Baseline and stress‐induced glucocorticoids during reproduction in the variable flying fox, Pteropus hypomelanus (Chiroptera: Pteropodidae)

Abstract

Baseline and stress-responsive glucocorticoid (GC) levels were assessed during early pregnancy, late pregnancy, and lactation in female variable flying foxes (Pteropus hypomelanus) and in males over the same time period. Animals were maintained in a breeding colony in captivity. High levels of both cortisol and corticosterone were detected, with total plasma GC levels being among the highest documented in vertebrates (up to 3000 ng/ml in individual animals, with cortisol being the primary GC, accounting for approximately 78% of total GCs), and significantly greater in males than in females. Plasma levels of cortisol and corticosterone showed nearly identical profiles within each sex, with the exception of females in late pregnancy, in which corticosterone, but not cortisol, increased significantly. Baseline levels of plasma cortisol were highest in September (when pups were between 1 and 2 months of age) in both sexes, which may be related to the approaching onset of the mating period. There was a continuum in the magnitude of the response to stress (handling and sampling) over time in females, with the greatest stress response in early pregnancy, a dampened response during late pregnancy, and no significant stress response during lactation. Surprisingly, males failed to exhibit elevated GCs after this stress, but did have significant stress-induced hyperglycemia and suppression of plasma testosterone levels. This may be due to their high (perhaps maximal) baseline levels, which suggests that being in a breeding group was chronically stressful for males.

Multi-year longitudinal profiles of cortisol and corticosterone recovered from baleen of North Atlantic right whales (Eubalaena glacialis)

“…Serial plasma samples collected over time from the same individuals (i.e., longitudinal sampling) have been particularly informative for clarifying relationships of GCs with a multitude of potentially important natural and anthropogenic stressors. Longitudinal sampling enables detailed study of cycles in GC secretion, relationships of GCs to long-lasting reproductive states such as pregnancy or lactation, and can help discriminate cases of chronic vs. acute stress events (e.g., Bettendorf et al, 1998;Grant et al, 2016;Koester et al, 2015;Reeder et al, 2004).…”

Reproduction elevates the corticosterone stress response in common fruit bats

“…A. jamaicensis shows a characteristic, sex-independent stress response with corticosterone levels rising from a baseline to a maximum followed by a subsequent decrease. Surprisingly, the corticosterone response in A. jamaicensis was less rapid than in M. lucifugus (significant 15 min after capture) and captive flying foxes, Pteropus hypomelanus (significant after 20 min of restraint; Widmaier and Kunz 1993;Reeder et al 2004b). Why is the corticosterone stress response in A. jamaicensis delayed compared to the other two species studied in subtropical and temperate settings?…”

“…In tropical bats, glucocorticoid levels are among the highest documented for mammals (Kwiecinski and Damassa 2000). However, most results so far stem predominantly from captive individuals (Widmaier and Kunz 1993;Widmaier et al 1994;Kwiecinski and Damassa 2000;Reeder et al 2004b) and data on free-ranging populations are largely lacking (but see Reeder et al 2004a). Extremely high GC levels may terminate pregnancies (Heideman 2000), triggering a life-protecting emergency life-history stage (Wingfield et al 1998).…”

“…Due to the low seasonality in the tropics and multiple reproductive events per year, these costs may be experienced yearround (Heideman 1995(Heideman , 2000Bernard and Cumming 1997). Third, research on captive flying foxes suggests that female bats may modulate their corticosterone stress response according to reproductive condition (Reeder et al 2004b).…”

Physiological biomarkers of Hendra virus infection in Australian Flying-foxes (Pteropus spp.)

“…Studies of Pteropus species have found that cortisol is the primary glucocorticoid occurring in plasma (Widmaier and Kunz 1993, Widmaier et al 1994, b Reeder et al 2004, and that animals exhibit significant elevations in plasma glucocorticoid levels in response to restraint stress. Widmaier et al (1994) concluded that bats possess a stress response similar in some ways to other mammals.…”