Pseudo-cryptic speciation in coccolithophores

Abstract

Coccolithophores are a group of calcifying unicellular algae that constitute a major fraction of oceanic primary productivity, play an important role in the global carbon cycle, and are key biostratigraphic marker fossils. Their taxonomy is primarily based on the morphology of the minute calcite plates, or coccoliths, covering the cell. These are diverse and include widespread fine scale variation, of which the biological͞taxonomic significance is unknown. Do they represent phenotypic plasticity, genetic polymorphisms, or species-specific characters? Our research on five commonly occurring coccolithophores supports the hypothesis that such variation represents pseudocryptic speciation events, occurring between 0.3 and 12.9 million years ago from a molecular clock estimation. This finding suggests strong stabilizing selection acting on coccolithophorid phenotypes. Our results also provide strong support for the use of fine scale morphological characters of coccoliths in the fossil record to improve biostratigraphic resolution and paleoceanographic data retrieval.

Elliptochloris bilobata var. corticola var. nov. (Trebouxiophyceae, Chlorophyta), a novel subaerial coccal green alga

“…corticola may seem similar in traditional morphological features, the wide use of molecular characters has recently pointed to a general previously underestimated genetic and taxonomic diversity within traditional morphospecies. Such semi-cryptic or pseudo-cryptic taxa with subtle morphological differences have now been reported in diverse algal groups, including haptophytes (Saez et al 2003), diatoms (Amato et al 2007), prasinophytes (Slapeta et al 2006), as well as coccoid green algae (e.g., Fawley et al 2005b;Vanormelingen et al 2007). In addition, both varieties differ ecologically, since the former was originally identified as a phycobiont in temperate-zone high mountains (altitude of 2200 m a.s.l.)…”

Cryptic species within the cosmopolitan desiccation-tolerant moss Grimmia laevigata

“…Some widespread taxa once thought to be ecological generalists are now known to be collections of genetically distinct and sometimes broadly sympatric populations specialized to different habitats, microhabitats, or species interactions. Recent examples, using analysis of DNA sequences or fragments, span a wide range of taxa, including sympatric fig wasps that use the same fig species (40), the widespread neotropical skipper butterfly Astraptes fulgerator that is now recognized as 10 species (41), the millipede Anadenobolus excisus in Jamaica that includes three deeply divergent clades (42), the black mould Stachybotrys chartarum (43) that includes two distinct lineages, and cooccurring clades of marine calcifying algae called coccolithophores that may differ in their ecological preferences (44).…”

Expressed sequence tag profiles from calcifying and non-calcifying cultures of Emiliania huxleyi

“…cDNA sequences can also be employed to identify and compare introns in corresponding genomic sequences to resolve more detailed relationships. Some of the nuclear encoded functional genes, such as nitrate reductase, light harvesting complex proteins, elongation factor Tu, glyceraldehydes-3-phosphate dehydrogenase, and FtsH that have been identified in our libraries, are ideally suited for these purposes and can be used to complement work being done with rRNA sequences (Saez et al 2003). Functional gene sequences and their products can define physiological capabilities and as such can provide independent information about paleoenvironmental features to which coccolithophorids have adapted.…”