Allopatric Diversification Research Articles

Alpine Crossroads or Origin of Genetic Diversity? Comparative Phylogeography of Two Sympatric Microgastropod Species

The Alpine Region, constituting the Alps and the Dinaric Alps, has played a major role in the formation of current patterns of biodiversity either as a contact zone of postglacial expanding lineages or as the origin of genetic diversity. In our study, we tested these hypotheses for two widespread, sympatric microgastropod taxa – Carychium minimum O.F. Müller, 1774 and Carychium tridentatum (Risso, 1826) (Gastropoda, Eupulmonata, Carychiidae) – by using COI sequence data and species potential distribution models analyzed in a statistical phylogeographical framework. Additionally, we examined disjunct transatlantic populations of those taxa from the Azores and North America. In general, both Carychium taxa demonstrate a genetic structure composed of several differentiated haplotype lineages most likely resulting from allopatric diversification in isolated refugial areas during the Pleistocene glacial periods. However, the genetic structure of Carychium minimum is more pronounced, which can be attributed to ecological constraints relating to habitat proximity to permanent bodies of water. For most of the Carychium lineages, the broader Alpine Region was identified as the likely origin of genetic diversity. Several lineages are endemic to the broader Alpine Region whereas a single lineage per species underwent a postglacial expansion to (re)colonize previously unsuitable habitats, e.g. in Northern Europe. The source populations of those expanding lineages can be traced back to the Eastern and Western Alps. Consequently, we identify the Alpine Region as a significant ‘hot-spot’ for the formation of genetic diversity within European Carychium lineages. Passive dispersal via anthropogenic means best explains the presence of transatlantic European Carychium populations on the Azores and in North America. We conclude that passive (anthropogenic) transport could mislead the interpretation of observed phylogeographical patterns in general.

Inverted patterns of genetic diversity in continental and island populations of the heather Erica scoparia s.l.

AbstractAim Using the heather Erica scoparia s.l. as a model, this paper aims to test theoretical predictions that island populations are genetically less diverse than continental ones and to determine the extent to which island and continental populations are connected by pollen‐ and seed‐mediated gene flow.Location Macaronesia, Mediterranean, Atlantic fringe of Europe.Methods Patterns of genetic diversity are described based on variation at two chloroplast DNA (cpDNA) loci and one nuclear DNA (nDNA) locus for 109 accessions across the entire distribution range of the species. Global patterns of genetic differentiation were investigated using principal coordinates analysis. Genetic differentiation between island and continental areas, estimations of pollen‐ and seed‐mediated gene flow, and the presence of phylogeographical signal were assessed by means of Fst/NST (continental scale) and Fij/Nij (local scale). Extant and past distribution ranges of the species were inferred from niche modelling using layers describing present and Last Glacial Maximum (LGM) macroclimatic conditions.Results The Azores exhibited a significantly higher genetic diversity than the continent. The lowest levels of genetic differentiation were observed between the Azores and the western Mediterranean, and the diversity observed in the Azores resulted from at least two colonization waves. Within the Azores, kinship coefficients showed a significant and much steeper decrease with geographical distance in the cpDNA than in the nDNA. The distribution predicted by LGM models was markedly different from the current potential distribution, particularly in western Europe, where no suitable areas were predicted by LGM models, and along the Atlantic coast of the African continent, where LGM models predicted highly suitable climatic conditions.Main conclusions The higher diversity observed in Azorean than in continental populations is inconsistent with MacArthur and Wilson’s equilibrium model and derived theoretical population genetic expectations. This inverted pattern may be the result of extinction on the continent coupled with multiple island colonization events and subsequent allopatric diversification and lineage hybridization in the Azores. The results highlight the role of allopatric diversification in explaining diversification on islands and suggest that this process has played a much more significant role in shaping Azorean biodiversity than previously thought.

