Cryptic diversity, diversification and vicariance in two species complexes ofTomocerus(Collembola, Tomoceridae) from China

Revisiting the type species of the genus Homidia (Collembola, Entomobryidae)

Homidiacingula Börner, 1906, the type species of the genus Homidia Börner, 1906, is widespread from India to Southeast Asia, but its detailed morphological characteristics have not yet been described. We examined the morphology of specimens of H.cingula from Indonesia and southwestern China and confirmed their conspecific status by comparing their DNA barcoding sequences. We also compared the morphology of H.cingula with other two closely related species, confirming the valid species status of H.subcingula Denis, 1948. Our study provides new taxonomic and molecular data for the genus Homidia.

Hotspot in ferruginous rock may have serious implications in Brazilian conservation policy

A hotspot of subterranean Collembola in ferruginous rock caves and Mesovoid Shallow Substratum is revealed by the analysis of pseudocryptic diversity. The diversity is accessed by detailed description of chaetotaxy and slight variation in morphology of 11 new species of Trogolaphysa Mills, 1938 (Collembola, Paronellidae, Paronellinae) and the 50 previously recorded species of springtails from caves, using optical and electronic microscopy. When combined with recent subterranean surveys, our results show an important reservoir of cave diversity in the Mesovoid Shallow Substratum. Contrastingly the conservation policy for subterranean fauna in metallogenic areas in Brazil prioritizes the caves instead the cave species, which may be extremely detrimental to the fauna in the shallow subterranean habitats not accessible to humans.

High-quality genomes reveal significant genetic divergence and cryptic speciation in the model organism Folsomia candida (Collembola)

The collembolan Folsomia candida Willem, 1902, is widely distributed throughout the world and has been frequently used as a test organism in soil ecology and ecotoxicology studies. However, it is questioned as an ideal "standard" because of differences in reproductive modes and cryptic genetic diversity between strains from various geographical origins. In this study, we obtained two high-quality chromosome-level genomes of F. candida, for a parthenogenetic strain (named as FCDK, 219.08 Mb, 25,139 protein-coding genes) and a sexual strain (named as FCSH, 153.09 Mb, 21,609 protein-coding genes), reannotated the genome of the parthenogenetic strain reported by Faddeeva-Vakhrusheva et al. in 2017 (named as FCBL, 221.7 Mb, 25,980 protein-coding genes), and conducted comparative genomic analyses of three strains. High genome similarities between FCDK and FCBL on synteny, genome architecture, mitochondrial and nuclear gene sequences support they are conspecific. The seven chromosomes of FCDK are each 25-54% larger than the corresponding chromosomes of FCSH, showing obvious repetitive element expansions and large-scale inversions and translocations but no whole-genome duplication. The strain-specific genes, expanded gene families and genes in nonsyntenic chromosomal regions identified in FCDK are highly related to the broader environmental adaptation of parthenogenetic strains. In addition, FCDK has fewer strain-specific microRNAs than FCSH, and their mitochondrial and nuclear genes have diverged greatly. In conclusion, FCDK/FCBL and FCSH have accumulated independent genetic changes and evolved into distinct species since 10 Mya. Our work provides important genomic resources for studying the mechanisms of rapidly cryptic speciation and soil arthropod adaptation to soil ecosystems.

Mitochondrial composition of and diffusion limiting factors of three social wasp genera Polistes, Ropalidia, and parapolybia (Hymenoptera: Vespidae)

Background

Social wasps Polistes, Ropalidia, and Parapolybia, belonging to the subfamily Polistinae, have obviously different distribution patterns, yet the factors leading to this difference remain unknown.

