Ecologic Novelty in Taxonomic Diversification: Evolution of Photosymbiosis in Planktic Foraminifera

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Norris 9505836 The relationship between ecologica and morphological diversification is currently much in debate. There is an increasing body of work that suggests that much speciation occurs in the absence of any change in ecology. This paradigm suggests that most speciation takes place by the passive erection of barriers to dispersal. In contrast, concepts such as "adaptive zone" imply that much speciation occurs when taxa evolve "key innovations" that permit them to scale unoccupied adative peaks. From this perspective, diversification is an active process mediated by changes in ecological strategies. Research will focus on phylogenetic and ecologic study of the globigerinid clade--the largest exant group of photosymbiotic foraminifera. The proposed study will use stable isotope methods to deduce the occurrence of photosymbiosis in extinct foraminifera and then map this ecological information onto a phylogenetic tree. It should be easy to disprove the key-innovation hypothesis if the results demonstrate that symbiosis was acquired long before or after the globigerinid radiation began or if photosymbiotic and non-symbiotic sister groups have similar evolutionary histories. Moreover, any linkage between symbiosis and taxonomic diversification can be tested by comparing patterns of radiation in symbiotic and non-symbiotic sister groups in Neogene globigerinids with a mostly complete data set for the photosymbiotic Paleocene morozovellids. The results may provide insights on the evolutionary role of photosymbiosis in other groups as well as chemosymbiosis in mollusc and other invertebrates.