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ABSTRACT: While reinforcement may play a role in all major modes of speciation, relatively little is known about the timescale over which species hybridize without evolving complete reproductive isolation. Birds have high potential for hybridization, and islands provide simple settings for uncovering speciation and hybridization patterns. Here we develop a phylogenetic hypothesis for a phenotypically diverse radiation of finch-like weaver-birds (Foudia) endemic to the western Indian Ocean islands. We find that unlike Darwin's finches, each island-endemic Foudia population is a monophyletic entity for which speciation can be considered complete. In explaining the only exceptions-mismatches between taxonomy, mitochondrial, and nuclear data-phylogenetic and coalescent methods support introgressive hybridization rather than incomplete lineage sorting. Human introductions of known timing of one island-endemic species, to all surrounding archipelagos provide two fortuitous experiments; (1) population sampling at known times in recent evolutionary history, (2) bringing allopatric lineages of an island radiation into secondary contact. Our results put a minimum time bound on introgression (235 years), and support hybridization between species in natural close contact (parapatry), but not between those in natural allopatry brought into contact by human introduction. Time in allopatry, rather than in sympatry, appears key in the reproductive isolation of Foudia species.
Evolution 05/2012; 66(5):1490-505. · 5.15 Impact Factor
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ABSTRACT: While reinforcement may play a role in all major modes of speciation, relatively little is known about the timescale over which species hybridize without evolving complete reproductive isolation. Birds have high potential for hybridization, and islands provide simple settings for uncovering speciation and hybridization patterns. Here we develop a phylogenetic hypothesis for a phenotypically-diverse radiation of finch-like weaver-birds (Foudia) endemic to the western Indian Ocean islands. We find that unlike Darwin’s finches, each island-endemic Foudia population is a monophyletic entity for which speciation can be considered complete. In explaining the only exceptions – mismatches between taxonomy, mitochondrial and nuclear data –phylogenetic and coalescent methods support introgressive hybridization rather than incomplete lineage sorting. Human introductions of known timing of one island-endemic species, to all surrounding archipelagos provide two fortuitous experiments; (1) population sampling at known times in recent evolutionary history, (2) bringing allopatric lineages of an island radiation into secondary contact. Our results put a minimum time bound on introgression (235 years), and support hybridization between species in natural close contact (parapatry), but not between those in natural allopatry brought into contact by human introduction. Time in allopatry, rather than in sympatry, appears key in the reproductive isolation of Foudia species.
Evolution. 01/2012;
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ABSTRACT: Madagascar is surrounded by archipelagos varying widely in origin, age and structure. Although small and geologically young, these archipelagos have accumulated disproportionate numbers of unique lineages in comparison to Madagascar, highlighting the role of waif-dispersal and rapid in situ diversification processes in generating endemic biodiversity. We reconstruct the evolutionary and biogeographical history of the genus Psiadia (Asteraceae), a plant genus with near equal numbers of species in Madagascar and surrounding islands. Analyzing patterns and processes of diversification, we explain species accumulation on peripheral islands and aim to offer new insights on the origin and potential causes for diversification in the Madagascar and Indian Ocean Islands biodiversity hotspot. Our results provide support for an African origin of the group, with strong support for non-monophyly. Colonization of the Mascarenes took place by two evolutionary distinct lineages from Madagascar, via two independent dispersal events, each unique for their spatial and temporal properties. Significant shifts in diversification rate followed regional expansion, resulting in co-occurring and phenotypically convergent species on high-elevation volcanic slopes. Like other endemic island lineages, Psiadia have been highly successful in dispersing to and radiating on isolated oceanic islands, typified by high habitat diversity and dynamic ecosystems fuelled by continued geological activity. Results stress the important biogeographical role for Rodrigues in serving as an outlying stepping stone from which regional colonization took place. We discuss how isolated volcanic islands contribute to regional diversity by generating substantial numbers of endemic species on short temporal scales. Factors pertaining to the mode and tempo of archipelago formation and its geographical isolation strongly govern evolutionary pathways available for species diversification, and the potential for successful diversification of dispersed lineages, therefore, appears highly dependent on the timing of arrival, as habitat and resource properties change dramatically over the course of oceanic island evolution. Copyright: ß 2012 Strijk et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by the European Union's HOTSPOTS Training Network (MEST-2005-020561), the French National Research Agency's Biodiversity program (ANR-06-BDIV-002) and the ''Laboratoire d'Excellence'' TULIP (ANR-10-LABX-41). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist.
