Human‐mediated dispersals do not explain tortoise distribution on the Indian Ocean's islands

Origins of giant tortoises on the Indian Ocean's islands have been debated, and most recently attributed to human translocation (see Wilmé, Patrick, & Ganzhorn, 2017). To resolve the issue, we analyse all available molecular sequences from extinct and extant Indian Ocean's giant tortoises, along with major clades of the family Testudinidae using phylogenetic methods, Bayesian inference and maximum likelihood, and a relaxed time calibration approach. Our results most strongly support giant tortoises of the genus Cylindraspis evolving in situ in the Mascarene Islands since the early mid‐Miocence, and Aldabra tortoises diverging from a Madagascan lineage in the early Oligocene. The geologic time‐scale of these speciation events and the resulting island endemism for each lineage do not support human translocation, but rather demonstrate the impressive ability of giant tortoises to disperse long distances across oceans.     

Fission and fusion in island taxa – serendipity,or something to be expected?

A well‐used metaphor for oceanic islands is that they act as ‘natural laboratories’ for the study of evolution. But how can islands or archipelagos be considered analogues of laboratories for understanding the evolutionary process itself? It is not necessarily the case that just because two or more related species occur on an island or archipelago, somehow, this can help us understand more about their evolutionary history. But in some cases, it can. In this issue of Molecular Ecology, Garrick et al. ( 2014 ) use population‐level sampling within closely related taxa of Galapagos giant tortoises to reveal a complex demographic history of the species Chelonoidis becki – a species endemic to Isabela Island, and geographically restricted to Wolf Volcano. Using microsatellite genotyping and mitochondrial DNA sequencing, they provide a strong case for C. becki being derived from C. darwini from the neighbouring island of Santiago. But the interest here is that colonization did not happen only once. Garrick et al. ( 2014 ) reveal C. becki to be the product of a double colonization event, and their data reveal these two founding lineages to be now fusing back into one. Their results are compelling and add to a limited literature describing the evolutionary consequences of double colonization events. Here, we look at the broader implications of the findings of Garrick et al. ( 2014 ) and suggest genomic admixture among multiple founding populations may be a characteristic feature within insular taxa.     

Unravelling the peculiarities of island life: vicariance, dispersal and the diversification of the extinct and extant giant Galápagos tortoises

In isolated oceanic islands, colonization patterns are often interpreted as resulting from dispersal rather than vicariant events. Such inferences may not be appropriate when island associations change over time and new islands do not form in a simple linear trend. Further complexity in the phylogeography of ocean islands arises when dealing with endangered taxa as extinctions, uncertainty on the number of evolutionary ‘units’, and human activities can obscure the progression of colonization events. Here, we address these issues through a reconstruction of the evolutionary history of giant Galápagos tortoises, integrating DNA data from extinct and extant species with information on recent human activities and newly available geological data. Our results show that only three of the five extinct or nearly extinct species should be considered independent evolutionary units. Dispersal from mainland South America started at approximately 3.2 Ma after the emergence of the two oldest islands of San Cristobal and Española. Dispersal from older to younger islands began approximately 1.74 Ma and was followed by multiple colonizations from different sources within the archipelago. Vicariant events, spurred by island formation, coalescence, and separation, contributed to lineage diversifications on Pinzón and Floreana dating from 1.26 and 0.85 Ma. This work provides an example of how to reconstruct the history of endangered taxa in spite of extinctions and human‐mediated dispersal events and highlights the need to take into account both vicariance and dispersal when dealing with organisms from islands whose associations are not simply explained by a linear emergence model.     

