Molecular prospecting for cryptic species in Phyllodistomum lacustri (Platyhelminthes,Gorgoderidae)

Rosas‐Valdez, R., Choudhury, A. & Pérez‐Ponce de León, G. (2011). Molecular prospecting for cryptic species in Phyllodistomum lacustri (Platyhelminthes, Gorgoderidae). —Zoologica Scripta, 40, 296–305. Partial sequences of the 28S ribosomal RNA and cytochrome c oxidase I (COI) genes were compared among populations of a widely distributed and morphologically uniform digenean species in North America, Phyllodistomum lacustri, a parasite characteristically associated with ictalurid catfishes. Specimens were collected from the urinary bladder of ictalurid hosts in six localities of North America, spanning most of the latitudinal range of this freshwater fish group. Sequences of other congeneric species, including a potentially close relative, P. staffordi, were also obtained and used for comparison. Analyses of both molecular markers show very low or no intrapopulation variation within each sampling site. However, samples of P. lacustri from different hosts and regions exhibit varying levels of interpopulation genetic differences. Such differences are explained by the wide geographical distribution and host range of the ictalurids they parasitize, particularly in ictalurids distributed in Mexican freshwaters where they experienced a diversification process. Variation in both nuclear and mitochondrial genes and phylogenetic analyses, in conjunction with geographical and host information (drainage isolation and endemicity of the host species), indicate that at least three populations show potential as cryptic species.     

From Africa via Europe to South America: migrational route of a species‐rich genus of Neotropical lowland rain forest trees (Guatteria,Annonaceae)

Aim Several recent studies have suggested that a substantial portion of today’s plant diversity in the Neotropics has resulted from the dispersal of taxa into that region rather than by vicariance. In general, three routes have been documented for the dispersal of taxa onto the South American continent: (1) via the North Atlantic Land Bridge, (2) via the Bering Land Bridge, or (3) from Africa directly onto the continent. Here a species‐rich genus of Neotropical lowland rain forest trees (Guatteria, Annonaceae) is used as a model to investigate these three hypotheses. Location The Neotropics. Methods The phylogenetic relationships within the long‐branch clade of Annonaceae were reconstructed (using maximum parsimony, maximum likelihood and Bayesian inference) in order to gain insight in the phylogenetic position of Guatteria. Furthermore, Bayesian molecular dating and Bayesian dispersal–vicariance (Bayes‐DIVA) analyses were undertaken. Results Most of the relationships within the long‐branch clade of Annonaceae were reconstructed and had high support. However, the relationship between the Duguetia clade, the Xylopia–Artabotrys clade and Guatteria remained unclear. The stem node age estimate of Guatteria ranged between 49.2 and 51.3 Ma, whereas the crown node age estimate ranged between 11.4 and 17.8 Ma. For the ancestral area of Guatteria and its sister group, the area North America–Africa was reconstructed in 99% of 10,000 DIVA analyses, while South America–North America was found just 1% of the time. Main conclusions The estimated stem to crown node ages of Guatteria in combination with the Bayes‐DIVA analyses imply a scenario congruent with an African origin followed by dispersal across the North Atlantic Land Bridge in the early to middle Eocene and further dispersal into North and Central America (and ultimately South America) in the Miocene. The phylogenetically and morphologically isolated position of the genus is probably due to extinction of the North American and European stem lineages in the Tertiary.     

Biogeographical and geological evidence for a smaller, completely-enclosed Pacific Basin in the Late Cretaceous

Aim To use biogeographical, palaeomagnetic, palaeosedimentary, and plate circuit data from Late Cretaceous regions in and around the Pacific to test the plate tectonic hypothesis of a pre‐Pacific superocean. Location East Asia, Australia, Antarctica, the western Americas, and the Pacific. Methods Literature surveys of the distributions of Cretaceous, circum‐Pacific taxa were compared with palaeomagnetic and palaeosedimentary data. Uncontroversial plate motions based on seafloor spreading data were also used to test the results of the biogeographical and palaeomagnetic analyses. Results The distributions of Cretaceous terrestrial taxa, mostly dinosaurs, imply direct, continental connections between Australia and East Asia, East Asia and North America, North America and South America, South America and Antarctica, and Antarctica and Australia. Palaeomagnetic, palaeosedimentary, and basic plate circuit analyses require little to no latitudinal motion of the Pacific plate with respect to the surrounding continents. Specifically, the data implies that western North America, East Asia, and the Pacific plate all increased in latitude by roughly the same amount (c. 11 ± 5°) since the Campanian – and that the Pacific Ocean Basin has increased in length north‐to‐south. Main conclusions Each of the analyses provides independent corroboration for the same conclusion: the Late Cretaceous Pacific plate was completely enclosed by the surrounding continents and has not experienced significant latitudinal motion with respect to North America, East Asia, or the Bering land bridge. This contrasts significantly with the plate tectonic history of the Pacific, implying instead that the Pacific plate formed in situ, pushing the continents apart as the plate and basin expanded. These results also substantiate recent biogeographical analyses that have concluded that a narrower Pacific Ocean Basin in the Mesozoic and early Tertiary provides the most reasonable explanation for the great number of trans‐Pacific disjunctions of poor dispersing taxa.     