PLoS ONE 01/2012; · 4.09 Impact Factor
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ABSTRACT: With 14 species, Badula (Primulaceae) is the most species-rich endemic angiosperm genus of the Mascarene Archipelago. The relationship between Badula and its ally Oncostemum (c. 100 spp; Madagascar and the Comoros Islands) is uncertain, with implications for the circumscription of Badula as a Mascarene endemic. Within Badula, species rarity (several being critically endangered) and a paucity of herbarium specimens hamper proper species delimitations. Here, we estimate the phylogenetic relationships of Badula based on DNA sequence data from the nuclear ribosomal internal transcribed spacer (ITS) and plastid trnS-trnG-trnG regions with complete taxon sampling of the genus and three samples or more of each taxon. The results strongly supported the monophyly of Badula. Paraphyly of Oncostemum was inferred with weak support; explicit hypothesis testing did not favour this hypothesis over one that forced the monophyly of Oncostemum. Monophyly of several Badula spp. was supported, particularly for taxa from the older islands of Mauritius and Rodrigues. Badula is inferred to have reached the Mascarene Archipelago through a single colonization event. The majority of species segregated into island clades, implying that few, rather than multiple, colonization events have occurred in Badula among the islands of the archipelago.
Botanical Journal of the Linnean Society 01/2012; 169:284-296. · 2.82 Impact Factor
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ABSTRACT: A corollary of island biogeographical theory is that islands are largely colonized from their nearest mainland source. Despite Madagascar’s extreme isolation from India and proximity to Africa, a high proportion of the biota of the Madagascar region has Asian affinities. This pattern has rarely been viewed as surprising, as it is consistent with Gondwanan vicariance. Molecular phylogenetic data provide strong support for such Asian affinities, but often not for their vicariant origin; most divergences between lineages in Asia and the Madagascar region post-date the separation of India and Madagascar considerably (up to 87 Myr), implying a high frequency of dispersal that mirrors colonization of the Hawaiian archipelago in distance. Indian Ocean bathymetry and the magnitude of recent sea-level lowstands support the repeated existence of sizeable islands across the western Indian Ocean, greatly reducing the isolation of Madagascar from Asia. We put forward predictions to test the role of this historical factor in the assembly of the regional biota.© The Willi Hennig Society 2009.
Cladistics 09/2010; 26(5):526 - 538. · 5.25 Impact Factor
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ABSTRACT: 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.
Journal of Biogeography 06/2010; 37(7):1227 - 1238. · 4.54 Impact Factor
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ABSTRACT: Three populations of the epiphyllous liverwort Drepanolejeunea madagascariensis collected in the cloud forests of Reunion Island (Mascarene Archipelago) were investigated for their volatile compounds, because of the pleasant, sweet, warm, woody-spicy, and herbaceous fragrance, slightly reminiscent of dill, of this species. By applying the headspace solid-phase microextraction (HS-SPME) technique coupled to GC/MS analysis, 34 compounds were detected in total, with p-menth-1-en-9-ol (28.8-43.5%), limonene (10.5-14.7%), beta-phellandrene (8.8-11.6%), and the so-called dill ether (8.5-16.6%) as the main components. The presence of 1-epi-alpha-pinguisene confirms the possible use of pinguisane-type sesquiterpenoids as a characteristic chemical marker for the order Jungermanniales.
Chemistry & Biodiversity 03/2010; 7(3):639-48. · 1.80 Impact Factor
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ABSTRACT: Pollinator-mediated selection and evolution of floral traits have long fascinated evolutionary ecologists. No other plant family shows as wide a range of pollinator-linked floral forms as Orchidaceae. In spite of the large size of this model family and a long history of orchid pollination biology, the identity and specificity of most orchid pollinators remains inadequately studied, especially in the tropics where the family has undergone extensive diversification. Angraecum (Vandeae, Epidendroideae), a large genus of tropical Old World orchids renowned for their floral morphology specialized for hawkmoth pollination, has been a model system since the time of Darwin.
