Biogeography of the Monimiaceae (Laurales): a role for East Gondwana and long‐distance dispersal,but not West Gondwana

Aim The biogeography of the tropical plant family Monimiaceae has long been thought to reflect the break‐up of West and East Gondwana, followed by limited transoceanic dispersal. Location Southern Hemisphere, with fossils in East and West Gondwana. Methods We use phylogenetic analysis of DNA sequences from 67 of the c. 200 species, representing 26 of the 28 genera of Monimiaceae, and a Bayesian relaxed clock model with fossil prior constraints to estimate species relationships and divergence times. Likelihood optimization is used to infer switches between biogeographical regions on the highest likelihood tree. Results Peumus from Chile, Monimia from the Mascarenes and Palmeria from eastern Australia/New Guinea form a clade that is sister to all other Monimiaceae. The next‐deepest split is between the Sri Lankan Hortonia and the remaining genera. The African Monimiaceae, Xymalos monospora, then forms the sister clade to a polytomy of five clades: (I) Mollinedia and allies from South America; (II) Tambourissa and allies from Madagascar and the Mascarenes; (III) Hedycarya, Kibariopsis and Leviera from New Zealand, New Caledonia and Australia; (IV) Wilkiea, Kibara, Kairoa; and (V) Steganthera and allies, all from tropical Australasia. Main conclusions Tree topology, fossils, inferred divergence times and ances‐tral area reconstruction fit with the break‐up of East Gondwana having left a still discernible signature consisting of sister clades in Chile and Australia. There is no support for previous hypotheses that the break‐up of West Gondwana (Africa/South America) explains disjunctions in the Monimiaceae. The South American Mollinedia clade is only 28–16 Myr old, and appears to have arrived via trans‐Pacific dispersal from Australasia. The clade apparently spread in southern South America prior to the Andean orogeny, fitting with its first‐diverging lineage (Hennecartia) having a southern‐temperate range. The crown ages of the other major clades (II–V) range from 20 to 29 Ma, implying over‐water dispersal between Australia, New Caledonia, New Zealand, and across the Indian Ocean to Madagascar and the Mascarenes. The endemic genus Monimia on the Mascarenes provides an interesting example of an island lineage being much older than the islands on which it presently occurs.     

Tri-locus sequence data reject a “Gondwanan origin hypothesis” for the African/South Pacific crab genus Hymenosoma

Crabs of the family Hymenosomatidae are common in coastal and shelf regions throughout much of the southern hemisphere. One of the genera in the family, Hymenosoma, is represented in Africa and the South Pacific (Australia and New Zealand). This distribution can be explained either by vicariance (presence of the genus on the Gondwanan supercontinent and divergence following its break-up) or more recent transoceanic dispersal from one region to the other. We tested these hypotheses by reconstructing phylogenetic relationships among the seven presently-accepted species in the genus, as well as examining their placement among other hymenosomatid crabs, using sequence data from two nuclear markers (Adenine Nucleotide Transporter [ANT] exon 2 and 18S rDNA) and three mitochondrial markers (COI, 12S and 16S rDNA). The five southern African representatives of the genus were recovered as a monophyletic lineage, and another southern African species, Neorhynchoplax bovis, was identified as their sister taxon. The two species of Hymenosoma from the South Pacific neither clustered with their African congeners, nor with each other, and should therefore both be placed into different genera. Molecular dating supports a post-Gondwanan origin of the Hymenosomatidae. While long-distance dispersal cannot be ruled out to explain the presence of the family Hymenosomatidae on the former Gondwanan land-masses and beyond, the evolutionary history of the African species of Hymenosoma indicates that a third means of speciation may be important in this group: gradual along-coast dispersal from tropical towards temperate regions, with range expansions into formerly inhospitable habitat during warm climatic phases, followed by adaptation and speciation during subsequent cooler phases.     

Embryology and relationships ofGyrocarpus andHernandia (Hernandiaceae)

Two representative genera of Hernandiaceae,Gyrocarpus andHernandia, were investigated embryologically to contribute to a better understanding of their respective evolutionary position. Comparisons with other lauralean families using Chloranthaceae or Annonaceae (as a representative of Magnoliales) as an outgroup of Laurales (if present, plus other related taxa) support a lauraceous affinity for the two genera because of the presence of ramified raphal vascular bundles at the chalaza (a synapomorphy), but do not provide evidence for the separation of Hernandiaceae from Lauraceae.Hernandia rather shares with Lauraceae two apomorphies (i.e., the seed pachychalazy and the ruminate seed) which may be homoplasies judged from results of cladistic and molecular studies published elsewhere.Hernandia is greatly divergent from an ancestral line common withGyrocarpus and is even diversified within the genus. Based on evidence from embryology as well as from other sources, it seems best to accept two separate subfamilies in Hernandiaceae as usually have been accepted: one is a derived subfamily Hernandioideae, and the other a less specialized Gyrocarpoideae.     

