Molecular phylogeny and dating of an insular endemic moth radiation inferred from mitochondrial and nuclear genes: The genus Galagete (Lepidoptera: Autostichidae) of the Galapagos Islands

The Galápagos Islands: biogeographic patterns and geology

In the traditional biogeographic model, the Galápagos Islands appeared a few million years ago in a sea where no other islands existed and were colonized from areas outside the region. However, recent work has shown that the Galápagos hotspot is 139 million years old (Early Cretaceous), and so groups are likely to have survived at the hotspot by dispersal of populations onto new islands from older ones. This process of metapopulation dynamics means that species can persist indefinitely in an oceanic region, as long as new islands are being produced. Metapopulations can also undergo vicariance into two metapopulations, for example at active island arcs that are rifted by transform faults. We reviewed the geographic relationships of Galápagos groups and found 10 biogeographic patterns that are shared by at least two groups. Each of the patterns coincides spatially with a major tectonic structure; these structures include: the East Pacific Rise; west Pacific and American subduction zones; large igneous plateaus in the Pacific; Alisitos terrane (Baja California), Guerrero terrane (western Mexico); rifting of North and South America; formation of the Caribbean Plateau by the Galápagos hotspot, and its eastward movement; accretion of Galápagos hotspot tracks; Andean uplift; and displacement on the Romeral fault system. All these geological features were active in the Cretaceous, suggesting that geological change at that time caused vicariance in widespread ancestors. The present distributions are explicable if ancestors survived as metapopulations occupying both the Galápagos hotspot and other regions before differentiating, more or less in situ.

Isolation on a remote island: genetic and morphological differentiation of a cosmopolitan odonate

Although low levels of genetic structure are expected in highly widespread species, geographical and/or ecological factors can limit species distributions and promote population structure and morphological differentiation. In order to determine the effects of geographical isolation on population genetic structure and wing morphology, 281 individuals of the cosmopolitan odonate Pantala flavescens were collected from four continental (Central and South America) and five insular sites (Polynesian islands and the Maldives). COI sequences and eight microsatellite loci were used to characterize genetic diversity and genetic structure between and within locations. Linear and geometric morphometry were used to evaluate differences in the size and shape of wings. Genetic analysis showed a global genetic difference between the continental and insular sites. American locations did not show genetic structure, even in locations separated by a distance of 5000 km. Easter Island showed the lowest values of genetic diversity (mainly mitochondrial diversity) and the highest values of genetic differences compared to other insular and continental sites. Individuals from Easter Island showed smaller forewings, a different abdomen length to thorax length ratio, and a different configuration of anal loop in the hindwings. Thus, the greater isolation, smaller area, and young geological age seem to have determined the genetic and morphological differences in P. flavescens of Easter Island, where selection could promote a loss of migratory behavior and may improve other life history traits, such as reproduction. This work provides new insight into how microevolutionary processes operate in isolated populations of cosmopolitan species.

Comparative phylogeography of oceanic archipelagos: Hotspots for inferences of evolutionary process

Remote island archipelagos offer superb opportunities to study the evolution of community assembly because of their relatively young and simple communities where speciation contributes to the origin and evolution of community structure. There is great potential for common phylogeographic patterns among remote archipelagos that originate through hotspot volcanism, particularly when the islands formed are spatially isolated and linearly arranged. The progression rule is characterized by a phylogeographic concordance between island age and lineage age in a species radiation. Progression is most likely to arise when a species radiation begins on an older island before the emergence of younger islands of a hotspot archipelago. In the simplest form of progression, colonization of younger islands as they emerge and offer appropriate habitat, is coincident with cladogenesis. In this paper, we review recent discoveries of the progression rule on seven hotspot archipelagos. We then discuss advantages that progression offers to the study of community assembly, and insights that community dynamics may offer toward understanding the evolution of progression. We describe results from two compelling cases of progression where the mosaic genome may offer insights into contrasting demographic histories that shed light on mechanisms of speciation and progression on remote archipelagos.

