Rapid and Repeated Climate Adaptation Involving Chromosome Inversions following Invasion of an Insect.

Following invasion, insects can become adapted to conditions experienced in their invasive range, but there are few studies on the speed of adaptation and its genomic basis. Here, we examine a small insect pest, Thrips palmi, following its contemporary range expansion across a sharp climate gradient from the subtropics to temperate areas. We first found a geographically associated population genetic structure and inferred a stepping-stone dispersal pattern in this pest from the open fields of southern China to greenhouse environments of northern regions, with limited gene flow after colonization. In common garden experiments, both the field and greenhouse groups exhibited clinal patterns in thermal tolerance as measured by critical thermal maximum (CTmax) closely linked with latitude and temperature variables. A selection experiment reinforced the evolutionary potential of CTmax with an estimated h2 of 6.8% for the trait. We identified 3 inversions in the genome that were closely associated with CTmax, accounting for 49.9%, 19.6%, and 8.6% of the variance in CTmax among populations. Other genomic variations in CTmax outside the inversion region were specific to certain populations but functionally conserved. These findings highlight rapid adaptation to CTmax in both open field and greenhouse populations and reiterate the importance of inversions behaving as large-effect alleles in climate adaptation.

Close Kin Dyads Indicate Intergenerational Dispersal and Barriers.

AbstractThe movement of individuals through continuous space is typically constrained by dispersal ability and dispersal barriers. A range of approaches have been developed to investigate these. Kindisperse is a new approach that infers recent intergenerational dispersal (σ) from close kin dyads and appears particularly useful for investigating taxa that are difficult to observe individually. This study, focusing on the mosquito Aedes aegypti, shows how the same close kin data can also be used for barrier detection. We empirically demonstrate this new extension of the method using genome-wide sequence data from 266 Ae. aegypti. First, we use the spatial distribution of full-sib dyads collected within one generation to infer past movements of ovipositing female mosquitoes. These dyads indicated the relative barrier strengths of two roads and performed favorably against alternative genetic methods for detecting barriers. We then use Kindisperse to quantify recent intergenerational dispersal (σ=81.5-197.1 m generation-1/2) from the difference in variance between the sib and the first cousin spatial distributions and, from this, estimate effective population density (ρ=833-4,864 km-2). Dispersal estimates showed general agreement with those from mark-release-recapture studies. Barriers, σ, ρ, and neighborhood size (331-526) can inform forthcoming releases of dengue-suppressing Wolbachia bacteria into this mosquito population.

Testing for adaptive changes linked to range expansion following a single introduction of the fall webworm.

Adaptive evolution following colonization can affect the impact of invasive species. The fall webworm (FWW) invaded China 40 years ago through a single introduction event involving a severe bottleneck and subsequently diverged into two genetic groups. The well-recorded invasion history of FWW, coupled with a clear pattern of genetic divergence, provides an opportunity to investigate whether there is any sign of adaptive evolution following the invasion. Based on genome-wide SNPs, we identified genetically separated western and eastern groups of FWW and correlated spatial variation in SNPs with geographical and climatic factors. Geographical factors explained a similar proportion of the genetic variation across all populations compared with climatic factors. However, when the two population groups were analysed separately, environmental factors explained more variation than geographical factors. SNP outliers in populations of the western group had relatively stronger response to precipitation than temperature-related variables. Functional annotation of SNP outliers identified genes associated with insect cuticle protein potentially related to desiccation adaptation in the western group and genes associated with lipase biosynthesis potentially related to temperature adaptation in the eastern group. Our study suggests that invasive species may maintain the evolutionary potential to adapt to heterogeneous environments despite a single invasion event. The molecular data suggest that quantitative trait comparisons across environments would be worthwhile.

Polygenic adaptation contributes to the invasive success of the Colorado potato beetle.

