Effect of gross morphology on modern planktonic foraminiferal test strength under compression

Pincelli M. Hull,Janet E. Burke

doi:10.1144/jmpaleo2016-007

Pincelli M. Hull, Janet E. Burke

Open Access

https://doi.org/10.1144/jmpaleo2016-007

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Abstract

Planktonic foraminifera are a source of important geochemical, palaeoceanographic, and palaeontological data. However, many aspects of their ecology remain poorly understood, including whether or not gross morphology has an ecological function. Here, we measure the force needed to crush multiple planktonic foraminiferal morphotypes from modern core top and tow samples. We find significant differences in the resistance of different morphotypes to compressional force. Three species, Globorotalia tumida (biconvex, keeled), Menardella menardii (discoidal, keeled), Truncorotalia truncatulinoides (conical, keeled), require on average 59% more force (1.07 v. 0.47 N) to crush than the least resistant species ( Orbulina universa and Trilobatus sacculifer ) in core-top samples. Towed samples of pre-gametogenic individuals also show significant differences of the same magnitude (0.693 v. 0.53 N) between the conical ( T. truncatulinoides ) and globular/spherical morphologies ( Globoconella inflata and O. universa ). We hypothesize that the greater compressional strength of certain shapes confers a fitness advantage against predators and could contribute to the repeated, convergent evolution of keeled, conical and bi-convex forms in planktonic foraminifer lineages. Supplementary material: Raw data for all crushing experiments, wall thickness measurements, and results for all pair-wise Kolmogorov-Smirnov Tests are available at https://doi.org/10.6084/m9.figshare.c.3725236.v1

Highlights

ObjectivesThe aim of this study was to understand how mean compressional force at test failure varies amongst species and how this might affect their ecology
The eight species targeted were chosen based on abundance, morphology and wall thickness, and included the globigerinoid foraminifer Trilobatus sacculifer (formerly Globigerinoides sacculifer, see Spezzaferri et al (2015)); the spherical Orbulina universa; the calcite-encrusted globigerinoid Globigerinoides conglobatus; the rounded, cuboidal Neogloboquadrina dutertrei; the inflated, semi-conical chambered turborotalid Globoconella inflata; the keeled, biconvex globorotalid Globorotalia tumida; the keeled, compressed, thin-walled globorotalid Menardella menardii; and the conical globorotalid Truncorotalia truncatulinoides (Fig. 1)
Modern planktonic foraminifera differ in their resistance to crushing, as measured by mean compressional force at test failure