DNA barcoding of crickets, katydids and grasshoppers (Orthoptera) from Central Europe with focus on Austria, Germany and Switzerland

We present a DNA barcoding study on the insect order Orthoptera that was generated in collaboration between four barcoding projects in three countries, viz. Barcoding Fauna Bavarica (Germany), German Barcode of Life, Austrian Barcode of Life and Swiss Barcode of Life. Our data set includes 748 COI sequences from 127 of the 162 taxa (78.4%) recorded in the three countries involved. Ninety-three of these 122 species (76.2%, including all Ensifera) can be reliably identified using DNA barcodes. The remaining 26 caeliferan species (families Acrididae and Tetrigidae) form ten clusters that share barcodes among up to five species, in three cases even across different genera, and in six cases even sharing individual barcodes. We discuss incomplete lineage sorting and hybridization as most likely causes of this phenomenon, as the species concerned are phylogenetically young and hybridization has been previously observed. We also highlight the problem of nuclear mitochondrial pseudogenes (numts), a known problem in the barcoding of orthopteran species, and the possibility of Wolbachia infections. Finally, we discuss the possible taxonomic implications of our barcoding results and point out future research directions.

Present diversity of Galápagos leaf-toed geckos (Phyllodactylidae: Phyllodactylus) stems from three independent colonization events

We re-examined the biogeography of the leaf-toed geckos (Phyllodactylus) endemic to the Galápagos Islands by analyzing for the first time samples of P. gilberti, a species endemic to Wolf island, in a phylogenetic framework. Our aim was to test the three-colonizations scenario previously proposed for these lizards and estimate the age of each colonization event. To achieve this we estimated simultaneously a species tree and divergence times with Bayesian methods. Our results supported the three-colonizations scenario. Similar to a previous hypothesis, the species tree obtained here showed that most species of Phyllodactylus are nested in a single clade with an age between 5.49 and 13.8Ma, whereas a second independent colonization corresponding to P. darwini from San Cristóbal island occurred 3.03Ma ago. The species from Wolf island, P. gilberti, stems from a more recent colonization event (0.69Ma). Thus, present diversity of Galápagos leaf-toed geckos stems from three independent, asynchronous colonization events. As with other Galápagos organisms, the Pacific coast of South America seems to be the source for the founders of P. gilberti.

Historical isolation of the Galápagos carpenter bee (Xylocopa darwini) despite strong flight capability and ecological amplitude

Colonization across the Galápagos Islands by the carpenter bee (Xylocopa darwini) was reconstructed based on distribution of mitochondrial haplotypes (cytochrome oxidase II (COII) sequences) and haplotype lineages. A total of 12 haplotypes were found in 118 individuals of X. darwini. Distributional, phylogenetic and phylogeographic analyses suggest early colonization of most islands followed by historical isolation in two main groups: eastern and central-western islands. Evidence of recurrent inter-island colonization of haplotypes is largely lacking, despite strong flight capability and ecological amplitude of the species. Recent palaeogeographic data suggest that several of the current islands were connected in the past and thus the isolation pattern may have been even more pronounced. A contrast analysis was also carried out on 10 animal groups of the Galápagos Islands, and on haplotype colonization of seven animal and plant species from several oceanic archipelagos (the Galápagos, Azores, Canary Islands). New colonization metrics on the number of potential vs. inferred colonization events revealed that the Galápagos carpenter bee shows one of the most significant examples of geographic isolation.

Convergent evolution of morphology and habitat use in the explosive Hawaiian fancy case caterpillar radiation

Species occurring in unconnected, but similar habitats and under similar selection pressures often display strikingly comparable morphology, behaviour and life history. On island archipelagos where colonizations and extinctions are common, it is often difficult to separate whether similar traits are a result of in situ diversification or independent colonization without a phylogeny. Here, we use one of Hawaii's most ecologically diverse and explosive endemic species radiations, the Hawaiian fancy case caterpillar genus Hyposmocoma, to test whether in situ diversification resulted in convergence. Specifically, we examine whether similar species utilizing similar microhabitats independently developed largely congruent larval case phenotypes in lineages that are in comparable, but isolated environments. Larvae of these moths are found on all Hawaiian Islands and are characterized by an extraordinary array of ecomorphs and larval case morphology. We focus on the 'purse cases', a group that is largely specialized for living within rotting wood. Purse cases were considered a monophyletic group, because morphological, behavioural and ecological traits appeared to be shared among all members. We constructed a phylogeny based on nuclear and mitochondrial DNA sequences from 38 Hyposmocoma species, including all 14 purse case species and 24 of non-purse case congeners. Divergence time estimation suggests that purse case lineages evolved independently within dead wood and developed nearly identical case morphology twice: once on the distant Northwest Hawaiian Islands between 15.5 and 9 Ma and once on the younger main Hawaiian Islands around 3.0 Ma. Multiple ecomorphs are usually found on each island, and the ancestral ecomorph of Hyposmocoma appears to have lived on tree bark. Unlike most endemic Hawaiian radiations that follow a clear stepwise progression of colonization, purse case Hyposmocoma do not follow a pattern of colonization from older to younger island. We postulate that the diversity of microhabitats and selection from parasitism/predation from endemic predators may have shaped case architecture in this extraordinary endemic radiation of Hawaiian insects.

