Geology topics

Aaron M. Foley

Publications and source records attributed to Aaron M. Foley.

4 recordsLinked to original sources

USGS2026

Toxoplasma gondii: Challenges and perspectives in interpreting longitudinal seroprevalence data for a chronic parasitic infection

Toxoplasma gondii —the causative agent of toxoplasmosis—is a zoonotic pathogen of warm-blooded hosts. Infection causes mild-to-severe symptoms, including lethargy, fever, muscle pain, abortion, ocular disease, and encephalitis. Toxoplasma affects many vertebrate species, although felids are the only known definitive hosts. Seroprevalence in wildlife is often assessed using cross-sectional data, but few studies have tracked individual-level infections through time. We present a 4-yr dataset from white-tailed deer ( Odocoileus virginianus ) with repeated sampling of individuals that highlights challenges associated with assigning serostatus to individuals. Using a modified agglutination test, we observed seroconversion from seronegative to seropositive within individuals, as expected. Although toxoplasmosis is known to be a chronic disease, we also found reversion from seropositive to seronegative. Accurate assignment of serostatus is necessary for evaluating effects of infection on behavioral and physiologic outcomes. However, longitudinal data from individuals whose titers oscillate around the positive threshold present novel challenges. Therefore, we discuss the implications for assigning serostatus for chronic toxoplasmosis infection for three proposed approaches: 1) ever positive, always positive; 2) negative until positive and then always positive; and 3) status by sampling period. Clarifying which approach is used to assign serostatus when analyzing longitudinal T. gondii data may enable more meaningful comparisons across systems and studies.

Journal of Wildlife Diseases↗

USGS2025

Regional differentiation in somatic growth and maturation attributes for loggerhead sea turtles (Caretta caretta) in the Northwest Atlantic

The ages and sizes at which organisms mature have significant implications for lifetime reproductive success. For species at risk of extinction, such as sea turtles, these attributes can ultimately impact probability of population persistence. Within the Northwest Atlantic Ocean, the broader loggerhead sea turtle ( Caretta caretta ) population comprises management units both along the US Gulf of America (formerly Gulf of Mexico) and Atlantic coasts. Although age, growth, and maturation have been more intensively studied along the US Atlantic, data specific to the Gulf of America have remained sparse. To address this data gap, we conducted skeletal growth mark analysis (skeletochronology) for 123 humerus bones collected from loggerheads found dead in the US Gulf of America from 1998 to 2021. We compared resulting age, growth, and maturation data with information from studies of US Atlantic coast loggerheads for similar size and year ranges, using the exact same skeletochronology methods, as well as with Gulf of America mark-recapture growth data. Results indicate that Gulf of America loggerheads exhibit significantly faster juvenile somatic growth. In addition, sizes at maturation were substantially smaller, corresponding with mean estimates of age at maturation 7.5 to 15 years earlier than US Atlantic counterparts. Finally, the maximum observed Gulf of America adult age estimate was 42.5 years, considerably less than the highest US Atlantic estimate of 77.0 years. These detailed data offer insights into regional variability in somatic growth dynamics and characteristics associated with maturation, which in turn can impact relative reproductive contributions and, ultimately, population trajectories.

Marine Biology↗

USGS2015

Changing migratory patterns in the Jackson elk herd

Migratory behavior in ungulates has declined globally and understanding the causative factors (environmental change vs. human mediated) is needed to formulate effective management strategies. In the Jackson elk herd of northwest Wyoming, demographic differences between summer elk ( Cervus elaphus ) population segments have led to changes in migratory patterns over a 35-year time period. The proportion of short-distance migrants (SDM) has increased and the proportion of long-distance migrants (LDM) has concurrently declined. The probability of winter-captured elk on the National Elk Refuge being LDM decreased from 0.99 (95% CI = 0.97–1.00) to 0.59 (95% CI = 0.47–0.70) from 1978 to 2012. We tested 4 hypotheses that could contribute toward the decline in the LDM segment: behavioral switching from LDM to SDM, differential survival, harvest availability, and calf recruitment. Switching rates from LDM to SDM were very low (0.2% each elk-year). Survival rates were similar between LDM and SDM, although harvest availability was relatively low for SDM that tended to use areas close to human development during the hunting season. Average summer calf/cow ratios of LDM declined from 42 to 23 calves per 100 cows from 1978–1984 to 2006–2012. Further, during 2006–2012, LDM summer calf/cow ratios were less than half of SDM (23 vs. 47 calves per 100 cows). Our data suggest recruitment is the driving factor behind the declining proportion of LDM in this region. Effectiveness of altering harvest management strategies to conserve the LDM portion of the Jackson elk herd may be limited.

Wyoming↗

USGS2015

Influences of supplemental feeding on winter elk calf:cow ratios in the southern Greater Yellowstone Ecosystem

Several elk herds in the Greater Yellowstone Ecosystem are fed during winter to alleviate interactions with livestock, reduce damage to stored crops, and to manage for high elk numbers. The effects of supplemental feeding on ungulate population dynamics has rarely been examined, despite the fact that supplemental feeding is partially justified as necessary for maintaining or enhancing population growth rates. We used linear regression to assess how the presence of feedgrounds, snowpack, summer rainfall, indices of grizzly bear density and wolves per elk, elk population trend counts, brucellosis seroprevalence, and survey date were correlated with midwinter calf:cow ratios, a metric correlated with population growth, from 1983–2010 from 12 ecologically similar elk herd units (7 fed and 5 unfed) in Wyoming, USA. Our statistical approach allowed for rigorous tests of the hypotheses that supplemental feeding had positive effects on calf:cow ratios and reduced sensitivity of calf:cow ratios to bottom-up limitation relative to top-down limitation from native predators. Calf:cow ratios generally declined across all herd units over the study period and varied widely among units with feedgrounds. We found no evidence that the presence of feedgrounds had positive effects on midwinter calf:cow ratios in Wyoming. Further, fed elk showed stronger correlations with environmental factors, whereas calf:cow ratios for unfed elk showed stronger correlations with predator indices. Although we found no consistent association between winter feeding and higher calf:cow ratios, we did not assess late winter mortality and differences in human offtake between fed and unfed regions, which remain a priority for future research.

Wyoming↗