Limited dispersal in an ectoparasitic mite,Laelaps giganteus,contributes to significant phylogeographic congruence with the rodent host,Rhabdomys

To explore how biogeography, parasite life history and host vagility influences evolutionary codivergences, we followed a comparative phylogeography approach using a host‐specific nonpermanent mite, Laelaps giganteus, that occurs on four rodent species within the genus Rhabdomys. A mtDNA COI haplotype network derived for 278 parasite specimens showed marked phylogeographic congruence with host distributions. Analysis of the less variable nuclear intron Tropomyosin was in part consistent with these results. Although distance‐based cophylogenetic analyses in axparafit failed to support significant mtDNA codivergences (P ≥ 0.02), event‐based analyses revealed significant cophylogeny between sampling localities of Rhabdomys and Laelaps using core‐pa (P = 0.046) and jane (P = 0.026; P = 0.00). These findings, in conjunction with the weak congruence previously reported among the permanent ectoparasitic lice Polyplax and Rhabdomys, suggest that host–parasite intimacy is not the most important driver of significant codivergence in our study system. Instead, the more restricted dispersal ability of L. giganteus, when compared to Polyplax, resulted in stronger spatial structuring and this could have resulted in significant codivergence. Host switching occurred predominantly on the edges of host distributions and was probably facilitated by climate‐induced range shifts. When host ranges shift, the phylogeographic structure of L. giganteus is not reflecting the host movements as most of the nest bound parasites do not disperse with the host (they miss the boat) and the genetic contribution of the few dispersing mite individuals is often overwhelmed by the large number of individuals already present in nests within the new environment (causing them to drown on arrival).     

A Gene Encoding a Cytochrome c Oxidase-Like Protein Is Located Closely to the Cytochrome c-553 Gene in the Anaerobic Bacterium,Desulfovibrio vulgaris (Miyazaki F)

The gene encoding cytochrome c-553 from Desulfovibrio vulgaris (Miyazaki F) was cloned using a synthetic oligodeoxyribonucleotide probe. The nucleotide sequence indicated that cytochrome c-553 was synthesized as a precursor protein with an NH₂-terminal signal sequence of 23 residues. In the cloned DNA fragment, there are three other open reading frames whose products have 191, 157, 541 amino acid residues, respectively. The putative ORF-4 product is highly homologous with the cytochrome c oxidase subunit I from various organisms.     

Genetic diversity of two mitochondrial DNA genes in Spirometra erinaceieuropaei (Cestoda: Diphyllobothridae) from Poland

The tapeworm species Spirometra erinaceieuropaei was documented mainly in Asia and Europe. In recent years, plerocercoid larvae (spargana) of this parasite have been found in different hosts in north‐eastern Poland. The evolutionary history and way of S. erinaceieuropaei spreading across Eurasia have been not described yet. However, this phenomenon could be closely related to the evolutionary history and migration routes of studied tapeworm host species. We investigated the genetic variability and divergence pattern among S. erinaceieuropaei populations in intermediate and paratenic hosts from north‐eastern Poland based on complete mitochondrial sequences of cytochrome b (cytb) and cytochrome c oxidase subunit I (cox1) genes. Analysis of 319 consolidated sequences of these two genes showed no genetic structure across study area. Comparison of sequences from Poland and China showed distinct separation of S. erinaceieuropaei populations from these two regions. They split from their common ancestor approximately 28.6 million years ago. Demographic expansion of Polish population of S. erinaceieuropaei started from glacial refugia approximately 12.5 thousand years ago, and recent population expansion has been observed in the tapeworm population from north‐eastern Poland.     