Results

The 17 newly sequenced mitogenomes of Polistes, Ropalidia, and Parapolybia contain 37 genes, and there are obvious differences among the compositions of the three genera. The monophyly of the genus Polistes and a monophyletic Ropalidiini: (Ropalidia + Parapolybia) are concordant with previous morphological analysis of the subfamily Polistinae. Our inferred divergence time demonstrates Polistes (at around 69 Ma) was diverged earlier than Ropalidia and Parapolybia (at around 61 Ma). The rearrangement of both trnY and trnL1 are shared by all the Polistinae. In addition, the unique rearrangement of TDRL derived at 69 Ma is detected in Polistes, and Ropalidia contains a Reversal which may derive at 61 Ma. Hereafter, the possibility is elaborated that Polistes originated in Aisa and then dispersed from Africa to South America, and Polistes and Ropalidia spread from Southeast Asia to Australia. At last, continental drift and Quaternary Ice Ages are inferred to be two main limiting factors in the current distributions of the three genera.

Conclusions

Obvious differences occur in the mitochondrial composition of Polistes, Ropalidia, and Parapolybia. According to the reconstructed time-calibrated framework, it is inquired that the continental drifts and the climate are mainly diffusion limiting factors of the three genera.

Supplementary information

The online version contains supplementary material available at 10.1186/s12862-022-02017-6.

Molecular phylogeny and trait evolution in an ancient terrestrial arthropod lineage: Systematic revision and implications for ecological divergence (Collembola, Tomocerinae)

Phylogenetic assessments of functional traits are important for mechanistically understanding the interactions between organisms and environments, but such practices are strongly limited by the availability of phylogenetic frameworks. The tomocerin springtails are an ancient, widespread and ecologically important group of terrestrial arthropods, whereas their phylogeny and trait evolution remained unaddressed. In the present study, we conducted the first comprehensive phylogenetic reconstruction of Tomocerinae, based on a multi-loci molecular dataset covering all major lineages within the subfamily, using Bayesian inference (BI), maximum-likelihood (ML) and maximum-parsimony (MP) approaches. Divergence time was estimated and ancestral character state reconstruction (ACSR) was performed to trace the evolutionary history of five ecomorphological traits correlated with sensory and locomotory functions. Our results support the monophyly of Tomocerinae, and indicate that current classification of Tomocerinae only partially reflects evolutionary relationships, notably the commonest and speciose genus Tomocerus is polyphyletic. The subfamily probably originated in Early Cretaceous and diversified in two Cretaceous and one Eocene radiation events. As indicated by the evolutionary patterns of functional traits, multiple ecological divergences took place during the diversification of Tomocerinae. The study suggests a potential underestimation of ecological divergence and functional diversity in terrestrial arthropods, calls for an update of present trait databases, and demonstrates the value of macroevolutionary knowledge for improving the trait-based ecology. In addition, Tomocerus, Tomocerina and Tritomurus are redefined, a new genus Yoshiicerusgen. n. and new subgenera Coloratomurussubgen. n., Ciliatomurussubgen. n., Striatomurussubgen. n. and Ocreatomurussubgen. n. are described in the appendix.

Evolutionary history of endangered and relict tree species Dipteronia sinensis in response to geological and climatic events in the Qinling Mountains and adjacent areas

Geological and climatic events are considered to profoundly affect the evolution and lineage divergence of plant species. However, the evolutionary histories of tree species that have responded to past geological and climate oscillations in central China's mountainous areas remain mostly unknown. In this study, we assessed the evolutionary history of the endangered and relict tree species Dipteronia sinensis in the Qinling Mountains (QM) and adjacent areas in East Asia based on variations in the complete chloroplast genomes (cpDNA) and reduced-genomic scale single nucleotide polymorphisms (SNPs). Population structure and phylogenetic analysis based on the cpDNA variations suggested that D. sinensis could be divided into two intraspecific genetic lineages in the eastern and western sides of the QM (EQM and WQM, respectively) in East Asia. Molecular dating suggested that the intraspecific divergence of D. sinensis occurred approximately 39.2 million years ago during the later Paleogene. It was significantly correlated with the orogeny of the QM, where the formation of this significant geographic barrier in the region may have led to the divergence of independent lineages. Bayesian clustering and demographic analysis showed that intraspecific gene flow was restricted between the EQM and WQM lineages. Isolation-with-migration analysis indicated that the two genetic lineages experienced significant demographic expansions after the Pleistocene ice ages. However, the genetic admixture was determined in some populations between the two lineages by the large scale of SNP variations due to DNA incompatibility, the large significant population size, and rapid gene flow of nuclear DNA markers. Our results suggest that two different conservation and management units should be constructed for D. sinensis in the EQM and WQM areas. These findings provide novel insights into the unprecedented effects of tectonic changes and climatic oscillations on lineage divergence and plant population evolution in the QM and adjacent areas in East Asia.

