Assessing reproduction in wolverines (Gulo gulo): Fecal progesterone levels in zoo and wild females

Wolverines (Gulo gulo) populations are under threat by increased human activities. A better understanding of their reproductive physiology would benefit research and monitoring of this species. The use of enzyme immunoassay (EIA) to measure fecal progesterone metabolites (FPM) is a powerful tool to understand wildlife reproductive physiology, and a non-invasive method for use in both zoo and wild populations. The main objective of this study was to determine reproductive status in female wolverines using FPM levels, first by monitoring of longitudinal changes in FPM in zoo housed females in breeding situations and second to compare those values to FPM measured in feces obtained from wild females observed in the field during reproductively active periods (Dec–Apr). Female reproductive physiology was assessed by measuring FPM in three zoo housed wolverines to determine species-specific levels arising from ovulation encompassing embryonic diapause and ovarian reactivation (resumption of ovarian luteal activity after diapause) during pregnancy or pseudopregnancy, which in turn enabled verification of reproductive status in 15 wild wolverines, monitored over three years. In the zoo females, FPM levels were sustained at basal levels if ovulation and/or breeding did not occur. After ovulation, both pregnancy or pseudopregnancy exhibited a bi-phasic pattern of FPM increases, with a 4.9-fold increase above baseline during embryonic diapause and a further 4.4-fold increase after ovarian reactivation. FPM levels during pregnancy and pseudopregnancy were indistinguishable, thus increases in FPM levels are only a confirmation of ovulation, and not diagnostic for pregnancy. In wild females, assessment of FPM levels in samples collected from December to February was able to predict a potentially pregnant/reproductively active female with levels above 8200 ng/g dried feces, or non-reproductive (nonovulatory) female during that period with levels below 1700 ng/g. Wild wolverine FPM levels indicative of pregnancy aligned with field observations of denning and/or lactation. FPM levels from samples collected from March and April were inconclusive as levels could be attributed to females being either postpartum or non-reproductive at that time. Timing of ovarian reactivation, and subsequent elevation of FPM, varied among individuals suggesting caution is warranted when assessing only one fecal sample per female. Understanding all factors that may impact reproductive success is essential for effective species conservation, particularly for species with low reproductive rates, like the wolverine. This study has demonstrated the potentially useful incorporation of non-invasive fecal hormone analysis for investigation of physiological parameters and reproductive status in wild wolverine females.