Phylogeography and systematics of Acanthogammarus s. str., giant amphipod crustaceans from Lake Baikal

Daneliya, M. E., Kamaltynov, R. M. & Väinölä, R. (2011). Phylogeography and systematics of Acanthogammarus s. str., giant amphipod crustaceans from Lake Baikal. —Zoologica Scripta, 40, 623–637.To illustrate the dynamics of evolution of the rich endemic crustacean diversity in the ancient Siberian Lake Baikal, we explored the phylogenetic relationships and intralake phylogeographic structure in members of the genus Acanthogammarus Stebbing (Amphipoda, Gammaridea, Acanthogammaridae), which involves some of the most spectacular gigantic freshwater amphipods in the world. Mitochondrial cytochrome oxidase I gene sequence data gave only partial support to either of the recent competing views of systematic diversity. The three species Acanthogammarus victorii, Acanthogammarus maculosus and Acanthogammarus lappaceus along with a fourth, undescribed taxon endemic to the Ushkanii archipelago, made a monophyletic group corresponding to the subgenus Ancyracanthus. A sister relationship of the vicarious ‘subspecies’A. victorii and A. maculosus was not supported, rather the southerly A. victorii was basal to the cluster of the three other northerly, overlapping species. The data generally supported full species rank for the previously debated subspecies taxa, apart from the purported distinction between ‘Acanthogammarus longispinus’ and Acanthogammarus lappaceus, which seems to represent intraspecies morphological variation, partly related to sexual dimorphism. The sister status of Acanthogammarus godlewskii and A. gracilispinus (and thus subgenus Acanthogammarus) had weak support; reassessment of museum collections showed that they both are widespread and sympatric throughout the lake. The observed interspecies sequence differences were 13–22% (23–64% in terms of model‐based distance), suggesting divergence times of several million years under conventional calibrations, calling the applicability of external clocks into question. Strong patterns of intraspecific, intralake phylogeographic subdivision were found in A. lappaceus, A. maculosus and A. gracilispinus, each comprising several disjunct lineages with 1–5% divergence. Other species showed only slight differentiation. In all, the patterns of geographical differentiation were unique for each species, varying from moderate allele frequency differentiation to well‐established geographically segregated lineages, presumably of Early and Middle Pleistocene age. The patterns of differentiation in Acanthogammarus support an important role of allopatric diversification in the evolution of Lake Baikal fauna.

Evolution of the central Mediterranean Centaurea cineraria group (Asteraceae): Evidence for relatively recent, allopatric diversification following transoceanic seed dispersal

AbstractWe explored the spatiotemporal diversification of the Centaurea cineraria group based on AFLP fingerprints and plastid DNA sequences applied to a broad sampling of Central Mediterranean taxa of the Acrolophus subgroup. Despite its morphological distinctness, monophyly of the C. cineraria group was not supported by our data. A distinct lineage mostly re ‐ stricted to Sicily (the Sicily group) comprised some members of the C. cineraria group but also included C. parlatoris, assumed to be a member of the C. dissecta group. The relationships of the Sicily group with other members of the Acrolophus subgroup could not be clarified. Molecular dating supported recent, presumably allopatric diversification whose onset dates back to less than 250,000 years within the Sicily group. Tunisia, the Aeolian Islands and the Island Ventotene in the central Tyrrhenian Sea were likely colonised from Sicily. The young age of diversification within the Sicily group rejects land bridges between Africa and Sicily, which were only available during significantly older periods, in favour of transoceanic seed dispersal. Dispersal might have been favoured by low sea levels during cold stages of the Pleistocene. The molecular data indicate that taxonomy of the C. cineraria group needs to be revised..

