Co-phylogeography and comparative population genetics of the threatened Galápagos hawk and three ectoparasite species: ecology shapes population histories within parasite communities

Comparative microevolutionary studies of multiple parasites occurring on a single host species can help shed light on the processes underlying parasite diversification. We compared the phylogeographical histories, population genetic structures and population divergence times of three co-distributed and phylogenetically independent ectoparasitic insect species, including an amblyceran and an ischnoceran louse (Insecta: Phthiraptera), a hippoboscid fly (Insecta: Diptera) and their endemic avian host in the Galápagos Islands. The Galápagos hawk (Aves: Falconiformes: Buteo galapagoensis) is a recently arrived endemic lineage in the Galápagos Islands and its island populations are diverging evolutionarily. Each parasite species differed in relative dispersal ability and distribution within the host populations, which allowed us to make predictions about their degree of population genetic structure and whether they tracked host gene flow and colonization history among islands. To control for DNA region in comparisons across these phylogenetically distant taxa, we sequenced ~1 kb of homologous mitochondrial DNA from samples collected from all island populations of the host. Remarkably, the host was invariant across mitochondrial regions that were comparatively variable in each of the parasite species, to degrees consistent with differences in their natural histories. Differences in these natural history traits were predictably correlated with the evolutionary trajectories of each parasite species, including rates of interisland gene flow and tracking of hosts by parasites. Congruence between the population structures of the ischnoceran louse and the host suggests that the ischnoceran may yield insight into the cryptic evolutionary history of its endangered host, potentially aiding in its conservation management.     

Insular black files (Diptera: Simuliidae) of North America: tests of colonization hypotheses

Aim To understand factors that facilitate insular colonization by black flies, we tested six hypotheses related to life‐history traits, phylogeny, symbiotes, island area, and distance from source areas. Location Four northern islands, all within 150 km of the North American mainland, were included in the study: Isle Royale, Magdalen Islands, Prince Edward Island, and Queen Charlotte Islands. Methods Immature black flies and their symbiotes were surveyed in streams on the Magdalen Islands, and the results combined with data from similar surveys on Isle Royale, Prince Edward Island, and the Queen Charlotte Islands. Black flies were analysed chromosomally to ensure that all sibling species were revealed. Tests of independence were used to examine the frequency of life‐history traits and generic representation of black flies on islands vs. source areas. Results A total of 13–20 species was found on each of the islands, but no species was unique to any of the islands. The simuliid faunas of the islands reflected the composition of their source areas in aspects of voltinism (univoltine vs. multivoltine), blood feeding (ornithophily vs. mammalophily), and phylogeny (genus Simulium vs. other genera). Five symbiotic species were found on the most distant island group, the Magdalen Islands, supporting the hypothesis that obligate symbiotes are effectively transported to near‐mainland islands. An inverse relationship existed between the number of species per island and distance from the source. The Queen Charlotte Islands did not conform to the species–area relationship. Main conclusions The lack of precinctive insular species and an absence of life‐history and phylogenetic characteristics related to the presence of black flies on these islands argue for gene flow and dispersal capabilities of black flies over open waters, possibly aided by winds. However, the high frequency of precinctive species on islands 500 km or more from the nearest mainland indicates that at some distance beyond 100 km, open water provides a significant barrier to colonization and gene exchange. An inverse relationship between number of species and distance from the source suggests that as long as suitable habitat is present, distance plays an important role in colonization. Failure of the Queen Charlotte Islands to conform to an area–richness trend suggests that not all resident species have been found.     

Genetic structure of the Canarian palm tree (Phoenix canariensis) at the island scale: does the ‘island within islands’ concept apply to species with high colonisation ability?

