Untangling the evolution of soldier beetles (Coleoptera: Cantharidae) and the evaluation of the morphological phylogenetic signal in a soft-bodied elateroid lineage

This study addresses the long-standing uncertainty about the internal classification of soldier beetles (Elateroidea: Cantharidae). Four datasets were compiled and analysed: 66 genes for 14 terminals, 15 mtDNA genes for 79 terminals, one mtDNA and two rRNA genes for 217 terminals, and barcodes for 576 terminals. Based on congruent topologies, Chauliognathinae is proposed as a sister to the remaining Cantharidae, followed by the redefined Malthininae (including Tytthonyxini), the paraphyletic "dysmorphocerine" lineages (Dysmorphocerinae sensu stricto and Heteromastiginae subfam. nov.), and Silinae + Cantharinae as a terminal clade. The present phylogeny supersedes earlier morphology and short-fragment molecular hypotheses that have not converged on a consensus. Few morphological characters corroborate the DNA-based relationships (see the adults and larval keys). However, morphology-based hypotheses have relied on a few informative characters, and no evidence strongly rejects the preferred molecular topology. The interpretation of morphological characters and uncertain polarity resulting from the high phenotypic disparity of Elateroidea are discussed in detail. The dated phylogeny hypothesizes the earliest split within the Cantharidae in the Berriasian stage (Early Cretaceous, ~141 Myr) and the diversification of most extant subfamilies and tribes already in the Late Cretaceous. The most diverse subfamily, Cantharinae, represents a delayed radiation that started during the Eocene climatic optimum, 55.5 Myr. The late origin of Cantharinae questions the classification of Cretaceous Cantharidae as members of Cantharinae. Instead, the results suggest their deeper rooting after separating from dysmorphocerine lineages and before the node between Cantharinae and Silinae.

Eocene aposematic patterns persist in modern European Lycidae beetles despite the absence of co-mimics

Ancient aposematic signals might have evolved under different ecological circumstances. Using European Cenozoic amber and phylogenetic reconstruction, we evaluated the evolution of net-winged beetle aposematism. We describe Priabonian Hiekeolycus winkleri sp. nov. from Baltic amber, review known fossil species, and suggest earlier high diversity and morphological conservativeness of European Lycidae since the Eocene. We hypothesize the presence of red and black/red aposematic patterns in Eocene Europe. The analyses suggest the Oligocene to Miocene dispersal of additional species from East Asia and their advergence to autochthonous patterns. Recently dispersed lycids have retained similarities with their East Asian relatives. Net-winged beetles are rare in Europe after the Quaternary climatic oscillations, and we hypothesize a currently relaxed selection for shared aposematic signals. Neophobia, and eventually inborn rejection of brightly colored prey, putatively preserved ancient aposematism under changing conditions. Evidence from paleontology and phylogenetics can provide insight into the long-term persistence of old adaptations under changing conditions.

The genome sequence of a soldier beetle, Podabrus alpinus (Paykull, 1798)

We present a genome assembly from an individual female Podabrus alpinus (soldier beetle; Arthropoda; Insecta; Coleoptera; Cantharidae). The genome sequence is 777 megabases in span. Most of the assembly is scaffolded into seven chromosomal pseudomolecules, including the assembled X sex chromosome. The mitochondrial genome has also been assembled and is 18.8 kilobases in length. Gene annotation of this assembly on Ensembl identified 30,955 protein coding genes.

