Photosynthetic Pigment and Genetic Differences Between Two Southern Ocean Morphotypes of Emiliania Huxleyi (Haptophyta)1

Abstract

The widespread coccolithophorid Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler plays a pivotal role in the carbon pump and is known to exhibit significant morphological, genetic, and physiological diversity. In this study, we compared photosynthetic pigments and morphology of triplicate strains of Southern Ocean types A and B/C. The two morphotypes differed in width of coccolith distal shield elements (0.11-0.24 μm, type A; 0.06-0.12 μm, type B/C) and morphology of distal shield central area (grill of curved rods in type A; thin plain plate in type B/C) and showed differences in carotenoid composition. The mean 19'-hexanoyloxyfucoxanthin (Hex):chl a ratio in type B/C was >1, whereas the type A ratio was <1. The Hex:fucoxanthin (fuc) ratio for type B/C was 11 times greater than that for type A, and the proportion of fuc in type A was 6 times higher than that in type B/C. The fuc derivative 4-keto-19'-hexanoyloxyfucoxanthin (4-keto-hex) was present in type A but undetected in B/C. DNA sequencing of tufA distinguished morphotypes A, B/C (indistinguishable from B), and R, while little variation was observed within morphotypes. Thirty single nucleotide polymorphisms were identified in the 710 bp tufA sequence, of which 10 alleles were unique to B/C and B morphotypes, seven alleles were unique to type A, and six alleles were unique to type R. We propose that the morphologically, physiologically, and genetically distinct Southern Ocean type B/C sensu Young et al. (2003) be classified as E. huxleyi var. aurorae var. nov. S. S. Cook et Hallegr.

Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

“…Since only morphotype B/C had been reported at and south of the Antarctic Polar Front, Cook et al (2013) concluded that the rapid drop in water temperature occurring at the Antarctic Polar Front may act as an open-ocean barrier to gene flow between these the two Southern Ocean E. huxleyi morphotypes or varieties. The nearly monospecific coccolith assemblages of E. huxleyi morphotype B/C collected by the 61 • S site traps (Plate 1) are consistent with those studies and support the idea that the physiological differences in light-harvesting pigments of morphotype B/C compared to other E. huxleyi varieties (Cook et al, 2011) may represent a critical ecological advantage in the cold and low-light waters of the AZ-S south of Australia.…”

“…This observation supports the hypothesis that the physiological differences in light-harvesting pigments of morphotype B/C (or E. huxleyi var. aurorae), compared to other Southern Ocean E. huxleyi varieties (Cook et al, 2011), may represent an ecological advantage in the cold, low-light and iron-limited environment of the Antarctic zone.…”

“…Based on the significant genetic variability found between Southern Ocean populations of morphotypes A and B/C, Cook et al (2011) classified these morphotypes as E. huxleyi var. huxleyi and E. huxleyi var.…”

Change in coccolith size and morphology due to response to temperature and salinity in coccolithophore &lt;i&gt;Emiliania huxleyi&lt;/i&gt; (Haptophyta) isolated from the Bering and Chukchi seas

“…4 shows the relationship between the width of the distal shield elements and LDS. The width of the distal shield elements for all strains was less than 0.1 µm from the range that fits within the plots of morphotype B/C determined by Cook et al (2011). However, the width of the distal shield element in MS1 was larger than that of the other strains.…”

“…According to Young and Westbroek (1991) and Cook et al (2011), the width of distal shield elements is also a useful parameter for classifying coccolith morphotypes. The relationship between the width of the distal shield elements and LDS was tested in the MR70N strain (Fig.…”