Zoological Science最新文献

Using mitochondrial DNA and genome-wide SNP, phylogenetic relationships in Chalcorana were investigated. Phylogenetic analyses based on subregions of mtDNA found possible lineages of several cryptic species, but did not support the phylogenetic relationships of some groups. Phylogenetic analyses based on SNP resulted in the same topology as mtDNA, with some exceptions, and clarified the phylogenetic relationships among all lineages. Genome-wide analyses successfully estimated taxonomic positions of several lineages that could not be resolved in mtDNA analyses.

To elucidate the control mechanism of tail resorption during Xenopus metamorphosis, the expression of mfge8, a macrophage-apoptotic cell bridging molecule that promotes phagocytosis in mammals, was examined. In both Xenopus tropicalis and Xenopus laevis, the mfge8 expression in the tail increased significantly during metamorphosis, reaching its peak at the metamorphic climax, when the tail shortens rapidly. This finding suggests that the up-regulation of mfge8 at metamorphic climax is involved in the clearance of apoptotic tail muscles. To investigate the significance of mfge8 up-regulation, mfge8-deficient X. tropicalis tadpoles were generated using the CRISPR/Cas9 method, and the effects of mfge8-deletion were examined. Delayed tail resorption process was observed in the mfge8-deficient mutants (from 9.8 days [wild type] to 13.2 days [F2 mutant]), suggesting that elevated mfge8 expression during the metamorphic climax contributes to the tail resorption.

Anemonefish have a characteristic vertical white barred color pattern on an orange background made by a specific distribution of three types of pigment cells: melanophores, xanthophores, and iridophores. This color pattern is an interesting alternative model to zebrafish to understand the cellular and molecular basis of complex color pattern formation. Using transmission electron microscopic observations, we have investigated the pigment cell composition in the skin of the anemonefish Amphiprion ocellaris and found that: 1) white skin comprises iridophores and isolated melanophores; 2) orange skin contains xanthophores and scattered melanophores; and 3) black skin encompasses melanophores only. All three pigment cells can be found in the dermis. Iridophores are also present in the hypodermis, but general cell morphology differs depending on the dermal layer, distinguishing them into S-type and L-type iridophores. While melanophores can mix with xanthophores and iridophores, xanthophores and iridophores are not in direct physical contact, always being separated by melanophores. Anemonefish with differing color patterns than A. ocellaris, either color mutants or other anemonefish species, possess different pigment cell distribution and organization reflecting their respective colors. Our analysis provides key data to inform on the mechanism generating the diversity of color patterns present in anemonefishes.

Many cnidarian animals possess multiple opsins, including a type known as cnidopsin, which is found throughout the phylum Cnidaria and is divided into several subgroups. Previous studies have suggested that cnidopsins from jellyfish and coral can light-dependently elevate intracellular cAMP levels, likely via activation of Gs-type G protein in cultured cells. However, their spectroscopic properties remain largely unclear, with the exception of jellyfish opsins. We recently identified eight cnidopsins from the reef-building coral Acropora tenuis and showed that they phylogenetically belong to different cnidopsin subgroups. Here, we spectroscopically analyzed one A. tenuis cnidopsin from each subgroup as a representative. We successfully obtained the absorption spectrum of one purified cnidopsin and found that it was blue-sensitive, with an absorption maximum at ∼460 nm. Blue light irradiation (460 nm) resulted in a red-shifted absorption spectrum, while subsequent irradiation with orange light (> 560 nm) caused a blue-shift. The difference spectra of after versus before repeated irradiation with alternating blue and orange light produced mirror images, indicating a bistable nature. We also successfully observed the absorption spectra of one of two other cnidopsins belonging to the same subgroup as the blue-sensitive A. tenuis cnidopsin. The spectral changes suggested that it was also a bistable opsin. These results suggest that these two coral cnidopsins, which belong to the same cnidopsin subgroup, are bistable-unlike jellyfish opsins, which belong to a different cnidopsin subgroup.

Rhabdocoel flatworms of the family Typhloplanidae are predominantly found in freshwater and limnoterrestrial environments, with only a few species inhabiting marine and brackish water ecosystems. In this study, a flatworm was discovered in moist soil containing nematodes in the Guizhou plateau of southwest China for the first time. A new species, Luticola nematophagus Zuo, gen. et sp. nov., belonging to a newly established genus, was described through morphological and phylogenetic analyses. The main distinguishing features of this new species include a rosette-shaped pharynx located at 1/2 of the body length, paired testes embedded in the vitellaria on either side of the pharynx, an independent copulatory bursa, and a short rod-like ascus. Additionally, a single gonopore is situated in the posterior 1/4 to 1/5 of the body length, with a distinct genito-bursal duct leading to the dorsal intestine. The new species was observed to prey on the soil nematode Meloidogyne incognita (Kofoid and White, 1919). Experiments demonstrated that the flatworms could reproduce normally over an extended period when fed on M. incognita. Isolated cultured flatworms can produce offspring, indicating their capability of self-fertilization. The findings of this study are anticipated to offer a novel solution for the biological control of agricultural soil nematodes.