How invasive species cope with novel selective pressures with limited genetic variation is a fundamental question in molecular ecology. Several mechanisms have been proposed, but they can lack generality. Here, we addressed an alternative solution, polygenic adaptation, wherein traits that arise from multiple combinations of loci may be less sensitive to loss of variation during invasion. We tested the polygenic signal of environmental adaptation of Colorado potato beetle (CPB) introduced in Eurasia. Population genomic analyses showed declining genetic diversity in the eastward expansion of Eurasian populations, and weak population genetic structure (except for the invasion fronts in Asia). Demographic history showed that all populations shared a strong bottleneck about 100 years ago when CPB was introduced to Europe. Genome scans revealed a suite of genes involved in activity regulation functions that are plausibly related to cold stress, including some well-founded functions (e.g., the activity of phosphodiesterase, the G-protein regulator) and discrete functions. Such polygenic architecture supports the hypothesis that polygenic adaptation and potentially genetic redundancy can fuel the adaptation of CPB despite strong genetic depletion, thus representing a promising general mechanism for resolving the genetic paradox of invasion. More broadly, most complex traits based on polygenes may be less sensitive to invasive bottlenecks, thus ensuring the evolutionary success of invasive species in novel environments.

Comparative genomic analysis of ABC transporter genes in Tenebrio molitor and four other tenebrionid beetles (Coleoptera: Tenebrionidea).

ATP-binding cassette (ABC) transporters, one of the largest transmembrane protein families, transport a diverse number of substate across membranes. Details of their diverse physiological functions have not been established. Here, we identified 87 ABC transporter genes in the genomes of Tenebrio molitor along with those from Asbolus verrucosus (104), Hycleus cichorii (65), and Hycleus phaleratus (80). Combining these genes (336 in total) with genes reported in Tribolium castaneum (73), we analyzed the phylogeny of ABC transporter genes in all five Tenebrionids. They are assigned into eight subfamilies (ABCA-H). In comparison to other species, the ABCC subfamily in this group of beetles appears expanded. The expression profiles of the T. molitor genes at different life stages and in various tissues were also investigated using transcriptomic analysis. Most of them display developmental specific expression patterns, suggesting to us their possible roles in development. Most of them are highly expressed in detoxification-related tissues including gut and Malpighian tubule, from which we infer their roles in insecticide resistance. We detected specific or abundant expressions of many ABC transporter genes in various tissues such as salivary gland, ovary, testis, and antenna. This new information helps generate new hypotheses on their biological significance within tissues.

Characterization and expression profiling of serine protease inhibitors in the yellow mealworm Tenebrio molitor.

Serine protease inhibitors (SPIs) act in diverse biological processes in insects such as immunity, development, and digestion by preventing the unwanted proteolysis. So far, the repertoire of genes encoding SPIs has been identified from few insect species. In this study, 62 SPI genes were identified from the genome of the yellow mealworm, Tenebrio molitor. According to their modes of action, they were classified into three families, serpin (26), canonical SPI (31), and α-macroglobulins (A2M) (5). These SPIs feature eight domains including serpin, Kazal, TIL, Kunitz, WAP, Antistasin, pacifastin, and A2M. In total, 39 SPIs contain a single SPI domain, while the others encode at least two inhibitor units. Based on the amino acids in the cleaved reactive sites, the abilities of these SPIs to inhibit trypsin, chymotrypsin, or elastase-like enzymes are predicted. The expression profiling based on the RNA-seq data showed that these genes displayed stage-specific expression patterns during development, suggesting to us their significance in development. Some of the SPI genes were exclusively expressed in particular tissues such as hemocyte, fat body, gut, ovary, and testis, which may be involved in biological processes specific to the indicated tissues. These findings provide necessary information for further investigation of insect SPIs.

Genomic and transcriptomic analyses of chitin metabolism enzymes in Tenebrio molitor.

