Abstract:
BACKGROUND : Glucocorticoids mediate responses to perceived stressors, thereby restoring homeostasis. However,
prolonged glucocorticoid elevation may cause homeostatic overload. Using extensive field investigations of banded
mongoose (Mungos mungo) groups in northern Botswana, we assessed the influence of reproduction, predation risk,
and food limitation on apparent homeostatic overload (n=13 groups, 1542 samples from 268 animals). We experimentally
manipulated reproduction and regulated food supply in captive mongooses, and compared their glucocorticoid
responses to those obtained from free-living groups.
RESULTS : At the population level, variation in glucocorticoid levels in free-living mongooses was explained by food
limitation: fecal organic matter, recent rainfall, and access to concentrated anthropogenic food resources. Soil macrofauna
density and reproductive events explained less and predation risk very little variation in glucocorticoid levels.
Reproduction and its associated challenges alone (under regulated feeding conditions) increased glucocorticoid
levels 19-fold in a captive group. Among free-living groups, glucocorticoid elevation was seasonal (occurring in late
dry season or early wet season when natural food resources were less available), but the timing of peak glucocorticoid
production was moderated by access to anthropogenic resources (groups with fewer anthropogenic food sources
had peaks earlier in dry seasons). Peak months represented 12- and 16-fold increases in glucocorticoids relative
to nadir months with some animals exhibiting 100-fold increases. Relative to the captive group nadir, some freeliving
groups exhibited 60-fold increases in peak glucocorticoid levels with some animals exhibiting up to 800-fold
increases. Most of these animals exhibited 1- to 10-fold increases relative to the captive animal peak.
CONCLUSIONS : Banded mongooses exhibit seasonal chronic glucocorticoid elevation, associated primarily with food
limitation and secondarily with reproduction. Magnitude and duration of this elevation suggests that this may be
maladaptive for some animals, with possible fitness consequences. In late dry season, this population may face convergence of stressors (food limitation, agonistic encounters at concentrated food resources, evictions, estrus, mate
competition, parturition, and predation pressure on pups), which may induce homeostatic overload.
