About the Author
Madeleine Becker (she/her) is a PhD candidate at the Smithsonian-Mason School of Conservation, George Mason University, and a graduate fellow in the Center for Conservation Genomics at the Smithsonian’s National Zoo & Conservation Biology Institute. Her research, advised by Dr. Jesús Maldonado and Dr. Cody Edwards, focuses on evolutionary and conservation genomics in wild mammal populations—with a particular interest in incorporating historical specimens to understand variation within species over time. Learn more about Madeleine on her website or follow her on Bluesky @mabscientist.
How ‘time series museomics’ informs evolutionary and conservation genomics
Island organisms are notorious for evolving rapidly, resulting in awe-inspiring radiations like Darwin’s Galapagos finches or Hawaiian silverswords. In comparison, the mild morphological and genetic differences accumulated over [at least] 12,000 years between the eight subspecies of California Channel Island deer mice might not seem as exciting an evolutionary subject. As members of the widespread Peromyscus maniculatus species group, they also may not seem like the greatest priority for conservation research. However, these animals make up for their apparent lack of novelty in one of the most scientifically valuable ways: abundance.
Channel Island mice have been documented in detail and vouchered in museum collections since the late nineteenth century (Figure 1). Some of these specimens were collected as part of far-reaching biological expeditions, such as the Los Angeles County Museum’s Channel Islands Biological Survey. Others were collected as bycatch in other small mammal studies, or in efforts to cull non-native rats. Moreover, island mice have continued to persist on all eight islands despite threats of invasive species, hantavirus outbreaks, and habitat degradation due to intensive ranching. As a result, they are an excellent candidate model for understanding short-term genetic change in wild mammal populations. Furthermore, with their close relationships and relatively short evolutionary history, the eight subspecies neatly form a cohort of natural experiments.
My research takes a “time-series museomics” approach to attempt to disentangle the complex signatures of island colonization, potential inter-island migration, and historically documented bottlenecks in this group to understand drivers of demographic and genetic change. With EECG funding, I am now able to sequence hundreds of low-coverage whole genomes from samples (largely museum specimens) collected over 120 years across all eight Channel Islands. These genomic data will help answer some outstanding questions in this system with broader applications for isolated wild mammal populations. For example, how do metrics of diversity, inbreeding, and mutational load correspond with population or island size? Island biogeography would predict that larger islands are more diverse, but these isolated lineages must be depauperate compared with their mainland relatives with huge effective population sizes. Quantifying these geographic differences, and tracking how these metrics changed throughout recent history will provide unprecedented insight into how small populations behave under a variety of ecological circumstances.
Furthermore, while these Peromyscus populations have historically occurred in extremely high densities on some islands (Drost & Fellers, 1991), these endemic rodents are still vulnerable to the forces that threaten many island organisms. Habitat degradation and invasive rats may have played a part in a temporary local extirpation on one island (Pergams et al., 2000), and a closely related island mouse in Baja California has gone extinct, likely caused by a single feral cat (Alvarez-Castañeda & Cortés-Calva, 1996). Extirpations would be catastrophic for Channel Island ecosystems, in which endemic foxes, skunks, and snakes rely on mice as their main source of prey. My past work using mitochondrial DNA demonstrated that Channel Island mice harbor surprisingly unique haplotypes (Figure 2), perhaps indicative of relictual biodiversity lost on the mainland (Becker et al., in press). This finding further underscores the importance of understanding how diverse these populations are, how recent changes on the islands affected this diversity, and whether their genomes demonstrate any risk for potential future collapse.
This award will help generate a treasure trove of new information: where island mice came from, how they have survived isolation over thousands of years, how they have been impacted by anthropogenic change, and how we can use all of this information to better inform conservation across the tree of life.
References
Alvarez-Castañeda ST & Cortés-Calva P. (1996). Anthropogenic extinction of the endemic deer mouse, Peromyscus maniculatus cineritius, on San Roque Island, Baja California Sur, Mexico. The Southwestern Naturalist, 41: 459–461.
Becker MA, Carrasco C, Kautt AF, Castañeda-Rico S, Orrock JL, Maldonado JE, Edwards CW. (In press) Phylogenetics of Channel Island deer mice based on the cytochrome b gene sheds light on multiple colonization events and supports current taxonomy. Western North American Naturalist.
Drost CA & Fellers GM. (1991). Density cycles in an island population of deer mice, Peromyscus maniculatus. Oikos, 60: 351–364.
Pergams ORW, Lacy RC, Ashley MV. (2000). Conservation and management of Anacapa Island deer mice. Conservation Biology, 14: 819–832.