Colliding fragment islands transport independent lineages of endemic rock-crawlers (Grylloblattodea: Grylloblattidae) in the Japanese archipelago

Unraveling the potential structure of a Parnassius butterfly in Japan: Insights into the expansion history

The Japanese Archipelago consists of a series of isolated yet interconnected islands off the Eurasian continent. The linear topography of the archipelago presents a unique biogeographic context for the dispersal of organisms from the continent. In this study, mitochondrial DNA (mtDNA) and single-nucleotide polymorphism (SNP) variation were employed to elucidate the dispersal history of the Japanese clouded butterfly (Parnassius glacialis) across the Japanese Archipelago, including the northern island (Hokkaido), the main island (Honshu), and Shikoku Island. Network analysis of 1192 bp of mtDNA (cytochrome oxidase I and II) regions revealed 49 haplotypes and three distinct haplotype groups, which correspond geographically to Eastern Japan, Western Japan, and Chugoku-Shikoku. The Chugoku-Shikoku group is the most ancient lineage. Divergence time estimates using whole-genome sequencing of mtDNA suggest that the Japanese lineage diverged from the continental P. glacialis approximately 3.08 million years ago (Ma). Subsequently, the Eastern Japan and Western Japan lineages diverged from the Chugoku-Shikoku lineage around 1.06 Ma, with subsequent divergence of the Eastern and Western Japan lineages at approximately 0.62 Ma. P. glacialis is estimated to have expanded its distribution via a land bridge that once connected China and the Japanese Archipelago. Population structure analysis based on 3067 SNP genotypes revealed five distinct genetic structures within the Japanese Archipelago, indicating geographical differentiation. Through mtDNA and SNP variation analyses, four primary genetic barriers were identified: between Hokkaido and Honshu, between Eastern and Central Japan, within the Kansai region, and in the Chugoku region. The first three barriers correspond to notable geographical features, the Blakiston Line, a line parallel to the Itoigawa-Shizuoka Tectonic Line, and a boundary crossing Lake Biwa. These findings suggest that Japanese P. glacialis diverged from the continental P. glacialis and expanded its range across the Japanese Archipelago via western routes, leading to its current distribution.

Systematics of cybaeid spiders endemic to the Japanese Archipelago, and their historical biogeographic implications (Araneae: Cybaeidae)

The epigean and subterranean spiders of the genus Cybaeus L. Koch, 1868 are distributed in the Holarctic, and are highly diversified in western North America and Japan. More than 100 species have been described from the Japanese Archipelago and several species assemblages have also been recognised among the Japanese Cybaeus based on their morphological similarities. However, their phylogenetic backbone remains unclear. Moreover, genus-level classification of several of the Japanese species appear to be questionable. In this study we performed extensive molecular analyses of the family Cybaeidae in East Asia, mainly the Japanese Archipelago, to clarify their fundamental phylogenetic relationships. We also conducted a divergence time estimation to provide insights into their historical biogeography and evolutionary history. Our divergence dating results indicate that the diversification of the major lineages of the East Asian cybaeid spiders might be related to the opening of the Sea of Japan c .20million years ago. On the basis of the morphological evaluation and obtained phylogenies, some East Asian species formerly placed in Cybaeus are transferred to the cybaeid genera Allocybaeina Bennett, 2020, Sincybaeus Wang & Zhang, 2022 and Cybaeina Chamberlin & Ivie, 1932, i.e. Allocybaeina petegarina (Yaginuma, 1972), comb. nov., Sincybaeus monticola (Kobayashi, 2006), comb. nov., Sincybaeus rarispinosus (Yaginuma, 1970), comb. nov., Sincybaeus yoshiakii (Yaginuma, 1968), comb. nov., and Cybaeina whanseunensis (Paik & Namkung, 1967), comb. nov. Our results clarify the genus-level richness of cybaeids in the Japanese Archipelago for the first time, and reveal the fine-scale phylogenetic relationships of Cybaeus species endemic to the Japanese Archipelago and adjacent regions. ZooBank: urn:lsid:zoobank.org:pub:AF2A3C0E-7F0F-4253-85BA-D995A075F00D.

Taxonomic insights and evolutionary history in East Asian terrestrial slugs of the genus Meghimatium

East Asia, specifically the Japanese Archipelago, is a biodiversity hotspot of both vertebrates and invertebrates. Mollusks represent a burst of species diversity in this region due to the effects of biotic and abiotic factors on their morphological traits, such as shell shape and size. However, the evolutionary history of terrestrial slugs in East Asia remains unknown. In the present study, we investigated the molecular phylogeny of terrestrial slugs of the genus Meghimatium. This genus includes three described and eight undescribed species, and our study used all except for two. Based on phylogeny and the species delimitation tests, the genus Meghimatium was split into many putative species, suggesting higher species diversity than previously thought based on morphological and anatomical studies and that almost undescribed species may be inappropriate. Therefore, morphological traits, such as body size and colour, conventionally considered for classification may easily vary or be similar across geographic region. Moreover, the divergence time of this genus is almost concordant with the geographical time scale of the formation of the Japanese mainland. Our findings suggest that molecular phylogenetics helps classify Japanese Meghimatium slugs, but comprehensive taxonomic revisions using multi-locus analyses are needed.