‘Out‐of‐Africa’ dispersal of tropical floras during the Miocene climatic optimum: evidence from Uvaria (Annonaceae)

Aim African–Asian disjunctions are common in palaeotropical taxa, and are typically explained by reference to three competing hypotheses: (1) ‘rafting’ on the Indian tectonic plate, enabling Africa‐to‐Asia dispersal; (2) migration via Eocene boreotropical forests; and (3) transoceanic long‐distance dispersal. These hypotheses are tested using Uvaria (Annonaceae), which is distributed in tropical regions of Africa, Asia and Australasia. Recent phylogenetic reconstructions of the genus show a clear correlation with geographical provenance, indicating a probable origin in Africa and subsequent dispersal to Asia and then Australasia. Ancestral areas and migration routes are inferred and compared with estimates of divergence times in order to distinguish between the prevailing dispersal hypotheses. Location Palaeotropics. Methods Divergence times in Uvaria are estimated by analysing the sequences of four DNA regions (matK, psbA–trnH spacer, rbcL and trnL–F) from 59 Uvaria species and 77 outgroup species, using a Bayesian uncorrelated lognormal (UCLD) relaxed molecular clock. The ancestral area of Uvaria and subsequent dispersal routes are inferred using statistical dispersal–vicariance analysis (s‐diva ). Results Uvaria is estimated to have originated in continental Africa 31.6 Ma [95% highest posterior density (HPD): 38.4–25.1 Ma] between the Middle Eocene and Late Oligocene. Two main migration events during the Miocene are identified: dispersal into Madagascar around 17.0 Ma (95% HPD: 22.3–12.3 Ma); and dispersal into Asia between 21.4 Ma (95% HPD: 26.7–16.7 Ma) and 16.1 Ma (95% HPD: 20.1–12.1 Ma). Main conclusions Uvaria fruits are widely reported to be consumed by primates, and are therefore unlikely candidates for successful long‐distance transoceanic dispersal. The other biogeographical hypotheses, involving rafting on the Indian tectonic plate, and dispersal via the European boreotropical forests associated with the Eocene thermal maximum, can be discounted due to incongruence with the divergence time estimates. An alternative scenario is suggested, involving dispersal across Arabia and central Asia via the tropical forests that developed during the late Middle Miocene thermal maximum (17–15 Ma), associated with the ‘out‐of‐Africa’ dispersal of primates. The probable route and mechanism of overland dispersal between Africa and Asia for tropical plant groups during the Miocene climatic optimum are clarified based on the Uvaria data.     

Out of Africa? A dated molecular phylogeny of the cicada tribe Platypleurini Schmidt (Hemiptera: Cicadidae), with a focus on African genera and the genus Platypleura Amyot & Audinet‐Serville

The Platypleurini is a large group of charismatic cicadas distributed from Cape Agulhas in South Africa, through tropical Africa, Madagascar, India and eastern Asia to Japan, with generic diversity concentrated in equatorial and southern Africa. This distribution suggests the possibility of a Gondwanan origin and dispersal to eastern Asia from Africa or India. We used a four‐gene (three mitochondrial) molecular dataset, fossil calibrations and molecular clock information to explore the phylogenetic relationships of the platypleurine cicadas and the timing and geography of their diversification. The earliest splits in the tribe were found to separate forest genera in Madagascar and equatorial Africa from the main radiation, and all of the Asian/Indian species sampled formed a younger clade nested well within the African taxa. The tribe appears to have diversified during the Cenozoic, beginning c. 50–32 Ma, with most extant African lineages originating in the Miocene or later, well after the breakup of the Gondwanan landmass. Biogeographical analysis suggests an African origin for the tribe and a single dispersal event founding the Asian platypleurines, although additional taxon sampling and genetic data will be needed to confirm this pattern because key nodes in the tree are still weakly supported. Two Platypleurini genera from Madagascar (Pycna Amyot & Audinet‐Serville, Yanga Distant) are found to have originated by late Miocene dispersal of a single lineage from Africa. The genus Platypleura is recovered as polyphyletic, with Platypleura signifera Walker from South Africa and many Asian/Indian species apparently requiring assignment to different genera, and a new Platypleura concept is proposed with the synonymization of Azanicada Villet syn.n. The genera Orapa Distant and Hamza Distant, currently listed within separate tribes but suspected of platypleurine affinity, are nested deeply within the Platypleurini radiation. The tribe Orapini syn.n . is here synonymized while the tribe Hamzini is pending a decision of the ICZN to preserve nomenclatorial stability.     

