tested individuals were negative for this parasite. Dating analysis placed the origin of Meladema in the Middle Miocene although diversification among extant Meladema lineages started in the early Pleistocene and took place in a relatively short time period. Phylogeographic analysis inferred a continental origin of Meladema, with an independent colonization of the Macaronesian and Mediterranean islands. From the south‐western Mediterranean region, the continental M. coriacea expanded its range up to Bulgaria and Turkey in the northern basin and to Tunisia in the southern. Results of niche modelling showed that seasonality is the critical factor in shaping the current distribution of Meladema. Island lineages (M. imbricata, M. lanio and the Tyrrhenian lineage of M. coriacea) occur in sites with low seasonality, within the range of the reconstructed ancestral climatic niche of the genus. On the contrary, continental M. coriacea expanded its range to localities outside the ancestral climatic range of the genus, with a higher seasonality and aridity.     

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.     

Female dimorphism in Japanese diving beetle Dytiscus marginalis czerskii (Coleoptera: Dytiscidae) evidenced by mitochondrial gene sequence analysis

Three species of the Japanese diving beetle Dytiscus have been identified: D. dauricus Gebler, 1832; D. marginalis czerskii Zeitzev, 1953; and D. sharpi. At present, the latter consists of the subspecies D. sharpi sharpi Wehncke, 1875 and D. sharpi validus Régimbart, 1899 based on the comparative data of mitochondrial DNA cytochrome‐c oxidase I (COI) sequences. Many Dytiscus species have smooth and grooved elytra, which are female dimorphic traits. For many years it has been thought that Japanese D. marginalis czerskii has a single morph, that is, only grooved females, although there were some collecting reports of smooth females occurring at the foot of Mt. Chokaisan in Yamagata and Akita Prefectures. However, the population of smooth females (smooth population) has not yet been identified by DNA markers. To understand the species status of the smooth population, we sequenced 769 bp of COI of a male derived from a smooth mother insect and compared it with the sequence from a known grooved female. The sequences of 769 bp of the COI gene in the smooth population were identical to that in the grooved female, indicating that Japanese D. marginalis czerskii has female dimorphic traits.     

Evolution of salinity tolerance in the diving beetle tribe Hygrotini (Coleoptera,Dytiscidae)

Some species of the diving beetle tribe Hygrotini (subfamily Hydroporinae) are among the few insects able to tolerate saline concentrations more than twice that of seawater. However, the phylogenetic relationships of the species of Hygrotini, and the origin and evolution of tolerance to salinity in this lineage, are unknown. In this work, we aim to reconstruct how many times salinity tolerance did evolve in Hygrotini, whether this evolution was gradual or if tolerance to hypersalinity could evolve directly from strictly freshwater (FW) species, and to estimate the probabilities of transition between habitats. We build a phylogeny with ca. 45% of the 137 species of Hygrotini, including all major lineages and almost all of the known halophile or tolerant species. We used sequence data of four mitochondrial (COI‐5′, COI‐3′, 16S + tRNA and NADH1) and three nuclear (28S, 18S and H3) gene fragments, plus ecological data to reconstruct the history of the salinity tolerance using Bayesian inference. Our results demonstrate multiple origins of the tolerance to salinity, although most saline and hypersaline species were concentrated in two lineages. The evolution of salinity was gradual, with no direct transitions from FW to hypersaline habitats, but with some reversals from tolerant to FW species. The oldest transition to saline tolerance, at the base of the clade with the highest number of saline species, was dated in the late Eocene‐early Oligocene, a period with decreasing temperature and precipitation. This temporal coincidence suggests a link between increased aridity and the development of tolerance to saline waters, in agreement with recent research in other groups of aquatic Coleoptera.     

Temperature-dependent regulation of reproduction in the diving beetle Dytiscus sharpi (Coleoptera: Dytiscidae)

The effects of temperature on the mating behavior, gonad development, germ cell maturation, and egg spawning of the predaceous diving beetle Dytiscus sharpi (Coleoptera; Dytiscidae), were investigated. By field observations, we found that mating behavior started in October and occurred more frequently from November to December. Under our laboratory breeding conditions, we observed almost the same seasonal variation in mating behavior. We found that temperatures lower than 20 degrees C were required to trigger mating behavior. We also found the same temperature threshold triggered gonadogenesis as well as spermatogenesis. Furthermore, for females, exposure to lower temperatures (<8 degrees C) during the winter was required for egg maturation and spawning in spring; that is, there was a second threshold for successful female reproduction. We conclude that the termination of summer reproductive diapause of D. sharpi is regulated in a temperature-dependent manner, thus effecting the adaptation of D. sharpi to southern warm habitats.     