Chitin is of great importance in the cuticle and inner cuticular linings of insects. Chitin synthases (CHSs), chitin deacetylases (CDAs), chitinases (CHTs), and ß-N-acetylhexosaminidases (HEXs) are important enzymes required for chitin metabolism, and play essential roles in development and metamorphosis. Although chitin metabolism genes have been well characterized in limited insects, the information in the yellow mealworm, Tenebrio molitor, a model insect, is presently still unavailable. With the help of bioinformatics, we identified 54 genes that encode putative chitin metabolism enzymes, including 2 CHSs, 10 CDAs, 32 CHTs, and 10 HEXs in the genome of T. molitor. All these genes have the conserved domains and motifs of their corresponding protein family. Phylogenetic analyses indicated that CHS genes were divided into two groups. CDA genes were clustered into five groups. CHT genes were phylogenetically grouped into 11 clades, among which 1 in the endo-ß-N-acetylglucosaminidases group and the others were classified in the glycoside hydrolase family 18 groups. HEX genes were assorted into six groups. Developmental and tissue-specific expression profiling indicated that the identified chitin metabolism genes showed dynamical expression patterns concurrent with specific instar during molting period, suggesting their significant roles in molting and development. They were predominantly expressed in different tissues or body parts, implying their functional specialization and diversity. The results provide important information for further clarifying their biological functions using the yellow mealworm as an ideal experimental insect.

Identification and expression profiling of serine protease-related genes in Tenebrio molitor.

In insects, serine proteases and serine protease homologs (SPs/SPHs) are involved in a variety of physiological processes including digestion, development, and immunity. Here, we identified 112 SP and 88 SPH genes in the genome of the yellow mealworm, Tenebrio molitor. Based on the features of domain structure, they were divided into "S" group containing single Tryp-SPc or Tryp-SPHc domain, "C" group containing 1-4 CLIP domain (CLIPA-D) and "M" group containing the CBD, CUB, EGF, Fz, Gd, LDLa, PAN, SEA, SR, Sushi, and TSP domains, and have 115, 48, and 37 gene members, respectively. According to the active sites in the catalytic triad, the putative trypsin, chymotrypsin, or elastase-like enzyme specificity of the identified SPs/SPHs were predicted. Phylogenetic and genomic location analyses revealed that gene duplication exists in the large amount of SPs/SPHs. Gene expression profiling using RNA-seq data along with real time reverse transcription-polymerase chain reaction analysis showed that most SP/SPH genes display life stage specific expression patterns, indicating their important roles in development. Many SP/SPH genes are specifically or highly expressed in the gut, salivary gland, fat body, hemocyte, ovary, and testis, suggesting that they participate in digestion, immunity, and reproduction. The findings lay the foundation for further functional characterization of SPs/SPHs in T. molitor.

Genome-wide and expression-profiling analyses of the cytochrome P450 genes in Tenebrionidea.

Cytochrome P450 monooxygenases (CYPs) are present in almost all areas of the tree of life. As one of the largest and most diverse superfamilies of multifunctional enzymes, they play important roles in the metabolism of xenobiotics and biosynthesis of endogenous compounds, shaping the success of insects. In this study, the CYPome (an omics term for all the CYP genes in a genome) diversification was examined in the four Tenebrionidea species through genome-wide analysis. A total of 483 CYP genes were identified, of which 103, 157, 122, and 101 were respectively deciphered from the genomes of Tebebrio molitor, Asbolus verucosus, Hycleus cichorii and Hycleus phaleratus. These CYPs were classified into four major clans (mitochondrial, CYP2, CYP3, and CYP4), and clans CYP3 and CYP4 are most diverse. Phylogenetic analysis showed that most CYPs of these Tenebrionidea beetles from each clan had a very close 1:1 orthology to each other, suggesting that they originate closely and have evolutionally conserved function. Expression analysis at different developmental stages and in various tissues showed the life stage-, gut-, salivary gland-, fat body-, Malpighian tubule-, antennae-, ovary- and testis-specific expression patterns of T. molitor CYP genes, implying their various potential roles in development, detoxification, immune response, digestion, olfaction, and reproduction. Our studies provide a platform to understand the evolution of Tenebrionidea CYP gene superfamily, and a basis for further functional investigation of the T. molitor CYPs involved in various biological processes.

