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.
Highlights
Molecular genetic studies of extant planktonic foraminifera continue to challenge our perception on the diversity within the group (e.g. Darling et al, 1999; de Vargas et al, 1999; de Vargas et al, 2002; Aurahs et al, 2009; Seears et al, 2012; Quillévéré et al, in press)
We suggest that the evolution of elongated chambers in two different genetic lineages is the result of parallel evolution, as it was shown before to have been the case for digitate chamber shapes in various morphospecies of planktonic foraminifera (Coxall et al, 2007) as well as for certain keel structures that appeared independently in closely related lineages (Norris, 1991a)
A comparison of the three morphologic groups with the original descriptions for members of the Globigerinella genus reveals that most of our genetic types correspond to the morphology of G. siphonifera
Summary
Molecular genetic studies of extant planktonic foraminifera continue to challenge our perception on the diversity within the group (e.g. Darling et al, 1999; de Vargas et al, 1999; de Vargas et al, 2002; Aurahs et al, 2009; Seears et al, 2012; Quillévéré et al, in press). Darling and Wade, 2008). Since most of these genetic types cannot be differentiated morphologically, they are often referred to as “cryptic species” and their discovery usually has no impact on the taxonomy of the morphospecies. Weiner et al / Marine Micropaleontology 114 (2015) 19–35 genetic evidence These examples underline that the connection between genetic and morphologic variability in planktonic foraminifera is complex and the resolution of species delineation requires a detailed combined genetic and morphometric analysis. We present such combined analysis for the genetically and morphologically diverse Globigerinella siphonifera/Globigerinella calida plexus
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
