Phylogeny, classification and taxonomy of European dragonflies and damselflies (Odonata): a review

Phylogeny, migration and geographic range size evolution of Anax dragonflies (Anisoptera: Aeshnidae)

The genus Anax is a group of cosmopolitan dragonflies noted for its conspicuous migratory behaviours and large size. Here we present the first dated, species-level, multigene, molecular phylogeny for the group to test generic and species-limits, as well as the evolution of migration and range size. Using five mitochondrial and nuclear gene regions (COI, COI/COII, CYTB/ND1, ITS1 and PRMT) from 20 species, we reconstructed a phylogeny of Anax using both a Bayesian and maximum likelihood approach. We found that Anax (including its hypothesized sister group Hemianax) forms a monophyletic group, and that 12 out of 20 species tested positive for monophyly were also monophyletic. The monophyly of several species of Anax is less clear. Migratory behaviour, which is known to occur in at least nine species, is recovered as the ancestral behaviour, which was lost and subsequently gained at least three times. Geographic range size seems to be tightly associated with migratory behaviour.

Coverage and quality of DNA barcode references for Central and Northern European Odonata

Background

Dragonflies and damselflies (Odonata) are important components in biomonitoring due to their amphibiotic lifecycle and specific habitat requirements. They are charismatic and popular insects, but can be challenging to identify despite large size and often distinct coloration, especially the immature stages. DNA-based assessment tools rely on validated DNA barcode reference libraries evaluated in a supraregional context to minimize taxonomic incongruence and identification mismatches.

Methods

This study reports on findings from the analysis of the most comprehensive DNA barcode dataset for Central European Odonata to date, with 103 out of 145 recorded European species included and publicly deposited in the Barcode of Life Data System (BOLD). The complete dataset includes 697 specimens (548 adults, 108 larvae) from 274 localities in 16 countries with a geographic emphasis on Central Europe. We used BOLD to generate sequence divergence metrics and to examine the taxonomic composition of the DNA barcode clusters within the dataset and in comparison with all data on BOLD.

Results

Over 88% of the species included can be readily identified using their DNA barcodes and the reference dataset provided. Considering the complete European dataset, unambiguous identification is hampered in 12 species due to weak mitochondrial differentiation and partial haplotype sharing. However, considering the known species distributions only two groups of five species possibly co-occur, leading to an unambiguous identification of more than 95% of the analysed Odonata via DNA barcoding in real applications. The cases of small interspecific genetic distances and the observed deep intraspecific variation in Cordulia aenea (Linnaeus, 1758) are discussed in detail and the corresponding taxa in the public reference database are highlighted. They should be considered in future applications of DNA barcoding and metabarcoding and represent interesting evolutionary biological questions, which call for in depth analyses of the involved taxa throughout their distribution ranges.

Italian odonates in the Pandora's box: A comprehensive DNA barcoding inventory shows taxonomic warnings at the Holarctic scale

The Odonata are considered among the most endangered freshwater faunal taxa. Their DNA-based monitoring relies on validated reference data sets that are often lacking or do not cover important biogeographical centres of diversification. This study presents the results of a DNA barcoding campaign on Odonata, based on the standard 658-bp 5' end region of the mitochondrial COI gene, involving the collection of 812 specimens (409 of which barcoded) from peninsular Italy and its main islands (328 localities), belonging to all the 88 species (31 Zygoptera and 57 Anisoptera) known from the country. Additional BOLD and GenBank data from Holarctic samples expanded the data set to 1,294 DNA barcodes. A multi-approach species delimitation analysis involving two distance (OT and ABGD) and four tree-based (PTP, MPTP, GMYC and bGMYC) methods was used to explore these data. Of the 88 investigated morphospecies, 75 (85%) unequivocally corresponded to distinct molecular operational units, whereas the remaining ones were classified as 'warnings' (i.e. showing a mismatch between morphospecies assignment and DNA-based species delimitation). These results are in contrast with other DNA barcoding studies on Odonata showing up to 95% of identification success. The species causing warnings were grouped into three categories depending on if they showed low, high or mixed genetic divergence patterns. The analysis of haplotype networks revealed unexpected intraspecific complexity at the Italian, Palearctic and Holarctic scale, possibly indicating the occurrence of cryptic species. Overall, this study provides new insights into the taxonomy of odonates and a valuable basis for future DNA and eDNA-based monitoring studies.