Inferring Evolutionary Timescales without Independent Timing Information: An Assessment of "Universal" Insect Rates to Calibrate a Collembola (Hexapoda) Molecular Clock

Previous estimates of nucleotide substitution rates are routinely applied as secondary or “universal” molecular clock calibrations for estimating evolutionary timescales in groups that lack independent timing information. A major limitation of this approach is that rates can vary considerably among taxonomic groups, but the assumption of rate constancy is rarely evaluated prior to using secondary rate calibrations. Here I evaluate whether an insect mitochondrial DNA clock is appropriate for estimating timescales in Collembola—a group of insect-like arthropods characterized by high levels of cryptic diversity. Relative rates of substitution in cytochrome oxidase subunit 1 (COI) were inferred via Bayesian analysis across a topologically constrained Hexapod phylogeny using a relaxed molecular clock model. Rates for Collembola did not differ significantly from the average rate or from the rates estimated for most other groups (25 of 30), suggesting that (1) their apparent cryptic diversity cannot be explained by accelerated rates of molecular evolution and (2) clocks calibrated using “universal” insect rates may be appropriate for estimating evolutionary timescales in this group. However, of the 31 groups investigated, 10 had rates that deviated significantly from the average (6 higher, 4 lower), underscoring the need for caution and careful consideration when applying secondary insect rate calibrations. Lastly, this study exemplifies a relatively simple approach for evaluating rate constancy within a taxonomic group to determine whether the use of secondary rates are appropriate for molecular clock calibrations.

Phylomitogenomic analyses on collembolan higher taxa with enhanced taxon sampling and discussion on method selection

Collembola are a basal group of Hexapoda renowned for both unique morphological characters and significant ecological roles. However, a robust and plausible phylogenetic relationship between its deeply divergent lineages has yet to be achieved. We carried out a mitophylogenomic study based on a so far the most comprehensive mitochondrial genome dataset. Our data matrix contained mitogenomes of 31 species from almost all major families of all four orders, with 16 mitogenomes newly sequenced and annotated. We compared the linear arrangements of genes along mitochondria across species. Then we conducted 13 analyses each under a different combination of character coding, partitioning scheme and heterotachy models, and assessed their performance in phylogenetic inference. Several hypothetical tree topologies were also tested. Mitogenomic structure comparison revealed that most species share the same gene order of putative ancestral pancrustacean pattern, while seven species from Onychiuridae, Poduridae and Symphypleona bear different levels of gene rearrangements, indicating phylogenetic signals. Tomoceroidea was robustly recovered for the first time in the presence of all its families and subfamilies. Monophyly of Onychiuroidea was supported using unpartitioned models alleviating LBA. Paronellidae was revealed polyphyletic with two subfamilies inserted independently into Entomobryidae. Although Entomobryomorpha has not been well supported, more than half of the analyses obtained convincing topologies by placing Tomoceroidea within or near remaining Entomobryomorpha. The relationship between elongate-shaped and spherical-shaped collembolans still remained ambiguous, but Neelipleona tend to occupy the basal position in most trees. This study showed that mitochondrial genomes could provide important information for reconstructing the relationships among Collembola when suitable analytical approaches are implemented. Of all the data refining and model selecting schemes used in this study, the combination of nucleotide sequences, partitioning model and exclusion of third codon positions performed better in generating more reliable tree topology and higher node supports than others.

