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Continental Islands (continental + island)
Selected AbstractsDeep, hierarchical divergence of mitochondrial DNA in Amplirhagada land snails (Gastropoda: Camaenidae) from the Bonaparte Archipelago, Western AustraliaBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010MICHAEL S. JOHNSON Continental islands have experienced cycles of isolation and connection. Although complex genetic patterns have been described for mainland species affected by glacial cycles of isolation, island biotas have received little attention. We examined mitochondrial DNA in Amplirhagada land snails from 16 islands and two adjacent mainland areas of the Bonaparte Archipelago, in the Kimberley region of northern Western Australia. Four major clades, with sequence divergence of 16,27% in the 16S ribosomal RNA gene, correspond to the major geographic groupings, separated by 10,160 km. Distinct lineages also characterize islands that are only a few kilometres apart. The large differences indicate that the lineages are much older than the islands themselves, and show no evidence of geologically recent connection. Three of the major clades match the morphological description of Amplirhagada alta. Either this named species comprises several morphologically cryptic species, or it is a single, genetically very diverse species, distributed over much of the Bonaparte Archipelago. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 141,153. [source] Continental speciation in the tropics: contrasting biogeographic patterns of divergence in the Uroplatus leaf-tailed gecko radiation of MadagascarJOURNAL OF ZOOLOGY, Issue 4 2008C. J. Raxworthy Abstract A fundamental expectation of vicariance biogeography is for contemporary cladogenesis to produce spatial congruence between speciating sympatric clades. The Uroplatus leaf-tailed geckos represent one of most spectacular reptile radiations endemic to the continental island of Madagascar, and thus serve as an excellent group for examining patterns of continental speciation within this large and comparatively isolated tropical system. Here we present the first phylogeny that includes complete taxonomic sampling for the group, and is based on morphology and molecular (mitochondrial and nuclear DNA) data. This study includes all described species, and we also include data for eight new species. We find novel outgroup relationships for Uroplatus and find strongest support for Paroedura as its sister taxon. Uroplatus is estimated to have initially diverged during the mid-Tertiary in Madagascar, and includes two major speciose radiations exhibiting extensive spatial overlap and estimated contemporary periods of speciation. All sister species are either allopatric or parapatric. However, we found no evidence for biogeographic congruence between these sympatric clades, and dispersal events are prevalent in the dispersal,vicariance biogeographic analyses, which we estimate to date to the Miocene. One sister-species pair exhibits isolated distributions that we interpret as biogeographic relicts, and two sister-species pairs have parapatric distributions separated by elevation. Integrating ecological niche models with our phylogenetic results finds both conserved and divergent niches between sister species. We also found substantial intra-specific genetic variation, and for the three most widespread species, poor intra-specific predictive performance for ecological niche models across the latitudinal span of Madagascar. These latter results indicate the potential for intra-specific niche specialization along environmental gradients, and more generally, this study suggests a complex speciation history for this group in Madagascar, which appears to include multiple speciation processes. [source] Phylogeographical structure in the coastal species Senecio rodriguezii (Asteraceae), a narrowly distributed endemic Mediterranean plantJOURNAL OF BIOGEOGRAPHY, Issue 7 2009Arántzazu Molins Abstract Aim, Our goals were (1) to assess the levels of chloroplast DNA variation in a narrowly distributed plant restricted to continental islands, (2) to ascertain whether a phylogeographical structure is present in plants restricted to coastal linear systems, and (3) to interpret the results in the light of the known palaeogeography of these islands. Location, The Eastern Balearic Islands (Majorca and Minorca) in the Western Mediterranean Basin. Methods, Sampling included 134 individuals from 28 populations of Senecio rodriguezii covering the entire range of the species. Sequences of the chloroplast genome (trnT,trnL spacer) were obtained and parameters of population genetic diversity and substructure were determined (hsht, Gst). The geographical structure of genetic variation was assessed by an analysis of molecular variance (AMOVA). Additionally, a spatial AMOVA (SAMOVA) was used to identify groups of populations that were geographically homogeneous and maximally differentiated from each other. Finally, a pattern of isolation by distance was assessed by testing the correlation between the matrix of pairwise ,ST values and the matrix of geographical distances between pairs of populations using a Mantel test. Results, Seven haplotypes were detected in S. rodriguezii. Only two of them were shared between islands; all of the others were restricted to Majorca (two) or Minorca (three). Overall, we found high levels of genetic diversity and significant geographical structuring of cpDNA markers. Most of the variation detected can be attributed to differences among populations (84.6%), but there was also a significant differentiation between the islands. Main conclusions, Our results support the view that the Balearic Islands constitute a reservoir of genetic diversity, not only for widespread Mediterranean taxa, but also for endemic ones. The intraspecific genetic structure found in S. rodriguezii suggests that its population history was dominated by both expansion and contraction events. This has resulted in a species that is highly structured genetically, showing very few shared haplotypes between islands, and a high number of haplotypes restricted to small geographical areas within the islands. Changes in habitat availability and dynamic processes of population fragmentation and connectivity due to repeated cycles of sea-level changes during the Quaternary are the possible underlying factors that have shaped the cpDNA pool of this endemic species on a regional scale. [source] Dispersal is fundamental to biogeography and the evolution of biodiversity on oceanic islandsJOURNAL OF BIOGEOGRAPHY, Issue 2 2006Robert H. Cowie Abstract Vicariance biogeography emerged several decades ago from the fusion of cladistics and plate tectonics, and quickly came to dominate historical biogeography. The field has since been largely constrained by the notion that only processes of vicariance and not dispersal offer testable patterns and refutable hypotheses, dispersal being a random process essentially adding only noise to a vicariant system. A consequence of this thinking seems to have been a focus on the biogeography of continents and continental islands, considering the biogeography of oceanic islands less worthy of scientific attention because, being dependent on stochastic dispersal, it was uninteresting. However, the importance of dispersal is increasingly being recognized, and here we stress its fundamental role in the generation of biodiversity on oceanic islands that have been created in situ, never connected to larger land masses. Historical dispersal patterns resulting in modern distributions, once considered unknowable, are now being revealed in many plant and animal taxa, in large part through the analysis of polymorphic molecular markers. We emphasize the profound evolutionary insights that oceanic island biodiversity has provided, and the fact that, although small in area, oceanic islands harbour disproportionately high biodiversity and numbers of endemic taxa. We further stress the importance of continuing research on mechanisms generating oceanic island biodiversity, especially detection of general, non-random patterns of dispersal, and hence the need to acknowledge oceanic dispersal as significant and worthy of research. [source] Darwin on island plantsBOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009SHERWIN CARLQUIST fls Islands played a key role in Charles Darwin's observations and experiments on plant dispersal. By means of these experiments, he expunged the old idea that a given species could originate at multiple times and in multiple places. More importantly, by seeing the capabilities for dispersal of plant seeds, fruits and branches, he was able to develop ideas of how plants reach islands and thus he is one of the founders of plant biogeography. For facts regarding floristic distribution of plants, Darwin relied on other workers, most notably Sir Joseph Dalton Hooker. Among his insights were the differences between oceanic and continental islands on a floristic basis, ideas on how age of island and distance from mainland areas influenced composition of island floras, the nature of endemism on islands and the role islands and archipelagos served as stepping stones in dispersal. Ingenious at proposing hypotheses, but always respectful of facts, Darwin sought explanations for plant adaptations on islands at a time when knowledge of island botany was little more than floristic in nature. These explanations are compared with selected recent works in island botany. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 20,25. [source] | ||||||||||