Speciation on the coasts of the new world: phylogeography and the evolution of bindin in the sea urchin genus Lytechinus

Abstract Beginning with E. Mayr's study in 1954, tropical sea urchins have played an important role in studies of speciation in the sea, but what are the processes of cladogenesis and divergence that give rise to new species in this group? We attempt to answer this question in the genus Lytechinus. Unlike the majority of other tropical sea urchin genera, which have circumtropical distributions, Lytechinus is mostly confined to the tropics and subtropics of the New World. We sequenced a region of mitochondrial cytochrome oxidase I and the entire molecule of nuclear bindin (a sperm gamete recognition protein) of nearly all species in the genus, and we assayed isozymes of three partially sympatric closely related species and subspecies. We found that in both mitochondrial DNA (mtDNA) and in bindin the genus Lytechinus is paraphyletic, encompassing Sphaerechinus granularis as the sister species of L. euerces. The rest of the species are arranged in an Atlantic clade composed of L. williamsi and L. variegatus, and a Pacific clade containing L. anamesus, L. pictus, L. semituberculatus, and L. panamensis. Divergence between these clades suggests that they were separated no later than the closure of the Isthmus of Panama, and possibly before this time. Our data confirm that L. anamesus and L. pictus from California are a single species, and provide no evidence of differentiation between L. variegatus variegatus from the Caribbean and L. variegatus atlanticus from Bermuda. Lytechinus variegatus variegatus mtDNA is distinct from that of L. variegatus carolinus from the North American seaboard and the Gulf of Mexico, whereas their bindins are very similar. However, there is clear evidence of introgression of mtDNA between the two subspecies and they share alleles in all sampled isozyme loci. Lytechinus williamsi from the Caribbean shares mtDNA haplotypes with L. variegatus variegatus, and they also share isozymes in all assayed loci. Their bindin, however, is distinct and coalesces within each morphospecies. A private clade of mtDNA in L. williamsi may be indicative of former differentiation in the process of being swamped by introgression, or of recent speciation. Recent sudden expansions in effective population size may explain the predominance of a few mitochondrial haplotypes common to the two species. Despite the high divergence of bindin (relative to differentiation of mtDNA) between L. variegatus and L. williamsi, comparison of amino acid replacement to silent substitutions by various methods uncovered no evidence for positive selection on the bindin of any clade of Lytechinus. With the possible exception of L. williamsi and L. variegatus, our results are consistent with a history of allopatric speciation in Lytechinus. The molecular results from Lytechinus, along with those of other similar studies of sea urchins, suggest that the general speciation patterns deduced in the middle of last century by Mayr from morphology and geography have held up, but also have uncovered peculiarities in the evolution of each genus.     

Speciation across the Tree of Life

Much of what we know about speciation comes from detailed studies of well-known model systems. Although there have been several important syntheses on speciation, few (if any) have explicitly compared speciation among major groups across the Tree of Life. Here, we synthesize and compare what is known about key aspects of speciation across taxa, including bacteria, protists, fungi, plants, and major animal groups. We focus on three main questions. Is allopatric speciation predominant across groups? How common is ecological divergence of sister species (a requirement for ecological speciation), and on what niche axes do species diverge in each group? What are the reproductive isolating barriers in each group? Our review suggests the following patterns. (i) Based on our survey and projected species numbers, the most frequent speciation process across the Tree of Life may be co-speciation between endosymbiotic bacteria and their insect hosts. (ii) Allopatric speciation appears to be present in all major groups, and may be the most common mode in both animals and plants, based on non-overlapping ranges of sister species. (iii) Full sympatry of sister species is also widespread, and may be more common in fungi than allopatry. (iv) Full sympatry of sister species is more common in some marine animals than in terrestrial and freshwater ones. (v) Ecological divergence of sister species is widespread in all groups, including ~70% of surveyed species pairs of plants and insects. (vi) Major axes of ecological divergence involve species interactions (e.g. host-switching) and habitat divergence. (vii) Prezygotic isolation appears to be generally more widespread and important than postzygotic isolation. (viii) Rates of diversification (and presumably speciation) are strikingly different across groups, with the fastest rates in plants, and successively slower rates in animals, fungi, and protists, with the slowest rates in prokaryotes. Overall, our study represents an initial step towards understanding general patterns in speciation across all organisms.     

