Rejecting strictly allopatric speciation on a continental island: prolonged postdivergence gene flow between Taiwan (Leucodioptron taewanus,Passeriformes Timaliidae) and Chinese (L. canorum canorum) hwameis

Allopatry is conventionally considered the geographical mode of speciation for continental island organisms. However, strictly allopatric speciation models that assume the lack of postdivergence gene flow seem oversimplified given the recurrence of land bridges during glacial periods since the late Pliocene. Here, to evaluate whether a continental island endemic, the Taiwan hwamei (Leucodioptron taewanus, Passeriformes Timaliidae) speciated in strict allopatry, we used weighted‐regression‐based approximate Bayesian computation (ABC) to analyse the genetic polymorphism of 18 neutral nuclear loci (total length: 8500 bp) in Taiwan hwamei and its continental sister species, the Chinese hwamei (L. canorum canorum). The nonallopatry model was found to fit better with observed genetic polymorphism of the two hwamei species (posterior possibility = 0.82). We also recovered unambiguous signals of nontrivial bidirectional postdivergence gene flow (N_em » 1) between Chinese hwamei and Taiwan hwamei until 0.5 Ma. Divergence time was estimated to be 3.5 to 2 million years earlier than that estimated from mitochondrial cytochrome b sequences. Finally, using the inferred nonallopatry model to simulate genetic variation at 24 nuclear genes examined showed that the adiponectin receptor 1 gene may be under divergent adaptation. Our findings imply that the role of geographical barrier may be less prominent for the speciation of continental island endemics, and suggest a shift in speciation studies from simply correlating geographical barrier and genetic divergence to examining factors that facilitate and maintain divergence, e.g. differential selection and sexual selection, especially in the face of interpopulation gene flow.     

Ecological differences between hamlet (Hypoplectrus: Serranidae) colour morphs: between-morph variation in diet

Dietary differences between hamlet Hypoplectrus spp. colour morphs were examined in fishes from Puerto Rico, U.S. Virgin Islands, Curacao, Honduras and Belize. Hamlet diet across all countries was characterized by large overlap between most colour morphs in both the proportion and numbers of dietary items consumed, although some differences between morphs were apparent. Indigo hamlets Hypoplectrus indigo were the only morph to consume fishes (blue chromis Chromis cyanea and sunshinefish Chromis insolata ) almost exclusively. The sympatric occurrence of other ecologically indistinguishable colour morphs, however, suggests that divergent ecological selection alone cannot explain population divergence in hamlets. Geographical variation in diet was also observed within black Hypoplectrus nigricans and yellowtail Hypoplectrus chlorurus hamlets which may reflect geographical differences in prey availability or differences in prey choice.     

A new cryptic species of Aphaenops (Coleoptera: Carabidae: Trechinae) from a French Pyrenean cave: Congruence between morphometrical and geographical data confirm species isolation

A new species of cave-dwelling beetle from the pyrenean massif, Aphaenops (Cerbaphaenops) jauzioni n. sp. (Coleoptera: Carabidae), is described. Geometric morphometric analyses based on five morphological structures and comparisons with two populations of the closely related species Aphaenops (Cerbaphaenops) cerberus Dieck 1869 support the uniqueness of the new species. The specific status of the new taxon is also confirmed by the male genitalia structures. A putative scenario of population isolation is proposed.     

Adaptation and speciation of Dolichopoda cave crickets (Orthoptera, Rhaphidophoridae): geographic variation of morphometric indices and allozyme frequencies

Morphometric analyses were carried out for 14 cave dwelling populations of Dolichopoda (Orthoptera, Rhaphidophoridae) from peninsular Italy belonging to the laetitiae-geniculata complex. The selected set of variables includes linear measures of body parts and appendages whose variation is expected to be adaptive and to reflect the degree of specialization to the cave environment.
Inter-population morphometric variation was compared with the patterns of allozyme variation, investigated electrophoretically in a previous paper, by means of ordination and classification multivariate analyses. Results from this comparison reject the hypothesis of parallel geographic variation of morphometric indices and allele frequencies, revealing independent trends for the two sets of characters.     