DO GEOLOGICAL OR CLIMATIC PROCESSES DRIVE SPECIATION IN DYNAMIC ARCHIPELAGOS? THE TEMPO AND MODE OF DIVERSIFICATION IN SOUTHEAST ASIAN SHREWS

Geological and climatic processes potentially alter speciation rates by generating and modifying barriers to dispersal. In Southeast Asia, two processes have substantially altered the distribution of land. Volcanic uplift produced many new islands during the Miocene-Pliocene and repeated sea level fluctuations during the Pleistocene resulted in intermittent land connections among islands. Each process represents a potential driver of diversification. We use a phylogenetic analysis of a group of Southeast Asian shrews (Crocidura) to examine geographic and temporal processes of diversification. In general, diversification has taken place in allopatry following the colonization of new areas. Sulawesi provides an exception, where we cannot reject within-island speciation for a clade of eight sympatric and syntopic species. We find only weak support for temporally declining diversification rates, implying that neither volcanic uplift nor sea level fluctuations had a strong effect on diversification rates. We suggest that dynamic archipelagos continually offer new opportunities for allopatric diversification, thereby sustaining high speciation rates over long periods of time, or Southeast Asian shrews represent an immature radiation on a density-dependent trajectory that has yet to fill geographic and ecological space.

Reassessment of the taxonomy of Mesopodopsis orientalis (Tattersall, 1908) (Crustacea, Mysida) and proposal of a new species for the genus with an appendix on M. zeylanica Nouvel, 1954

The Indo‐Australasian mysid Mesopodopsis orientalis (Tattersall, 1908) has been recorded throughout the southwestern coast of India and the Philippines. As a result of its abundance, this mysid is regarded as one of the most important species of the shallow‐water crustacean community. Recent ecological studies of this conventionally identified species have revealed significant differences in certain life history features among populations, in particular between coastal and estuarine populations, which seemed to be associated with some differences in morphology. Following the examination of the syntypes and topotypes, the identity of M. orientalis was redefined, and a new species, M. tenuipes, was subsequently proposed on the basis of the further assessment of morphological and DNA analyses. At several sites, these two species coexist, although M. tenuipes usually inhabits inner estuaries or less haline waters compared with M. orientalis. Our analyses also suggest a possibly higher allopatric diversification within each lineage along their geographical transitions. In addition, earlier records of M. orientalis from India need to be reanalysed to rectify confusion with M. zeylanica Nouvel, 1954.

Paleodistributions and Comparative Molecular Phylogeography of Leafcutter Ants (Atta spp.) Provide New Insight into the Origins of Amazonian Diversity

The evolutionary basis for high species diversity in tropical regions of the world remains unresolved. Much research has focused on the biogeography of speciation in the Amazon Basin, which harbors the greatest diversity of terrestrial life. The leading hypotheses on allopatric diversification of Amazonian taxa are the Pleistocene refugia, marine incursion, and riverine barrier hypotheses. Recent advances in the fields of phylogeography and species-distribution modeling permit a modern re-evaluation of these hypotheses. Our approach combines comparative, molecular phylogeographic analyses using mitochondrial DNA sequence data with paleodistribution modeling of species ranges at the last glacial maximum (LGM) to test these hypotheses for three co-distributed species of leafcutter ants (Atta spp.). The cumulative results of all tests reject every prediction of the riverine barrier hypothesis, but are unable to reject several predictions of the Pleistocene refugia and marine incursion hypotheses. Coalescent dating analyses suggest that population structure formed recently (Pleistocene-Pliocene), but are unable to reject the possibility that Miocene events may be responsible for structuring populations in two of the three species examined. The available data therefore suggest that either marine incursions in the Miocene or climate changes during the Pleistocene—or both—have shaped the population structure of the three species examined. Our results also reconceptualize the traditional Pleistocene refugia hypothesis, and offer a novel framework for future research into the area.

Replaying the tape: recurring biogeographical patterns in Cape Verde Conus after 12 million years