Genetic diversity and population structure of the commercially harvested sea urchin Paracentrotus lividus (Echinodermata, Echinoidea)

The population structure of the edible Atlanto-Mediterranean sea urchin Paracentrotus lividus is described by analysing sequence variation in a fragment of the mitochondrial gene cytochrome c oxidase subunit I in 127 individuals from 12 localities across south-west Europe. The study revealed high levels of genetic diversity but low levels of genetic structure, suggesting a large degree of gene flow between populations and panmixis within each, the Mediterranean and Atlantic basins. However, we found significant genetic differentiation between the two basins probably due to restricted gene flow across the geographical boundary imposed by the area of the Strait of Gibraltar. Populations of P. lividus appeared to have experienced a recent demographic expansion in the late Pleistocene. We provide new evidence on the population structure of this commercial species, predicting a healthy stock of this sea urchin on the Mediterranean and Atlantic coasts.     

Brazilian populations of Drosophila maculifrons (Diptera: Drosophilidae): low diversity levels and signals of a population expansion after the Last Glacial Maximum

The Quaternary period was marked by considerable changes in climate. Such palaeoclimatic changes affected the population dynamics of many species, both in the Northern and in the Southern Hemisphere. However, the extent of these impacts on the demographic patterns of Neotropical species presenting different ecological requirements remains unclear. Drosophila maculifrons DUDA 1947 belongs to the guaramunu group of Drosophila and represents a potential indicator of the genetic consequences caused by the climatic fluctuations of the Quaternary, because it seems to be sensitive to temperature and humidity shifts. The aim of this study was to evaluate the evolutionary processes subjacent to the patterns of intraspecific diversity and structure of different populations of D. maculifrons. In total, 152 individuals were collected in the south and south‐east Brazil. Phylogenetic and phylogeographical analyses were performed based on sequences of COI and COII mitochondrial genes. In general, the results pointed to Brazilian populations of D. maculifrons being extremely impoverished in terms of mitochondrial diversity and population structure, which could be explained by a recent population expansion event dated to approximately 12 000 years ago. In fact, with the assistance of species palaeo‐distribution modelling strategies, it was possible to infer that most of the sampled region did not present the D. maculifrons environmental suitability requirements at least during the period of the Last Glacial Maximum. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 55–66.     

DNA barcoding of the genus Lepidion (Gadiformes: Moridae) with recognition of Lepidion eques as a junior synonym of Lepidion lepidion

DNA sequences of cytochrome c oxidase I gene (COI) from Lepidion spp. were employed to test the efficiency of species identification. A sample of 32 individuals from five Lepidion species was sequenced and combined with 26 sequences from other BOLD projects. As a result, 58 Lepidion DNA sequences of the COI gene belonging to eight of the nine recognized Lepidion species were analysed. Sequences were aligned and formed seven clades in a Bayesian phylogenetic tree, where Lepidion lepidion and Lepidion eques grouped jointly. The Kimura 2‐parameter genetic distances, among congeners were, on average, 4.28%, 16 times greater than among conspecifics (0.27%). The main diagnostic meristic data of Lepidion spp. were compiled and a detailed morphological revision of the congeneric species L. eques and L. lepidion was made. The eye diameter was significantly different between L. eques and L. lepidion (P < 0.001). The number of anal fin rays ranged from 45 to 51 in L. lepidion and from 47 to 54 in L. eques, but no significant differences were obtained in the mean values of this variable (P = 0.07). According to the morphological and genetic analyses, the results strongly suggest that the Mediterranean codling L. lepidion and the North Atlantic codling L. eques are conspecific, making L. eques a junior synonym of L. lepidion.     