Making environmental DNA count

The arc of reception for a new technology or method – like the reception of new information itself – can pass through predictable stages, with audiences’ responses evolving from ‘I don't believe it’, through ‘well, maybe’ to ‘yes, everyone knows that’ to, finally, ‘old news’. The idea that one can sample a volume of water, sequence DNA out of it, and report what species are living nearby has experienced roughly this series of responses among biologists, beginning with the microbial biologists who developed genetic techniques to reveal the unseen microbiome. ‘Macrobial’ biologists and ecologists – those accustomed to dealing with species they can see and count – have been slower to adopt such molecular survey techniques, in part because of the uncertain relationship between the number of recovered DNA sequences and the abundance of whole organisms in the sampled environment. In this issue of Molecular Ecology Resources, Evans et al. ( 2015 ) quantify this relationship for a suite of nine vertebrate species consisting of eight fish and one amphibian. Having detected all of the species present with a molecular toolbox of six primer sets, they consistently find DNA abundances are associated with species’ biomasses. The strength and slope of this association vary for each species and each primer set – further evidence that there is no universal parameter linking recovered DNA to species abundance – but Evans and colleagues take a significant step towards being able to answer the next question audiences tend to ask: ‘Yes, but how many are there?’     

Recent rapid speciation and ecomorph divergence in Indo‐Australian sea snakes

The viviparous sea snakes (Hydrophiinae) are a young radiation of at least 62 species that display spectacular morphological diversity and high levels of local sympatry. To shed light on the mechanisms underlying sea snake diversification, we investigated recent speciation and eco‐morphological differentiation in a clade of four nominal species with overlapping ranges in Southeast Asia and Australia. Analyses of morphology and stomach contents identified the presence of two distinct ecomorphs: a ‘macrocephalic’ ecomorph that reaches >2 m in length, has a large head and feeds on crevice‐dwelling eels and gobies; and a ‘microcephalic’ ecomorph that rarely exceeds 1 m in length, has a small head and narrow fore‐body and hunts snake eels in burrows. Mitochondrial sequences show a lack of reciprocal monophyly between ecomorphs and among putative species. However, individual assignment based on newly developed microsatellites separated co‐distributed specimens into four significantly differentiated clusters corresponding to morphological species designations, indicating limited recent gene flow and progress towards speciation. A coalescent species tree (based on mitochondrial and nuclear sequences) and isolation‐migration model (mitochondrial and microsatellite markers) suggest between one and three transitions between ecomorphs within the last approximately 1.2 million to approximately 840 000 years. In particular, the macrocephalic ‘eastern’ population of Hydrophis cyanocinctus and microcephalic H. melanocephalus appear to have diverged very recently and rapidly, resulting in major phenotypic differences and restriction of gene flow in sympatry. These results highlight the viviparous sea snakes as a promising system for speciation studies in the marine environment.     

Sympatric speciation without borders?

The biogeography of speciation remains a controversial issue and the process of allopatric speciation reigns. Sympatric speciation differs from allopatric speciation in terms of geographic setting and the role of selection in bringing about reproductive isolating mechanisms, making it a particularly fascinating and controversial subject for evolutionary biologists. Mayr (1947) explained the difference eloquently: for allopatric speciation, populations spatially diverge and then become reproductively isolated; for sympatric speciation, populations first become reproductively isolated and then diverge. Because of this, sympatric speciation is difficult to show empirically and most evolutionary biologists agree that strict ecological, evolutionary, and geographic criteria must be met ( Coyne & Orr 2004 ). In this issue, Crow et al. (2010) challenge us to expand the definition of sympatric speciation by studying species of marine fishes that they propose have arisen by sympatric speciation in a setting that does not appear to conform to the usual geographical criteria.     