The complete mitochondrial genome of an enigmatic predaceous springtail Metisotoma macnamarai from northeast China

The complete mitogenome of Metisotoma macnamarai (Folsom 1918) (Collembola, Isotomidae), a member of obligatory predaceous genus Metisotoma Maynard, 1951, was sequenced. It has a length of 15,177 bp, comprising 13 protein-coding genes, 22 tRNAs, and 2 rRNAs. The mitogenome has the following base composition: A = 37.1%, T = 33.3%, G = 11.8%, and C = 17.4%. Phylogenetic analysis using maximum likelihood (ML) indicates that M. macnamarai clusters as sister taxon to the genus Isotomurus, with high statistical support.

Molecular phylogeny of Entomobrya (Collembola: Entomobryidae) from China: Color pattern groups and multiple origins

Highly diversified colorations among springtails (Collembola) have been widely used for species diagnosis, but their phylogenetic significance is poorly known. We addressed this issue in the largest Entomobryinae genus Entomobrya, which possesses variable color patterns among species. The relationships within the genus and to other genera have also rarely been studied. Based on material mainly from China, we have conducted a multilocus phylogeny and topology tests with likelihood and Bayesian algorithms, and accordingly demonstrated the non-monophyly of Chinese Entomobrya. The division of five clades, including Entomobrya and several related genera, coincided well with five types of colorations, respectively. Further analyses of divergence time and historical biogeography revealed that Chinese Entomobrya originated mainly from Palearctic (northern and western) China in the Paleocene and Eocene. This study highlights the great phylogenetic values as well as taxonomic uses of coloration in Chinese Entomobrya. Multiple phylogenetic and biogeographic origins of Entomobrya imply its complicated relationships with both scaled and unscaled genera of Entomobryinae.

DNA-based approaches uncover cryptic diversity in the European Lepidocyrtus lanuginosus species group (Collembola: Entomobryidae)

DNA sequence data and phylogenies are useful tools for species delimitation, especially in taxa comprising cryptic species. The Lepidocyrtus lanuginosus species group (Collembola: Entomobryidae) comprises three morphospecies and distinct cryptic species. We applied three DNA-based methods to delimit species boundaries in the L. lanuginosus species group across central and southern Europe. Using cytochrome c oxidase subunit I and II, we identified gaps of genetic distances that indicate species boundaries and found 10 and 9 distinct genetic lineages in L. cyaneus and L. lanuginosus, respectively. The nuclear gene elongation factor 1-α delimited 89% of the lineages but 28S rDNA (D1–2 domain) was too conserved for this purpose. The phylogenetic trees showed that L. cyaneus and L. lanuginosus are polyphyletic, suggesting that body colour is insufficient for delimiting species in the L. lanuginosus species group. Our study challenges the current morphology-based species delimitation in the L. lanuginosus species group and suggests that molecular approaches are needed for fast and accurate determination of Collembola species in both taxonomic and ecological studies. Overall, the results suggest that wide geographic sampling combined with molecular phylogenetic approaches is needed to delimit species and to understand the full range of cryptic diversity in Collembola.

Molecular and morphological characterization of the predatory mite Amblyseius largoensis (Acari: Phytoseiidae): surprising similarity between an Asian and American populations