• Oceanic islands are dynamic settings that often promote within‐island patterns of strong population differentiation. Species with high colonisation abilities, however, are less likely to be affected by genetic barriers, but island size may impact on species genetic structure regardless of dispersal ability.
• The aim of the present study was to identify the patterns and factors responsible for the structure of genetic diversity at the island scale in Phoenix canariensis, a palm species with high dispersal potential. To this end, we conducted extensive population sampling on the three Canary Islands where the species is more abundant and assessed patterns of genetic variation at eight microsatellite loci, considering different within‐island scales.
• Our analyses revealed significant genetic structure on each of the three islands analysed, but the patterns and level of structure differed greatly among islands. Thus, genetic differentiation fitted an isolation‐by‐distance pattern on islands with high population densities (La Gomera and Gran Canaria), but such a pattern was not found on Tenerife due to strong isolation between colonised areas. In addition, we found a positive correlation between population geographic isolation and fine‐scale genetic structure.
• This study highlights that island size is not necessarily a factor causing strong population differentiation on large islands, whereas high colonisation ability does not always promote genetic connectivity among neighbouring populations. The spatial distribution of populations (i.e. landscape occupancy) can thus be a more important driver of plant genetic structure than other island, or species′ life‐history attributes.

     

Island history affects faunal composition: the treeshrews (Mammalia: Scandentia: Tupaiidae) from the Mentawai and Batu Islands,Indonesia

The Mentawai and Batu Island groups off the west coast of Sumatra have a complicated geological and biogeographical history. The Batu Islands have shared a connection with the Sumatran ‘mainland’ during periods of lowered sea level, whereas the Mentawai Islands, despite being a similar distance from Sumatra, have remained isolated from Sumatra, and probably from the Batu Islands as well. These contrasting historical relationships to Sumatra have influenced the compositions of the respective mammalian faunas of these island groups. Treeshrews (Scandentia, Tupaiidae) from these islands have, at various times in their history, been recognized as geographically circumscribed populations of a broadly distributed Tupaia glis, subspecies, or distinct species. We used multivariate analyses of measurements from the skull and hands to compare the island populations from Siberut (Mentawai Islands) and Tanahbala (Batu Islands) with the geographically adjacent species from the southern Mentawai Islands (T. chrysogaster) and Sumatra (T. ferruginea). Results from both the skull and manus of the Siberut population show that it is most similar to T. chrysogaster, whereas the Tanahbala population is more similar to T. ferruginea, confirming predictions based on island history. These results are further corroborated by mammae counts. Based on these lines of evidence, we include the Siberut population in T. chrysogaster and the Tanahbala population in T. ferruginea. Our conclusions expand the known distributions of both the Mentawai and Sumatran species. The larger geographical range of the endangered T. chrysogaster has conservation implications for this Mentawai endemic, so populations and habitat should be re‐evaluated on each of the islands it inhabits. However, until such a re‐evaluation is conducted, we recommend that the IUCN Red List status of this species be changed from ‘Endangered’ to ‘Data Deficient’. Published 2013. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2014, 111 , 290–304.     

Spiders on a Hot Volcanic Roof: Colonisation Pathways and Phylogeography of the Canary Islands Endemic Trap-Door Spider Titanidiops canariensis (Araneae,Idiopidae)

Studies conducted on volcanic islands have greatly contributed to our current understanding of how organisms diversify. The Canary Islands archipelago, located northwest of the coast of northern Africa, harbours a large number of endemic taxa. Because of their low vagility, mygalomorph spiders are usually absent from oceanic islands. The spider Titanidiops canariensis, which inhabits the easternmost islands of the archipelago, constitutes an exception to this rule. Here, we use a multi-locus approach that combines three mitochondrial and four nuclear genes to investigate the origins and phylogeography of this remarkable trap-door spider. We provide a timeframe for the colonisation of the Canary Islands using two alternative approaches: concatenation and species tree inference in a Bayesian relaxed clock framework. Additionally, we investigate the existence of cryptic species on the islands by means of a Bayesian multi-locus species delimitation method. Our results indicate that T. canariensis colonised the Canary Islands once, most likely during the Miocene, although discrepancies between the timeframes from different approaches make the exact timing uncertain. A complex evolutionary history for the species in the archipelago is revealed, which involves two independent colonisations of Fuerteventura from the ancestral range of T. canariensis in northern Lanzarote and a possible back colonisation of southern Lanzarote. The data further corroborate a previously proposed volcanic refugium, highlighting the impact of the dynamic volcanic history of the island on the phylogeographic patterns of the endemic taxa. T. canariensis includes at least two different species, one inhabiting the Jandia peninsula and central Fuerteventura and one spanning from central Fuerteventura to Lanzarote. Our data suggest that the extant northern African Titanidiops lineages may have expanded to the region after the islands were colonised and, hence, are not the source of colonisation. In addition, T. maroccanus may harbour several cryptic species.     

