Biogeographic patterns and cryptic speciation in bryophytes

Bryophytes (mosses, liverworts, hornworts) typically have broad geographical distributions that span two or more continents. Many species show classic patterns of disjunction that are similar to those found in many other groups of organisms (e.g. eastern Asia–eastern North America), and which are thought to result from fragmentation of previously continuous ranges (i.e. vicariance). However, in the bryophytes, these disjunctions often occur at the infra-specific level and suggest that morphological uniformity may belie complex underlying genetic structure. Recent demonstrations of cryptic speciation, revealed by analyses of isozymes and DNA sequence variation, support the interpretation that genetic subdivision has occurred within some morphologically uniform species. Evidence for cryptic or nearly cryptic speciation exists for seven species of liverworts and seven mosses. In most (but not all) cases, cryptic species have broadly overlapping geographical ranges, although many are ecologically differentiated. Future work should focus on species that display 'classic' patterns of disjunction at higher taxonomic levels in other organisms (e.g. eastern North America–eastern Asia, eastern or western North America–Europe, Gondwanic), and should utilize explicitly phylogenetic approaches.     

Phylogeny of the tribe Indigofereae (Leguminosae-Papilionoideae): Geographically structured more in succulent-rich and temperate settings than in grass-rich environments

This analysis goes beyond many phylogenies in exploring how phylogenetic structure imposed by morphology, ecology, and geography reveals useful evolutionary data. A comprehensive range of such diversity is evaluated within tribe Indigofereae and outgroups from sister tribes. A combined data set of 321 taxa (over one-third of the tribe) by 80 morphological characters, 833 aligned nuclear ribosomal ITS/5.8S sites, and an indel data set of 33 characters was subjected to parsimony analysis. Notable results include the Madagascan dry forest Disynstemon resolved as sister to tribe Indigofereae, and all species of the large genus Indigofera comprise just four main clades, each diagnosable by morphological synapomorphies and ecological and geographical predilections. These results suggest niche conservation (ecology) and dispersal limitation (geography) are important processes rendering signature shapes to the Indigofereae phylogeny in different biomes. Clades confined to temperate and succulent-rich biomes are more dispersal limited and have more geographical phylogenetic structure than those inhabiting tropical grass-rich vegetation. The African arid corridor, particularly the Namib center of endemism, harbors many of the oldest Indigofera lineages. A rates analysis of nucleotide substitutions confirms that the ages of the oldest crown clades are mostly younger than 16 Ma, implicating dispersal in explaining the worldwide distribution of the tribe.     

Partial island submergence and speciation in an adaptive radiation: a multilocus analysis of the Cuban green anoles

Sympatric speciation is often proposed to account for species-rich adaptive radiations within lakes or islands, where barriers to gene flow or dispersal may be lacking. However, allopatric speciation may also occur in such situations, especially when ranges are fragmented by fluctuating water levels. We test the hypothesis that Miocene fragmentation of Cuba into three palaeo-archipelagos accompanied species-level divergence in the adaptive radiation of West Indian Anolis lizards. Analysis of morphology, mitochondrial DNA (mt DNA) and nuclear DNA in the Cuban green anoles (carolinensis subgroup) strongly supports three pre dictions made by this hypothesis. First, three geographical sets of populations, whose ranges correspond with palaeo-archipelago boundaries, are distinct and warrant recognition as independent evolutionary lineages or species. Coalescence of nuclear sequence fragments sampled from these species and the large divergences observed between their mtDNA haplotypes suggest separation prior to the subsequent unification of Cuba ca. 5 Myr ago. Second, molecular phylogenetic relationships among these species reflect historical geographical relationships rather than morphological similarity. Third, all three species remain distinct despite extensive geographical contact subsequent to island unification, occasional hybridization and introgression of mtDNA haplotypes. Allopatric speciation initiated during partial island submergence may play an important role in speciation during the adaptive radiation of Anolis lizards.     