Phylogeographic analyses reveal distinct lineages of the liverworts Metzgeria furcata (L.) Dumort. and Metzgeria conjugata Lindb. (Metzgeriaceae) in Europe and North America

Seed plant genera often exhibit intercontinental disjunctions where different species are found on different continents. Many morphologically circumscribed bryophyte species exhibit similar disjunctions. We used nucleotide sequences from the plastid and nuclear genomes to test hypotheses of phylogeography within representatives of the genus Metzgeria: Metzgeria furcata, Metzgeria conjugata, and Metzgeria myriopoda. The first two species have sexual and asexual populations, exhibit disjunctions between North America and Europe, and have been split into separate species, numerous subspecies or varieties. The third species occurs in eastern North America but is not reported from Europe. Phylogenetic analyses resolved three distinct lineages within the morphologically defined species, M. furcata: one in North America, and two in Europe. Similarly, three morphologically cryptic clades of M. conjugata were resolved by the molecular data: northern North America, Europe, and south‐eastern North America. For both species, molecular divergence among taxa occurred in the absence of morphological change. In the case of M. myriopoda, all plants from eastern North America were both morphologically uniform and genetically homogeneous (although not identical). The present study provides significant insight into a plant group with complex taxonomy, and indicates that these liverwort taxa with wide distributions, extreme sex ratios, and continental disjunctions harbor cryptic lineages. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 745–756.     

Phylogenetic analysis of the minute brown scavenger beetles (Coleoptera: Latridiidae), and recognition of a new beetle family,Akalyptoischiidae fam.n. (Coleoptera: Cucujoidea)

We infer the first phylogenetic hypothesis for Latridiidae Erichson (Coleoptera: Cucujoidea). Portions of seven genes (18S ribosomal DNA, 28S ribosomal DNA, 12S ribosomal DNA, 16S ribosomal DNA, cytochrome c oxidase I and II and histone III) were analysed. Twenty‐seven latridiid species were included, representing both subfamilies and more than half of the currently recognized genera. Eight outgroup taxa from other families of Cucujoidea were included. Parsimony and partitioned Bayesian analyses were performed on the combined dataset. In both phylogenetic analyses, the enigmatic Akalyptoischion Andrews (Latridiinae) was recovered outside of Latridiidae. The subfamilies Corticariinae and Latridiinae (without Akalyptoischion) were each recovered as monophyletic in both analyses. A new family, Akalyptoischiidae fam.n. is erected based on the results of the phylogenetic study and further support from adult morphology, key features of which are illustrated.     

Historical biogeography of the arid‐adapted velvet ant Sphaeropthalma arota (Hymenoptera: Mutillidae) reveals cryptic species

Aim To investigate the phylogeographic patterns among populations of the wide‐ranging velvet ant Sphaeropthalma arota to (1) examine the biogeographic patterns within this species, and (2) associate major genetic divergences to historical vicariance events in order to gain insight into the processes that drove diversification in arid‐adapted organisms. Location Western North America. Methods Phylogenetic relationships were determined by analysing the two ribosomal DNA internal transcribed spacers (ITS1 and ITS2) in Mr Bayes . Divergence dates were estimated for major nodes using two different molecular dating analyses: a penalized likelihood approach to rate smoothing using the program r8s , and a Bayesian MCMC averaging approach to rate smoothing using the program beast . Both analyses were calibrated using fossils from Dominican amber. Haplotype networks were estimated using tcs . Ecological niche models (ENMs) were developed using six bioclimatic variables from the WorldClim data set in the program Maxent . Results The phylogenetic reconstructions indicate that S. arota can be split into four deeply divergent lineages that probably represent distinct species. No morphological characters were found that can be used to identify these four species, making the S. arota species complex the first documented cryptic species complex in the family Mutillidae. Ecological niche models provide estimated distributions, which indicate that each of the four species inhabits a distinct niche. Divergence date estimates suggest that major diversification events occurred in the late Neogene. Main conclusions Sphaeropthalma arota is composed of four genetically distinct species that cannot be distinguished morphologically based on current methods. We suggest that the members of this group be identified as the S. arota species complex. Major diversification events in this species complex can be linked to late Neogene mountain building and aridification events, specifically the uplift of the mountain ranges in southern California and the expansion of the Bouse Sea.     