First record of the host plant and larvae of Pachyrhynchus sonani (Coleoptera: Curculionidae) on Lanyu Island,Taiwan

Pachyrhynchus sonani Kôno, 1930, a legally protected species in Taiwan, is endemic to Lanyu Island (Orchid Island) and Ludao Island (Green Island). Because of its unclear life history, the host and immature stages of this species in the wild have not so far been recorded. On Lanyu Island, we recently identified Barringtonia asiatica as a host plant of P. sonani, with several larvae feeding on its xylem. Herein, we describe its biology and the habitat surrounding the host plant.     

Evolutionary effects of geographic and climatic isolation between Rhododendron tsusiophyllum populations on the Izu Islands and mainland Honshu of Japan

Geographic and environmental isolations of islands and the mainland offer excellent opportunity to investigate colonization and survival dynamics of island populations. We inferred and compared evolutionary processes and the demographic history of Rhododendron tsusiophyllum, in the Izu Islands and the much larger island Honshu, treated here as the mainland, using thousands of nuclear SNPs obtained by ddRAD-seq from eight populations of R. tsusiophyllum and three populations of R. tschonoskii as an outgroup. Phylogenetic relationships and their habitats suggest that R. tsusiophyllum had evolved and migrated from cold north to warm south regions. We detected clear genetic divergence among populations in three regions of Honshu and the Izu Islands, suggesting restricted migration between them due to isolated habitats on mountains even in the mainland. The three regions have different changes in effective population size, especially, genetic diversity and population size of the Izu Islands are small compared to the others. Further, habitats of populations in the Izu Islands are warmer than those in Honshu, suggesting that they have undergone adaptive evolution. Our study provides evidences of montane rather than insular isolation on genetic divergence, survival of populations and significance of adaptive evolution for island populations with small population size and low genetic diversity, despite close proximity to mainland populations.Subject terms: Genetic variation, Plant evolution, Conservation biology     

Birds are islands for parasites

Understanding the mechanisms driving the extraordinary diversification of parasites is a major challenge in evolutionary biology. Co-speciation, one proposed mechanism that could contribute to this diversity is hypothesized to result from allopatric co-divergence of host–parasite populations. We found that island populations of the Galápagos hawk (Buteo galapagoensis) and a parasitic feather louse species (Degeeriella regalis) exhibit patterns of co-divergence across variable temporal and spatial scales. Hawks and lice showed nearly identical population genetic structure across the Galápagos Islands. Hawk population genetic structure is explained by isolation by distance among islands. Louse population structure is best explained by hawk population structure, rather than isolation by distance per se, suggesting that lice tightly track the recent population histories of their hosts. Among hawk individuals, louse populations were also highly structured, suggesting that hosts serve as islands for parasites from an evolutionary perspective. Altogether, we found that host and parasite populations may have responded in the same manner to geographical isolation across spatial scales. Allopatric co-divergence is likely one important mechanism driving the diversification of parasites.     

