Fig. 2: Change in age distribution among “wild type” PRNP homozygote mule deer at Table Mesa.

Proportional distribution of sampled Table Mesa mule deer (Odocoileus hemionus) homozygous for serine (S) at PRNP codon 225 (225SS)—“wild type”—across three age groups (1–2-year-old, 3–4 year-old, or ≥5-year-old) in 2005 (n = 85) or in 2018–2019 (n = 74). The change in age distributions between the two study periods (2 × 3 Fisher’s exact test P = 0.035) appeared to be driven by capture of fewer individuals ≥5 years old and an accompanying increase in 3–4-year-old individuals in the 2018–2019 sample. Because captures tended to focus on obviously adult animals our samples may have underrepresented the younger age class by largely excluding 1-year-olds, but this potential bias was consistent between the two study periods and would not give rise to differential capture/sampling probabilities between the two older age groups. Bars are the proportion of the sample in an age group from the respective study periods. Capped vertical lines are 95% binomial confidence intervals; numbers shown at the bottom of bars are respective sample sizes (number of individual deer).