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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Keywords
PHYLOGEOGRAPHY , GENETIC VARIATION