LIPID BIOMARKER DIVERSITY IN THE COCCOLITHOPHORID EMILIANIA HUXLEYI(PRYMNESIOPHYCEAE) AND THE RELATED SPECIES GEPHYROCAPSA OCEANICA1

Abstract

Twenty‐four strains of Emiliania huxleyi and two strains of Gephyrocapsa oceanica were grown at 15°C under identical culture conditions to assess genetic variability in key lipid biomarker profiles (C 37‐C 39 alkenones, C 36 and C 37 alkyl alkenoates, and C 31‐C 38 alkenes). Under our culture conditions, little divergence an biomarker composition was detected between E. huxleyi strains from different oceanic regions or between E. huxleyi and G. oceanica even though the strains originated from biogeographical regions as diverse as the subpolar North Atlantic and subtropical Western Pacific. The major differences observed were in tetraunsaturated alkenone abundance and alkene profiles, which tended to separate neritic from open ocean strains. Different strains from the same locality were as different as strains originating from widely separated ocean basins, indicating extreme genotypic diversity within a population. Replicate cultures of the same strain showed significant variability in their biomarker profiles even though the culture temperature varied by only ±0.3°C, indicating that their synthesis ratios are influenced by environmental and/or physiological variable(s), as yet unidentified, in addition to temperature. Strong covariance in C 37 and C 38 methyl alkenone unsaturation ratios (U k37 and U k38Mρ respectively) and, in coastal strains, C 33, alkene and alkenone unsaturation ratios indicates that these compounds are biochemically linked.