ORIGIN AND BIOGEOGRAPHY OF AESCULUS L. (HIPPOCASTANACEAE): A MOLECULAR PHYLOGENETIC PERSPECTIVE

Sequences of chloroplast gene matK and internal transcribed spacers of nuclear ribosomal RNA genes were used for phylogenetic analyses of Aesculus, a genus currently distributed in eastern Asia, eastern and western North America, and southeastern Europe. Phylogenetic relationships inferred from these molecular data are highly correlated with the geographic distributions of species. The identified lineages closely correspond to the five sections previously recognized on the basis of morphology. Ancestral character-state reconstruction, a molecular clock, and fossil evidence were used to infer the origin and biogeographic history of the genus within a phylogenetic framework. Based on the molecular phylogenetic reconstruction of the genus, sequence divergence, and paleontological evidence, we infer that the genus originated during the transition from the Cretaceous to the Tertiary (~65 M.Y.B.P.) at a high latitude in eastern Asia and spread into North America and Europe as an element of the “boreotropical flora”; the current disjunct distribution of the genus resulted from geological and climatic changes during the Tertiary.     

Phylogeny,divergence times and biogeography of window flies (Scenopinidae) and the therevoid clade (Diptera: Asiloidea)

The evolution of the ‘therevoid’ clade, with an emphasis on window flies (Scenopinidae), is presented by combining DNA sequence data with morphological characters for living and fossil species. The therevoid clade represents a group of four families (Apsilocephalidae, Evocoidae, Scenopinidae and Therevidae) of lower brachyceran Diptera in the superfamily Asiloidea. A comprehensive phylogenetic analysis using parsimony and likelihood methods was undertaken using extensive taxon sampling from all families and subfamilies, and compared with outgroup taxa sampled from the related families Asilidae, Mydidae, Apioceridae and Empididae. Fifty‐nine morphological characters (adult, larval and pupal) were combined with 6.4 kb of DNA sequences for two ribosomal genes (16S and 18S ribosomal DNA) and three protein‐encoding genes [cytochrome oxidase I (COI), triose phosphate isomerase (TPI) and the CPSase region of carbamoyl‐phosphate synthase‐aspartate transcarbamoylase‐dihydroorotase (CAD)]. Results from combined analyses of morphological and molecular data for 78 taxa representing all families of the therevoid clade are presented. Specific hypotheses of the relationship between respective families and subfamilies were tested statistically using four‐cluster likelihood mapping. The therevoid clade is a well‐supported monophyletic group within Asiloidea, with Evocoidae sister to Apsilocephalidae and Therevidae sister to Scenopinidae. Temporal and zoogeographical aspects of therevoid clade evolution were investigated using Bayesian divergence time estimates and Lagrange ancestral range scenarios. The effect of inclusion of fossils as terminal taxa on phylogenetic and divergence time estimation was investigated, with morphological scoring for fossil representatives included in the analyses rather than used simply as minimum age constraints. In each analysis there was either improvement in estimation, or only marginal and localized loss in tree resolution, and with younger estimates of divergence time across the tree. The historical biogeography of the therevoid clade was examined with multiple trans‐Antarctic vicariance events between Australasia and South America evident during the Late Cretaceous to early Palaeogene. Scenopininae is newly subdivided into two tribes, Metatrichini trib.n. and Scenopinini Fallén stat.r. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:4974EBF8‐3117‐4189‐B6DE‐7D5BF9B23E53 .     