Isolated oceanic islands are excellent natural laboratories to test the relative role of historical contingency and determinism in evolutionary diversification. Endemics of the marine venomous snail Conus in the Cape Verde archipelago were originated from at least two independent colonizations of 'small' and 'large' shelled species separated by 12 million years. In this study, we have reconstructed phylogenetic relationships within large-shelled Conus (C. ateralbus, C. pseudonivifer, C. trochulus, and C. venulatus) based on mitochondrial cox1 and nad4 haplotype sequences. The reconstructed molecular phylogeny revealed three well-supported and relatively divergent clades (A, B, and C) that do not correspond to current species classification based on shell colour and banding patterns. Clade A grouped specimens assigned either to C. pseudonivifer or C. trochulus, clade B is composed of specimens assigned to C. venulatus, and clade C comprises specimens assigned either to C. venulatus or C. ateralbus. Geometric morphometric analyses found significant differences between the radular teeth shape of C. pseudonivifer/C. trochulus and C. venulatus/C. ateralbus. In clades A and B, northwestern Boavista and Maio specimens cluster together to the exclusion of eastern Boavista samples. In Sal, populations form a monophyletic island assemblage (clade C). The large-shelled Conus have remarkably replicated biogeographical patterns of diversification of small-shelled Conus. Similar selective forces (i.e. nonplanktonic lecithotrophy with limited larval dispersal and allopatric diversification) together with repeated instances of low sea level stands during glacial maxima that allowed connection between islands, have overcome the effect of historical contingency, and explain the observed recurring biogeographical patterns.

Origin and diversification of the soldier meadow springsnails (Hydrobiidae: Pyrgulopsis), a species flock in the northwestern Great Basin, United States

ABSTRACTThe large, western North American hydrobiid gastropod genus Pyrgulopsis (commonly known as springsnails) includes a series of locally endemic faunas that are thought to be species flocks. Although these assemblages are of interest from the evolutionary, biogeographic and conservation perspectives, their monophyly and phylogenetic relationships have yet to be rigorously evaluated. Here we present a molecular phylogeny (based on mitochondrial sequence data) of a putative flock of four thermal spring-dwelling springsnails that is distributed in many sites in Soldier Meadow and a single locality in Bog Hot Valley (northwestern Nevada). Our analyses support monophyly of this assemblage (‘Soldier Meadow clade’) and a close relationship with other regional species and suggest that the invasion of thermal habitats by these springsnails occurred independently of other such radiations within the genus. The divergence of the Soldier Meadow clade relative to its sister group is substantial (6.79-10.36% for COI, 10.35-15.88% for NDI), suggesting a split in the early Pliocene, based on the application of a COI clock for Pyrgulopsis. The splits within the Soldier Meadow clade into three main subunits also appear to be old events, based on their 5.78-8.54% COI divergence relative to each other. These findings are consistent with a long history of springsnail evolution in Soldier Meadow, which is intriguing given that this basin was flooded by Lake Lahontan during periods of the early and middle Pleistocene. We suggest that progenitors of the contemporary fauna survived in high elevation springs that may have been present in the basin during these pluvial periods and subsequently colonized contemporary habitats following the termination of the extreme Lake Lahontan highstands. We speculate that the broadly disjunct population (of P. militaris) in Bog Hot Valley, which is consistently nested within the Soldier Meadow clade in our phylogenetic analyses, is either a vicariant relict of a spring zone that may have once extended between these two areas; or was founded by a past ‘jump’ dispersal event from Soldier Meadow. Phylogeographic structure of springsnail populations in Soldier Meadow bears the strong stamp of geologically recent, allopatric diversification, perhaps reflecting the short time that basin floor habitats have been occupied. We describe a new species (P. varneri) for a series of recently discovered populations that are monophyletic, substantially divergent and morphologically distinctive. Additional studies will be necessary to confidently assess the taxonomic status of morphologically distinctive P. limaria and P. umbilicata, which are shown herein to be little divergent genetically; and a recently discovered minute springsnail that is morphologically divergent yet closely similar genetically to P. notidicola.

