Genetic structure of Japanese threadfin bream, nemipterus japonicus (bloch, 1791) along the coast of Peninsular Malaysia
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Date
2009-10
Authors
Hong Chiun, Lim
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Abstract
Genetics and morphometric approaches were employed to assess the differentiation
among ten Nemipterus japonicus (Japanese threadfin bream) populations along the Coast of
Peninsular Malaysia A total of 278 samples were collected from eight West Coast of
Peninsular Malaysia populations as well as two from the East Coast. Genetic analysis of N.
japonicus populations was conducted based on partial mitochrondrial cytochrome b ( cyt b)
gene (982 bp) and the sequences were edited and aligned using the MEGA 4.0 program.
Values of genetic divergence (Kimura 2 parameter) among the ten populations ranged from
0.50% to 4.6% (average 1.4%). The constructed Neighbour Joining (NJ) and Maximum
Parsimony (MP) phylogenetic trees based on haplotypes showed similar topologies, with the
Kuala Besar population forming its own cluster. Structure analysis of the ten populations a
priori assigned into four regions was conducted based on AMOV A. The results revealed that
most of the variations occurred within populations with a fairly low but significant level of
regional differentiation (FsT = 0.070, p < 0.05, Fsc = 0.00, p = 0.520 and Fer= 0.070, p <
0.05). The p value after Bonferroni correction revealed that only pairwise FsT values
involving the Kuala Besar population with the others were significant. Further investigation
revealed that the N japonicus populations apart from Kuala Besar were relatively
homogeneous and the Kuala Besar population may be considered as a different taxon or
cryptic species. Morphometric analysis was also conducted based on traditional and Truss
Network measurements. The quantitative data were then analysed using Analysis of
Variance (ANOVA), Principal Component Analysis (PCA) and Discriminant Function
Analysis (DFA) using SPSS version 11.5 software. Twenty and nineteen characters
including standard length identified from 9 homologous landmarks were measured for the
traditional and the Truss Network measurements respectively. Neither of the univariate
statistics, PCA nor DF A of the traditional morphometric could discriminate any single
population, indicating that there is little differentiation among the I 0 N. japonicus
populations. On the other hand, the Truss Network morphometries presented a better and
clearer discrimination of the N.japonicus populations. Three variables, A4, A5 and Bl were
able to discriminate the I 0 populations by generating I 0 subsets in the SNK test. In the PCA,
only Principal Component (PC) I had eigenvalues of more than 1 explaining 88.7% of the
total variation and significantly associated size component as the main source of variation
among populations. DF A with a combination of Function I and Function 2 successfully
discriminated most of the populations. Function I showed that the head region (variable A I
and A3) and mid body region (A4 and A5) played an important role in discriminating the
populations except between the Kuala Kedah A and the Kuala Kedah B populations while
Kuala Besar and Bagan Pancor were discriminated by Function 2. These results showed that
some morphometric characters of N japonicus have considerable discriminatory power to
distinguish populations. However, the controversial population in the genetic analysis (Kuala
Besar) showed no differentiation with the Bagan Pancor population in Functions I of DF A.
Overall, two distinct results were revealed from both analyses where by the genetic analysis
proposed a generally homogeneous population (except for Kuala Besar) but the
morphometric analysis proposed that the contrast in morphometric (Truss Network)
characters was able to differentiate most of the N japonicus populations. This is probably
due to the different selection pressures on each type of character in this species.
Description
Keywords
Japanese threadfin bream , Nemipterus japonicus (bloch, 1791)