The geography of speciation in narrow‐range endemics of the ‘Haenydra’ lineage (Coleoptera,Hydraenidae, Hydraena)

Aim We test whether species of western Mediterranean aquatic Coleoptera of the ‘Haenydra’ lineage (Hydraenidae, Hydraena) originated through: (1) successive periods of dispersal and speciation, (2) range fragmentation by random vicariance, or (3) range fragmentation by geographic isolation owing to a general reduction of population density. Location Europe. Methods To discriminate between scenarios we use contrasting predictions of the relationship between phylogenetic and geographic distance. The phylogeny was based on 3 kb of four mitochondrial and two nuclear gene fragments of about half of the known species of ‘Haenydra’, including most western Mediterranean taxa. Divergences were estimated using a molecular clock. The relationship between phylogenetic and geographic distance was tested using bivariate plots, Mantel tests and comparison of the observed phylogeny with the one minimizing geographic distances between species, as measured using Euclidean minimum spanning trees (EMSTs). Results The monophyly of ‘Haenydra’ was strongly supported, although its phylogenetic placement was not resolved. ‘Haenydra’ was estimated to be of late Miocene age, with most species originating during the Pleistocene. In two clades (Hydraena tatii and Hydraena emarginata clades) there was a significant association between geographic and phylogenetic distance, and the reconstructed phylogeny was identical to that obtained through the EMST, demonstrating a strong non‐randomness of the geographic distribution of the species. In two other clades (Hydraena iberica and Hydraena bitruncata clades) there was no association between geographic and phylogenetic distance, and the observed phylogeny was not the one minimizing geographic distances. In one of the clades this seems to be due to a secondary, recent range expansion of one species (H. iberica), which erased the geographic signal of their distributions. Main conclusions We show that it is possible to obtain strong evidence of stasis of the geographic ranges of narrow‐range endemic species through the study of their phylogenetic relationships and current distributions. In at least two of the studied clades, current species seem to have originated through the fragmentation of a more widely distributed species, without further range movements. A process of range expansion and fragmentation may have occurred repeatedly within the ‘Haenydra’ lineage, contributing to the accumulation of narrow‐range endemics in Mediterranean Pleistocene refugia.     

Speciation and dietary specialization in Drupa,a genus of predatory marine snails (Gastropoda: Muricidae)

Claremont, M., Reid, D.G. & Williams, S.T. (2012) Speciation and dietary specialization in Drupa, a genus of predatory marine snails (Gastropoda: Muricidae). —Zoologica Scripta, 41, 137–149. We test the competing predictions of allopatric speciation and of ecological speciation by dietary specialization in Drupa, an Indo‐Pacific genus of carnivorous marine gastropods in the family Muricidae. We use a well‐resolved molecular phylogeny (reconstructed from one nuclear and two mitochondrial genes) to show the validity of the traditional species D. elegans, D. rubusidaeus, D. clathrata, D. morum and D. speciosa.‘Drupa ricinus’ is shown to consist of three species: D. ricinus s. s., D. albolabris and a new species, possibly endemic to Japan. ‘Purpura’aperta is transferred to Drupa. Despite potential widespread dispersal and a high degree of range overlap among sister species, range sizes between sister species are highly asymmetric, suggesting that speciation has been predominately peripatric. The exception is the sister pair D. ricinus s. s. and D. albolabris, which have symmetric range sizes and are sympatric over broad Indo‐Pacific ranges. Such symmetry and extensive sympatry are contrary to the predictions of the (peripatric) allopatric model of speciation. Nevertheless, contrary to the predictions of an ecological speciation model based upon dietary specialization, broad dietary range appears to be identical between the species. Small differences in microhabitat preferences (or hypothetical dietary specialization at a fine taxonomic scale) may have been significant in the speciation process or, if initial divergence was allopatric, in permitting subsequent sympatry. Broad dietary shifts appear to have accompanied more ancient divergences within the genus Drupa.     

