Land Bridge Connection Research Articles

Complete phylogeny of Micrathena spiders suggests multiple dispersal events among Neotropical rainforests, islands and landmasses, and indicates that Andean orogeny promotes speciation.

The Neotropical region is the most diverse on the planet, largely owing to its mosaic of tropical rainforests. Multiple tectonic and climatic processes have been hypothesized to contribute to generating this diversity, including Andean orogeny, the closure of the Isthmus of Panama, the GAARlandia land bridge and historical connections among currently isolated forests. Micrathena spiders are diverse and widespread in the region, and thus a complete phylogeny of this genus allows the testing of hypotheses at multiple scales. We estimated a complete, dated phylogeny using morphological data for 117 Micrathena species and molecular data of up to five genes for a subset of 79 species. Employing event-based approaches and biogeographic stochastic mapping while considering phylogenetic uncertainty, we estimated ancestral distributions, the timing and direction of dispersal events and diversification rates among areas. The phylogeny is generally robust, with uncertainty in the position of some of the species lacking sequences. Micrathena started diversifying around 25 Ma. Andean cloud forests show the highest in-situ speciation, while the Amazon is the major dispersal source for adjacent areas. The Dry Diagonal generated few species and is a sink of diversity. Species exchange between Central and South America involved approximately 23 dispersal events and started ~20 Ma, which is consistent with a Miocene age for the Isthmus of Panama closure. We inferred four dispersal events from Central America to the Antilles in the last 20 Myr, indicating the spiders did not reach the islands through the GAARlandia land bridge. We identified important species exchange routes among the Amazon, Andean cloud forests and Atlantic forests during the Plio-Pleistocene. Sampling all species of the genus was fundamental to the conclusions above, especially in identifying the Andean forests as the area that generated the majority of species. This highlights the importance of complete taxonomic sampling in biogeographic studies.

Systematics of the New World bats Eptesicus and Histiotus suggest trans-marine dispersal followed by Neotropical cryptic diversification

Biodiversity can be boosted by colonization of new habitats such as remote islands and separated continents. Molecular studies have suggested that recently evolved organisms probably colonized already separated continents by dispersal, either via land bridge connections or crossing the ocean. Here we test the on-land and trans-marine dispersal hypotheses by evaluating possibilities of colonization routes over the Bering land bridge and across the Atlantic Ocean in the cosmopolitan bat genus Eptesicus (Chiroptera, Vespertilionidae). Previous molecular studies have found New World Eptesicus more closely related to Histiotus, a Neotropical endemic lineage with enlarged ears, than to Old World Eptesicus. However, phylogenetic relationships within the New World group remained unresolved and their evolutionary history was unclear. Here we studied the systematics of New World Eptesicus and Histiotus using extensive taxonomic and geographic sampling, and genomic data from thousands of ultra-conserved elements (UCEs). We estimated phylogenetic trees using concatenation and multispecies coalescent. All analyses supported four major New World clades and a novel topology where E. fuscus and Histiotus are sister clades that together diverged from two sister clades of Neotropical Eptesicus. Intra-clade divergence suggested cryptic diversity that has been concealed by morphological features, especially in the Neotropics where taxonomic re-evaluations are warranted. Molecular dating estimated that Old World and New World clades diverged around 17 million years ago followed by radiation of major New World clades in the mid-Miocene, when climatic changes might have facilitated global dispersal and radiation events. Biogeographic ancestral reconstruction supported the Neotropical origin of the New World clades, suggesting a trans-Atlantic colonization route from North Africa to the northern Neotropics. We highlight that trans-marine dispersal may be more prevalent than currently acknowledged and may be an important first step to global biodiversification.