The evolutionary origin of Indian Ocean tortoises (Dipsochelys)

Today, the only surviving wild population of giant tortoises in the Indian Ocean occurs on the island of Aldabra. However, giant tortoises once inhabited islands throughout the western Indian Ocean. Madagascar, Africa, and India have all been suggested as possible sources of colonization for these islands. To address the origin of Indian Ocean tortoises (Dipsochelys, formerly Geochelone gigantea), we sequenced the 12S, 16S, and cyt b genes of the mitochondrial DNA. Our phylogenetic analysis shows Dipsochelys to be embedded within the Malagasy lineage, providing evidence that Indian Ocean giant tortoises are derived from a common Malagasy ancestor. This result points to Madagascar as the source of colonization for western Indian Ocean islands by giant tortoises. Tortoises are known to survive long oceanic voyages by floating with ocean currents, and thus, currents flowing northward towards the Aldabra archipelago from the east coast of Madagascar would have provided means for the colonization of western Indian Ocean islands. Additionally, we found an accelerated rate of sequence evolution in the two Malagasy Pyxis species examined. This finding supports previous theories that shorter generation time and smaller body size are related to an increase in mitochondrial DNA substitution rate in vertebrates.     

How marine currents influenced the widespread natural overseas dispersal of reptiles in the Western Indian Ocean region

In a recent contribution to this journal, Wilmé et al. (2016) proposed that the giant tortoises of the islands of the Western Indian Ocean (WIO: Aldabra, the Mascarenes, and the Granitic Seychelles) might have originated from translocation by early Austronesian sailors. Prompted by this paper we review recent literature and show that natural overseas dispersal was remarkably widespread in the colonization history of terrestrial reptiles in the WIO region. Almost 90% of the successful colonization events are supported by prevailing marine surface currents. However, these currents may change over geological (and evolutionary) time‐scales, and eddies and counter‐currents may facilitate transport against the main current direction. We review the cases of the extant and extinct WIO giant tortoises and suggest that the current distribution of all lineages can be convincingly explained by overseas dispersal.     

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.     

Dispersal and diversification: macroevolutionary implications of the MacArthur–Wilson model, illustrated by Simulium (Inseliellum) Rubstov (Diptera: Simuliidae)

Aim Provide an empirical test of the ‘radiation zone’ hypothesis of the MacArthur–Wilson theory of island biogeography using the taxon‐pulse hypothesis of Erwin and Brooks Parsimony Analysis (BPA) on Simulium (Inseliellum) Rubstov. Location Micronesia, Cook Islands, Austral Islands, Society Islands, Marquesas Islands, Fiji and New Caledonia. Methods Primary and secondary BPA of the phylogeny of Inseliellum. Results Primary BPA showed that 15% of the taxon area cladogram contained area reticulations. Secondary BPA (invoking the area duplication convention) generated a clear sequence of dispersal for Inseliellum. The sequence follows a Micronesia – Cook Islands – Marquesas Islands – Society Islands dispersal, with a separate dispersal from the Cook Islands to the Austral Islands less than 1 Ma. A radiation in the island of Tahiti (Society Islands) produced numerous dispersals from Tahiti to other islands within the Society Islands system. Islands close to Tahiti (source island) have been colonized from Tahiti more often than islands far from Tahiti, but a higher proportion of those species colonizing distant islands have become distinct species. Main conclusions The dispersal sequence of Inseliellum exhibits both old to young island dispersal and young to old island dispersal. This is due to habitat availability on each island. Inseliellum is a model system in exemplifying the ‘radiation zone’ hypothesis of MacArthur and Wilson. As well, islands close to the source are colonized more often that those far from the source, but colonization of islands far away from the source results in a higher proportion of speciation events than for islands close to the source. The diversification of Inseliellum corresponds to a taxon‐pulse radiation, with a centre of diversification on Tahiti resulting from its large area and abundant freshwater habitats. This study illustrates the utility of BPA in identifying complex scenarios that can be used to test theories about the complementary roles of ecology and phylogeny in historical biogeography.     