Taxonomy of the proterosuchid archosauriforms (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa,and implications for the early archosauriform radiation

Proterosuchidae is one of the first clades of Archosauriformes (archosaurs and closely related species) to appear in the fossil record, with the richest sample of the group coming from the Lystrosaurus Assemblage Zone (earliest Triassic) of South Africa. Four nominal proterosuchid species were described from South Africa during the twentieth century (Proterosuchus fergusi, Chasmatosaurus vanhoepeni, Chasmatosaurus alexanderi and Elaphrosuchus rubidgei), but interpretations of their taxonomy have been widely disparate. The most recent taxonomic revision concluded that P. fergusi is the only valid species and that the other nominal species are junior subjective synonyms of this taxon. This proposal was based on the interpretation that anatomical differences between the nominal species could be explained as a result of ontogenetic changes and/or post‐mortem deformation. The recent discoveries of multiple new South African proterosuchid specimens provide an impetus to revisit their taxonomy. Based upon a comprehensive re‐examination of all known specimens, as well as examination of other proterosuchid taxa in collections worldwide, we conclude that the holotype of Proterosuchus fergusi is undiagnostic. As a result, we propose a neotype (RC 846) for the species. ‘Chasmatosaurus vanhoepeni’ and ‘Elaphrosuchus rubidgei’ are considered subjective junior synonyms of P. fergusi. ‘Chasmatosaurus’ alexanderi is considered a valid species, for which we propose the new combination P. alexanderi comb. nov. A third species, P. goweri sp. nov., is erected on the basis of a single specimen (NMQR 880). All three species recognized here are taxonomically distinct from a previously described archosauriform maxilla from the lower Lystrosaurus AZ. As a result, we recognize a minimum of four archosauriform species following the Permo‐Triassic mass extinction in South Africa. Our results suggest a greater species richness of earliest Triassic archosauriforms than previously appreciated, but that archosauriform morphological disparity remained low and did not expand until the late Early Triassic – early Mid‐Triassic.     

Divergence in calls but not songs in the orchard oriole complex: Icterus spurius and I. fuertesi

Birdsong has important functions in attracting and competing for mates, and song characteristics are thought to diverge rapidly during the process of speciation. In contrast, other avian vocalizations that may have non‐reproductive functions, such as calls, are thought to be more evolutionarily conserved and may diverge more slowly among taxa. This study examines differences in both male song and an acoustically simpler vocalization, the ‘jeet’ call, between two closely related taxa, Icterus spurius and I. fuertesi. A previous study comparing song syllable type sharing within and between I. spurius and I. fuertesi indicated that their songs do not differ discernibly. Here we measured 18 acoustic characteristics of their songs and found strong evidence supporting this prior finding. In contrast, we measured 17 acoustic characteristics of jeet calls and found evidence of significant divergence between the two taxa in many of these characteristics. Calls in I. fuertesi have a longer duration, a larger frequency bandwidth, a lower minimum frequency, a lower beginning frequency, and greater levels of both frequency and amplitude modulation in comparison to the calls of I. spurius. In addition, I. fuertesi calls contain two distinct parts, while the calls of I. spurius have only one part. Thus, we find evidence of divergence in the calls of the two taxa but not their songs challenging the widespread assumption that complex bird song evolves more rapidly than other types of vocalizations. Understanding divergence in multiple vocalization types as well as other behavioral, morphological, and molecular traits is important to understanding the earliest stages of speciation.     

MORE THAN BINDIN DIVERGENCE: REPRODUCTIVE ISOLATION BETWEEN SYMPATRIC SUBSPECIES OF A SEA URCHIN BY ASYNCHRONOUS SPAWNING

The evolution of reproductive barriers is crucial to the process of speciation. In the Echinoidea, studies have focused on divergence in the gamete recognition protein, bindin, as the primary isolating mechanism among species. As such, the capacity of alternate mechanisms to be effective reproductive barriers and the phylogenetic context in which they arise is unclear. Here, we examine the evolutionary histories and factors limiting gene exchange between two subspecies of Heliocidaris erythrogramma that occur sympatrically in Western Australia. We found low, but significant differentiation between the subspecies in two mitochondrial genes. Further, coalescent analyses suggest that they diverged in isolation on the east and west coasts of Australia, with a subsequent range expansion of H. e. erythrogramma into Western Australia. Differentiation in bindin was minimal, indicating gamete incompatibility is an unlikely reproductive barrier. We did, however, detect strong asynchrony in spawning seasons; H. e. erythrogramma spawned over summer whereas H. e. armigera spawned in autumn. Taken together, we provide compelling evidence for a recent divergence of these subspecies and their reproductive isolation without gamete incompatibility. Western Australian H. erythrogramma may therefore present an intriguing case of incipient speciation, which depends on long‐term persistence of the factors underlying this spawning asynchrony.     

