This study investigates how extreme climate fluctuations of the Ice Ages over the past several hundred thousand years might have affected the geographic distributions, genetic structure, and diversity of species. Theory suggests that fluctuating climates may have acted as a force promoting diversification. To better understand the specific effects of ancient climate fluctuations on the diversification of species, this project focuses on a group of marsupials (Thylamys opossums) that live in the Andes Mountains of South America. Genetic data and computational tools will be used to make inferences about events that occurred in the distant past. With this genetic evidence in hand, hypotheses concerning the impact of ancient climate change on species diversity can be tested.
Only a handful of studies have examined the evolutionary patterns of Andean mammals in the context of ancient climate fluctuations, and prior to this work, none has considered these factors for Thylamys species. This project is significant and distinct from previous efforts because it will explicitly test alternative evolutionary hypotheses using multiple types of genetic data, ecological models of each population's geographic distribution, and sophisticated computational tools. When complete, this project will illustrate from multiple perspectives the impact of climatic shifts on biodiversity in Thylamys. Finally, the species considered here live in a biodiversity hotspot (the Tropical Andes), and a clear understanding of genetic patterns for this group can be used to guide localized conservation strategies for this unique group of mammals.
This project resulted in several important findings that improve our understanding of both the biodiversity currently present in the tropical Andes and the evolutionary processes that may have led to this biodiversity. We focused on the marsupial genus Thylamys, a group of marsupials from the southern part of South America. We uncovered three pairs of cryptic species; that is, species that were impossible to identify by eye and required the use of sophisticated DNA-based studies. We also used computational tools to investigate how ancient climate changes (e.g., the ice ages) might have influenced the evolution of this group, particularly species that live in the mountains. Our results provide support for many of our hypotheses concerning the patterns that we expected to observe when mountain-dwelling populations experience climate cooling and warming over hundreds of thousands of years. One core finding is that the last interglacial period in the Earth's history, which took place approximately 125,000 years ago, was the period during which multiple species first began to diverge. This finding highlights the importance of climate warming in driving mountain-dwelling populations into more isolated habitats. As we contend with the effects of anthropogenic climate change in the coming years, a solid understanding of how species responded to past climate changes can serve as a useful guide to predicting how modern-day species might react to warming climates.