Observations on bipolar disjunctions of moonwort ferns (Botrychium,Ophioglossaceae)

Peter Raven, in 1963, included two fern taxa of the genus Botrychium in his list of plant species exhibiting American amphitropical bipolar disjunctions. He attributed the southern hemisphere occurrences to post‐Pleistocene long‐distance dispersal from counterparts in the northern hemisphere, probably assisted by annual bird migrations between the disjunct areas. Using genetic evidence gathered through worldwide analyses of phylogenetic relationship in Botrychium, we now review and reconsider Raven's conclusions. Genetic similarities indicate that South American Botrychium dusenii is an allotetraploid taxon closely related to B. spathulatum, a North American endemic, and that B. lunaria in New Zealand possesses a genotype identical to that of a taxon in North America derived through introgressive hybridization between B. lunaria and an endemic North American species, B. neolunaria. Both North American counterparts exhibit Raven's characteristics of bipolar disjuncts in their occurrence in mountain and coastal meadows, copious production of small propagules (spores in Botrychium), occurrence in habitats frequented by transpolar bird migrants, and ability to found new colonies through inbreeding. We discuss these characteristics in Botrychium and relative to other ferns and suggest further studies on Botrychium and related taxa to address questions of time, number, and mode of bipolar dispersals.     

Molecular Phylogeny of Mobilid and Sessilid Ciliates Symbiotic in Eastern Pacific Limpets (Mollusca: Patellogastropoda)

The phylogenetic relationships of the ciliate subclass Peritrichia, composed of the orders Mobilida and Sessilida, have recently come under debate as morphological and molecular analyses have struck contrasting conclusions as to the monophyly of the group. We provide additional molecular data to assess the monophyly of the Peritrichia by sequencing the small subunit ribosomal RNA genes of two symbiotic peritrichs, Urceolaria korschelti and Scyphidia ubiquita, found inhabiting the mantle cavity of limpets. Although phylogenetic analyses indicated a nonmonophyletic Peritrichia, approximately unbiased tests revealed that the monophyletic hypothesis could not be rejected. With regard to the Mobilida, our analysis showed divergence within the family Trichodinidae related to host taxa—a molluscan clade and a fish clade. For the Sessilida, the family Scyphidiidae was sister to the Astylozoidae. In our sampling of U. korschelti and S. ubiquita, both species showed significant genetic divergence among geographically isolated, yet morphologically indistinguishable populations. We hypothesize that cryptic speciation has produced these morphologically identical species and argue that more extensive genomic analyses are required to fully assess the monophyly, biogeography, and ultimately biodiversity of the peritrichs.     

Systematics and macroevolution of extant and fossil scalopine moles (Mammalia,Talpidae)

Scalopini is one of the two fully fossorial mole tribes in the family Talpidae, with remarkable adaptations to subterranean lifestyles. Most living Scalopini species are distributed in North America while a sole species occurs in China. On the other hand, scalopine fossils are found in both Eurasia and North America from upper Oligocene strata onwards, implying a complex biogeographical history. The systematic relationships of both extant and fossil Scalopini across North America and Eurasia are revised by conducting phylogenetic analyses using a comprehensive morphological character matrix together with 2D geometric–morphometric analyses of the humeral shape, with a specific emphasis on Mioscalops, a genus commonly found in North America and formerly known as Scalopoides. Our phylogenetic analyses support the monophyly of the tribe Scalopini as well as a proposed two‐subtribe‐division scenario of Scalopini (i.e. Scalopina and Parascalopina), although Proscapanus could not be assigned to either subgenus. Our geometric–morphometric analyses indicate that the European Mioscalops from southern Germany should be allocated to Leptoscaptor, which in turn implies that Mioscalops may be endemic to North America and never arrived in Europe. Examination of biogeographical patterns does not unambiguously determine the geographical origin of Scalopini. Nevertheless, it does support multiple transcontinental colonization events across Asia, Europe and North America. Scapanulus oweni, distributed in central China, is the only remaining representative of one of those out‐of‐North‐America migrations, whereas scalopine moles are common in North America nowadays with up to five species.     

