Genetic species identification and population structure of Halophila(Hydrocharitaceae) from the Western Pacific to the Eastern Indian Ocean

Abstract

BackgroundThe Indo-Pacific region has the largest number of seagrass species worldwide and this region is considered as the origin of the Hydrocharitaceae. Halophila ovalis and its closely-related species belonging to the Hydrocharitaceae are well-known as a complex taxonomic challenge mainly due to their high morphological plasticity. The relationship of genetic differentiation and geographic barriers of H. ovalis radiation was not much studied in this region. Are there misidentifications between H. ovalis and its closely related species? Does any taxonomic uncertainty among different populations of H. ovalis persist? Is there any genetic differentiation among populations in the Western Pacific and the Eastern Indian Ocean, which are separated by the Thai-Malay peninsula? Genetic markers can be used to characterize and identify individuals or species and will be used to answer these questions.ResultsPhylogenetic analyses of the nuclear ribosomal internal transcribed spacer region based on materials collected from 17 populations in the Western Pacific and the Eastern Indian Ocean showed that some specimens identified as H. ovalis belonged to the H. major clade, also supported by morphological data. Evolutionary divergence between the two clades is between 0.033 and 0.038, much higher than the evolutionary divergence among H. ovalis populations. Eight haplotypes were found; none of the haplotypes from the Western Pacific is found in India and vice versa. Analysis of genetic diversity based on microsatellite analysis revealed that the genetic diversity in the Western Pacific is higher than in the Eastern Indian Ocean. The unrooted neighbor-joining tree among 14 populations from the Western Pacific and the Eastern Indian Ocean showed six groups. The Mantel test results revealed a significant correlation between genetic and geographic distances among populations. Results from band-based and allele frequency-based approaches from Amplified Fragment Length Polymorphism showed that all samples collected from both sides of the Thai-Malay peninsula were clustered into two clades: Gulf of Thailand and Andaman Sea.ConclusionsOur study documented the new records of H. major for Malaysia and Myanmar. The study also revealed that the Thai-Malay peninsula is a geographic barrier between H. ovalis populations in the Western Pacific and the Eastern Indian Ocean.

Is Halophila major (Zoll.) Miquel a big H. ovalis (R. Brown) J.D. Hooker? An evaluation based on age, morphology, and ITS sequence

“…This study was the first report, which combined both morphological features and molecular information to identify H. major and suggested some key characters to identify this closely similar species. Unlike the study of Nguyen et al 20 , where high genetic diversity of H. ovalis was reported across the Indo-Pacific Ocean, our results showed the identical sequences of H. major or between Trang and Krabi provinces (haplotype Hm.1, Fig. 4), however a much smaller scale.…”

“…major is reported to be distributed in Western Pacific region including Vietnam, Indonesia, Malaysia and the Indian Ocean including Thailand and Myanmar either through the morphological or molecular information 12,19,20 . This study was the first report, which combined both morphological features and molecular information to identify H. major and suggested some key characters to identify this closely similar species.…”

“…Besides, molecular studies by Uchimura et al 12 revealed that H. major occurred in Thailand, which was the first record of H. major in Thailand. A recent report by Nguyen et al 20 suggested the occurrence of H. major in Thailand; however its morphological features had never been examined.…”

“…Recent studies using var- ious genetic markers of plastid sequences have clarified the identification of the Halophila species 21,22 . Ribosomal internal transcribed spacer (ITS) sequences could be used to study and identify the genetic relation between Halophila closely related species 12,20,23,24 . It is unknown weather there is any difference in ITS molecular analysis between big and small leaf morphological forms of H. ovalis.…”

Temporal variation of intertidal seagrass in southern China (2008–2014)

“…One of the most predominant seagrass species in this region is Halophila ovalis (Zheng et al 2013), which is also common throughout the Indo-Pacific (Nguyen et al 2014). Little information exists on long-term (> 5 yr) dynamics of H. ovalis in China; studies have focused mainly on community structure, eco-physiology, etc., or have been conducted over a relatively short period (< 2 yr) (Huong et al 2003).…”