Deep sympatric mtDNA divergence in the autumnal moth (Epirrita autumnata)

Deep sympatric intraspecific divergence in mtDNA may reflect cryptic species or formerly distinct lineages in the process of remerging. Preliminary results from DNA barcoding of Scandinavian butterflies and moths showed high intraspecific sequence variation in the autumnal moth, Epirrita autumnata. In this study, specimens from different localities in Norway and some samples from Finland and Scotland, with two congeneric species as outgroups, were sequenced with mitochondrial and nuclear markers to resolve the discrepancy found between mtDNA divergence and present species-level taxonomy. We found five COI sub-clades within the E. autumnata complex, most of which were sympatric and with little geographic structure. Nuclear markers (ITS2 and Wingless) showed little variation and gave no indications that E. autumnata comprises more than one species. The samples were screened with primers for Wolbachia outer surface gene (wsp) and 12% of the samples tested positive. Two Wolbachia strains were associated with different mtDNA sub-clades within E. autumnata, which may indicate indirect selection/selective sweeps on haplotypes. Our results demonstrate that deep mtDNA divergences are not synonymous with cryptic speciation and this has important implications for the use of mtDNA in species delimitation, like in DNA barcoding.

Pleistocene climate change promoted rapid diversification of aquatic invertebrates in Southeast Australia

Background

The Pleistocene Ice Ages were the most recent geohistorical event of major global impact, but their consequences for most parts of the Southern hemisphere remain poorly known. We investigate a radiation of ten species of Sternopriscus, the most species-rich genus of epigean Australian diving beetles. These species are distinct based on genital morphology but cannot be distinguished readily by mtDNA and nDNA because of genotype sharing caused by incomplete lineage sorting. Their genetic similarity suggests a Pleistocene origin.

Results

We use a dataset of 3858 bp of mitochondrial and nuclear DNA to reconstruct a phylogeny of Sternopriscus using gene and species trees. Diversification analyses support the finding of a recent rapid speciation event with estimated speciation rates of up to 2.40 species per MY, which is considerably higher than the proposed average rate of 0.16 species per MY for insects. Additionally, we use ecological niche modeling and analyze data on habitat preferences to test for niche divergence between species of the recent Sternopriscus radiation. These analyses show that the species can be characterized by a set of ecological variables referring to habitat, climate and altitude.

Conclusions

Our results suggest that the repeated isolation of populations in glacial refugia might have led to divergent ecological adaptations and the fixation of morphological traits supporting reproductive isolation and therefore may have promoted speciation. The recent Sternopriscus radiation fulfills many characteristics of a species flock and would be the first described example of an aquatic insect species flock. We argue that the species of this group may represent a stage in speciation past the species flock condition because of their mostly broad and often non-overlapping ranges and preferences for different habitat types.

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.

A hitchhikers guide to the Galápagos: co-phylogeography of Galápagos mockingbirds and their parasites

Background

Parasites are evolutionary hitchhikers whose phylogenies often track the evolutionary history of their hosts. Incongruence in the evolutionary history of closely associated lineages can be explained through a variety of possible events including host switching and host independent speciation. However, in recently diverged lineages stochastic population processes, such as retention of ancestral polymorphism or secondary contact, can also explain discordant genealogies, even in fully co-speciating taxa. The relatively simple biogeographic arrangement of the Galápagos archipelago, compared with mainland biomes, provides a framework to identify stochastic and evolutionary informative components of genealogic data in these recently diverged organisms.

