Phylogeography of postglacial range expansion in Nigronia serricornis Say (Megaloptera: Corydalidae)

Similar pattern, different paths: tracing the biogeographical history of Megaloptera (Insecta: Neuropterida) using mitochondrial phylogenomics

The sequential breakup of the supercontinent Pangaea since the Middle Jurassic is one of the crucial factors that has driven the biogeographical patterns of terrestrial biotas. Despite decades of effort searching for concordant patterns between diversification and continental fragmentation among taxonomic groups, increasing evidence has revealed more complex and idiosyncratic scenarios resulting from a mixture of vicariance, dispersal and extinction. Aquatic insects with discreet ecological requirements, low vagility and disjunct distributions represent a valuable model for testing biogeographical hypotheses by reconstructing their distribution patterns and temporal divergences. Insects of the order Megaloptera have exclusively aquatic larvae, their adults have low vagility, and the group has a highly disjunct geographical distribution. Here we present a comprehensive phylogeny of Megaloptera based on a large-scale mitochondrial genome sequencing of 99 species representing >90% of the world genera from all major biogeographical regions. Molecular dating suggests that the deep divergence within Megaloptera pre-dates the breakup of Pangaea. Subsequently, the intergeneric divergences within Corydalinae (dobsonflies), Chauliodinae (fishflies) and Sialidae (alderflies) might have been driven by both vicariance and dispersal correlated with the shifting continent during the Cretaceous, but with strikingly different and incongruent biogeographical signals. The austral distribution of many corydalids appears to be a result of colonization from Eurasia through southward dispersal across Europe and Africa during the Cretaceous, whereas a nearly contemporaneous dispersal via northward rafting of Gondwanan landmasses may account for the colonization of extant Eurasian alderflies from the south.

Spatial Origin and Diversification of the Lycocerus fainanus Species Group (Coleoptera, Cantharidae), with Descriptions of Four New Species from China and Vietnam

Simple Summary

Lycocerus Gorham, 1889 has about 320 species worldwide at present, of which a small part have been attributed into 13 species groups, but the rest remain uncertain in their status. In the present study, five previously known species and another four new species from China and Vietnam were classified to the Lycocerusfainanus species group, based on their morphological characters. Then the distribution pattern of this group was analyzed with ArcGIS techniques. It showed that all species were constricted to the subtropical area of the Oriental region and distributed in both Taiwan and the continent. Further, the ancestral distribution range was reconstructed with the aid of the Reconstruct Ancestral State in Phylogenies (RASP) software, based on a phylogeny of morphological data. The results showed that the spatial origin was located in northern Vietnam and southwest China. Subsequently, two dispersal routes occurred: the first originated from the continent and then to Taiwan, the second from Taiwan to the continent, and the divergence between the species was caused by dispersal and vicariance. Unfortunately, it was difficult to estimate the timing of origin because of the lack of direct fossil evidence and molecular data.

Abstract

Five previously known species were attributed to the Lycocerus fainanus species group, including L. inopaciceps (Pic 1926), L. oberthueri (Gorham 1889), L. oudai (Švihla 2004), L. metallipennis (Fairmaire 1887), and L. nigripes (Wittmer, 1995). Four new species of this group were discovered from China and Vietnam, L. binotatus sp. nov., L. testacicollis sp. nov., L. daliensis sp. nov., and L. vietnamensis sp. nov. An updated key to all species was provided. A geographical distribution map is presented, which shows that all the members were located between 18.69041–33.93441° N, and between 98.61413–121.77102° E. The ancestral geographical range was reconstructed based on a phylogeny of morphological data by the Bayesian Binary MCMC method. The result showed that the spatial origin of L. fainanus species group was probably located in northern Vietnam and southwest China. The divergence of the species in southwest China and Taiwan was caused by vicariance about 24 Ma ago, when the latter was separated in the Qinghai-Tibet Plateau, and the remaining species of mainland China all originated from Taiwan after traveling around Southeast Asia and back to China. Nevertheless, this conclusion should be verified when fossil evidence and molecular data are available.

Megaloptera of Canada

An updated summary on the fauna of Canadian Megaloptera is provided. Currently, 18 species are recorded in Canada, with six species of Corydalidae and 12 species of Sialidae. This is an increase of two species since 1979. An additional seven species are expected to be discovered in Canada. Barcode Index Numbers are available for ten Canadian species.

