Widespread mermithid nematode parasitism of Cretaceous insects.

Mermithid nematodes are obligate invertebrate parasites dating back to the Early Cretaceous. Their fossil record is sparse, especially before the Cenozoic, thus little is known about their early host associations. This study reports 16 new mermithids associated with their insect hosts from mid-Cretaceous Kachin amber, 12 of which include previously unknown hosts. These fossils indicate that mermithid parasitism of invertebrates was already widespread and played an important role in the mid-Cretaceous terrestrial ecosystem. Remarkably, three hosts (bristletails, barklice, and perforissid planthoppers) were previously unknown to be parasitized by mermithids both past and present. Furthermore, our study shows that in contrast to their Cenozoic counterparts, Cretaceous nematodes including mermithids are more abundant in non-holometabolous insects. This result suggests that nematodes had not completely exploited the dominant Holometabola as their hosts until the Cenozoic. This study reveals what appears to be a vanished history of nematodes that parasitized Cretaceous insects.

A review of Chifengiinae (Insecta: Orthoptera: Prophalangopsidae) with description of new Jurassic material from the northwestern Junggar Basin, China.

A complete and well-preserved forewing assigned to the orthopteran insect Parahagla cheni Xu, Fang and Zhang, 2023 is described from the Lower Jurassic Badaowan Formation of the northwestern Junggar Basin (Karamay, Xinjiang, northwestern China), based on which the species is diagnostically revised. It represents the earliest record of the subfamily Chifengiinae under the family Prophalangopsidae. The subfamily Chifengiinae is reviewed and a key to its genera and species is provided in the discussion. A further discuss of the palaeobiogeographic distribution of Chifengiinae shows that the subfamily probably first appeared in the Palaeoarctic in the earliest Jurassic, and later quickly migrated and occupied most areas of eastern Palaeoarctic from the Middle Jurassic to the Early Cretaceous.

High acoustic diversity and behavioral complexity of katydids in the Mesozoic soundscape.

Acoustic communication has played a key role in the evolution of a wide variety of vertebrates and insects. However, the reconstruction of ancient acoustic signals is challenging due to the extreme rarity of fossilized organs. Here, we report the earliest tympanal ears and sound-producing system (stridulatory apparatus) found in exceptionally preserved Mesozoic katydids. We present a database of the stridulatory apparatus and wing morphology of Mesozoic katydids and further calculate their probable singing frequencies and analyze the evolution of their acoustic communication. Our suite of analyses demonstrates that katydids evolved complex acoustic communication including mating signals, intermale communication, and directional hearing, at least by the Middle Jurassic. Additionally, katydids evolved a high diversity of singing frequencies including high-frequency musical calls, accompanied by acoustic niche partitioning at least by the Late Triassic, suggesting that acoustic communication might have been an important driver in the early radiation of these insects. The Early-Middle Jurassic katydid transition from Haglidae- to Prophalangopsidae-dominated faunas coincided with the diversification of derived mammalian clades and improvement of hearing in early mammals, supporting the hypothesis of the acoustic coevolution of mammals and katydids. Our findings not only highlight the ecological significance of insects in the Mesozoic soundscape but also contribute to our understanding of how acoustic communication has influenced animal evolution.

A New Cretaceous Dustywing Genus (Neuroptera: Coniopterygidae) with Peculiar Wing Venation.

The species and morphological diversity of dustywings (Neuroptera: Coniopterygidae) from the Cretaceous, of which the knowledge is rapidly increasing by recent studies on the species from the mid-Cretaceous Kachin amber, provide valuable evidence for understanding the phylogeny and early evolution of this highly specialized lacewing lineage. Here we describe a new genus and two new species of this genus in Coniopterygidae from the mid-Cretaceous (lowermost Cenomanian) of northern Myanmar, namely Paradoxoconis szirakii gen. et sp. nov. and Paradoxoconis longipalpa gen. et sp. nov. The new genus possesses a peculiar combination of wing characters, e.g., the terminal fusion or connection between ScP and RA, the terminal connection of RA to RP, the presence of forewing A3, and the presence of a distal gradate series of crossveins. Despite uncertain subfamilial placement, this new genus morphologically resembles the extant genus Coniocompsa Enderlein, 1905 of the subfamily Aleuropteryginae and the extant genus Flintoconis Sziráki, 2007 of the subfamily Brucheiserinae. Our finding highlights the palaeodiversity of dustywings from the Cretaceous.

