The effect of extreme weather events on hair cortisol and body weight in a wild ring-tailed lemur population (Lemur catta) in southwestern Madagascar.

Madagascar is known for its hypervariable climate with periodic droughts and cyclones, but little is known of the impact of such events on lemur physiology. We examined the effects of sequential weather periods, drought, normal, cyclone and post-cyclone, on hair cortisol concentrations (HCC) and body weight in wild ring-tailed lemurs, Lemur catta (n = 185), at the Bezà Mahafaly Special Reserve in southwestern Madagascar. Data were modeled and analyzed by sex, age, and troop. Given the ecological consequences of extreme climatic perturbations, we hypothesized that drought and cyclone would significantly impact lemur HCC. Among adults, drought was associated with higher HCC than other periods and the lowest HCC was associated with the post-cyclone period. Adult females had greater variation in HCC during drought and males had greater variation during cyclone and Post-cyclone periods, suggesting sexes were differentially affected in terms of how individuals responded to extreme weather events. Low HCC in the post-cyclone period followed a 12-month period of reduced availability of primary and fallback food resources. Based on the known extreme and chronic nutritional stress during this time, our results indicate hypocortisolism in the animals included in our analysis. Higher HCC in sub-adults during the cyclone also suggests that immature lemurs may experience extreme weather events differently than adults. Body weight, used as a gauge for environmental stress, was lowest during the post-cyclone for sub-adults, young adults, and adults. Body weight did not differ by sex among adults across any of the weather events. Overall, ring-tailed lemur's HCC appear to be more immediately impacted by drought, or stressors associated with that specific weather event, and influenced by the long-term impact of cyclones on resource availability evidenced by data from the post-cyclone period.

Adrenal-dependent diurnal modulation of conditioned fear extinction learning.

Post traumatic stress disorder (PTSD) is associated with altered conditioned fear extinction expression and impaired circadian function including dysregulation of glucocorticoid hormone secretion. We examined in adult male rats the relationship between conditioned fear extinction learning, circadian phase, and endogenous glucocorticoids (CORT). Rats maintained on a 12h light:dark cycle were trained and tested across 3 separate daily sessions (conditioned fear acquisition and 2 extinction sessions) that were administered during either the rats' active or inactive circadian phase. In an initial experiment we found that rats at both circadian phases acquired and extinguished auditory cue conditioned fear to a similar degree in the first extinction session. However, rats trained and tested at zeitgeber time-16 (ZT16) (active phase) showed enhanced extinction memory expression during the second extinction session compared to rats trained and tested at ZT4 (inactive phase). In a follow-up experiment, adrenalectomized (ADX) or sham surgery rats were similarly trained and tested across 3 separate daily sessions at either ZT4 or ZT16. ADX had no effect on conditioned fear acquisition or conditioned fear memory. Sham ADX rats trained and tested at ZT16 exhibited better extinction learning across the two extinction sessions compared to all other groups of rats. These results indicate that conditioned fear extinction learning is modulated by time of day, and this diurnal modulation requires the presence of adrenal hormones. These results support an important role of CORT-dependent circadian processes in regulating conditioned fear extinction learning, which may be capitalized upon to optimize effective treatment of PTSD.