Evolutionary assembly of island faunas reverses the classic island–mainland richness difference in Anolis lizards

Aim Islands are widely considered to be species depauperate relative to mainlands but, somewhat paradoxically, are also host to many striking adaptive radiations. Here, focusing on Anolis lizards, we investigate if cladogenetic processes can reconcile these observations by determining if in situ speciation can reduce, or even reverse, the classical island–mainland richness discrepancy. Location Caribbean islands and the Neotropical mainland. Methods We constructed range maps for 203 mainland anoles from museum records and evaluated whether geographical area could account for differences in species richness between island and mainland anole faunas. We compared the island species–area relationship with total mainland anole diversity and with the richness of island‐sized mainland areas. We evaluated the role of climate in the observed differences by using Bayesian model averaging to predict island richness based on the mainland climate–richness relationship. Lastly, we used a published phylogeny and stochastic mapping of ancestral states to determine if speciation rate was greater on islands, after accounting for differences in geographical area. Results Islands dominated by in situ speciation had, on average, significantly more species than similarly sized mainland regions, but islands where in situ speciation has not occurred were species depauperate relative to mainland areas. Results were similar at the scale of the entire mainland, although marginally non‐significant. These findings held even after accounting for climate. Speciation has not been faster on islands; instead, when extinction was assumed to be low, speciation rate varied consistently with geographical area. When extinction was high, there was some evidence that mainland speciation was faster than expected based on area. Main conclusions Our results indicate that evolutionary assembly of island faunas can reverse the general pattern of reduced species richness on islands relative to mainlands.     

Invasive species and land bird diversity on remote South Atlantic islands

Invasive species pose significant threats to biodiversity, especially on islands. They cause extinctions and population declines, yet little is known about their consequences on the emergent, metacommunity-level patterns of native species in island assemblages. We investigated differences in species–area relationships, nestedness, and occupancy of 9 species of native land birds between island assemblages with and without invasive Norway rats (Rattus norvegicus) in the Falkland Archipelago. We found that species–area curves, nestedness, and individual species’ occurrences differed between island assemblages with and without rats. Rat-free islands had, on average, 2.1 more land bird species than rat-infested islands of similar size. Passerine bird communities on islands with and without rats were significantly nested, but nestedness was significantly higher on rat-free islands than on rat-infested islands. The presence of rats was associated with differences in the incidence of many, but not all bird species. On rat free islands the occurrence of all species increased with island area. The occurrence of most, albeit not all, bird species was lower on islands with than on islands without rats. Two species of conservation concern, Troglodytes aedon cobbi and Cinclodes antarcticus, were abundant on rat-free islands, but absent or found at very low frequencies on islands with rats. The occurrence of three species was not associated with the presence of rats. The patterns presented here can be used to evaluate the consequences of ongoing rat eradications for passerine diversity, distribution, and abundance.     

Annotated check-list of the family Tachinidae (Diptera: Calyptratae: Oestroidea) in the Canary Islands

Summary

A commented check-list of the tachinid species inhabiting the Canary Islands (Spain) is provided, with special emphasis on hosts species and floral resources. Nine new local records are provided and Cylindromyia rufipes is reported for the first time for the Canary Islands, thus increasing the species number to 52. Zoogeographic analysis of the area revealed that there are differences in chorotype composition among islands, with the easternmost islands being richer in Mediterranean species and poorer in endemics. These differences may be due to ecological differences between the easternmost island and the remaining islands. Relevance regarding influence of tachinid as pollinators is discussed.     

Xenopsylla spp. (Siphonaptera: Pulicidae) in murid rodents from the Canary Islands: An update

The geographical and host distributions of Xenopsylla fleas parasitizing murid rodents on the Canary Islands have been reported. Three Xenopsylla species, X. cheopis, X. brasiliensis and X. guancha, have been detected on two rodents species, Mus musculus and Rattus rattus. X. guancha has been the most prevalent species detected, specifically on M. musculus, the most abundant rodent, but it has been detected only on three eastern islands, where the species is endemic. X. cheopis has been shown to be the most widely distributed species throughout the archipelago and the species most frequently found on R. rattus. X. brasiliensis has been shown to be the least prevalent Xenopsylla species, with the lowest geographical distribution on the Canary Islands and focused only on R. rattus. The detection of both X. cheopis and X. brasiliensis on the island of Lanzarote, and of X. guancha on the island of Fuerteventura and the islet of La Graciosa represents the first report of these species on those particular Canary Islands.     