Dispersal, not vicariance, explains the biogeographic origin of iguanas on Madagascar

Lizards of the clade Iguanidae (sensu lato) are primarily a New World group. Thus, the remarkable presence of an endemic lineage of iguanas (family Opluridae) on the isolated Indian Ocean island of Madagascar has long been considered a biogeographic anomaly. Previous work attributed this disjunct extant distribution to: (1) vicariance at about 140–165 Ma, caused by the breakup of Gondwana and the separation of South America, Africa, and Madagascar (with subsequent extinction of iguanas on Africa, and potentially other Gondwanan landmasses), (2) vicariance at about 80–90 Ma, caused by the sundering of hypothesized land-bridge connections between South America, Antarctica, India, and Madagascar, or (3) long-distance overwater dispersal from South America to Madagascar. Each hypothesis has been supported with molecular divergence dating analyses, and thus the biogeographic origin of the Opluridae is not yet well resolved. Here we utilize genetic sequences of ultraconserved elements for all Iguania families and the majority of Iguanidae (s.l.) genera, and morphological data for extant and fossil taxa (used for divergence dating analyses), to produce the most comprehensive dataset applied to date to test these origin hypotheses. We find strong support for a sister relationship between the Opluridae (Madagascar) and Leiosauridae (South America). Divergence of the Opluridae from Leiosauridae is dated to between the late Cretaceous and mid-Paleogene, at a time when Madagascar was already an island and was isolated from all other Gondwanan landmasses. Consequently, our results support a hypothesis of long-distance overwater dispersal of the Opluridae lineage, either directly from South America to Madagascar or potentially via Antarctica or Africa, leading to this radiation of iguanas in the Indian Ocean.

Isolated petrosal of the extinct sloth Glossotherium tropicorum (Xenarthra, Folivora, Mylodontidae) from the island of Trinidad

This report is the first to identify the presence of the extinct ground sloth Glossotherium tropicorum from Pleistocene-aged tar pit deposits in Trinidad. G. tropicorum is known primarily from extensive skeletal material recovered from the Pleistocene of western Ecuador and Peru. Our identification is based on an isolated left petrosal bone, which exhibits a variety of derived diagnostic features of mylodontid sloths in general, e.g., the presence of an epitympanic recess, and the genus Glossotherium in particular, including a reduced anteroventral process of the tegmen tympani. This represents only the second published record of the genus Glossotherium from outside continental South America, and is a substantial range extension for the species G. tropicorum. The present study also represents the first published description of a mylodontid sloth fossil from Trinidad. The specimen is part of a collection that was initially documented in an unpublished Master’s thesis, and that includes additional sloths and other Pleistocene mammals. This fauna confirms the presence of extensive savanna-type habitats on Trinidad during the Pleistocene, and is consistent with the presence of a land bridge connection between the island and mainland South America at that time.

The role of sea-level and climate changes in the assembly of Sri Lankan biodiversity: A perspective from the Miocene Jaffna Limestone

As part of the Western Ghats-Sri Lanka biodiversity hotspot, Sri Lanka harbors a rich and diverse fauna with a considerable number of endemic species, especially in the wet southwestern part of the island. Understanding the origin of this biodiversity requires consideration of the land bridge history between the island and southern Peninsular India. To examine the influence of fluctuating sea levels and climate on island connectivity and isolation during the Miocene, we describe the lithological succession of the Jaffna Limestone in surface outcrops of north(west)ern Sri Lanka and interpret it with respect to palaeoenvironments and sequence stratigraphy. A stack of three marine intervals was identified, which were deposited in seagrass-, coral reef-, and nearshore siliciclastic environments of a land-attached carbonate platform and are separated by caliche and palaeokarst unconformities. They represent high sea-level peaks during the long-term sea-level maximum related to the Middle Miocene Climate Optimum (MMCO). In support of divergence time from Sri Lankan and south Indian species, it is argued that the Palk Isthmus connected Sri Lanka to mainland India prior the MMCO (~17–15 Ma) and after the Middle Miocene Climate Transition (~15–13 Ma), whereas a marine barrier continued to persist during low sea-level stands associated with the Mi2, Mi3a and Mi3 glaciations within this period of time. The early and middle Miocene landbridge connections opened up dispersal opportunities for terrestrial animals. Species migrations via the Palk Isthmus were, however, impacted by a climatic filter, which promoted a high level of ancient endemism on Sri Lanka. Our results indicate that the Sri Lankan sub-center of biodiversity started to evolve in response to increased sea-level and climate variability associated with Antarctic ice dynamics and the initiation of the South Asian monsoon system during the early stage of the current ice house period.