Integrative taxonomy of the Clavus canalicularis species complex (Drilliidae,Conoidea, Gastropoda) with description of four new species

ABSTRACT

The conoidean family Drilliidae Olsson, 1964 is a species-rich lineage of marine gastropods, showing a high degree of diversification in comparison to other families of Conoidea. Despite intensive molecular phylogenetic studies during the last decade that have led to notable rearrangements of conoidean systematics, the genus- and species-level taxonomy of Drilliidae has not thus far been affected and remains entirely based on shell features. In the current study we revisit species delimitation in a morphological cluster of species from the Indo-Pacific referred to as the Clavus canalicularis complex, using an integrative taxonomy approach. The species in the complex possess robust thick-walled shells typically over 15?mm in height with sculpture of prominent rounded nodules located at the whorl’s shoulder, sometimes sharp and squamiform, or producing long spines. We find that in addition to five known species, the complex comprises four new species. These are described as Clavus brianmayi n. sp. (New Caledonia), Clavus davidgilmouri n. sp. (the Philippines), Clavus andreolbrichi n. sp. (Vanuatu and New Ireland) and Clavus kirkhammetti n. sp. (Madagascar). Clavus exasperatus (Reeve, 1843), which was previously considered widely distributed in Indo-Pacific, is shown to be confined to the western Indian Ocean.     

A question of time: the land snail Murella muralis (Gastropoda: Pulmonata) reveals constraints on past ecological speciation

The lively debate about speciation currently focuses on the relative importance of factors driving population differentiation. While many studies are increasingly producing results on the importance of selection, little is known about the interaction between drift and selection. Moreover, there is still little knowledge on the spatial‐temporal scales at which speciation occurs, that is, arrangement of habitat patches, abruptness of habitat transitions, climate and habitat changes interacting with selective forces. To investigate these questions, we quantified variation on a fine geographical scale analysing morphological (shell) and genetic data sets coupled with environmental data in the land snail Murella muralis, endemic to the Mediterranean island of Sicily. Analysis of a fragment of the mitochondrial DNA cytochrome oxidase I gene (COI) and eight nuclear microsatellite loci showed that genetic variation is highly structured at a very fine spatial scale by local palaeogeographical events and historical population dynamics. Molecular clock estimates, calibrated here specifically for Tyrrhenian land snails, provided a framework of palaeogeographical events responsible for the observed geographical variations and migration routes. Finally, we showed for the first time well‐documented lines of evidence of selection in the past, which explains divergence of land snail shell shapes. We suggest that time and palaeogeographical history acted as constraints in the progress along the ecological speciation continuum. Our study shows that testing for correlation among palaeogeography, morphology and genetic data on a fine geographical scale provides information fundamental for a detailed understanding of ecological speciation processes.     

The genomic bases of morphological divergence and reproductive isolation driven by ecological speciation in Senecio (Asteraceae)

Ecological speciation, driven by adaptation to contrasting environments, provides an attractive opportunity to study the formation of distinct species, and the role of selection and genomic divergence in this process. Here, we focus on a particularly clear‐cut case of ecological speciation to reveal the genomic bases of reproductive isolation and morphological differences between closely related Senecio species, whose recent divergence within the last ~200 000 years was likely driven by the uplift of Mt. Etna (Sicily). These species form a hybrid zone, yet remain morphologically and ecologically distinct, despite active gene exchange. Here, we report a high‐density genetic map of the Senecio genome and map hybrid breakdown to one large and several small quantitative trait loci (QTL). Loci under diversifying selection cluster in three 5 cM regions which are characterized by a significant increase in relative (F_ST), but not absolute (d_XY), interspecific differentiation. They also correspond to some of the regions of greatest marker density, possibly corresponding to ‘cold‐spots’ of recombination, such as centromeres or chromosomal inversions. Morphological QTL for leaf and floral traits overlap these clusters. We also detected three genomic regions with significant transmission ratio distortion (TRD), possibly indicating accumulation of intrinsic genetic incompatibilities between these recently diverged species. One of the TRD regions overlapped with a cluster of high species differentiation, and another overlaps the large QTL for hybrid breakdown, indicating that divergence of these species may have occurred due to a complex interplay of ecological divergence and accumulation of intrinsic genetic incompatibilities.     