Results

Mitochondrial DNA sequences were obtained for four species of Galápagos mockingbirds and three sympatric species of ectoparasites - two louse and one mite species. These data were complemented with nuclear EF1α sequences in selected samples of parasites and with information from microsatellite loci in the mockingbirds. Mitochondrial sequence data revealed differences in population genetic diversity between all taxa and varying degrees of topological congruence between host and parasite lineages. A very low level of genetic variability and lack of congruence was found in one of the louse parasites, which was excluded from subsequent joint analysis of mitochondrial data. The reconciled multi-species tree obtained from the analysis is congruent with both the nuclear data and the geological history of the islands.

Conclusions

The gene genealogies of Galápagos mockingbirds and two of their ectoparasites show strong phylogeographic correlations, with instances of incongruence mostly explained by ancestral genetic polymorphism. A third parasite genealogy shows low levels of genetic diversity and little evidence of co-phylogeny with their hosts. These differences can mostly be explained by variation in life-history characteristics, primarily host specificity and dispersal capabilities. We show that pooling genetic data from organisms living in close ecological association reveals a more accurate phylogeographic history for these taxa. Our results have implications for the conservation and taxonomy of Galápagos mockingbirds and their parasites.

Gelechiidae moths are capable of chemically dissolving the pollen of their host plants: first documented sporopollenin breakdown by an animal

BACKGROUND

Many insects feed on pollen surface lipids and contents accessible through the germination pores. Pollen walls, however, are not broken down because they consist of sporopollenin and are highly resistant to physical and enzymatic damage. Here we report that certain Microlepidoptera chemically dissolve pollen grains with exudates from their mouthparts.

METHODOLOGY/PRINCIPAL FINDINGS

Field observations and experiments in tropical China revealed that two species of Deltophora (Gelechioidea) are the exclusive pollinators of two species of Phyllanthus (Phyllanthaceae) on which their larvae develop and from which the adults take pollen and nectar. DNA sequences placed the moths and plants phylogenetically and confirmed that larvae were those of the pollinating moths; molecular clock dating suggests that the moth clade is younger than the plant clade. Captive moths with pollen on their mouthparts after 2-3 days of starvation no longer carried intact grains, and SEM photographs showed exine fragments on their proboscises. GC-MS revealed cis-β-ocimene as the dominant volatile in leaves and flowers, but GC-MS analyses of proboscis extracts failed to reveal an obvious sporopollenin-dissolving compound. A candidate is ethanolamine, which occurs in insect hemolymphs and is used to dissolve sporopollenin by palynologists.

CONCLUSIONS/SIGNIFICANCE

This is the first report of any insect and indeed any animal chemically dissolving pollen.

Phylogeographic analyses of the 30 degrees S south-east Pacific biogeographic transition zone establish the occurrence of a sharp genetic discontinuity in the kelp Lessonia nigrescens: vicariance or parapatry?

Phylogeographic studies are lacking in the Southern Hemisphere, and in particular in the south-eastern Pacific. To infer the possible scenario for the debated biogeographic transition zone located at 30-33 degrees S along the Chilean coast, we investigated whether there is a concordance between the phylogeographic pattern and the biogeographic transition in the intertidal kelp Lessonia nigrescens whose distribution is continuous across this transition zone. Using a combination of four makers located in the three genomic compartments (chloroplast, mitochondria and nucleus), we showed the presence of two main divergent lineages, possibly cryptic species. There was an exact match of the phylogeographic break with the 30 degrees S biogeographic transition zone, suggesting a common origin. The combined information given by the multilocus approach and by the population analysis suggested the occurrence of a budding speciation, with a northward range expansion.

