Extensive trans-species mitochondrial polymorphisms in the carabid beetles Carabus subgenus Ohomopterus caused by repeated introgressive hybridization

To study the potential importance of introgressive hybridization to the evolutionary diversification of a carabid beetle lineage, we studied intraspecific and trans-species polymorphisms in the mitochondrial NADH dehydrogenase subunit 5 (ND5) gene sequence (1083 bp) in four species of the subgenus Ohomopterus (genus Carabus) in central and eastern Honshu, Japan. Of the four species, C. insulicola is parapatric with the other three, and can hybridize naturally with at least two. This species possesses two haplotypes of remote lineages. We classified ND5 haplotypes using polymerase chain reaction-restriction fragment length polymorphism with TaqI endonuclease for 524 specimens, and sequenced 143 samples. Analysis revealed that each species was polyphyletic in its mitochondrial DNA phylogeny, representing a marked case of trans-species polymorphism. Recent one-way introgression of mitochondria from C. arrowianus nakamurai to C. insulicola, and from C. insulicola to C. esakii, was inferred from the frequency of identical sequences between these species and from direct evidence of hybridization in their contact zones. Other intraspecific polymorphisms in the four species may be due to undetected introgressive hybridization (e.g. C. insulicola to C. maiyasanus) or from stochastic lineage sorting of ancestral polymorphisms. This beetle group has a genital lock-and-key system, with species-specific or subspecies-specific genital morphology that may act as a barrier to hybridization. However, our results demonstrate that introgressive hybridization has occurred multiple times, at least for mitochondria, despite differences among, and stability within, morphological characters that distinguish local populations. Thus, hybridization and introgression could have been key processes in the evolutionary diversification of Ohomopterus.     

Mechanical barriers to introgressive hybridization revealed by mitochondrial introgression patterns in Ohomopterus ground beetle assemblages

To reveal the role of diverged body size and genital morphology in reproductive isolation among closely related species, we examined patterns of, and factors limiting, introgressive hybridization between sympatric Ohomopterus ground beetles in central Japan using mitochondrial NADH dehydrogenase subunit 5 (ND5) gene sequences. We sampled 17 local assemblages that consisted of two to five species and estimated levels of interspecific gene flow using the genetic distance, D(A), and maximum-likelihood estimates of gene flow. Sharing of haplotypes or haplotype lineages was detected between six of seven species that occurred in the study areas, indicating mitochondrial introgression. The intensity and direction of mitochondrial gene flow were variable among species pairs. To determine the factors affecting introgression patterns, we tested the relationships between interspecific D(A) and five independent variables: difference in body size, difference in genital size, phylogenetic relatedness (nuclear gene sequence divergence), habitat difference, and species richness of the assemblage. Body and genital size differences contributed significantly to preventing gene flow. Thus, mechanical isolation mechanisms reduce the chance of introgressive hybridization between closely related species. Our results highlight the role of morphological divergence in speciation and assemblage formation processes through mechanical isolation.     

Parallel formation of hybrid swarms of ground beetles in the genus Carabus (Coleoptera: Carabidae) in adjacent river basins

Populations of forms intermediate between Carabus (Ohomopterus) insulicola and Carabus (Ohomopterus) arrowianus occur at the boundaries between the two species in the Kiso Valley, Nagano Prefecture, central Honshu, Japan. Morphological and mitochondrial DNA analyses revealed that these populations are derived from a hybrid swarm established as a result of secondary contact between the two species. A similar hybrid swarm has been reported in the Ina Valley, an adjacent river basin separated by the Kiso Mountain Range, where the two species are distributed parapatrically. The hybrid swarm individuals in the two valleys show parallelism in the morphological evolution of the male genitalia upon secondary contact and subsequent formation of hybrid swarms between the two Carabus species.     

Reproductive isolation via divergent genital morphology due to cascade reinforcement in Ohomopterus ground beetles

Secondary contact between incipient species and selection against maladaptive hybridization can drive reinforcement between populations in contact and result in reproductive character displacement (RCD). Resultant divergence in mating traits within a species may generate downstream reproductive isolation between populations with displaced and non-displaced traits, referred to as the cascade reinforcement hypothesis. We examined this hypothesis using three allopatric populations of the ground beetle Carabus maiyasanus with a genital lock-and-key system. This species shows RCD in male and female genital morphologies in populations in contact with the sister species C. iwawakianus. In a reciprocal mating experiment using three allopatric populations with differences in male and female genital sizes, insemination failure increased as the difference in genital size increased. Based on the reproductive isolation index, insemination failure was the major postmating-prezygotic isolation barrier, at least in one population pair with comparable total isolation to those of other species pairs. By contrast, there was only incomplete premating isolation among populations. These results suggest that RCD in genital morphologies drives incipient allopatric speciation, supporting the cascade reinforcement hypothesis. These findings provide insight into the roles of interspecific interactions and subsequent trait diversification in speciation processes.     