Population history of the golden eagle inferred from whole-genome sequencing of three of its subspecies

AbstractThe application of evolutionary genetic research to investigate the potential for endangered species to adapt to changing environments is important for conservation biology. Effective population size (Ne) is informative for understanding adaptive potential as it refers to the genetic variation in breeding individuals who have contributed to contemporary and historic population diversity. We reconstruct fluctuations in Ne in three golden eagle subspecies (Japanese, Scottish, North American) using the pairwise sequential Markovian coalescent (PSMC) model based on whole-genome sequence data. Our results indicate the timing of subspeciation events and suggest significant ongoing demographic reductions since the start of the Last Glacial Period. Importantly, we find evidence for gene flow from continental populations into the ancestral Japanese population resulting in a short, sharp recovery in genetic diversity. Timing agrees with the palaeogeographic estimates of land bridge connections between the Japanese archipelago and Asian continent and matches a similar Ne spike in the Scottish population, but not in the North American population. Given contemporary declines in isolated Japanese and UK island populations, our study highlights a concerning loss of local genetic diversity, but also indicates the likely response of populations to genetic reinforcement from neighbouring subspecies, increasing management options and encouraging a range-wide species conservation approach.

Diversification of shrub frogs (Rhacophoridae, Pseudophilautus) in Sri Lanka – Timing and geographic context

Pseudophilautus comprises an endemic diversification predominantly associated with the wet tropical regions of Sri Lanka that provides an opportunity to examine the effects of geography and historical climate change on diversification. Using a time-calibrated multi-gene phylogeny, we analyze the tempo of diversification in the context of past climate and geography to identify historical drivers of current patterns of diversity and distribution. Molecular dating suggests that the diversification was seeded by migration across a land-bridge connection from India during a period of climatic cooling and drying, the Oi-1 glacial maximum around the Eocene-Oligocene boundary. Lineage-through-time plots suggest a gradual and constant rate of diversification, beginning in the Oligocene and extending through the late Miocene and early Pliocene with a slight burst in the Pleistocene. There is no indication of an early-burst phase of diversification characteristic of many adaptive radiations, nor were there bursts of diversification associated with favorable climate shifts such as the intensification of monsoons. However, a late Miocene (8.8 MYA) back-migration to India occurred following the establishment of the monsoon. The back migration did not trigger a diversification in India similar to that manifest in Sri Lanka, likely due to occupation of available habitat, and consequent lack of ecological opportunity, by the earlier radiation of a sister lineage of frogs (Raorchestes) with similar ecology. Phylogenetic area reconstructions show a pattern of sister species distributed across adjacent mountain ranges or from different parts of large montane regions, highlighting the importance of isolation and allopatric speciation. Hence, local species communities are composed of species from disparate clades that, in most cases, have been assembled through migration rather than in situ speciation. Lowland lineages are derived from montane lineages. Thus, the hills of Sri Lanka acted as species pumps as well as refuges throughout the 31 million years of evolution, highlighting the importance of tropical montane regions for both the generation and maintenance of biodiversity.

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.

Discovery of the Critically Endangered Tarantula Species of the Genus Poecilotheria (Araneae: Theraphosidae), Poecilotheria hanumavilasumica, From Sri Lanka

The arboreal spiders in the genus Poecilotheria is represented by 16 species and restricted to India and Sri Lanka. Each country has eight endemic species. During a survey on mygalomorph spiders in the Northern Province of Sri Lanka, the critically endangered species of Theraphosidae Poecilotheria hanumavilasumica was discovered for the first time outside of its native habitat in India, expanding its range to northern Sri Lanka. The discovery of P. hanumavilasumica is unique, as it used to be a critically endangered and endemic species of the genus Poecilotheria found in India, and it is evident that during the land bridge connection between India and Sri Lanka, when the Pleistocene epoch biotic exchange took place between the two countries, taxa were dispersed through the land connections.