The population genetics of host specificity: genetic differentiation in dove lice (Insecta: Phthiraptera)

Some species of parasites occur on a wide range of hosts while others are restricted to one or a few host species. The host specificity of a parasite species is determined, in part, by its ability to disperse between host species. Dispersal limitations can be studied by exploring the genetic structure of parasite populations both within a single species of host and across multiple host species. In this study we examined the genetic structure in the mitochondrial cytochrome oxidase I (COI) gene of two genera of lice (Insecta: Phthiraptera) occurring on multiple sympatric species of doves in southern North and Central America. One genus, Columbicola, is generally less host-specific than the other, Physconelloides. For both genera we identified substantial genetic differentiation between populations of conspecific lice on different host species, generally 10-20% sequence divergence. This level of divergence is in the range of that often observed between species of these two genera. We used nested clade analysis to explore fine scale genetic structure within species of these feather lice. We found that species of Physconelloides exhibited more genetic structure, both among hosts and among geographical localities, than did species of Columbicola. In many cases, single haplotypes within species of Columbicola are distributed on multiple host species. Thus, the population genetic structure of species of Physconelloides reveals evidence of geographical differentiation on top of high host species specificity. Underlying differences in dispersal biology probably explain the differences in population genetic structure that we observed between Columbicola and Physconelloides.     

Algal Parasite Herpodiscus durvillaeae (Phaeophyceae: Sphacelariales) Inferred to have Traversed the Pacific Ocean with its Buoyant Host

The parasitic phaeophycean endophyte Herpodiscus durvillaeae (Lindauer) G. R. South has previously only been recorded from New Zealand, in association with a single host species, Durvillaea antarctica (Chamisso) Hariot (southern bull‐kelp). Here we use DNA sequence data from plastid and nuclear markers (chloroplast rbcL, ribosomal LSU, and a nuclear pseudogene copy of COI) to test for the presence of H. durvillaeae beyond the New Zealand region, and on host species other than D. antarctica. Analyses of samples from the Falkland Islands confirm the first record of H. durvillaeae from the Atlantic Ocean. We report that Falkland Islands H. durvillaeae are genetically indistinguishable from samples of this species from New Zealand's sub‐Antarctic Campbell Island, suggesting recent dispersal of the parasite across the Pacific Ocean, presumably by rafting with its buoyant macroalgal host. We also here record H. durvillaeae from New Zealand endemics Durvillaea poha Fraser et al. and D. willana Lindauer.     

A genetic perspective on the taxonomy and evolution of the medically important flea,Dinopsyllus ellobius (Siphonaptera: Dinopsyllinae), and the resurrection of Dinopsyllus abaris

Dinopsyllus ellobius is considered a common and widespread flea in southern Africa and can act as a vector for plague. Due to differences in the interpretation of geographical variation in male sternite VIII, the taxonomy of the species is characterized by uncertainty. In an attempt to provide a better understanding of the systematics of D. ellobius, and also to provide new insights into the mechanisms that play a role in the diversification of the taxon, we sampled 830 small mammals at 31 localities throughout the distribution range of the parasite. Mitochondrial cytochrome c oxidase subunit II (COII) sequence data were generated for 151 D. ellobius specimens from 19 positive localities and this data set was supplemented with partial data derived from an elongation factor 1 alpha (EF1‐α) intron. A parsimony haplotype network of the mtDNA and a Splitstree analyses revealed the existence of two genetic clades that were separated by 5.53% (± 1.78) sequence divergence. Although the nuclear DNA data were unresolved, significant size differences were detected between head, coxa, femur and tibia lengths of male individuals belonging to the two mtDNA lineages. The exact mechanisms that could have caused the diversification among lineages are not clear but the two lineages seem to be geographically separated and may have different ecological requirements. The present study strongly supports the notion that the two lineages are representative of D. ellobius (probably more associated with the host body and better adapted to mesic conditions) and Dinopsyllus abaris (probably more associated with the host nest and diverse climatic conditions) as originally proposed based on the single morphological character confined to male sternite VIII.     