Origins of endemic island tortoises in the western Indian Ocean: a critique of the human‐translocation hypothesis

How do organisms arrive on isolated islands, and how do insular evolutionary radiations arise? In a recent paper, Wilmé et al. ( 2016a ) argue that early Austronesians that colonized Madagascar from Southeast Asia translocated giant tortoises to islands in the western Indian Ocean. In the Mascarene Islands, moreover, the human‐translocated tortoises then evolved and radiated in an endemic genus (Cylindraspis). Their proposal ignores the broad, established understanding of the processes leading to the formation of native island biotas, including endemic radiations. We find Wilmé et al.'s suggestion poorly conceived, using a flawed methodology and missing two critical pieces of information: the timing and the specifics of proposed translocations. In response, we here summarize the arguments that could be used to defend the natural origin not only of Indian Ocean giant tortoises but also of scores of insular endemic radiations world‐wide. Reinforcing a generalist's objection, the phylogenetic and ecological data on giant tortoises, and current knowledge of environmental and palaeogeographical history of the Indian Ocean, make Wilmé et al.'s argument even more unlikely.     

The origin and diversification of Galapagos mockingbirds

Abstract Evolutionary radiations of colonists on archipelagos provide valuable insight into mechanisms and modes of speciation. The apparent diversification of Galapagos mockingbirds (Nesomimus) provoked Darwin's initial conception of adaptive radiation, but the monophyly of this historically important exemplar has not been evaluated with molecular data. Additionally, as with most Galapagos organisms, we have a poor understanding of the temporal pattern of diversification of the mockingbirds following colonization(s) from source populations. Here we present a molecular phylogeny of Galapagos and other mockingbird populations based on mitochondrial sequence data. Monophyly of Galapagos mockingbirds was supported, suggesting a single colonization of the archipelago followed by diversification. Our analyses also indicate that Nesomimus is nested within the traditional genus Mimus, making the latter paraphyletic, and that the closest living relatives of Galapagos mockingbirds appear to be those currently found in North America, northern South America, and the Caribbean, rather than the geographically nearest species in continental Ecuador. Thus, propensity for over‐water dispersal may have played a more important role than geographic proximity in the colonization of Galapagos by mockingbirds. Within Galapagos, four distinct mitochondrial DNA clades were identified. These four clades differ from current taxonomy in several important respects. In particular, mockingbirds in the eastern islands of the archipelago (Española, San Cristóbal, and Genovesa) have very similar mitochondrial DNA sequences, despite belonging to three different nominal species, and mockingbirds from Isabela, in the west of the archipelago, are more phylogenetically divergent than previously recognized. Consistent with current taxonomy is the phylogenetic distinctiveness of the Floreana mockingbird (N. trifasciatus) and close relationships among most mockingbirds from the central and northern region of the archipelago (currently considered conspecific populations of N. parvulus). Overall, phylogeographic patterns are consistent with a model of wind‐based dispersal within Galapagos, with colonization of more northerly islands by birds from more southern populations, but not the reverse. Further radiation in Galapagos would require coexistence of multiple species on individual islands, but this may be prevented by relatively limited morphological divergence among mockingbirds and by lack of sufficient habitat diversity in the archipelago to support more than one omnivorous mimid     

Long‐distance dispersal syndromes matter: diaspore–trait effect on shaping plant distribution across the Canary Islands

Oceanic islands emerge lifeless from the seafloor and are separated from continents by long stretches of sea. Consequently, all their species had to overcome this stringent dispersal filter, making these islands ideal systems to study the biogeographic implications of long‐distance dispersal (LDD). It has long been established that the capacity of plants to reach new islands is determined by specific traits of their diaspores, historically called dispersal syndromes. However, recent work has questioned to what extent such dispersal‐related traits effectively influence plant distribution between islands. Here we evaluated whether plants bearing dispersal syndromes related to LDD – i.e. anemochorous (structures that favour wind dispersal), thalassochorous (sea dispersal), endozoochorous (internal animal dispersal) and epizoochorous (external animal dispersal) syndromes – occupy a greater number of islands than those with unspecialized diaspores by virtue of their increased dispersal ability. We focused on the native flora of the lowland xeric communities of the Canary Islands (531 species) and on the archipelago distribution of the species. We controlled for several key factors likely to affect the role of LDD syndromes in inter‐island colonization, namely: island geodynamic history, colonization time and phylogenetic relationships among species. Our results clearly show that species bearing LDD syndromes have a wider distribution than species with unspecialized diaspores. In particular, species with endozoochorous, epizoochorous and thalassochorous diaspore traits have significantly wider distributions across the Canary archipelago than species with unspecialized and anemochorous diaspores. All these findings offer strong support for a greater importance of LDD syndromes on shaping inter‐island plant distribution in the Canary Islands than in some other archipelagos, such as Galápagos and Azores.     

