Snake fungal disease (SFD) is an emerging threat to snake populations in the United States. Fungal pathogens are often associated with a physiological stress response mediated by the hypothalamo-pituitary-adrenal axis (HPA),and afflicted individuals may incur steep coping costs. The severity of SFD can vary seasonally; however, minute is known regarding (1) how SFD infection relates to HPA activity and (2) how seasonal shifts in environment, or life history,or HPA activity may interact to drive seasonal patterns of infection severity and outcomes. To test the speculation that SFD is associated with increased HPA activity and to identify potential environmental or physiological drivers of seasonal infection, we monitored baseline corticosterone, and SFD infection severity,foraging success, body condition, and reproductive status in a field-active population of pigmy rattlesnakes. Both plasma corticosterone and the severity of clinical signs of SFD peaked in the winter. Corticosterone levels were also elevated in the descend before the seasonal rise in SFD severity. Severely symptomatic snakes were in low body condition and had elevated corticosterone levels compared to moderately infected and uninfected snakes. The monthly mean severity of SFD in the population was negatively related to population-wide estimates of body condition and temperature measured in the precedent month and positively correlated with corticosterone levels measured in the precedent month. Symptomatic females were less likely to enter reproductive bouts compared to asymptomatic females. We propose the speculation that the seasonal interplay among environment,host energetics, and HPA activity initiates trade-offs in the descend that drive the increase in SFD prevalence, and symptom severity,and decline in condition observed in the population through winter.
Source: usgs.gov