Fine-Scale Genetic Structure and Demographic History in the Miyako Islands of the Ryukyu Archipelago

The Ryukyu Archipelago is located in the southwest of the Japanese islands and is composed of dozens of islands, grouped into the Miyako Islands, Yaeyama Islands, and Okinawa Islands. Based on the results of principal component analysis on genome-wide single-nucleotide polymorphisms, genetic differentiation was observed among the island groups of the Ryukyu Archipelago. However, a detailed population structure analysis of the Ryukyu Archipelago has not yet been completed. We obtained genomic DNA samples from 1,240 individuals living in the Miyako Islands, and we genotyped 665,326 single-nucleotide polymorphisms to infer population history within the Miyako Islands, including Miyakojima, Irabu, and Ikema islands. The haplotype-based analysis showed that populations in the Miyako Islands were divided into three subpopulations located on Miyakojima northeast, Miyakojima southwest, and Irabu/Ikema. The results of haplotype sharing and the D statistics analyses showed that the Irabu/Ikema subpopulation received gene flows different from those of the Miyakojima subpopulations, which may be related with the historically attested immigration during the Gusuku period (900 − 500 BP). A coalescent-based demographic inference suggests that the Irabu/Ikema population firstly split away from the ancestral Ryukyu population about 41 generations ago, followed by a split of the Miyako southwest population from the ancestral Ryukyu population (about 16 generations ago), and the differentiation of the ancestral Ryukyu population into two populations (Miyako northeast and Okinawajima populations) about seven generations ago. Such genetic information is useful for explaining the population history of modern Miyako people and must be taken into account when performing disease association studies.     

Parasites and the island syndrome: the colonization of the western Mediterranean islands by Heligmosomoides polygyrus (Dujardin, 1845)

Aim Populations of free‐living vertebrates on islands frequently differ from their mainland counterparts by a series of changes in morphometric, life‐history, behavioural, physiological and genetic traits, collectively referred to as the ‘island syndrome’. It is not known, however, whether the ‘island syndrome’ also affects parasitic organisms. The present study establishes the colonization pattern of the Mediterranean islands by the nematode Heligmosomoides polygyrus, a direct and specific parasite of rodent hosts of the Apodemus genus, and evaluates the effects of island colonization by this species on two components of the island syndrome: the loss of genetic diversity and the enlargement of the ecological niche. Location Heligmosomoides polygyrus was sampled on seven western Mediterranean islands ? Corsica, Crete, Elba, Majorca, Minorca, Sardinia and Sicily ? as well as in 20 continental locations covering the Mediterranean basin. Methods The mitochondrial cytochrome b gene (690 base pairs) was sequenced in 166 adult H. polygyrus individuals sampled in the 27 continental and island locations. Phylogenetic reconstructions in distance, parsimony, maximum likelihood and Bayesian posterior probabilities were carried out on the whole cytochrome b gene data set. The levels of nucleotide, haplotype and genetic divergence (Kimura two‐parameter distance estimator) diversities were estimated in each island population and in the various continental lineages. Results Phylogenetic reconstructions show that the mainland origins of H. polygyrus were continental Spain for the Balearic Islands (Majorca, Minorca), northern Italy for the Tyrrhenian Islands (Corsica, Sardinia, Elba), southern Italy for Sicily, and the Balkan region for Crete. A comparison of island H. polygyrus populations with their mainland source populations revealed two characteristic components of the island syndrome in this parasite. First, island H. polygyrus populations display a significant loss of genetic diversity, which is related (r² = 0.73) to the distance separating the island from the mainland source region. Second, H. polygyrus exhibits a niche enlargement following insularization. Indeed, H. polygyrus in Corsica is present in both A. sylvaticus and Mus musculus domesticus, while mainland H. polygyrus populations are present exclusively in Apodemus hosts. Main conclusions Our results show that H. polygyrus has undergone a loss of genetic diversity and a niche (host) enlargement following colonization of the western Mediterranean islands. To our knowledge, this study provides the first evidence for components of the ‘island syndrome’ in a parasitic nematode species.     