From the Neotropics to the Namib: evidence for rapid ecological divergence following extreme long‐distance dispersal

Extreme long‐distance dispersal is an important process in plant biogeography. Such events can lead to rapid diversification due to founder effects, genetic drift and novel selection in recipient environments. Balloon vines (Cardiospermum spp.) are mainly Neotropical, but include two native southern African species, the endemic desert‐adapted C. pechuelii and the moist subtropical C. corindum (which also occurs in the Neotropics). We used phylogenetic approaches (internal transcribed spacer (ITS), rpl32 and trnL‐trnF DNA sequencing data) and population genetics (amplified fragment length polymorphism (AFLP) analyses) to confirm the long‐distance dispersal of C. corindum to southern Africa and to reveal the subsequent divergence of the morphologically and ecologically extreme but genetically close C. pechuelii. We could not judge whether incongruences between ecological requirements and morphology and gene trees for the African species resulted from ongoing gene flow or incomplete lineage sorting, but our findings do support recent divergence of C. pechuelii from C. corindum in Africa following transoceanic dispersal of the lineage. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 477–486.     

Biogeographical history of cuckoo‐shrikes (Aves: Passeriformes): transoceanic colonization of Africa from Australo‐Papua

Aim Cuckoo‐shrikes and allies (Campephagidae) form a radiation of birds widely distributed in the Indo‐Pacific and Africa. Recent studies on the group have been hampered by poor taxon sampling, causing inferences about systematics and biogeography to be rather speculative. With improved taxon sampling and analyses within an explicit spatiotemporal framework, we elucidate biogeographical patterns of dispersal and diversification within this diverse clade of passerine birds. Location Africa, Asia, Australo‐Papua, the Pacific, the Philippines and Wallacea. Methods We use model‐based phylogenetic methods (Mr Bayes and garli ) to construct a phylogenetic hypothesis of the core Campephagidae (Campephagidae with the exclusion of Pericrocotus). The phylogeny is used to assess the biogeographical history of the group with a newly developed Bayesian approach to dispersal–vicariance analysis (Bayes‐diva) . We also made use of a partitioned beast analysis, with several calibration points taken from island ages, passerine mitochondrial substitution rates and secondary calibration points for passerine birds, to assess the timing of diversification and dispersal. Results We present a robust molecular phylogeny that includes all genera and 84% of the species within the core Campephagidae. Furthermore, we estimate divergence dates and ancestral area relationships. We demonstrate that Campephagidae originated in Australo‐Papua with a single lineage (Pericrocotus) dispersing to Asia early. Later, there was further extensive transoceanic dispersal from Australo‐Papua to Africa involving lineages within the core Campephagidae radiation. Main conclusions The phylogenetic relationships, along with the results of the ancestral area analysis and the timing of dispersal events, support a transoceanic dispersal scenario from Australo‐Papua to Africa by the core Campephagidae. The sister group to core Campephagidae, Pericrocotus, dispersed to mainland Asia in the late Oligocene. Asia remained uncolonized by the core Campephagidae until the Pliocene. Transoceanic dispersal is by no means an unknown phenomenon, but our results represent a convincing case of colonization over a significant water gap of thousands of kilometres from Australo‐Papua to Africa.     

Historical biogeography and phenotype‐phylogeny of Chroodiscus (lichenized Ascomycota: Ostropales: Graphidaceae)

Aim To analyse the historical biogeography of the lichen genus Chroodiscus using a phenotype‐based phylogeny in the context of continental drift and evolution of tropical rain forest vegetation. Location All tropical regions (Central and South America, Africa, India, Southeast Asia, north‐east Australia). Methods We performed a phenotype‐based phylogenetic analysis and ancestral character state reconstruction of 14 species of the lichen genus Chroodiscus, using paup * and mesquite ; dispersal–vicariance analysis (DIVA) and dispersal–extinction–cladogenesis (DEC) modelling to trace the geographical origin of individual clades; and ordination and clustering by means of pc‐ord , based on a novel similarity index, to visualize the biogeographical relationships of floristic regions in which Chroodiscus occurs. Results The 14 species of Chroodiscus show distinctive distribution patterns, with one pantropical and one amphi‐Pacific taxon and 12 species each restricted to a single continent. The genus comprises four clades. DIVA and DEC modelling suggest a South American origin of Chroodiscus in the mid to late Cretaceous (120–100 Ma), with subsequent expansion through a South American–African–Indian–Southeast Asian–Australian dispersal route and late diversification of the argillaceus clade in Southeast Asia. Based on the abundance of extant taxa, the probability of speciation events in Chroodiscus is shown to be extremely low. Slow dispersal of foliicolous rain forest understorey lichens is consistent with estimated phylogenetic ages of individual species and with average lengths of biological species intervals in fungi (10–20 Myr). Main conclusions The present‐day distribution of Chroodiscus can be explained by vicariance and mid‐distance dispersal through the interconnection or proximity of continental shelves, without the need for recent, trans‐oceanic long‐distance dispersal. Phylogenetic reconstruction and age estimation for Chroodiscus are consistent with the ‘biotic ferry’ hypothesis: a South American origin and subsequent eastward expansion through Africa towards Southeast Asia and north‐eastern Australia via the Indian subcontinent. The present‐day pantropical distributions of many clades and species of foliicolous lichens might thus be explained by eastward expansion through continental drift, along with the evolution of modern rain forests starting 120 Ma, rather than by the existence of a hypothetical continuous area of pre‐modern rain forest spanning South America, Africa and Southeast Asia during the mid and late Cretaceous.     

