DISENTANGLING SYNERGISTIC CLIMATE DRIVERS ON THE ANAGENETIC EVOLUTION OF PLANKTONIC FORAMINIFERA

Evolution is driven by a combination of biotic and abiotic factors. When quantifying the effects of abiotic drivers, evolutionary change is generally described as a response to a single environmental parameter assumed to represent global climate. However, climate is a complex system consisting of many interacting factors and characterized by high regional variability. Therefore, to undertake an in-depth analysis of the role of climate in evolutionary change, we need to consider multiple global and regional environmental parameters and their interactions.

The deep-sea microfossil record is sufficiently complete that multivariate climatic and multivariate morphological trait data can be obtained from the same samples. Here we present morphological records of the planktonic foraminifera species Globoconella puncticulata and Truncorotalia crassaformis from mid-latitude (IODP Site U1313, ~40° N) and sub-polar (ODP Site 981, ~55° N) settings in the North Atlantic Ocean over a ~500,000-year interval directly preceding the extinction of G. puncticulata (2.41 Ma). Test size and shape of over 20,000 individuals were measured and compared to site-specific records of sea surface temperature, primary productivity and marine aeolian dust deposition, as well as to records of global ice volume, ocean circulation and atmospheric CO₂.

Morphological parameters respond very weakly to individual climate parameters, but ~35% of their variance was explained when interactions among all studied climate parameters were incorporated. Principal Component Analysis indicates that size and CO₂ vary along the same axis, which is orthogonal to an axis of Neodymium, ice volume and sea surface temperature variation. However, the PCA is limited by assuming no temporal changes in covariance patterns. Observed covariances between environmental parameters vary strongly with glacial-interglacial cyclicity, implying that relative influences of the studied parameters on morphology change over time. Furthermore species’ responses differed between geographic locations, impressing the need to test how interactions among multiple climate variables at different regional settings shape the microevolutionary biotic response to local and global abiotic change.