Colonization history of Galapagos giant tortoises: Insights from mitogenomes support the progression rule

Galapagos giant tortoises (Chelonoidis spp.) are a group of large, long-lived reptiles that includes 14 species, 11 of which are extant and threatened by human activities and introductions of non-native species. Here, we evaluated the phylogenetic relationships of all extant and two extinct species (Chelonoidis abingdonii from the island of Pinta and Chelonoidis niger from the island of Floreana) using Bayesian and maximum likelihood analysis of complete or nearly complete mitochondrial genomes. We also provide an updated phylogeographic scenario of their colonization of the Galapagos Islands using chrono-phylogenetic and biogeographic approaches. The resulting phylogenetic trees show three major groups of species: one from the southern, central, and western Galapagos Islands; the second from the northwestern islands; and the third group from the northern, central, and eastern Galapagos Islands. The time-calibrated phylogenetic and ancestral area reconstructions generally align with the geologic ages of the islands. The divergence of the Galapagos giant tortoises from their South American ancestor likely occurred in the upper Miocene. Their diversification on the Galapagos adheres to the island progression rule, starting in the Pleistocene with the dispersal of the ancestral form from the two oldest islands (San Cristóbal and Española) to Santa Cruz, Santiago, and Pinta, followed by multiple colonizations from different sources within the archipelago. Our work provides an example of how to reconstruct the history of endangered taxa in spite of extinctions and human-mediated dispersal events and provides a framework for evaluating the contribution of colonization and in situ speciation to the diversity of other Galapagos lineages.     

Genetic differentiation within and among island populations of the endangered plant Aster miyagii (Asteraceae), an endemic to the Ryukyu Islands

Genetic diversity was examined at 17 putative allozyme loci in 18 populations of the insular endemic plant Aster miyagii (Asteraceae). This species is geographically restricted to only three islands of the Ryukyu Islands and is on the federal list of threatened plants. Genetic differentiation within an island is small, suggesting that gene flow among populations on the same island is sufficiently large to prevent divergence. By contrast, genetic differentiation among islands is large, especially between Amamioshima Island and the other two islands, suggesting that gene flow between the islands is highly restricted. Two unique alleles are nearly fixed in populations on Amamioshima Island, which is the southernmost island of the three. Comparatively, genetic diversity is the smallest on Amamioshima Island. This genetic paucity on Amamioshima Island is probably a result of a population bottleneck at colonization or the small effective population size on this island. Genetic diversity at the species level of A. miyagii is larger than those of the species with a similar life history and of the congeneric widespread species, suggesting that the species has an old origin as an insular endemic species.     

Relationships between the demography and distribution of two bird-dispersed plants in an island archipelago

Aim I evaluated relationships between the demography and distribution of two bird‐dispersed shrubs in an island archipelago to better understand the life history precursors of different island distributional patterns. Location Barkley Sound, Vancouver Island, British Columbia, Canada (48°80′ N, 125°20′ W). Methods The abundance and occurrence of Lonicera involucrata Rich. (Caprifoliaceae) and Ribes divaricatum Dougl. (Grossulariaceae) were measured on 69 islands measuring between 25 and 800 m². Light and soil conditions were quantified to broadly characterize changes in environmental conditions with island area and isolation. Several experiments and field observations were conducted to evaluate the life history response of each species to changes in island environments. Results Lonicera showed a typical island distribution; it increased in abundance and occurrence with island area. Ribes had a more unusual distributional pattern; it showed no differences in occurrence or abundance with island area. The distribution of both species was unrelated to island isolation. Small islands had less soil and more light than large islands, while environmental conditions were unrelated to island isolation. Lonicera had higher seed germination rates and adult survivorship in large island environments, but similar rates of seed dispersal, seedling survivorship and sapling survivorship in large and small island environments. Ribes had similar rates of seed dispersal, germination and adult survivorship in large and small island environments. However, slightly higher seedling survivorship in large island environments was offset by decreased sapling survivorship. Conclusions Demographic advantages accrued at particular life history stages were either enhanced (Lonicera) or erased (Ribes) at other life history stages. Nevertheless, overall life history trends were consistent with distributional patterns, and suggest different suites of life history characteristics promote different island distributions.     