POPULATION STRUCTURE AND SPECIATION IN TROPICAL SEAS: GLOBAL PHYLOGEOGRAPHY OF THE SEA URCHIN DIADEMA

Abstract.— The causes of speciation in the sea are rarely obvious, because geographical barriers are not conspicuous and dispersal abilities or marine organisms, particularly those of species with planktonic larvae, are hard to determine. The phylogenetic relations of species in cosmopolitan genera can provide information on the likely mode of their formation. We reconstructed the phylogeny of the pantropical and subtropical sea urchin genus Diadema, using sequences of mitochondrial DNA from 482 individuals collected around the world, to determine the efficacy of barriers to gene flow and to ascertain the history of possible dispersal and vicariance events that led to speciation. We also compared 22 isozyme loci between all described species except D. palmeri. The mitochondrial DNA data show that the two deepest lineages are found in the Indian and West Pacific Oceans. (Indo‐Pacific) Diadema setosum diverged first from all other extant Diadema, probably during the initiation of wide fluctuations in global sea levels in the Miocene. The D. setosum clade then split 3‐5 million years ago into two clades, one found around the Arabian Peninsula and the other in the Indo‐West Pacific. On the lineage leading to the other species of Diadema, the deepest branch is composed of D. palmeri, apparently separated when the climate of New Zealand became colder and other tropical echinoids at these islands went extinct. The next lineage to separate is composed of a currently unrecognized species of Diadema that is found at Japan and the Marshall Islands. Diadema mexicanum in the eastern Pacific separated next, whereas D. paucispinum, D. savignyi, and D. antillarum from the western and central Atlantic, and (as a separate clade) D. antillarum from the eastern Atlantic form a shallow polytomy. Apparently, Indo‐Pacific populations of Diadema maintained genetic contact with Atlantic ones around the southern tip of Africa for some time after the Isthmus of Panama was complete. Diadema paucispinum contains two lineages: D. paucispinum sensu stricto is not limited to Hawaii as previously thought, but extends to Easter Island, Pitcairn, and Okinawa; A second mitochondrial clade of D. paucispinum extends from East Africa and Arabia to the Philippines and New Guinea. A more recent separation between West Indian Ocean and West Pacific populations was detected in D. setosum. Presumably, these genetic discontinuities are the result of water flow restrictions in the straits between northern Australia and Southeast Asia during Pleistocene episodes of low sea level. Diadema savignyi is characterized by high rates of gene flow from Kiribati in the central Pacific all the way to the East African Coast. In the Atlantic, there is a biogeographic barrier between the Caribbean and Brazil, possibly caused by fresh water outflow from the Amazon and the Orinoco Rivers. Diadema antillarum populations of the central Atlantic islands of Ascension and St. Helena are genetically isolated and phylogenetically derived from Brazil. Except for its genetic separation by the mid‐Atlantic barrier, Diadema seems to have maintained connections through potential barriers to dispersal (including the Isthmus of Panama) more recently than did Eucidaris or Echinometra, two other genera of sea urchins in which phylogeography has been studied. Nevertheless, the mtDNA phylogeography of Diadema includes all stages expected from models of allopatric differentiation. There are anciently separated clades that now overlap in their geographic distribution, clades isolated in the periphery of the genus range that have remained in the periphery, clades that may have been isolated in the periphery but have since spread towards the center, closely related clades on either side of an existing barrier, and closely related monophyletic entities on either side of an historical barrier that have crossed the former barrier line, but have not attained genetic equilibrium. Except for D. paucispinum and D. savignyi, in which known hybridization may have lodged mtDNA from one species into the genome of the other, closely related clades are always allopatric, and only distantly related ones overlap geographically. Thus, the phylogenetic history and distribution of extant species of Diadema is by and large consistent with allopatric speciation.     

