SYSTEMATICS OF SOUTHEAST ASIAN SNAKEHEADS USING MOLECULAR & MORPHOLOGICAL DATA

Abstract

Despite the ecological and economic importance of snakeheads in southeast Asia, very little is known about their biology. This project aimed to study the phylogeny of nine species of snakeheads, eight of which are found in southeast Asia. The project used morphological and molecular characters which could be easily obtained from museum specimens without mutilating the specimens. The morphological data used included morphometrics, meristics and qualitative morphological characters. The molecular data used included DNA and polypeptide sequences. Morphometric data were obtained from traditional multivariate analysis of external measurements as well as landmark-based Procrustes analysis of body shape. Meristic counts were analysed by distance, parsimony and compatibility methods of phylogenetic inference. Qualitative morphological data were encoded and analysed by parsimony and compatibility methods. DNA was extracted from small amounts of frozen or preserved muscle tissue. A 376 bp segment of the mitochondrial cytochrome b gene was amplified from the DNA extract by 40 cycles of polymerase chain reaction (PCR). The double-stranded PCR products were purified and sequenced directly using the dideoxynucleotide chain termination method. The DNA sequences were analysed by distance, parsimony, compatibility and maximum likelihood methods. They were then translated into polypeptide sequences and analysed by distance and parsimony methods. Results showed that the most useful characters for inferring phylogeny were landmark-based morphometrics, meristics and DNA sequences. Qualitative morphological characters and polypeptide sequences did not produce well-resolved phylogenetic trees. Of all the different character types, DNA sequences provided almost all of the useful phylogenetic information. In general, phylogenetic trees obtained from morphological data tended to separate the species by body shape into dorso-ventrally and laterally flattened species. Phylogenetic trees obtained from molecular data separated the species according to their biogeographic distribution. A phylogenetic hypothesis, obtained by congruence analysis of both morphological and molecular data trees, supported the biogeographic over the body-shape separation. The phylogenetic hypothesis proposed that the snakeheads could be divided into two phyletic groups. One group consisted of species that are endemic to southeast Asia (Channa bankanensis, C. lucius, C. melasoma and C. pleurophthalma). The other group consisted of species found in south Asia ( C. gachua, C. micropeltes, C. orientalis and C. striata). The phylogenetic hypothesis, with supporting evidence from the channid fossil record and palaeogeography, indicated that snakeheads originated in south Asia in the Eocene, spread to southeast Asia in the Pleistocene, and gave rise to the southeast Asian phyletic group. The ninth species, C. marulioides, reported from southeast Asia, was found to belong to the south Asian phyletic group. Data based on morphometrics, meristics and morphological characters suggested the species to be the same as C. marulius, a species also found in south Asian. This would explain its south Asian lineage. In summary, the study established a method of inferring phylogeny from preserved snakehead specimens which could be used to elucidate the complete phylogeny of all 24 species of snakeheads in the world.