DOES DEVELOPMENTAL PLASTICITY INFLUENCE SPECIATION? USING HIGH-RESOLUTION CT SCANNING TO QUANTIFY ONTOGENETIC TRAJECTORIES IN PLANKTONIC FORAMINIFERA BEFORE, DURING AND AFTER SPECIATION

Variation among individuals forms the raw material for evolution. During their lifetime, individuals can often adjust their state in response to environmental conditions. This plasticity in developmental history is hypothesized to stimulate the expression of novel trait combinations, increasing mean population fitness and accelerating local adaptation. However, very few empirical data exist to test this hypothesis on macroevolutionary time scales, as developmental history is often impossible to reconstruct from fossilized remains.

Here, we use the exceptionally resolved fossil record of planktonic foraminifera to study developmental plasticity in deep time. Foraminifera retain their entire life history inside their calcium carbonate shells, allowing for detailed morphometric analyses at different ontogenetic stages. Using micro-CT scans, we reconstruct individual chamber volume and shape as well as coordinates in xyz-space to reconstruct 3-dimensional growth trajectories. We analyse morphological changes before, during and after speciation in the Menardella limbata – Menardella exilis lineage to study the influence of developmental plasticity on macroevolutionary processes.

The resulting developmental trajectories show that growth rates vary among species, as well as through time, implying evolutionary controls on ontogeny. Next, environmental conditions reconstructed from the chemical composition of the shells are compared to morphological change to test whether plasticity promotes adaptation to changing environments, and ultimately the origination of new species.