Phylogenetic analyses of Tolpis Adans. (Asteraceae) reveal patterns of adaptive radiation,multiple colonization and interspecific hybridization

The plant genus Tolpis (Asteraceae) has been the subject of several investigations on the evolution of oceanic island plants. Its insular species were utilized in studies of artificial hybrid fertility, testing the validity of Baker’s law, the application of DNA barcodes, and the phylogenetic utility of inter‐simple sequence repeat markers. Despite this considerable interest in Tolpis, little is known about its phylogenetic history. Past investigations were unable to resolve most of the interspecific relationships, especially within the Canary Islands, where the genus is particularly diverse. Incomplete taxon sampling, the use of ambiguous outgroups and the limited utility of slowly evolving chloroplast DNA markers precluded detailed reconstructions. The present investigation presents a comprehensive molecular phylogeny of Tolpis. By utilizing highly variable nuclear DNA markers and a comprehensive taxon set, we have resolved the majority of interspecific relationships in the genus. Evaluations of competing tree topologies and ancestral area reconstructions complemented the analyses. Our results highlight the presence of three dominant mechanisms of island plant evolution—island colonization, adaptive radiation and interspecific hybridization—in Tolpis: (i) the extant distribution of the genus is the result of two independent colonization pathways, (ii) Tolpis has colonized at least one archipelago multiple times, (iii) the present insular diversity is the product of adaptive radiation, (iv) potential hybridization was detected between species now inhabiting different islands and archipelagoes, indicating sympatric historical distributions, and (v) several undescribed species await taxonomic recognition.     

Scrophularia arguta,a widespread annual plant in the Canary Islands: a single recent colonization event or a more complex phylogeographic pattern?

Many studies have addressed evolution and phylogeography of plant taxa in oceanic islands, but have primarily focused on endemics because of the assumption that in widespread taxa the absence of morphological differentiation between island and mainland populations is due to recent colonization. In this paper, we studied the phylogeography of Scrophularia arguta, a widespread annual species, in an attempt to determine the number and spatiotemporal origins of dispersal events to Canary Islands. Four different regions, ITS and ETS from nDNA and psbA‐trnH and psbJ‐petA from cpDNA, were used to date divergence events within S. arguta lineages and determine the phylogenetic relationships among populations. A haplotype network was obtained to elucidate the phylogenetic relationships among haplotypes. Our results support an ancient origin of S. arguta (Miocene) with expansion and genetic differentiation in the Pliocene coinciding with the aridification of northern Africa and the formation of the Mediterranean climate. Indeed, results indicate for Canary Islands three different events of colonization, including two ancient events that probably happened in the Pliocene and have originated the genetically most divergent populations into this species and, interestingly, a recent third event of colonization of Gran Canaria from mainland instead from the closest islands (Tenerife or Fuerteventura). In spite of the great genetic divergence among populations, it has not implied any morphological variation. Our work highlights the importance of nonendemic species to the genetic richness and conservation of island flora and the significance of the island populations of widespread taxa in the global biodiversity.     