Revisiting the Great American Biotic Interchange through analyses of amphitropical bees

The Great American Biotic Interchange (GABI) is zoogeographic event characterized by the exchange of taxa between North and South America, typically associated with the rise of the Isthmus of Panama in the late Pliocene. Recent geologic evidence suggests the connections between North and South America may be much older, and that the interchange of organisms between the two continents could have therefore happened much earlier than 3 Ma. Most of the research investigating the GABI has come from tropical vertebrate taxa; little work has been done on invertebrates or on non‐tropical species. To investigate how the GABI shaped the distribution of arid‐adapted species, particularly those with amphitropical distributions (i.e. taxa found in South and North American xeric regions yet absent from the tropics), we examine the historical biogeography of the bee genus Diadasia using a hypothesis of Diadasia phylogenetic relationships. Nuclear and mitochondrial genetic loci are used to reconstruct a phylogeny of Diadasia, which is then used to estimate divergence dates and reconstruct ancestral area relationships. Our analyses suggest the divergence between North and South American Diadasia species occurred between 20.5 and 15 Ma, long before the formation of the Isthmus of Panama. This study is the first to show a Miocene connection for an amphitropically‐distributed insect group. It suggests that the biotic connection between continents is more complicated than previously thought and may have initiated long before the late Pliocene.     

Phylogeny and biogeography of the dung beetle genus Phanaeus (Coleoptera: Scarabaeidae)

Abstract The dung beetle genus Phanaeus as currently recognized by Edmonds (1994) consists of 51 species placed in 13 species groups and two subgenera. Here, I examine the phylogeny and biogeography of this genus by analysing the mitochondrial cytochrome oxidase subunit I (530 bp), nuclear large subunit ribosomal RNA (28S, D2 region), and 67 morphological characters for 28 species of Phanaeus. Both maximum parsimony and Bayesian analyses from the combined data yielded well‐resolved trees, although low bootstrap and posterior probability support were found for basal nodes. The phylogenetic hypotheses presented here suggest that the subgenera Phanaeus s.str. and Notiophanaeus should each be elevated to the status of full genus. With the exception of the eucraniine outgroups, the paleano species group of the genus Phanaeus is recovered as sister to all other taxa, including the outgroups Oxysternon, Sulcophanaeus and Coprophanaeus. High bootstrap values and posterior probabilities supported the species groups endymion, tridens and vindex. Biogeographical analyses suggest an ancestral distribution for Phanaeus in the Andes in South America, although numerous dispersal events evidently have produced a complicated biogeographical history.     

Phylogeny of the genus Hesperodiaptomus (Copepoda) based on nucleotide sequence data of the nuclear ribosomal gene

The genus Hesperodiaptomus Light, 1938, one of the most diverse groups of freshwater copepods that occur in North and Central America, plays a major role in the food webs of the alpine freshwater communities. Phylogenetic relationships of these taxa remain poorly understood due to difficulties in obtaining reliable morphological characters for phylogenetic analyses. To understand the phylogenetic relationships within this group, we reconstructed a partial phylogeny of the genus Hesperodiaptomus based on nuclear ribosomal gene sequences. Phylogenetic analyses based upon the taxa examined supported the monophyly the genus and revealed two clades. The eiseni clade comprised species that are morphologically similar to Hesperodiaptomus eiseni (Lilljeborg, 1889), and the shoshone clade included species morphologically similar to Hesperodiaptomus shoshone (S.A. Forbes, 1882). The two groups can be distinguished by a modification of the right basis, the arrangement of spinules on the distal pad of the second exopod, and the degree of presence the inner lamellar expansion of the right coxa. Handling editor: P. Spaak     

Phylogeny of North American amblemines (Bivalvia, Unionoida): prodigious polyphyly proves pervasive across genera

Abstract. The subfamily Ambleminae is the most diverse subfamily of fresh‐water mussels (order Unionoida), a globally diverse and ecologically prominent group of bivalves. About 250 amblemine species occur in North America; however, this diversity is highly imperiled, with the majority of species at risk. Assessing and protecting this diversity has been hampered by the uncertain systematics of this group. This study sought to provide an improved phylogenetic framework for the Ambleminae. Currently, 37 North American genera are recognized in Ambleminae. Previous phylogenetic studies of amblemines highlighted the need for more extensive sampling due to the uncertainties arising from polyphyly of many currently recognized taxa. The present study incorporated all amblemine genera occurring in North America north of the Rio Grande, with multiple species of most genera, including the type species for all but seven genera. A total of 192 new DNA sequences were obtained for three mitochondrial gene regions: COI, 16S, and ND1. In combination with published data, this produced a data matrix incorporating 357 gene sequences for 143 operational taxonomic units, representing 107 currently recognized species. Inclusion of published data provides additional taxa and a summary of present molecular evidence on amblemine phylogeny, if at the cost of increasing the amount of missing data. Parsimony and Bayesian analyses suggest that most amblemine genera, as currently defined, are polyphyletic. At higher taxonomic levels, the tribes Quadrulini, Lampsilini, and Pleurobemini were supported; the extent of Amblemini and the relationships of some genera previously assigned to that tribe remain unclear. The eastern North American amblemines appear monophyletic. Gonidea and some Eurasian taxa place as probable sister taxa for the eastern North American Ambleminae. The results also highlight problematic taxa of particular interest for further work.     