Postlarval development in shallow and deep-sea ophiuroids (Echinodermata: Ophiuroidea) of the NE Atlantic Ocean

The postlarval phase is an essential period in the life history of marine invertebrates; vulnerable to high mortality, it ultimately influences the distribution and abundance of adult populations. In the deep NE Atlantic, a large number of posdarval ophiuroids have been found during certain times of the year, but their identification is difficult. The present work describes the ontogenesis of 12 post-metamorphic shallow-water or deep-sea ophiuroids from samples collected during the Biofar and Rockall Trough Programmes in the NE Atlantic Ocean. Analysis of the posdarval development reveals that species can be identified from a very early post-metamorphic phase using particular morphological characters. The ontogeny of homologous structures reveals similarities within related groups. However, at the same time, these structures give rise to different adult structures in different taxa. Data on the postlarval development of Ophiura qffinis suggest that this species is more closely related to the genus Ophiocten and a change in generic status is proposed.     

Description, biology and conservation of a new species of Australian tree frog (Amphibia: Anura: Hylidae: Litoria) and an assessment of the remaining populations of Litoria genimaculata Horst, 1883: systematic and conservation implications of an unusual speciation event

The Australian populations of the green-eyed tree frog Litoria genimaculata consist of a northern and southern genetic lineage that meet in a mosaic contact zone comprising two independent areas of contact: one where the main ranges of the lineages overlap, and the second where a population of the southern lineage is isolated within the range of the northern lineage. A recent study failed to find significant reproductive isolation between the main ranges of the two lineages, despite deep genetic divergence, partial postzygotic isolation, and call differences. The study did, however, demonstrate rapid phenotypic divergence and speciation of the isolated population of the southern lineage from both the parapatric northern lineage and from the allopatric, but genetically similar, main range of the southern lineage. Herein, the isolated population of the southern lineage is described as a distinct species, Litoria myola sp. nov. , whereas the remainder of the southern lineage and the northern lineage are retained as a single, paraphyletic species, Litoria genimaculata . Resolving this unusual systematic situation demonstrates the value of using multiple lines of evidence in delimiting species. Litoria myola sp. nov. has a very small distribution and population size and warrants a Critically Endangered listing (B1, 2) under IUCN criteria. Threats and management recommendations are outlined, and the conservation of hybrid zones as areas of evolutionary novelty is discussed.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 549–563.     

Microdistribution within a population ofAcrocnida brachiata (Montagu), (Echinodermata: Ophiuroidea) in Little Killary, west coast of Ireland

Acrocnida brachiata (Montagu), like many other infaunal ophiuroids, has a penchant for gregariousness. In Little Killary, a small embayment on the west coast of Ireland, it colonises an extensive tract of sandy inshore ground (ca 7 m depth), at densities of 150–200 individuals/m². In the course of a two-year study, variation in regular suction-sampling returns prompted a detailed study of the species distribution pattern. Towards this end, 256 contiguous and stratified core samples were taken along a line of transect, in May 1995. These showed randomness with respect to the population at large, but exposed an aggregated distribution for juveniles and adults separately, at different levels within the sediment. Juveniles formed wide, ‘loose’ patches in the surficial deposit, while adults formed smaller, denseer patches deeper within the sediment. It remains to be seen what this approach may expose, when applied in different seasons, or during different phases of the species life cycle.     

Ecological divergence and speciation in common bottlenose dolphins in the western South Atlantic

Coastal and offshore ecotypes of common bottlenose dolphins have been recognized in the western South Atlantic, and it is possible that trophic niche divergence associated with social interactions is leading them to genetic and phenotypic differentiation. The significant morphological differentiation observed between these ecotypes suggests they represent two different subspecies. However, there is still a need to investigate whether there is congruence between morphological and genetic data to rule out the possibility of ecophenotypic variation accompanied by gene flow. Mitochondrial DNA (mtDNA) control region sequence data and 10 microsatellite loci collected from stranded and biopsied dolphins sampled in coastal and offshore waters of Brazil as well as 106 skulls for morphological analyses were used to determine whether the morphological differentiation was supported by genetic differentiation. There was congruence among the data sets, reinforcing the presence of two distinct ecotypes. The divergence may be relatively recent, however, given the moderate values of mtDNA nucleotide divergence (dA = 0.008), presence of one shared mtDNA haplotype and possibly low levels of gene flow (around 1% of migrants per generation). Results suggest the ecotypes may be in the process of speciation and reinforce they are best described as two different subspecies until the degree of nuclear genetic divergence is thoroughly evaluated: Tursiops truncatus gephyreus (coastal ecotype) and T. t. truncatus (offshore ecotype). The endemic distribution of T. t. gephyreus in the western South Atlantic and number of anthropogenic threats in the area reinforces the importance of protecting this ecotype and its habitat.     

