Phylogenomics and biogeography of sawflies and woodwasps (Hymenoptera, Symphyta)

Phylogenomic approaches have recently helped elucidate various insect relationships, but large-scale comprehensive analyses on relationships within sawflies and woodwasps are still lacking. Here, we infer the relationships and long-term biogeographic history of these hymenopteran groups using a large dataset of 354 UCE loci collected from 385 species that represent all major lineages. Early Hymenoptera started diversifying during the Early Triassic ∼249 Ma and spread all over the ancient supercontinent Pangaea. We recovered Xyeloidea as a monophyletic sister group to other Hymenoptera and Pamphilioidea as sister to Unicalcarida. Within the diverse family Tenthredinidae, our taxonomically and geographically expanded taxon sampling highlights the non-monophyly of several traditionally defined subfamilies. In addition, the recent removal of Athalia and related genera from the Tenthredinidae into the separate family Athaliidae is supported. The deep historical biogeography of the group is characterised by independent dispersals and re-colonisations between the northern (Laurasia) and southern (Gondwana) palaeocontinents. The breakup of these landmasses led to ancient vicariance in several Gondwanan lineages, while interchange across the Northern Hemisphere has continued until the Recent. The little-studied African sawfly fauna is likewise a diverse mixture of groups with varying routes of colonization. Our results reveal interesting parallels in the evolution and biogeography of early hymenopterans and other ancient insect groups.

Comparative genomics of the miniature wasp and pest control agent Trichogramma pretiosum

Background

Trichogrammatids are minute parasitoid wasps that develop within other insect eggs. They are less than half a millimeter long, smaller than some protozoans. The Trichogrammatidae are one of the earliest branching families of Chalcidoidea: a diverse superfamily of approximately half a million species of parasitoid wasps, proposed to have evolved from a miniaturized ancestor. Trichogramma are frequently used in agriculture, released as biological control agents against major moth and butterfly pests. Additionally, Trichogramma are well known for their symbiotic bacteria that induce asexual reproduction in infected females. Knowledge of the genome sequence of Trichogramma is a major step towards further understanding its biology and potential applications in pest control.

Results

We report the 195-Mb genome sequence of Trichogramma pretiosum and uncover signatures of miniaturization and adaptation in Trichogramma and related parasitoids. Comparative analyses reveal relatively rapid evolution of proteins involved in ribosome biogenesis and function, transcriptional regulation, and ploidy regulation. Chalcids also show loss or especially rapid evolution of 285 gene clusters conserved in other Hymenoptera, including many that are involved in signal transduction and embryonic development. Comparisons between sexual and asexual lineages of Trichogramma pretiosum reveal that there is no strong evidence for genome degradation (e.g., gene loss) in the asexual lineage, although it does contain a lower repeat content than the sexual lineage. Trichogramma shows particularly rapid genome evolution compared to other hymenopterans. We speculate these changes reflect adaptations to miniaturization, and to life as a specialized egg parasitoid.

Conclusions

The genomes of Trichogramma and related parasitoids are a valuable resource for future studies of these diverse and economically important insects, including explorations of parasitoid biology, symbiosis, asexuality, biological control, and the evolution of miniaturization. Understanding the molecular determinants of parasitism can also inform mass rearing of Trichogramma and other parasitoids for biological control.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0520-9) contains supplementary material, which is available to authorized users.

Changes to the Fossil Record of Insects through Fifteen Years of Discovery

The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well.

From Fossil Parasitoids to Vectors: Insects as Parasites and Hosts

Within Metazoa, it has been proposed that as many as two-thirds of all species are parasitic. This propensity towards parasitism is also reflected within insects, where several lineages independently evolved a parasitic lifestyle. Parasitic behaviour ranges from parasitic habits in the strict sense, but also includes parasitoid, phoretic or kleptoparasitic behaviour. Numerous insects are also the host for other parasitic insects or metazoans. Insects can also serve as vectors for numerous metazoan, protistan, bacterial and viral diseases. The fossil record can report this behaviour with direct (parasite associated with its host) or indirect evidence (insect with parasitic larva, isolated parasitic insect, pathological changes of host). The high abundance of parasitism in the fossil record of insects can reveal important aspects of parasitic lifestyles in various evolutionary lineages. For a comprehensive view on fossil parasitic insects, we discuss here different aspects, including phylogenetic systematics, functional morphology and a direct comparison of fossil and extant species.

