PHYLOGEOGRAPHY AND GENETIC VARIATION OF THE BIGHEAD CATFISH, Clarias macrocephalus (GÜNTHER, 1864) FROM PENINSULAR MALAYSIA AND MEKONG RIVER BASIN BASED ON MITOCHONDRIAL AND MICROSATELLITE MARKERS

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Date
2014-08
Authors
ABDUL KADAR, NAZIA
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Abstract
Mitochondrial and microsatellite markers were utilised to investigate the genetic diversity and phylogenetic relationships among catfish, Clarias macrocephalus populations from Peninsular Malaysia and two Mekong River Basin regions, namely Cambodia and Vietnam. For mitochondrial analyses, 332 individuals from 19 populations were sequenced for Cytochrome b (609 bp) gene while 382 individuals from 19 populations were analysed for the D-loop (479 bp) gene. Both genes detected possible hybrids between C. macrocephalus and other species or presence of previously undocumented species. Further analyses on unambiguous C. macrocephalus sequences revealed 39 haplotypes for Cyt b gene and 47 haplotypes for D-loop sequences. Haplotype diversity ranged from h=0 to 0.908 ± 0.048 (Cyt b); h=0 to 0.892 ± 0.044 (D-loop) and nucleotide diversity ranged from π=0 to 0.008 ± 0.005 (Cyt b); h=0 to 0.012 ± 0.007 (D-loop). These values were highest in the Cambodian populations. Both genes revealed high gene flow especially between adjacent populations. However, D-loop gene demonstrated higher genetic structuring of populations within region compared to the slower evolving Cyt b gene. In the next phase of the study, eight polymorphic microsatellite markers for C. macrocephalus were developed using the modified selective hybridization method. These markers were further utilised to assess the genetic variation of 393 individuals of C. macrocephalus from 15 populations as well as cross-amplification in selected Clarias species. Most of the loci were highly polymorphic except for locus NCm-H2 that harboured low PIC value. Number of alleles in C. macrocephalus populations ranged from 36 to 111 alleles. Two populations were in HWE, two populations showed heterozygous excess while the rest showed homozygous excess due to null alleles in several loci and inbreeding in several populations. Low but highly significant pairwise FST values were obtained for all the populations compared to mitochondrial analyses that displayed several non-significant values. None of the populations showed evidence of bottlenecks. Apart from a few populations, moderate to high genetic variation were observed, where the Mekong River populations was the most diverse. Further analyses revealed two evolutionary units, which were Peninsular Malaysia and the Mekong River Basin. This study suggests that C. macrocephalus has originated from Indo-China possibly Cambodia before invading Peninsular Malaysia. Combination of mitochondrial and microsatellite markers has provided detailed information on the genetic variation and population structure of C. macrocephalus. This is important for selection of broodstocks for a breeding programme as well as conservation of wild populations.
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PHYLOGEOGRAPHY , GENETIC VARIATION
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