Hauling field gear up Gothic Mountain…
Connects epigenetic clocks and DNA methylation research on aging across mammalian species with field ecology of deer mice and burying beetles in mountain environments.
The small mammals of the Gunnison Basin — deer mice (Peromyscus maniculatus), montane voles (Microtus montanus), and western jumping mice (Zapus princeps) — sit at the center of a research program that ties together population ecology, evolutionary biology, and the molecular biology of aging. These rodents are abundant, short-lived, and easy to trap, which makes them ideal subjects for studying how populations cycle through time, how parasites move through wildlife communities, and how mammals as a group have evolved very different life spans. They also matter ecologically: when small mammals die, their carcasses become a rare and valuable resource that feeds an entire community of carrion specialists, especially burying beetles in the genus Nicrophorus.
Several concepts run through the work in this area. DNA methylation refers to small chemical tags that attach to the cytosine bases of DNA; the pattern of these tags changes predictably with age, and statistical models called epigenetic clocks can read those patterns to estimate how old an animal is — and to compare aging rates across species with very different life span variation. The MHC class II genes, by contrast, are immune genes whose diversity helps populations respond to pathogen threats, and their behavior under fluctuating population sizes is a long-standing puzzle in rodent biology. Infection prevalence — the fraction of a population carrying a given parasite — connects these immune systems back to host population dynamics.
On the carrion side, carcass burial is the defining behavior of Nicrophorus burying beetles: a male and female pair locate a small vertebrate carcass, bury it underground, and then provide biparental maternal care, feeding regurgitated tissue to their larvae. Because carcasses are rare and ephemeral, intrusion competition from other beetles is intense, and stridulation (sound produced by rubbing body parts together) may help pairs coordinate defense. Researchers use non-invasive sampling, such as hair tubes that collect fur without trapping animals, to estimate small mammal abundance, and they use plant bioassays — measuring how well seedlings grow in soil — to assess what carrion decomposition returns to the ground.
Early comparative work on rodent biology at RMBL and elsewhere established the deer mouse and its relatives as model organisms for everything from placental structure (Enders, 1965) to hemoglobin physiology at altitude (Gough & Kilgore, 1964) and chromosomal evolution . Parallel work on small-mammal communities documented how human land use shapes them: surveys in exurban Colorado showed that residential development restructures songbird and medium-sized mammal communities along measurable distance gradients from houses .
Parental behaviors including female-pup interactions, vigilance, and antipredator behaviors that influence offspring survival and development
The selective choices made by organisms regarding where to construct nests, influenced by environmental factors that affect offspring survival and rep...
The diversity in maximum life spans across mammalian species, ranging from months to over 200 years.
Proportion of individuals in a population showing signs of pathogen infection
Age estimator based on DNA methylation levels that uses penalized regression to relate chronological age to methylation levels of individual cytosines
Competition where individuals attempt to take over established breeding resources from other pairs
Burying beetle reproductive strategy where pairs bury small carrion for breeding and larval development
Field experiment comparing reproductive success of burying beetle species across habitat types using breeding pairs, mouse carcasses, and environmenta...
Standardized metal can pitfall traps baited with chicken drumsticks, deployed along elevation gradients to monitor burying beetle abundance and specie...
Use of oat seedling growth parameters including root weight fraction to assess soil nutrient availability and quality following various treatments.
454 sequencing to characterize genetic diversity at the DRB Class II locus in montane voles.
Experimental manipulation of beetle stridulation ability by surgically removing the plectrum through V-shaped cuts to the elytra, with controls receiv...
A microarray-based approach to profile DNA methylation at conserved CpG sites across diverse mammalian species without requiring species-specific refe...
FASTA file of 21 MHC Class II Mimo-DRB alleles recovered from a wild population of montane vole (Microtus montanus). Samples were obtained between 200...
Genetic variation at the MHC is vitally important for wildlife populations to respond to pathogen threats. Because natural populations can fluctuate g...
