Effects of Ancient Climate Change on Population Size of Thylamys Mouse Opossums

Abstract

Since the peak of the last ice age, approximately 23,000 years ago, climates have grown increasingly warmer on earth. This climate change has affected the habitats in the extremely biodiverse region of the Andes Mountains in South America. In order to determine the effect of the climate change on the populations of organisms inhabiting this region, I am exploring the changes in effective population sizes of the Thylamys mouse opossum species. Using multiple individual samples, I have focused specifically on the species Thylamys venustus, T. pallidior, and T. sponsorius. I hypothesize that the effective population sizes of Thylamys venustus and T. sponsorius have decreased since the last glacial maximum because their habitats have moved farther up the mountains and decreased in size. Multilocus nuclear genetic data was used to examine the genetic changes occurring in the Thylamys populations. Fifteen unlinked nuclear loci were amplified across multiple individuals for each species. PCR products were sequenced, aligned, and compared using phylogenetic software to examine phylogenetic relationships and effective population size over time. Data confirmed that my hypothesis is supported by a decrease in the effective population size of Thylamys sponsorius in the last 10,000 years. However, an increase in population size was observed for Thylamys pallidior over the last 25,000 years. Thylamys venustus population sizes seem to be relatively unchanged over the last 50,000 years. A possible reason for increased or unchanged population sizes could be expansion of territory of these Thylamys species and movement southward where the climate is colder. This project is significant because few studies have been conducted to examine the effect of past climate fluctuations on the evolutionary patterns of Thylamys. The Tropical Andes is considered a biodiversity hotspot and understanding evolutionary genetic patterns for the Thylamys species could be used to assist conservation tactics for these marsupials. Ultimately, this project arouses the question: what will happen in the future if the climate continues to grow warmer?