Holococcolithophore-heterococcolithophore (Haptophyta) life cycles: flow cytometric analysis of relative ploidy levels

Several coccolithophore species are known to exhibit heteromorphic life cycles. In certain species, notably Emiliania huxleyi, the heterococcolith-bearing phase alternates with a non-calcifying stage, whereas in others the heterococcolith-bearing phase alternates with a holococcolith-bearing phase....

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Bibliographic Details
Published in:Systematics and biodiversity 2004-06, Vol.1 (4), p.453-465
Main Authors: Houdan, Aude, Billard, Chantal, Marie, Dominique, Not, Fabrice, Sáez, Alberto G., Young, Jeremy R., Probert, Ian
Format: Article
Language:English
Subjects:
Calcidiscus leptoporus
Coccolithophore
Coccolithus huxleyi
Coccolithus pelagicus
Coronosphaera mediterranea
Emiliania huxleyi
haplo-diploid
Haptophyta
heterococcolith
holococ-colith
life cycle
Life cycles
Marine
microalgae
Mineralization
ploidy
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Summary:Several coccolithophore species are known to exhibit heteromorphic life cycles. In certain species, notably Emiliania huxleyi, the heterococcolith-bearing phase alternates with a non-calcifying stage, whereas in others the heterococcolith-bearing phase alternates with a holococcolith-bearing phase. Heterococcolithophore-holococcolithophore life cycles have previously been observed for only one species in culture, but have also been inferred from an increasing number of observations of combination coccospheres. 18S rDNA sequences from pure cultures of both the heterococcolith-bearing and holococcolith-bearing phases of Coccolithus pelagicus were identical, providing an additional indication of their identity as different life cycle stages of the same species. Flow cytometric analyses have been undertaken on SybrGreen-stained nuclei isolated from pure cultures of the two phases of four coccolithophore species (Coccolithus pelagicus, Calcidiscus leptoporus, Coronosphaera mediterranea and Emiliania huxleyi) in order to determine relative DNA content. Results confirm the hypothesis that holococcolithophore-heterococcolithophore life cycles are haplo-diploid in nature. Light microscope observations of the processes of sexual fusion and meiosis are reported for two of the experimental species. The results are discussed in the context of the evolution of biomineralization in the coccolithophores and the possible ubiquity of haplo-diploidy in the haptophytes.
ISSN:1477-2000
1478-0933
DOI:10.1017/S1477200003001270