Examining the evolutionary loss of calcification in coccolithophores

Prof Toby Tyrrell, Dr Glen Wheeler, MBA; Dr Katherine Helliwell, MBA
Rationale: 

Coccolithophores are unicellular photosynthetic organisms that build intricate calcium carbonate plates, called coccoliths, with which they surround themselves (see electron microscope image below). They are important contributors to carbon cycling in the oceans. Individual cells can be extracted from the natural environment and kept alive in artificial seawater, where, if the laboratory conditions are suitable, they continuously divide and multiply. A few institutes around the world maintain “culture collections” of different coccolithophore species and strains. Although not previously reported in the scientific literature, it is well known to those maintaining the collections that, over many generations (e.g. within a year), coccolithophores frequently lose their ability to calcify (i.e. to produce coccoliths) or start producing impaired (malformed) coccoliths. One possible reason is that coccoliths provide protection against predation in nature; in the absence of predators in culture, coccoliths are therefore no longer beneficial. This observation, if supported by this PhD work, could help us understand better why coccolithophores calcify and will add to the body of evidence that traits or functions no longer under the protection of purifying natural selection degenerate or disappear over time. This has potential wider implications for species no longer living in natural conditions, including domesticated ones.

 

Methodology: 

The PhD will consist of (1) computer modelling, (2) experimental evolution of cultured coccolithophores, and (3) evidence collation.

  1. Computer modelling: You will develop a new conceptual model in which coccolith construction will be controlled by a set of genes, which in turn experience mutation and crossover in a population of coccolithophores. A metric (fitness function) will be used to estimate the benefit to the organism from reduced predation, together with the energetic cost of calcification. The outcome of the trade-off (value of the fitness function) will determine the numbers of descendants of each organism in the next generation. The model will be made to fit available data and the consequences of removing the benefit of calcification will be examined.
  2. Experimental evolution to examine loss of calcification: Freshly isolated calcifying coccolithophore strains will be maintained in culture at NOCS over many generations and regularly monitored for loss of calcification.
  3. Evidence collation: You will collect (via in person and/or virtual meetings with culture collection curators worldwide) and synthesise data on, for example: (1) time taken to loss of calcification; (2) frequency of loss for different species; and (3) whether coccolith production ceases entirely or whether malformed coccoliths are produced.

 

Location: 
NOC/UoS
Training: 

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted in the School of Ocean and Earth Science. Specific training will include:

You will be trained in various aspects of modelling and computer programming, depending on prior experience, such as: debugging, distributed version control, dimensional checking of equations, and sensitivity analyses. You will also receive full training in coccolithophore culturing techniques. All laboratory work will be carried out with the assistance of an experienced technician. You will attend masters-level courses as appropriate. You will benefit greatly from interactions with the large number of PhD students, PDRAs and academic staff involved in biological oceanography, evolution and modelling at NOCS and MBA.

 

Eligibility & Funding Details: 

Please see https://inspire-dtp.ac.uk/how-apply for details.

 

Background Reading: 

Monteiro, F. M., et al. (2016). Why marine phytoplankton calcify. Science Advances, 2(7), e1501822.

Jeffery, W.R., 2009. Regressive evolution in Astyanax cavefish. Annual review of genetics, 43, pp.25-47.

Wilkens, H., 2020. The role of selection in the evolution of blindness in cave fish. Biological Journal of the Linnean Society, 130(3), pp.421-432.

 

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