Molecular phylogeography - Oxyrrhis marina

Introduction

Understanding mechanisms of adaptive response remains a central goal for evolutionary and ecological biology and it is the key issue for biodiversity conservation.  Contemporary genomics and statistical techniques provide powerful tools necessary to achieve this, yet formal attempts to do so in natural systems are scarce. 

In this project we are applying genetic, genomic, and ecophysiological approaches to characterise spatial genetic structure and adaptive variation in Oxyrrhis marina, a widely distributed marine heterotrophic flagellate that is commonly used as a model experimental organism.  This NERC funded project (NE/F005237/1) is a collaboration between Phill Watts, David Montagnes, Chris Lowe, and Laura Martin.










Fig.1 Oxyrrhis marina under a light microscope. Image from Begun et al. (2004)

What does the project involve?




Fig.2 Examples of ideal sampling locations for Oxyrrhis marina

 Using aquatic free living protists as a model, we are quantifying the extent of spatial variation in adaptive traits and demographic parameters (e.g. population boundaries, population sizes, and migration rates) that determine the relative roles of natural selection and random drift in driving adaptive divergence and spatial genetic structure.

To achieve this we are collecting a large number of O. marina isolates, predominately from European waters, but also globally.  We then are using a range of genetic approaches (e.g. microsatellite genotyping, large scale sequencing, and gene expression assays) to characterise population structure and signatures of selection and local adaptation.  In addition, we are assessing the physiological responses (predominately growth rate) of different isolates to important environmental variables, such as temperature and salinity, to understand how such variables might influence O. marina distributions.

 

Can you help us, please? 

A major component of this study is the collection of O. marina from a range of locations throughout the world -  Figures 3 and 4 indicate areas where we have sampled - and where we have found O. marina.

If you are able to collect samples for us, simply e-mail one of the team and we will get back to you with details about the sampling - even samples from established locations are useful. Samples are very easy to collect; just find a tide pool on the beach or rocky shore, get any plastic container such as a soft drink bottle and fill it up with sea water.



Fig.3 Present global sampling effort for O. marina. Red circles indicate presence of O. marina, Grey circles indicate water sample that did not contain O. marina.

 

The Organism

Protists, in general, are a useful taxon to study spatial structure and adaptation, as they are ecologically important, widespread, species-rich, occupy a range of environments, and provide an experimentally amenable system.  Oxyrrhis marina, a small (~20 µm) heterotrophic flagellate is an ideal model to study such processes as it is likely ubiquitous, and is easy to culture.  As a result, O. marina is used widely in experimental studies to quantify, for example, response to prey type and concentration (Flynn & Davidson 1993); salinity (Lowe et al. 2005); feeding specificity and prey recognition; interactive effects of temperature and food concentration on growth rate (Kimmance et al. 2006), ingestion rate, cell size and production; dimethyl sulphide production and grazing selectivity (Wolfe 2000); and potential control of red-tide organisms (Jeong et al. 2003; Johnson et al. 2003).

 

The project to date

Thanks to a huge sampling effort from a range of collaborators, we have collected hundreds of Oxyrrhis marina isolates - but we would still like more!  Our genetic data suggest that there are at least four O. marina lineages with overlapping distributions (Lowe et al. 2009).  One component of the project is now assessing how extensive the differences between lineages are and whether they are likely to be different species.

Fig.4 Present European sampling effort for O. marina. Red circles indicate presence of O. marina, grey circles indicate water sample that did not contain O. marina.

 

References

Lowe C, Montagnes DJSMartin L, Watts PC (2010) Patterns of genetic diversity in marine heterotrophic flagellate Oxyrrhis marina (alveolata: dinophyceae). Protist 161:212-221 PDF

Flynn KJ & Davidson K (1993) Predator-prey interactions between Isochrysis galbana and Oxyrrhis marina I. Changes in particulate delta 13C. J Plank Res 15:455–463.

Jeong HJ, Kim JS, Yoo YD, Kim ST, Kim TH, Park MG, Lee CH, Seong KA, Kang NS & Shim JH (2003) Feeding by the heterotrophic dinoflagellate Oxyrrhis marina on the red-tide Raphidophyte Heterosigma akashiwo: a potential biological method to control red tides using mass-cultured grazers. J Eukaryot Microbiol 50:274–282.

Johnson MD, Rome M & Stoecker DK (2003) Microzooplankton grazing on Prorocentrum minimum and Karlodinium micrum in Chesapeake Bay. Limnol Oceanogr 48:238–248.

Kimmance S, Atkinson D, Montagnes DJS (2006) Do temperature - food interactions matter? Responses of production and its components in the model heterotrophic flagellate Oxyrrhis marina. Aquat Microb Ecol 42:63-73 PDF

Lowe CD, Kemp SJ, Bates AD, Montagnes DJS (2005) There are high levels of functional and genetic diversity on Oxyrrhis marina. J Euk Microbiol 52:250-257 PDF

Wolfe GV (2000) The chemical defense ecology of marine unicellular plankton: constraints, mechanisms, and impacts. Biol Bull 198:225–244.