Graduate Exit Seminar - Marissa Roseman

Plan to join Marissa Roseman's graduate exit seminar on December 15, 2025, at 10:00 am at Kottman Hall Room 333 or via Zoom. Marissa will present, "Genomic Consequences of Isolation and Population Declines in Timber Rattlesnakes"

Abstract: Accelerating global biodiversity declines may be exacerbated by a loss of genetic diversity that can decrease future population viability for species of conservation concern. Strong genetic drift in small and isolated populations may be compounded by the lingering effects of historic demography, making consequences of recent and historic declines difficult to disentangle. Additionally, not all types of genetic diversity are desirable, and the distribution of adaptive “good” mutations vs. “bad” mutational load may be influenced by the strength of genetic drift over time with implications for conservation. Here, I explore the genomic consequences of demographic change in several populations of timber rattlesnake (Crotalus horridus), a pit viper with a broad range across the eastern U.S. that is threatened or endangered in several states. I generated a reference genome and whole-genome resequencing dataset for 78 rattlesnakes from eight populations spanning a gradient of population size and isolation. Using this data, I aimed to quantify the effective size, degree of isolation, and inbreeding for contemporary populations and infer the demographic history that shaped their genetics. I then assessed the functional genomic consequences of different demographic patterns for harmful mutations and disease-related adaptive potential. I found that measures of overall genetic diversity were correlated with contemporary habitat patch size and the smallest populations showed evidence of recent inbreeding. While ancient bottlenecks likely also reduced diversity, simulation-based demographic inference suggested that populations remained large and more contiguous until recent declines. As a result of shrinking population size, the smallest populations also showed increased likelihood of suffering the effects of harmful recessive mutations, while all populations had reduced adaptive potential in disease-related genes. These results highlight the need for patch-level management to boost population size and connectivity and prevent further accumulation of harmful mutations and loss of beneficial variation in this species of conservation concern.

Advisor: Dr. Bill Peterman