The molecular systematics of Leiopotherapon unicolor (Günther, 1859): testing for cryptic speciation in Australia's most widespread freshwater fish

Leiopotherapon unicolor is the most widespread freshwater fish species in Australia. A comprehensive allozyme and mitochondrial DNA 16S rRNA data set was assembled from 141 specimens of L. unicolor collected Australia-wide in order to test for cryptic speciation in this far-ranging species. Surprisingly, little genetic diversity was observed within L. unicolor and provided no evidence for the existence of cryptic species within this lineage. In contrast, a small sample set of L. aheneus used as the outgroup showed two highly divergent haplotypes strongly suggestive of cryptic speciation. L. unicolor has a number of ecological and life history attributes that may explain the lack of significant genetic divergence over substantial geographical distances. The occurrence of other widespread fish and crustacean species that also display only limited genetic diversity indicate that climate conditions more favourable to dispersal across central and northern Australia than is suggested by the extent of present-day aridity have occurred in the relatively recent geological past.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 537–552.     

Phylogeography of North Atlantic intertidal tardigrades: refugia,cryptic speciation and the history of the Mid‐Atlantic Islands

Aim To analyse the phylogeographical history of intertidal tardigrades in the North Atlantic in order to improve our understanding of geographical differentiation in microscopic organisms, and to understand the potential importance of the Mid‐Atlantic Islands as stepping stones between the American and European coasts of the Atlantic Ocean. Location Twenty‐four localities from the Mid‐Atlantic Islands (Greenland, Iceland and the Faroe Islands) and both sides of the North Atlantic Ocean. Methods A mitochondrial marker (cytochrome c oxidase subunit I) was sequenced from individual tardigrades belonging to the genus Echiniscoides. The existence of cryptic species was detected using generalized mixed Yule coalescence analysis; lineage ages were estimated with relaxed clock methods; and the degree of geographical differentiation was analysed with samova analyses, haplotype networks and Mantel tests. Results Echiniscoides hoepneri, previously known only from Greenland, was recovered throughout the Mid‐Atlantic Islands. The Faroe Islands population was isolated from Greenland and Iceland, but overall genetic variation was low. The morphospecies Echiniscoides sigismundi had high genetic variation and consisted of at least two cryptic species. A northern and a southern species were both recovered on both sides of the Atlantic, but only the northern species was found on the Mid‐Atlantic Islands. The northern species showed signs of long‐term isolation between the Western and Eastern Atlantic, despite the potential of the Mid‐Atlantic islands to act as stepping‐stones. There was no sign of long‐term isolation in the southern species. The Mid‐Atlantic individuals of the northern species were of Eastern Atlantic origin, but Greenland and Iceland showed signs of long‐term isolation. The genetic pattern found in the southern species is not clearly geographical, and can probably be best explained by secondary contact between former isolated populations. Main conclusions North Atlantic intertidal tardigrades from the genus Echiniscoides showed strong geographical differentiation, and the Mid‐Atlantic Islands seemed unimportant as stepping stones across the Atlantic. The geographical variation of the northern species of E. sigismundi suggests post‐glacial recolonization from several refugia.     

Disentangling the genetic and morphological structure of Patella candei complex in Macaronesia (NE Atlantic)

The uptake of natural living resources for human consumption has triggered serious changes in the balance of ecosystems. In the archipelagos of Macaronesia (NE Atlantic), limpets have been extensively exploited probably since islands were first colonized. This has led to profound consequences in the dynamics of rocky shore communities. The Patella candei complex includes various subspecies of limpets that are ascribed to a particular archipelago and has been the focus of several taxonomic surveys without much agreement. Under a conservational perspective, we apply morphometric and genetic analyses to test subspecies boundaries in P. candei and to evaluate its current population connectivity throughout Macaronesia (Azores, Madeira, and Canaries). A highly significant genetic break between archipelagos following isolation by distance was detected (F_ST = 0.369, p < .001). Contrastingly, significant genetic differentiation among islands (i.e., Azores) was absent possibly indicating ongoing gene flow via larval exchange between populations. Significant shell‐shape differences among archipelagos were also detected using both distance‐based and geometric morphometric analyses. Adaptive processes associated with niche differentiation and strong barriers to gene flow among archipelagos may be the mechanisms underlying P. candei diversification in Macaronesia. Under the very probable assumption that populations of P. candei from each archipelago are geographically and/or ecologically isolated populations, the various subspecies within the P. candei complex may be best thought of as true species using the denomination: P. candei in Selvagens, Patella gomesii in Azores, Patella ordinaria in Madeira, and Patella crenata for Canaries. This would be in agreement with stock delimitation and units of conservation of P. candei sensu latu along Macaronesia.     

