Abstract
Copepods, small aquatic crustaceans, are the most abundant metazoan zooplankton and outnumber every other group of multicellular animals on earth. In spite of ecological and biological importance in aquatic environment, their morphological plasticity, originated from their various lifestyles and their incomparable capacity to adapt to a variety of environments, has made the identification of species challenging, even for expert taxonomists. Molecular approaches to species identification have allowed rapid detection, discrimination, and identification of cryptic or sibling species based on DNA sequence data. We examined sequence variation of a partial mitochondrial cytochrome C oxidase I gene (COI) from 133 copepod individuals collected from the Korean Peninsula, in order to identify and discriminate 94 copepod species covering six copepod orders of Calanoida, Cyclopoida, Harpacticoida, Monstrilloida, Poecilostomatoida and Siphonostomatoida. The results showed that there exists a clear gap with ca. 20 fold difference between the averages of within-specific sequence divergence (2.42%) and that of between-specific sequence divergence (42.79%) in COI, suggesting the plausible utility of this gene in delimitating copepod species. The results showed, with the COI barcoding data among 94 copepod species, that a copepod species could be distinguished from the others very clearly, only with four exceptions as followings: Mesocyclops dissimilis–Mesocyclops pehpeiensis (0.26% K2P distance in percent) and Oithona davisae–Oithona similis (1.1%) in Cyclopoida, Ostrincola japonica–Pseudomyicola spinosus (1.5%) in Poecilostomatoida, and Hatschekia japonica–Caligus quadratus (5.2%) in Siphonostomatoida. Thus, it strongly indicated that COI may be a useful tool in identifying various copepod species and make an initial progress toward the construction of a comprehensive DNA barcode database for copepods inhabiting the Korean Peninsula.
Highlights
Copepods are one of the prevalent taxonomic groups among crustaceans, encompassing approximately 14,000 described species worldwide [1, 2, 3], of which about 695 species from 97 families have been known to occur in Korean waters
The size of the C oxidase I gene (COI) fragments amplified in the present study varied from 650 to 1,024 bp, the nucleotides at both ends were trimmed to only use high-quality, well matched data
This study examined sequence variation of partial COI sequences and its utility as a DNA barcoding marker to identify and discriminate copepod species from six different copepod orders including Calanoida, Cyclopoida, Harpacticoida, Monstrilloida, Poecilostomatoida and Siphonostomatoida collected from the Korean Peninsula
Summary
Copepods are one of the prevalent taxonomic groups among crustaceans, encompassing approximately 14,000 described species worldwide [1, 2, 3], of which about 695 species from 97 families have been known to occur in Korean waters (http://www.kbr.go.kr/home/find/ find02001l.do). The identification and classification of copepods have fundamentally been based on their morphological and anatomical characteristics [1, 2, 4] Such conventional ways may have some limitation in precisely estimating the abundance of copepod species in a certain environment, because they are time-consuming and necessitate special training or professional skills. Another difficulty may be the existence of closely related taxa that are barely distinguishable [12, 14,15,16]. The application of a rapid and promising protocol for the species identification is critically needed for the estimation of copepod diversity
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