The Central American Isthmus (CAI) closed about three million years ago, providing the backdrop for one of the most remarkable natural experiments of genomic divergence and adaptation in tropical marine organisms.

The rise of the CAI simultaneously separated marine populations that were previously connected and profoundly shaped the physical environments of the two newly isolated oceans. Since then the Tropical Eastern Pacific (TEP) and the Tropical Western Atlantic (TWA) differ across several major environmental axes.

These include temperature, pH, dissolved oxygen and productivity, parameters that are now rapidly changing on a global scale. Moreover, within the TEP, seasonal upwelling in the Gulf of Panama relative to a lack of upwelling in the adjacent Gulf of Chiriquí generates striking differences across many of the same environmental variables that distinguish the two oceans.

We propose to exploit this powerful natural experiment to study the intersection between past and contemporary evolutionary processes and the role they play in the resilience and adaptability of marine organisms. This project builds on decades of research that have identified so-called ‘geminate species’ that were separated by the closure of the CAI, representing replicated instances of genomic divergence and adaptation.

Our experimental approach couples insights gained from sampling genomic variation in natural fish populations and transcriptional variation in a common-garden experiment.

These data will allow insights into how tropical marine species adapt to changing environmental conditions, providing the opportunity to ultimately predict how they will respond to global change.