Ecological speciation in sympatric palms: 4. Demographic analyses support speciation of Howea in the face of high gene flow

The idea that populations must be geographically isolated (allopatric) to evolve into separate species has persisted for a long time. It is now clear that new species can also diverge despite ongoing genetic exchange, but few accepted cases of speciation in sympatry have held up when scrutinized using modern approaches. Here, we examined evidence for speciation of the Howea palms of Lord Howe Island, Australia, in light of new genomic data. We used coalescence‐based demographic models combined with double digest restriction site associated DNA sequencing of multiple individuals and provide support for previous claims by Savolainen et al. that speciation in Howea did occur in the face of gene flow.     

When rare species become endangered: cryptic speciation in myrmecophilous hoverflies

The myrmecophilous hoverfly, Microdon mutabilis, is listed as a ‘Rare’ or ‘Nationally Notable Species’ in UK Red Data Books. As an obligate social parasite, feeding only from ant colonies, its life‐style satisfies theoretical conditions under which cryptic speciation is predicted to evolve; namely, strong selection for nonmorphological adaptations that enhance its exploitation of a local subspecies or populations of its host. Samples of larvae and pupae in Ireland, Scotland and England showed that M. mutabilis exploits a single and different host ant species on different sites across its range. In nine southern English colonies, 95.6% of infested nests were of Myrmica scabrinodis whereas in six Irish and two Scottish colonies 100% and 94.2%, respectively, of the infested nests were of Formica lemani, despite M. scabrinodis being common at all sites. Although the adults from ‘scabrinodis’ (and lemani) populations are cryptic, morphometric measurements of pupae showed consistent diagnostic characters that were sufficiently distinct for these ecotypes to be classed as separate species. We conclude that M. mutabilis is the ‘lemani‐type’ and designate the ‘scabrinodis‐type’ as a new species, Microdon myrmicae spec. nov. Thus, one of the listed threatened species of the British Isles becomes two species, each possessing about half the number of populations and occupying half the range of the original ‘species’. Each also inhabits a different serai stage within grassland or heathland, and will require a different management regime if its declining populations are to be conserved. ‘M. mutabilis’ is reported with other host ant species on the European continent. In the light of our results, these may prove to be additional cryptic species. We suggest that cryptic speciation is apt to evolve in species, such as myrmecophiles, endoparasites and koinobiont parasitoids, whose life‐styles result in strong selection on their physiological or behavioural characters. The implications for Red Data Book classifications and for practical conservation are discussed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75 , 291–300.     

Size and shape interspecific divergence patterns partly reflect phylogeny in an Onthophagus species‐complex (Coleoptera: Scarabaeidae)

Polyphenism has been suggested as an accelerator for morphological evolution and speciation. In the dung beetles of the genus Onthophagus, horn expression is polyphenic: large males develop horns whereas smaller males express greatly reduced or no horns. Horn static allometries seem to diverge rapidly amongst extant taxa, a process which might trigger changes in the male genital morphology, thus possibly promoting speciation as a by‐product. It can therefore be hypothesized that interspecific distances in allometries and, possibly, in other morphological traits mirror phylogenetic distances. In this study we first assessed the phylogenetic relationships amongst three closely related taxa belonging to the so‐called ‘Onthophagus fracticornis‐similis‐opacicollis’ species‐complex by sequencing the mitochondrial gene cytochrome oxidase subunit 1 (cox1). Biomolecular results indicated three independent lineages, the closest relationships being found between Onthophagus similis and Onthophagus opacicollis. Then we assessed the extent to which divergence pattern of horn static allometries and size and shape divergence patterns of one genital (paramere) and two nongenital (head and epipharynx) structures mirrored the phylogenetic relationships. Interspecific divergence patterns of horn static allometries, paramere, and head shape were found to be congruent with the evolutionary relationships inferred from biomolecular data. Nevertheless, paramere size and epipharynx shape showed patterns not consistent with the phylogeny. Furthermore, the relative size of nongenital structures showed little interspecific divergence compared to their shapes. Our results suggest that size and shape interspecific divergence mirror phylogeny only in part; they also indicate that distinct morphological traits may differ in their tendency to evolve in concert, and that size and shape of the same trait can evolve independently across species. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 482–498.     

