Chromosome-Aware Phylogenomics of Assassin Bugs (Hemiptera: Reduvioidea) Elucidates Ancient Gene Conflict.

Though the phylogenetic signal of loci on sex chromosomes can differ from those on autosomes, chromosomal-level genome assemblies for nonvertebrates are still relatively scarce and conservation of chromosomal gene content across deep phylogenetic scales has therefore remained largely unexplored. We here assemble a uniquely large and diverse set of samples (17 anchored hybrid enrichment, 24 RNA-seq, and 70 whole-genome sequencing samples of variable depth) for the medically important assassin bugs (Reduvioidea). We assess the performance of genes based on multiple features (e.g., nucleotide vs. amino acid, nuclear vs. mitochondrial, and autosomal vs. X chromosomal) and employ different methods (concatenation and coalescence analyses) to reconstruct the unresolved phylogeny of this diverse (∼7,000 spp.) and old (>180 Ma) group. Our results show that genes on the X chromosome are more likely to have discordant phylogenies than those on autosomes. We find that the X chromosome conflict is driven by high gene substitution rates that impact the accuracy of phylogenetic inference. However, gene tree clustering showed strong conflict even after discounting variable third codon positions. Alternative topologies were not particularly enriched for sex chromosome loci, but spread across the genome. We conclude that binning genes to autosomal or sex chromosomes may result in a more accurate picture of the complex evolutionary history of a clade.

Convergence of dominance and neglect in flying insect diversity.

Most of arthropod biodiversity is unknown to science. Consequently, it has been unclear whether insect communities around the world are dominated by the same or different taxa. This question can be answered through standardized sampling of biodiversity followed by estimation of species diversity and community composition with DNA barcodes. Here this approach is applied to flying insects sampled by 39 Malaise traps placed in five biogeographic regions, eight countries and numerous habitats (>225,000 specimens belonging to >25,000 species in 458 families). We find that 20 insect families (10 belonging to Diptera) account for >50% of local species diversity regardless of clade age, continent, climatic region and habitat type. Consistent differences in family-level dominance explain two-thirds of variation in community composition despite massive levels of species turnover, with most species (>97%) in the top 20 families encountered at a single site only. Alarmingly, the same families that dominate insect diversity are 'dark taxa' in that they suffer from extreme taxonomic neglect, with little signs of increasing activities in recent years. Taxonomic neglect tends to increase with diversity and decrease with body size. Identifying and tackling the diversity of 'dark taxa' with scalable techniques emerge as urgent priorities in biodiversity science.

Weapon performance drives weapon evolution.

Many sexually selected traits function as weapons, and these weapons can be incredibly diverse. However, the factors underlying weapon diversity among species remain poorly understood, and a fundamental hypothesis to explain this diversity remains untested. Although weapons can serve multiple functions, an undeniably important function is their role in fights. Thus, a crucial hypothesis is that weapon diversification is driven by the evolution of weapon modifications that provide an advantage in combat (e.g. causing more damage). Here, we test this fighting-advantage hypothesis using data from 17 species of coreid bugs. We utilize the fact that male-male combat in coreids often results in detectable damage, allowing us to link different weapon morphologies to different levels of damage among species. We find that certain weapon morphologies inflict much more damage than others, strongly supporting the fighting-advantage hypothesis. Moreover, very different weapon morphologies can inflict similarly severe amounts of damage, leading to a weapon performance landscape with multiple performance peaks. This multi-peak pattern could potentially drive different lineages towards divergent weapon forms, further increasing weapon diversity among species. Overall, our results may help explain how sexually selected weapons have evolved into the diversity of forms seen today.

The evolution of autotomy in leaf-footed bugs.

Sacrificing body parts is one of many behaviors that animals use to escape predation. This trait, termed autotomy, is classically associated with lizards. However, several other taxa also autotomize, and this trait has independently evolved multiple times throughout Animalia. Despite having multiple origins and being an iconic antipredatory trait, much remains unknown about the evolution of autotomy. Here, we combine morphological, behavioral, and genomic data to investigate the evolution of autotomy within leaf-footed bugs and allies (Insecta: Hemiptera: Coreidae + Alydidae). We found that the ancestor of leaf-footed bugs autotomized and did so slowly; rapid autotomy (<2 min) then arose multiple times. The ancestor likely used slow autotomy to reduce the cost of injury or to escape nonpredatory entrapment but could not use autotomy to escape predation. This result suggests that autotomy to escape predation is a co-opted benefit (i.e., exaptation), revealing one way that sacrificing a limb to escape predation may arise. In addition to identifying the origins of rapid autotomy, we also show that across species variation in the rates of autotomy can be explained by body size, distance from the equator, and enlargement of the autotomizable appendage.

Integrative taxonomy reveals two sympatric species of the genus Eucriotettix Hebard, 1930 (Orthoptera: Tetrigidae).

Limno-terrestrial pygmy grasshoppers are mostly recognised using morphology but characters used are not always clear-cut for species identification. From a faunistic survey in Singapore, Eucriotettix were collected and two new species are identified and described here: E. guentheri sp. nov. and E. simulans sp. nov. This was done by iteratively incorporating morphological, molecular, morphometric, and ecological data. Mitochondrial COI trees, COI cluster analysis, microhabitat preference, and morphometric analyses provide strong enough indirect evidence that the specimens comprise a pair of species. A key to species of Eucriotettix from Singapore is also provided.

Evolution of the assassin's arms: insights from a phylogeny of combined transcriptomic and ribosomal DNA data (Heteroptera: Reduvioidea).

