Akihisa Iwata

Evolutionary aspects of gobioid fishes based upon a phylogenetic analysis of mitochondrial cytochrome b genes

The Gobioidei is a large suborder in the order Perciformes and consists of more than 2000 species belonging to about 270 genera. The vast number of species and their morphological specialization adapted to diverse habits and habitats makes the classification of the gobioid fishes very difficult.A comprehensive estimation of the evolutionary scenario of all gobioid fishes using only morphological information is difficult for two major reasons: first, in addition to wide ecological diversification, there is a trend towards specialization and degeneration of morphological characters among these species; second, an appropriate outgroup of gobioid fishes has not been recognized. Based upon nucleotide sequence comparisons of gobioid mitochondrial cytochrome b genes, we established the phylogenetic relationships of their differentiation into many groups of morphological and ecological diversity. The phylogenetic trees obtained show that most species examined have diverged from each other almost simultaneously or during an extremely short period of time.

Genetic divergence, variation and zoogeography of a freshwater goby, Odontobutis obscura

Gene products of 18 allozyme loci from 995 Japanese donko (Odontobutis obscura, a freshwater goby) from 80 localities, were analyzed so as to determine the extent of genetic divergence and variation. The zoogeography of donko is discussed based on cluster and cladistic analyses. The first colonization of Japan by donko is thought to have occurred directly from China to the Second Setouchi Basin, a large freshwater system that existed in the Miocene and Pliocene epochs. Japanese donko subsequently formed five geographic groups:viz. West Kyushu, West Seto, East Seto, Sanin·Biwa·Ise and Hikimi Groups. The West and East Seto Groups apparently occurred in the West and East Setouchi Paleorivers, respectively, that flowed during the glacial age. Similarly, the Ariake Paleoriver might have included the West Kyushu Group. The Sanin·Biwa·Ise Group is heterogeneous, each population in the group being thought to have been isolated for a longer time than populations of the other groups, except the Hikimi Group. the last-mentioned, probably a relatively specialized group, has also been isolated for a long time. Some population invasions from the West and East Seto Groups toward the rivers of the San-in·Biwa·Ise and Hikimi Groups, probably caused by relatively recent piracies or spill-over between rivers, are recognized.

Occurrence of larval Pacific lamprey Entosphenus tridentatus from Japan, detected by random amplified polymorphic DNA (RAPD) analysis

Species identifications of the Pacific lamprey Entosphenus tridentatus from four other Japanese lampreys, Lethenteron japonicum, L. kessleri, and two undescribed Lethenteron species (L. sp. N and L. sp. S), were carried out on the basis of random amplified polymorphic DNA (RAPD) using the polymerase chain reaction (PCR) method. Of 65 RAPD loci, seven loci possessing species-specific fragments were obtained for E. tridentatus. Based on these RAPD loci, four larval individuals of E. tridentatus from the Naka River (eastern Honshu Island, Japan) were recognized in 2001 and 2002. The existence of larval individuals of E. tridentatus, as well as spawning adults previously reported from the same river, indicated the possibility of residence in that species.

Developmental Characteristics of a Freshwater Goby, Micropercops swinhonis, from Korea

Abstract The embryonic and larval development of a freshwater goby, Micropercops swinhonis (Odontobutidae; Gobioidei), from Korea are described. One female spawned several times from mid-April to early July. About 100 to 500 eggs per batch were laid on the under surface of the nest guarded by a male. Eggs hatched 12 days after spawning. Larvae, about 3.7 mm in total length (TL) just after hatching, passed the exogenous feeding larval stage, and reached the juvenile stage of about 16 mm TL in about one month. The developmental process of M. swinhonis is quite different from that of the fluvial Odontobutis of the same family, which skips the exogenous feeding larval stage, but is rather similar to that of amphidromous Gobiidae. On the other hand, the left and right pelvic fin buds of M. swinhonis appear distant from each other as in Odontobutis, rather than Gobiidae.

