Dissertation Defense: Andrew Zamora

Andrew Zamora will be defending his doctoral dissertation on Friday, June 12th at 10am EST
Location: Machmer E24 and Zoom: 

Title: The Soul of the Sifaka: Ecological, Demographic, and Genomic Influences on the Evolution of the Sifaka (Propithecus)

Abstract: 
The impressive diversity of primate social behavior has been of perennial interest to primatologists, biological anthropologists, and many others. Social behavior has evolved across the primate order through an interaction between primate populations and their environments. What specific aspects of the environment are involved, the levels of biological organization upon which they act, and the time scales over which this occurs, are subject to debate. Sifakas (Propithecus), a genus of lemur species endemic to Madagascar, present a compelling study system for these kinds of questions. Here I examine the social lives of sifakas at multiple scales of organization, space, and time.

Using a comparative database I developed, I identify key ways in which sifaka species vary in the size and composition of their social groups, and to what degree this corresponds to their ecology. Sifaka groups are notably consistent in their size across ecological contexts, although subtle differences exist, with western populations tending to exhibit slightly larger groups than their eastern congeners. Moreover, I find widespread evidence consistent with ecological pressures acting to keep group sizes small. I then examine the factors impacting variation in sifaka population densities across Madagascar. In particular, I expand on earlier work that found unusually high levels of environmental unpredictability across Malagasy field sites. I extend this framework to include several other measures of environmental predictability and how it predicts sifaka population densities across the island. My results suggest a trade-off between climatic predictability and the frequency of cyclones. Additionally, I examine variation in sifaka population size history using whole genome sequence data to model population changes over the past 10 million years. Remarkably, western species that live in unpredictable environments in the present have also experienced greater population change in their past.

My examinations then push deeper into evolutionary time, where I first infer the phylogeny of all nine sifaka species using whole-genome single nucleotide polymorphism data. Compared to previously published phylogenies, it is clear that the relationships among sifaka lineages are complex and I highlight the need of incorporating information from across the genome. I then examine how selection has acted upon over 2,000 protein coding genes across the sifaka genome. I discuss the effects of selection on the sifaka genome peculiar to individual species, specific sifaka clades, and to indriid lemurs relative to other lemur taxa.

Finally, I conclude by highlighting demography as a key mediator of sifaka social evolution, and propose a conceptual model within which this can be examined. The social lives of sifakas are a complex of traits evolved in response to the inherent ecological uncertainties of life on Madagascar. Their remarkable ability to tolerate, even thrive, under uncertainty parallels that of humans, but the question of the limits of this capability looms large. In light of the continually changing relationship between humanity and the environment, this emphasizes the shared plight of Madagascar’s humans and lemurs.