New Cretaceous Lacewings in a Transitional Lineage of Myrmeleontoidea and Their Phylogenetic Implications.

The extinct neuropteran families Cratosmylidae and Babinskaiidae hitherto only known from the Cretaceous represent the transitional lineage between Nymphidae and advanced myrmeleontoids (e.g., Nemopteridae and Myrmeleontidae) in the superfamily Myrmeleontoidea. Here, we describe two new species, which respectively belong to Cratosmylidae and Babinskaiidae, namely, Araripenymphes burmanus sp. nov. and Paradoxoleon chenruii gen. et sp. nov., from the mid-Cretaceous Kachin amber of Myanmar. Cratosmylidae, which was previously only recorded from the Lower Cretaceous of Brazil (Crato Formation), is first reported from the mid-Cretaceous Kachin amber of Myanmar, and the co-occurrence of Araripenymphes Menon, Martins-Neto and Martill, 2005 across South America and Asia further documents the Gondwanan origin of the northern Myanmar amber lacewing paleofauna. The first finding of a deeply bifurcated forewing MP with two free branches in Babinskaiidae (viz., Paradoxoleon chenruii gen. et sp. nov.) highlights the morphological diversity of this extinct family. The phylogenetic positions of Araripenymphes burmanus sp. nov. and Paradoxoleon chenruii gen. et sp. nov. were recovered on the basis of a morphology-based phylogenetic analysis, and the monophyly of Cratosmylidae + Babinskaiidae was corroborated. Given the paraphyly of Cratosmylidae, its familial status is discussed.

Ecological radiations of insects in the Mesozoic.

The Mesozoic is a key era for the rise of the modern insect fauna. Among the most important evolutionary events in Mesozoic insects are the radiation of holometabolous insects, the origin of eusocial and parasitoid insects, diversification of pollinating insects, and development of advanced mimicry and camouflage. These events are closely associated with the diversification of insect ecological behaviors and colonization of new ecospaces. At the same time, insects had evolved more complex and closer ecological associations with various plants and animals. Mesozoic insects played a key and underappreciated ecological role in reconstructing and maintaining terrestrial ecosystems. A greater understanding of the history of insects may help to mitigate future changes in insect diversity and abundance.

Aposematic coloration from Mid-Cretaceous Kachin amber.

Aposematic coloration is among the most diverse antipredator strategies, which can signal unpleasantness of organisms to potential predators and reduce the probability of predation. Unlike mimesis, aposematic coloration allows organisms to warn their predators away by conspicuous and recognizable colour patterns. However, aposematism has been a regular puzzle, especially as the long-term history of such traits is obscured by an insufficient fossil record. Here, we report the discovery of aposematic coloration in an orthopteran nymph from Mid-Cretaceous Kachin amber (99 million years old). It is attributed to the extinct family Elcanidae and erected as a new genus identified by conspicuous dark/light-striped coloration, four apical spurs on the metatibia, a two-segmented metatarsus and unsegmented stylus. It represents the first fossil orthopteran preserved with aposematic coloration from the Mesozoic, demonstrating that orthopterans had evolved aposematism by the Mid-Cretaceous. Our findings provide novel insights into the early evolution of anti-predator strategies among orthopterans. Together with mimesis, debris-carrying camouflage and aposematism previously reported, our findings demonstrate the relative complexity of prey-predator interactions in the Mesozoic, especially in the Mid-Cretaceous Kachin amber forest. This article is part of the theme issue 'The impact of Chinese palaeontology on evolutionary research'.

The family Polycentropodidae (Insecta, Trichoptera) in mid-Cretaceous Burmese Amber.