Inter- and intrasexual dimorphism in the diving beetle Hydroporus memnonius Nicolai (Coleoptera: Dytiscidae)

Sexual conflict can drive rapid intersexual arms races, and lead to pronounced sexual dimorphism. Such dimorphism is frequent in diving beetles, where males typically possess expanded front and middle tarsi, supplied with adhesive setae to grasp females during mating, and females often have rough dorsal surfaces which hinder male attachment. In a number of species, females are dimorphic, being either smooth and male-like, or heavily sculptured dorsally. Smooth and sculptured females often have distinct biogeographies, and may be expected to be associated with specific counter-adaptations in males. The European diving beetle, Hydroporus memnonius Nicolai, includes a smooth male-like female, and a matt morph, var. castaneus Aubé, which are largely allopatric in distribution. We show that the two morphs differ in the density and intensity of their surface microreticulation, and that matt females are associated with morphologically distinct males, which have developed specific countermeasures on their tarsi, including a greater number of large adhesive setae, individually larger in area. Such males are expected to be more successful in pairing with both matt and shining females, and it is suggested that a process of population replacement, partly driven by sexual interactions, may occur where the two forms overlap in range.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 685–697.     

Eye and optic lobe metamorphosis in the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae)

Nearly nothing is known about the transition that visual brain regions undergo during metamorphosis, except for Drosophila in which larval eyes and the underlying neural structure are strongly reduced. We have studied the larvae of the sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae), which are sophisticated visually oriented predators characterized by six elaborate stemmata on each side of the head and an associated large optic lobe. We used general neurohistological staining and 3D reconstruction to determine how the eyes and optic lobe of T. marmoratus change morphologically during metamorphosis. We find that in third (last) instar larvae, the adult neuropils are already forming de novo dorsally and slightly anteriorly to the larval neuropils, while the latter rapidly degenerate. Larval eyes are eventually reduced to distinct areas with dark pigmentation. This complete reorganization, which may be an evolutionarily conserved trait in holometabolous insects, occurs despite the considerable costs that must apply to such a visually complex animal. Our findings are consistent with the concept that stemmata are homologous to the most posterior ommatidia of hemimetabolous insects, an idea also recently supported by molecular data.     

Evolution of the Juan Fernández diving beetle,Rhantus selkirki (Coleoptera,Dytiscidae)

Here we provide evidence that confinement in Robinson Crusoe Island (located about 660 km west of continental Chile) over evolutionary time leads to strong morphological modifications in diving beetle (Dytiscidae) larvae. We analysed a large set of morphological larval characters for all currently recognised genera of Colymbetinae as a framework, to infer phylogenetic relationships within the large genus Rhantus Dejean, 1833 and, in particular, of the charismatic Juan Fernández diving beetle, Rhantus selkirki Jäch, Balke & Michat, 2015, comparing our results with a recent phylogeny of the Colymbetinae based on DNA sequence data. We suggest that adaptation to the island's particular habitats resulted in the reversal of certain characters of R. selkirki back to the plesiomorphic states. This may cause the species to be erroneously interpreted as more ‘primitive’ if only morphological characters are analysed. Confinement in the particular, shallow and barely vegetated aquatic habitats of Robinson Crusoe Island for a long time seems to have led to this divergent morphology, particularly in characters related to swimming ability such as several leg and urogomphal setae. In this way, R. selkirki larvae secondarily resemble those of some earlier diverging dytiscid lineages such as Agabinae and Copelatinae, which typically creep on the bottom of water bodies and do not swim well.     

Predaceous diving beetle, Dytiscus sharpi sharpi (Coleoptera: Dytiscidae) larvae avoid cannibalism by recognizing prey

Larvae of diving beetles such as the various Dytiscus species (Coleoptera: Dytiscidae) are carnivorous and usually prey on other aquatic animals. Cannibalism among larvae of Dytiscus sharpi sharpi (Wehncke) was observed to begin when they were starved for more than two days under artificial breeding conditions. However, the 2-day starved larvae did not show cannibalism in the presence of intact, motionless, frozen tadpoles, or frozen shrimps. The beetle larvae attacked and captured intact tadpoles faster (15 sec) than other motionless and frozen tadpoles (120 sec), indicating that prey movement was an important factor in stimulating feeding behavior in larvae. Prey density does not have an effect on larval cannibalism. In cases in which preys are present at lower densities than that of larvae, a group of beetle larvae frequently fed on single prey. This feeding behavior, therefore, provides direct evidence of self-other recognition at the species level. Using two traps in one aquarium that allows the larvae to detect only prey smell, one containing tadpoles and another empty, the beetle larvae were attracted to the trap with tadpoles at high frequency, but not to the empty trap. In another experiment, the beetle larvae were not attracted to the trap containing a beetle larva. These results suggest that the larvae of D. sharpi sharpi are capable of recognizing prey scent, which enables the promotion of foraging behavior and the prevention of cannibalism.     