The barriers to oceanic island radiation in bryophytes: insights from the phylogeography of the moss Grimmia montana

Aim In contrast to angiosperms, bryophytes do not appear to have radiated in Macaronesia and the western Mediterranean. We evaluate if: (1) the apparent lack of radiation in bryophytes reflects our failure to recognize cryptic endemic species; (2) bryophytes are characterized by extremely low evolutionary rates; or (3) bryophytes have a high dispersal ability, which prevents genetic isolation. Location Worldwide, with a special emphasis on Macaronesia and the western Mediterranean. Methods Three chloroplast regions were sequenced from samples of the moss Grimmia montana from its entire distribution range. Network analyses, Fst and Nst statistics were used to describe and interpret the phylogeographical signal in the data. Results Despite significant phylogeographical signal in the chloroplast genome, which demonstrates limits to gene flow at the continental scale, repeated sister group relationships observed among accessions from different geographical areas suggest recurrent colonization patterns. These observations are consistent with mounting evidence that intercontinental distributions exhibited by many bryophyte species result from long‐distance dispersal rather than continental drift. Madeiran and western Mediterranean island haplotypes are either shared by, or closely related to, European and North American ones. Fst values between Madeira, western Mediterranean islands, North America and Europe are not significantly different from zero, and suggest that Madeira and the south‐western Mediterranean are subject to strong transatlantic gene flow. By contrast, haplotypes found in the Canary Islands are shared or closely related to those of populations from south‐western Europe or southern Africa. Main conclusions Multiple origins and colonization events are not consistent with the hypothesis of a relictual origin of the Macaronesian moss flora. One possible reason for the failure of taxa that experienced multiple colonization events to radiate is niche pre‐emption. We suggest that strong gene flow, coupled with the occupancy of all suitable niches, either by earlier conspecific colonizers or by other species, could be the mechanism preventing island radiation in G. montana and other cryptogams with high long‐distance dispersal abilities.     

Cryptic species of mites (Uropodoidea: Uroobovella spp.) associated with burying beetles (Silphidae: Nicrophorus): The collapse of a host generalist revealed by molecular and morphological analyses

Uroobovella (Mesostigmata: Uropodoidea: Urodinychidae) species are among the most common mites associated with carrion-feeding Nicrophorus (Silphidae) beetles. Previous taxonomic understanding suggests that a single host generalist, U. nova, disperses and lives with Nicrophorus species worldwide (reported from at least seven host species). Using morphometrics and morphological characteristics, as well as partial cytochrome oxidase I (COI) and the entire internal transcribed spacer 2 (ITS2) markers, we tested whether this apparent generalist is truly a generalist or rather a complex of cryptic species with narrower host ranges. Based on deutonymph mites collected from 14 host species across six countries and 17 provinces or states, we show that U. nova represents at least five morphologically similar species with relatively restricted host ranges. Except for one species which yielded no molecular data (but did exhibit morphological differences), both molecular and morphological datasets were congruent in delimiting species boundaries. Moreover, comparing the mite phylogeny with the known ecology and phylogenetic relationships of their host species suggests that these mites are coevolving with their silphid hosts rather than tracking ecologically similar species.     

DNA‐based species delimitation separates highly divergent populations within morphologically coherent clades of poorly dispersing beetles

We compared species‐level entities recovered using distance, tree‐based, and DNA‐character based methods with morphologically defined species in poorly dispersing lyponiine net‐winged beetles. The phylogenetic relationships were investigated using the cytochrome c oxidase 1–2 mtDNA fragment. We identified 31 species using a morphology‐based concept and additional candidate species were delimited by the general mixed Yule‐coalescent method and barcoding threshold within the morphologically coherent lineages owing to high genetic divergence (up to 10.97% within morphologically defined species, highest density 2.5–6.5%). Genetic divergence was positively correlated with geographical distance: lower in continental China where no apparent dispersal barriers are present (r² = 0.172, P ≤ 0.001, average increase of genetic distance of 0.32% per 100 km) and much higher in Japan (r² = 0.490, P ≤ 0.001, 1.81% per 100 km). We hypothesize that low dispersal propensity contributed to the high level of intraspecific, geographically structured divergence. DNA‐based methods suggested a high number of morphologically undistinguishable species. The observed patterns agree with the model of neutral evolution. The poor dispersers produce gradually divergent populations across the range of the morphologically coherent lineages. We pose the question of what size of range and level of genetic difference justify formal acceptance of a species without morphological divergence from both the taxonomical and conservation management view points. © 2015 The Linnean Society of London     