Out of Africa: Biogeography and diversification of the pantropical pond skater genus Limnogonus Stål, 1868 (Hemiptera: Gerridae)

Gondwanan vicariance, long‐distance dispersal (LDD), and boreotropical migration have been proposed as alternative hypotheses explaining the pantropical distribution pattern of organisms. In this study, the historical biogeography of the pond skater genus Limnogonus was reconstructed to evaluate the impact of biogeographical scenarios in shaping their modern transoceanic disjunction. We sampled almost 65% of recognized Limnogonus species. Four DNA fragments including 69 sequences were used to reconstruct a phylogram. Divergence time was estimated using a Bayesian relaxed clock method and three fossil calibrations. Diversification dynamics and ancestral area reconstruction were investigated by using maximum likelihood and Bayesian approaches. Our results showed the crown group of Limnogonus originated and diversified in Africa in the early Eocene (49 Ma, HPD: 38–60 Ma), subsequently expanding into other regions via dispersal. The colonization of the New World originated from the Oriental Region probably via the Bering Land Bridge in the late Eocene. Two split events between the Old World and New World were identified: one between Neotropics and Oriental region around the middle Oligocene (30 Ma, HPD: 22–38 Ma), and the other between Neotropics and Africa during the middle Miocene (14 Ma, HPD: 8–21 Ma). The evolutionary history of Limnogonus involved two biogeographical processes. Gondwanan vicariance was not supported in our analyses. The diversification of Limnogonus among Africa, Oriental, and Neotropical regions corresponded with the age of land bridge connection and dispersed as a member associated with the broad boreotropical belt before local cooling (34 Ma). The current transoceanic disjunctions in Limnogonus could be better explained by the disruption of “mixed‐mesophytic” forest belt; however, the direct transoceanic LDD between the Neotropics and Africa could not be ruled out. In addition, the “LDD” model coupled with island hopping could be a reasonable explanation for the diversification of the Oriental and Australian regions during the Oligocene.     

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

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

Molecular biogeography and origins of the Hawaiian fern flora

Located approximately 4000 km from the nearest continent, the Hawaiian Islands comprise the most isolated archipelago on Earth. This isolation has resulted in a unique flora that includes nearly 200 native ferns and lycophytes, 77% of which are endemic to the islands. Because the Hawaiian Islands are volcanic in origin, all abiotically dispersed organisms must have arrived there via the wind or the water. Fern spores are most likely dispersed through the air, and thus patterns of air movement have undoubtedly played a significant role in determining the geographic origins of the ancestors of the Hawaiian ferns. We have identified four possible climate-based or weather-based spore dispersal hypotheses that could have resulted in the movement of ancestral spores to the Hawaiian Islands: (1) the northern subtropical jetstream, moving spores from Indo-Pacific regions; (2) the trade winds, dispersing spores from Central and North America; (3) storms carrying spores from southern Mexico and/or Central America; and (4) a dispersal mechanism carrying spores from the South Pacific across the equator resulting from the combined influence of a seasonal southern shift of the Intertropical Convergence Zone (ITCZ), Hadley Cell air movement, and the trade winds. Utilizing recently published molecular phylogenetic studies of three fern genera (Dryopteris, Polystichum, andHymenophyllum) and new analyses of three additional genera (Adenophorus, Grammitis, andLellingeria), each of which is represented in the Hawaiian Islands by at least one endemic lineage, we reviewed the biogeographical implications for the Hawaiian taxa in light of the possible common dispersal patterns and pathways. We hypothesize that three of the five endemicDryopteris lineages, both of the endemicPolystichum lineages, at least one endemicHymenophyllum lineage in the Hawaiian Islands, and, perhaps, one endemicGrammitis lineage resulted from ancestral spores of each lineage dispersing to the Hawaiian Islands via the northern subtropical jetstream.Adenophorus is sister to a mostly neotropical clade, therefore, it is likely that the ancestor of the Hawaiian clade dispersed to the Hawaiian Islands via the trade winds or a storm system. The ancestor of the endemicLellingeria lineage may have dispersed to the Hawaiian Islands from the neotropics via the trade winds or a storm system, or from the South Pacific across the equator through the combination of a seasonal southern shift of the ITCZ, Hadley Cells, and the trade winds.     

Phylogeography of Ptychadena mascareniensis suggests transoceanic dispersal in a widespread African-Malagasy frog lineage

Aim The Mascarene ridged frog, Ptychadena mascareniensis, is the only African amphibian species thought to occur on Madagascar and on the Seychelles and also Mascarene islands. We explored its phylogenetic relationships and intraspecific genetic differentiation to contribute to the understanding of transoceanic dispersal in amphibians. Methods Fragments of the mitochondrial 16S rRNA gene were sequenced from specimens collected over most of the distribution area of P. mascareniensis, including populations from Madagascar, Mascarenes and Seychelles. Results We identified five deeply divergent clades having pairwise divergences >5%, which probably all represent cryptic species in a P. mascareniensis complex. One of these seems to be restricted to Madagascar, the Mascarenes and the Seychelles. Sequences obtained from topotypic material (Réunion) were identical to the most widespread haplotype from Madagascar. The single Mauritian/Seychellean haplotype differed by only one mutation from a Malagasy haplotype. Main conclusions It is likely that the Mascarene and Seychellean populations were introduced from Madagascar by humans. In contrast, the absence of the Malagasy haplotypes from Africa and the distinct divergences among Malagasy populations (16 mutations in one divergent hapolotype from northern Madagascar) suggest that Madagascar was populated by Ptychadena before the arrival of humans c. 2000 years ago. Because Madagascar has been separated from Africa since the Jurassic, this colonization must have taken place by overseas rafting, which may be a more widespread dispersal mode in amphibians than commonly thought.     

