Using hair cortisol analysis to understand the biological factors that affect black-footed ferret (Mustela nigripes) stress physiology

Abstract

The black-footed ferret (Mustela nigripes) was driven to near extinction due to habitat loss and an introduced disease, sylvatic plague (Yersinia pestis). After 35 years of breeding in ex situ facilities, the black-footed ferret has been experiencing infertility with seminal traits declining in males and only about a third of breeding-aged females are whelping. Our goal was to use hair cortisol analysis to determine if the ex situ population was experiencing chronic stress that was affecting reproduction by comparing captive ferrets to wild individuals. Our specific objectives were to (i) compare hair cortisol concentrations (HCCs) between age classes (juveniles versus adults), (ii) compare the HCCs of in situ and across different ex situ facilities and (iii) determine the relationship between HCCs and reproductive success. Overall, wild juveniles had higher HCC than wild adults. Our generalized linear mixed model determined that the parameters that best predict HCC for adults were the interactions among sex, in situ versus ex situ facilities and season. During both seasons, wild females had higher HCCs compared to the ex situ females. During the breeding season, male HCCs across breeding facilities varied and males at the breeding facility with the largest ferret habitats had HCCs similar to wild males. At one breeding facility, HCC was higher in males that sired compared to those that did not sire. In conclusion, ex situ ferrets do not have higher HCC than wild individuals when controlling for season and ex situ habitat size, and ex situ males with higher HCC tended to sire. This suggests that HCC may be metabolically driven and/or that low HCC may be an indication of hypothalamus-pituitary-adrenal axis dysregulation and warrants further investigation both for laboratory validation and biological relevance.

Keywords: Age; enzyme immunoassay; ex situ; glucocorticoids; season; sex; wild.

Figure 1

Mean (±SEM) HCCs (ng/g) of wild black-footed ferrets during the non-breeding season. Letters indicate differences (P < 0.05) among age class and sex. Number in the bar is the number of individuals evaluated.

Figure 2

Boxplot of median cortisol concentrations (HCC; ng/g hair) of adult male and female black-footed ferrets by location including the wild individuals (n = 31 females, n = 34 males) from Conata Basin and from ex situ facilities including FCC (n = 10 females) and the SCBI (n = 11 females) during the non-breeding season. The median value is the center line in each box. The upper whisker extends from Q3 to the largest value and does not extend further than 1.5 * IQR; the lower whisker extends from Q1 to the smallest value and does not extend beyond 1.5 * IQR. Any data points that fall beyond the upper and lower whiskers are depicted as outliers, which were included in our analyses. Letters indicate differences (P < 0.05) across location and sex.

Figure 3

Boxplot of median HCCs (ng/g) of adult male and females black-footed ferret by location including the wild individuals (n = 9 females, n = 12 males) from Conata Basin and from ex situ facilities including FCC (n = 14 females; n = 97 males), the SCBI (n = 13 males) and the LZG (n = 14 males) during the breeding season. The median value is the center line in each box. The upper whisker extends from Q3 to the largest value and does not extend further than 1.5 * IQR; the lower whisker extends from Q1 to the smallest value and does not extend beyond 1.5 * IQR. Any data points that fall beyond the upper and lower whiskers are depicted as outliers, which were included in our analyses. Letters indicate differences (P < 0.05) across location and sex.