Takayoshi Ueda

Genetic Introgression by the Rose Bitterling, Rhodeus ocellatus ocellatus, into the Japanese Rose Bitterling, R. o. kurumeus (Teleostei: Cyprinidae)

Abstract The Japanese rose bitterling, Rhodeus ocellatus kurumeus, is an endangered cyprinid species. The main reason of drastic diminution of R. o. kurumeus has been suggested to be due to hybridization between this subspecies and R. o. ocellatus introduced from China. Both RFLP analysis of mitochondrial DNA and RAPD-PCR analysis of genomic DNA were performed to elucidate the genetic introgression of R. o. ocellatus into R. o. kurumeus. The two subspecies were distinguished in the D-loop region of mtDNA by six restriction endonucleases. Rhodeus o. kurumeus had eleven subspecies-specific RAPD markers and R. o. ocellatus had two. Except some R. o. kurumeus populations, most of the populations of R. ocellatus in Japan were hybrids, equipped with subspecies-specific RAPD markers for the two subspecies, respectively. The genetic constitution of these markers in hybrids, however, greatly differed among populations. The R. o. ocellatus mtDNA was predominantly observed in hybrid populations, except two populations with mtDNAs of the two subspecies. Judging from the genetic dominance of morphological and physiological characters of R. o. ocellatus against R. o. kurumeus, hybrids probably have the same ecological dominance as R. o. ocellatus against R. o. kurumeus. Therefore, it is considered that R. o. kurumeus not only has its genetic property spoiled by hybridization with R. o. ocellatus, but also is expelled by R. o. ocellatus and hybrids. The replacement of mtDNA and genomes of R. o. kurumeus with those of R. o. ocellatus in hybridization might be accelerated by the backcross between hybrids and R. o. ocellatus.

FISH-mapping of 18S ribosomal RNA genes and telomeric sequences in the Japanese bitterlings Rhodeus ocellatus kurumeus and Tanakia limbata (Pisces, Cyprinidae) reveals significant cytogenetic differences in morphologically similar karyotypes.

The Japanese rose bitterling, Rhodeus ocellatus kurumeus, and the oily bitterling, Tanakia limbata, were cytogenetically studied by silver (Ag)- and chromomycin A3 (CMA3)-staining, by C-banding and by mapping of the 18S ribosomal genes and of the (TTAGGG)n telomeric sequence. These two representative species of related genera of the subfamily Acheilognathinae show very similar chromosome complements. Nevertheless, significant differences in the chromosomal distribution of nucleolus organizer regions (NORs) and interstitial telomeric sequences were observed. Whereas R. ocellatus kurumeus shows a single NOR-bearing chromosome pair, T. limbata is characterized by a higher number of variable NORs. Multiple telomeric sequence sites were found at the pericentromeric regions of several chromosomes in the rose bitterling. No telomeric sequence sites were detected near centromeres, but they were found to be scattered along the NORs in the oily bitterling. Two karyoevolutive trends might have been identified in the subfamily.

Flexibility on the karyotype evolution in bitterlings (Pisces, Cyprinidae).

In bitterlings (Acheilognathinae) C- and Ag-banding karyotypes of 6 species-subspecies collected in China and South Korea were analyzed. The chromosomal constitution of 2n = 46 (4 SM + 42 ST) in Rhodeus atremius fangi was quite different from that of 2n = 48 (8 M + 20 SM + 20 ST) in other species-subspecies in Rhodeus. It was concluded from the analysis of banded chromosomes that the increase in number of ST during the karyotype change from 2n = 48 to 2n = 46 was achieved by a series of pericentric inversions from 24 M-SM to 24 ST, and the decrease in the diploid number was caused by an additional tandem fusion of 4 ST chromosomes, forming a new ST pair in the 2n = 46 karyotype. The karyotype of Tanakia koreensis, T. signifer, and Acheilognathus macropterus is 2n = 48 (8 M + 20 SM + 20 ST), 2n = 48 (8 M + 20 SM + 14–16 ST + 4–6 A), 2n = 44 (14 M + 16 SM + 14 ST), respectively. In R. ocellatus ocellatus, T. koreensis, T. signifer and A. macropterus, karyotype changes from 2n = 48 to 2n = 44 due to centric fusion and inversion have also been estimated. It was suggested that C-banding heterochromatin was greatly concerned with the karyotype evolution in bitterlings.