The effects of island ontogeny on species diversity and phylogeny

A major goal of island biogeography is to understand how island communities are assembled over time. However, we know little about the influence of variable area and ecological opportunity on island biotas over geological timescales. Islands have limited life spans, and it has been posited that insular diversity patterns should rise and fall with an island''s ontogeny. The potential of phylogenies to inform us of island ontogenetic stage remains unclear, as we lack a phylogenetic framework that focuses on islands rather than clades. Here, we present a parsimonious island-centric model that integrates phylogeny and ontogeny into island biogeography and can incorporate a negative feedback of diversity on species origination. This framework allows us to generate predictions about species richness and phylogenies on islands of different ages. We find that peak richness lags behind peak island area, and that endemic species age increases with island age on volcanic islands. When diversity negatively affects rates of immigration and cladogenesis, our model predicts speciation slowdowns on old islands. Importantly, we find that branching times of in situ radiations can be informative of an island''s ontogenetic stage. This novel framework provides a quantitative means of uncovering processes responsible for island biogeography patterns using phylogenies.     

A comparison of populations of island and adjacent mainland species of Caribbean Selenops (Araneae: Selenopidae) spiders

The role of the landscape in structuring populations has been the focus of numerous studies, in particular, the extent to which islands provide opportunities for isolation, and the consistency of such an effect across lineages. The current study examines this phenomenon using a series of relatively widespread taxa, all within a single genus of spiders, Selenops. We focus on the Caribbean Islands and adjacent Mesoamerican mainland to examine how the islands per se dictate structure across lineages. We use molecular genetic data from mitochondrial and nuclear genes to examine the population structure of seven species of Selenops. Comparisons are made between species found in the Greater Antilles, Lesser Antilles, and adjacent mainland. Results indicate that geography has little effect on the population structure of mainland species. In contrast, population structure appears to be partitioned by island in the insular Caribbean. Within islands, the amount of population structure for each species is variable and may be dictated more by ecological or demographic parameters, rather than geographic location. The overall conclusion is that the extent to which a given lineage is structured is highly variable across species, with this variability overwhelming any general signal of geographical isolation.     

ACCELERATED EVOLUTION OF LAND SNAILS MANDARINA IN THE OCEANIC BONIN ISLANDS: EVIDENCE FROM MITOCHONDRIAL DNA SEQUENCES

An endemic land snail genus Mandarina of the oceanic Bonin (Ogasawara) Islands shows exceptionally rapid evolution not only of morphological and ecological traits, but of DNA sequence. A phylogenetic relationship based on mitochondrial DNA (mtDNA) sequences suggests that morphological differences equivalent to the differences between families were produced between Mandarina and its ancestor during the Pleistocene. The inferred phylogeny shows that species with similar morphologies and life habitats appeared repeatedly and independently in different lineages and islands at different times. Sequential adaptive radiations occurred in different islands of the Bonin Islands and species occupying arboreal, semiarboreal, and terrestrial habitat arose independently in each island. Because of a close relationship between shell morphology and life habitat, independent evolution of the same life habitat in different islands created species possesing the same shell morphology in different islands and lineages. This rapid evolution produced some incongruences between phylogenetic relationship and species taxonomy. Levels of sequence divergence of mtDNA among the species of Mandarina is extremely high. The maximum level of sequence divergence at 16S and 12S ribosomal RNA sequence within Mandarina are 18.7% and 17.7%, respectively, and this suggests that evolution of mtDNA of Mandarina is extremely rapid, more than 20 times faster than the standard rate in other animals. The present examination reveals that evolution of morphological and ecological traits occurs at extremely high rates in the time of adaptive radiation, especially in fragmented environments.