The pollination biology of A. cadetii, an endemic species of the islands of Mauritius and Reunion (Mascarene Islands, Indian Ocean) displaying atypical flowers for the genus (white and medium-size, but short-spurred) was investigated. Natural pollinators were observed by means of hard-disk camcorders. Pollinator-linked floral traits, namely spur length, nectar volume and concentration and scent production were also investigated. Pollinator efficiency (pollen removal and deposition) and reproductive success (fruit set) were quantified in natural field conditions weekly during the 2003, 2004 and 2005 flowering seasons (January to March).
Angraecum cadetii is self-compatible but requires a pollinator to achieve fruit set. Only one pollinator species was observed, an undescribed species of raspy cricket (Gryllacrididae, Orthoptera). These crickets, which are nocturnal foragers, reached flowers by climbing up leaves of the orchid or jumping across from neighbouring plants and probed the most 'fresh-looking' flowers on each plant. Visits to flowers were relatively long (if compared with the behaviour of birds or hawkmoths), averaging 16.5 s with a maximum of 41.0 s. At the study site of La Plaine des Palmistes (Pandanus forest), 46.5 % of flowers had pollen removed and 27.5 % had pollinia deposited on stigmas. The proportion of flowers that set fruit ranged from 11.9 % to 43.4 %, depending of the sites sampled across the island.
Although orthopterans are well known for herbivory, this represents the first clearly supported case of orthopteran-mediated pollination in flowering plants.
Annals of Botany 03/2010; 105(3):355-64. · 4.03 Impact Factor
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ABSTRACT: To evaluate the interpopulation variability of volatile compounds in Melicope obscura, four samples representing four populations were collected all over the distribution area of the species in Reunion Island (Indian Ocean). The samples were extracted by hydrodistillation, and analyzed using GC/FID and GC/MS techniques. The study revealed that, in the four essential oils obtained, oxygenated sesquiterpenes were one of the major chemical classes (9.2-35.2%), mainly consisting of a new compound, (+)-6-ethenyl-2-hydroxy-6,10-dimethylundeca-2,9-dien-4-one (1), called melicopenol (8.6-30.1%). The compound was isolated by column chromatography and identified by spectral analyses including 1D- and 2D-NMR.
Chemistry & Biodiversity 02/2010; 7(2):467-75. · 1.80 Impact Factor
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ABSTRACT: A corollary of island biogeographical theory is that islands are largely colonized from their nearest mainland source. Despite Madagascar�s extreme isolation from India and proximity to Africa, a high proportion of the biota of the Madagascar region has Asian affinities. This pattern has rarely been viewed as surprising, as it is consistent with Gondwanan vicariance. Molecular phylogenetic data provide strong support for such Asian affinities, but often not for their vicariant origin; most divergences between lineages in Asia and the Madagascar region post-date the separation of India and Madagascar considerably (up to 87 Myr), implying a high frequency of dispersal that mirrors colonization of the Hawaiian archipelago in distance. Indian Ocean bathymetry and the magnitude of recent sea-level lowstands support the repeated existence of sizeable islands across the western Indian Ocean, greatly reducing the isolation of Madagascar from Asia. We put forward predictions to test the role of this historical factor in the assembly of the regional biota.
