Project: Connecting local, regional and global scales of gene flow in planktonic marine diatoms

Description from NSF award abstract:
Diatoms are ubiquitous, unicellular, eukaryotes that generate about 40% of the organic carbon fixed annually in the sea. Interpretation of diatom species distributions and abundances in relation to environmental conditions has relied on two assumptions: (1) cells with identical morphologies represent the same species and (2) high potentials for dispersal and gene flow in passively drifting diatoms prevent local adaptation. Recent studies have challenged both assumptions, suggesting diatoms possess rich patterns of genetic and physiological variation both within and between species. Although there is emerging evidence of intra-specific population differentiation on local scales (~100km), it is commonly assumed that planktonic microbes are homogenously distributed on global scales (e.g. Fenchel and Finlay 2004). There is currently no data on diatoms to support this assumption. Aside from intriguing data on local scales, nothing is known about regional and global-scale population genetics and biogeography of diatoms.

The research proposed here will focus on the essential questions of if and how populations of planktonic diatoms are connected at local, regional and global scales. Connectivity among populations can influence a species'' ecology, adaptive potential, evolutionary longevity and ultimately speciation potential. The proposed research will examine how local populations are connected to each other on regional scales and how regional dynamics connect to global-scale biogeographies using two model diatom species. rDNA sequence variation will be used to test whether broad species distributions observed in diatoms result from cryptic speciation. Within species, microsatellite markers will be used to identify genetically distinct populations, determine their relatedness to each other and examine spatial patterns of differentiation. The degree of physiological variation that accompanies genetic differentiation between populations will also be examined. Samples will be collected in a framework of existing oceanography and biodiversity programs, permitting genetic data to be interpreted in the context of larger, often long-term, studies. Because little is known about diatom biogeography, this work will begin to shed light on the connections between local and global population dynamics. Because the proposed research will represent the first large-scale sampling of diatom population genetics, it will also serve to generate many new hypotheses about the mechanisms that regulate ecological processes such as bloom formation over space and time and evolutionary processes such as the development of reproductive isolation and eventual speciation in planktonic organisms.

Related publications:
Rynearson, T.A., E.O. Lin and E.V. Armbrust. 2009. Metapopulation structure in the planktonic diatom Ditylum brightwellii (Bacillariophyceae). Protist, 160(1):111-121. doi:10.1016/j.protis.2008.10.003

Whittaker, K., Rignanese, D., Olson, R., Rynearson, T., 2012. Molecular subdivision of the marine diatom Thalassiosira rotula in relation to geographic distribution, genome size, and physiology. BMC Evolutionary Biology, 12:209. doi:10.1186/1471-2148-12-209

Boyd, P.W., Rynearson, T.A., Armstrong, E.A., Fu, F., Hayashi, K., Hu, Z., Hutchins, D.A., Kudela, R.M., Litchman, E., Mulholland, M.R., Passow, U., Strzepek, R.F., Whittaker, K.A., Yu, E., Thomas, M.K., 2013. Marine Phytoplankton Temperature versus Growth Responses from Polar to Tropical Waters - Outcome of a Scientific Community-Wide Study. PLoS One, 8(5), e63091. doi:10.1371/journal.pone.0063091