Background: The identification of free-living marine nematodes is difficult because of the paucity of easily scorable diagnostic morphological characters. Consequently, molecular identification tools could solve this problem. Unfortunately, hitherto most of these tools relied on 18S rDNA and 28S rDNA sequences, which often lack sufficient resolution at the species level. In contrast, only a few mitochondrial COI data are available for free-living marine nematodes. Therefore, we investigate the amplification and sequencing success of two partitions of the COI gene, the M1-M6 barcoding region and the I3-M11 partition. Methodology: Both partitions were analysed in 41 nematode species from a wide phylogenetic range. The taxon specific primers for the I3-M11 partition outperformed the universal M1-M6 primers in terms of amplification success (87.8\% vs. 65.8\%, respectively) and produced a higher number of bidirectional COI sequences (65.8\% vs 39.0\%, respectively). A threshold value of 5\% K2P genetic divergence marked a clear DNA barcoding gap separating intra-and interspecific distances: 99.3\% of all interspecific comparisons were 〉0.05, while 99.5\% of all intraspecific comparisons were 〈0.05 K2P distance. Conclusion: The I3-M11 partition reliably identifies a wide range of marine nematodes, and our data show the need for a strict scrutiny of the obtained sequences, since contamination, nuclear pseudogenes and endosymbionts may confuse nematode species identification by COI sequences.
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Hydrological regimes are seasonally variable in river-floodplain ecosystems. Thus, since in these environments the local and regional factors change at different temporal scales, factors structuring metacommunities might also differ over time. However, temporal dynamics of metacommunities have rarely been assessed. Here, we investigated the influence of environmental and spatial factors over time on the metacommunity structuring of periphytic ostracods in the river-floodplain system of the Upper Paraná River (Brazil). The spatial factors turned out to be more important than environmental factors, and differences in the percentage of explanation of the factors structuring ostracod metacommunities over time were significant, mainly during extreme drought period. Our results showed that the high spatial influence might be related to the low connectivity amongst environments during such extreme drought period, which can increase dispersal limitation, and consequently can increase the turnover of ostracod species throughout the region, leading to a higher beta-diversity of ostracod metacommunities.
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RBINS Staff Publications 2019