Island biogeography of Galápagos lava lizards (Tropiduridae: Microlophus): species diversity and colonization of the archipelago

The "lava lizards" (Microlophus) are distributed throughout the Galápagos Archipelago, and consist of radiations derived from two independent colonizations. The "Eastern Radiation" includes M. bivittatus and M. habeli endemic to San Cristobal and Marchena Islands. The "Western Radiation" includes five to seven historically recognized species distributed across almost the entire Archipelago. We combine dense geographic sampling and multilocus sequence data to estimate a phylogenetic hypothesis for the Western Radiation, to delimit species boundaries in this radiation, and to estimate a time frame for colonization events. Our phylogenetic hypothesis rejects two earlier topologies for the Western Radiation and paraphyly of M. albemarlensis, while providing strong support for single colonizations on each island. The colonization history implied by our phylogeny is consistent with general expectations of an east-to-west route predicted by the putative age of island groups, and prevailing ocean currents in the Archipelago. Additionally, combined evidence suggests that M. indefatigabilis from Santa Fe should be recognized as a full species. Finally, molecular divergence estimates suggest that the two colonization events likely occurred on the oldest existing islands, and the Western Radiation represents a recent radiation that, in most cases, has produced species that are considerably younger than the islands they inhabit.

Cryptic differentiation in the endemic micromoth Galagete darwini (Lepidoptera, Autostichidae) on Galápagos volcanoes

To gain insight into the early stages of speciation, we reconstructed a DNA-based phylogeny, using combined mitochondrial (cytochrome c oxidase subunits I and II: 1008 bp) and nuclear (elongation factor 1-alpha and wingless: 1062 bp) markers of populations of the moth Galagete darwini endemic to the Galápagos, which belongs to an insular radiation similar in size to that of Darwin's finches. Adults of G. darwini were collected in the arid lowlands of 11 of the Galápagos Islands (Baltra, Española, Fernandina, Floreana, Isabela, Pinta, Pinzón, San Cristobal, Santa Cruz, Santiago and Seymour) and the humid highlands of a subset of 5 of them (Fernandina, Floreana, Isabela, Santa Cruz and Santiago). The combined phylogeographic analysis surprisingly revealed that G. darwini populations at higher elevation on the western islands (Fernandina, Isabela and Santiago) represent a distinct lineage from the one in the low arid zones of these same islands. This is the first reported case in the archipelago of genetic cryptic differentiation correlated with elevation on the western Galápagos volcanoes.

Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biogeographical synthesis

Remote oceanic islands have long been recognized as natural models for the study of evolutionary processes involved in diversification. Their remoteness provides opportunities for isolation and divergence of populations, which make islands remarkable settings for the study of diversification. Groups of islands may share a relatively similar geological history and comparable climate, but their inhabitants experience subtly different environments and have distinct evolutionary histories, offering the potential for comparative studies. A range of organisms have colonized the Galápagos Islands, and various lineages have radiated throughout the archipelago to form unique assemblages. This review pays particular attention to molecular phylogenetic studies of Galápagos terrestrial fauna. We find that most of the Galápagos terrestrial fauna have diversified in parallel to the geological formation of the islands. Lineages have occasionally diversified within islands, and the clearest cases occur in taxa with very low vagility and on large islands with diverse habitats. Ecology and habitat specialization appear to be critical in speciation both within and between islands. Although the number of phylogenetic studies is continuously increasing, studies of natural history, ecology, evolution and behaviour are essential to completely reveal how diversification proceeded on these islands.

Nuclear and mitochondrial sequences confirm complex colonization patterns and clear species boundaries for flightless weevils in the Galápagos archipelago

Nuclear sequence data were collected from endemic Galápagos species and an introduced close relative, and contrasted with mitochondrial DNA sequences, continuing investigation into the colonization history and modes of diversification in the weevil genus Galapaganus. The current combined phylogeny together with previously published penalized likelihood age estimates builds a complex picture of the archipelago's colonization history. The present reconstruction relies on submerged platforms to explain the early divergence of the young southern Isabela endemics or the Española or San Cristobal populations. Diversity is later built through inter-island divergence starting on older islands and continuing on two simultaneous tracks towards younger islands. The amount of diversity generated through intra-island processes is skewed towards older islands, suggesting that island age significantly influences diversity. Phylogenetic concordance between nuclear and mitochondrial datasets and well-supported monophyletic species in mitochondrial derived topologies appear to reject the possibility of inter-species hybridization. These clear species boundaries might be related to the tight host associations of adult weevils in discrete ecological zones. If shared hosts facilitate hybridization, then host- or habitat-promoted divergences could prevent it, even in the case of species that share islands, since the altitudinal partitioning of habitats minimizes range overlap.