The accurate characterization of biological control agents is a key step in control programs. Recently, Amblyseius largoensis from Thailand were introduced in Brazil to evaluate their efficiency for the control of the red palm mite, Raoiella indica. The aim of this study was to confirm their identification and to characterize the population from Thailand, comparing it to populations of the Americas and Indian Ocean islands. In addition, a population of A. largoensis from New Caledonia, Oceania, of which DNA sequences were available, was included in phylogenetic analyses. Morphometric data obtained for the population of A. largoensis from Thailand were compared to those of populations from Reunion Island and the Americas through univariate and multivariate analyses. Two DNA fragments were amplified and sequenced: the nuclear ribosomal region ITSS and the mitochondrial 12S rRNA. Haplotypes (12S rRNA) and genotypes (ITSS) were identified and phylogenetic analyses using both fragments were conducted separately and combined using maximum likelihood and the Bayesian information criterion. The integrative approach reveals morphometric and molecular variabilities among populations of A. largoensis and shows that the population identified as A. largoensis collected in Thailand, as well as that from New Caledonia, are conspecific to the populations of the Americas and Indian Ocean islands. Populations from the Americas and Asia are more related to each other than with that from the Indian Ocean islands. Hypotheses to explain this clustering are proposed. Data on the molecular intraspecific variability of this predatory mite from remote areas will be helpful for the development of molecular diagnosis.

Unusually low genetic divergence at COI barcode locus between two species of intertidal Thalassaphorura (Collembola: Onychiuridae)

Species classification is challenging when taxa display limited morphological differences. In this paper, we combined morphology and DNA barcode data to investigate the complicated taxonomy of two Onychiurid Collembolan species. Thalassaphorura thalassophila and Thalassaphorura debilis are among the most common arthropod species in intertidal ecosystems and are often considered to be synonymous. Based on morphological and barcode analyses of fresh material collected in their type localities, we redescribed and compared the two species. However, their morphological distinctiveness was supported by a molecular divergence much smaller than previously reported at the interspecific level among Collembola. This divergence was even smaller than inter-population divergences recognized in the related edaphic species T. zschokkei, as well as those known between MOTUs within many Collembolan species. Our results may indicate a link between low genetic interspecific divergence and intertidal habitat, as the only biological peculiarity of the two species of interest compared to other Collembolan species analyzed to date is their strict intertidal life.

Colouration, chaetotaxy and molecular data provide species-level resolution in a species complex of Dicranocentrus (Collembola : Entomobryidae)

Integrative taxonomic approaches are increasingly providing species-level resolution to ‘cryptic’ diversity. In the absence of an integrative taxonomic approach, formal species validation is often lacking because of inadequate morphological diagnoses. Colouration and chaetotaxy are the most commonly used characters in collembolan taxonomy but can cause confusion in species diagnoses because these characters often have large intraspecific variation. Here, we take an integrative approach to the genus Dicranocentrus in China where four species have been previously recognised, but several members of the genus have been morphologically grouped as a species complex based on having paired outer teeth on unguis and seven colour patterns. Molecular delimitations based on distance- and evolutionary models recovered four candidate lineages from three gene markers and revealed that speciation events likely occurred during the late Neogene (4–13million years ago). Comparison of intact dorsal chaetotaxy, whose homologies were erected on the basis of first instar larva, further validated these candidates as formal species: D. gaoligongensis, sp. nov., D. similis, sp. nov., D. pallidus, sp. nov. and D. varicolor, sp. nov., and increase the number of Dicranocentrus species from China to eight. Our study further highlights the importance of adequate taxonomy in linking morphological and molecular characters within integrative taxonomy.

Delimiting species of Protaphorura (Collembola: Onychiuridae): integrative evidence based on morphology, DNA sequences and geography

Species delimitation remains a significant challenge when the diagnostic morphological characters are limited. Integrative taxonomy was applied to the genus Protaphorura (Collembola: Onychiuridae), which is one of most difficult soil animals to distinguish taxonomically. Three delimitation approaches (morphology, molecular markers and geography) were applied providing rigorous species validation criteria with an acceptably low error rate. Multiple molecular approaches, including distance- and evolutionary model-based methods, were used to determine species boundaries based on 144 standard barcode sequences. Twenty-two molecular putative species were consistently recovered across molecular and geographical analyses. Geographic criteria were was proved to be an efficient delimitation method for onychiurids. Further morphological examination, based on the combination of the number of pseudocelli, parapseudocelli and ventral mesothoracic chaetae, confirmed 18 taxa of 22 molecular units, with six of them described as new species. These characters were found to be of high taxonomical value. This study highlights the potential benefits of integrative taxonomy, particularly simultaneous use of molecular/geographical tools, as a powerful way of ascertaining the true diversity of the Onychiuridae. Our study also highlights that discovering new morphological characters remains central to achieving a full understanding of collembolan taxonomy.