Analysis of the Holarctic Dictyoptera aurora Complex (Coleoptera, Lycidae) Reveals Hidden Diversity and Geographic Structure in Müllerian Mimicry Ring

The elateroid family Lycidae is known for limited dispersal propensity and high species-level endemism. The red net-winged beetle, Dictyoptera aurora (Herbst, 1874), differs from all relatives by the range comprising almost the entire Holarctic region. Based on a five-marker phylogeny and 67 barcode entries (cox1-5' mtDNA) from the whole range, we recovered two genetically distinct species within traditionally defined D. aurora and resurrected the name D. coccinata (Say, 1835) as the oldest available synonym for Nearctic populations. Yet, no reliable morphological trait distinguishes these species except for minute differences in the male genitalia. D. coccinata is a monophylum resulting from a single Miocene dispersal event, ~15.8 million years ago, and genetic divergence implies long-term isolation by the Bering Strait. Far East Asian and west European populations are also genetically distinct, although to a lower extent. Two independent colonization events established the Fennoscandian populations after the last glacial maximum. Besides intrinsic factors, the high morphological similarity might result from stabilizing selection for shared aposematic signals. The rapidly accumulating barcode data provide valuable information on the evolutionary history and the origins of regional faunas.

Beetle bioluminescence outshines extant aerial predators

We understand very little about the timing and origins of bioluminescence, particularly as a predator avoidance strategy. Understanding the timing of its origins, however, can help elucidate the evolution of this ecologically important signal. Using fireflies, a prevalent bioluminescent group where bioluminescence primarily functions as aposematic and sexual signals, we explore the origins of this signal in the context of their potential predators. Divergence time estimations were performed using genomic-scale datasets providing a robust estimate for the origin of firefly bioluminescence as both a terrestrial and as an aerial signal. Our results recover the origin of terrestrial beetle bioluminescence at 141.17 (122.63-161.17) Ma and firefly aerial bioluminescence at 133.18 (117.86-152.47) Ma using a large dataset focused on Lampyridae; and terrestrial bioluminescence at 148.03 (130.12-166.80) Ma, with the age of aerial bioluminescence at 104.97 (99.00-120.90) Ma using a complementary Elateroidea dataset. These ages pre-date the origins of all known extant aerial predators (i.e. bats and birds) and support much older terrestrial predators (assassin bugs, frogs, ground beetles, lizards, snakes, hunting spiders and harvestmen) as the drivers of terrestrial bioluminescence in beetles. These ages also support the hypothesis that sexual signalling was probably the original function of this signal in aerial fireflies.

Phylogenomic and mitogenomic data can accelerate inventorying of tropical beetles during the current biodiversity crisis

Conservation efforts must be evidence-based, so rapid and economically feasible methods should be used to quantify diversity and distribution patterns. We have attempted to overcome current impediments to the gathering of biodiversity data by using integrative phylogenomic and three mtDNA fragment analyses. As a model, we sequenced the Metriorrhynchini beetle fauna, sampled from ~700 localities in three continents. The species-rich dataset included ~6,500 terminals, ~1,850 putative species delimited at 5% uncorrected pairwise threshold, possibly ~1,000 of them unknown to science. Neither type of data could alone answer our questions on biodiversity and phylogeny. The phylogenomic backbone enabled the integrative delimitation of robustly defined natural genus-group units that will inform future research. Using constrained mtDNA analysis, we identified the spatial structure of species diversity, very high species-level endemism, and a biodiversity hotspot in New Guinea. We suggest that focused field research and subsequent laboratory and bioinformatic workflow steps would substantially accelerate the inventorying of any hyperdiverse tropical group with several thousand species. The outcome would be a scaffold for the incorporation of further data from environmental sequencing and ecological studies. The database of sequences could set a benchmark for the spatiotemporal evaluation of biodiversity, would support evidence-based conservation planning, and would provide a robust framework for systematic, biogeographic, and evolutionary studies.