Seed dispersal by Galápagos tortoises

Aim Large‐bodied vertebrates often have a dramatic role in ecosystem function through herbivory, trampling, seed dispersal and nutrient cycling. The iconic Galápagos tortoises (Chelonoidis nigra) are the largest extant terrestrial ectotherms, yet their ecology is poorly known. Large body size should confer a generalist diet, benign digestive processes and long‐distance ranging ability, rendering giant tortoises adept seed dispersers. We sought to determine the extent of seed dispersal by Galápagos tortoises and their impact on seed germination for selected species, and to assess potential impacts of tortoise dispersal on the vegetation dynamics of the Galápagos. Location Galápagos, Ecuador. Methods To determine the number of seeds dispersed we identified and counted intact seeds from 120 fresh dung piles in both agricultural and national park land. To estimate the distance over which tortoises move seeds we used estimated digesta retention times from captive tortoises as a proxy for retention times of wild tortoises and tortoise movement data obtained from GPS telemetry. We conducted germination trials for five plant species to determine whether tortoise processing influenced germination success. Results In our dung sample, we found intact seeds from > 45 plant species, of which 11 were from introduced species. Tortoises defecated, on average, 464 (SE 95) seeds and 2.8 (SE 0.2) species per dung pile. Seed numbers were dominated by introduced species, particularly in agricultural land. Tortoises frequently moved seeds over long distances; during mean digesta retention times (12 days) tortoises moved an average of 394 m (SE 34) and a maximum of 4355 m over the longest recorded retention time (28 days). We did not find evidence that tortoise ingestion or the presence of dung influenced seed germination success. Main conclusions Galápagos tortoises are prodigious seed dispersers, regularly moving large quantities of seeds over long distances. This may confer important advantages to tortoise‐dispersed species, including transport of seeds away from the parent plants into sites favourable for germination. More extensive research is needed to quantify germination success, recruitment to adulthood and demography of plants under natural conditions, with and without tortoise dispersal, to determine the seed dispersal effectiveness of Galápagos tortoises.     

Centres of speciation and ecological differentiation in the Galapagos land bird fauna

Summary The Hamilton-Rubinoff model of evolution in the avifauna of the Galapagos Islands suggests that speciation occurs on small outlying islands, and that new species invade the central island region, where ecological differentiation takes place. I present an alternative model in which both speciation and ecological differentiation leading to origin of actively colonizing taxa occur on the large islands, with colonization of small and outlying islands being primarily one way. Although forms on outlying islands may differentiate to the level of new species, their fate is postulated to be extinction rather than re-invasion of central islands. Data on species with expanding, differentiating, fragmenting, and relict distributions support this second model. Polytypy and incompleteness of distributions on the large islands indicate that isolation is adequate for differentiation to occur. Distributions of expanding taxa centre on the large islands, and their distributions show sequences leading from large islands to smaller and more outlying islands. Curves of occupancy of large islands versus total islands also agree with the prediction that expansions begin in the large islands.     

Dynamic colonization exchanges between continents and islands drive diversification in paradise‐flycatchers (Terpsiphone,Monarchidae)

Aim We use parametric biogeographical reconstruction based on an extensive DNA sequence dataset to characterize the spatio‐temporal pattern of colonization of the Old World monarch flycatchers (Monarchidae). We then use this framework to examine the role of dispersal and colonization in their evolutionary diversification and to compare plumages between island and continental Terpsiphone species. Location Africa, Asia and the Indian Ocean. Methods We generate a DNA sequence dataset of 2300 bp comprising one nuclear and three mitochondrial markers for 89% (17/19) of the Old World Monarchidae species and 70% of the Terpsiphone subspecies. By applying maximum likelihood and Bayesian phylogenetic methods and implementing a Bayesian molecular clock to provide a temporal framework, we reveal the evolutionary history of the group. Furthermore, we employ both Lagrange and Bayes‐ Lagrange analyses to assess ancestral areas at each node of the phylogeny. By combining the ancestral area reconstruction with information on plumage traits we are able to compare patterns of plumage evolution on islands and continents. Results We provide the first comprehensive molecular phylogenetic reconstruction for the Old World Monarchidae. Our phylogenetic results reveal a relatively recent diversification associated with several dispersal events within this group. Moreover, ancestral area analyses reveal an Asian origin of the Indian Ocean and African clades. Ancestral state reconstruction analyses of plumage characters provide an interpretation of the plumage differentiation on islands and continents. Ancestral plumage traits are inferred to be close to those of the Asian paradise‐flycatcher (Terpsiphone paradisi), and island species display a high degree of plumage autapomorphy compared with continental species. Main conclusions Terpsiphone paradisi is polyphyletic and comprises populations that have retained the ancestral plumage of the widespread Terpsiphone genus. The genus appears to have colonized south‐west Asia, the Indian Ocean and Africa from eastern Asia. The phylogeny and divergence time estimates indicate multiple simultaneous colonizations of the western Old World by Terpsiphone. These results reinforce a hypothesis of range expansions of a Terpsiphone paradisi‐like ancestor into eastern Asia and the western Old World.     

