Species identification and phylogenetic analysis of genus Nassarius (Nassariidae) based on mitochondrial genes
ABSTRACT Genus Nassarius contains many subgenera, such as Zeuxis, Telasco, Niotha, Varicinassa, Plicarcularia, Nassarius s. str. and Reticunassa. On the basis of morphological characteristics of the shell and radula and sequences of mitochondrial cytochrome oxidase
subunit I (COI) and 16S rRNA genes, Nassarius specimens collected from the South China Sea were identified and phylogenetically analyzed. Although Nassarius sp. and Nassarius (Varicinassa) variciferus were morphologically different in their shells, few variations were found among their radular teeth and sequences of mtCOI
and mt16S RNA genes. Therefore, Nassarius sp. should be classified as N. (Varicinassa) variciferus. Nassarius (Zeuxis) sp. has only a subtle difference from Nassarius (Zeuxis) algidus on the shell, but it shows obvious differences in radular teeth and DNA sequence, indicating that they are two distinct species.
Sequence divergence of mtCOI and mt16S RNA genes within Nassarius species was much lower than that between species, suggesting that these two genes are suitable for Nassarius species identification. Phylogenetic analysis (neighbor-joining and maximum parsimony) based on mtCOI and mt16S rRNA genes
revealed the presence of two groups in genus Nassarius and a closest relationship between subgenera Zeuxis and Telasco. Species of subgenus Plicarcularia did not form a single clade. The molecular phylogeny was not congruent with the previous morphological phylogeny. The subgeneric
divisions of genus Nassarius appear to be uncertain and unreliable.
-species identification-mtCOI gene-mt16S rRNA gene
- SourceAvailable from: Nigel P Barker[show abstract] [hide abstract]
ABSTRACT: The southern African tick shell, Nassarius kraussianus (Dunker, 1846), has been identified as being the earliest known ornamental object used by human beings. Shell beads dated from approximately 75,000 years ago (Pleistocene era) were found in a cave located on South Africa's south coast. Beads made from N. kraussianus shells have also been found in deposits in this region dating from the beginning of the Holocene era (<10,000 years ago). These younger shells were significantly smaller, a phenomenon that has been attributed to a change in human preference. We investigated two alternative hypotheses explaining the difference in shell size: a) N. kraussianus comprises at least two genetic lineages that differ in size; b) the difference in shell size is due to phenotypic plasticity and is a function of environmental conditions. To test these hypotheses, we first reconstructed the species' phylogeographic history, and second, we measured the shell sizes of extant individuals throughout South Africa. Although two genetic lineages were identified, the sharing of haplotypes between these suggests that there is no genetic basis for the size differences. Extant individuals from the cool temperate west coast had significantly larger shells than populations in the remainder of the country, suggesting that N. kraussianus grows to a larger size in colder water. The decrease in fossil shell size from Pleistocene to Holocene was likely due to increased temperatures as a result of climate change at the beginning of the present interglacial period. We hypothesise that the sizes of N. kraussianus fossil shells can therefore serve as indicators of the climatic conditions that were prevalent in a particular region at the time when they were deposited. Moreover, N. kraussianus could serve as a biomonitor to study the impacts of future climate change on coastal biota in southern Africa.PLoS ONE 02/2007; 2(7):e614. · 3.73 Impact Factor
- 11/2003; 25:547-572.
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ABSTRACT: Morphological classification of snail shells is sometimes arbitrary and misleading in correct species delimitation. This topic is investigated in four nominal species of the minute gastropods of the genus Vallonia (V. pulchella, V. excentrica, V. costata and V. enniensis). First, individuals are classified according to their shell morphology. Second, variation in ribosomal internal transcribed spacer 1 DNA (ITS-1 rDNA) is analysed. Using a cladistic approach, the nucleotide positions of the ITS-1 are elucidated on apomorphic and plesiomorphic character states (outgroup=Acanthinula aculeata; Valloniidae). The molecular data yield evidence that the morphospecies V. excentrica is a paraphyletic group, comprising just a loose arrangement of individuals with similar shells. Data on fossil shells and putative divergence time are also elucidated. In the monograph on Vallonia it has been suggested that the split between the branch of V. costata and the branch of V. pulchella, V. excentrica and V. enniensis could have been in the upper Cretaceous. Based on the ITS-1 sequence alignment and the number of variable nucleotide positions, it is suggested that the last common ancestor of both branches lived at some time during the Miocene or even the Pliocene. Therefore, the fossil stem lines of Vallonia should be newly interpreted.Journal of Zoology 02/2006; 260(3):275 - 283. · 2.04 Impact Factor