Early Miocene origin and cryptic diversification of South American salamanders

BackgroundThe currently recognized species richness of South American salamanders is surprisingly low compared to North and Central America. In part, this low richness may be due to the salamanders being a recent arrival to South America. Additionally, the number of South American salamander species may be underestimated because of cryptic diversity. The aims of our present study were to infer evolutionary relationships, lineage diversity, and timing of divergence of the South American Bolitoglossa using mitochondrial and nuclear sequence data from specimens primarily from localities in the Andes and upper Amazon Basin. We also estimated time of colonization of South America to test whether it is consistent with arrival via the Panamanian Isthmus, or land bridge connection, at its traditionally assumed age of 3 million years.ResultsDivergence time estimates suggest that Bolitoglossa arrived in South America from Central America by at least the Early Miocene, ca. 23.6 MYA (95% HPD 15.9-30.3 MYA), and subsequently diversified. South American salamanders of the genus Bolitoglossa show strong phylogeographic structure at fine geographic scales and deep divergences at the mitochondrial gene cytochrome b (Cytb) and high diversity at the nuclear recombination activating gene-1 (Rag1). Species often contain multiple genetically divergent lineages that are occasionally geographically overlapping. Single specimens from two southeastern localities in Ecuador are sister to the equatoriana-peruviana clade and genetically distinct from all other species investigated to date. Another single exemplar from the Andes of northwestern Ecuador is highly divergent from all other specimens and is sister to all newly studied samples. Nevertheless, all sampled species of South American Bolitoglossa are members of a single clade that is one of several constituting the subgenus Eladinea, one of seven subgenera in this large genus.ConclusionsThe ancestors of South American salamanders likely arrived at least by the Early Miocene, well before the completion of the Late Pliocene Panamanian land bridge (widely accepted as ca. 3 MYA). This date is in agreement with recent, controversial, arguments that an older, perhaps short-lived, land connection may have existed between South America and present-day Panama 23–25 MYA. Since its arrival in South America, Bolitoglossa has diversified more extensively than previously presumed and currently includes several cryptic species within a relatively small geographic area. Rather than two upper Amazonian species currently recorded for this region, we propose that at least eight should be recognized, although these additional lineages remain to be formally described.

Colliding fragment islands transport independent lineages of endemic rock-crawlers (Grylloblattodea: Grylloblattidae) in the Japanese archipelago

Fragment islands, viewed from the paradigm of island biogeographic theory, depend on continual immigration from continental sources to maintain levels of species diversity, or otherwise undergo a period of relaxation where species diversity declines to a lower equilibrium. Japan is a recently derived fragment island with a rich endemic flora and fauna. These endemic species have been described as paleoendemics, and conversely as recently derived Pleistocene colonists. Geological events in the Miocene period, notably the fragmentation and collision of islands, and the subsequent uplift of mountains in central Japan, provided opportunities for genetic isolation. More recently, cyclical climatic change during the Pliocene and Pleistocene periods led to intermittent land bridge connections to continental Asia. Here we investigate the pattern and timing of diversification in a diverse endemic lineage in order to test whether ongoing migration has sustained species diversity, whether there is evidence of relaxation, and how geological and climatic events are associated with lineage diversification. Using multi-locus genetic data, we test these hypotheses in a poorly dispersing, cold-adapted terrestrial insect lineage (Grylloblattodea: Grylloblattidae) sampled from Japan, Korea, and Russia. In phylogenetic analyses of concatenated data and a species tree approach, we find evidence of three deeply divergent lineages of rock-crawlers in Japan consistent with the pattern of island fragmentation from continental Asia. Tests of lineage diversification rates suggest that relaxation has not occurred and instead endemism has increased in the Japanese Grylloblattidae following mountain-building events in the Miocene. Although the importance of climate change in generating species diversity is a commonly held paradigm in Japanese biogeography, our analyses, including analyses of demographic change and phylogeographic range shifts in putative species, suggests that Pleistocene climatic change has had a limited effect on the diversification of rock-crawlers.