CONTRASTING PATTERNS AND PROCESSES OF EVOLUTIONARY CHANGE IN THE TARWEED–SILVERSWORD LINEAGE: REVISITING CLAUSEN, KECK, AND HIESEY'S FINDINGS1

Abstract Jens C. Clausen, David D. Keck, and William M. Hiesey's biosystematic research on continental tarweeds (Madiinae; Compositae) provided diverse examples of evolutionary change for Clausen's synthesis, Stages in the Evolution of Plant Species. Subsequent anatomical work by Sherwin Carlquist demonstrated that the tarweed lineage also includes a spectacular example of adaptive radiation, the Hawaiian silversword alliance. Molecular phylogenetic data and evidence from genetic and hybridization studies have allowed additional perspectives on Clausen et al.'s and Carlquist's hypotheses of tarweed–silversword evolution. In Californian Layia, Clausen et al.'s evidence for gradual allopatric diversification for the n = 7 taxa accords with patterns of molecular divergence and decay of interfertility across lineages inferred from a rate-constant rDNA tree. In contrast, recent evidence on patterns and timing of diversification in an n = 8 Layia clade indicates multiple examples of accelerated phenotypic evolu...

Variación del color de flores y números cromosómicos en el noroeste del área de distribución de <i>Turnera sidoides</i> (Turneraceae)

En el marco de los estudios evolutivos que se desarrollan en el complejo autopoliploide Turnera sidoides (x= 7) se realizó un muestreo sistemático en el noroeste de su área de distribución. Se hallaron 6 poblaciones con flores de color salmón y 35 con flores amarillas de la subsp. pinnatifida. La distribución de estas poblaciones está asociada con variables climáticas y espaciales. Las poblaciones que presentan flores de color salmón viven en los bosques semiáridos (Provincia Biogeográfica del Chaco Boreal) y las de flores amarillas en los valles interandinos (Provincia Biogeográfica Boliviano-Tucumana). Todas las poblaciones analizadas son diploides. Los resultados obtenidos sustentan el modelo de diversificación alopátrica de las poblaciones con diferente color de flores a nivel diploide, probablemente favorecido por el sistema de barreras orográficas y los cambios climáticos surgidos a partir del levantamiento de los Andes y de las glaciaciones del Cuaternario. Además, el análisis evidencia que el noroeste del área de T. sidoides constituye un importante centro de variación de la subsp. pinnatifida y es el mayor centro de diploides hasta ahora detectado

Evolution and Phylogeography of Arctic and Alpine Plants in Europe: Introduction

of the Arctic and alpine floras of has intrigued botanists for many decades. After formation of the European mountain system and world-wide climatic cooling during Late Tertiary, the evolution and radiation of the modem European arctic and alpine floras began. Geographic influences from central Asia, plus ancient Arctic and European elements, can be documented in plant diversity that now resides in our modem mountain systems. It has been shown that alloand autopolyploidy have been important evolutionary mechanisms. It has been hypothesized that recent evolutionary events have been driven by recurrent cycles of Quaternary glaciations, leading to formation of new species plus diversification (and divergence) of evolutionary lineages. Molecular methods offer new possibilities for studying the evolution of Arctic and alpine plant diversity in Europe. In particular, it is now possible to test hypotheses more effectively that deal with refugia, re-migrations, and survival on nunataks deriving from Pleistocene glaciations. In September 2002 at the Sixth International Congress of Systematic and Evolutionary Biology (ICSEB-VI) in Patras, Greece, a symposium entitled Evolution and Phylogeography of Arctic and Alpine Plants in Europe and organized by Andreas Tribsch and Tod F. Stuessy, was sponsored by the International Association for Plant Taxonomy (IAPT). The aim of the symposium was to provide an overview of recent studies on the mountain floras of Europe, ranging from Arctic and subarctic regions to the southern mountains. Evolutionary patterns and inferred processes are explored that involve infraspecific phylogeographic diversification, evolution of alpine species, and radiation of genera. Five invited presentations, which are featured here, were complemented by three papers and several posters. The success of the symposium and the importance of the collective synthesis recommended that the main contributions be published together. This issue of Taxon features those five papers. Christian Brochmann and co-authors present an overview of several phylogeographical studies that tackle in the North Atlantic biota the challenging question: Glacial survival or tabula rasa? Phylogeographical evidence from several taxa distributed in the North Atlantic r gion suggest that it is not necessary to assume glacial survival on nunataks to explain extant patterns. Endemism and disjunct distributions correlate to a large degree. All endemic taxa (except one) are polyploid, suggesting recent, even postglacial, origin. The observed patterns are in strong contrast to those of more southern latitudes, where vicariance during the ice ages has lead to partly strong phylogeographical patterns, evolutionary divergence of lineages, and remarkable patterns of endemism also on the diploid level. The second paper by Hans Peter Comes and coauthors reviews phylogeographic data from several European mountain taxa, both within and between species, to provide insights on the origin and evolution of the European high mountain flora. Results are congruent with hypotheses of evolution of alpine species from lowland forms from Asia and the Mediterranean region in the late Tertiary and allopatric diversification during the Quaternary. Pablo Vargas in the third paper reviews phylogenetic data from several oro-mediterranean taxa and gives a preliminary synthesis with special emphasis on the Iberian peninsula. The data document that modes of speciation and colonization routes are different in all taxa. While some taxa diversified in the mountain ranges of the Iberian peninsula and immigrated to other parts of Europe, others immigrated to the Iberian mountains from the outside. In any case at least at the infraspecific level, diversifications are dated to the Quaternary ice ages. A comparison of patterns of endemism and phylogeographic patterns in the Alps with presumed Pleistocene refugia is central in the fourth paper by Andreas Tribsch and Peter Sch6nswetter. For the Eastern Alps available paleontological and paleoclimatological data suggest that in some regions cold-adapted plants survived the Pleistocene in situ, although large areas were glaciated. Potential glacial refugia are at the eastern and southern margin of the Alps, which remained widely unglaciated, but also within the ice shield on peripheral nunataks. Refugial areas are characterized by high levels