Conspicuousness, phylogenetic structure, and origins of Müllerian mimicry in 4000 lycid beetles from all zoogeographic regions

Biologists have reported on the chemical defences and the phenetic similarity of net-winged beetles (Coleoptera: Lycidae) and their co-mimics. Nevertheless, our knowledge has remained fragmental, and the evolution of mimetic patterns has not been studied in the phylogenetic context. We illustrate the general appearance of ~ 600 lycid species and ~ 200 co-mimics and their distribution. Further, we assemble the phylogeny using the transcriptomic backbone and ~ 570 species. Using phylogenetic information, we closely scrutinise the relationships among aposematically coloured species, the worldwide diversity, and the distribution of aposematic patterns. The emitted visual signals differ in conspicuousness. The uniform coloured dorsum is ancestral and was followed by the evolution of bicoloured forms. The mottled patterns, i.e. fasciate, striate, punctate, and reticulate, originated later in the course of evolution. The highest number of sympatrically occurring patterns was recovered in New Guinea and the Andean mountain ecosystems (the areas of the highest abundance), and in continental South East Asia (an area of moderate abundance but high in phylogenetic diversity). Consequently, a large number of co-existing aposematic patterns in a single region and/or locality is the rule, in contrast with the theoretical prediction, and predators do not face a simple model-like choice but cope with complex mimetic communities. Lycids display an ancestral aposematic signal even though they sympatrically occur with differently coloured unprofitable relatives. We show that the highly conspicuous patterns evolve within communities predominantly formed by less conspicuous Müllerian mimics and, and often only a single species displays a novel pattern. Our work is a forerunner to the detailed research into the aposematic signalling of net-winged beetles.

Click Beetle Mitogenomics with the Definition of a New Subfamily Hapatesinae from Australasia (Coleoptera: Elateridae)

Elateridae is a taxon with very unstable classification and a number of conflicting phylogenetic hypotheses have been based on morphology and molecular data. We assembled eight complete mitogenomes for seven elaterid subfamilies and merged these taxa with an additional 22 elaterids and an outgroup. The structure of the newly produced mitogenomes showed a very similar arrangement with regard to all earlier published mitogenomes for the Elateridae. The maximum likelihood and Bayesian analyses indicated that Hapatesus Candèze, 1863, is a sister of Parablacinae and Pityobiinae. Therefore, Hapatesinae, a new subfamily, is proposed for the Australian genera Hapatesus (21 spp.) and Toorongus Neboiss, 1957 (4 spp.). Parablacinae, Pityobiinae, and Hapatesinae have a putative Gondwanan origin as the constituent genera are known from the Australian region (9 genera) and Neotropical region (Tibionema Solier, 1851), and only Pityobius LeConte, 1853, occurs in the Nearctic region. Another putative Gondwanan lineage, the Afrotropical Morostomatinae, forms either a serial paraphylum with the clade of Parablacinae, Pityobiinae, and Hapatesinae or is rooted in a more terminal position, but always as an independent lineage. An Eudicronychinae lineage was either recovered as a sister to Melanotini or as a deep split inside Elaterinae and we herein transfer the group to Elaterinae as Eudicronychini, a new status. The mitochondrial genomes provide a sufficient signal for the placement of most lineages, but the deep bipartitions need to be compared with phylogenomic analyses.

Biodiversity Inventory and Distribution of Metriorrhynchina Net-Winged Beetles (Coleoptera: Lycidae), with the Identification of Generic Ranges

Simple Summary

We reviewed the classification of ~900 Metriorrhynchina net-winged beetles, and modified the alpha-taxonomy to reflect recently proposed phylogenetic hypotheses. There were >200 species transferred between subtribes and genera. The resulting checklist enabled us to identify New Guinea as the hotspot of Metriorrhynchina diversification. The centers of endemism include Sulawesi and New Guinea (in total 14 genera) in contrast with a single endemic genus in continental Australia. Most genera are diverse in New Guinea and the Wallacea, and only certain species crossed zoogeographic lines and colonized South East Asia. The study should boost the biodiversity research in the group and support biogeographic and evolutionary studies.