Contrasting patterns and mechanisms of spatial turnover for native and exotic freshwater fish in Europe

Aim We compare the distribution patterns of native and exotic freshwater fish in Europe, and test whether the same mechanisms (environmental filtering and/or dispersal limitation) govern patterns of decrease in similarity of native and exotic species composition over geographical distance (spatial species turnover). Locations Major river basins of Europe. Methods Data related to geography, habitat diversity, regional climate and species composition of native and exotic freshwater fish were collated for 26 major European river basins. We explored the degree of nestedness in native and exotic species composition, and quantified compositional similarity between river basins according to the beta‐sim (independent of richness gradient) and Jaccard (dependent of richness gradient) indices of similarity. Multiple regression on distance matrices and variation‐partitioning approaches were used to quantify the relative roles of environmental filtering and dispersal limitation in shaping patterns of decreasing compositional similarity over geographical distance. Results Native and exotic species exhibited significant nested patterns of species composition, indicating that differences in fish species composition between river basins are primarily the result of species loss, rather than species replacement. Both native and exotic compositional similarity decreased significantly with increasing geographical distance between river basins. However, gradual changes in species composition with geographical distance were found only for exotic species. In addition, exotic species displayed a higher rate of similarity decay (higher species turnover rate) with geographical distance, compared with native species. Lastly, the majority of explained variation in exotic compositional similarity was uniquely related to geography, whereas native compositional similarity was either uniquely explained by geography or jointly explained by environment and geography. Main conclusions Our study suggests that large‐scale patterns of spatial turnover for exotic freshwater fish in Europe are generated by human‐mediated dispersal limitation, whereas patterns of spatial turnover for native fish result from both dispersal limitation relative to historical events (isolation by mountain ranges, glacial history) and environmental filtering.     

The diversity and distribution of diatoms: from cosmopolitanism to narrow endemism

It has been claimed that microbial taxa will not exhibit endemism because their enormous populations remove dispersal as an effective constraint on geographical range. Here we review evidence that challenges this ubiquity hypothesis for the most speciose group of microbial eukaryotes, the diatoms. Detailed taxonomic inventories using fine-grained morphological characteristics, molecular markers, and crossing experiments have revealed that the geographic distribution of diatoms ranges from global to narrow endemic. Records of human-mediated introductions of exotic species further provide a strong indication that geographic dispersal was limiting in the past. Finally, recent studies have revealed that diatom community structure and diversity are influenced by geographical factors independent of environmental conditions. Diatom communities are thus regulated by the same processes that operate in macro-organisms, although possibly to a different degree, implying that dispersal limitation is significant and the endemism observed in isolated areas is real. These results underscore the pressing need to (1) continue research into diatom biology, ecology and the factors driving diatom species diversity and geographic distributions, and (2) protect relatively isolated areas against further introductions of exotic species. Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.     

Recent divergence,intercontinental dispersal and shared polymorphism are shaping the genetic structure of amphi‐Atlantic peatmoss populations

Several lines of evidence suggest that recent long‐distance dispersal may have been important in the evolution of intercontinental distribution ranges of bryophytes. However, the absolute rate of intercontinental migration and its relative role in the development of certain distribution ranges is still poorly understood. To this end, the genetic structure of intercontinental populations of six peatmoss species showing an amphi‐Atlantic distribution was investigated using microsatellite markers. Methods relying on the coalescent were applied (im and migrate ) to understand the evolution of this distribution pattern in peatmosses. Intercontinental populations of the six peatmoss species were weakly albeit significantly differentiated (average F_ST = 0.104). This suggests that the North Atlantic Ocean is acting as a barrier to gene flow even in bryophytes adapted to long‐range dispersal. The im analysis suggested a relatively recent split of intercontinental populations dating back to the last two glacial periods (9000–289 000 years ago). In contrast to previous hypotheses, analyses indicated that both ongoing migration and ancestral polymorphism are important in explaining the intercontinental genetic similarity of peatmoss populations, but their relative contribution varies with species. Migration rates were significantly asymmetric towards America suggesting differential extinction of genotypes on the two continents or invasion of the American continent by European lineages. These results indicate that low genetic divergence of amphi‐Atlantic populations is a general pattern across numerous flowering plants and bryophytes. However, in bryophytes, ongoing intercontinental gene flow and retained shared ancestral polymorphism must both be considered to explain the genetic similarity of intercontinental populations.     