Re‐colonization by common eiders Somateria mollissima in the Aleutian Archipelago following removal of introduced arctic foxes Vulpes lagopus

Islands provide refuges for populations of many species where they find safety from predators, but the introduction of predators frequently results in elimination or dramatic reductions in island‐dwelling organisms. When predators are removed, re‐colonization for some species occurs naturally, and inter‐island phylogeographic relationships and current movement patterns can illuminate processes of colonization. We studied a case of re‐colonization of common eiders Somateria mollissima following removal of introduced arctic foxes Vulpes lagopus in the Aleutian Archipelago, Alaska. We expected common eiders to resume nesting on islands cleared of foxes and to re‐colonize from nearby islets, islands, and island groups. We thus expected common eiders to show limited genetic structure indicative of extensive mixing among island populations. Satellite telemetry was used to record current movement patterns of female common eiders from six islands across three island groups. We collected genetic data from these and other nesting common eiders at 14 microsatellite loci and the mitochondrial DNA control region to examine population genetic structure, historical fluctuations in population demography, and gene flow. Our results suggest recent interchange among islands. Analysis of microsatellite data supports satellite telemetry data of increased dispersal of common eiders to nearby areas and little between island groups. Although evidence from mtDNA is suggestive of female dispersal among island groups, gene flow is insufficient to account for recolonization and rapid population growth. Instead, near‐by remnant populations of common eiders contributed substantially to population expansion, without which re‐colonization would have likely occurred at a much lower rate. Genetic and morphometric data of common eiders within one island group two and three decades after re‐colonization suggests reduced movement of eiders among islands and little movement between island groups after populations were re‐established. We predict that re‐colonization of an island group where all common eiders are extirpated could take decades.     

Biogeography and systematics of endemic island damselflies: The Nesobasis and Melanesobasis (Odonata: Zygoptera) of Fiji

The study of island fauna has greatly informed our understanding of the evolution of diversity. We here examine the phylogenetics, biogeography, and diversification of the damselfly genera Nesobasis and Melanesobasis, endemic to the Fiji Islands, to explore mechanisms of speciation in these highly speciose groups. Using mitochondrial (COI, 12S) and nuclear (ITS) replicons, we recovered Garli ‐part maximum likelihood and Mrbayes Bayesian phylogenetic hypotheses for 26 species of Nesobasis and eight species/subspecies of Melanesobasis. Biogeographical patterns were explored using Lagrange and Bayes ‐Lagrange and interpreted through beast relaxed clock dating analyses. We found that Nesobasis and Melanesobasis have radiated throughout Fiji, but are not sister groups. For Nesobasis, while the two largest islands of the archipelago—Viti Levu and Vanua Levu—currently host two distinct species assemblages, they do not represent phylogenetic clades; of the three major groupings each contains some Viti Levu and some Vanua Levu species, suggesting independent colonization events across the archipelago. Our Beast analysis suggests a high level of species diversification around 2–6 Ma. Our ancestral area reconstruction (Rasp ‐Lagrange ) suggests that both dispersal and vicariance events contributed to the evolution of diversity. We thus conclude that the evolutionary history of Nesobasis and Melanesobasis is complex; while inter‐island dispersal followed by speciation (i.e., peripatry) has contributed to diversity, speciation within islands appears to have taken place a number of times as well. This speciation has taken place relatively recently and appears to be driven more by reproductive isolation than by ecological differentiation: while species in Nesobasis are morphologically distinct from one another, they are ecologically very similar, and currently are found to exist sympatrically throughout the islands on which they are distributed. We consider the potential for allopatric speciation within islands, as well as the influence of parasitic endosymbionts, to explain the high rates of speciation in these damselflies.     

