Phylogeography of Semiterrestrial Isopod, Tylos granuliferus, on East Asian Coasts

Phylogeography of the true freshwater crab, Geothelphusa dehaani: Detected dual dispersal routes via land and sea

Dispersal is an important factor that determines the potential for colonization to pioneer sites. Although most decapods employ seaward migration for reproduction with a planktonic larval phase, true freshwater crabs spend their entire life cycle in freshwater. Therefore, it is expected that genetic regionality can be easily detected. In this study, we focused on true freshwater crabs, Geothelphusa Stimpson, 1858. Herein, we reveal the evolutionary history and dispersal patterns of freshwater crustaceans. We collected and genetically analyzed 283 specimens at 138 localities across the Japanese Islands. Phylogenetic analyses were conducted on the combined dataset (mtDNA COI, 16S, and nDNA ITS1, histone H3 regions) and the data set based on the mtDNA COI region. The phylogenetic relationships detected 10 clades that were highly monophyletic. The highlights of this study were the discovery of several cryptic species or undescribed species, and the completely different heterogeneous dual dispersal pathways within a single species; i.e., both land and ocean routes. Although it was concluded that Japanese crabs are basically genetically divided by straits, strong evidence for dispersion via ocean currents was also detected (i.e., a "sweepstake"). It was also confirmed that Geothelphusa dehaani (White, 1847) could survive in seawater.

Possible dispersal of the coastal and subterranean carabid beetle Thalassoduvalius masidai (Coleoptera) by ocean currents

The spatial genetic structures of insects are reflected in their habitats. Coastal insects tend to have less genetic differentiation than subterranean insects. However, the general pattern of population structure of coastal species residing in subterranean habitats is unknown. Thalassoduvalius masidai (Coleoptera: Carabidae: Trechinae), endemic to Japan, is a coastal and subterranean beetle. Here, we hypothesized that T. masidai populations disperse among regions by ocean currents, floods and tsunamis, despite their habitat being underground. To test this hypothesis, we performed a phylogeographical analysis of T. masidai using single nucleotide polymorphism data from multiplexed inter-simple sequence repeat genotyping by sequencing (MIG-seq) and the mitochondrial COI gene. The phylogenetic network and tree and STRUCTURE analyses indicated that T. masidai populations were divided into three groups: the western Seto Inland Sea–Izu Peninsula coasts, the eastern Seto Inland Sea–Kii Peninsula coasts and the Japan Sea coasts. The genetic diversity of T. masidai was higher in sites with lower longitude and latitude. These results suggest that T. masidai migrated and dispersed from the south-western area of Japan by ocean currents, despite its underground habitat. The genetic analysis data from the present study would also be helpful for the conservation and taxonomic revision of this species.

Population Structure of Two Flightless Weevils of Genus Scepticus Roelofs (Coleoptera, Curculionidae) with Seashore Habitat in Japan

To elucidate the genetic population structure of two coastal weevils, Scepticus griseus and S. tigrinus, we conducted molecular phylogenetic analyses of the mitochondrial DNA cytochrome c oxidase subunit I (COI) region (1308 bp) and cytochrome c oxidase subunit II (COII) region (584 bp). A total of 650 individuals (S. griseus, 444 individuals; S. tigrinus, 206 individuals) were obtained from 64 sites. The haplotype networks of both species showed three major lineages with roughly regional distribution. However, the two species show quite different genetic structures; S. griseus has a complicated structure while that of S. tigrinus is simple. We hypothesize that the genetic structure of each of these two weevil species reflects climatic oscillations during the Pleistocene, and the differences in genetic structure between S. griseus and S. tigrinus may represent a unique evolutionary history scenario in each species.

Out of Asia: mitochondrial evolutionary history of the globally introduced supralittoral isopod Ligia exotica

The native ranges and invasion histories of many marine species remain elusive due to a dynamic dispersal process via marine vessels. Molecular markers can aid in identification of native ranges and elucidation of the introduction and establishment process. The supralittoral isopod Ligia exotica has a wide tropical and subtropical distribution, frequently found in harbors and ports around the globe. This isopod is hypothesized to have an Old World origin, from where it was unintentionally introduced to other regions via wooden ships and solid ballast. Its native range, however, remains uncertain. Recent molecular studies uncovered the presence of two highly divergent lineages of L. exotica in East Asia, and suggest this region is a source of nonindigenous populations. In this study, we conducted phylogenetic analyses (Maximum Likelihood and Bayesian) of a fragment of the mitochondrial 16S ribosomal (r)DNA gene using a dataset of this isopod that greatly expanded previous representation from Asia and putative nonindigenous populations around the world. For a subset of samples, sequences of 12S rDNA and NaK were also obtained and analyzed together with 16S rDNA. Our results show that L. exotica is comprised of several highly divergent genetic lineages, which probably represent different species. Most of the 16S rDNA genetic diversity (48 haplotypes) was detected in East and Southeast Asia. Only seven haplotypes were observed outside this region (in the Americas, Hawai'i, Africa and India), which were identical or closely related to haplotypes found in East and Southeast Asia. Phylogenetic patterns indicate the L. exotica clade originated and diversified in East and Southeast Asia, and only members of one of the divergent lineages have spread out of this region, recently, suggesting the potential to become invasive is phylogenetically constrained.