In situsurvey of life cycle phases of the coccolithophoreEmiliania huxleyi(Haptophyta)

Abstract

The cosmopolitan coccolithophore Emiliania huxleyi is characterized by a strongly differentiated haplodiplontic life cycle consisting of a diploid phase, generally bearing coccoliths (calcified) but that can be also non-calcified, and a non-calcified biflagellated haploid phase. Given most studies have focused on the bloom-producing calcified phase, there is little-to-no information about non-calcified cells in nature. Using field mesocoms as experimental platforms, we quantitatively surveyed calcified and non-calcified cells using the combined calcareous detection fluorescent in situ hybridization (COD-FISH) method and qualitatively screened for haploid specific transcripts using reverse transcription-PCR during E. huxleyi bloom successions. Diploid, calcified cells formed dense blooms that were followed by the massive proliferation of E. huxleyi viruses (EhVs), which caused bloom demise. Non-calcified cells were also detected throughout the experiment, accounting for a minor fraction of the population but becoming progressively more abundant during mid-late bloom periods concomitant with EhV burst. Non-calcified cell growth also paralleled a distinct window of haploid-specific transcripts and the appearance of autotrophic flagellates morphologically similar to haploid cells, both of which are suggestive of meiosis and sexual life cycling during natural blooms of this prominent marine phytoplankton species.

Is coccolithophore distribution in the Mediterranean Sea related to seawater carbonate chemistry?

“…Differences in the morphology and ecology of the two life phases enable the species to survive under a wider range of environmental conditions and could result in a wider distribution range in space and/or time. For instance, blooms of Emiliania huxleyi in heterococcolith phase can end due to viral attacks (Martínez et al, 2007; Vardi et al, 2012) which the haploid phase (i.e., holococcolithophores) can resist (Frada et al, 2008(Frada et al, , 2012: Therefore, the occurrence of haploid individuals would serve as new starting point in the case of viral attack in the heterococcolith phase. Another factor that could have affected the results presented here is zooplankton grazing: although generally zooplankton grazing does not cause E. huxleyi blooms to end (Nejstgaard et al, 1997), their effect on smaller populations could be more important.…”

Global marine plankton functional type biomass distributions: coccolithophores

“…Cytoplasm dimensions have been published for very few coccolithophore species, with species descriptions usually providing the more easily observed coccosphere dimensions only. Observations of 16 species of coccolithophore from laboratory and field studies show cytoplasm diameter varying from 30 to 90 % of the total coccosphere diameter, depending on the species and level of calcification (Table 2); naked coccolithophores have also been observed for some species, although they are relatively rare in field samples (Frada et al, 2012). While these 16 species represent only a small fraction (10 %) of the species represented in the database, they include some of the more dominant coccolithophores in terms of both abundance and frequency of observation: these 16 species together account for an average of 75 ± 32 % of coccolithophore abundance per sample (median = 92 %), and we therefore consider them to be reasonably representative for the purposes of estimating coccolithophore biomass.…”

Defining the ecological and physiological traits of phytoplankton across marine ecosystems

“…The life cycle of E. huxleyi is thought to fluctuate between diploid and haploid stages, with calcification only occurring in the diploid stage, and motility occuring during the haploid stage (Paasche, 2001). The coordinated increase of genes associated with calcification with the decrease of genes associated with haploid life stage, particularly DYH, which is integral to the flagella, highlight this known association of calcification and ploidy state (Frada et al, 2012). Interestingly, recent work has suggested the erosiion of the 1N-specific genes, such as those integral to flagella formation, in several oligotrophic strains of E. hxuleyi (von Dassow et al, 2015).…”

“…These analyses were run with edgeR using default parameters to calculate dispersion and to assess differential abundance of both individual transcripts and orthologous groups of each of the amended incubations compared to the no-addition control. Genes thought to be associated with nitrogen and phosphorus metabolism (Dyhrman et al, 2006;Rokitta et al, 2014;McKew et al, 2015) and with calcification and ploidy state Mackinder et al, 2011;Frada et al, 2012) were compared against the translated proteins comprising the orthologous groups used in this study (tblastn with an e-value cutoff of 1e-20).…”

“…Vacuolar H+-ATPase V0 sector subunits c/c (ATPVcc)). Simultaneously in N-amended incubations, there was a significant decrease in the abundance of two genes used as markers of haploid life phase (Frada et al, 2012), dynein heavy chain (DYH) and histone H2A (H2A). The life cycle of E. huxleyi is thought to fluctuate between diploid and haploid stages, with calcification only occurring in the diploid stage, and motility occuring during the haploid stage (Paasche, 2001).…”