A river metapopulation structure of a Japanese freshwater goby, Odontobutis obscura, deduced from allozyme genetic indices

Gene products of 18 allozyme loci from 1268 individuals of a Japanese freshwater goby called donko, Odontobutis obscura (Odontobutidae; Gobioidei), from 33 localities in the Koya River, Yamaguchi Prefecture, Japan, were investigated to determine the extent of genetic divergence and gene flow within a river metapopulation. Genetic indices including GST(mean FST 0.182), FIT(mean 0.192) and D(mean 0.015) indicated a considerable divergence of local populations in the river. The genetic distance (D) and channel distance between pairs of populations did not show a good correlation, and geographical neighbors were not always genetic neighbors. Therefore, the genetic divergence of populations is attributable to independent genetic drift with restricted gene flow among populations. The agricultural dams and weirs constructed across the river must be responsible for the restricted gene flow. The metapopulation structure of O. obscura in the Koya River may be barely sustained by one-way gene flow only from the upper to the lower populations. An occasional artificial transplantation of some individuals from the lower to the upper populations may be one alternative to maintain a river metapopulation structure safely.

Histological Comparisons of Intestines in Parasitic and Nonparasitic Lampreys, with Reference to the Speciation Hypothesis

Abstract Histological comparisons of intestinal internal structures were made for the monophyletic lamprey group comprising parasitic Lethenteron japonicum, and nonparasitic L. kessleri and the northern form of L. reissneri, in order to verify the speciation hypothesis that the nonparasitic species have been derived from a congeneric parasitic species. In the larval stage of each species, the mucosal epithelial cells were regularly arranged around an inner layer of intestine, including the typhlosole. At the metamorphosed stage, L. japonicum possessed functional mucosal folds, reflecting an adaptive change for parasitic feeding after metamorphosis. The two nonparasitic species, in which feedings are absent after metamorphosis, also exhibited mucosal folds albeit in a degenerative condition, indicating the likely presence of functional or at least rudimentary mucosal folds in an ancestral parasitic species. This finding supports a previously advocated direction of speciation in lamprey satellite species, namely nonparasitic L. kessleri and the northern form of L. reissneri speciated from ancestral stocks of parasitic L. japonicum.

Embryonic development of the Pacific lamprey, Entosphenus tridentatus.

Abstract Embryonic development of the Pacific lamprey, Entosphenus tridentatus, from Japan is described. Egg sizes averaged 1.249 mm (longest axis) and 1.145 mm (shortest axis), the time required for hatching being 11 days at 18°C, shorter than previously reported for a lower water temperature (19 days at 15°C). Early development in E. tridentatus proceeded at a similar rate to that in other lampreys, in spite of different rearing water temperatures for the latter, indicating possible specific differences in basic developmental rates.

Odontobutis hikimius n. sp.: A New Freshwater Goby from Japan, with a Key to Species of the Genus

Abstract The freshwater goby, Odontobutis hikimius n. sp., is described based on specimens collected from Shimane Prefecture, Japan. The species is unique among Odontobutis in having a connection between the transverse and longitudinal sensory papillae rows on the opercle. It is also distinguishable from congeners by the following combination of characteristics: only a short sensory canal present posterodorsally to eye, lateral scale rows 38–49. Diagnosis of the genus Odontobutis is revised and a key to the seven known species is provided.

Tomiyamichthys alleni: A New Species of Gobiidae from Japan and Indonesia

Abstract Tomiyamichthys alleni is described from eight specimens from Japan and Indonesia. The species is distinguishable from the only congener T. oni and closely related genus Flabelligobius in having the following combination of characters: occipital region narrow, equal to interorbital width, separated from upper margin of cheek by an irregularly curved groove; anterior oculoscapular canal with pores B′, C(S), D(S), F, and G′ (F located in groove between occipital region and cheek); first dorsal fin triangular, first and second spines elongated and filamentous; second dorsal and anal fin soft rays 10. The species occurs between 15 m and 40 m on fine sandy bottoms and is associated with the shrimp Alpheus randalli.

Isolation and characterization of 39 microsatellite loci in the endangered Japanese loach Leptobotia curta.

A microsatellite‐enriched genomic library was obtained for the endangered Japanese loach Leptobotia curta, and 39 dinucleotide markers were successfully isolated and characterized. These markers had between one and nine alleles, with expected heterozygosity ranging from 0 to 0.839, in a population from the Lake Biwa–Yodo River system of Japan. Linkage equilibrium was observed in most loci, and only one locus showed significant deviation from Hardy–Weinberg equilibrium. These microsatellite markers will be useful for genetic diversity studies of wild and captive L. curta populations.