Baltorussus total makeover: rejuvenation and sex change in an ancient parasitoid wasp lineage

The Orussidae is a small and rare but phylogenetically important family of parasitoid wasps. The fossil record of the family is also very poor. Baltorussus velteni was described from Baltic amber from an allegedly female specimen. This and another recently discovered specimen are examined with microCT scanning and standard microscopy. We reveal that both the holotype and the new specimen are actually males. Furthermore, the results of the microCT scanning allow us to integrate the fossils in a morphological data set assembled for extant Orussidae. Phylogenetic analyses consistently retrieve Baltorussus as a separate basal lineage within the crown group, whereas two Cretaceous fossils are placed as stem group orussids and a Dominican amber fossil in an extant genus. Based on the positions of the fossils, we estimate that the extant Orussidae radiated in the mid-Cretaceous (approx. 100 Ma ago). This is considerably younger than a previously suggested Early Jurassic date (180 Ma ago), which was primarily based on biogeographic evidence.

Phylogeny of the ophrynopine clade revisited: review of the parasitoid sawfly genera Ophrella Middlekauff, Ophrynopus Konow and Stirocorsia Konow (Hymenoptera : Orussidae)

The rare family Orussidae comprises the only parasitoid sawflies and are sister to the Apocrita, the latter comprising most of Hymenoptera. Because of this, their morphology and relationships have been particularly important for interpreting the morphology of and biological transitions within the order as a whole. Within the Orussidae the ophrynopines are a comparatively diverse clade with a predominantly southern hemisphere distribution. Here, a revised and expanded morphological dataset incorporating several new taxa is used to test ophrynopine relationships and provide further insights into their evolutionary history. The analyses largely corroborate previous results. The distribution pattern and the fossil record indicate that the ophrynopines radiated in the early Cenozoic in the Australasian-Oceanian and the Neotropic regions and later dispersed into the Nearctic, Eastern Palaearctic and Indomalayan regions. The South American genus Ophrella Middlekauff, 1985 is well supported as a monophyletic genus, whereas Ophrynopus Konow, 1897 is paraphyletic with respect to Stirocorsia Konow, 1897. Three new species, Ophrella eldorado Vilhelmsen, sp. nov., Ophrynopus guarani Blank, D.R. Smith & Vilhelmsen, sp. nov., and Ophrynopus rupestris Vilhelmsen, Costa & Alvarenga, sp. nov. are described. Ophrella lingulata Middlekauff, 1985 is treated as a junior synonym of Ophrella amazonica (Westwood, 1874). Stirocorsia is treated as a junior synonym of Ophrynopus. The species Ophrynopus apicalis (Togashi, 2000), Ophrynopus kohli (Konow, 1897), Ophrynopus maculipennis (F. Smith, 1859) and Ophrynopus tosensis (Tosawa & Sugihara, 1934), formerly in Stirocorsia, are transferred to Ophrynopus. Revised keys to the species of Ophrella, Ophrynopus and the genera in the ophrynopine clade are provided. In addition, Orussidae are recorded from Bolivia and French Guiana for the first time.

Per arborem ad astra: morphological adaptations to exploiting the woody habitat in the early evolution of Hymenoptera

We survey morphological features of larval and adult wasps that undergo their entire larval development inside wood and interpret them in view of the lifestyle. The evolution of some of the characters is explored by mapping them on a recently published phylogeny of Hymenoptera. Based on this phylogeny, it is reasonable to assume that wood-living wasps evolved from a xylophagous/mycetophagous stage as displayed by woodwasps to a carnivorous/parasitoid lifestyle, preying on woodboring insect larvae. The latter mode of life is probably ancestral to the Apocrita which comprise the majority of the order; they share this lifestyle with their sister group, the Orussidae. However, most apocritan wasps have radiated into other habitats, the Orussidae and Stephanidae apparently being the only taxa that have retained the ancestral lifestyle of carnivorous wasps. Other apocritan lineages associated with wood (e.g., Aulacidae, Megalyridae, basal Cynipoidea and some Ichneumonoidea and Chalcidoidea) possibly entered this habitat secondarily and independently acquired morphological traits associated with it. The woody habitat was occupied by Hymenoptera during a crucial stage in their evolution where the transition from the phytophagous to carnivorous lifestyle took place. The anatomy of both larva and adults was extensively transformed in the process.