The evolution of Atlantic and Pacific sister species has also been the subject of decades worth of research that has measured rates of evolutionary change on the molecular level by calibrating the molecular clock with the geologic data on the dates of the rise of the isthmus of Panama, which is thought to have occurred about 3.5 million years ago, although this hypothesis is now contested, as an alternative, but not conclusive, date of approximately 18-20 million years has been proposed for the rise of the isthmus. Nevertheless, the rise of the isthmus has permitted one of the most important and extensively studied natural experiments in evolution, a natural experiment that now allows scientists to test specific predictions considering the ecological and evolutionary dynamics that have allowed species to adapt to the biotic and abiotic conditions in different environments.
Adaptation to different environment conditions can impose differential selection pressures on reproductively isolated populations. Therefore, we should predict that physiological and behavioral traits should confer adaptive value to the different conditions found in the coastal marine environments of Panama. We have recently tested the effects of adaptive radiation to different environmental conditions of the Pacific and Atlantic Oceans on the strategies of larval development in two geminate species of coastal mud snails (Potamididae) across the Isthmus of Panama, Cerithideopsis californica on the Pacific coast and C. pliculosa on the Atlantic. Differences in the productivity of western Atlantic and eastern Pacific coastal environments in this region allowed us to predict that in an environment of relatively low productivity (the Atlantic), natural selection will favor the evolution of larval developmental strategies that allow it to survive in these environments of low productivity through increased maternal investment and reduced larval duration in development.