213-10 Protoplasmic Plasticity: Structural and Functional Keys to the Success of Foraminifera in Extreme Environments

Session: Cushman Symposium: Microfossils of Extremophiles: Living in the Danger Zone

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As recorded in the fossil record, foraminifera have adapted to many extreme aquatic habitats, but the biological basis for their adaptation to extremes has not yet been fully explained. In an effort to fill this gap in knowledge, the concept of “protoplasmic plasticity” is introduced, which unifies decades of cell biological and behavioral research on foraminifera. At the structural level, foraminiferal cytoplasm appears moth-eaten when viewed by light or electron microscopy due to the presence of numerous large vacuoles. This extensive vacuolar system plays important roles in compartmentalization of various metabolic/respiratory processes (e.g., denitrification, storage of polyphosphate, test calcification) and is intimately involved in housing a wide array of prokaryotic and algal (unicellular or plastid) symbionts. In terms of cell behavior, the characteristic pseudopodial network (reticulopodia) of foraminifera act as a cellular “Swiss army knife” that exert forces locally for certain activities, e.g., rending metazoan prey or bacterial biofilms (skyllocytosis), and globally for others, e.g., whole-cell locomotion or test construction. Their constitutive alternation of generations is likewise plastic, being augmented with various types of gametes (amoeboid, bi- or tri-flagellated) and production of clonal offspring via budding or disparate forms of cell fragmentation. At the molecular level, foraminiferal genomes are extensively endoreplicated, which necessarily leads to enhanced genetic diversity of individuals. Ongoing transcriptomic studies are expected to yield a much greater understanding of the impact of endoreplicated genomes on population fitness.

In sum, the evolutionary success of foraminifera seems underpinned by an extraordinary level of structural, physiological, molecular, and behavioral flexibility (protoplasmic plasticity) that facilitates their adaptation to environmental extremes. Exploring the molecular basis of foraminiferal protoplasmic plasticity should prove to be a fruitful avenue for future research.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6790

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