Two morphologically similar species of gizzard shad, Nematalosa japonica Regan and N. come (Richardson), sympatrically distributed off Okinawa Island, Japan, were examined using an allozyme locus (SOD*) and two nuclear polymerase chain reaction (PCR)-based DNA markers (ITS-1 and CaM), which provided diagnostic identification of each species. In addition, a multiplex PCR-based mitochondrial DNA (mtDNA) marker (16S) was used to characterize the distribution of mtDNA haplotypes among specimens. The species composition of sympatric and allopatric population samples from Tungkang, southern Taiwan, to Okinawa and the Shikoku Islands, Japan, were also examined. Gizzard shad with hybrid genotypes were detected in three populations from Okinawa Island, with hybrid frequency ranging from 1 to 67%. A backcross level of 2% was detected in the dominant hybrid frequencies of one population sample only. Morphological examination of hybrids showed intermediate forms, with hybrid indices of three meristic characters falling between those of the parental species (range 39-53; mean 45). Although principal component analysis showed differences between N. japonica and N. come based on the first principal component scores, hybrids were difficult to identify. Accordingly, satisfactory identification of species and hybrids could be achieved only using genetic tools. We also discuss the cause of hybridization and its relationship with recently conducted reclamation on Okinawa Island.
Scanning electron microscopy (SEM) was used to compare the micromorphology of the male first gonopods (G1) of 22 species of common Taiwanese potamid crabs of the genus Geothelphusa Stimpson, 1858. Electron micrographs were taken from dorsal, lateral, and apical views of the terminal segment, the sub-terminal segment, and the synovial membrane; and a total of five measurements was taken, i.e., synovial membrane length (SML) and width (SMW), sub-terminal segment width (SW), and terminal segment length (TSL) and width (TSW). In addition, the diameter of the apical opening of the ejaculatory canal (AD), the number of scale rings, the setal type, and the direction of the curve of the tip of the terminal segment were recorded. In adult female crabs, the mean of the diameter of the gonopores and the distance between these were also measured. The scanning electron micrographs of the G1 are all shown in the present paper. RÉSUMÉLa microscopie électronique à balayage (SEM) a été utilisée pour comparer la micromorphologie des premiers gonopodes mâles (G1) de 22 espèces communes de crabes Potamidae de Taiwan du genre Geothelphusa Stimpson, 1858. Les microphotographies du segment terminal, du segment subterminal et de la membrane synoviale ont été prises en vues dorsales, latérales et apicales; un total de cinq mesures a été effectué, soient la longueur de la membrane synoviale (SML) et sa largeur (SMW), la largeur du segment sub-terminal (SW), ainsi que la longueur du segment terminal (TSL) et sa largeur (TSW). De plus, le diamètre de l'ouverture apicale du canal éjaculateur (AD), le nombre des anneaux d'écailles, le type de soies et la direction de la courbe de l'extrémité du segment terminal ont été examinés. Chez les crabes adultes femelles, la moyenne du diamètre des gonopores et la distance entre ces derniers ont été également mesurées. Les microphotographies à balayage des G1 sont toutes présentées dans le présent article.
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