Phylogeography and population diversity of Simulium hirtipupa Lutz (Diptera: Simuliidae) based on mitochondrial COI sequences

High morphological homogeneity and cryptic speciation may cause the diversity within Simuliidae to be underestimated. Recent molecular studies on population genetics and phylogeography have contributed to reveal which factors influenced the diversity within this group. This study aimed at examining the genetic diversity of Simulium hirtipupa Lutz, 1910 in populations from the biomes Caatinga, Cerrado, and Atlantic Forest. In this study, we carried out phylogeographic and population genetic analyses using a fragment of the mitochondrial gene COI. The 19 populations studied were clustered into seven groups, most of which are associated with geography indicating certain genetic structure. The northern region of the state of Minas Gerais is most likely the center of origin of this species. The average intergroup genetic distance was 3.7%, indicating the presence of cryptic species. The species tree as well as the haplotype network recovered all groups forming two major groups: the first comprises groups Gr-Bahia (in which the São Francisco river has not acted as geographical barrier), Gr-Pernambuco, and Gr-Mato Grosso do Sul. The second included groups comprising populations of the states of Goiás, Tocantins, Minas Gerais, Bahia, São Paulo, and Espírito Santo. The mismatch distribution for groups was consistent with the model of demographic expansion, except for the Gr-Central-East_1 group. The diversification in this group occurred about 1.19 Mya during the Pleistocene, influenced by paleoclimatic oscillations during the Quaternary glacial cycles.

Climate oscillations, glacial refugia, and dispersal ability: factors influencing the genetic structure of the least salmonfly, Pteronarcella badia (Plecoptera), in Western North America

Background

Phylogeographic studies of aquatic insects provide valuable insights into mechanisms that shape the genetic structure of communities, yet studies that include broad geographic areas are uncommon for this group. We conducted a broad scale phylogeographic analysis of the least salmonfly Pteronarcella badia (Plecoptera) across western North America. We tested hypotheses related to mode of dispersal and the influence of historic climate oscillations on population genetic structure. In order to generate a larger mitochondrial data set, we used 454 sequencing to reconstruct the complete mitochondrial genome in the early stages of the project.

Results

Our analysis revealed high levels of population structure with several deeply divergent clades present across the sample area. Evidence from five mitochondrial genes and one nuclear locus identified a potentially cryptic lineage in the Pacific Northwest. Gene flow estimates and geographic clade distributions suggest that overland flight during the winged adult stage is an important dispersal mechanism for this taxon. We found evidence of multiple glacial refugia across the species distribution and signs of secondary contact within and among major clades.

Conclusions

This study provides a basis for future studies of aquatic insect phylogeography at the inter-basin scale in western North America. Our findings add to an understanding of the role of historical climate isolations in shaping assemblages of aquatic insects in this region. We identified several geographic areas that may have historical importance for other aquatic organisms with similar distributions and dispersal strategies as P. badia. This work adds to the ever-growing list of studies that highlight the potential of next-generation DNA sequencing in a phylogenetic context to improve molecular data sets from understudied groups.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0553-4) contains supplementary material, which is available to authorized users.

Less pollen-mediated gene flow for more signatures of glacial lineages: congruent evidence from balsam fir cpDNA and mtDNA for multiple refugia in eastern and central North America

The phylogeographic structure and postglacial history of balsam fir (Abies balsamea), a transcontinental North American boreal conifer, was inferred using mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) markers. Genetic structure among 107 populations (mtDNA data) and 75 populations (cpDNA data) was analyzed using Bayesian and genetic distance approaches. Population differentiation was high for mtDNA (dispersed by seeds only), but also for cpDNA (dispersed by seeds and pollen), indicating that pollen gene flow is more restricted in balsam fir than in other boreal conifers. Low cpDNA gene flow in balsam fir may relate to low pollen production due to the inherent biology of the species and populations being decimated by recurrent spruce budworm epidemics, and/or to low dispersal of pollen grains due to their peculiar structural properties. Accordingly, a phylogeographic structure was detected using both mtDNA and cpDNA markers and population structure analyses supported the existence of at least five genetically distinct glacial lineages in central and eastern North America. Four of these would originate from glacial refugia located south of the Laurentide ice sheet, while the last one would have persisted in the northern Labrador region. As expected due to reduced pollen-mediated gene flow, congruence between the geographic distribution of mtDNA and cpDNA lineages was higher than in other North American conifers. However, concordance was not complete, reflecting that restricted but nonetheless detectable cpDNA gene flow among glacial lineages occurred during the Holocene. As a result, new cpDNA and mtDNA genome combinations indicative of cytoplasmic genome capture were observed.