Abstract

We reviewed the species-level classification of Metriorrhynchina net-winged beetles to make the group accessible for further studies. Altogether, 876 valid species are listed in a checklist along with known synonyms, combinations, and distribution data. The compilation of geographic distribution showed that Metriorrhynchina is distributed mainly in the Australian region with very high diversity in the islands at the northern edge of the Australian craton, i.e., in the Moluccas and New Guinea (54 and 423 spp. respectively). The neighboring northern part of the Australian continent houses a majority of known Australian species (112 spp.) and the diversity of net-winged beetles gradually decreases to the south (43 spp.). The fauna of Sulawesi is highly endemic at the generic level (4 of 10 genera, 67 of 84 spp.). Less Metriorrhynchina occur in the Solomon Islands and Oceania (in total 22 spp.). The Oriental Metriorrhynchina fauna consists of a few genera and a limited number of species, and most of these are known from the Philippines (51 of 94 Oriental spp.). We identified a high species level turn-over between all neighboring landmasses. The genus-level endemism is high in Sulawesi (4 genera) and New Guinea (11 genera), but only a single genus is endemic to Australia. During the compilation of the checklist, we identified some homonyms, and we propose the following replacement names and a new synonym: Metriorrhynchus pseudobasalis, nom. nov. for M. basalis Lea, 1921 nec M. basalis Bourgeois, 1911; Metriorrhynchus pseudofunestus, nom. nov. for M. funestus Lea, 1921 nec M. funestus (Guérin-Méneville, 1838), Trichalus pseudoternatensis, nom. nov. for T. ternatensis Kleine, 1930 nec T. ternatensis Bourgeois, 1900, Procautires subparallelus, nom. nov. for P. parallelus (Pic, 1926) nec P. parallelus (Bourgeois, 1883), and Cautires pseudocorporaali, nom. nov. for C. corporaali (Pic, 1921: 12), (formerly Odontocerus and Cladophorus) nec C. corporaali (Pic, 1921) (formerly Bulenides, later Cautires). Diatrichalus biroi Kleine, 1943, syn. nov. is proposed as a junior subjective synonym of D. subarcuatithorax (Pic, 1926). Altogether, 161 new combinations are proposed, and 47 species earlier placed in Xylobanus Waterhouse, 1879 transferred from Cautirina to Metriorrhynchina incertae sedis. The study clarifies the taxonomy of Metriorrhynchini and should serve as a restarting point for further taxonomic, evolutionary, and biogeographic studies.

Sexually dimorphic characters and shared aposematic patterns mislead the morphology-based classification of the Lycini (Coleoptera: Lycidae)

The Lycini (Elateroidea: Lycidae) contains > 400 species placed in four typologically based genera and numerous subgenera. We assembled a mito-ribosomal dataset representing ~100 species from the whole range and recovered a phylogeny rejecting Lycus and Lycostomus as polyphyletic assemblages. The male-specific wide elytra and elytral thorns are identified in unrelated Neolycus and Lycus. The morphological similarity based on sexual dimorphism and aposematic patterns defined terminal clades and misled the genus-rank classification. We delimit Neolycus, Rhyncheros reinst. name (= Thoracocalon syn. nov. = Lyconotus syn. nov.), LipernesLycostomus, Haplolycus and Lycus. Demosis and six subgenera of Lycus are synonymized with Lycus. Celiasis Laporte, 1840 is kept in the classification as a nomen dubium until any specimen is available. The deep lineages are known from the Americas and Asia. Africa was colonized by Lycus and Haplolycus. Each specific aposematic pattern occurs in a limited range, and the similar body shape and coloration evolved in unrelated sympatrically occurring lineages. High intraspecific polymorphism is putatively a result of the adaptation of various populations to local mimetic assemblages. Therefore, the delimitation of many phenotypically diverse species should be investigated.

Persistence of multiple patterns and intraspecific polymorphism in multi-species Müllerian communities of net-winged beetles

BACKGROUND

In contrast to traditional models of purifying selection and a single aposematic signal in Müllerian complexes, some communities of unprofitable prey contain members with multiple aposematic patterns. Processes responsible for diversity in aposematic signaling are poorly understood and large multi-species communities are seldom considered.