Sexual dimorphism and sexual conflict in the diving beetle Agabus uliginosus (L.) (Coleoptera: Dytiscidae)

Sexual conflict can drive intersexual arms races, with female resistance and male persistence traits coevolving antagonistically. Such arms races are well documented in some diving beetles, although the extent of sexual conflict in this family remains unclear. The European dytiscid Agabus uliginosus has a strikingly dimorphic female; individuals from most regions are smooth and male‐like, whereas those from some populations have a strongly roughened dorsum, a trait that has attracted the name dispar. We demonstrate that rough and smooth females differ consistently in the development of dorsal surface microreticulation, and that these females are associated with males that differ in the development of their persistence traits. These findings extend the occurrence of pre‐insemination sexual conflict and associated intrasexual dimorphism in Dytiscidae, and suggest that such mating systems are relatively widespread in these beetles.     

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.     

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.     

The life history of the diving beetle, Lancetes angusticollis (Curtis) (Coleoptera: Dytiscidae), on sub-Antarctic South Georgia

Two populations of the world's most southerly diving beetle (Lancetes angusticollis) were studied on sub-Antarctic South Georgia between November 1995 and April 1996. Parallel observations were made on laboratory cultures of each life stage. All juvenile stages of L. angusticollis are voracious predators, preying mainly on the herbivorous copepod Boeckella poppei. Adult beetles additionally predate benthic ostracods. Laboratory predation rates and field population densities found in this study suggest that L. angusticollis has a more significant impact on its prey than recognised in recent studies of South Georgian lakes. Spring field samples contained only a few individuals of larval instar IV and adults. Young larvae were present from December onwards, with a rapid progression through juvenile instars during the summer months. Fourth instar larvae left the water for pupation between mid-December and at least mid-February. Combining these observations with known developmental threshold temperatures for each life stage implies that L. angusticollis has a complex biennial (minimum) life-cycle, with overwintering possible in three life stages [aquatic larvae, terrestrial pupae (not proven) and aquatic adults]. L. angusticollis may be a suitable indicator species in the context of climate warming studies: a small (1°C) rise in mean environmental temperatures, comparable to that already observed at several sub-Antarctic and maritime Antarctic localities, would allow completion of an annual (univoltine) life-cycle, with concomitant rapid population increase, and serious implications for trophic interactions in these simple lake ecosystems. Received: 24 November 1997 / Accepted: 12 April 1998     

Speciation and mitochondrial DNA diversification of the diving beetles Agabus bipustulatus and A. wollastoni (Coleoptera, Dytiscidae) within Macaronesia

Diversification of populations of two morphologically similar diving beetles within the Agabus tristis group, A. wollastoni and A. bipustulatus, was investigated, with partial mtDNA cytochrome b (Cyt b) sequences, allozymes and landmark‐based morphometrics. The Madeiran endemic A. wollastoni was collected from 11 localities. Population genetic and morphological variation was compared to Scandinavian localities of the widespread west Palearctic A. bipustulatus, recorded also from the Azores. Agabus wollastoni and European A. bipustulatus specimens representing eight and 13 localities respectively, were used in evaluating their phylogenetic relationship. Maximum parsimony analysis of the Cyt b sequences showed that both the A. bipustulatus and A. wollastoni specimens form well‐supported monophyletic groups. Three lines of evidence suggest that Agabus wollastoni has speciated through a few founders: (1) a well‐supported mtDNA line; (2) the mean heterozygosity of A. wollastoni is lower when compared to A. bipustulatus on the mainland; and (3) several uncommon alleles of A. bipustulatus are missing in A. wollastoni. The Azorean A. bipustulatus population was drastically affected by the colonization event, since several loci have become fixed with a resulting lower mean heterozygosity. The colonization was relatively recent, as the mtDNA lineage represented in the Azores is deeply nested within the A. bipustulatus clade. Population structure shows moderate inbreeding of A. wollastoni, and extensive substructuring at all localities with moderate gene‐flow between them. Morphological variation in A. wollastoni showed significant differentiation among several populations. Island colonizations, population structure of A. wollastoni, and an observed pattern of variation of the α‐glycerophosphate dehydrogenase locus are discussed. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 653–666.     