HISTORICAL ISOLATION, RANGE EXPANSION, AND SECONDARY CONTACT OF TWO HIGHLY DIVERGENT MITOCHONDRIAL LINEAGES IN SPOTTED SALAMANDERS (AMBYSTOMA MACULATUM)

The high species diversity of aquatic and terrestrial faunas in eastern North America has been attributed to range reductions and allopatric diversification resulting from historical climate change. The role these processes may have played in speciation is still a matter of considerable debate; however, their impacts on intraspecific genetic structure have been well documented. We use mitochondrial DNA sequences to reconstruct an intraspecific phylogeny of the widespread North American spotted salamander, Ambystoma maculatum, and test whether phylogenetic patterns conform to regional biogeographical hypotheses about the origins of diversity in eastern North America. Specifically, we address the number and locations of historical refugia, the extent and patterns of postglacial colonization by divergent lineages, and the origin and affinities of populations in the Interior Highland region. Despite apparent morphological uniformity, genetic discontinuities throughout the range of this species suggest that populations were historically fragmented in at least two refugia in the southern Appalachian Mountains. The ranges of these two highly divergent clades expanded northward, resulting in two widely distributed lineages that are sympatric in regions previously proposed as suture zones for other taxa. The evolutionary history of spotted salamander populations underscores the generality of biogeographical processes in eastern North America: despite differences in population size, glacial refugia, and vagility, similar signatures of differentiation are evident among and within widespread taxa.

The role of parasites in sympatric and allopatric host diversification.

Exploiters (parasites and predators) are thought to play a significant role in diversification, and ultimately speciation, of their hosts or prey. Exploiters may drive sympatric (within-population) diversification if there are a variety of exploiter-resistance strategies or fitness costs associated with exploiter resistance. Exploiters may also drive allopatric (between-population) diversification by creating different selection pressures and increasing the rate of random divergence. We examined the effect of a virulent viral parasite (phage) on the diversification of the bacterium Pseudomonas fluorescens in spatially structured microcosms. Here we show that in the absence of phages, bacteria rapidly diversified into spatial niche specialists with similar patterns of diversity across replicate populations. In the presence of phages, sympatric diversity was greatly reduced, as a result of phage-imposed reductions in host density decreasing competition for resources. In contrast, allopatric diversity was greatly increased as a result of phage-imposed selection for resistance, which caused populations to follow divergent evolutionary trajectories. These results show that exploiters can drive diversification between populations, but may inhibit diversification within populations by opposing diversifying selection that arises from resource competition.