Descriptions of a new genus and a new species, Grylloprimevala jilina (Grylloblattidae) from China

We erected a new genus (Grylloprimevala Zhou & Ren gen. nov.) and defined a new species (Grylloprimevala jilina Zhou & Ren sp. nov.) from a natural cave in the primeval forest of Jilin Province, China, according to the morphological, behavioral, and molecular evidence. Grylloprimevala gen. nov. is distinguishable from other genera of Grylloblattodea primarily by morphological characters, including the slightly concave posterior margin of the pronotum and no poorly sclerotized zones, six intramarginal and nine intermarginal setae on the cervical sclerite, one tooth on the lacinia, no pulvilli on tarsal segments, and a symmetrical epiproct with a pointed triangular and middle-depressed median projection on the posterior margin. Based on the morphological features mentioned above, we further identified a new species, G. jilina sp. nov. At the aspect of behavior, G. jilina sp. nov. displays the typical characteristics of troglobites, including degraded visual senses, developed body surface sensors, and predation between individuals. Furthermore, molecular phylogenetic analyses also supported the morphological delimitation of G. jilina sp. nov. due to the separate clade of G. jilina sp. nov. Our results provide materials for the determination and conservation of Grylloblattodea in China.

Genome-wide molecular phylogenetic analyses and mating experiments which reveal the evolutionary history and an intermediate stage of speciation of a giant water bug

The intermediate stages of speciation are important for understanding the processes involved in the creation of biodiversity, and also comprise a number of interesting phenomena. However, difficulties are associated with dividing clear speciation stages because speciation is a continuous process. Therefore, the elucidation of speciation is an interesting and important task in evolutionary biology. We herein present an example of a species in an intermediate stage of speciation using the giant water bug Appasus japonicus (Heteroptera, Belostomatidae) that was investigated using mating experiments and phylogenetic analyses of the mtDNA COI (658 bp) and 16S rRNA (435 bp) regions, and nDNA SSR (13 loci) and its genome-wide SNPs (11,241 SNPs). The results of our phylogenetic analyses based on their mtDNA dataset and the genome-wide SNPs dataset strongly supported the paraphyly of the Japanese populations. Therefore, it is suggested that their ancestral lineage which being distributed in the Japanese Archipelago subsequently migrated to the Eurasian Continent (i.e., "back-dispersal" occurred). Furthermore, the results of the mating experiments suggested that among A. japonicus, even between closely related lineages, pre-mating reproductive isolation has been established by the differentiation of copulatory organ morphologies. In contrast, pre-mating reproductive isolation is not established in the absence of the differentiation of copulatory organ morphologies, even if genetic differentiation is prominent. These results suggested that their phylogenetic distance does not predict pre-mating reproductive isolation. Furthermore, in the present study, we present a clear example of pre-mating reproductive isolation driving speciation between closely related lineages.

Comparative transcriptomics of ice-crawlers demonstrates cold specialization constrains niche evolution in a relict lineage

Key changes in ecological niche space are often critical to understanding how lineages diversify during adaptive radiations. However, the converse, or understanding why some lineages are depauperate and relictual, is more challenging, as many factors may constrain niche evolution. In the case of the insect order Grylloblattodea, highly conserved thermal breadth is assumed to be closely tied to their relictual status, but has not been formerly tested. Here, we investigate whether evolutionary constraints in the physiological tolerance of temperature can help explain relictualism in this lineage. Using a comparative transcriptomics approach, we investigate gene expression following acute heat and cold stress across members of Grylloblattodea and their sister group, Mantophasmatodea. We additionally examine patterns of protein evolution, to identify candidate genes of positive selection. We demonstrate that cold specialization in Grylloblattodea has been accompanied by the loss of the inducible heat shock response under both acute heat and cold stress. Additionally, there is widespread evidence of selection on protein-coding genes consistent with evolutionary constraints due to cold specialization. This includes positive selection on genes involved in trehalose transport, metabolic function, mitochondrial function, oxygen reduction, oxidative stress, and protein synthesis. These patterns of molecular adaptation suggest that Grylloblattodea have undergone evolutionary trade-offs to survive in cold habitats and should be considered highly vulnerable to climate change. Finally, our transcriptomic data provide a robust backbone phylogeny for generic relationships within Grylloblattodea and Mantophasmatodea. Major phylogenetic splits in each group relate to arid conditions driving biogeographical patterns, with support for a sister-group relationship between North American Grylloblatta and Altai-Sayan Grylloblattella, and a range disjunction in Namibia splitting major clades within Mantophasmatodea.

