Molecular subdivision of the marine diatom Thalassiosira rotulain relation to geographic distribution, genome size, and physiology

BMC Evolutionary Biology

Research Article

Robert J Olson¹  Dayna R Rignanese²  Tatiana A Rynearson²  Kerry A Whittaker² 

[1] Biology Department, Woods Hole Oceanographic Institution, 02543, Woods Hole, MA, USA;Graduate School of Oceanography, South Ferry Road, University of Rhode Island, 02882, Narragansett, RI, USA;

关键词: Phytoplankton;    Phylogeography;    Dispersal;    Physiology;    Intraspecific diversity;   

DOI  :  10.1186/1471-2148-12-209

 received in 2011-12-29, accepted in 2012-09-22,  发布年份 2012

来源: Springer

【 摘 要 】

BackgroundMarine phytoplankton drift passively with currents, have high dispersal potentials and can be comprised of morphologically cryptic species. To examine molecular subdivision in the marine diatom Thalassiosira rotula, variations in rDNA sequence, genome size, and growth rate were examined among isolates collected from the Atlantic and Pacific Ocean basins. Analyses of rDNA included T. gravida because morphological studies have argued that T. rotula and T. gravida are conspecific.ResultsCulture collection isolates of T. gravida and T. rotula diverged by 7.0 ± 0.3% at the ITS1 and by 0.8 ± 0.03% at the 28S. Within T. rotula, field and culture collection isolates were subdivided into three lineages that diverged by 0.6 ± 0.3% at the ITS1 and 0% at the 28S. The predicted ITS1 secondary structure revealed no compensatory base pair changes among lineages. Differences in genome size were observed among isolates, but were not correlated with ITS1 lineages. Maximum acclimated growth rates of isolates revealed genotype by environment effects, but these were also not correlated with ITS1 lineages. In contrast, intra-individual variation in the multi-copy ITS1 revealed no evidence of recombination amongst lineages, and molecular clock estimates indicated that lineages diverged 0.68 Mya. The three lineages exhibited different geographic distributions and, with one exception, each field sample was dominated by a single lineage.ConclusionsThe degree of inter- and intra-specific divergence between T. gravida and T. rotula suggests they should continue to be treated as separate species. The phylogenetic distinction of the three closely-related T. rotula lineages was unclear. On the one hand, the lineages showed no physiological differences, no consistent genome size differences and no significant changes in the ITS1 secondary structure, suggesting there are no barriers to interbreeding among lineages. In contrast, analysis of intra-individual variation in the multicopy ITS1 as well as molecular clock estimates of divergence suggest these lineages have not interbred for significant periods of time. Given the current data, these lineages should be considered a single species. Furthermore, these T. rotula lineages may be ecologically relevant, given their differential abundance over large spatial scales.

【 授权许可】

Unknown   
© Whittaker et al.; licensee BioMed Central Ltd. 2012. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.