Holocene climatic changes and vegetation development in the Kuril Islands

The response of Kuril Island vegetation to climatic changes during the Holocene is reconstructed from data obtained from key sections that included various depositional environments. These climatic fluctuations were not as marked in the Kuril archipelago as they were in nearby continental margins and large islands. During the Early Holocene dwarf stone pine, coniferous and birch forest, prevailed in the South Kurils, and tundra landscapes in the North Kurils. The greatest northward movement of Kuril vegetation zones occurred during the Holocene Optimum (∼6600–5000 14C BP). Mean annual temperatures in the Kuril Islands were 2–3 °C higher than modern. Shifts in the location of warm and cold marine currents, which strengthened or dampened insolation-driven climatic changes, played an important role in vegetation development. Cool-temperate broadleaf forests and mixed coniferous-broadleaf forests were widespread on South Kurils. Rising Holocene sea levels flooded land bridge connections to Hokkaido Island and the mainland, resulting in the formation of several small islands in the South Kurils, meadows and boggy landscapes prevailed. This flooding had a great effect on repopulation of island biota as did the deep straits that separate southern islands from the Central and North Kurils. All paleovegetation associations can be found on the current landscape, although their geographic distribution has changed during the Holocene. No introduction of plants from adjacent land occurred in the Holocene. Forb and graminoid meadows characterized the Middle Holocene vegetation of Central Kurils. On North Kurils forb meadows were widespread, tundra area decreased. Climatic changes did not occur synchronously throughout the Kurils, at times not even on the closest islands. Local volcanism played a special role in Kuril vegetation history. The considerable microclimatic variability within the islands also has been important in determining the development and preservation of vegetation communities and their reaction to more regional climatic changes.

Biogeography of tenebrionid beetles (Coleoptera: Tenebrionidae) in the circum-Sicilian islands (Italy, Sicily): Multiple biogeographical patterns require multiple explanations

The tenebrionid beetles on 25 circum-Sicilian islands were studied to determine the influence of island geographical and landscape features on three main intercorrelated biogeographical patterns: (1) species richness, studied using species-area and species environment relationships, (2) species assemblage composition, investigated using Canonical Correspondence Analysis (CCA), and (3) inter-site faunal similarity, investigated using Canonical Correlation Analysis (CANCOR) applied to multidimensional scaling of inter-island faunal dissimilarities. Species richness was mostly influenced by island area and landscape heterogeneity (expressed using various indices of diversity based on land cover categories). When species identities were considered in the CCA, no substantial effect of landscape was detected. Current island isolation did not have a strong influence on species richness, but has a distinct effect in determining species assortments on the remotest islands. Historical influences of Pleistocene landbridge connections were not detectable in species richness relationships using geographical variables in species richness analyses or in assemblage gradients in the CCA, but emerged distinctly from inter-island similarities in the CANCOR.

The Central American land bridge as an engine of diversification in New World doves

Aim The closure of the Central American land-bridge connection between North and South America 3.5 million years ago was a major biogeographic event that allowed considerable interchange of the previously isolated faunas of these continents. However, the role that this connection may have had in diversification of North and South American faunas is less well understood. The goal of this study was to evaluate the potential role of the formation of this land connection in generating diversity, through repeated rare dispersal events followed by isolation. Location North and South America. Methods We evaluated the role of the Central American land-bridge connection in avian diversification using a molecular phylogeny based on four gene regions for mid-sized New World doves. Diversification events were dated using a Bayesian relaxed clock analysis and internal calibration points for endemic island taxa with known island ages. Results The reconstructed phylogenetic tree was well supported and recovered monophyly of the genera Leptotila and Zenaida, but the quail-doves (Geotrygon) were paraphyletic, falling into three separate lineages. The phylogeny indicated at least nine dispersal-driven divergence events between North and South America. There were also five dispersal events in the recent past that have not yet led to differentiation of taxa (polymorphic taxa). Main conclusions Most of these dispersal-driven diversification events occurred at the time of or after the formation of the Central American land bridge, indicating that this land connection played a role in facilitating divergence via dispersal of doves between continents.

Intercontinental dispersal by a microendemic burrowing reptile (Dibamidae).