Multiple speciation events in an arthropod with divergent evolution in sexual morphology

Sexual selection can facilitate divergent evolution of traits related to mating and consequently promote speciation. Theoretically, independent operation of sexual selection in different populations can lead to divergence of sexual traits among populations and result in allopatric speciation. Here, we show that divergent evolution in sexual morphology affecting mating compatibility (body size and genital morphologies) and speciation have occurred in a lineage of millipedes, the Parafontaria tonominea species complex. In this millipede group, male and female body and genital sizes exhibit marked, correlated divergence among populations, and the diverged morphologies result in mechanical reproductive isolation between sympatric species. The morphological divergence occurred among populations independently and without any correlation with climatic variables, although matching between sexes has been maintained, suggesting that morphological divergence was not a by-product of climatic adaptation. The diverged populations underwent restricted dispersal and secondary contact without hybridization. The extent of morphological difference between sympatric species is variable, as is diversity among allopatric populations; consequently, the species complex appears to contain many species. This millipede case suggests that sexual selection does contribute to species richness via morphological diversification when a lineage of organisms consists of highly divided populations owing to limited dispersal.     

Assessment of gene flow across a hybrid zone in red-tailed chipmunks (Tamias ruficaudus)

The role of hybridization in animal speciation is controversial and recent research has challenged the long-standing criterion of complete reproductive isolation to attain species status. The speciation-with-gene-flow model posits that the genome is semi-permeable and hybridization may be a phase in the process of divergence. Here, we apply these concepts to a previously identified zone of mtDNA introgression between the two strongly morphologically differentiated subspecies of red-tailed chipmunk ( Tamias ruficaudus ) in the US Inland Northwest. Using multilocus genotype data from the southern, older contact zone, we demonstrate that neutral gene flow is unusually low between the subspecies across the Lochsa River. This is geographically congruent with the discontinuity in bacular morphology, indicating that the cline of mitochondrial DNA (mtDNA) haplotypes is displaced. Furthermore, we elucidate the evolutionary forces responsible by testing hypotheses of lineage sorting and hybridization. We determined that introgressive hybridization is the cause of mtDNA/morphology incongruence because there are non-zero levels of migration and gene flow. Although our estimate of the age of the hybrid zone has wide credibility intervals, the hybridization events occurred in the Late Pleistocene and the divergence occurred in the Middle Pleistocene. Finally, we assessed substructure within and adjacent to the hybrid zone and found that the hybrid zone constitutes a set of populations that are genetically differentiated from parental sets of populations; therefore, hybridization in this system is not likely an evolutionary sink, but has generated novel combinations of genotypes.     

Weak premating isolation between Clitarchus stick insect species despite divergent male and female genital morphology

Documenting natural hybrid systems builds our understanding of mate choice, reproductive isolation and speciation. The stick insect species Clitarchus hookeri and C. tepaki differ in their genital morphology and hybridize along a narrow peninsula in northern New Zealand. We utilize three lines of evidence to understand the role of premating isolation and species boundaries: (a) genetic differentiation using microsatellites and mitochondrial DNA; (b) variation in 3D surface topology of male claspers and 2D morphometrics of female opercular organs; and (c) behavioural reproductive isolation among parental and hybrid populations through mating crosses. The genetic data show introgression between the parental species and formation of a genetically variable hybrid swarm. Similarly, the male and female morphometric data show genital divergence between the parental species as well as increased variation within the hybrid populations. This genital divergence has not resulted in reproductive isolation between species, instead weak perimating isolation has enabled the formation of a hybrid swarm. Behavioural analysis demonstrates that the entire mating process influences the degree of reproductive isolation between species undergoing secondary contact. Mechanical isolation may appear strong, whereas perimating isolation is weak.     