Symbiosis is a key driver of evolution in life-history traits and reproductive strategies. Some symbiotic microorganisms manipulate host reproduction to enhance their own transmission, a phenomenon well studied in insects but less understood in crustaceans. Among these microorganisms, Cardinium manipulates host reproductive systems, such as parthenogenesis, cytoplasmic incompatibility, and male killing in arthropods. However, its role in ostracods, small bivalve-shelled crustaceans, remains unclear. Some ostracod species reproduce via parthenogenesis, and high Cardinium infection rates in these lineages suggest a potential link between the symbiont and asexual reproduction. To investigate this relationship, we examined Cardinium localization in the parthenogenetic ostracod Heterocypris spadix from Japan. Using tissue clearing and fluorescence in situ hybridization (FISH), we visualized Cardinium within the ovaries. FISH observations revealed a widespread infection across the germarium, nurse cells, and oocytes. In early-stage oocytes, bacteria were evenly dispersed throughout the cytoplasm, whereas in more-developed oocytes, they clustered around the nucleus. Additionally, Cardinium was also detected in the hepatopancreas, indicating infection of both the reproductive and digestive systems. The presence of Cardinium in host reproductive structures, particularly the germarium, nurse cells, and developing oocytes, suggests its role in reproductive manipulation. To our knowledge, this study provides the first detailed localization of Cardinium in ostracods, reinforcing its potential influence on reproduction. Future research using antibiotics and genomic analysis will be crucial to confirm Cardinium's role in parthenogenesis induction.

Three non-encysted digenean metacercariae were found parasitic in the mesoglea of two of 13 individuals of the staurozoan cnidarian Haliclystus tenuis Kishinouye, 1910 from Yoichi, Hokkaido, Japan. The metacercariae comprised two morphospecies (one oval, the other elongate), for which the gross morphology is described. Partial sequences of the 18S and 28S rRNA genes and the internal transcribed spacer 2 region were determined for both species, and a partial sequence of the cytochrome c oxidase subunit I gene was determined for the oval species. Molecular phylogenetic analyses revealed both digeneans to be in the family Lepocreadiidae, a taxon not previously reported from staurozoans. The oval species was a member of the "Diploproctodaeum Clade." The elongate species was identified as Prodistomum orientale (Layman, 1930), known to use marine fishes in the genus Scomber Linnaeus, 1758 as definitive hosts. Second intermediate hosts of P. orientale known around Australia include five hydrozoan, one scyphozoan (Cnidaria), and one ctenophoran species. This is the first information on a second intermediate host from Japan; however, we cannot rule out the possibility that staurozoans may also be dead-end hosts. Including an opecoelid species previously reported, three digenean species in two families are now known from a single staurozoan species in the small region comprising the northwestern coast of Hokkaido. Future surveys for parasites in other staurozoan species and regions will likely detect additional digeneans and other parasite groups utilizing staurozoans.

An understanding of the food web in forest ecosystems is essential to ensuring that society lives in harmony with nature; however, this can be challenging in areas mainly composed of forest environments, such as in the Japanese Archipelago. Examining fecal samples collected from the forest edge can aid in determining the ecological roles of host species. In this study, a DNA barcoding method using original primers was applied to identify the carnivoran host species from fecal samples. DNA metabarcoding using ITS2 and COI markers was then conducted to elucidate the plant and invertebrate diets of the Japanese marten, Martes melampus (Carnivora, Mustelidae). The dietary analyses revealed that M. melampus consumed a diverse array of plants and animals. Most of the consumed plant species were fresh fruits, reflecting the fruiting season of the detected plants. This implies a role for M. melampus in seed dispersal and thus in forest maintenance. Considering the activity seasons, we also found that various adult-stage insects (beetles, cicadas, sphinx moths, and grasshoppers) contributed to the marten's diet, together with invertebrates (earthworms, etc.), which are easily digested and therefore difficult to detect through traditional methods. Although the COI marker used was designed for invertebrate species, one bird species, the brown-eared bulbul, Microscelis amaurotis, was found to make up a small part of the winter to early spring diet. These results show that, while M. melampus mainly consumes seasonal fruits, it can adapt its diet in response to environmental changes, such as by including invertebrates and small vertebrates.

Copy number variation (CNV) in gene loci in animals can be driven by adaption to the environment. The relationship between CNV in genes for amylase (AMY), which hydrolyzes starch, and dietary adaptation has been well studied. Copy number (CN) of AMY is higher in human populations with high-starch diets, compared with those with low-starch diets. Although CNV in AMY has been reported in humans and some domestic animals, there have been few studies of animals in the wild. The brown bear (Ursus arctos), widespread in the Northern Hemisphere, shows large dietary variation among individuals and groups. Brown bear population genetic structures are associated with the dispersal history due to climate change over the past few tens of thousands of years, and this together with dietary variation should have led to CNV in AMY. In this study, we investigated CNV in AMY in brown bears worldwide by using whole genome sequencing data. We detected AMY CNV among regional groups. AMY CN was similar among brown bears in geographically proximate populations, such as between Hokkaido (Japan) and East Asia, and between the North America mainland and the ABC islands. CNs were smaller in bears from East Asia, including Hokkaido, compared to those from other regions across brown bears' distribution. Our results suggest that CNs of AMY reflect the population demographic history of brown bears after the Last Glacial Maximum.

Snails of the family Eulimidae are parasites of echinoderms in all five extant classes. Despite long years of taxonomic research on Eulimidae in Japan, their local species richness remains to be investigated, and few studies have focused on a eulimid fauna of a certain echinoderm taxon, even if it is a common species. Here, we conducted a comprehensive sampling of Melanella species parasitizing the black sea cucumber Holothuria leucospilota in Shirahama, Wakayama, central Japan. The data used in this study were partly obtained during a summer education program of the Seto Marine Biological Laboratory, Kyoto University. Melanella kuronamako and M. spina parasitized the external surface, and two unidentified species were found inside the host's body cavity. This study represents the first record of M. spina in Japanese waters and eulimids exploiting the internal habitat of H. leucospilota. Morphological and molecular comparisons between the present four species and other Japanese Melanella specimens suggested that they generally exhibit wide geographic distributions and low host specificity. Additionally, the two species from the body cavity were probably seldom observed in central Japan, as inferred from the accumulated results of the dissection of H. leucospilota through a long-running, annual education program at Shirahama.