Genetic and morphometric evidence for parallel evolution of the Globigerinella calida morphotype

Abstract

Molecular genetic investigations of the highly abundant extant planktonic foraminifera plexus Globigerinella siphonifera/Globigerinella calida have recently shown this group to be the genetically most diverse one within planktonic foraminifera, separating it into 12 distinct genetic types belonging to three main genetic lineages. Independently, several morphological or physiological variants have been described within the group, but the correlation between the high genetic diversity and the phenotypic variability remains unclear. In this study, we combine genetic data with morphometric analyses of shell shape and porosity of genotyped individuals of the different genetic lineages. Our morphometric measurements suggest a differentiation of three morphotypes within the plexus, two of which possess the elongated chambers described as a typical trait of G. calida. These two morphotypes with elongated chambers are associated with two distinct genetic lineages. The G. calida morphology therefore appears to have evolved twice in parallel. Unexpectedly, we show that the two morphotypes with elongated chambers can be separated from each other by characters seen in the lateral view of their shells. This implies that the taxonomy of the extant members of the genus Globigerinella should be revised. A comparison with the original descriptions and type specimens of members of the genus shows that two genetic types of one major lineage correspond to G. calida. The second group with elongated chambers is associated with a recently diverged genetic type and we propose to reinstate the name Globigerinella radians for this distinct form. The remaining nine of the 12 genetic types correspond to the G. siphonifera morphology, and in the absence of evidence for morphological differentiation, they form a paraphyletic morpho-taxon. Our results highlight the prevalence of parallelism in the evolution of shell morphology in planktonic foraminifera even at the lowest level of relatedness represented by genetic types

Planktic foraminifer and coccolith contribution to carbonate export fluxes over the central Kerguelen Plateau

“…Under this hypothesis, colder SST south of the Polar Front might explain larger individuals of N. pachyderma at M6 and A3 sites. However the fact that Crozet communities of T quinqueloba and G. bulloides have a significantly homogeneous size in the PFZ and AAZ suggests that temperature is not the only factor at play and that population dynamics (Schiebel et al, 1997) and the availability of prey (Schmidt et al, 2004) as well as genetic diversity within a given morphospecies (Weiner et al, 2015) might also constrain planktonic foraminifer size.…”

Methodology for Single-Cell Genetic Analysis of Planktonic Foraminifera for Studies of Protist Diversity and Evolution

“…Preservation in ethanol, a hypothetical third option commonly used for metazoans, is not recommended for foraminifera as it inhibits the amplification of DNA by PCR (Holzmann and Pawlowski, 1996;Lecroq, 2014). Drying and freezing has been used preferably in the last years, since it allows faster handling of foraminiferal specimens (André et al, 2013;Weiner et al, 2014Weiner et al, , 2015. A considerably larger number of specimens can be preserved using this method, as it does not involve individual selection and placement in microtubes immediately after sampling.…”

“…Since the development of DNA extraction methods which leave the calcite shell intact, the DNA sequences can be directly associated with the morphology of the same individual, establishing a definitive link between genetic diversity and subtle morphological variability (e.g., Morard et al, 2009Morard et al, , 2011Quillévéré et al, 2013). In some cases, the combination of genetics and morphology has even led to a revision of the original morphological taxonomy (Darling et al, 2006;Aurahs et al, 2011;Weiner et al, 2015).…”

Factors Influencing Porosity in Planktonic Foraminifera

“…Differences in porosity have been observed among genetic species within two morphospecies complexes: Orbulina universa and Globigerinella siphonifera (Huber et al, 1997;de Vargas et al, 1999;Morard et al, 2009;Morard et al, 2013;Marshall et al, 2015;Weiner et al, 2015). In fact, it is the sole characteristic by which two cryptic species of Globigerinella siphonifera can be identified in empty tests (Huber et al, 1997).…”

“…Ecophenotypy in planktonic foraminifera has largely fallen out of favor as an explanation for variation in morphology, with the observations that ecophenotypes often align with different genetic complexes (Huber et al, 1997;de Vargas et al, 1999;de Vargas et al, 2001;Morard et al, 2009;Quillévéré et al, 2011;Morard et al, 2013;Marshall et al, 2015;Weiner et al, 2015). However, it is well-established that the expression of any phenotypic trait is a product of both its genes and its environment (e.g.…”