Historical divergence of mechanical isolation agents in the ground beetle Carabus arrowianus as revealed by phylogeographical analyses

In the carabid genus Carabus subgenus Ohomopterus , diverged body size and genital morphology serve as mechanical reproductive barriers. To elucidate the diverging process of body and genital sizes in Carabus arrowianus , which exhibits marked morphological diversity among geographical populations and may represent an early stage of speciation, we analysed a mitochondrial gene sequence for 1051 individuals from 63 populations and male morphology for 359 individuals from 47 populations. Two discrete morphological groups segregated by geographical barriers were distinguished, one of which possessed smaller bodies and shorter genitalia ( S group) than the other ( L group), which exhibited larger bodies and exaggerated genitalia. Genetic divergence between the two groups was significant but not large. Phylogeographical and population genetic analyses indicated that the L group was derived from the S group, and a coalescent simulation revealed that the two groups diverged during the latest middle Pleistocene (0.13 million years ago), with a much larger effective population size in the L group than the S group. Because the body size divergence could not be explained by adaptation to climatic conditions and genital morphology is considered to be subject to sexual selection, we postulated that a population division and colonization in favourable habitats caused by the Pleistocene climatic and geographical change might facilitate natural and sexual selection for enlarged body and genital sizes in the L group.     

Evolutionary history of Scinax treefrogs on land‐bridge islands in south‐eastern Brazil

Aim We investigated how Pleistocene refugia and recent (c. 12,000 years ago) sea level incursions shaped genetic differentiation in mainland and island populations of the Scinax perpusillus treefrog group. Location Brazilian Atlantic Forest, São Paulo state, south‐eastern Brazil. Methods Using mitochondrial and microsatellite loci, we examined population structure and genetic diversity in three species from the S. perpusillus group, sampled from three land‐bridge islands and five mainland populations, in order to understand the roles of Pleistocene forest fragmentation and sea level incursions on genetic differentiation. We calculated metrics of relatedness and genetic diversity to assess whether island populations exhibit signatures of genetic drift and isolation. Two of the three island populations in this study have previously been described as new species based on a combination of distinct morphological and behavioural characters, thus we used the molecular datasets to determine whether phenotypic change is consistent with genetic differentiation. Results Our analyses recovered three distinct lineages or demes composed of northern mainland São Paulo populations, southern mainland São Paulo populations, and one divergent island population. The two remaining island populations clustered with samples from adjacent mainland populations. Estimates of allelic richness were significantly lower, and estimates of relatedness were significantly higher, in island populations relative to their mainland counterparts. Main conclusions Fine‐scale genetic structure across mainland populations indicates the possible existence of local refugia within São Paulo state, underscoring the small geographic scale at which populations diverge in this species‐rich region of the Atlantic Coastal Forest. Variation in genetic signatures across the three islands indicates that the populations experienced different demographic processes after marine incursions fragmented the distribution of the S. perpusillus group. Genetic signatures of inbreeding and drift in some island populations indicate that small population sizes, coupled with strong ecological selection, may be important evolutionary forces driving speciation on land‐bridge islands.     

Hybridization and barriers to gene flow in an island bird radiation

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.     

The time of divergence between the two species of uacari monkeys: Cacajao calvus and Cacajao melanocephalus

It has been suggested in the literature that primates of the genus Cacajao have been restricted to flooded-forest habitats of western Amazonia since their split from the Chiropotes line in the Tertiary. It has been proposed further that the differentiation of the two species of this genus, Cacajao melanocephalus and Cacajao calvus, occurred during the Pleistocene period as a result of the fragmentation of the Amazon forest and the isolation of populations in these forest fragments or refuges. However, recent evidence has shown that at least C. melanocephalus is not dependent on flooded-forest habitats, and molecular analysis of mitochondrial DNA shows that the two species had already differentiated during the Pliocene, thus Pleistocene glaciations do not explain the speciation in Cacajao. Considering that C. melanocephalus and its closest relative, Chiropotes, inhabit terra firme forests, it is suggested that preference for flooded-forest habitats may be an apomorphy in C. calvus.     

Phylogeography of the longhorn cactus beetle Moneilema appressum LeConte (Coleoptera: Cerambycidae): was the differentiation of the Madrean sky islands driven by Pleistocene climate changes?

