Evolution of symbiosis in a warmer world

Dr Tom Ezard, Dr Alexandra Auderset. University of Southampton; Dr Kirsty Edgar, University of Birmingham

The major bio-limiting nutrients in low to mid-latitude surface waters are nitrogen and phosphorous and their availability through time likely played a major role in evolution. In these areas of the ocean the majority of planktic foraminifera host endosymbionts, sharing their metabolic N and P with the autotrophic symbionts in exchange for organic carbon (C) in contrast to feeding on phytoplankton, other heterotrophs and particulate N (PN) when more nutrients are present. Thus, the origination and history of these symbioses may reflect changes in the ocean’s nutrient cycling [1].


Despite its importance, identifying photosymbiotic and trophic activity in extinct species is challenging. However, recent instrumental and methodological developments we have been involved in have allowed the measurement of the nitrogen and carbon isotopes (δ15N, δ13C) on the organic matter that lies embedded within the mineral structure of ancient foraminifera (foraminifera-bound, FB), which are distinct between symbiotic-bearing and non-symbiotic foraminifera. Therefore, these promising new tools open a whole new archive to study symbiotic relationships and foraminifera ecology in the past [2], [3].


Within this project the PhD candidate will carry out coupled analyses of foraminifera-bound nitrogen and carbon isotopes to answer the following questions:

  •          How did photosymbiotic activity and dietary sources within planktic foraminifera change over the past 60 million years?
  •          What can the symbiotic relationships tell us about nutrient availability in the surface ocean?
  •          How did photosymbiotic activity in foraminifera change as a response to global warming and ocean acidification in the past?

Novel geochemical proxies (FB-δ15N, FB-δ13C) and more established proxies (δ13Ccalcite, δ18Ocalcite) will be applied on planktic foraminifera in marine sediment samples. Starting with core-top and Pleistocene sediment samples, where symbiotic relationships are relatively well studied. Later within the project the focus will shift to extinct Cenozoic foraminifera. In the last part of the project, the student will investigate past periods of prolonged warmth, which act as potential climate analogues for future global warming, e.g. the Middle Miocene Climate Optimum (MMCO, ca. 16 million years ago), the Middle Eocene Climate Optimum (MECO, ca. 40 million years ago) and Paleocene-Eocene Thermal Maximum (PETM, ca. 56 million years ago) to study symbiosis under environmental stress on evolutionary and shorter timescales.



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 at [INSERT HOST ORGANISATION/DEPARTMENT]. Specific training will


  • Sediment preparation & foraminifera species/genus identification with binocular microscope for geochemical analysis.
  • Study of multi-species and multi-genus planktic foraminifera from different timescales: (1) Core top samples, which can be collected during North Atlantic cruise, (2) Pleistocene samples and (3) Cenozoic samples, which can be obtained from the “International Ocean Discovery Program, IODP”. This will allow us to identify symbiotic relationship, starting with modern and Pleistocene foraminifera samples and later comparing them with extinct foraminifera species and genera.
  • Foraminifera-bound nitrogen isotopes using the denitrifier method at the Max Planck Institute for Chemistry, Mainz, Germany and isotopic mass ratio spectrometry.
  • Foraminifera-bound carbon isotopes using the nano Element Analyzer at Princeton University, US/ University of Southampton/NOCS
  • Carbon/ Oxygen isotopes on foraminifera shell using GasBench at University of Southampton/NOCS
  • Modern graphical software packages and web-based archives.
  • Presenting complex scientific material in spoken, written and graphical forms.
  • Time management.
  • Gaining experience working on a research vessel in the North Atlantic.


Eligibility & Funding Details: 

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


Background Reading: 

[1] Ezard, T. H., Aze, T., Pearson, P. N., and Purvis, A., 2011, Interplay between changing climate and species’ ecology drives macroevolutionary dynamics: science, v. 332, no. 6027, p. 349-351.

[2] Ren, H., Sigman, D., Meckler, A., Plessen, B., Robinson, R., Rosenthal, Y., and Haug, G., 2009, Foraminiferal isotope evidence of reduced nitrogen fixation in the ice age Atlantic Ocean: Science, v. 323, no. 5911, p. 244-248.

[3] Swart, K. A., Oleynik, S., Martinez-Garcia, A., Haug, G. H., and Sigman, D. M., 2021, Correlation between the carbon isotopic composition of planktonic foraminifera-bound organic matter and surface water pCO2 across the equatorial Pacific: Geochimica et Cosmochimica Acta, v. 306, p. 281-303.