Asymmetric hybridization in Cordulegaster (Odonata: Cordulegastridae): Secondary postglacial contact and the possible role of mechanical constraints

Two Cordulegaster dragonflies present in Italy, the Palaearctic and northern distributed Cordulegaster boltonii and the endemic to the south of the peninsula Cordulegaster trinacriae, meet in central Italy and give rise to individuals of intermediate morphology. By means of mitochondrial and nuclear markers and of Geometric Morphometrics applied to sexual appendages, we defined i) the geographical boundaries between the two species in Italy and ii) we determined the presence, the extent, and the genetic characteristics of the hybridization. Genetic data evidenced asymmetric hybridization with the males of C. trinacriae able to mate both interspecifically and intraspecifically. The results contrast with expectations under neutral gene introgression and sexual selection. This data, along with the morphological evidence of significant differences in size and shape of sexual appendages between the males of the two species, seem indicative of the role of mechanical constraints in intraspecific matings. The origin of the two species is dated about to 1.32 Mya and the hybridization resulted related to range expansion of the two species after Last Glacial Maximum and this led to the secondary contact between the two taxa in central Italy. At last, our results indicate that the range of C. trinacriae, a threatened and protected species, has been moving northward probably driven by climate changes. As a result, the latter species is currently intruding into the range of C. boltonii. The hybrid area is quite extended and the hybrids seem well adapted to the environment. From a conservation point of view, even if C. trinacriae has a strong genetic identity, the discovery of hybridization between the two species should be considered in a future species management.

Genetic diversity of the families Aeshnidae, Gomphidae and Libellulidae through COI gene from South China

Adult dragonflies (Anisoptera) were collected from different localities of South China covering eight provinces. Representative sequences were sixty-one, including 16 species, 11 genera and three families (Aeshnidae, Gomphidae and Libellulidae), under cytochrome oxidase subunit I (COI) gene. After alignment of sequences by BioEdit v6, genetic interaction and divergence were computed by MEGA 7 whereas all the indices of genetic diversity were calculated by DnaSP v5 software. Phylogenetic trees were constructed through Neighbor-Joining method under Jukes-Cantor model, and all species of respective families were assembled with each other into individual groups. Maximum divergence was observed by Trithemis genus (18.69%), followed by Orthetrum genus (18.16%), whereas a minimum value of divergence was noted for Pantala genus (0.31%). On the other hand, maximum genetic diversity was recorded for Orthetrum genus up to 142 mutations, followed by Trithemis genus (126 mutations), while the minimum value (two mutations) was observed for Pantala genus. Genetic diversity for overall and Libellulidae family sequences was much higher, up to 404 mutations and 344 mutations, respectively. Current results suggest a high diversity of odonates in the South China region and results are valuable in gaining a total obligation of the diversity of Asian odonates and conservation measures of this insect group.

Elytra reduction may affect the evolution of beetle hind wings

Beetles are one of the largest and most diverse groups of animals in the world. Conversion of forewings into hardened shields is perceived as a key adaptation that has greatly supported the evolutionary success of this taxa. Beetle elytra play an essential role: they minimize the influence of unfavorable external factors and protect insects against predators. Therefore, it is particularly interesting why some beetles have reduced their shields. This rare phenomenon is called brachelytry and its evolution and implications remain largely unexplored. In this paper, we focused on rare group of brachelytrous beetles with exposed hind wings. We have investigated whether the elytra loss in different beetle taxa is accompanied with the hind wing shape modification, and whether these changes are similar among unrelated beetle taxa. We found that hind wings shape differ markedly between related brachelytrous and macroelytrous beetles. Moreover, we revealed that modifications of hind wings have followed similar patterns and resulted in homoplasy in this trait among some unrelated groups of wing-exposed brachelytrous beetles. Our results suggest that elytra reduction may affect the evolution of beetle hind wings.

