Evolution of Photosymbiosis in Oligocene-Miocene Planktic Foraminifera

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9706394 Norris Symbioses are ubiquitous in the diversity of life and are often cited as a source of evolutionary novelty. I propose to test the role of photosymbiosis in the diversification of planktic foraminifera-a large group of pelagic protistans that have a complex and well preserved fossil record. Equally important for this study, planktic foraminifera preserve a clear isotopic signal of foraminiferal-algal symbiosis in their calcareous shells that permits the history and evolution of symbiosis to be studied in extinct species. My previous isotopic and phylogenetic work has established that a large clade of planktic foraminifera (the morozovellids) diversified simultaneously with their evolution of foraminiferal-algal symbiosis. Evidence from the ecology of living photosymbiotic foraminifera and changes in the taxonomic diversity of extinct groups strongly suggest that at least some clades radiated as soon as they acquired photosymbionts-perhaps because the photosymbiosis permitted the foraminifera to diversify into oligotrophic surface waters. It remains to study other clades of photosymbiotic foraminifera to determine whether these symbioses consistently initiate major diversifications of the host foraminifera. This proposal will examine two large clades: the Neogene globiginids (which may have harbored symbionts following the major extinction of photosymbiotic species in the middle Eocene). Data from both clades will be compared to a previously studied group: the Paleogene morozovellids. The globigerinids are almost exclusively photosymbiotic today as demonstrated both by observation of living foraminifera and isotopic analyses of their shells. Yet, a small number of isotopic analyses done as a pilot study for this project suggest the surprising conclusion that the globigerinids only recently acquired the photosymbiotic ecology. At least some of the early Miocene and Oligocene representatives of the group were apparently asymbiotic. Should this conclusion be supported by further cladistic and isotopic study, this will weaken the hypothesized link between the evolution of symbiosis and taxonomic radiation of the host group. Conversely, evidence for the recent evolution of photosymbiosis in both the globigerinids and globoquadrinids will provide strong evidence that symbioses are easily established in planktic foraminifera-a point also suggested by recent molecular phylogenetic data that find that the same symbiotic dinoflagellate species within diverse groups of globigerinid foraminifera. This study is significant because it compares isotopic and cladistic evidence from three major clades of planktic foraminifera that have independently evolved photosymbiosis to determine whether symbioses play an important evolutionary role in the diversification of these plankton. These analyses will result in a detailed history of the photosymbiotic strategy in planktic foraminifera for the last 65 million years. The history of photosymbiosis can then be compared with the oceanographic record to assess the paleoceanographic control on the evolution of photosymbiosis.