Dasya adela sp. nov. (Rhodophyta,Ceramiales), an enigmatic new Dasya from a landlocked fjord in southwest Norway

We here report a new Dasya species found in a landlocked fjord or poll in southwestern Norway; Dasya adela sp. nov. The thallus of this species is small (1–3 cm), normally sparsely branched, and its axes are completely covered with cortex cells. The species is set with long (3–4 mm) and flaccid monosiphonous pseudolaterals, and during autumn it showed high growth of adventitious monosiphonous branches. Only a few individuals with tetrasporangia have been recorded, and no sexual reproductive structures have been observed in field collections. In culture stichidia readily developed on the pseudolaterals, with four tetrasporangia per section. The spores showed high mortality. A few sporelings survived in culture, and developed into small and loosely organized filaments with no upright axes. After 2 years in culture a few plants bearing spermatangial branches were observed, but no individuals with carpogonia. The monosiphonous branches are readily shed in culture, attach themselves by rhizoids and rapidly develop into new thalli, some of which have produced tetrasporangial stichidia. Sequences analyses of partial COI and the rbc L gene showed that the new taxon belongs within Dasyoideae. However, no close relationship was found with other European species of Dasya. The new taxon was compared to other Dasya taxa with which it shared a number of selected characters, but none of these taxa shared all characters of the new Dasya.     

Hagfish phylogeny and taxonomy,with description of the new genus Rubicundus (Craniata,Myxinidae)

A recent phylogenetic analysis of the Myxinidae based on the 16S rRNA gene resulted in synonymization of Paramyxine with Eptatretus. This created homonymy of Paramyxine fernholmi with Eptatretus fernholmi and Paramyxine wisneri with Eptatretus wisneri. In order to resolve this nomenclatural dilemma, we made a more extensive phylogenetic assessment of the Myxinidae and examined the nomenclature of the family. We used 75 sequences (37 of which new for this study) of a 561 bp fragment of the 16S rRNA gene, representing 33 species, and 72 sequences (37 of which new for this study) of a 687 bp fragment of the cytochrome c oxidase subunit I (COI) gene, representing 23 species, to reconstruct the phylogeny of Myxinidae. The monophyly of the subfamily Myxininae, traditionally characterized by having a single pair of external gill openings, was rejected (0.50 Bayesian posterior probability) by the 16S analysis, but supported by the COI and combined COI+16S analyses (0.99 and 0.81 Bpp, respectively). The monophyly of the subfamily Eptatretinae, characterized by having several pairs of external gill openings, was not supported by the 16S analysis and rejected by the COI and combined COI+16S analysis due to the placement of Eptatretus lopheliae as the earliest branch of Myxinidae (0.71 and 0.57 Bpp, respectively). Eptatretus lopheliae and Eptatretus rubicundus formed a monophyletic group and were allocated to a new genus, Rubicundus, characterized by the presence of an elongated tubular nostril and reddish coloration. A new monotypic subfamily, Rubicundinae, was proposed for Rubicundus. The synonymy of the genera Paramyxine and Quadratus with Eptatretus was confirmed. E. fernholmi is renamed Eptatretus luzonicus. Eptatretus wisneri was renamed Eptatretus bobwisneri. Petromyzon cirrhatus Forster, 1801, Homea banksii Fleming, 1822, and Bdellostoma forsteri Müller, 1836 are synonyms, but no type specimens are known to exist. Petromyzon cirrhatus was designated as type species of Eptatretus, conserving present usage. Gastrobranchus dombeyi Shaw, 1804 has priority over other names for Chilean myxinids. Bdellostoma stoutii was designated as type species of Polistotrema Gill. The validity of the Western Atlantic Myxine limosa as distinct from the Eastern Atlantic Myxine glutinosa was confirmed.     