A phylogenetic assessment of the colonisation patterns in <Emphasis Type="Italic">Spauligodon atlanticus</Emphasis> Astasio-Arbiza et al., 1987 (Nematoda: Oxyurida: Pharyngodonidae), a parasite of lizards of the genus <Emphasis Type="Italic">Gallotia</Emphasis> Boulenger: no simple answers

Parasite taxonomy traditionally relies on morphometric and life-cycle characteristics which may not reflect complex phylogenetic relationships. However, genetic analyses can reveal cryptic species within morphologically described parasite taxa. We analysed the phylogenetic variation within the nematode Spauligodon atlanticus Astasio-Arbiza, Zapatero-Ramos, Ojeda-Rosas & Solera-Puertas, 1987, a parasite of the Canarian lizard genus Gallotia Boulenger, inferring the origin of their current association. We also attempted to determine its relationship with other Spauligodon spp. Three different markers, mitochondrial COI plus nuclear 18S and 28S ribosomal RNA, were used to estimate the evolutionary relationships between these nematodes. S. atlanticus was found to be paraphyletic, suggesting that Gallotia spp. were colonised by two independent lineages of Spauligodon. Additional analyses of other Spauligodon spp. are required for a more complete interpretation of the evolution of this genus from the Canarian archipelago and its closest taxa. Our results emphasise the importance of extensive sampling and phylogenetic studies at the intrageneric level, and highlight the limitations of a morphologically based taxonomy in these parasites.     

Scale‐dependent post‐establishment spread and genetic diversity in an invading mollusc in South America

Aims Our study aimed to characterize the dispersal dynamics and population genetic structure of the introduced golden mussel Limnoperna fortunei throughout its invaded range in South America and to determine how different dispersal methods, that is, human‐mediated dispersal and downstream natural dispersal, contribute to genetic variation among populations. Location Paraná–Uruguay–Río de la Plata watershed in Argentina, Brazil, Paraguay and Uruguay. Methods We performed genetic analyses based on a comprehensive sampling strategy encompassing 22 populations (N = 712) throughout the invaded range in South America, using the mitochondrial cytochrome c oxidase subunit I (COI) gene and eight polymorphic nuclear microsatellites. We employed both population genetics and phylogenetic analyses to clarify the dispersal dynamics and population genetic structure. Results We detected relatively high genetic differentiation between populations (F_ST = ?0.041 to 0.111 for COI, ?0.060 to 0.108 for microsatellites) at both fine and large geographical scales. Bayesian clustering and three‐dimensional factorial correspondence analyses consistently revealed two genetically distinct clusters, highlighting genetic discontinuities in the invaded range. Results of all genetic analyses suggest ship‐mediated ‘jump’ dispersal as the dominant mode of spread of golden mussels in South America, while downstream natural dispersal has had limited effects on contemporary genetic patterns. Main conclusions Our study provides new evidence that post‐establishment dispersal dynamics and genetic patterns vary across geographical scales. While ship‐mediated ‘jump’ dispersal dominates post‐establishment spread of golden mussels in South America, once colonies become established in upstream locations, larvae produced may be advected downstream to infill patchy distributions. Moreover, genetic structuring at fine geographical scales, especially within the same drainages, suggests a further detailed understanding of dynamics of larval dispersal and settlement in different water systems. Knowledge of the mechanisms by which post‐establishment spread occurs can, in some cases, be used to limit dispersal of golden mussels and other introduced species.     