Cryptic diversity in a fig wasp community—morphologically differentiated species are sympatric but cryptic species are parapatric

A key debate in ecology centres on the relative importance of niche and neutral processes in determining patterns of community assembly with particular focus on whether ecologically similar species with similar functional traits are able to coexist. Meanwhile, molecular studies are increasingly revealing morphologically indistinguishable cryptic species with presumably similar ecological roles. Determining the geographic distribution of such cryptic species provides opportunities to contrast predictions of niche vs. neutral models. Discovery of sympatric cryptic species increases alpha diversity and supports neutral models, while documentation of allopatric/parapatric cryptic species increases beta diversity and supports niche models. We tested these predictions using morphological and molecular data, coupled with environmental niche modelling analyses, of a fig wasp community along its 2700‐km latitudinal range. Molecular methods increased previous species diversity estimates from eight to eleven species, revealing morphologically cryptic species in each of the four wasp genera studied. Congeneric species pairs that were differentiated by a key morphological functional trait (ovipositor length) coexisted sympatrically over large areas. In contrast, morphologically similar species, with similar ovipositor lengths, typically showed parapatric ranges with very little overlap. Despite parapatric ranges, environmental niche models of cryptic congeneric pairs indicate large regions of potential sympatry, suggesting that competitive processes are important in determining the distributions of ecologically similar species. Niche processes appear to structure this insect community, and cryptic diversity may typically contribute mostly to beta rather than alpha diversity.     

How to define nativeness in organisms with high dispersal capacities? A comment on Essl et al.

Essl and colleagues documented worldwide invasion patterns in bryophytes, which so far have been neglected in invasion biology. In the absence of historical evidence, Essl and colleagues used criteria such as anomalous geographical distribution, preference for disturbed habitats, and indirect associations with some means of human transport as criteria to identify aliens. Because bryophytes exhibit high long‐distance dispersal capabilities, disjunct distribution patterns are, however, the rule rather than the exception in the group. In our opinion, none of the previously proposed criteria to characterize aliens can be satisfactorily applied to groups like bryophytes, for which historical and fossil records are extremely scarce. We suggest that, in order to validate the conclusions of Essl and colleagues, further taxonomic and phylogeographical studies are needed. This is especially true for island floras, for which recent critical taxonomic work and updated checklists, which compose the primary source of information for biodiversity, are largely missing.     

Life-history traits are correlated with geographical distribution patterns of western European forest herb species

Aim To investigate whether six plant life‐history traits that have been related to colonization ability at local scales are also related to the geographical range characteristics of 273 forest plant species. Location Continental western Europe, five countries in particular: France, Luxemburg, Belgium, the Netherlands and Germany. The region is situated between 42° and 55°N and 5°W and 15°E and has a summed total area of 971,404 km². Methods Distribution data were compiled from five national data bases and converted to a 10′ grid. Life‐history traits were taken from existing compilations of autecological information of European species. The spatial arrangement of occupied grid cells was investigated using Ripley's K. Cross‐species correlations and phylogenetically independent contrasts were used to investigate the relationships between plant life‐history traits and three range characteristics: area of occupancy, latitudinal extent and centroid latitude. Results For herbaceous species, seed dispersal mode, seed production and seed bank longevity exhibited significant associations with geographical range characteristics, including area of occupancy. Woody plant species exhibited fewer significant associations, although maximum height was positively associated with range centroid latitude within the study area. Furthermore, the ranges of species with limited dispersal ability were found to be more clustered than the ranges of species with morphological adaptations for long‐distance seed dispersal. Main conclusions For western European forest plant species, life‐history traits that are related to colonization ability at local scales are associated with variation in large‐scale geographical range characteristics. This finding implies that the distributions of some forest plant species in the study area may be limited by seed dispersal and colonization capacity rather than climate or other environmental factors.     