Glacial cycles as an allopatric speciation pump in north-eastern American freshwater fishes

Allopatric speciation may be the principal mechanism generating new species. Yet, it remains difficult to judge the generality of this process because few studies have provided evidence that geographic isolation has triggered the development of reproductive isolation over multiple species of a regional fauna. Here, we first combine results from new empirical data sets (7 taxa) and published literature (9 taxa) to show that the eastern Great Lakes drainage represents a multispecies suture zone for glacial lineages of freshwater fishes with variable levels of genetic divergence. Second, we performed amplified fragment length polymorphism analyses among four pairs of lineages. Results indicate that lineages with relatively deep levels of mtDNA 5' COI (barcode) sequence divergence (>2%) developed strong reproductive barriers, while lineages with lower levels of divergence show weaker reproductive isolation when found in sympatry. This suggests that a threshold of 2% sequence divergence at mtDNA could be used as a first step to flag cryptic species in North American freshwater fishes. By describing different levels of divergence and reproductive isolation in different co-occurring fishes, we offer strong evidence that allopatric speciation has contributed significantly to the diversification of north-eastern American freshwater fishes and confirm that Pleistocene glacial cycles can be viewed as a 'speciation pump' that played a predominant role in generating biodiversity.

Early evolution and historical biogeography of fishflies (Megaloptera: Chauliodinae): implications from a phylogeny combining fossil and extant taxa

Fishflies (Corydalidae: Chauliodinae) are one of the main groups of the basal holometabolous insect order Megaloptera, with ca. 130 species distributed worldwide. A number of genera from the Southern Hemisphere show remarkably disjunctive distributions and are considered to be the austral remnants or "living fossils" of Gondwana. Hitherto, the evolutionary history of fishflies remains largely unexplored due to limited fossil record and incomplete knowledge of phylogenetic relationships. Here we describe two significant fossil species of fishflies, namely Eochauliodes striolatus gen. et sp. nov. and Jurochauliodes ponomarenkoi Wang & Zhang, 2010 (original designation for fossil larvae only), from the Middle Jurassic of Inner Mongolia, China. These fossils represent the earliest fishfly adults. Furthermore, we reconstruct the first phylogenetic hypothesis including all fossil and extant genera worldwide. Three main clades within Chauliodinae are recognized, i.e. the Dysmicohermes clade, the Protochauliodes clade, and the Archichauliodes clade. The phylogenetic and dispersal-vicariance (DIVA) analyses suggest Pangaean origin and global distribution of fishflies before the Middle Jurassic. The generic diversification of fishflies might have happened before the initial split of Pangaea, while some Gondwanan-originated clades were likely to be affected by the sequential breakup of Pangaea. The modern fauna of Asian fishflies were probably derived from their Gondwanan ancestor but not the direct descendents of the Mesozoic genera in Asia.

Climate change and evolutionary adaptations at species' range margins

During recent climate warming, many insect species have shifted their ranges to higher latitudes and altitudes. These expansions mirror those that occurred after the Last Glacial Maximum when species expanded from their ice age refugia. Postglacial range expansions have resulted in clines in genetic diversity across present-day distributions, with a reduction in genetic diversity observed in a wide range of insect taxa as one moves from the historical distribution core to the current range margin. Evolutionary increases in dispersal at expanding range boundaries are commonly observed in virtually all insects that have been studied, suggesting a positive feedback between range expansion and the evolution of traits that accelerate range expansion. The ubiquity of this phenomenon suggests that it is likely to be an important determinant of range changes. A better understanding of the extent and speed of adaptation will be crucial to the responses of biodiversity and ecosystems to climate change.

