Oxytocin reduces asymmetries in dominance relationships between pairs of captive female lions

Abstract

Free-ranging female African lions maintain symmetrical social relationships by respecting each other's "ownership" of valuable food items rather than by supplanting subordinates according to well-defined dominance hierarchies. However, captivity often skews relationships in captive carnivores, hence we investigated whether captive female lions demonstrate obvious dominance relationships. Oxytocin has been shown to elicit context-specific impacts that equalize dominant subordinate relationships, thus we hypothesized that oxytocin would reduce any asymmetries found between dominants and subordinates in captive lions. We designed two experimental protocols for investigating pairwise relationships. We first identified dominant individuals by performing neutral trials that allowed each female equal opportunity to possess the food item. Second, we performed non-neutral trials that biased the opportunity for subordinates to gain possession ("ownership") of the food and thereby determined whether dominants would still gain access to the resource. The neutral tests revealed that pairs of captive females do display dominance relationships, with one individual possessing the resource more than the other. However, in non-neutral trials, subordinates behaved less submissively by increasing aggression and their possession of the resource after receiving oxytocin compared to receiving saline solution. Our study not only reaffirms the social dynamics altered by captivity, but also highlights the potential for oxytocin to mitigate these disturbances.

Keywords: African lions; Behavioral management; Captivity; Dominance; Oxytocin; Social behavior.

Fig. 1

Dominance in female African lions as determined by possession of the food resource. A high value resource (meat) is held at the fence allowing two females to compete for the resource. A) one female behaves submissively while the other dominates the resource. B) the possessor of the resource defends herself, behaving less submissively than in (A) to maintain possession of the resource.

Fig. 2

Asymmetrical resources possession, demonstrating dominant-subordinate relationships, decreases with oxytocin (n = 10 pairs, 380 rounds). Data show mean within-pair proportion that dominant or subordinate individual possessed the resource under neutral (N) and non-neutral (NN) treatments. Error bars show standard error. In all treatments, the subordinate individual was less likely to possess the resource than the dominant (Binomial GLMM β: −5.3 ± 0.59, p < 0.0001 for neutral, β: −1.98 ± 0.3, p < 0.0001 for non-neutral). However, in non-neutral trials testing the “ownership” rule, the subordinate displayed a significant increase in maintaining possession after oxytocin (β: 1.2 ± 0.4, p = 0.01), decreasing asymmetry in pairwise dominance relationships.

Fig. 3

Subordinate female lions increase aggression in order to maintain possession of resources after oxytocin administration during non-neutral ownership trials. a-d) Changes in displayed aggression across trials. a-b) mean presence of vocal or physical aggression; c) mean level of physical aggression, and d) mean total aggression level. Error bars show standard error. e–f) effect sizes from Binomial and Poisson GLMM models indicating significant differences in both dominant and subordinate aggressive behavior post oxytocin (* p < 0.05, ** p < 0.005), subordinates increased occurrence of physical aggression, mean aggression level, and total aggression, while dominants decreased vocal aggression thus indicating context-dependent effects of oxytocin administration.