Comparative genomic analysis of carboxylesterase genes in Tenebrio molitor and other four tenebrionids.

Carboxylesterases (COEs) have various functions in wide taxons of organisms. In insects, COEs are important enzymes involved in the hydrolysis of a variety of ester-containing xenobiotics, neural signal transmission, pheromone degradation, and reproductive development. Understanding the diversity of COEs is basic to illustrate their functions. In this study, we identified 53, 105, 37, and 39 COEs from the genomes of Tenebrio molitor, Asbolus verucosus, Hycleus cichorii, and H. phaleratus in the superfamily of Tenebrionidea, respectively. Phylogenetic analysis showed that 234 COEs from these four species and those reported in Tribolium castaneum (63) could be divided into 12 clades and three major classes. The α-esterases significantly expanded in T. molitor, A. verucosus, and T. castaneum compared to dipteran and hymenopteran insects. In T. molitor, most COEs showed tissue and stage-specific but not a sex-biased expression. Our results provide insights into the diversity and evolutionary characteristics of COEs in tenebrionids, and lay a foundation for the functional characterization of COEs in the yellow mealworm.

The Wnt gene family in Tenebrio molitor and other coleopterans.

The Wnt gene family is involved in a wide range of developmental processes. Despite its significance, the evolution and function of Wnt genes remain largely unclear. Here, an exhaustive survey of Wnt genes was conducted in Tenebrio molitor and 17 other beetle genomes. A total of 146 Wnt genes were identified, creating a comprehensive coleopteran Wnt gene catalog. Comparative genomics indicates that dynamic evolutionary patterns of Wnt gene loss and duplication occurred in Coleoptera, leading to the diverse Wnt gene repertoire in various beetles. A striking loss of particular Wnt gene subfamilies occurs in Coleoptera. Remarkably, Wnt gene duplication was discovered for the first time in insects. Further analysis of Wnt gene expression in T. molitor indicates that each Wnt gene, including the duplicated ones, has a unique spatial or temporal expression pattern. The current study provides valuable insight into the evolution and functional validation of Wnt genes in Coleoptera.

Local climate adaptation and gene flow in the native range of two co-occurring fruit moths with contrasting invasiveness.

Invasive species pose increasing threats to global biodiversity and ecosystems. While previous studies have characterized successful invaders based on ecological traits, characteristics related to evolutionary processes have rarely been investigated. Here we compared gene flow and local adaptation using demographic analyses and outlier tests in two co-occurring moth pests across their common native range of China, one of which (the peach fruit moth, Carposina sasakii) has maintained its native distribution, while the other (the oriental fruit moth, Grapholita molesta) has expanded its range globally during the past century. We found that both species showed a pattern of genetic differentiation and an evolutionary history consistent with a common southwestern origin and northward expansion in their native range. However, for the noninvasive species, genetic differentiation was closely aligned with the environment, and there was a relatively low level of gene flow, whereas in the invasive species, genetic differentiation was associated with geography. Genome scans indicated stronger patterns of climate-associated loci in the noninvasive species. While strong local adaptation and reduced gene flow across its native range may have decreased the invasiveness of C. sasakii, this requires further validation with additional comparisons of invasive and noninvasive species across their native range.

Comparative mitogenomics and phylogenetics of the stinging wasps (Hymenoptera: Aculeata).