Phylogeographic analysis and environmental niche modeling of the plain-bellied watersnake (Nerodia erythrogaster) reveals low levels of genetic and ecological differentiation

Species that exhibit geographically defined phenotypic variation traditionally have been divided into subspecies. Subspecies based on phenotypic features may not comprise monophyletic groups due to selection, gene flow, and/or convergent evolution. In many taxonomic groups the number of species once designated as widespread is dwindling rapidly, and many workers reject the concept of subspecies altogether. We tested whether currently recognized subspecies in the plain-bellied watersnake Nerodia erythrogaster are concordant with relationships based on mitochondrial markers, and whether it represents a single widespread species. The range of this taxon spans multiple potential biogeographic barriers (especially the Mississippi and Apalachicola Rivers) that correspond with lineage breaks in many species, including other snakes. We sequenced three mitochondrial genes (NADH-II, Cyt-b, Cox-I) from 156 geo-referenced specimens and developed ecological niche models using Maxent and spatially explicit climate data to examine historical and ecological factors affecting variation in N. erythrogaster across its range. Overall, we found little support for the recognized subspecies as either independent evolutionary lineages or geographically circumscribed units and conclude that although some genetic and niche differentiation has occurred, most populations assigned to N. erythrogaster appear to represent a single, widespread species. However, additional sampling and application of nuclear markers are necessary to clarify the status of the easternmost populations.

Towards a comprehensive barcode library for arctic life - Ephemeroptera, Plecoptera, and Trichoptera of Churchill, Manitoba, Canada

Background

This study reports progress in assembling a DNA barcode reference library for Ephemeroptera, Plecoptera, and Trichoptera ("EPTs") from a Canadian subarctic site, which is the focus of a comprehensive biodiversity inventory using DNA barcoding. These three groups of aquatic insects exhibit a moderate level of species diversity, making them ideal for testing the feasibility of DNA barcoding for routine biotic surveys. We explore the correlation between the morphological species delineations, DNA barcode-based haplotype clusters delimited by a sequence threshold (2%), and a threshold-free approach to biodiversity quantification--phylogenetic diversity.

Results

A DNA barcode reference library is built for 112 EPT species for the focal region, consisting of 2277 COI sequences. Close correspondence was found between EPT morphospecies and haplotype clusters as designated using a standard threshold value. Similarly, the shapes of taxon accumulation curves based upon haplotype clusters were very similar to those generated using phylogenetic diversity accumulation curves, but were much more computationally efficient.

Conclusion

The results of this study will facilitate other lines of research on northern EPTs and also bode well for rapidly conducting initial biodiversity assessments in unknown EPT faunas.

Comparative phylogeography of unglaciated eastern North America

Regional phylogeographical studies involving co-distributed animal and plant species have been conducted for several areas, most notably for Europe and the Pacific Northwest of North America. Until recently, phylogeographical studies in unglaciated eastern North America have been largely limited to animals. As more studies emerge for diverse lineages (including plants), it seems timely to assess the phylogeography across this region: (i) comparing and contrasting the patterns seen in plants and animals; (ii) assessing the extent of pseudocongruence; and (iii) discussing the potential applications of regional phylogeography to issues in ecology, such as response to climatic change. Unglaciated eastern North America is a large, geologically and topographically complex area with the species examined having diverse distributions. Nonetheless, some recurrent patterns emerge: (i) maritime - Atlantic vs. Gulf Coast; (ii) Apalachicola River discontinuity; (iii) Tombigbee River discontinuity; (iv) the Appalachian Mountain discontinuity; (v) the Mississippi River discontinuity; and (vi) the Apalachicola River and Mississippi River discontinuities. Although initially documented in animals, most of these patterns are also apparent in plants, providing support for phylogeographical generalizations. These patterns may generally be attributable to isolation and differentiation during Pleistocene glaciation, but in some cases may be older (Pliocene). Molecular studies sometimes agree with longstanding hypotheses of glacial refugia, but also suggest additional possible refugia, such as the southern Appalachian Mountains and areas close to the Laurentide Ice Sheet. Many species exhibit distinct patterns that reflect the unique, rather than the shared, aspects of species' phylogeographical histories. Furthermore, similar modern phylogeographical patterns can result from different underlying causal factors operating at different times (i.e. pseudocongruence). One underemphasized component of pseudocongruence may result from the efforts of researchers to categorize patterns visually - similar patterns may, in fact, not fully coincide, and inferring agreement may obscure the actual patterns and lead to erroneous conclusions. Our modelling analyses indicate no clear spatial patterning and support the hypothesis that phylogeographical structure in diverse temperate taxa is complex and was not shaped by just a few barriers.