Coccolithophores (Calcihaptophycideae, Haptophyta) are characterised by a heteromorphic life cycle with alternating haploid and diploid generations. Typically, diploid cells produce heterococcoliths, whereas haploid cells produce holococcoliths. An important source of evidence for coccolithophore life cycles comes from observations of combination coccospheres, which are cells bearing both types of coccoliths and thus interpreted as capturing the transition from haploid to diploid phase or vice-versa. Such observations are rare and many heterococcolith and holococcolith-bearing taxa remain non-associated to a life cycle phase counter-part. Information on life cycles is even completely missing for entire lineages. Here we report the first observations of heterococcolithophore-holococcolithophore combinations in the family Pontosphaeraceae, consisting of the associations of the morpho-species Scyphosphaera apsteinii with Syracolithus schilleri and of Pontosphaera japonica with an undescribed Syracolithus-like holococcolithophore. These new observations provide clear evidence that the Pontosphaeraceae have dimorphic haplo-diploid life cycles, further supporting the hypothesis that this life cycle pattern is ubiquitous among calcihaptophytes. Moreover, our results highlight a high degree of morphological convergence between holococcolithophores belonging to different lineages, since Syracolithus-like holococcolithophores are also present in the life cycle of species within the Helicosphaeraceae and Calcidiscaceae, the latter family being phylogenetically distant from the Pontosphaeraceae. These morphological resemblances may provide evidence for: (1) morpho-structural constraints on holococcolith construction, and/or (2) ecological convergence of the haploid phases of different coccolithophores.
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We would like to thank the Atlantic Meridional Transect program (AMT 16), namely Tony Bale as well as the officers and crew of the RRS Discovery. This work was supported by a US NSF grant DEB-0415351, an ATIP grant by the Centre National de la Recherche Scientifique (France). This work is part of MF's Ph.D. thesis, funded by the “Fundação Para a Ciência e a Tecnologia”, Portugal, fellowship SFRH/BD/16851/2004, co-financed by the POCI 2010 and FSE. Research on coccolithophores from Tyrrhenian waters (IsaP) was supported by the project VECTOR (VulnErability of the Italian Coastlines and of the marine ecosystems to climate changes and their role in the oceanic caRbon cycle) funded by the Italian Ministry of University and Research. This work is part of the MarBEF EU FP6 Network of Excellence “Marine Biodiversity and Ecosystem Functioning” (contract no. GOCE-CT-2003-505446), and the pluridisciplinary project BOOM (Biodiversity of Open Oceans Microcalcifiers) funded by the French Agence National de la Recherche, grant ANR-05-BDIV-004.
- convergent evolution
- life cycles