Phylogenetic biogeography of the leafy liverwort Herbertus (Jungermanniales, Herbertaceae) based on nuclear and chloroplast DNA sequence data: correlation between genetic variation and geographical distribution

Aim The cosmopolitan genus Herbertus is notorious for having a difficult taxonomy and for the fact that there is limited knowledge of species ranges and relationships. Topologies generated from variable molecular markers are used to discuss biogeographical patterns in Herbertus and to compare them with the geological history of continents and outcomes reported for other land plants. Location Africa, Asia, Azores, Europe, southern South America, northern South America, North America, New Zealand. Methods Phylogenetic analyses of nuclear ribosomal internal transcribed spacer and chloroplast (cp) trnL–trnF sequences of 66 accessions of Herbertus and the outgroup species Triandrophyllum subtrifidum and Mastigophora diclados were used to investigate biogeographical patterns in Herbertus. Areas of putative endemism were defined based on the distribution of species included in the analyses. Maximum parsimony analyses were undertaken to reconstruct ancestral areas and intraspecies migration routes. Results The analyses reveal species‐level cladograms with a correlation between genetic variation and the geographical distribution of the related accessions. The southern South American Herbertus runcinatus is sister to the remainder of the genus, which is split into two main clades. One contains the Neotropical–African Herbertus juniperoideus and the New Zealand/Tasmanian Herbertus oldfieldianus. An African accession of H. juniperoideus is nested within Neotropical accessions. The second main clade includes species that inhabit Asia, the Holarctic, Africa, and northern South America. Maximum parsimony analyses indicate that this clade arose in Asia. Herbertus sendtneri originated in Asia and subsequently colonized the Holarctic and northern South America. An Asian origin and colonization into Africa is indicated for H. dicranus. Main conclusions The current distribution of Herbertus cannot be explained by Gondwanan vicariance. A more feasible explanation of the range is a combination of short‐distance dispersal, rare long‐distance dispersal events (especially into regions that faced floral displacements as a result of climatic changes) extinction, recolonization, and diversification. The African Herbertus flora is a mixture of Asian and Neotropical elements. Southern South America harbours an isolated species. The molecular data indicate partial decoupling of molecular and morphological variation in Herbertus. Biogeographical patterns in Herbertus are not dissimilar to those of other groups of bryophytes, but elucidation of the geographical ranges requires a molecular approach. Some patterns could be the result of maintenance of Herbertus in the inner Tropics during glacial maxima, and dispersal into temperate regions in warm phases.     

Marine dispersal as a pre‐requisite for Gondwanan vicariance among elements of the galaxiid fish fauna

Aim The aim of this study was to determine the contributions of Gondwanan vicariance and marine dispersal to the contemporary distribution of galaxiid fishes. This group has been central in arguments concerning the roles of dispersal and vicariance in the Southern Hemisphere, as some taxa have marine life history stages through which transoceanic dispersal may have been facilitated, yet other galaxiids are entirely restricted to freshwaters. Location Southern Hemisphere land masses of Gondwanan derivation. Methods Biogeographic hypotheses of Gondwanan vicariance and marine dispersal were tested using four lines of evidence: (1) concordance of species–area phylogenetic relationships, (2) molecular estimates of lineage divergence times with a priori expectations based on plate tectonics, (3) reconstructions of ancestral dispersal capabilities, and (4) reconstructions of distribution inheritance scenarios (using the dispersal–extinction–cladogenesis model to infer historical ranges and dispersal and extinction events). Results Phylogenetic relationships were reconstructed from 4531 mitochondrial and nuclear nucleotide characters, and 181 morphological characters, across 53 of the 56 presently recognized species. Phylogenetic relationships were generally well resolved and supported among galaxiids using the combined dataset, and conflicting relationships between molecular and morphological datasets typically received low topological support from either or both datasets. Transoceanic disjunctions were exhibited at 16 nodes, but only three pre‐dated relevant continental fragmentation events; furthermore, ancestral distribution inheritance scenarios for two of these nodes reflected cladogenesis within, rather than between, Gondwanan land masses, and ancestral marine dispersal capability could not be rejected for all three. Instead, the four lines of evidence surveyed suggest that Gondwanan vicariance occurred twice, but in both instances was preceded by marine dispersal between land masses, and in at least one instance was initiated by the cessation of marine dispersal subsequent to continental fragmentation. Main conclusions Gondwanan vicariance appears to have been preceded by marine dispersal in the few instances where it may explain contemporary galaxiid distribution, such that these biogeographic mechanisms may sometimes have a synergistic relationship.     