Although it has been suggested that Pleistocene climate changes drove population differentiation and speciation in many groups of organisms, population genetic evidence in support of this scenario has been ambiguous, and it has often been difficult to distinguish putative vicariance from simple isolation by distance. The sky island communities of the American Southwest present an ideal system in which to compare late Pleistocene range fragmentations documented by palaeoenvironmental studies with population genetic data from organisms within these communities. In order to elucidate the impact of Pleistocene climate fluctuations on these environments, biogeographic patterns in the flightless longhorn cactus beetle, Moneilema appressum were examined using mitochondrial DNA sequence data. Gene tree relationships between haplotypes were inferred using parsimony, maximum-likelihood, and Bayesian analysis. Nested clade analysis, Mantel tests, and coalescent modelling were employed to examine alternative biogeographic scenarios, and to test the hypothesis that Pleistocene climate changes drove population differentiation in this species. The program mdiv was used to estimate migration and divergence times between populations, and to measure the statistical support for isolation over ongoing migration. These analyses showed significant geographic structure in genetic relationships, and implicated topography as a key determinant of isolation. However, although the coalescent analyses suggested that a history of past habitat fragmentation underlies the observed geographic patterns, the nested clade analysis indicated that the pattern was consistent with isolation by distance. Estimated divergence times indicated that range fragmentation in M. appressum is considerably older than the end of the most recent glacial, but coincided with earlier interglacial warming events and with documented range expansions in other, desert-dwelling species of Moneilema.     

Out of Cuba: overwater dispersal and speciation among lizards in the Anolis carolinensis subgroup

Overwater dispersal and subsequent allopatric speciation contribute importantly to the species diversity of West Indian Anolis lizards and many other island radiations. Here we use molecular phylogenetic analyses to assess the contribution of overwater dispersal to diversification of the Anolis carolinensis subgroup, a clade comprising nine canopy-dwelling species distributed across the northern Caribbean. Although this clade includes some of the most successful dispersers and colonists in the anole radiation, the taxonomic status and origin of many endemic populations have been ambiguous. New mitochondrial and nuclear DNA sequences from four species occurring on small islands or island banks (Anolis brunneus, Anolis longiceps, Anolis maynardi, Anolis smaragdinus) and one species from the continental United States (A. carolinensis) are presented and analysed with homologous sequences sampled from related species on Cuba (Anolis allisoni and Anolis porcatus). Our analyses confirm that all five non-Cuban species included in our study represent distinct, independently evolving lineages that warrant continued species recognition. Moreover, our results support Ernest Williams's hypothesis that all of these species originated by overseas colonization from Cuban source populations. However, contrary to Williams's hypothesis of Pleistocene dispersal, most colonization events leading to speciation apparently occurred earlier, in the late Miocene-Pliocene. These patterns suggest that overwater dispersal among geologically distinct islands and island banks is relatively infrequent in anoles and has contributed to allopatric speciation. Finally, our results suggest that large Greater Antillean islands serve as centres of origin for regional species diversity.     

DIVERSIFICATION AND GENE FLOW IN NASCENT LINEAGES OF ISLAND AND MAINLAND NORTH AMERICAN TREE SQUIRRELS (TAMIASCIURUS)

Pleistocene climate cycles and glaciations had profound impacts on taxon diversification in the Boreal Forest Biome. Using population genetic analyses with multilocus data, we examined diversification, isolation, and hybridization in two sibling species of tree squirrels (Tamiasciurus douglasii and Tamiasciurus hudsonicus) with special attention to the geographically and genetically enigmatic population of T. hudsonicus on Vancouver Island, Canada. The two species differentiated only about 500,000 years ago, in the Late Pleistocene. The island population is phylogenetically nested within T. hudsonicus according to our nuclear analysis but within T. douglasii according to mitochondrial DNA. This conflict is more likely due to historical hybridization than to incomplete lineage sorting, and it appears that bidirectional gene flow occurred between the island population and both species on the mainland. This interpretation of our genetic analyses is consistent with our bioclimatic modeling, which demonstrates that both species were able to occupy this region throughout the Late Pleistocene. The divergence of the island population 40,000 years ago suggests that tree squirrels persisted in a refugium on Vancouver Island at the last glacial maximum, 20,000 years ago. Our observations demonstrate how Pleistocene climate change and habitat shifts have created incipient divergence in the presence of gene flow.     

