臺灣鬚鱲 (鯉形目: 鯉科) 的親緣地理及形態變異之研究

Abstract

Abstract In the present study, I employed the mitochondrial cytochrome b (mtDNA cyt b) gene as a molecular marker to investigate the phylogeographical patterns and genetic diversity of Candidia barbatus in Taiwan. Integrating the geohistorical events with genetic differentiation within C. barbatus can provide an appropriate model to reconstruct the originating pattern of the primary freshwater ichthyofauna of Taiwan. MtDNA cyt b sequences of 1140 bp in length were scored from 337 specimens collected from 26 localities covering 21 rivers in western Taiwan from among which 23 different haplotypes were identified. The maximum parsimony (MP), maximum likelihood (ML), neighbor-joining (NJ), and Bayesian inference (BI) revealed similar mtDNA cyt b genealogies designated as Candidia lineages A~F. The deep genetic divergences occurring among lineages A~F suggest that cryptic species may exist within C. barbatus. The approximate molecular dating among lineages A~F indicate differentiations between them occurring earlier on the Asian mainland with subsequent multiple invasions toward Taiwan via a land bridge in the shallow-water zone of the Taiwan Strait during several glacial periods of the Pleistocene (1.6~0.02 million years). Lineage F was probable the first settler of this kind of dispersal toward the southernmost part of Taiwan as evidenced by its possession of more haplotypes. The low genetic variability within populations resulted in an extremely high genetic divergence between populations and between geographical regions. Moreover, this was associated with a relatively low gene flow among the 26 populations (average Fst = 0.76) or even within the same drainage (average Fst = 0.44 in the Danshui River drainage; average Fst = 0.93 in the Kaoping River drainage). AMOVA could subdivide the likely population structure of C. barbatus into northern, central, southern (excluding the Ailiao tributary), and Pingtung (including the Ailiao tributary) groups. Pore lateral line scales and transverse scale rows can be used to separate C. barbatus into two morphs: the northern type designated as Candidia A~C, with respective scale formulae of 54-56 and 11-12, and the southern type of Candidia D~F with formulae of 50-52 and 9-10. The northern type is identical with that shown in the original description. In addition to scale counts, other morphological variants could not be used to distinguish Candidia lineages A~F. A more-detailed study of the morphology is necessary, and the“concept of reproductive isolation”should be borne in mind.