Genetic differentiation and detection of cryptic species in the genus Lepismachilis (Insecta: Microcoryphia) from the Western Mediterranean region

Different species of the bristletail genus Lepismachilis were collected in 14 localities in Italy and Spain and an allozyme electrophoretic survey was carried out to estimate the degree of genetic variability and differentiation at intra- and interspecific levels. Four morphological species were initially identified (L osellai, L. y-signata, L. affinis, L. targionii), but the electrophoretic analysis demonstrated the presence of two additional species among the individuals of L. targionii (Lepismachilis spl and sp2). The validity of these species and their differentiation from L targionii were demonstrated by the fixation of alternative allelic patterns at several loci (7 in Lepismachilis spl and 8 in Lepismachilis sp2), coupled with fixed, previously undetected, morphological differences. In addition, Lepismachilis sp2 was sympatric with L. targionii in three collecting sites, where the fixation of alternative allelic patterns unequivocally demonstrated reproductive isolation. Genetic variability did not seem to be correlated with local ecological factors, and differences between species should rather be explained by different historical factors. Low levels of gene flow, estimated with two different indirect methods, were observed in L. targionii and L. y-signata, and were due to high levels of structuring among populations. Genetic differentiation among conspecific populations was not correlated to their geographical arrangement and the presence of loci fixed for different alleles among them suggested that stochastic factors (such as genetic drift) may have played a role in determining genetic differentiation of geographically isolated populations. Genetic divergence values indicated that the six species are well differentiated and allozyme profiles were diagnostic for all of them. On the other hand, allozyme data did not provide adequate information to resolve evolutionary relationships among the species, nor did they confirm the validity of the two subgenera (Lepismachilis and Berlesilis) in which the genus Lepismachilis is traditionally divided.     

Glacial refuges and cryptic speciation in a Southern Palearctic tiger beetle (Coleoptera: Cicindelidae)

Pleistocene glaciations had a determining role for shaping the current distribution and diversity of organisms, especially in the Palearctic region. In this work, we carry out a phylogeographic analysis of Iberian and two Eastern European populations of the tiger beetle Calomera littoralis (Fabricius, 1787) in order to infer the processes that may have affected their evolutionary history. According to our results, the genetic diversity of central Iberian C. littoralis populations is very low. The haplotype networks also suggest that these populations experienced a genetic bottleneck in the past, possibly related to the last glacial maxima, similar to that observed in other cicindelid taxa. These results highlight the remarkable dispersal capacity of this species, being able to move freely from one locality to another, despite the relatively long distances of sub-optimal habitat that separates them. The genetic data of central Iberian populations contrast with those of the Eastern European populations, with higher genetic diversity and no hints of any past bottleneck. This can be explained by the different characteristics of both (Iberian and Pontic) glacial refuges. The high degree of genetic differentiation between the three C. littoralis clades, and the inclusion of C. lunulata between them, suggests that the three analysed populations could be considered as different cryptic species. In that case, C. littoralis may correspond to a species complex that is still undergoing a process of speciation, similar to that observed in Cicindela campestris.     

Sibling species and cryptic speciation in the Brachionus plicatilis species complex (Rotifera)

An attempt is made to identify sibling species within the Brachionus plicatilis complex (Rotifera). Allozyme and morphological data for nine strains from all over the world are provided. Although the analysis of morphological data classified individuals from nine strains into two groups, cluster analysis using genetic distance data obtained from allozyme data revealed at least three groups. A male choice design is described for the first time in rotifers and was used to test for male mating preferences among sympatric strains belonging to three distinct species. The results suggest that the B. plicatilis complex is actually composed of more than three sibling species.     

Analysis of segment number and enzyme variation in a centipede reveals a cryptic species, Geophilus easoni sp. nov., and raises questions about speciation

Geophilomorph centipedes provide an unusual opportunity to examine patterns of variation in segment number within extant species. (Most other arthropod species are invariant in this respect.) Recent work on several geophilomorph species has revealed latitudinal clines in segment number, but has generally not called into question the identities of the species themselves. However, analysis of a unique pattern of variation in British populations of Geophilus carpophagus Leach, coupled with other morphological and enzyme data, reveals a cryptic species, Geophilus easoni sp. nov. This species has not yet been detected on the European mainland. Four distinct hypotheses are advanced regarding the speciation event through which G. easoni arose and the phylogeographic processes that resulted in the present distributions of the two species in Britain. Further study will be necessary to test these hypotheses. In any event, G. carpophagus and G. easoni provide something that has until now been absent: a case study of the genetic differences between closely-related geophilomorph species.     