RESULTS

We analyzed the phylogeny and aposematic patterns of closely related Eniclases net-winged beetles in New Guinea using mtDNA and nextRAD data. We suggest three clades of closely related and incompletely reproductively isolated lineages, detail the extent of polymorphism among Eniclases, and categorize their low-contrast aposematic patterns. The warning signal of Eniclases consists of body shape and color, with ambiguous color perception under some circumstances, i.e., when resting on the undersides of leaves. Field observations suggest that perception of the aposematic signal is affected by beetle behavior and environmental conditions. Local communities containing Eniclases consisted of 7-85 metriorrhynchine species assigned to 3-10 colour patterns.

CONCLUSION

As a result, we suggest that under certain light conditions the aposematic colour signal is less apparent than the body shape in net-winged beetle communities. We document variable environmental factors in our study area and highly diverse multi-species communities of other net-winged beetles. Which implies dynamically changing community structure in space and time. Variable environmental conditions and diverse community composition are suggested to be favorable for the persistence of multiple aposematic patterns, imperfect mimics, and intraspecific polymorphism. Further research should identify the relative effect of these factors on purifying selection and the alleles which are responsible for phenotypic differences.

Drilidae Blanchard, 1845: multi-gene molecular phylogenies versus morphological similarity. An answer to Kovalev et al

In a recent issue of Zootaxa, Kovalev et al. (2019) reported the description of a new drilid genus Drilorhinus Kovalev, Kirejtshuk et Shapovalov, 2019 and they discuss at length the relationships and systematic classification of the drilid lineage. Although they did not formally propose a new status for Drilidae Blanchard, 1845 [not Lacordaire, 1857, as cited in their study] in the sense of the Code (ICZN 1999), they in fact resurrected the traditional concept of Drilidae as a separate 'cantharoid' family and rejected Drilini in Elateridae: Agrypninae of Kundrata Bocak (2011). The authors strongly defended the historical classification of the genera Selasia Laporte, 1838, Malacogaster Bassi, 1834, Drilus Olivier, 1790, Drilorhinus, and putatively also their relatives (Kundrata et al. 2017), as a separate 'cantharoid' family in the sense proposed in 19th century and held until recently by some traditional morphologists (Blanchard 1845; Crowson 1955, 1972; Lawrence Newton 1982, 1995; Branham Wenzel 2003; Lawrence et al. 2011; Kazantsev 2013; Lawrence Ślipiński 2013; Lawrence 2016). Although no new data were presented or methodological flaws of earlier analyses identified by Kovalev et al., the authors argued that the present evidence is insufficient for the placement of the Drilini in Elateridae, Agrypninae. Unfortunately, they did not take into account recent molecular analyses suggesting multiple origins of soft-bodied elateroid families, i.e., the polyphyly of the historical cantharoid group of families, and the relationships of drilids and agrypnine click beetles (Bocakova et al. 2007; Hunt et al., 2007; Timmermans et al. 2010, 2016; Kundrata et al. 2014; McKenna et al. 2015; Bocak et al. 2016; Kusy et al. 2018a, b; Linard et al. 2018; Zhang et al. 2018). They only discussed a single molecular analysis by Kundrata Bocak (2011).

Genomic and Mitochondrial Data Identify Different Species Boundaries in Aposematically Polymorphic Eniclases Net-Winged Beetles (Coleoptera: Lycidae)