Vicariance or long‐distance dispersal: historical biogeography of the pantropical subfamily Chrysophylloideae (Sapotaceae)

Aim Continental disjunctions in pantropical taxa have been explained by vicariance or long‐distance dispersal. The relative importance of these explanations in shaping current distributions may vary, depending on historical backgrounds or biological characteristics of particular taxa. We aimed to determine the geographical origin of the pantropical subfamily Chrysophylloideae (Sapotaceae) and the roles vicariance and dispersal have played in shaping its modern distribution. Location Tropical areas of Africa, Australasia and South America. Methods We utilized a recently published, comprehensive data set including 66 species and nine molecular markers. Bayesian phylogenetic trees were generated and dated using five fossils and the penalized likelihood approach. Distributional ranges of nodes were estimated using maximum likelihood and parsimony analyses. In both biogeographical and molecular dating analyses, phylogenetic and branch length uncertainty was taken into account by averaging the results over 2000 trees extracted from the Bayesian stationary sample. Results Our results indicate that the earliest diversification of Chrysophylloideae was in the Campanian of Africa c. 73–83 Ma. A narrow time interval for colonization from Africa to the Neotropics (one to three dispersals) and Australasia (a single migration) indicates a relatively rapid radiation of this subfamily in the latest Cretaceous to the earliest Palaeocene (c. 62–72 Ma). A single dispersal event from the Neotropics back to Africa during the Neogene was inferred. Long‐distance dispersal between Australia and New Caledonia occurred at least four times, and between Africa and Madagascar on multiple occasions. Main conclusions Long‐distance dispersal has been the dominant mechanism for range expansion in the subfamily Chrysophylloideae. Vicariance could explain South American–Australian disjunction via Antarctica, but not the exchanges between Africa and South America and between New Caledonia and Australia, or the presence of the subfamily in Madagascar. We find low support for the hypothesis that the North Atlantic land bridge facilitated range expansions at the Palaeocene/Eocene boundary.     

Phylogeographic diversification of antelope squirrels (Ammospermophilus) across North American deserts

We investigated the biogeographic history of antelope squirrels, genus Ammospermophilus, which are widely distributed across the deserts and other arid lands of western North America. We combined range‐wide sampling of all currently recognized species of Ammospermophilus with a multilocus data set to infer phylogenetic relationships. We then estimated divergence times within identified clades of Ammospermophilus using fossil‐calibrated and rate‐calibrated molecular clocks. Lastly, we explored generalized distributional changes of Ammospermophilus since the last glacial maximum using species distribution models, and assessed responses to Quaternary climate change by generating demographic parameter estimates for the three wide‐ranging clades of A. leucurus. From our phylogenetic estimates we inferred strong phylogeographic structure within Ammospermophilus and the presence of three well‐supported major clades. Initial patterns of historical divergence were coincident with dynamic alterations in the landscape of western North America, and the formation of regional deserts during the Late Miocene and Pliocene. Species distribution models and demographic parameter estimates revealed patterns of recent population expansion in response to glacial retreat. When combined with evidence from co‐distributed taxa, the historical biogeography of Ammospermophilus provides additional insight into the mechanisms that impacted diversification of arid‐adapted taxa across the arid lands of western North America. We propose species recognition of populations of the southern Baja California peninsula to best represent our current understanding of evolutionary relationships among genetic units of Ammospermophilus. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 949–967.     

Phylogenetic relationships among populations of the Nacobbus aberrans (Nematoda,Pratylenchidae) complex reveal the existence of cryptic species

The plant‐parasitic nematode Nacobbus aberrans sensu lato is an agricultural pest of quarantine importance. Due to the morphometric, physiological and genetic variability observed within the species, there is no agreement on the taxonomy of this nematode. The objective of this study was to analyse the ITS rDNA region and the D2–D3 expansion segments of 28S rDNA in 10 Argentine populations and one from Ecuador and to establish their phylogenetic relationship with other known sequences from South and North America. Phylogenetic trees of the ITS gene showed seven statistically well‐supported clades; the high and significant F_st values obtained among these groups confirmed this partitioning. The Argentine populations here considered were separated into three clades: one comprising a population from the Andean region and two grouping nematodes from lower altitudes. Three other clades were distinguished for South American populations, which included known sequences of individuals from Peru, Bolivia and north of Argentina. The other clade included sequences from Mexico, Ecuador and two Argentine populations of unknown origin. The important degree of genetic divergence observed among Andean populations suggests that the Andes may have played a crucial role in speciation of Nacobbus, which would have originated in this region. Although D2–D3 segments exhibited lower variation, they were useful for establishing phylogenetic relationships among the Argentine populations considered in this work. As there are no other GenBank sequences available for these segments, it was not possible to make comparisons with other populations from South and North America. The considerable genetic differentiation observed in ITS rDNA region among Nacobbus populations showed evidence of cryptic species within the N. aberrans s.l. complex. Integration of morphological and morphometric studies and molecular analyses considering other genes may aid in the identification of species and their phylogenetic relationships within this genus.