Phylogeography of the Rice Spittle Bug (Callitettix versicolor) Implies Two Long-Term Mountain Barriers in South China

South China is a region of remarkable topographic complexity. However, the impact of climate fluctuations in the Pleistocene on the local fauna and especially insects has not been extensively studied. We integrated mitochondrial DNA (mtDNA) and microsatellite data of the rice spittle bug, Callitettix versicolor, to determine the genetic structure, potential biogeographic barriers, and historical demography of this species. The mtDNA data revealed two distinct lineages (Western and Eastern) congruent with the geographically separated western and eastern sub-regions of the Hengduan Mountains. The Eastern lineage was subdivided into two sub-lineages, E1 and E2, congruent with the geographically separated northern and southern sub-regions of the Dabie Mountains. E2 was further subdivided into two sub-groups, E2-1 and E2-2, with a hybrid zone (Guizhou and Hunan Provinces) in which their areas were contiguous. The genetic structures constructed using mtDNA were corroborated by four clusters (G1-G4) of microsatellite data. The populations of each cluster were nearly consistent with a sub-lineage of the mtDNA gene tree (G1-G4 corresponded to the Western, E1, E2-2 and E2-1 lineages, respectively). The divergence time estimated between the Western and Eastern lineages was 1.17 (0.50-2.37) to 0.89 (0.39-1.78) Mya, indicating that the lineages diversified on both geographic and temporal scales. The historical demography of the Eastern lineage showed continuous population growth after the Last Interglacial (LIG) and a stable population during the Last Glacial Maximum (LGM) period. However, the Western lineage remained largely unchanged during the LIG and LGM periods. This suggests that the historical demography of C. versicolor is probably related not only to the paleoclimate of South China, but also to the geological restriction and specific habitat preferences of species.

New Australian Paronellidae (Collembola) reveal anomalies in existing tribal diagnoses

We describe here two new species, Zhuqinia jingwanae, gen. & sp. nov. and Paronellides praefectus, sp. nov., both from Mount Twynam, New South Wales, Australia. The systematic position of Zhuqinia, gen. nov. in relation to other paronellids is not clear because the new genus possesses pointed, heavily striated scales similar to species of Callyntrurini. However, unlike species in that tribe, it lacks dental scales. Instead, Zhuqinia, gen. nov. is more similar to the unscaled genus Paronellides (Cremastocephalini) in other characters (abundant tergal macrochaetae, 2, 2|1, 2, 2, ?, 3 tergal S-chaetae, moderately long mucro with two teeth, etc.) but body scales are absent in all species of Paronellides. Multilocus phylogeny shows Zhuqinia, gen. nov. clustering with Paronellides rather than Callyntrurini or other Cremastocephalini genera. This study provides new information on the relationships between paronellid taxa, and changes the current higher classification of the family, particularly that of the tribes Cremastocephalini and Callyntrurini. As the new genus is known only from two peaks in the Snowy Mountain range, our data emphasise the role of montane areas as refugia for short-range endemic taxa.

