Ciliate diversity and distribution across an environmental and depth gradient in Long Island Sound, USA

Authors

  • Mary Doherty,

    Corresponding author
    1. Department of Organismic and Evolutionary Biology, 611 North Pleasant Street University of Massachusetts, Amherst, MA 01003, USA.
      E-mail mdoherty@uga.edu; Tel. (+1) 912 485 2203; Fax (+1) 912 485 2133.
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  • Maiko Tamura,

    1. Department of Biological Sciences, Clark Science Center, Smith College, Northampton, MA 01063, USA.
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  • Barbara A. Costas,

    1. Department of Marine Sciences, 1080 Shennecossett Road, University of Connecticut, Groton, CT 06340, USA.
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  • Mark E. Ritchie,

    1. Syracuse University, Department of Biology, 108 College Place, Syracuse, NY 13244, USA.
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  • George B. McManus,

    1. Department of Marine Sciences, 1080 Shennecossett Road, University of Connecticut, Groton, CT 06340, USA.
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  • Laura A. Katz

    1. Department of Organismic and Evolutionary Biology, 611 North Pleasant Street University of Massachusetts, Amherst, MA 01003, USA.
    2. Department of Biological Sciences, Clark Science Center, Smith College, Northampton, MA 01063, USA.
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E-mail mdoherty@uga.edu; Tel. (+1) 912 485 2203; Fax (+1) 912 485 2133.

Summary

The nature and extent of microbial biodiversity remain controversial with persistent debates over patterns of distributions (i.e. cosmopolitanism versus endemism) and the processes that structure these patterns (neutrality versus selection). We used culture-independent approaches to address these issues focusing on two groups of ciliates, the Oligotrichia (Spirotrichea) and Choreotrichia (Spirotrichea) across an environmental gradient. We assessed SSU rDNA diversity in ciliate communities at six stations in Long Island Sound spanning the frontal region that separates the fresher Connecticut River outflow plume from the open Sound. As in previous studies, we find one abundant cosmopolitan species (Strombidium biarmatum), a few moderately abundant sequences, and a long list of rare sequences. Furthermore, neither ciliate diversity nor species composition showed any clear relationship to measured environmental parameters (temperature, salinity, accessory pigment composition and chorophyll). Overall, we observed that diversity decreased moving from nearshore to offshore. We also conducted analyses to detect clustering among the sampled communities using the software Unifrac. This approach revealed three significant clusters grouping samples from nearshore, surface and deep/well mixed stations. We find no strong fit of our communities to log series, geometric or log normal distributions, though one of the 3 clusters is most consistent with a log series distribution. However, when we remove the abundant cosmopolitan species S. biarmatum, all three clusters fit to a log series distribution. These analyses suggest that, with the exception of one cosmopolitan species, the oligotrich and choreotrich communities at these stations may be distributed in a neutral manner.

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