Pellets of proof: First glimpse of the dietary composition of adult odonates as revealed by metabarcoding of feces

Recent advances in molecular techniques allow us to resolve the diet of unstudied taxa. Odonates are potentially important top-down regulators of many insects. Yet, to date, our knowledge of odonate prey use is based mainly on limited observations of odonates catching or eating their prey. In this study, we examine the potential use of metabarcoding in establishing the diet of three adult odonate species (Lestes sponsa, Enallagma cyathigerum, and Sympetrum danae) at a site in southwestern Finland. To this purpose, we compared three different methods for extracting DNA from fecal samples: the Macherey-Nagel Nucleospin XS kit, a traditional salt extraction, and the Zymo Research Fecal Microprep kit. From these extracts, we amplified group-specific mitochondrial markers (COI and 16S rRNA) from altogether 72 odonate individuals, and compared them to comprehensive reference libraries. The three odonate species show major overlap in diet, with no significant differences between individuals of different size and/or gender, reflecting opportunistic foraging of adult odonates. Of a total of 41 different prey species detected, the most frequently consumed ones were Diptera, with additional records of six other orders. Based on our data, the best DNA extraction method is the traditional salt extraction, as it provides the most information on prey content while also being the most economical. To our knowledge, this is the first study to resolve the species-level diet of adult odonates. Armed with the appropriate methodological caveats, we are ready to examine the ecological role of odonates in both terrestrial and aquatic food webs, and in transferring subsidies between these two realms.

Effects of the urban heat island on the phenology of Odonata in London, UK

Urbanisation is one of the major drivers of ecosystem change and includes increased temperatures in cities leading to an urban heat island (UHI). This study quantified the phenological response of odonates across London, UK, from 1990 to 2012, using a database of 1,031,277 historical sightings. The ordinal flight dates of each species were used to calculate the leading edge, middle and trailing edge of the flight period (P5, P50 and P95, respectively). The results suggest that the phenology of odonates is affected by the UHI only at a community level: no significant changes in the P5 or P50 of the flight period were found, although the P95 shows a mean advance of 4.13 days compared to rural areas, thus suggesting a contraction of the flight period in urban areas. However, only one individual species (Sympetrum striolatum) exhibited an advance in the P95 of the flight period in urban areas compared to rural areas. On the other hand, climate change (minimum temperature) had a much stronger impact on the phenology of odonates at the community level with a significant advance of 6.9 days °C^-1 in the P5 of the flight period, 3.1 days °C^-1 in the P50 and 3.3 days °C^-1 in the P95 flight date. Similarly, a significant advance in P5 was found in 7 of the 15 species tested in response to minimum temperature, and 2 species showed a significant advance in P50 in response to minimum temperature, but no species showed a shift in the P95 flight date due to minimum temperature. As shown in previous studies, life history influences the phenological response of odonates, with spring species and those species lacking an egg diapause being the most responsive to increased temperatures, although summer species and species with obligate egg diapause also respond to the UHI by advancing the P95 by 3.8 and 4.5 days, respectively, compared to rural areas, thus contracting the flight period. The present study shows that the UHI has negligible impacts on emergence patterns of odonates compared to climate change, which may result from the capacity of aquatic habitats to buffer the microclimatic conditions of the surrounding terrestrial habitats. We conclude by highlighting the importance of climate change on freshwater habitats over the impacts of the UHI.

Phylogenetic relationships of North American Gomphidae and their close relatives

Intrafamilial relationships among clubtail dragonflies (Gomphidae) have been the subject of many morphological studies, but have not yet been systematically evaluated using molecular data. Here we present the first molecular phylogeny of Gomphidae. We include six of the eight subfamilies previously suggested to be valid, and evaluate generic relationships within them. We have included examples of all genera reported from the Nearctic except Phyllocycla. This sample includes all North American species of Ophiogomphus, which has allowed us to explore intrageneric relationships in that genus. Our particular focus is on the closest relatives of the genus Gomphus, especially those North American species groups that have been commonly treated as subgenera of Gomphus. The Gomphus complex is split into additional genera, supported by molecular and morphological evidence: Phanogomphus, Stenogomphurus, Gomphurus and Hylogomphus are here considered to be valid genera. The genus Gomphus, in our restricted sense, does not occur in the western hemisphere; in addition, G. flavipes is transferred to Stylurus.

Extreme adaptations for probable visual courtship behaviour in a Cretaceous dancing damselfly

Courtship behaviours, frequent among modern insects, have left extremely rare fossil traces. None are known previously for fossil odonatans. Fossil traces of such behaviours are better known among the vertebrates, e.g. the hypertelic antlers of the Pleistocene giant deer Megaloceros giganteus. Here we describe spectacular extremely expanded, pod-like tibiae in males of a platycnemidid damselfly from mid-Cretaceous Burmese amber. Such structures in modern damselflies, help to fend off other suitors as well as attract mating females, increasing the chances of successful mating. Modern Platycnemidinae and Chlorocyphidae convergently acquired similar but less developed structures. The new findings provide suggestive evidence of damselfly courtship behaviour as far back as the mid-Cretaceous. These data show an unexpected morphological disparity in dancing damselfly leg structure, and shed new light on mechanisms of sexual selection involving intra- and intersex reproductive competition during the Cretaceous.