Pleistocene climatic fluctuations explain the disjunct distribution and complex phylogeographic structure of the Southern Red-backed Salamander, <Emphasis Type="Italic">Plethodon serratus</Emphasis>

The southeastern United States (U.S.) has experienced dynamic climatic changes over the past several million years that have impacted species distributions. In many cases, contiguous ranges were fragmented and a lack of gene flow between allopatric populations led to genetic divergence and speciation. The Southern Red-backed Salamander, Plethodon serratus, inhabits four widely disjunct regions of the southeastern U.S.: the southern Appalachian Mountains, the Ozark Plateau, the Ouachita Mountains, and the Southern Tertiary Uplands of central Louisiana. We integrated phylogenetic analysis of mitochondrial DNA sequences (1399 base pairs) with ecological niche modeling to test the hypothesis that climate fluctuations during the Pleistocene drove the isolation and divergence of disjunct populations of P. serratus. Appalachian, Ozark, and Louisiana populations each formed well-supported clades in our phylogeny. Ouachita Mountain populations sorted into two geographically distinct clades; one Ouachita clade was sister to the Louisiana clade whereas the other Ouachita clade grouped with the Appalachian and Ozark clades but relationships were unresolved. Plethodon serratus diverged from its sister taxon, P. sherando, ~5.4 million years ago (Ma), and lineage diversification within P. serratus occurred ~1.9–0.6 Ma (Pleistocene). Ecological niche models showed that the four geographic isolates of P. serratus are currently separated by unsuitable habitat, but the species was likely more continuously distributed during the colder climates of the Pleistocene. Our results support the hypothesis that climate-induced environmental changes during the Pleistocene played a dominant role in driving isolation and divergence of disjunct populations of P. serratus.     

Evolutionary trends in wading birds

For the most part populations ot wading birds have expanded and contracted with the variations in the extent of their habitats during the Pleistocene. It is suggested that as a result of geographical isolation, populations of the same species have evolved to a level at which secondary hybridization has resulted on their again coming together. 'Southern' forms of some wading birds have resulted from this secondary hybridization and in some cases the increased heterogeneity has given rise to new evolutionary potential. It is suggested that this may have occurred many times during the Pleistocene and that microevolution has played a significant part in the evolution of wading birds.     

Pleistocene genetic connectivity in a widespread,open‐habitat‐adapted mosquito in the Indo‐Oriental region

Aim The environmental effect of Pleistocene climatic change in the Indo‐Oriental region has resulted in allopatric fragmentation and the generation of diversity in forest‐associated species. The aim of this study was to determine the extent to which Pleistocene climatic change has resulted in the fragmentation and speciation of an open‐habitat‐adapted mosquito, Anopheles vagus s.l., across its range. Location Anopheles vagus s.l. was sampled across the Indo‐Oriental region. Methods We generated 116 mitochondrial cytochrome c oxidase subunit I (COI) and 121 nuclear internal transcribed spacer 2 (ITS2) DNA sequences from 18 populations. Relationships between mitochondrial haplotypes were reconstructed using minimum spanning networks, and population structure was examined using analyses of molecular variance. The population history, including lineage divergence times, population expansion and gene flow, was inferred using beast and the isolation with migration (IM) model. Results There was no evidence to support the presence of the endemic Philippines species, A. limosus; instead, Philippine populations were closely related to, and derived from, A. vagus on the eastern Southeast Asian mainland. The most distinct populations were those from Java and East Timor, which differed from all other populations by all individuals having a 4‐bp insertion in the ITS2 sequence. The corresponding mitochondrial haplotypes had an estimated divergence time of 2.6 Ma [95% confidence interval (CI) 1.9–3.6 Ma]. Haplotype networks and analysis of molecular variance for COI supported western (Sri Lanka, India and Myanmar) and eastern (Thailand, Singapore, Cambodia, Vietnam and the Philippines) population groupings. This grouping structure results from the divergence of an eastern and a western mitochondrial lineage, estimated to have occurred 0.37 Ma (95% CI 0.26–0.55 Ma). Subsequent migration from the east to the west (0.16 Ma) is inferred to have created an admixture zone in Myanmar and Thailand. Main conclusions With the possible exception of populations from Java and East Timor, A. vagus appears to be one widespread genetically diverse taxon across its extensive range. The abundance of grassland during long interglacial periods may have facilitated population connectivity and range expansion across the Oriental and western Australasian regions.     