Three described species, Neureclipsistriangula sp. nov., Neureclipsisacuta sp. nov., and Neureclipsisobtusa sp. nov., expand the Neureclipsis cluster to six species dominating the Polycentropodidae in Burmese amber. The new species Plectrocnemiaohlhoffi sp. nov. and Plectrocnemiabowangi sp. nov. of the Polycentropus cluster add to the comparatively low occurrence of Polycentropodidae in Burmese mid-Cretaceous amber.

The mid-Miocene Zhangpu biota reveals an outstandingly rich rainforest biome in East Asia.

During the Mid-Miocene Climatic Optimum [MMCO, ~14 to 17 million years (Ma) ago], global temperatures were similar to predicted temperatures for the coming century. Limited megathermal paleoclimatic and fossil data are known from this period, despite its potential as an analog for future climate conditions. Here, we report a rich middle Miocene rainforest biome, the Zhangpu biota (~14.7 Ma ago), based on material preserved in amber and associated sedimentary rocks from southeastern China. The record shows that the mid-Miocene rainforest reached at least 24.2°N and was more widespread than previously estimated. Our results not only highlight the role of tropical rainforests acting as evolutionary museums for biodiversity at the generic level but also suggest that the MMCO probably strongly shaped the East Asian biota via the northern expansion of the megathermal rainforest biome. The Zhangpu biota provides an ideal snapshot for biodiversity redistribution during global warming.

Rostromedial tegmental nucleus-substantia nigra pars compacta circuit mediates aversive and despair behavior in mice.

GABAergic neurons in the rostromedial tegmental nucleus (RMTg) receive major input from the lateral habenula (LHb), which conveys negative reward and motivation related information, and project intensively to midbrain dopamine neurons, including those in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). The RMTg-VTA circuit has been shown to be linked to the affective behavior, but the role of the RMTg-SNc circuit in aversion and depression has not been well understood. This study demonstrated that exciting or inhibiting VgatRMTg-SNc neurons was sufficient to increase or decrease immobility time in the forced swim test (FST), respectively. Furthermore, exciting the VgatRMTg-SNc pathway caused aversive behavior. Ninety percent of the SNc putative dopamine neurons were inhibited in extracellular recordings. Furthermore, inhibiting the VgatRMTg-SNc pathway reversed behavioral despair in chronic restraint stress (CRS) depression model mice. Manipulations of the pathway did not affect the hedonic value of the reward in the sucrose-preference test (SPT) or general motor function. In conclusion, these results indicate that the VgatRMTg-SNc pathway regulates aversive and despair behavior, which suggests that the RMTg may mediate the role of LHb in negative behaviors through regulating the activity of SNc neurons.

Medial Habenula-Interpeduncular Nucleus Circuit Contributes to Anhedonia-Like Behavior in a Rat Model of Depression.

The habenula is a nuclear complex composed of the lateral habenula (LHb) and medial habenula (MHb), two distinct structures. Much progress has been made to emphasize the role of the LHb in the pathogenesis of depression. In contrast, relatively less research has focused on the MHb. However, in recent years, the role of the MHb has begun to gain increasing attention. The MHb connects to the interpeduncular nucleus (IPN) both morphologically and functionally. The MHb-IPN pathway plays an important role in regulating higher brain functions, including cognition, reward, and decision making. It indicates a role of the MHb in the pathogenesis of depression. Thus, we investigated the role of the MHb-IPN pathway in depression. MHb metabolic activity was increased in the chronic unpredictable mild stress (CUMS)-exposed rat model of depression. MHb lesions in the CUMS-exposed rats reversed anhedonia-like behavior, as observed in the sucrose preference test, and significantly downregulated the elevated metabolic activity of the IPN. Substance P (SP)-containing neurons of the MHb were found to innervate the IPN and to be the main source of SP in the IPN. SP content of IPN tissue of the CUMS-exposed rats was increased and MHb lesions reversed this change. In the in vitro experiment, firing rate recordings showed that SP perfusion increased the activity of IPN neurons. Our results suggest that hyperactivity of the MHb-IPN circuit is involved in the anhedonia-like behavior of depression, and that SP mediates the effect of the MHb on IPN neurons.