New cave-dwelling species of Tomoceridae from China, with a study on the pattern of mesothoracic bothriotricha in Tomocerinae (Collembola, Entomobryomorpha)

Two new troglobitic species of Tomoceridae are described from Guizhou and Guangxi provinces, China. Tomocerustianisp. n. resembles Tomoceruskinoshitai Yosii, 1954, Tomoceruscaecus Yu & Deharveng, 2015 and Tomocerussimilis Chen & Ma, 1997 but differs from them mainly in the body colour, the cephalic chaetotaxy and the number of manubrial pseudopores. Monodontoceruscinereussp. n. is similar to Monodontocerusmulunensis Yu, Deharveng & Zhang, 2014 but is different from the latter in the body colour, the length of antennae, the number of ungual teeth and the chaetotaxy on Abd. III and Abd. IV. Special remarks are made on the mesothoracic bothriotricha in Tomocerinae.

Species delimitation in northern European water scavenger beetles of the genus Hydrobius (Coleoptera, Hydrophilidae)

The chiefly Holarctic Hydrobius species complex (Coleoptera, Hydrophilidae) currently consists of Hydrobius arcticus Kuwert, 1890, and three morphological variants of Hydrobius fuscipes (Linnaeus, 1758): var. fuscipes, var. rottenbergii and var. subrotundus in northern Europe. Here molecular and morphological data are used to test the species boundaries in this species complex. Three gene segments (COI, H3 and ITS2) were sequenced and analyzed with Bayesian methods to infer phylogenetic relationships. The Generalized Mixed Yule Coalescent (GMYC) model and two versions of the Bayesian species delimitation method BPP, with or without an a priori defined guide tree (v2.2 & v3.0), were used to evaluate species limits. External and male genital characters of primarily Fennoscandian specimens were measured and statistically analyzed to test for significant differences in quantitative morphological characters. The four morphotypes formed separate genetic clusters on gene trees and were delimited as separate species by GMYC and by both versions of BPP, despite specimens of Hydrobius fuscipes var. fuscipes and Hydrobius fuscipes var. subrotundus being sympatric. Hydrobius arcticus and Hydrobius fuscipes var. rottenbergii could only be separated genetically with ITS2, and were delimited statistically with GMYC on ITS2 and with BPP on the combined data. In addition, six or seven potentially cryptic species of the Hydrobius fuscipes complex from regions outside northern Europe were delimited genetically. Although some overlap was found, the mean values of six male genital characters were significantly different between the morphotypes (p < 0.001). Morphological characters previously presumed to be diagnostic were less reliable to separate Hydrobius fuscipes var. fuscipes from Hydrobius fuscipes var. subrotundus, but characters in the literature for Hydrobius arcticus and Hydrobius fuscipes var. rottenbergii were diagnostic. Overall, morphological and molecular evidence strongly suggest that Hydrobius arcticus and the three morphological variants of Hydrobius fuscipes are separate species and Hydrobius rottenbergii Gerhardt, 1872, stat. n. and Hydrobius subrotundus Stephens, 1829, stat. n. are elevated to valid species. An identification key to northern European species of Hydrobius is provided.

Dental scales could occur in all scaled subfamilies of Entomobryidae (Collembola): new definition of Entomobryinae with description of a new genus and three new species

Body scales are fundamental in the classification of Entomobryidae at all taxonomical levels. Traditionally, scales on dens were considered to be absent in Entomobryinae, but present in other scaled subfamilies; however, this opinion was strongly challenged by recent morphological advances in tergal specialised chaetae (S-chaetae). A new genus, Lepidodens, is strikingly similar to the scaled Entomobryinae genus Willowsia in having pointed scales with relatively long ribs and 2, 2|1, 2, 2, 8, 3 tergal S-chaetae, but differs from it in having dental scales and a unique position of S-microchaetae on the first abdominal segment. Multilocus phylogeny and topology tests also support this view, the new genus clustering with Entomobryinae rather than Seirinae. Three new species, L. nigrofasciatus, L. similis and L. hainanicus, are described from South China. This study clearly undermines the traditional separation of Entomobryinae and Seirinae/Lepidocyrtinae, and demonstrates that dental scales could occur in all entomobryid subfamilies containing scaled taxa. In this new phylogenetic hypothesis, Entomobryinae has the greatest diversity in scale morphology and distribution among scaled collembolan groups, indicating multiple independent origins of scales.