Analysis of range expansion in two species undergoing character displacement: why might invaders generally ‘win’ during character displacement?

Ecological character displacement occurs when interacting species diverge in resource use and associated traits in response to selection to minimize resource competition between them. Yet, when resource quality is asymmetric, the species that monopolizes the more profitable resource following character displacement may have higher fitness and therefore be deemed the ‘winner’. Here, we ask: does the winner tend to be the resident species (i.e. the earlier inhabitant of the geographic region where character displacement occurred) or the invader (i.e. the subsequent inhabitant of the region)? We focus on two spadefoot toad species that have undergone character displacement. Previous studies revealed that Spea bombifrons gains the higher quality resource following character displacement; consequently, Spea multiplicata must use the lower quality resource, and as a result, experiences negative fitness consequences. Where the two species have undergone character displacement, three lines of evidence implicate S. bombifrons as the invader: S. bombifrons possess lower haplotype and nucleotide diversity; they do not exhibit isolation by distance (in contrast to S. multiplicata); and they display much higher population growth rates. We hypothesize that historical patterns of selection in its ancestral range pre‐adapted S. bombifrons to evolve phenotypes capable of monopolizing the superior resource. Generally, because superior competitive abilities may facilitate successful invasions, invaders may be well positioned to win during character displacement.     

Complete mitochondrial genomes throw light on budding speciation in three Biston species (Lepidoptera,Geometridae)

Biston panterinaria, Biston thibetaria and Biston perclara are very closely related species in the genus Biston, judged on the basis of both morphological and molecular evidence. The distribution area and altitudes, and host plants of these three species also show both consistency and differences. However, the exact relationship between the three species is unclear. In this study, we used the ‘distance‐based method’, the ‘tree‐based method’ and Bayesian phylogenetics and phylogeography to elucidate the relationship between the three species. Phylogenetic trees based on mitogenomes, COI+CYTB+16S and three nuDNA genes were constructed. The results of the phylogenetic trees revealed that B. thibetaria and B. perclara were derived from B. panterinaria and render the latter paraphyletic. The budding process of speciation is therefore presumed to be the main factor causing a phylogenetic relationship of this pattern. A host shift from broad‐leaved plants living at low altitudes to gymnosperms living at relatively high altitudes provides evidence of budding speciation in these three species. The divergence time suggests that the budding speciation occurred at approximately 1.38 Ma, which is consistent with the Kunlun‐Yellow River Movement. Tectonic movements occurring around the Qinghai–Tibet Plateau may be the driver of the budding speciation.     

Congeneric phylogeography: hypothesizing species limits and evolutionary processes in Patagonian lizards of the Liolaemus boulengeri group (Squamata: Liolaemini)

In poorly known groups for which data are insufficient to develop biologically plausible model‐based approaches to phylogeographical analyses, a ‘first hypotheses’ protocol is suggested as offering the best way to generate hypotheses for subsequent model‐based tests. Preliminary hypotheses are formulated about species boundaries and population processes in three species complexes of the Liolaemus boulengeri group in the context of mtDNA ‘congeneric phylogeography’. The temperate South American Liolaemus provides a model with ancient and recent allopatric divergence across ecologically and geologically complex landscapes, incipient speciation, secondary contact, and discordance between molecular and morphological patterns of variation. Moderately dense sampling of widely distributed ‘inertial’ species in the Patagonian Steppe has revealed hidden genetic and probably species diversity, and also hinted at demographic and historical processes that may have shaped the histories of these taxa. Five of the seven focal species of the present study were paraphyletic for mtDNA genealogies, suggesting that they represent complexes of species, and nested clade phylogeographical analysis (NCPA) analyses suggest that different historical and demographic processes have shaped the observed patterns. Introgression and incomplete lineage sorting are hypothesized as being the cause of some of the observed paraphyly. Provisional delimitations of species are proposed and NCPA is used to generate hypotheses of population history, all of which are subject to further testing. Multi‐faceted studies, involving phylogenetic assessments of independent molecular markers and morphological variation across codistributed taxa with estimates of niche breadths in a landscape context, will likely yield the most promising returns for cross‐validation of hypotheses of population and speciation histories. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89 , 241–275.     