Grylloblattodea of Canada

The enigmatic insect order Grylloblattodea comprises two described species in Canada, which are limited to the Montane Cordillera and Pacific Maritime ecozones. One of the described species has three Canadian subspecies of uncertain taxonomic ranking, and there are two additional undescribed or unreported species known in close proximity to the Canadian border in western Alberta and British Columbia that likely also occur in Canada. Thus, as much as 50% of the total taxonomic diversity of Grylloblattodea in Canada is still undocumented. Targeted surveys and taxonomic work, as well as studies that describe the ecology and conservation status of Grylloblattodea are important goals for future research.

Phylogeography of freshwater planorbid snails reveals diversification patterns in Eurasian continental islands

Background

Islands have traditionally been the centre of evolutionary biological research, but the dynamics of immigration and differentiation at continental islands have not been well studied. Therefore, we focused on the Japanese archipelago, the continental islands located at the eastern end of the Eurasian continent. While the Japanese archipelago is characterised by high biodiversity and rich freshwater habitats, the origin and formation mechanisms of its freshwater organisms are not clear. In order to clarify the history of the planorbid gastropod fauna, we conducted phylogenetic analysis, divergence time estimation, ancestral state reconstruction, and lineage diversity estimations.

Results

Our analyses revealed the formation process of the planorbid fauna in the Japanese archipelago. Most lineages in the Japanese archipelago have closely related lineages on the continent, and the divergence within the Japanese lineages presumably occurred after the late Pliocene. In addition, each lineage is characterised by different phylogeographical patterns, suggesting that immigration routes from the continent to the Japanese archipelago differ among lineages. Furthermore, a regional lineage diversity plot showed that the present diversity in the Japanese archipelago potentially reflects the differentiation of lineages within the islands after the development of the Japanese archipelago.

Conclusions

Although additional taxon sampling and genetic analysis focused on each lineage are needed, our results suggest that immigration from multiple routes just prior to the development of the Japanese archipelago and subsequent diversification within the islands are major causes of the present-day diversity of the Japanese planorbid fauna.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1273-3) contains supplementary material, which is available to authorized users.

The Jurassic Bajanzhargalanidae (Insecta: Grylloblattida?): New genera and species, and data on postabdominal morphology

The presumed phylogenetic link between extant ice-crawlers (Grylloblattidae = 'crown-Grylloblattida') and fossil species of the taxon concept Grylloblattida sensu Storozhenko (2002) is essentially based on postabdominal morphology. However, the fossil data are limited, and the interpretation is open to debate. Here we investigate a sample of a poorly known fossil 'grylloblattidan' family, the Bajanzhargalanidae, collected from the Daohugou locality (Middle Jurassic, China). We describe Sinonele fangi gen. nov., sp. nov., Sinonele hei gen. nov., sp. nov., Sinonele phasmoides gen. nov., sp. nov., and Sinonele mini gen. nov., sp. nov. Thanks to the abundance and exceptional preservation of the material, we could document wing venation intra-specific variability, provide cues to identify male and female individuals, describe and tentatively interpret various body structures of both sexes, and discuss them with a broad pterygotan phylogenetic perspective. The Bajanzhargalanidae exhibit a puzzling combination of postabdominal characters leaving us inconclusive on their affinities, or lack thereof, with crown-Grylloblattida. Our contribution suggests that a substantial effort will be needed to further investigate postabdominal structures from comparatively ancient fossil insects preserved as rock imprints, because of their broad morphological disparity.

Contrasting genetic structure of closely related giant water bugs: phylogeography of Appasus japonicus and Appasus major (Insecta: Heteroptera, Belostomatidae)

Appasus japonicus and A. major, two belostomatid species of the giant water bug found in parts of East Asia, have very similar morphological characteristics and ecological niches, and also overlapping habitats. However, the results of our previous published study utilizing molecular phylogenetic analyses of mitochondrial and nuclear DNA revealed extensive genetic differences, which indicated that the possibility of inter-specific hybridization was extremely unlikely. We collected A. japonicus and A. major from the Japanese Archipelago, Korean Peninsula, and Russian Far East, and conducted molecular analyses of mitochondrial DNA COI and 16S rRNA to compare phylogenetic relationships between these species. Three major clades were recognized within A. japonicus. Specimens from the Korean population constituted a monophyletic clade, and were a sister group of the western region of the Japanese Archipelago. The Eastern Japanese clade was clearly differentiated. Four major clades were recognized within A. major. Specimens from the Japanese and Korean populations revealed two distinct monophyletic clades. Significant differentiation was clearly observed between their genetic structures. Furthermore, the results of mismatch distribution and Bayesian skyline plot analyses suggested the possibility of a bottleneck effect or founder effect in two of the A. major clades. Collectively, these results demonstrated both similarities and differences in these two species even though their distribution widely overlaps in East Asia, with their morphological characteristics and ecological niches being very similar. These differences in genetic structures are considered to be due to their evolutionary history.