Egg clutch patterning in Lestes virens (Odonata, Lestidae) with evolutionary emphasis on endophytic oviposition in lestid dragonflies

Egg deposition within plants is one of the most widely distributed and ancient behaviors in Odonata. The resulting clutch consists of eggs placed in peculiar pattern that can be a characteristic for certain groups of Odonata. Despite their importance for paleontological and evolutionary research, data on egg-clutch positioning are missing or insufficient for most species. Here, patterning of egg clutches in Lestes virens was measured and described in detail for the first time. The female usually produces a linear row of single eggs directed at an angle rightward or leftward to the longitudinal axis of plant substrate. Less often eggs are arranged in egg-sets consisting of up to 4 eggs. Apparently, the female insect follows the rigid behavior stereotypes during oviposition and is unable to easily switch to the alternate stereotypical behavior of single egg deposition or production of multiegg sets. Based on a literature review and original data, egg clutch patterning of European Lestidae is overlaid on preexisting phylogenies. The resulting evolutionary scenario of egg-clutch patterning can be considered in the framework of egg-laying behavior in Lestidae.

Odonata (dragonflies and damselflies) as a bridge between ecology and evolutionary genomics

Odonata (dragonflies and damselflies) present an unparalleled insect model to integrate evolutionary genomics with ecology for the study of insect evolution. Key features of Odonata include their ancient phylogenetic position, extensive phenotypic and ecological diversity, several unique evolutionary innovations, ease of study in the wild and usefulness as bioindicators for freshwater ecosystems worldwide. In this review, we synthesize studies on the evolution, ecology and physiology of odonates, highlighting those areas where the integration of ecology with genomics would yield significant insights into the evolutionary processes that would not be gained easily by working on other animal groups. We argue that the unique features of this group combined with their complex life cycle, flight behaviour, diversity in ecological niches and their sensitivity to anthropogenic change make odonates a promising and fruitful taxon for genomics focused research. Future areas of research that deserve increased attention are also briefly outlined.

Nonadaptive radiation in damselflies

Adaptive radiations have long served as living libraries to study the build‐up of species richness; however, they do not provide good models for radiations that exhibit negligible adaptive disparity. Here, we review work on damselflies to argue that nonadaptive mechanisms were predominant in the radiation of this group and have driven species divergence through sexual selection arising from male–female mating interactions. Three damselfly genera (Calopteryx,Enallagma and Ischnura) are highlighted and the extent of (i) adaptive ecological divergence in niche use and (ii) nonadaptive differentiation in characters associated with reproduction (e.g. sexual morphology and behaviours) was evaluated. We demonstrate that species diversification in the genus Calopteryx is caused by nonadaptive divergence in coloration and behaviour affecting premating isolation, and structural differentiation in reproductive morphology affecting postmating isolation. Similarly, the vast majority of diversification events in the sister genera Enallagma and Ischnura are entirely driven by differentiation in genital structures used in species recognition. The finding that closely related species can show negligible ecological differences yet are completely reproductively isolated suggests that the evolution of reproductive isolation can be uncoupled from niche‐based divergent natural selection, challenging traditional niche models of species coexistence.

Iberian Odonata distribution: data of the BOS Arthropod Collection (University of Oviedo, Spain)

Odonata are represented from the Iberian Peninsula by 79 species. However, there exists a significant gap in accessible knowledge about these species,especially regarding their distribution. This data paper describes the specimen-based Odonata data of the Arthropod Collection of the Department of Biología de Organismos y Sistemas (BOS), University of Oviedo, Spain. The specimens were mainly collected from the Iberian Peninsula (98.63% of the data records), especially the northern region. The earliest specimen deposited in the collection dates back to 1950, while the 1980's and 2000's are the best-represented time periods. Between 1950 and 2009, 16, 604 Odonata specimens were deposited and are documented in the dataset. Approximately 20% of the specimens belong to the families Coenagrionidae and Calopterygidae. Specimens include the holotype and paratypes of the Iberian subspecies Calopteryx haemorrhoidalis asturica Ocharan, 1983 and Sympetrum vulgatum ibericum Ocharan, 1985. The complete dataset is also provided in Darwin Core Archive format.