Assassin bugs (Reduvioidea) are one of the most diverse (>7,000 spp.) lineages of predatory animals and have evolved an astounding diversity of raptorial leg modifications for handling prey. The evolution of these modifications is not well understood due to the lack of a robust phylogeny, especially at deeper nodes. We here utilize refined data from transcriptomes (370 loci) to stabilize the backbone phylogeny of Reduvioidea, revealing the position of major clades (e.g., the Chagas disease vectors Triatominae). Analyses combining transcriptomic and Sanger-sequencing datasets result in the first well-resolved phylogeny of Reduvioidea. Despite amounts of missing data, the transcriptomic loci resolve deeper nodes while the targeted ribosomal genes anchor taxa at shallower nodes, both with high support. This phylogeny reveals patterns of raptorial leg evolution across major leg types. Hairy attachment structures (fossula spongiosa), present in the ancestor of Reduvioidea, were lost multiple times within the clade. In contrast to prior hypotheses, this loss is not directly correlated with the evolution of alternative raptorial leg types. Our results suggest that prey type, predatory behavior, salivary toxicity, and morphological adaptations pose intricate and interrelated factors influencing the evolution of this diverse group of predators.

Reduvius frommeri, a new species of Reduviidae from the Western United States (Hemiptera: Reduviidae), with a synopsis of the Nearctic species of Reduvius Fabricius.

The rate of discovery of new species of Reduviidae (Insecta: Heteroptera) from North America has slowed in the 21st century. This is not surprising, given the conspicuousness and large distribution ranges of many Nearctic assassin bug species that are often collected using general insect collecting techniques. Nevertheless, biodiversity discovery in Nearctic Reduviidae is ongoing. We here describe a new species, Reduvius frommeri, n. sp., from Southern California that is so far only known from a small endemic range in the Sonoran Desert. With about 197 species, the genus Reduvius Fabricius is one of the most speciose genera of Reduviidae. The majority of species occur in arid- and semi-arid areas in the Afrotropical, Oriental, and Palearctic regions and only three species are New World endemics. A fourth species that occurs in the United States, Reduvius personatus Fabricius, is cosmopolitan and has been introduced to the Western Nearctic. The new species of Reduvius stands out amongst the four other Nearctic Reduvius species by the small size and pale body coloration with a contrasting dark head. Image plates documenting habitus and selected morphological details and maps are provided for the five species in the Nearctic. We conclude that efforts to document species diversity and distribution ranges even for conspicuous insects such as assassin bugs in fairly well studied biogeographic regions need to continue.

Evolutionary history of assassin bugs (insecta: hemiptera: Reduviidae): insights from divergence dating and ancestral state reconstruction.

Assassin bugs are one of the most successful clades of predatory animals based on their species numbers (∼6,800 spp.) and wide distribution in terrestrial ecosystems. Various novel prey capture strategies and remarkable prey specializations contribute to their appeal as a model to study evolutionary pathways involved in predation. Here, we reconstruct the most comprehensive reduviid phylogeny (178 taxa, 18 subfamilies) to date based on molecular data (5 markers). This phylogeny tests current hypotheses on reduviid relationships emphasizing the polyphyletic Reduviinae and the blood-feeding, disease-vectoring Triatominae, and allows us, for the first time in assassin bugs, to reconstruct ancestral states of prey associations and microhabitats. Using a fossil-calibrated molecular tree, we estimated divergence times for key events in the evolutionary history of Reduviidae. Our results indicate that the polyphyletic Reduviinae fall into 11-14 separate clades. Triatominae are paraphyletic with respect to the reduviine genus Opisthacidius in the maximum likelihood analyses; this result is in contrast to prior hypotheses that found Triatominae to be monophyletic or polyphyletic and may be due to the more comprehensive taxon and character sampling in this study. The evolution of blood-feeding may thus have occurred once or twice independently among predatory assassin bugs. All prey specialists evolved from generalist ancestors, with multiple evolutionary origins of termite and ant specializations. A bark-associated life style on tree trunks is ancestral for most of the lineages of Higher Reduviidae; living on foliage has evolved at least six times independently. Reduviidae originated in the Middle Jurassic (178 Ma), but significant lineage diversification only began in the Late Cretaceous (97 Ma). The integration of molecular phylogenetics with fossil and life history data as presented in this paper provides insights into the evolutionary history of reduviids and clears the way for in-depth evolutionary hypothesis testing in one of the most speciose clades of predators.

Polymerase chain reaction detection of Trypanosoma cruzi in suboptimally preserved vectors and comparative infection rates 2007-2010 in Escondido, Southern California.

We investigate the effect of specimen preservation on reliable detection of infection rates of the Chagas disease agent Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) in the Californian endemic vector Triatoma protracta (Uhler) (Hemiptera: Reduviidae) by using polymerase chain reaction. Infection rates in suboptimally preserved specimens (dry or low-percentage ethanol) were found to be not significantly different from optimally preserved samples. Based on our samples, the infection rate of vectors in one population in Escondido, San Diego County, has not changed significantly between 2007 and 2010.

Infection rates of Triatoma protracta (Uhler) with Trypanosoma cruzi in Southern California and molecular identification of trypanosomes.

We report Trypanosoma cruzi infection rates of the native kissing bug Triatoma protracta in southern California. The rates are within the historically reported range, but differ significantly between the two sites (19% in Escondido and 36% in Glendora). Identification of T. cruzi in T. protracta was conducted for the first time by using partial 18S ribosomal RNA and 24Sα ribosomal RNA sequences. Incongruence of 24Sα ribosomal RNA phylogeny with current T. cruzi genotype classification supports non-clonality of some T. cruzi genotypes.