Validation and measurement of physiological stress and reproductive hormones in wolf hair and claws

The use of keratinized tissues (e.g., hair, claws) to investigate physiological effects of environmental and anthropogenic stressors in free-ranging wildlife populations has increased because these tissues retain steroid hormones during growth and are relatively easy to collect and store in the field. We measured reproductive and stress-related steroid hormones in wolves (Canis lupus ligoni; n = 31) captured on Prince of Wales Island, Alaska, USA, during 1993-1994 and 2012-2014, representing periods of time when both wolf harvest and densities ranged from high to moderate. We validated enzyme immunoassay kits to measure steroid hormone concentrations in wolf guard hair, undercoat hair, and claw tip samples. Progesterone, testosterone, and cortisol were extracted and measured in the 3 keratinous tissues from wolves of different age class, sex, residency status, and collection periods. Within each tissue type, progesterone and testosterone were positively correlated (guard hair, r = 0.59, P = 0.003; undercoat hair, r = 0.55, P = 0.011; claws, r = 0.62, P <= 0.001) and cortisol concentrations were not related to either reproductive hormone. We were able to measure hormone concentrations in archived keratinous tissues collected up to 25 years earlier to assess stress and reproductive activity in historical samples. Our study validates a method for measuring steroid hormones in hair, and for the first time, continuously growing claws in wolves. Measurement of hormone concentrations in keratinous tissues may aid in the assessment of reproductive activity and physiological stress responses in wolf populations over long-term time periods (i.e., decades) to enhance conservation efforts of an important apex predator.

Automated summary

The use of keratinized tissues to investigate physiological effects in wildlife populations is becoming popular. A study on wolves found that progesterone and testosterone concentrations in different tissues were positively correlated, while cortisol concentrations were not related to reproductive hormones.