Taxonomic review and phylogenetic analysis of fifteen North American Entomobrya (Collembola, Entomobryidae), including four new species

The chaetotaxy of 15 species of eastern North American Entomobrya is redescribed in order to determine potential characters for the diagnosis of cryptic lineages and evaluate the diagnostic and phylogenetic utility of chaetotaxy. As a result, four new species (Entomobrya citrensis Katz & Soto-Adames, sp. n., Entomobrya jubata Katz & Soto-Adames, sp. n., Entomobrya neotenica Katz & Soto-Adames, sp. n. and Entomobrya unifasciata Katz & Soto-Adames, sp. n.) are described, and new diagnoses are provided for Entomobrya assuta Folsom, Entomobrya atrocincta Schött, Entomobrya decemfasciata (Packard), Entomobrya ligata Folsom, Entomobrya multifasciata (Tullberg), and Entomobrya quadrilineata (Bueker). Furthermore, previously undocumented levels of intraspecific variation in macrosetal pattern are reported, tempering the exclusive use of chaetotaxy for species delimitation. Phylogenetic relationships, estimated using both morphological and molecular data, indicate that Entomobrya is likely paraphyletic. The phylogenies also suggest that unreliable character homology, likely fostered by Entomobrya's profusion of macrosetae, may limit the phylogenetic utility of chaetotaxy in groups characterized by an abundance of dorsal macrosetae.

Intraspecific Phenotypic Variation and Morphological Divergence of Strains of Folsomia candida (Willem) (Collembola: Isotomidae), the "Standard" Test Springtaill

We describe and compare the external morphology of eleven clonal strains and one sexual lineage of the globally distributed Folsomia candida, known as “standard” test Collembola. Of the 18 morphological characters studied, we measured 14 to have significant between-strains genetic variations, 9 of these had high heritabilities (>78%). The quantified morphological polymorphism was used to analyse the within-species relationships between strains by using both a parsimony analysis and a distance tree. These two detailed morphological phylogenies have revealed that the parthenogenetic strains grouped themselves into two major clades. However the exact position of the sexual strain remains unclear and further analysis is needed to confirm its exact relationship with the parthenogenetic ones. The two morphologically based clades were found to be the same as the ones previously described using molecular analysis. This shows that despite large within-strain variations, morphological characters can be used to differentiate some strains that have diverged within a single morphospecies. We discuss the potential evolutionary interpretations and consequences of these different levels of phenotypic variability.

Molecular phylogeny supports S-chaetae as a key character better than jumping organs and body scales in classification of Entomobryoidea (Collembola)

The jumping organ (furcula) is the most characteristic structure among collembolans, and it is of great taxonomical values at higher levels. The largest superfamily Entomobryoidea is traditionally classified into four families only by the morphology of the furcula. Actually, many taxa among these families are strikingly similar in morphology without considering furcula. The phylogeny of Entomobryoidea was reconstructed here based on mitochondrial and ribosomal fragments. This indicated that both Paronellidae and Cyphoderidae were ingroups within Entomobryidae with the former polyphyletic. Topology tests, which used the likelihood and Bayesian approaches, also rejected the traditional hypotheses relying on furcula morphology. Further ancestral state reconstructions have revealed that traditional taxonomical characters, i.e., furcula and body scales, had multiple independent origins in Entomobryoidea whereas tergal specialized chaetae (S-chaetae) exhibited strong phylogenetic signals. By integrating both molecular and morphological evidence, the results of this study drastically undermine the present classification of Entomobryoidea. Tergal S-chaetotaxic pattern in combination with other characters are more reasonable in taxonomy at suprageneric levels than convergent furcula. This study provides new insights of the jumping organ, which could be adaptively modified during evolution of Collembola.