Mitochondrial DNA analysis of the genetic relationships among populations of scad mackerel (Decapterus macarellus, D-macrosoma, and D-russelli) in South-East Asia

The genetic relationships among South-East Asian populations of the scad ma ckerels Decapterus macarellus, D. macrosoma and D. russelli (Pisces: Carang idae) were investigated. In 1995 and 1996, 216 fish were sampled in seven l ocalities spanning the seas of Indonesia and were examined for restriction- site polymorphisms using ten restriction enzymes for the mitochondrial (mt) DNA control region, amplified by the polymerase chain-reaction. The inferr ed phylogeny of haplotypes led to the recognition of three distinct mitocho ndrial lineages or phylads consistent with the distinctions of current taxo nomy. All 15 mtDNA hap lotypes found in D. macarellus and all 9 haplotypes found in D. macarellus were arranged as star-like clusters, suggesting rece nt evolutionary history. In contrast, the phylad formed by 6 haplotypes in D. russelli from the Sulawesi Sea exhibited diffuse topology, suggesting th at ancestral lineages of this species have been retained to the present. Av erage nucleotide-divergence estimates between haplotypes of different phyla ds were between 0.042 and 0.135, suggesting ancient separation, in consiste ncy with published allozyme data. High levels of haplotype diversity, but n o geographical heterogeneity, was detected within D. macarellus from the Mo lucca Sea and the Panda Sea. Populations of D. macrosoma exhibited both sig nificant differences between adjacent regions (Sunda Strait and Java Sea), and broadscale genetic homogeneity from the South China Sea to the Sulawesi Sea via the Java Sea and Makassar Strait. The geographic isolation of the D. macrosoma population sampled in the Sunda Strait suggests that this regi on constitute a sharp transition zone between the Indian Ocean-and the Sund a Shelf. Near-monomorphism of haplotypes and low nucleotide diversity (d(x) ) were observed in the samples of D. macrosoma from the continental shelf ( haplotype-diversity estimates, h, = 0.00 to 0.25 +/- 0.08 and d(x) = 0.000 to 0.002). This was in contrast to the comparatively high haplotype and nuc leotide diversities observed in other pelagic fish species including D. mac arellus (h = 0.82 +/- 0.05, d(x) = 0.012 to. 0.015) and D. russelli (h = 0. 63 +/- 0.12, d(x) = 0.016), and in the oceanic D. macrosoma population:samp led in the Sunda Strait (I? = 0.67 +/- 0.31, d(x) = 0.005). We hypothesise that this may be the consequence Of recent and perhaps repeated bottleneck events that have affected the D. macrosoma population sampled on the contin ental shelf.