Fecal testosterone is elevated in high ranking female ibexes (Capra nubiana) and associated with increased aggression and a preponderance of male offspring

Abstract

We monitored fecal testosterone and progesterone levels in 26 adult ibexes (17 males, 9 females) in a captive herd Nubian ibex held on 250 ha tract to test if testosterone is associated with dominance. The ibexes were observed over a 20-month period, and including two mating seasons, during which time we collected fecal samples twice during early gestation and postpartum intervals and once during lactation and pre-rut season intervals. The social hierarchy was linear with age in adult males and nearly linear in adult females. High ranking males were in solitude, but females were aggregated with the kids in the presence of a dominant female. The testosterone concentration in the males in the pre-rut (211+/-12 ng/g; N=13; dominant male 296 ng/g) was significant higher than other seasons (P<0.05). High testosterone in dominant male at pre-rut was associated with a decrease in confrontations. The individuals with the highest average testosterone concentrations were the dominant male and female (166+/-82 ng/g; 130+/-32 ng/g, N=6, respectively). In females, testosterone was highest in during the post-partum interval and was associated with an increase in aggression. The three highest fertile ranking females had higher testosterone (119+/-14 ng/g vs. 92+/-18 ng/g, P<0.05) than the four subordinate females. The sex ratio of the offspring was 8M/3F for the three older females and 5M/7F for the younger females. In early gestation period, females with only male fetuses had higher testosterone than other gravidities (119+/-14 ng/g, N=6 vs. 91+/-18 ng/g, N=7, P<0.01). Progesterone was significantly higher in the eight multiparous pregnancies than in those with the five singletons (210+/-19 ng/g vs. 186+/-12 ng/g, P<0.02). We conclude that high testosterone in females is associated with an increase in aggressive confrontations in early- and mid-lactation. In contrast, increased testosterone during pre-rut in males is associated with fewer confrontations. In addition, the data support the hypothesis that higher ranking, older dimorphic female ungulates have higher testosterone concentrations and have more male births than subordinate females.