Astragalus microcymbus, the skiff milkvetch, is a perennial forb endemic to Gunnison and Saguache counties in Colorado, United States. In 1995 Denver ...
This version includes the software packages from the Mammalian Methylation Consortium: 1- Genome coordinates for different species 2- R code for align...
A second foundational thread focused on burying beetles as a tractable system for studying reproduction on a limiting resource. Smith and Merrick (Smith & Merrick, 2001) showed that Nicrophorus investigator populations near Gothic depend on the same small rodents (Peromyscus, Microtus, Zapus) that other RMBL researchers were censusing, directly tying beetle demography to small mammal demography. Smith (Smith, 2002) then demonstrated that larval body size strongly predicts overwinter survival, so parental decisions about brood size translate into fitness through the following spring.
A first major result is that small-mammal populations and the parasites and predators they support are tightly linked. In cyclic montane voles, cestode prevalence and intensity rose with host density while Eimeria prevalence declined, and older males carried the heaviest parasite loads (Winternitz et al., 2012). Despite repeated population bottlenecks, montane voles show strong purifying — rather than balancing — selection at the MHC DRB locus, suggesting that gene duplication and demographic fluctuations together shape immune-gene diversity in ways earlier theory did not predict (Winternitz & Wares, 2013). Methodological work has shown that hair tubes can substitute for live trapping: hair-tube counts correlate tightly with mark-recapture estimates of small mammal abundance, opening the door to lower-impact long-term monitoring (Sandoval, 2018); (Sandoval, 2019).
A second body of work uses these same small mammals as carcasses to study burying-beetle ecology. Burial dramatically reduces carcass detection by competitors, and ongoing parental maintenance of the buried carcass reduces it further (Chamberlin, 2025). Habitat strongly structures which species wins: N. investigator dominates open meadows and N. defodiens dominates aspen forests, a pattern that recurs across years and experiments (Oliver, 2013); (Menzel, 2015). Recent work shows that this is not just preference but performance — each species achieves higher brood success in its preferred habitat, in part because meadow surface temperatures can exceed lethal limits (over 100°F) while moist aspen soils keep developing larvae cooler (Muse, 2024). Parental care experiments show that solo females rear broods as successfully as pairs, while solo males do poorly (Lamb, 2014), and that larvae can in fact complete development with no post-hatching care at all (Pekny, 2013) — refining our view of why biparental care evolved in this group.
A third strand connects these mammals to the molecular biology of aging. By assembling DNA methylation profiles from 185 mammalian species, the Mammalian Methylation Consortium built universal epigenetic clocks that predict age with correlations above 0.96 across tissues, and showed that age deviations track mortality risk, caloric restriction, and growth-hormone mutations (Lu et al., 2023). A companion analysis of 348 species found that methylation-based phyloepigenetic trees recapitulate traditional phylogenies and that specific co-methylation modules — particularly ones enriched in HOXL developmental genes and pluripotency factors like OCT4 and SOX2 — correlate with maximum life span across mammals (Haghani et al., 2023); (de Mendoza, 2023).
Early work in the 1990s and 2000s established the basic natural history of Gunnison Basin small mammals and their burying beetles. Studies since 2020 have shifted in two directions. First, climate-driven range shifts are now detectable in the beetle community: comparing surveys from 2009 and 2021, N. defodiens has declined at lower elevations while N. guttula has expanded upslope, consistent with climate-model predictions (Rawinski, 2021). Recent experiments are also drilling into mechanism — how burial depth, maintenance behavior, habitat temperature, and soil moisture interact to determine reproductive success (Chamberlin, 2025); (Muse, 2024); (Cantu, 2024). Second, carcass decomposition is being reframed as a nutrient-cycling process: bioassays using oat seedlings show that beetle-processed soils deliver more phosphorus and potassium than carcasses alone, quantifying the ecosystem service these insects provide (Guijosa, 2022); (Guijosa, 2023).