Out of the Orient: Post‐Tethyan transoceanic and trans‐Arabian routes fostered the spread of Baorini skippers in the Afrotropics

The origin of taxa presenting a disjunct distribution between Africa and Asia has puzzled biogeographers for more than a century. This biogeographic pattern has been hypothesized to be the result of transoceanic long‐distance dispersal, Oligocene dispersal through forested corridors, Miocene dispersal through the Arabian Peninsula or passive dispersal on the rifting Indian plate. However, it has often been difficult to pinpoint the mechanisms at play. We investigate biotic exchange between the Afrotropics and the Oriental region during the Cenozoic, a period in which geological changes altered landmass connectivity. We use Baorini skippers (Lepidoptera, Hesperiidae) as a model, a widespread clade of butterflies in the Old World tropics with a disjunct distribution between the Afrotropics and the Oriental region. We use anchored phylogenomics to infer a robust evolutionary tree for Baorini skippers and estimate divergence times and ancestral ranges to test biogeographic hypotheses. Our phylogenomic tree recovers strongly supported relationships for Baorini skippers and clarifies the systematics of the tribe. Dating analyses suggest that these butterflies originated in the Oriental region, Greater Sunda Islands, and the Philippines in the early Miocene c. 23 Ma. Baorini skippers dispersed from the Oriental region towards Africa at least five times in the past 20 Ma. These butterflies colonized the Afrotropics primarily through trans‐Arabian geodispersal after the closure of the Tethyan seaway in the mid‐Miocene. Range expansion from the Oriental region towards the African continent probably occurred via the Gomphotherium land bridge through the Arabian Peninsula. Alternative scenarios invoking long‐distance dispersal and vicariance are not supported. The Miocene climate change and biome shift from forested areas to grasslands possibly facilitated geodispersal in this clade of butterflies.     

GENETIC STRUCTURE OF GIANT CLAM (TRIDACNA MAXIMA) POPULATIONS IN THE WEST PACIFIC IS NOT CONSISTENT WITH DISPERSAL BY PRESENT-DAY OCEAN CURRENTS

The Pacific marine biota, particularly species with long planktonic larval stages, are thought to disperse widely throughout the Pacific via ocean currents. The little genetic data available to date has supported this view in that little or no significant regional differentiation of populations has been found over large geographical distances. However, recent data from giant clams has demonstrated not only significant regional differentiation of populations, but routes of gene flow that run perpendicular to the main present-day ocean currents. Extensive surveys of genetic variation at eight polymorphic loci in 19 populations of the giant clam Tridacna maxima, sampled throughout the West and Central Pacific, confirmed that the patterns of variation seen so far in T. gigas were not unique to that species, and may reflect a fundamental genetic structuring of shallow-water marine taxa. Populations of T. maxima within highly connected reef systems like the Great Barrier Reef were panmictic (average F_ST < 0.003), but highly significant genetic differences between reef groups on different archipelagos (average F_ST = 0.084) and between West and Central Pacific regions (average F_ST = 0.156) were found. Inferred gene flow was high (N_em usually > 5) between the Philippines and the Great Barrier Reef, between the Philippines and Melanesia (the Solomon Islands and Fiji), and between the Philippines and the Central Pacific island groups (Marshall Islands, Kiribati, Tuvalu and Cook Islands). Gene flow was low between these three sets of island chains (N_em < 2). These routes of gene flow are perpendicular to present-day ocean currents. It is suggested that the spatial patterns of gene frequencies reflect past episodes of dispersal at times of lower sea levels which have not been erased by subsequent dispersal by present-day circulation. The patterns are consistent with extensive dispersal of marine species in the Pacific, and with traditional views of dispersal from the Indo-Malay region. However, they demonstrate that dispersal along present-day ocean surface currents cannot be assumed, that other mechanisms may operate today or that major dispersal events are intermittent (perhaps separated by several thousands of years), and that the nature and timing of dispersal of Pacific marine species is more complex than has been thought.     