Nuclear locus divergence at the early stages of speciation in the Orchard Oriole complex

As two lineages diverge from one another, mitochondrial DNA should evolve fixed differences more rapidly than nuclear DNA due to its smaller effective population size and faster mutation rate. As a consequence, molecular systematists have focused on the criteria of reciprocal monophyly in mitochondrial DNA for delimiting species boundaries. However, mitochondrial gene trees do not necessarily reflect the evolutionary history of the taxa in question, and even mitochondrial loci are not expected to be reciprocally monophyletic when the speciation event happened very recently. The goal of this study was to examine mitochondrial paraphyly within the Orchard Oriole complex, which is composed of Icterus spurius (Orchard Oriole) and Icterus fuertesi (Fuertes' Oriole). We increased the geographic sampling, added four nuclear loci, and used a range of population genetic and coalescent methods to examine the divergence between the taxa. With increased taxon sampling, we found evidence of clear structure between the taxa for mitochondrial DNA. However, nuclear loci showed little evidence of population structure, indicating a very recent divergence between I. spurius and I. fuertesi. Another goal was to examine the genetic variation within each taxon to look for evidence of a past founder event within the I. fuertesi lineage. Based on the high amounts of genetic variation for all nuclear loci, we found no evidence of such an event – thus, we found no support for the possible founding of I. fuertesi through a change in migratory behavior, followed by peripheral isolates speciation. Our results demonstrate that these two taxa are in the earliest stages of speciation, at a point when they have fixed differences in plumage color that are not reflected in monophyly of the mitochondrial or nuclear DNA markers in this study. This very recent divergence makes them ideal for continued studies of species boundaries and the earliest stages of speciation.     

Secondary galling: a novel feeding strategy among ‘non‐pollinating’ fig wasps from Ficus curtipes

相似文献   

The cold‐adapted population of Folsomia manolachei (Hexapoda,Collembola) from a glaciated karst doline of Central Europe: evidence for a cryptic species?

Folsomia manolachei Bagnall, 1939 (Collembola), is a widespread and common European species. However, it may represent a complex of species also associated with the climatically more extreme environments of the karst landforms. Three species of the genus Folsomia, distributed in the Slovak Karst region (Central Europe), namely three different populations of F. manolachei, and one population of F. penicula and F. candida, were analysed using a partial sequence of the mitochondrial cytochrome c oxidase subunit I (COI barcoding section). The DNA barcoding suggested the existence of cryptic diversity in populations of the eurytopic species Folsomia manolachei. The cold‐adapted population of ‘F. manolachei’ was abundant in primary soil on stony debris near the permanent floor ice (yearly air temperature ~0°C) in the collapsed karst doline of the Silická ?adnica Ice Cave. It showed a genetic differentiation supported by intra‐ and interspecific distances that ranged from 0.0% to 1.4% and from 19.2% to 24.0%, respectively. Analysis using Taxon DNA showed a large barcoding gap between intra‐ and interspecific COI sequences. Genetic differentiation suggests a scenario of cryptic speciation in the population of ‘F. manolachei’ occupying harsh soils near the floor ice. A survival test showed the different responses of ‘F. manolachei’ and other populations to low temperature. Within a temperature range from ?3 to ?10°C, the ‘F. manolachei’ population from Silická ?adnica was the most cold‐resistant, showing a lethal dose LD₅₀ of ?7.8°C. The two forest populations of F. manolachei had LD₅₀ ?6.1°C and ?6.0°C, respectively; the most cold‐sensitive F. penicula showed an LD₅₀ of ?5.4°C. The survival of the tested springtails significantly decreased with temperature (p < 0.0001). The lethal temperature and the shape of the survival–temperature curves were different in different populations. The impact of population was significant at p < 0.0001, and the interaction between population and temperature at p < 0.039 was significant as well. Crypticity vs. phenotypic plasticity in Folsomia manolachei populations is discussed in terms of DNA barcoding and the cold tolerance data provided by this study.