Intercontinental dispersal via land bridge connections has been important in the biogeographic history of many Holarctic plant and animal groups. Likewise, some groups appear to have accomplished trans-oceanic dispersal via rafting. Dibamid lizards are a clade of poorly known fossorial, essentially limbless species traditionally split into two geographically disjunct genera: Dibamus comprises approximately 20 Southeast Asian species, many of which have very limited geographical distributions, and the monotypic genus Anelytropsis occupies a small area of northeastern Mexico. Although no formal phylogeny of the group exists, a sister-taxon relationship between the two genera has been assumed based on biogeographic considerations. We used DNA sequence data from one mitochondrial and six nuclear protein-coding genes to construct a phylogeny of Dibamidae and to estimate divergence times within the group. Surprisingly, sampled Dibamus species form two deeply divergent, morphologically conserved and geographically concordant clades, one of which is the sister taxon of Anelytropsis papillosus. Our analyses indicate Palaearctic to Nearctic Beringian dispersal in the Late Palaeocene to Eocene. Alternatively, a trans-Pacific rafting scenario would extend the upper limit on dispersal to the Late Cretaceous. Either scenario constitutes a remarkable long-distance dispersal in what would seem an unlikely candidate.

Mitogenomic perspectives into iguanid phylogeny and biogeography: Gondwanan vicariance for the origin of Madagascan oplurines

Complete or nearly complete nucleotide sequences of mitochondrial genomes (mtDNAs) were determined from eight species which, together with previous mtDNA data for two other taxa, cover most subfamilies of Iguanidae sensu lato. These iguanid mtDNAs were found to be rather conservative with respect to gene arrangements and molecular evolutionary rates, which contrasts with mtDNAs of Acrodonta (Agamidae and Chamaeleonidae) in which several gene rearrangements and highly accelerated molecular evolutionary rates have been known. Phylogenetic analyses consistently suggested the earliest shoot-off of a Malagasy subfamily Oplurinae and an affinity of Polychrotinae and Tropidurinae sensu stricto. However, even with the ample molecular characters derived from complete mtDNA sequences, phylogenetic relationships between iguanid subfamilies were poorly resolved in general, presumably due to the rapid ancient cladogenesis. Divergence time estimation without assuming the molecular clock suggested the Late Triassic/Early Jurassic divergence of Iguanidae from acrodonts and the Middle/Late Jurassic divergence of Oplurinae from the other iguanids. Together with geological and paleontological evidence, these results led us to propose Gondwanan vicariance for the origin of Malagasy oplurines without invoking a land bridge connection between South America/Antarctica and drifting Madagascar/India.

A unique A. palustris lineage across the Otranto strait: botanical evidence for a past land-bridge?

Phylogeography allows to reconstruct the history of genealogic lineages at the intra- and interspecific level. Previous studies on the distribution of minisatellite and microsatellite plastid haplotypes in populations of the Mediterranean marsh orchid Anacamptis palustris revealed that populations from the Salento peninsula (Apulia region, west coast of Otranto strait) formed a distinct and isolated lineage. To further explore the peculiarity of this biogeographic region, in the present study we examined both fresh samples and herbarium specimens of the rare orchid Anacamptis palustris from populations located on the eastern coast of the Otranto strait (i.e. on the Greek-Albanian side). All the investigated samples exhibited a unique combination of chloroplast microsatellites, which was previously found exclusively in populations from the Salento peninsula. Samples from Corfu, Igoumenitsa and Durazzo showed a novel minisatellite repeat type, while those of Zakynthos possessed the widespread ancestral repeat type. Interestingly, the novel repeat type and those previously found in Salento populations clustered together on a well-differentiated evolutionary branch in a minisatellite repeat type network of the A. palustris lineages. This finding indicates a close relationship between the populations from both sides of the Otranto strait and supports the geological evidence for the occurrence of an ancient land-bridge connection between the southern most part of Italy and Greece during the Messinian desiccation and/or the ``Lago-Mare'' period.