Species delineation is essential for any evolutionary and biodiversity research, and recent advances in genomic sequencing have made it possible to robustly define species boundaries and detect hidden diversity. Here, we studied 14 species of aposematically colored New Guinean Eniclases (Coleoptera: Lycidae) whose conventional morphology- and single-locus mtDNA-based taxonomy has been contentious. We analyzed mitochondrial and restriction site associated DNA fragments to obtain a phylogenetic hypothesis and compared relationships recovered by the RAD analysis with species limits based on other information. The results show the presence of cryptic diversity and common mitonuclear discordance when over 30% of individuals were incorrectly assigned to species if only mitogenomic markers were considered. Nuclear data falsified the species rank of one species and identified one earlier unrecognized lineage deserving species rank. Further, our analyses demonstrate a highly variable phenotypic differentiation, with several pairs of cryptic species standing in contrast with genetically close but phenotypically highly divergent lineages. We show that morphological and mitogenomic analyses produce reliable information for taxonomy in most cases. Nevertheless, the species boundaries among closely related species should be based on all lines of evidence, including nuclear markers.

Genome sequences identify three families of Coleoptera as morphologically derived click beetles (Elateridae)

Plastoceridae Crowson, 1972, Drilidae Blanchard, 1845 and Omalisidae Lacordaire, 1857 (Elateroidea) are families of the Coleoptera with obscure phylogenetic relationships and modified morphology showing neotenic traits such as soft bodies, reduced wing cases and larviform females. We shotgun sequenced genomes of Plastocerus, Drilus and Omalisus and incorporated them into data matrices of 66 and 4202 single-copy nuclear genes representing Elateroidea. Phylogenetic analyses indicate their terminal positions within the broadly defined well-sclerotized and fully metamorphosed Elateridae and thus Omalisidae should now be considered as Omalisinae stat. nov. in Elateridae Leach, 1815. The results support multiple independent origins of incomplete metamorphosis in Elateridae and indicate the parallel evolution of morphological and ecological traits. Unlike other neotenic elateroids derived from the supposedly pre-adapted aposematically coloured and unpalatable soft-bodied elateroids, such as fireflies (Lampyridae) and net-winged beetles (Lycidae), omalisids and drilids evolved from well-sclerotized click beetles. These findings suggest sudden morphological shifts through incomplete metamorphosis, with important implications for macroevolution, including reduced speciation rate and high extinction risk in unstable habitats. Precise phylogenetic placement is necessary for studies of the molecular mechanisms of ontogenetic shifts leading to profoundly changed morphology.

Genome sequencing of Rhinorhipus Lawrence exposes an early branch of the Coleoptera

Background

Rhinorhipidae Lawrence, 1988 is an enigmatic beetle family represented by a single species, Rhinorhipus tamborinensis Lawrence, 1988, from Australia, with poorly established affinities near the superfamily Elateroidea (click beetles, soldier beetles and fireflies) or the more inclusive series (infraorder) Elateriformia. Its evolutionary position may inform the basal relationships of the suborder Polyphaga, the largest clade of Coleoptera.

Results

We analyzed four densely sampled DNA datasets of major coleopteran lineages for mitogenomes, rRNA genes and single copy nuclear genes. Additionally, genome sequencing was used for incorporation of R. tamborinensis into a set of 4220 orthologs for 24 terminals representing 12 polyphagan superfamilies. Topologies differed to various degrees, but all consistently refute the proposed placement of Rhinorhipidae in Elateroidea and instead indicate either sister relationships with other Elateriformia, frequently together with Nosodendridae, another divergent small family hitherto placed in Derodontoidea, or in an isolated position among the deepest lineages of Polyphaga. The phylogenomic analyses recovered Rhinorhipus in a sister position to all other Elateriformia composed of five superfamilies. Therefore, we erect the new superfamily Rhinorhipoidea Lawrence, 1988, stat. Nov., with the type-family Rhinorhipidae. The origins of the Rhinorhipidae were dated to the Upper Triassic/Lower Jurassic at the very early phase of polyphagan diversification.

Conclusions

Thus, Rhinorhipidae adds another example to several recently recognized ancient relict lineages which are interspersed within contemporaneous hugely species-rich lineages of Coleoptera.

Electronic supplementary material

The online version of this article (10.1186/s12983-018-0262-0) contains supplementary material, which is available to authorized users.