Zoological Science最新文献

Rhizocephalan barnacles (Thecostraca: Cirripedia) are parasitic crustaceans that lack appendages, segmentation, and a digestive system in adults, while instead infiltrating their hosts with a nutrient-absorbing system of rootlets. Sacculinids, belonging to the Rhizocephala order, are known for their various parasitization-induced effects on their decapod hosts, such as parasitic castration, reduction in the growth of secondary sexual characteristics, feminization of male crabs, and alteration of host behavior. In this study, we conducted field surveys in Japan at Manazuru Town (Kanagawa) on the Pacific coast, and on Sado Island and Noto Peninsula on the Sea of Japan side, and found that sacculinid-parasite-ratios on the grapsid crab Pachygrapsus crassipes were particularly high on the Sea of Japan coast. Molecular phylogenetic analysis revealed that the Manazuru population forms a single clade with Sacculina yatsui, and both Sado and Noto populations form a single clade with S. confragosa. We further demonstrated that external morphologies of male P. crassipes parasitized by sacculinids were changed to female phenotypes. This host-parasite interaction will be a useful model for understanding molecular mechanisms underlying rhizocephalan-driven morphological and behavioral feminization and castration.

Salmincola californiensis is a parasitic copepod of freshwater salmonids in the North Pacific rim countries. Sixteen adult females of the species were found alive on the gills of an ocean-age 4, maturing steelhead trout, Oncorhynchus mykiss, caught in offshore waters (50°30'N, 179°30'W) of the North Pacific Ocean in July 1997. This is the first evidence of live individuals of S. californiensis from ocean-migrating salmonids. When found, copepods were attached to the distal ends of gill filaments, and their bodies were observed to be slowly moving in Petri dishes with seawater. Ocean-migrating steelhead trout comprise individuals originating from western Kamchatka (Russia) and western North America. Based on the date and catch location of the infected fish, it is inferred that it originated from western North America, where it acquired S. californiensis infection in fresh water. As this fish spent about 4 years in the ocean, the copepods likely survived the same period at sea. However, if the fish was a kelt, the survival period of the copepods in the ocean may be shorter than four years. To confirm identification of the copepods, adult females of S. californiensis are briefly described using the specimens collected from the fish.

Eunice aphroditois (Pallas, 1788) is a large polychaete worm (up to 3 m in length) and the type species of the genus. In Japan, a similar but potentially different species, Eunice cf. aphroditois, is distributed mainly in the rocky shores of the temperate and warm Pacific coasts. Juveniles and adults were suggested to be distinguished by their body color. The juvenile form was previously regarded as distinct species, Eunice flavopicta Izuka, 1912 and Eunice ovalifera Fauvel, 1936, although they are now considered synonymous with E. aphroditois. In this study, we revisited the validity of the present taxonomy based on morphological observations including SEM and microCT, and three molecular markers (cytochrome c oxidase subunit I [COI], 16S rRNA, and histone H3 genes) and investigated the phylogenetic position of E. cf. aphroditois in the family Eunicidae using the combined dataset of three genes (COI + 16S rRNA + 18S rRNA). The adult and juvenile forms were different in body size, color, the distribution of the branchiae and subacicular hooks, and maxillae shape, but not in other characteristics. One individual showed an intermediate body color between the two forms. The adult and juvenile forms shared major haplotypes and the maximum K2P genetic distance of COI was 1.7%, which can be considered within intraspecific variation. In the phylogenetic tree based on the combined gene dataset, E. cf. aphroditois was closely related to Eunice roussaei Quatrefages, 1866 and Eunice cf. violaceomaculata Ehlers, 1887, which are large species from the Mediterranean Sea and the Caribbean Sea, respectively.

The circadian system of many multicellular organisms consists of a hierarchical structure of multiple clocks, including central and peripheral clocks. The temporal structure has been analyzed in terms of central-to-peripheral regulation but rarely from the opposite perspective. In this study, the potential control of the central clock in the optic lobe by the peripheral clock in the compound eye was investigated in the cricket Gryllus bimaculatus. The locomotor activity rhythm of crickets in which one of the two bilateral optic lobe clocks was surgically removed was tested in constant darkness at three environmental temperatures (20°C, 25°C, and 30°C) and compared with that of crickets in which the optic nerve connecting between the compound eye and optic lobe of the intact side was also severed. When the optic nerve was severed at 30°C, the free-running period and its stability were significantly increased and decreased, respectively, compared to those of intact and sham-operated crickets, whereas at 20°C, only the free-running period was significantly lengthened, and at 25°C, no significant changes were observed in these parameters. At 30°C, the changes in these two parameters were reproduced when the anterior half of the compound eye was removed, while the removal of the posterior half induced period lengthening only. Together with previous data, these results suggest that the free-running period and stability of the locomotor rhythm are regulated through reciprocal coupling between the clocks in the compound eye and the optic lobe.

A new fish leech, Branchellion brevicaudatae sp. n., is described based on specimens parasitizing the gills of the short-tail stingray, Bathytoshia brevicaudata (Hutton, 1875), collected from Japanese waters. The new species can be distinguished from other congeners by having: i) pulsating vesicles emerging from posterior base of branchiae, one pair per somite; ii) dorsal white spots, not arranged in longitudinal row; and iii) blackish body. A phylogenetic tree based on partial sequences of the mitochondrial cytochrome c oxidase subunit I gene from the new species and other piscicolid worms showed that the new species is sister to Branchellion torpedinis Savigny, 1822. This is the first record of Branchellion Savigny, 1822 from Japanese waters.

Captive propagation and reintroduction are the major steps in the ex-situ conservation of locally extirpated endangered species in a historical region. In a species restoration project conducted in South Korea, we examined temporal changes in demographics and genetic diversity of oriental storks (Ciconia boyciana). Demographic and genetic data from 1996-2018 were analyzed for 80% of all captive and recently reintroduced individuals. Founder establishment and pair formation induced increases in population size and genetic diversity during the early stage of captive propagation. The degree of genetic diversity was found to become saturated and stable with long-term captive propagation. However, this might be a concern for future genetic diversity of both captive and reintroduced populations simultaneously due to the extraction of captive populations at the early stage of reintroduction. Our findings suggest that periodic evaluation of genetic diversity and selection for releasing individuals, using effective genetic markers, would assist in balancing the genetic diversity of the captive and reintroduced oriental storks at the early stage of reintroduction.

The fecal pellets of Marphysa sp. E sensu Abe et al. (2019) (Annelida, Eunicidae) living in the Yoro tidal flat (Ichihara, Chiba, Japan) contain high levels of polycyclic aromatic hydrocarbons (PAHs), and the concentrations rapidly decrease over time. To investigate the origin of the high-concentration PAHs in the fecal pellets and food sources of the worms, the PAH concentrations, carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N), total organic carbon, and total nitrogen for two types of sediment (sands and reduced muds), fecal pellets, and the body of the worms were determined. The PAH concentrations and chemical properties of the fecal pellets were similar to those of the reduced muds (20-30 cm sediment depth). The δ¹³C, δ¹⁵N, and C/N values of reduced muds were the same as the typical values of terrestrial C3 plants, suggesting that reduced muds were derived from terrestrial plants. These data indicated that the worms selectively take up reduced muds containing high levels of PAHs. The δ¹³C and δ¹⁵N values of the worm bodies indicated that the worms did not use the organic carbon derived from terrestrial C3 plants as primary nutrition. Taking into consideration their selective uptake of reduced muds, excretion, and subsequent rapid decrease of PAHs in the fecal pellets, the worms could contribute to the remediation of chemical pollutants in the tidal flat sediments.