The shaping of mitochondrial DNA phylogeographic patterns of the brown hare ( Lepus europaeus) under the combined influence of Late Pleistocene climatic fluctuations and anthropogenic translocations

The phylogeographic structure of the brown hare ( Lepus europaeus) was studied by analysing mtDNA control region sequences of 98 individuals from continental and insular Greece, Bulgaria, Cyprus and northern Israel, together with 44 published sequences from Italy and central Europe. We found two distinct clades separated by an average nucleotide divergence of 6.6%, which may correspond to a Balkan and to an Asia Minor refugium. The estimated time of separation of the two clades was dated back to 105,000– 490,000 years ago. These two clades coexist in the area of northeastern Greece and Bulgaria, most likely as a result of a post-glacial northward expansion. Within the southern Balkan refugium, network analyses showed geographical structuring, which supports the hypothesis of several isolated Late Pleistocene populations. The central European and Italian populations appear to have originated from a non-detected northern Balkan population that was genetically closely related to some northern Greek populations, as a result of postglacial expansion, translocations or a combination of both. Moreover, several cases of ancient and recent translocations by humans were detected, especially for some island populations, while the eastern Aegean islands off the Asia Minor coast were most likely colonized naturally through Late Pleistocene land bridge connection. The genetic analysis presented here provides a framework for designing proper conservation and management guidelines for this species.

Evolutionary significance of cranial variation in Asian Homo erectus.

Homo erectus inhabited a wide geographic area of Asia, ranging from 40 degrees north latitude in China to 8 degrees south latitude in island Southeast Asia. Yet variation within Asian H. erectus and its relation to ecological and temporal parameters have been little studied. I synthesize the revised radiometric chronologies for hominid sites in Asia and their relation to new oxygen isotope curves (proxies for climatic fluctuations and landbridge connections). These data suggest substantial opportunities in the later Pleistocene for both regional isolation and gene flow between hominids in mainland and Southeast Asia. They also suggest that the most northerly located Chinese sites (Zhoukoudian and Nanjing) may have been occupied during sequential, interglacial periods. Probably reflecting these periods of isolation, nonmetric features and principal components analysis (PCA) of calvarial shape suggest regional differentiation between northern Asian and Southeast Asian H. erectus. The most recent Southeast Asian fossils (e.g., Ngandong) conform to the Southeast Asian pattern. Except perhaps in brain size, there is no evidence that the temporally intermediate Chinese fossils are intermediate in morphology between older and younger Indonesian fossils. In fact, northern Chinese calvaria are easier to exclude from the larger Asian H. erectus hypodigm than are the Ngandong fossils. The Chinese specimens differ from the others based on their narrower occipitals and frontals for their cranial size. The Chinese sample from Zhoukoudian alone is thus not a good proxy for the morphology and variation seen within Asian H. erectus. Both the Chinese and late Indonesian samples exhibit less variation than does the early Indonesian sample; this along with their shared morphological bauplan suggests a common origin and no more than subspecific differentiation. This shared morphology, despite regional differences, was likely maintained by the increasing intensity of multiple glaciations (and longer-lasting land bridge connections) between mainland and island Southeast Asia during the last million years.

Multiple causation of phylogeographical pattern as revealed by nested clade analysis of the bamboo viper (Trimeresurus stejnegeri) within Taiwan.

In order to assess the utility of nested clade analysis, both standard phylogenetic algorithms and nested clade analysis were performed on a geographically widespread survey of mitochondrial DNA haplotypes of the bamboo viper, Trimeresurus stejnegeri, within Taiwan. Gross tree topologies were congruent for all analyses and indicated the presence of two geographically overlapping clades within Taiwan. The smaller lineage was restricted to the north and east coasts, whereas the larger lineage occupied all but the northern range of the species within Taiwan including the Pacific offshore populations of Green and Orchid Islands. The phylogeographical pattern supports the existence of at least one colonization event from the continent since the initial isolation of Taiwan from the mainland in the Pliocene. However, determining the exact number of colonization events was not possible due to the simultaneous vicariant forces of hypothesized continental landbridge connections and the occurrence of dramatic in situ orogenesis throughout the Pleistocene. Nested clade analysis provided multiple temporal and spatial population historical inferences that are not possible with standard analyses and therefore should become widely applied to future phylogeographical studies.