The stinging wasps (Hymenoptera: Aculeata) include diverse groups such as vespid wasps, ants and bees. Phylogenetic relationships among major lineages of stinging wasps have been inferred from molecular and morphological data. However, the genomic features of the mitochondrial genomes and their phylogenetic utility remain to be explored. In this study, we determined 23 mitochondrial genomes from the Aculeata. Four Mutillidae species showed relatively low A + T content compared to other species of the Aculeata (69.7%-77.4%). Eleven out of 44 species, mainly from the Chrysididae and the Pompilidae, showed reversals of GC skews. Gene rearrangements occurred across the species. Patterns of tRNA rearrangement were conserved in some groups, including the Chrysididae, Bethylidae, Pompilidae, Scolioidea and Vespoidea. Rearrangement of protein-coding genes were found in 12 out of 44 species of the Aculeata, including all four species from the Chrysididae, both species from the Bethylidae, one species from the Dryinidae, all three Scolioidea species and two Apoidea species. Phylogenetic inference showed a long branch in species with unusual genomic features, such as in the Mutillidae and Bethylidae. By excluding these species, we found paraphyly of the Chrysidoidea and a sister group relationship between the Formicoidea and Vespoidea. These results improve our understanding of the evolution of mitochondrial genomes in the Aculeata and, in general, the evolution across this subclade.

Low levels of genetic differentiation with isolation by geography and environment in populations of Drosophila melanogaster from across China.

The fruit fly, Drosophila melanogaster, is a model species in evolutionary studies. However, population processes of this species in East Asia are poorly studied. Here we examined the population genetic structure of D. melanogaster across China. There were 14 mitochondrial haplotypes with 10 unique ones out of 23 known from around the globe. Pairwise FST values estimated from 15 novel microsatellites ranged from 0 to 0.11, with geographically isolated populations showing the highest level of genetic uniqueness. STRUCTURE analysis identified high levels of admixture at both the individual and population levels. Mantel tests indicated a strong association between genetic distance and geographical distance as well as environmental distance. Full redundancy analysis (RDA) showed that independent effects of environmental conditions and geography accounted for 62.10% and 31.58% of the total explained genetic variance, respectively. When geographic variables were constrained in a partial RDA analysis, the environmental variables bio2 (mean diurnal air temperature range), bio13 (precipitation of the wettest month), and bio15 (precipitation seasonality) were correlated with genetic distance. Our study suggests that demographic history, geographical isolation, and environmental factors have together shaped the population genetic structure of D. melanogaster after its introduction into China.

Guizhi-Shaoyao-Zhimu decoction attenuates bone erosion in rats that have collagen-induced arthritis via modulating NF-κB signalling to suppress osteoclastogenesis.

CONTEXT: Guizhi-Shaoyao-Zhimu decoction (GSZD) is commonly used to treat rheumatoid arthritis (RA), but its mechanism is unclear. OBJECTIVE: To investigate the effect of GSZD on bone erosion in type II collagen (CII)-induced arthritis (CIA) in rats and to identify the underlying mechanism. MATERIALS AND METHODS: The CIA model was prepared in male Wistar rats by two subcutaneous injections of CII, 1 mg/mL. Fifty CIA rats were randomized equally into the control group given saline daily, the positive group given saline daily and methotrexate 0.75 mg/kg once a week, and three GSZD-treated groups gavaged daily with 800, 1600 and 3200 mg/kg of GSZD for 21 days. GSZD effects were assessed by paw volume, arthritic severity index and histopathology. Cytokine levels were determined by ELISA. The effects of GSZD on RAW264.7 cells were evaluated by receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis and bone resorption assay. Expression of IκB-α and p65 was measured by Western blotting. Major components of GSZD were identified by HPLC. RESULTS: Arthritis index score, paw volume and bone destruction score showed that GSZD improved inflammatory symptoms and reduced joint tissue erosion (p < 0.01). GSZD decreased RANKL, and the number of osteoclasts (OCs) in joint tissues (p < 0.01) and increased osteoprotegerin levels (p < 0.01). GSZD inhibited RANKL-induced RAW264.7 differentiation and reduced bone resorption by OCs. GSZD upregulated IκB (p < 0.01) and p65 (p < 0.01) in the cytoplasm and downregulated p65 (p < 0.01) in the cell nucleus. CONCLUSIONS: Guizhi-Shaoyao-Zhimu decoction has an anti-RA effect, suggesting its possible use as a supplement and alternative drug therapy for RA.