Deciphering patterns of transoceanic dispersal: the evolutionary origin and biogeography of coastal lizards (Cryptoblepharus) in the Western Indian Ocean region

Aim Cryptoblepharus is a genus of small arboreal or rock‐dwelling scincid lizards, widespread through the Indo‐Pacific and Australian regions, with a disjunct outlier in the Malagasy region. The taxonomy within this genus is controversial, with different authors ranking the different forms (now some 36) at various levels, from different species to subspecies of a single species, Cryptoblepharus boutonii. We investigated the biogeography and genetic differentiation of the Cryptoblepharus from the Western Indian Ocean region, in order to understand their origin and history. Location Western Indian Ocean region. Methods We analysed sequences of mitochondrial DNA (partial 12s and 16s rRNA genes, 766 bp) from 48 specimens collected in Madagascar, Mauritius, the four Comoros islands and East Africa, and also in New Caledonia, representing the Australo‐Pacific unit of the distribution. Results Pairwise sequence divergences of c. 3.1% were found between the New Caledonian forms and the ones from the Western Indian Ocean. Two clades were identified in Madagascar, probably corresponding to the recognized forms cognatus and voeltzkowi, and two clades were identified in the Comoro islands, where each island population formed a distinct haplotype clade. The East African samples form a monophyletic unit, with some variation existing between Pemba, Zanzibar and continental Tanzania populations. Individuals from Mauritius form a divergent group, more related to populations from Moheli and Grand Comore (Comoros islands) than to the others. Main conclusions The level of divergence between the populations from the Western Indian Ocean and Australian regions and the geographic coherence of the variation within the Western Indian Ocean group are concordant with the hypothesis of a colonization of this region by a natural transoceanic dispersal (from Australia or Indonesia). The group then may have diversified in Madagascar, from where it separately colonized the East African coast, the Comoros islands (twice), and Mauritius. The genetic divergence found is congruent with the known morphological variation, but its degree is much lower than typically seen between distinct species of reptiles.     

Biogeography of ‘tropical Anagallis’ (Myrsinaceae) inferred from nuclear and plastid DNA sequence data

Aim ‘Tropical Anagallis’ corresponds to one of two evolutionary lineages within the genus Anagallis L. Generally, species within this lineage have a limited distribution in (sub‐)tropical regions in Africa or Madagascar. Two species, however, are endemic to South America, and exhibit a trans‐Atlantic disjunction with the rest of the species within the lineage. To investigate this disjunct distribution, as well as other dispersal events, the distribution of extant taxa was used to hypothesize the ancestral area(s) of distribution. Location Africa, Madagascar, Europe and South America. Methods Dispersal–vicariance analysis (DIVA) was used to optimize distribution areas onto parsimony and Bayesian phylogenies based on sequence data from four chloroplast loci and the nuclear internal transcribed spacers (ITS). Results Parsimony analysis gave one most parsimonious tree while Bayesian analysis resulted in a collapsed node due to alternative placements of Anagallis nummularifolia Baker, endemic to Madagascar. Optimization of the present distribution using DIVA, and the most parsimonious tree and six alternative topologies of the Bayesian analysis, show an origin of the lineage in Europe as most likely, although one topology indicates a broader ancestral distribution area. Dispersal to Africa appears to have been a single event, while two parallel dispersal events seem to have resulted in the American as well as Madagascan distributions. Main conclusions The lineage ‘tropical Anagallis’ evolved in Europe and may have been present in the Eocene boreotropical forests, although scarcity of fossils makes assessment of age difficult. Dispersal to South America is proposed to have been via the North Atlantic land bridge, or, more likely, through transport by the North Equatorial Current. Dispersal from Europe to Africa represents a single event, while dispersal to Madagascar from mainland Africa has occurred twice.     

Phylogenetics of the allodapine bee genus Braunsapis: historical biogeography and long-range dispersal over water

Aim A previous study of the allodapine bee genus Braunsapis suggested an African origin, with dispersal events into Madagascar and Asia, and from Asia into Australia. We re‐examine the phylogeny of this genus, using an expanded set of taxa from Madagascar and Malawi and additional sequence data, in order to determine the number of dispersals and the timeframe over which they occurred. Location Africa, Madagascar, Malawi, Asia and Australia. Methods One nuclear (EF‐1α F2) and two mitochondrial (CO1 and Cyt b) gene regions were sequenced for 36 allodapine bee species (including members of the genera Braunsapis, Nasutapis, Allodape, Allodapula, and Macrogalea) and one ceratinine species (Ceratina japonica). We used Bayesian analyses to examine phylogenetic structure and a penalized likelihood approach to estimate approximate ages for key divergences in our phylogeny. Results Our analyses indicate a tropical African origin for Braunsapis in the early Miocene followed by very early dispersal into Asia and then a subsequent dispersal, following Asian diversification, into Australia during the late Miocene. There have also been two dispersals of Braunsapis from Africa to Madagascar and this result, when combined with phylogenetic and biogeographical data for other allodapines, suggests that these bees have the ability to cross moderately large ocean expanses. These dispersals may have been aided by the West Wind Drift, but rafting across the Mozambique Channel is also possible, and could be aided by the existence of developmental stages that require minimal or no feeding and by tolerance to sea water and spume. Accumulating evidence suggests that many biogeographical patterns in the southern hemisphere may be better explained by dispersal than by Gondwanan vicariance hypotheses. Our results add to this growing body of data and raise the possibility that some puzzling trans‐Indian Ocean distributions may also be explained by historical dispersal events across oceanic barriers that now seem insuperable.     