Preference of oviposition plant and hatchability of the diving beetle,Dytiscus sharpi (Coleoptera: Dytiscidae) in the laboratory

For the conservation of the diving beetle, Dytiscus sharpi (Wehncke) (Coleoptera: Dytiscidae), which is included in the Red List of Japan, it is critical to understand its ecological background. In the present study, oviposition preference and hatchability were investigated under laboratory conditions. Possible candidates of oviposition plants were observed in the natural breeding habitats of D. sharpi. Eight aquatic plants were identified, and Oenanthe javanica (Blume) was the major species present in March, when first instar larvae appeared. The number of eggs laid was investigated under the following conditions: (i) eight field plants were authentically recreated at a similar covering rate to that in the natural habitat; (ii) each of the eight plants was set at the same covering rate; (iii) a single plant taken from the field was placed separately. Significant oviposition preference for O. javanica was found when these eight aquatic plants were present in the same aquaria. In addition, hatchability in O. javanica was significantly higher than that in any of the other plants. These results suggest that O. javanica is an important aquatic plant for oviposition by D. sharpi.     

Status of Japanese Dytiscus species (Coleoptera: Dytiscidae) based on mitochondrial DNA sequence data

We sequenced 628 base pairs of the mitochondrial cytochrome‐c oxidase subunit 1 (cox1) gene to investigate the genetic differentiation among Japanese Dytiscus diving beetles (Coleoptera: Dytiscidae). Dytiscus beetles are a charismatic part of the fauna of lakes, ponds and swamps. Three species are known from Japan: D. dauricus Gebler, 1832; D. marginalis czerskii Zeitzev * , 1953; and D. sharpi Wehncke, 1875. Adults of D. sharpi collected in Chiba and Ishikawa Prefectures were morphologically highly similar, but here we found that they differed by 20 cox1 base pairs (3.18%). Our results imply that conservation strategies especially for Japanese D. sharpi sharpi and D. sharpi validus Régimbart, 1899 might need to be adjusted to address the presence of two evolutionarily significant units.     

Retinal ultrastructure may mediate polarization sensitivity in larvae of the Sunburst diving beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae)

A number of invertebrates are known to be sensitive to the polarization of light and use this trait in orientation, communication, or prey detection. In these animals polarization sensitivity tends to originate in rhabdomeric photoreceptors that are more or less uniformly straight and parallel. Typically, polarization sensitivity is based on paired sets of photoreceptors with orthogonal orientation of their rhabdomeres. Sunburst diving beetle larvae are active swimmers and highly visual hunters which could potentially profit from polarization sensitivity. These larvae, like those of most Dytiscids, have a cluster of six lens eyes or stemmata (designated E1 through E6) on each side of the head capsule. We examined the ultrastructure of the photoreceptor cells of the principal eyes (E1 and E2) of first instar larvae to determine whether their rhabdomeric organization could support polarization sensitivity. A detailed electron microscopical study shows that the proximal retinas of E1 and E2 are in fact composed of photoreceptors with predominantly parallel microvilli and that neighboring rhabdomeres are oriented approximately perpendicularly to one another. A similar organization is observed in the medial retina of E1, but not in the distal retinas of E1&2. Our findings suggest that T. marmoratus larvae might be able to analyze polarized light. If so, this could be used by freshly hatched larvae to find water or within the water to break the camouflage of common prey items such as mosquito larvae. Physiological and behavioral tests are planned to determine whether larvae of T. marmoratus can actually detect and exploit polarization signals.     

Phylogeny and historical biogeography of Agabinae diving beetles (Coleoptera) inferred from mitochondrial DNA sequences

The Agabinae, with more than 350 species, is one of the most diverse lineages of diving beetles (Dytiscidae). Using the mitochondrial genes 16S rRNA and cytochrome oxidase I we present a phylogenetic analysis based on 107 species drawn mostly from the four main Holarctic genera. Two of these genera (Ilybius and Ilybiosoma) are consistently recovered as monophyletic with strong support, Platambus is never recovered as monophyletic, and Agabus is found paraphyletic with respect to several of the species groups of Platambus. Basal relationships among the main lineages are poorly defined, although within each of them relationships are in general robust and very consistent across the parameter space, and in agreement with previous morphological analyses. In each of the two most diverse lineages (Ilybius and Agabus including part of Platambus) there is a basal split between Palearctic and Nearctic clades, estimated to have occurred in the late Eocene. The Palearctic clade in turn splits into a Western Palearctic clade and a clade containing mostly Eastern Palearctic species, and assumed to be ancestrally Eastern Palearctic but with numerous transitions to a Holarctic or Nearctic distribution. These results suggest an asymmetry in the colonization routes, as there are very few cases of transcontinental range expansions originating from the Nearctic or the Western Palearctic. According to standard clock estimates, we do not find any transcontinental shift during the Pliocene, but numerous speciation events within each of the continental or subcontinental regions.