In situ genetic differentiation in a Hispaniolan lizard (Ameiva chrysolaema): a multilocus perspective

A previous phylogeographic study of mitochondrial haplotypes for the Hispaniolan lizard Ameiva chrysolaema revealed deep genetic structure associated with seawater inundation during the late Pliocene/early Pleistocene and evidence of subsequent population expansion into formerly inundated areas. We revisit hypotheses generated by our previous study using increased geographic sampling of populations and analysis of three nuclear markers (alpha-enolase intron 8, alpha-cardiac-actin intron 4, and beta-actin intron 3) in addition to mitochondrial haplotypes (ND2). Large genetic discontinuities correspond spatially and temporally with historical barriers to gene flow (sea inundations). NCPA cross-validation analysis and Bayesian multilocus analyses of divergence times (IMa and MCMCcoal) reveal two separate episodes of fragmentation associated with Pliocene and Pleistocene sea inundations, separating the species into historically separate Northern, East-Central, West-Central, and Southern population lineages. Multilocus Bayesian analysis using IMa indicates asymmetrical migration from the East-Central to the West-Central populations following secondary contact, consistent with expectations from the more pervasive sea inundation in the western region. The West-Central lineage has a genetic signature of population growth consistent with the expectation of geographic expansion into formerly inundated areas. Within each lineage, significant spatial genetic structure indicates isolation by distance at comparable temporal scales. This study adds to the growing body of evidence that vicariant speciation may be the prevailing source of lineage accumulation on oceanic islands. Thus, prior theories of island biogeography generally underestimate the role and temporal scale of intra-island vicariant processes.     

Mitochondrial DNA phylogeography and population history of Meladema diving beetles on the Atlantic Islands and in the Mediterranean basin (Coleoptera,Dytiscidae)

The phylogeny and population history of Meladema diving beetles (Coleoptera, Dytiscidae) were examined using mitochondrial DNA sequence from 16S ribosomal RNA and cytochrome oxidase I genes in 51 individuals from 22 populations of the three extant species (M. imbricata endemic to the western Canary Islands, M. lanio endemic to Madeira and M. coriacea widespread in the Western Mediterranean and on the western Canaries), using a combination of phylogenetic and nested clade analyses. Four main lineages are observed within Meladema, representing the three recognized species plus Corsican populations of M. coriacea. Phylogenetic analyses demonstrate the sister relationship of the two Atlantic Island taxa, and suggest the possible paraphyly of M. coriacea. A molecular clock approach reveals that speciation within the genus occurred in the Early Pleistocene, indicating that the Atlantic Island endemics are not Tertiary relict taxa as had been proposed previously. Our results point to past population bottlenecks in all four lineages, with recent (Late-Middle Pleistocene) range expansion in non-Corsican M. coriacea and M. imbricata. Within the Canary Islands, M. imbricata seems to have independently colonized La Gomera and La Palma from Tenerife (although a colonization of La Palma from La Gomera cannot be discarded), and M. coriacea has independently colonized Tenerife and Gran Canaria from separate mainland lineages. In the Mediterranean basin this species apparently colonized Corsica on a single occasion, relatively early in its evolutionary history (Early Pleistocene), and has colonized Mallorca recently on multiple occasions. On the only island where M. coriacea and M. imbricata are broadly sympatric (Tenerife), we report evidence of bidirectional hybridization between the two species.     

Rapid evolution of sexual signals in sympatric Calopteryx damselflies: reinforcement or ‘noisy‐neighbour’ ecological character displacement?

Enhanced prezygotic isolation in sympatry is one of the most intriguing patterns in evolutionary biology and has frequently been interpreted as evidence for reinforcement. However, the frequency with which reinforcement actually completes speciation remains unclear. The Jewelwing damselflies (Calopteryx aequabilis and C. maculata) have served as one of the few classic examples of speciation via reinforcement outside of Drosophila. Although evidence for wing pattern displacement and increased mate discrimination in this system have been demonstrated, the degree of hybridization and gene flow in nature are unknown. Here, we show that sympatric populations of these two species are the result of recent secondary contact, as predicted under a model of speciation via reinforcement. However, we found no phenotypic evidence of hybridization in natural populations and a complete association between species-specific haplotypes at two different loci (mitochondrial CO I and nuclear EF1-alpha), suggesting little or no contemporary gene flow. Moreover, genealogical and coalescent-based estimates of divergence times and migration rates indicate that, speciation occurred in the distant past. The rapid evolution of wing colour in sympatry is recent, therefore, relative to speciation and seems to be better explained by selection against wasting mating effort and/or interspecific aggression resulting from a 'noisy neighbour' signalling environment.