Phylogenetic Relationships of Bitterling Fishes (Teleostei: Cypriniformes: Acheilognathinae), Inferred from Mitochondrial Cytochrome b Sequences

Bitterling (Teleostei: Acheilognathinae) are small cyprinid fishes with a discrete distribution in East Asia and Europe. We used a complete mitochondrial cytochrome b sequence (1141 bp) from 49 species or subspecies in three genera (Tanakia, Rhodeus, and Acheilognathus), sampled across the major part of their distribution, to elucidate their phylogeny and biogeography, focusing particularly on their origin and dispersal. Based on high support value, the monophyletic Acheilognathinae separated into two major clades, Acheilognathus and Tanakia-Rhodeus. In the latter clade, the monophyly of Rhodeus was poorly supported, though it was topologically nested in Tanakia. On the basis of molecular-clock calibration, both clades diverged in the middle Miocene, with Tanakia-Rhodeus diverging slightly earlier than Acheilognathus. The Tanakia-Rhodeus clade expanded its distribution westward from the Far East, eventually reaching Europe, while Acheilognathus dispersed in the temperate regions of East Asia. A feature common to both clades is that most extant species, including Japanese endemics, appeared by the end of the Pliocene, corresponding with the present delineation of the Japanese archipelago. Autumn-spawning species with an embryonic diapause, unique to bitterling among cyprinid fishes, formed two distinct lineages (barbatulusrhombeus and longipinnis-typus) within Acheilognathus. The estimated time of divergence of the two lineages was approximately from the late Pliocene, a period characterized by glaciations. The timing of divergence suggests that the shift of spawning from spring to autumn, coupled with embryonic diapause, convergently emerged twice in the evolution of bitterling, possibly as an adaptation to the climate of the late Pliocene.

Ag-NOR variation in chromosomes of Chinese bitterlings,Rhodeus lighti andTanakia himantegus (Cypriniformes, Cyprinidae)

:Department of Biology Faculty of Education, Utsunomiya University, 350 Mine, Utsunomiya 321, Japan (e-mail: ueda@ce.utsunomiya-u.ac.jp) :Natural History Museum and Institute, Chiba, 955-2 Aoba-cho, Chuo-ku, Chiba 260. Japan 3Kannonzaki Nature Museum, 4-1120 Kamoi, Yokosuka 239, Japan 4Department of Biological Sciences. Graduate School of Science, University of To,o. 7-3--1 Hongo, Bunkyo-ku, To~o 113, Japan SIchthyological Division. Shanghai Fisheries University. 334 Jun Gong Road. Shanghai 200090, P. R. China

Rhodeus pseudosericeus sp. nov., a new bitterling from South Korea (Cyprinidae, Acheilognathinae)

Abstract A new bitterling, Rhodeus pseudosericeus sp. nov., is described on the basis of 31 specimens from five localities included in the Namhan River system, South Korea. The new species is distinguished from other Rhodeus species by the following combination of characters: branched dorsal fin rays 9–10 (mode 9); branched anal fin rays 9–11 (mode 10); longest simple ray of dorsal fin strong and stiff, distally segmented; pelvic fin rays i, 6–7; iris of males blackish; dorsal and anal fins of males grayish in breeding season; karyotype with 2n = 48 (8m + 20sm + 20st). Rhodeus pseudosericeus sp. nov. is similar to Rhodeus sericeus sericeus in the number of pelvic fin and branched dorsal fin rays and the melanophores present on the dorsal fin membrane, but differs from the latter in having a greater body depth, more branched anal fin rays, fewer vertebrae, a lower number of scales in the lateral series, and differing male nuptial coloration.

Karyological study of the dolly vardenSalvelinus malma from Alaska

The karyotype of the dolly vardenSalvelinus malma from Alaska was analysed. A pair of huge acrocentrics, which could have resulted from either tandem fusion or centric fusion followed by pericentric inversion, was observed. Ag-NORs were observed at the terminal regions of the second largest chromosome pair, and individual size-differences in Ag-NORs and in chromosomes with Ag-bands were found. From a comparison of the karyotypes of the dolly varden from Alaska and Hokkaido (Japan), karyotype differentiation by pericentric inversion and translocation was discussed.