Molecular phylogeny,biogeography and chromosome evolution of Malagasy dwarf geckos of the genus Lygodactylus (Squamata,Gekkonidae)

We performed a phylogenetic analysis using nuclear (RAG‐1, RAG‐2) and mitochondrial (16S) markers, a statistical Bayesian reconstruction of ancestral distribution areas and a karyological analysis on most Malagasy species of the gekkonid genus Lygodactylus. The phylogenetic analysis largely confirms major basal branching pattern of previous molecular studies, but highlights significant differences concerning both the relationships between different species groups as well as those within groups. The biogeographic analysis supports a Malagasy origin of Lygodactylus, an oversea dispersal to continental Africa and a return to Madagascar. The L. madagascariensis group (also including a new candidate species identified herein) is the most basal clade in Lygodactylus, and the sister group of a clade with all the remaining species. The second most basal clade is the L. verticillatus group, placed as the sister group of a clade comprising African and Malagasy species. The sister lineage of the L. verticillatus group originated the African radiation through an oversea dispersal out of Madagascar. Eventually, the sister lineage of the L. capensis group originated secondary dispersals from Africa to Madagascar. In Madagascar, lineage diversification in different species groups mainly occurred from southern to northern and eastern regions. Dispersal, vicariance and paleoclimatic refugia probably played a relevant role in the evolutionary history of closely related taxa and in speciation mechanisms. The cytogenetic analysis evidenced a high karyotypic variability in Lygodactylus (from 2n = 34 to 2n = 40), which is at least partly consistent with the phylogenetic relationships and the composition of the various species group. Chromosome evolution occurred independently in different lineages, mainly through a reduction in the chromosome number and starting from a putative primitive karyotype of 2n = 40 with all telocentric elements.     

The antiquity of Madagascar’s grasslands and the rise of C4 grassy biomes

Aim Grasslands and savannas, which make up > 75% of Madagascar’s land area, have long been viewed as anthropogenically derived after people settled on the island c. 2 ka. We investigated this hypothesis and an alternative – that the grasslands are an insular example of the post‐Miocene spread of C₄ grassy biomes world‐wide. Location Madagascar, southern Africa, East Africa. Methods We compared the number of C₄ grass genera in Madagascar with that in southern and south‐central African floras. If the grasslands are recent we would expect to find fewer species and genera in Madagascar relative to Africa and for these species and genera to have very wide distribution ranges in Madagascar. Secondly, we searched Madagascan floras for the presence of endemic plant species or genera restricted to grasslands. We also searched for evidence of a grassland specialist fauna with species endemic to Madagascar. Plant and animal species endemic to C₄ grassy biomes would not be expected if these are of recent origin. Results Madagascar has c. 88 C₄ grass genera, including six endemic genera. Excluding African genera with only one or two species, Madagascar has 86.6% of southern Africa’s and 89.4% of south‐central Africa’s grass genera. C₄ grass species make up c. 4% of the flora of both Madagascar and southern Africa and species : genus ratios are similar (4.3 and 5.1, respectively). Turnover of grasses along geographical gradients follows similar patterns to those in South Africa, with Andropogoneae dominating in mesic biomes and Chlorideae in semi‐arid grassy biomes. At least 16 monocot genera have grassland members, many of which are endemic to Madagascar. Woody species in frequently burnt savannas include both Madagascan endemics and African species. A different woody flora, mostly endemic, occurs in less frequently burnt grasslands in the central highlands, filling a similar successional niche to montane C₄ grasslands in Africa. Diverse vertebrate and invertebrate lineages have grassland specialists, including many endemic to Madagascar (e.g. termites, ants, lizards, snakes, birds and mammals). Grassland use of the extinct fauna is poorly known but carbon isotope analysis indicates that a hippo, two giant tortoises and one extinct lemur ate C₄ or CAM (crassulacean acid metabolism) plants. Main conclusions The diversity of C₄ grass lineages in Madagascar relative to that in Africa, and the presence of plant and animal species endemic to Madagascan grassy biomes, does not fit the view that these grasslands are anthropogenically derived. We suggest that grasslands invaded Madagascar after the late Miocene, part of the world‐wide expansion of C₄ grassy biomes. Madagascar provides an interesting test case for biogeographical analysis of how these novel biomes assembled, and the sources of the flora and fauna that now occupy them. A necessary part of such an analysis would be to establish the pre‐settlement extent of the C₄ grassy biomes. Carbon isotope analysis of soil organic matter would be a feasible method for doing this.