On the molecular side, the frontier is the integration of pan-mammalian methylation data with the comparative biology of long-lived versus short-lived species, with growing attention to how environmental stressors and reproductive investment register on the epigenetic clock.
Several big questions remain. Do parasites actually drive vole population cycles in the Gunnison Basin, or merely track them? How will continued warming reshape the elevational sorting of burying-beetle species, and will small-mammal carcass supply keep pace? Can epigenetic clocks built from laboratory and zoo animals be calibrated for wild RMBL rodents to measure how environmental stress, reproduction, and elevation accelerate biological aging in nature? And what are the consequences for nutrient cycling if scavenging-insect communities are restructured by climate or by the loss of their small-mammal prey base? Answering these will require linking long-term mark-recapture and hair-tube monitoring to molecular tools that are only now becoming portable into field systems.
Cantu, A. (2024). The Fate of Burying Beetles and their Carcasses: Hardships, Competition and Environmental Factors. →
Chamberlin, A. (2025). Out of sight, out of mind: The role of carcass burial and maintenance in reducing competition in Nicrophorus investigator. →
de Mendoza, A. (2023). A mammalian DNA methylation landscape. Science. →
Enders, A. (1965). A comparative study of the fine structure of the trophoblast in several hemochorial placentas. American Journal of Anatomy. →
Gough, B., Kilgore, W. (1964). A comparative hematological study of Peromyscus in Louisiana and Colorado. Journal of Mammalogy. →
Guijosa, A. (2022). The Impact of Carrion Insects on Human Impacted Soil. →
Guijosa, A. (2023). Plant Bioassay Testing Soil Quality Following Carrion Insect Activity. →
Haghani, A., et al. (2023). DNA methylation networks underlying mammalian traits. Science. →
Lu, A., et al. (2023). Universal DNA methylation age across mammalian tissues. Nature Aging. →
Muse, A. (2024). Coexistence in Burying Beetles: The Niche of Reproductive Temperatures. →
Odell, E., Knight, R. (2001). Songbird and Medium-Sized Mammal Communities Associated with Exurban Development in Pitkin County, Colorado. Conservation Biology. →
Rawinski, M. (2021). Abundance and elevational range shifts of three species of burying beetle in Gunnison County, Colorado. →
Smith, R. (2002). Effect of larval body size on overwinter survival and emerging adult size in the burying beetle, Nicrophorus investigator. Canadian Journal of Zoology. →
Smith, R., Merrick, M. (2001). Resource availability and population dynamics of Nicrophorus investigator, an obligate carrion breeder. Ecological Entomology. →
Snyder, L. (1980). Evolutionary conservation of linkage groups: additional evidence from murid and cricetid rodents. Biochemical Genetics. →
Winternitz, J., et al. (2012). Parasite infection and host dynamics in a naturally fluctuating rodent population. Canadian Journal of Zoology. →
Winternitz, J., Wares, J. (2013). Duplication and population dynamics shape historic patterns of selection and genetic variation at the major histocompatibility complex in rodents. Ecology and Evolution. →
Major histocompatibility complex genes involved in antigen presentation and immune response
A small chemical modification that occurs in most cytosines that are followed by a guanine (CpGs) in mammalian genomes, serving as an epigenetic marke...
Sampling methods that do not require capturing or handling animals, such as hair tube traps that collect hair samples
Relative number of small mammals detected through camera trap monitoring expressed as activity indices
Sound production in insects by rubbing body parts together, in burying beetles occurs when plectrum on elytra rubs against par stridens on abdomen
Successful production of larvae that develop to feeding stage on buried carcasses
Precisely-timed seasonal cycles of reproduction fundamental to animal populations adapting to northern and montane environments
Reproductive strategy where organisms reproduce multiple times throughout their lifetime
Approach to compare genome features across multiple species to identify conserved and variable elements.