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Measuring RNA:DNA ratios in individual Acartia tonsa (Copepoda)

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Abstract

Acartia tonsa Dana is a dominant copepod in coastal waters and is therefore an important link in the food web between microplankton and higher trophic levels. RNA:DNA ratios have been used to describe growth and nutritional condition of field-collected copepods and to show strong correlation between RNA:DNA ratios and group egg production (EP). A method was developed using a sensitive, nucleic acid-specific fluorescent dye, and automated microplate fluorometer to measure DNA, RNA, and the RNA:DNA ratio of individual A. tonsa. DNA, RNA, and RNA:DNA ratios and EP were all significantly higher in copepods fed Thalassiosira sp. compared to starved copepods. There was a general trend toward an increase in RNA:DNA ratios with increase in EP, but due to the high degree of variation in both RNA:DNA ratios and EP among individual copepods there was no significant correlation between RNA:DNA ratios and EP. Significant differences in RNA:DNA ratios between fed (7.2) and starved (3.3) copepods were found after 2 days. This assay may be applied to other species of copepods sampled in the field to provide an index of the health of planktonic food webs.

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Acknowledgments

We greatly appreciate Cindy Faulk for advice on developing the protocol and Cammie Hyatt for her technical assistance. Funded in part by R/ES-88 of Institutional Grant NA16RG1078 to Texas A&M University by the National Oceanic and Atmospheric Administration, US Department of Commerce. C. L. Speekmann was partially supported by an E. J. Lund Fellowship. This is The University of Texas Marine Science Institute Contribution No. 976. We would also like to thank the anonymous reviewers for their comments and suggestions, which improved this manuscript.

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Authors and Affiliations

  1. Marine Science Institute, The University of Texas at Austin, 750 Channel View Dr., Port Aransas, TX, 78373, USA

    Christa L. Speekmann, B. Scott Nunez & Edward J. Buskey

  2. Department of Biology, Temple University, 1900 N. 12th St., Philadelphia, PA, 19122, USA

    Christa L. Speekmann

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  1. Christa L. Speekmann
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  2. B. Scott Nunez
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  3. Edward J. Buskey
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Correspondence to Christa L. Speekmann.

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Communicated by J.P. Grassle, New Brunswick.

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Speekmann, C.L., Nunez, B.S. & Buskey, E.J. Measuring RNA:DNA ratios in individual Acartia tonsa (Copepoda). Mar Biol 151, 759–766 (2007). https://doi.org/10.1007/s00227-006-0520-0

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  • DOI: https://doi.org/10.1007/s00227-006-0520-0

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