Biogeography and evolution of the Galapagos: integration of the biological and geological evidence

Biogeographic tracks are mapped for Galapagos endemics representing 25 plant and animal taxa and including organisms with good and poor means of dispersal. These patterns confirm standard biogeographic tracks linking Galapagos with Central America, western North and South America, the Caribbean, Asia and Australasia. Discovery of the Galapagos Gore in the 1970s corroborates the biogeographic prediction for a major tectonic centre associated with the Galapagos. The biogeographic model developed by Croizat in 1958 of Galapagos colonization involving an ancestral biota inhabiting eastern Pacific geosynclinal forelands is congruent with plate tectonic models supporting a Pacific island arc origin for western American terranes. American relatives of Galapagos endemics may have originated within an eastern Pacific paleogeography rather than representing centres of origin for dispersal to the Galapagos. Galapagos colonization by an eastern Pacific biota between late Cretaceous and mid-Tertiary has significant implications for understanding the tempo and mode for both the origins of island biota and general models of evolutionary differentiation. Popular assertions that overwater dispersal represents the only viable origin for the entire Galapagos biota is no longer biogeographically or geologically tenable.     

Genetically depauperate in the continent but rich in oceanic islands: Cistus monspeliensis (Cistaceae) in the Canary Islands

Background

Population genetic theory holds that oceanic island populations are expected to have lower levels of genetic variation than their mainland counterparts, due to founder effect after island colonization from the continent. Cistus monspeliensis (Cistaceae) is distributed in both the Canary Islands and the Mediterranean region. Numerous phylogenetic results obtained in the last years allow performing further phylogeographic analyses in Cistus.

Methodology/Principal Findings

We analyzed sequences from multiple plastid DNA regions in 47 populations of Cistus monspeliensis from the Canary Islands (21 populations) and the Mediterranean basin (26 populations). The time-calibrated phylogeny and phylogeographic analyses yielded the following results: (1) a single, ancestral haplotype is distributed across the Mediterranean, whereas 10 haplotypes in the Canary Islands; (2) four haplotype lineages are present in the Canarian Islands; (3) multiple colonization events across the archipelago are inferred; (4) the earliest split of intraspecific lineages occurred in the Early to Middle Pleistocene (<930,000 years BP).

Conclusions/Significance

The contrasting pattern of cpDNA variation is best explained by genetic bottlenecks in the Mediterranean during Quaternary glaciations, while the Canarian archipelago acted as a refugium of high levels of genetic diversity. Active colonization across the Canarian islands is supported not only by the distribution of C. monspeliensis in five of the seven islands, but also by our phylogeographic reconstruction in which unrelated haplotypes are present on the same island. Widespread distribution of thermophilous habitats on every island, as those found throughout the Mediterranean, has likely been responsible for the successful colonization of C. monspeliensis, despite the absence of a long-distance dispersal mechanism. This is the first example of a plant species with higher genetic variation among oceanic island populations than among those of the continent.     

Description of a New Galapagos Giant Tortoise Species (Chelonoidis; Testudines: Testudinidae) from Cerro Fatal on Santa Cruz Island

The taxonomy of giant Galapagos tortoises (Chelonoidis spp.) is currently based primarily on morphological characters and island of origin. Over the last decade, compelling genetic evidence has accumulated for multiple independent evolutionary lineages, spurring the need for taxonomic revision. On the island of Santa Cruz there is currently a single named species, C. porteri. Recent genetic and morphological studies have shown that, within this taxon, there are two evolutionarily and spatially distinct lineages on the western and eastern sectors of the island, known as the Reserva and Cerro Fatal populations, respectively. Analyses of DNA from natural populations and museum specimens, including the type specimen for C. porteri, confirm the genetic distinctiveness of these two lineages and support elevation of the Cerro Fatal tortoises to the rank of species. In this paper, we identify DNA characters that define this new species, and infer evolutionary relationships relative to other species of Galapagos tortoises.