Incongruence of morphology and genetic markers in Hyles tithymali (Lepidoptera: Sphingidae) from the Canary Islands

Hyles t. tithymali on the Canary Islands has been observed to occur in two larval morphotypes, connected by intermediate forms along a geographical cline from east to west. In this study, it was tested whether this distribution of phenotypes reflects a genealogical division of the population. mtDNA sequence data (COI + II, tRNA-leu) and genomic fingerprints from intersimple sequence repeat (ISSR)-PCR data were used. The sequence data had low variation (max. 0.4%), and phylogenetic analyses did not reveal groups that correlated with the morphotype. The samples did not group according to their island of origin and the most common haplotype was shared among all islands. Although nine haplotypes occurred only on the westernmost islands, the data showed little phylogeographical structure. The population of H. t. tithymali appears to reflect a comparatively rapid and recent colonization event of the Canary Islands. The ISSR-PCR data were very variable and did not reveal patterns corresponding to morphological variation or geographical distribution. Although the two morphs observed may represent the first stage of differentiation between two lineages, the recent origin of H. t. tithymali provided insufficient time for complete lineage sorting of ancestral polymorphism. Hence, the population of Hyles t. tithymali on the Canary Islands appears genetically more homogeneous than that was expected from the phenotypic distribution of the two morphotypes in the population.     

Molecular phylogeny of the superfamily Tephritoidea (Insecta: Diptera) reanalysed based on expanded taxon sampling and sequence data

Phylogenenetic relationships of the superfamily Tephritoidea (Diptera: Tephritidae) were reanalysed based upon four mitochondrial gene fragments (12S, 16S, cytochrome c oxidase I and cytochrome c oxidase II) from 53 tephritoid (10 families) and 30 outgroup (14 families) species. The data set of Han and Ro (Mol Phylogenet Evol, 39, 2005, 416) was expanded in terms of the number of taxa as well as molecular characters. We were able to sample the enigmatic families Ctenostylidae and Eurygnathomyiidae for the first time. Based on increased taxon sampling (from 49 to 83 species) and additional sequences (combined length of DNA fragments increased from 2451 to 4490 bp), the inferred phylogenetic trees suggest a number of interesting phylogenetic relationships, some of which were not recovered from the previous study. Some of the important findings are as follows: (1) monophyly of the superfamily Tephritoidea; (2) all the included tephritoid families except for Tephritidae were recovered as monophyletic groups; (3) Tephritoidea can be divided into two monophyletic groups – the Piophilidae Family Group (Pallopteridae, Circumphallidae?, Lonchaeidae, Piophilidae and Eurygnathomyiidae) and the Tephritidae Family Group (Richardiidae, Ulidiidae, Platystomatidae, Tephritidae, Ctenostylidae and Pyrgotidae); (4) Eurygnathomyiidae is recognized as an independent monophyletic family apart from Pallopteridae; (5) the enigmatic family Ctenostylidae is a member of the superfamily Tephritoidea; (6) parasitic Pyrgotidae + Ctenostylidae + Tachiniscinae and mostly phytophagous Tephritidae are recovered within a monophyletic group; and (7) according to an inferred chronogram, the first Tephritoidea might have evolved around the middle of Paleocene Epoch [~59 Million years ago (mya)] and the family Tephritidae around the late Eocene (~36 mya).     

DNA‐based phylogeny of the marine genus Heterodrilus (Annelida,Clitellata, Naididae)