Evolution of oviposition strategies and speciation in the globeflower flies Chiastocheta spp. (Anthomyiidae)

Trollius europaeus (Ranunculaceae) is involved in an intimate interaction with several species of Chiastocheta flies (Anthomyiidae) that are both seed predators and pollinators. In this paper, we analyse the oviposition strategy of the six Chiastocheta species found to coexist on T. europaeus in 19 populations from the French Alps. We show that the species are not equivalent in their oviposition behaviour: C. rotundiventris usually deposits no more than one egg per flower in first-day flowers whereas C. dentifera aggregates its eggs on fruits and thus does not contribute to pollination at all; the four remaining species deposit eggs sequentially during the flowering period from the 2nd to the 7th day. Hence, the outcomes of the interaction in terms of net seed production for the plant greatly depend on the Chiastocheta species visiting it, ranging from a mutualistic to a purely parasitic interaction. We assessed mitochondrial divergence between Chiastocheta spp. by sequencing a 1320-bp mitochondrial DNA fragment. The low divergence observed between species (0–4.15%) suggests that genus diversification took place recently. Unlike in other plant–insect systems where diversification is usually thought to be driven by cospeciation or host shifts, we propose that Chiastocheta speciation took place within the host plant. Basal separation of a particularly mutualistic species provided favourable conditions for plant specialization on this seed-parasite as a pollinator early in the evolution of the association. The parasitic species ovipositing on fruits derived from a species ovipositing on flowers. Diversification of the intermediate strategies probably occurred in relation with the Pleistocene climatic events, reproductive isolation between species being reinforced by niche partitioning for oviposition and/or sexual selection.     

Evolution and speciation of cave-dwelling Fulgoroidea in the Canary Islands (Homoptera: Gixiidae and Meenoplidae)

Ten new cavernicolous Fulgoroidea species of the families Cixiidae and Meenoplidae are described from the Canary Islands: Cixius palmeros, C. pinarcoladus, C. ratonicus, C. tacandus, Memoplus claustrophilus from La Palma, C. ariadne, C. nycticolus, M. charon from El Hierro, and Tachycixius crypticus, T. retrusus from Tenerife. Notes on their ecology and distribution are given, and where possible, phylogenetic affinities to existing epigean species of the corresponding families are discussed. Despite the present-day relict status of the majority of cavernicolous species, it cannot be concluded with certainty whether their evolution has followed allopatric or parapatric modes of speciation.     

Assemblages of sea stars (Echinodermata: Asteroidea) and brittle stars (Echinodermata: Ophiuroidea) in the Weddell Sea (Antarctica) and off Northeast Greenland (Arctic): a comparison of diversity and abundance

Composition and distribution of asteroid and ophiuroid assemblages were investigated by means of Agassiz trawl catches at 34 stations in 220- to 1,200-m depth in the Weddell Sea and at 17 stations in 90- and 830-m depth off Northeast Greenland. A total of 86 species (48 sea stars, 38 brittle stars) were identified in the Weddell Sea whereas off Northeast Greenland a total of 26 species (16 sea stars, 10 brittle stars) were recorded. In both study areas, brittle stars were numerically more important than sea stars, and abundances generally decreased with water depths. Multivariate analyses revealed a conspicuous depth zonation of sea and brittle stars off Greenland. Very high abundances of Ophiocten sericeum and Ophiura robusta characterized the assemblages on shallow shelf banks whereas in greater depths Ophiopleura borealis, Ophioscolex glacialis and Ophiacantha bidentata became dominant, albeit at significantly lower densities. Mass occurrences of brittle stars, such as those recorded on Greenlandic shelf banks, have not been discovered in the Weddell Sea, where distinct assemblages were discriminated in deep shelf trenches as well as on the eastern and southern shelf. Ophioplocus incipiens, Ophiurolepis martensi and Ophiurolepis brevirima were the most prominent species on the eastern shelf. Ophiacantha antarctica, Ophiurolepis gelida and Ophionotus victoriae on the southern shelf, and Ophiosparte gigas as well as the asteriod Hymenaster sp., in the shelf trenches. Overall, the Weddell Sea housed conspicuously more asterozoan species than the waters off Greenland. Higher species diversity was also evident at both a regional and local scale, especially for the eastern Weddell Sea shelf. However, because many species from the Weddell Sea are closely related, the Weddell Sea assemblages were not significantly different from the Greenland ones in terms of taxonomic diversity and distinctness. Received: 29 April 1996/Accepted: 10 June 1996