Anti-proliferation and anti-migration effects of an aqueous extract of Cinnamomi ramulus on MH7A rheumatoid arthritis-derived fibroblast-like synoviocytes through induction of apoptosis, cell arrest and suppression of matrix metalloproteinase.

CONTEXT: Cinnamomi ramulus, the dry twig of Cinnamomum cassia Presl. (Lauraceae), has been reported to exert several activities such as antitumor, anti-inflammatory, and analgesic effects. OBJECTIVE: This study investigates the effects of an aqueous extract of Cinnamomi ramulus (ACR) on rheumatoid arthritis (RA). MATERIALS AND METHODS: TNF-α-induced RA-derived fibroblast-like synoviocyte MH7A cells were incubated with ACR (0.1-2 mg/mL) for 24 h. The proliferation was tested using CCK-8 and colony formation assays. The migration and invasion abilities were measured using transwell tests and wound healing assays. Apoptosis and cell cycle were examined by flow cytometry. The potential mechanisms were determined by western blotting and quantitative real-time PCR. UPLC-QE-MS/MS was used for chromatographic analysis of ACR and its compounds were identified. Molecular docking strategy was used to screen the potential anti-RA active compounds of ACR. RESULTS: We found that ACR induced apoptosis in MH7A cells at concentrations of 0.4, 0.8, and 1.2 mg/mL. The proliferation of MH7A cells was reduced and the cell cycle was blocked in the G2/M phase at concentrations of 0.2, 0.4, 0.6 mg/mL. Migration and invasion of MH7A cells were reduced through inhibiting the expression of MMP-1, MMP-2, and MMP-3. The molecular docking strategy results showed that 9 compounds in ACR have good affinity with protein crystal, and benzyl cinnamate (10-100 µg/mL) could inhibit cell migration and induce apoptosis. CONCLUSIONS: The anti-RA effect of ACR may be attributed to its anti-proliferative and anti-migration effects on synovial fibroblasts. These data suggest that Cinnamomi ramulus may have therapeutic value for the treatment of RA.

Mitochondrial phylogenomics of the Hymenoptera.

The insect order Hymenoptera presents marvelous morphological and ecological diversity. Higher-level hymenopteran relationships remain controversial, even after recent phylogenomic analyses, as their taxon sampling was limited. To shed light on the origin and diversification of Hymenoptera, in particular the poorly studied Parasitica, we undertook phylogenetic analyses of 40 newly and 43 previously sequenced mitochondrial genomes representing all major clades of Hymenoptera. Various Bayesian inferences using different data partitions and phylogenetic methods recovered similar phylogenetic trees with strong statistical support for almost all nodes. Novel findings of the mitogenomic phylogeny mainly affected the three infraorders Ichneumonomorpha, Proctotrupomorpha and Evaniomorpha, the latter of which was split into three clades. Basal relationships of Parasitica recovered Stephanoidea + (Gasteruptiidae + Aulacidae) as the sister group to Ichneumonomorpha + (Trigonalyoidea + Megalyroidea). This entire clade is sister to Proctotrupomorpha, and Ceraphronoidea + Evaniidae is sister to Aculeata (stinging wasps). Our divergence time analysis indicates that major hymenopteran lineages originated in the Mesozoic. The radiation of early apocritans may have been triggered by the Triassic-Jurassic mass extinction; all extant families were present by the Cretaceous.

Field-evolved resistance and cross-resistance of the two-spotted spider mite, Tetranychus urticae, to bifenazate, cyenopyrafen and SYP-9625.