EVOLUTIONARY DIVERGENCE IN THE RED ALGAE CALOGLOSSA LEPRIEURII AND C. APOMEIOTICA

Morphological comparisons, hybridization experiments, and molecular phylogenetic analyses using the RUBISCO spacer region were undertaken on 12 populations of Caloglossa leprieurii (Montagne) J. Agardh in order to clarify their relationships. In addition, data from one population of the morphologically similar but asexual species, C. apomeiotica (West et Zuccarello), were included in the assessment. Three morphological types were recognized on the basis of the number of cell rows at nodes of the main axis opposite to the lateral branch and blade width: single/ broad (with three mating groups), multiple/broad (three mating groups) and multiple/slender (one mating group). In the molecular analyses, C. leprieurii was resolved as two clusters that correspond phenetically to the single and multiple cell row types. Both the morphological and molecular data indicate that the asexual species was derived from sexual plants of the multiple cell row type. The reproductive compatibility correlates with genetic distance rather than geographical distance. Sympatric mating groups are completely incompatible and have 10–21 nucleotide changes in the examined region, whereas mating groups that produce abnormal progeny or pseudocystocarps are allopatrically distributed with 5–7 nucleotide changes. The present data suggest that the two populations, one with single and the other with multiple cell rows, which are sympatrically distributed in southeastern Japan, have probably evolved by allopatric speciation. The single/broad type that is restricted to the western Pacific, may have diverged genetically between eastern and western Australia, with subsequent dispersal from the western population as far as Japan.     

Comparative landscape genetics and the adaptive radiation of Darwin's finches: the role of peripheral isolation

We use genetic divergence at 16 microsatellite loci to investigate how geographical features of the Galápagos landscape structure island populations of Darwin's finches. We compare the three most genetically divergent groups of Darwin's finches comprising morphologically and ecologically similar allopatric populations: the cactus finches (Geospiza scandens and Geospiza conirostris), the sharp-beaked ground finches (Geospiza difficilis) and the warbler finches (Certhidea olivacea and Certhidea fusca). Evidence of reduced genetic diversity due to drift was limited to warbler finches on small, peripheral islands. Evidence of low levels of recent interisland migration was widespread throughout all three groups. The hypothesis of distance-limited dispersal received the strongest support in cactus and sharp-beaked ground finches as evidenced by patterns of isolation by distance, while warbler finches showed a weaker relationship. Support for the hypothesis that gene flow constrains morphological divergence was only found in one of eight comparisons within these groups. Among warbler finches, genetic divergence was relatively high while phenotypic divergence was low, implicating stabilizing selection rather than constraint due to gene flow. We conclude that the adaptive radiation of Darwin's finches has occurred in the presence of ongoing but low levels of gene flow caused by distance-dependent interisland dispersal. Gene flow does not constrain phenotypic divergence, but may augment genetic variation and facilitate evolution due to natural selection. Both microsatellites and mtDNA agree in that subsets of peripheral populations of two older groups are genetically more similar to other species that underwent dramatic morphological change. The apparent decoupling of morphological and molecular evolution may be accounted for by a modification of Lack's two-stage model of speciation: relative ecological stasis in allopatry followed by secondary contact, ecological interactions and asymmetric phenotypic divergence.     

Seven new species within western Atlantic Starksia atlantica, S. lepicoelia, and S. sluiteri (Teleostei, Labrisomidae), with comments on congruence of DNA barcodes and species

Specimens of Starksia were collected throughout the western Atlantic, and a 650-bp portion of the mitochondrial gene cytochrome oxidase-c subunit I (COl) was sequenced as part of a re-analysis of species diversity of western Central Atlantic shorefishes. A neighbor-joining tree constructed from the sequence data suggests the existence of several cryptic species. Voucher specimens from each genetically distinct lineage and color photographs of vouchers taken prior to dissection and preservation were examined for diagnostic morphological characters. The results suggest that Starksia atlantica, Starksia lepicoelia, and Starksia sluiteri are species complexes, and each comprises three or more species. Seven new species are described. DNA data usually support morphological features, but some incongruence between genetic and morphological data exists. Genetic lineages are only recognized as species if supported by morphology. Genetic lineages within western Atlantic Starksia generally correspond to geography, such that members of each species complex have a very restricted geographical distribution. Increasing geographical coverage of sampling locations will almost certainly increase the number of Starksia species and species complexes recognized in the western Atlantic. Combining molecular and morphological investigations is bringing clarity to the taxonomy of many genera of morphologically similar fishes and increasing the number of currently recognized species. Future phylogenetic studies should help resolve species relationships and shed light on patterns of speciation in western Atlantic Starksia.     