Heterodrilus is a group of marine Naididae, common worldwide in subtropical and tropical areas, and unique among the oligochaetes by their tridentate chaetae. The phylogenetic relationships within the group are assessed from the nuclear 18S rDNA gene, and the mitochondrial cytochrome c oxidase subunit I (COI) and 16S rDNA genes. Sequence data were obtained from 16 Heterodrilus species and 13 out‐group taxa; 48 sequences are new for this study. The data were analysed by Bayesian inference. Monophyly of the genus is corroborated by the resulting tree, with Heterodrilus ersei (a taxon representing a small group of species with aberrant male genitalia) proposed to be outside all other sampled species. Although earlier regarded as a member of the subfamily Rhyacodrilinae, both molecular and morphological data seem to support that Heterodrilus is closely related to Phallodrilinae. However, the results are not conclusive as to whether the genus is the sister group of, or a group nested inside, or separate from this latter subfamily. The studied sample of species suggests at least two major clades in Heterodrilus with different geographical distributions, in one of the clades, most species are from the Indo‐West Pacific Ocean, while in the other, the majority are from the Western Atlantic Ocean. Morphological characters traditionally used in Heterodrilus taxonomy are optimized on the phylogenetic tree, revealing a high degree of homoplasy.     

Comparison of three organelle markers for phylogeographic inference in Batrachospermum helminthosum (Batrachospermales, Rhodophyta) from North America

Phylogeographic signal provided by the newly developed 23S plastid rRNA marker (universal plastid amplicon, UPA) and the cytochrome oxidase subunit I gene marker (COI) in the freshwater red alga Batrachospermum helminthosum, throughout its range in North America, was investigated. These markers were compared in individuals from a previous study using the cytochrome oxidase 2–3 spacer region ( cox 2–3), which has yielded the most useful data to date with 13 haplotypes among geographic locations. Five haplotypes were resolved for the UPA, differing by only one to two base pairs (bp), and we conclude that this marker may be more appropriate for studying interspecific variation. In contrast, the COI gene revealed 16 haplotypes, differing from one to 44 base pairs or up to 6.6% sequence variation. The intraspecific variation of COI in this taxon is much greater than that reported thus far for marine red algae (generally <5 bp). The intraspecific variation within B. helminthosum is in accord with levels shown in Batrachospermum macrosporum (48 bp within distant locations in Brazil). The COI gene is comparable to the cox 2–3 spacer for phylogeographic studies as the haplotype networks were similar and showed the same geographic patterns. To our knowledge, this is the first comparison of these three regions for phylogeographic research in the red algae.     

Multilocus analysis of nucleotide variation and speciation in three closely related Populus (Salicaceae) species

Historical tectonism and climate oscillations can isolate and contract the geographical distributions of many plant species, and they are even known to trigger species divergence and ultimately speciation. Here, we estimated the nucleotide variation and speciation in three closely related Populus species, Populus tremuloides, P. tremula and P. davidiana, distributed in North America and Eurasia. We analysed the sequence variation in six single‐copy nuclear loci and three chloroplast (cpDNA) fragments in 497 individuals sampled from 33 populations of these three species across their geographic distributions. These three Populus species harboured relatively high levels of nucleotide diversity and showed high levels of nucleotide differentiation. Phylogenetic analysis revealed that P. tremuloides diverged earlier than the other two species. The cpDNA haplotype network result clearly illustrated the dispersal route from North America to eastern Asia and then into Europe. Molecular dating results confirmed that the divergence of these three species coincided with the sundering of the Bering land bridge in the late Miocene and a rapid uplift of the Qinghai‐Tibetan Plateau around the Miocene/Pliocene boundary. Vicariance‐driven successful allopatric speciation resulting from historical tectonism and climate oscillations most likely played roles in the formation of the disjunct distributions and divergence of these three Populus species.     

Diversification of the climatic niche drove the recent processes of speciation in Sigmodontinae (Rodentia,Cricetidae)

Evolutionary radiations are among the most intriguing natural phenomena. Sigmodontine rodents form a megadiverse group for which doubts exist about the adaptive or non‐adaptive nature of its radiation. We analysed whether or not the rates of diversification of species of Sigmodontinae are related to the rates of diversification of the climatic niches occupied by the species. Our results show a clear association between niche diversification and speciation processes. However, this association is linked to recent and independent processes of diversification in sigmodontines, as opposed to an early link that would indicate a niche‐filling consistent with an adaptive radiation of the subfamily.