The acaricide bifenazate acts as complex III inhibitor whereas cyenopyrafen and SYP-9625 act as complex II inhibitors. All these acaricides are commonly used to control two-spotted spider mite (TSSM), Tetranychus urticae Koch. We examined field-evolved and laboratory-selected resistance of TSSM to these three acaricides and determined cross-resistance among them. Six field populations of TSSM showed low levels of resistance to bifenazate with resistance ratios ranging from 2.20 to 10.65 compared to a susceptible strain. SYP-9625, structurally similar to cyenopyrafen, showed slightly higher activity to TSSMs but significant cross-resistance in both field populations and a laboratory-selected strain by SYP-9625. However, low levels of resistance to these two chemicals were found in field populations even when used for short time periods. Cross-resistance was not found between bifenazate and Complex II inhibitors, cyenopyrafen and SYP-9625, in both field populations and the laboratory-selected strain. Field-evolved resistance of TSSM to the tested acaricides is still low and should be delayed by the implementation of resistance management practices. Cross-resistance between cyenopyrafen and SYP-9625 is obvious, so they should not be used together in resistance management strategies based on mode of action rotation.

Multiple refugia from penultimate glaciations in East Asia demonstrated by phylogeography and ecological modelling of an insect pest.

BACKGROUND: Refugial populations in Quaternary glaciations are critical to understanding the evolutionary history and climatic interactions of many extant species. Compared with the well-studied areas of Europe and Northern America, refugia of species in eastern Asia remain largely unknown. Here, we investigated the phylogeographic history of a globally important insect pest, the oriental fruit moth Grapholita molesta, in its native range of China. RESULTS: Genetic structure analyses unveiled three distinct groups and a set of populations with admixture. Approximate Bayesian Computation (ABC) analyses support range expansion of this moth from southwest groups of Yunnan and Sichuan to northern and eastern China. A set of admixed populations was found around these two ancestral groups. This pattern of genetic structure points to two refugia located in the Yunnan region and Sichuan Basin. The split of the two refugia was dated to 329.2 thousand years ago in the penultimate glacial period. One of the lineages was exclusively found around the Sichuan Basin, indicating the formation of endemic populations in this refugium. Ecological niche model analysis suggested a shrinking distribution from the LIG period to the MID period in the Sichuan lineage but a wide and stable distribution in the other lineage. CONCLUSIONS: Our results for the first time suggest that Yunnan and Sichuan jointly served as two large-scale refugia in eastern Asia in Quaternary glaciations, helping to maintain genetic diversity overall.

Gene arrangement and sequence of mitochondrial genomes yield insights into the phylogeny and evolution of bees and sphecid wasps (Hymenoptera: Apoidea).

The Apoidea represent a large and common superfamily of the Hymenoptera including the bees and sphecid wasps. A robust phylogenetic tree is essential to understanding the diversity, taxonomy and evolution of the Apoidea. In this study, features of apoid mitochondrial genomes were used to reconstruct phylogenetic relationships. Twelve apoid mitochondrial genomes were newly sequenced, representing six families and nine subfamilies. Gene rearrangement events have occurred in all apoid mitochondrial genomes sequenced to date. Sphecid wasps have both tRNA and protein-coding gene rearrangements in 5 of 8 species. In bees, the only rearranged genes are tRNAs; long-tongued bees (Apidae + Megachilidae) are characterized by movement of trnA to the trnI-trnQ-trnM tRNA cluster. Phylogenetic analyses of mitochondrial gene sequences support the known paraphyly of sphecid wasps, with bees nested within this clade. The Ampulicidae is sister to the remaining Apoidea. Crabronidae is paraphyletic, split into Crabronidae s.s. and Philanthidae, with the latter group a sister clade to bees. The monophyletic bees are either classified into two clades, long-tongued bees (Apidae + Megachilidae) and short-tongued bees (Andrenidae + Halictidae + Colletidae + Melitidae), or three groups with the Melitidae sister to the other bees. Our study showed that both gene sequences and arrangements provide information on the phylogeny of apoid families.