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ABSTRACT: An important challenge of invasion biology is to understand how interactions between species traits and ecosystem properties enable alien species to become invasive at particular locations. We investigated how gap dynamics in a tropical rain forest on the island of Réunion affected the invasiveness of alien plants. In the 12 000-m 2 study area, alien plants occupied 24.9% of the area of gaps, which represented 5.62% of the forest area, but only 0.8% of the understorey area. The most abundant invasive species was Rubus alceifolius, which formed dense, monospecific stands in the largest gaps (> 25 m 2). Although plants could persist in the shade, a germination experiment revealed that canopy openings were essential for seedling establishment. A cyclone that struck the study area in 2002 caused a temporary thinning of the canopy, increasing light levels to above the threshold needed for germination of R. alceifolius and also stimulating the growth of established plants. We conclude that the ability of this and other alien species to colonize intact lowland tropical rain forest is strongly influenced by the prevailing gap dynamics. Because gaps are also essential for the regeneration of many native trees in our study area, there is a real danger of the forest being progressively degraded by alien plants. There are no simple solutions to controlling species such as Rubus alceifolius, but efforts should be focused mainly upon the larger gaps where the species are most invasive.
Journal of Tropical Ecology Copyright ©. 01/2008; 24:1-9.
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ABSTRACT: Rubus alceifolius Poiret (Rosaceae) was introduced to the island of Runion in the southeastern Indian Ocean about 1850 and is now highly invasive. This bramble, native from southeastern Asia and Malaysia, has invaded a wide variety of habitats (lowland rainforest, mountain and submountain rainforest, Acacia heterophylla rainforest) from sea level to 1700 m. It is suspected to be monoclonal so, its remarkable success may be due in part to great phenotypic plasticity. On Runion, bud, flower, fruit and seed production, the duration of the flowering period and the importance of the seed bank were found to be negatively correlated with elevation (50-1500 m a.s.l.). At a lowland site, fruit production in mature stands averaged between 30 and 80 fruits/m2 during 1999 and 2000. No fruit set occurred above 1100 m. This fruit production pattern was similar over two years. Although the number of leaves per unit area is similar along the whole gradient studied, decrease of fruit set in upland areas might be compensated for by an increase in vegetative growth. Temperature variation is very sharp along the elevation gradient and may control the fruit and the seed production. Fruit production allows establishment of new populations all around the island via bird dissemination. Once established, R. alceifolius maintains dense patches that can grow vegetatively. Our results may be relevant for eradication programs that should take into account variation in reproductive strategy in lowland vs. highland habitats.
Plant Ecology 05/2004; 172(2):265 -273. · 1.83 Impact Factor
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ABSTRACT: The aim of this study was to identify the developmental stages of Rubus alceifolius and to determine one or more characteristic morphological markers for each stage. The developmental reconstitution method used involved a detailed description of many individuals throughout the different stages of growth, from germination to the development of an adult shoot capable of fruiting. Results revealed that R. alceifolius passes through five developmental stages that can be distinguished by changes in several morphological markers such as internode length and diameter, pith diameter and plant shape. This analysis indicated that R. alceifolius has a heteroblastic developmental pattern, midway between that of a bush and a liana. Moreover, results showed that this species taps environmental resources early in its development, i.e. foliarization is high (the foliar component overrides the caulinary component) and an autotrophic stage is rapidly reached, whereas it 'explores' the environment during the adult stage, i.e. axialization is substantial (the caulinary component overrides the foliar component) and autotrophy occurs at a later stage. The morphological markers identified could benefit land-use managers attempting to control this species before it reaches its optimum developmental stage.
Annals of Botany 02/2003; 91(1):39-48. · 4.03 Impact Factor
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Dominique Strasberg
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ABSTRACT: Because lowland rain forests of oceanic islands have almost always been destroyed soon after human colonization, there exist few quantitative descriptions of tree species composition and diversity in such forests. For this reason, the diversity and structure of a lowland tropical rain forest were studied on a 1-ha permanent plot on the oceanic island of La Runion. A total of 1270 individuals of gbh 25 cm (girth at breast height), including at least 43 species, were mapped, measured and identified. Several species were represented only by large individuals. Ten species among the 23 common enough to test are randomly distributed over the hectare, while 13 show aggregated spatial distributions. The tree species diversity, size structure and spatial distribution observed in this island plot are discussed in light of patterns occurring in continental lowland tropical rain forests. In the study area, the high density of trees and the tendency of conspecific individuals to be clumped may be linked to several factors: hurricane disturbance, lack of seed dispersers and patchy seed rain.
Biodiversity and Conservation 06/1996; 5(7):825-840. · 2.24 Impact Factor