Speciation below ground: Tempo and mode of diversification in a radiation of endogean ground beetles

Dispersal is a critical factor determining the spatial scale of speciation, which is constrained by the ecological characteristics and distribution of a species’ habitat and the intrinsic traits of species. Endogean taxa are strongly affected by the unique qualities of the below‐ground environment and its effect on dispersal, and contrasting reports indicate either high dispersal capabilities favoured by small body size and mediated by passive mechanisms, or low dispersal due to restricted movement and confinement inside the soil. We studied a species‐rich endogean ground beetle lineage, Typhlocharina, including three genera and more than 60 species, as a model for the evolutionary biology of dispersal and speciation in the deep soil . A time‐calibrated molecular phylogeny generated from >400 individuals was used to delimit candidate species, to study the accumulation of lineages through space and time by species–area–age relationships and to determine the geographical structure of the diversification using the relationship between phylogenetic and geographic distances across the phylogeny. Our results indicated a small spatial scale of speciation in Typhlocharina and low dispersal capacity combined with sporadic long distance, presumably passive dispersal events that fuelled the speciation process. Analysis of lineage growth within Typhlocharina revealed a richness plateau correlated with the range of distribution of lineages, suggesting a long‐term species richness equilibrium mediated by density dependence through limits of habitat availability. The interplay of area‐ and age‐dependent processes ruling the lineage diversification in Typhlocharina may serve as a general model for the evolution of high species diversity in endogean mesofauna.     

Galápagos' Opuntia (prickly pear) cacti: extensive morphological diversity, low genetic variability

Due to the pronounced morphological variation and geographical distribution of Galápagos' Opuntia cacti, numerous hypotheses have been advanced regarding their radiation, diversification, and classification. The currently accepted classification is based on morphology and recognizes six species and fourteen varieties, but the plasticity of many of the characteristics renders any morphological taxonomy problematic. Our analysis of previously published morphological data agrees only partially with the current classification. We present the first molecular phylogeny of these plants. Multiple DNA sequences indicate little genetic distinction among the currently identified species, despite restricted gene flow and limited long distance dispersal within the archipelago. No clear relationship exists between morphological and genetic differences. These results suggest that both molecular and morphological data should be used in conservation planning.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 451–461.     

Molecular phylogeny and phylogeography of the Cuban cave-fishes of the genus Lucifuga: evidence for cryptic allopatric diversity

Underground environments are increasingly recognized as reservoirs of faunal diversity. Extreme environmental conditions and limited dispersal ability of underground organisms have been acknowledged as important factors promoting divergence between species and conspecific populations. However, in many instances, there is no correlation between genetic divergence and morphological differentiation. Lucifuga Poey is a stygobiotic fish genus that lives in Cuban and Bahamian caves. In Cuba, it offers a unique opportunity to study the influence of habitat fragmentation on the genetic divergence of stygobiotic species and populations. The genus includes four species and one morphological variant that have contrasting geographical distributions. In this study, we first performed a molecular phylogenetic analysis of the Lucifuga Cuban species using mitochondrial and nuclear markers. The mitochondrial phylogeny revealed three deeply divergent clades that were supported by nuclear and morphological characters. Within two of these main clades, we identified five lineages that are candidate cryptic species and a taxonomical synonymy between Lucifuga subterranea and Lucifuga teresinarum. Secondly, phylogeographic analysis using a fragment of the cytochrome b gene was performed for Lucifuga dentata, the most widely distributed species. We found strong geographical organization of the haplotype clades at different geographic scales that can be explained by episodes of dispersal and population expansion followed by population fragmentation and restricted gene flow. At a larger temporal scale, these processes could also explain the diversification and the distribution of the different species.