Testing yawning hypotheses in wild populations of two strepsirrhine species: Propithecus verreauxi and Lemur catta.
Yawning, although easily recognized, is difficult to explain. Traditional explanations stressed physiological mechanisms, but more recently, behavioral processes have received increasing attention. This is the first study to test a range of hypotheses on yawning in wild primate populations. We studied two sympatric strepsirrhine species, Lemur catta, and Propithecus verreauxi, of the Ankoba forest (24.99°S, 46.29°E, Berenty reserve) in southern Madagascar. Sexual dimorphism is lacking in both species. However, their differences in ecological and behavioral characteristics facilitate comparative tests of hypotheses on yawning. Our results show that within each species males and females yawned with similar frequencies supporting the Dimorphism Hypothesis, which predicts that low sexual dimorphism leads to little inter-sexual differences in yawning. In support of the State Changing Hypothesis yawning frequencies was linked to the sleep-wake cycle and punctuated transitions from one behavior to another. Accordingly, yawning frequencies were significantly higher in L. catta than in P. verreauxi, because L. catta has a higher basal level of activity and consequently a higher number of behavioral transitions. In agreement with the Anxiety Hypothesis, yawning increased significantly in the 10 min following predatory attacks or aggression. Our findings provide the first empirical evidence of a direct connection between anxiety and yawning in lemurs. Our results show that yawning in these two strepsirrhines occurs in different contexts, but more research will be necessary to determine if yawns are a single, unitary behavior.
['Zannella|Alessandra|A|', 'Norscia|Ivan|I|', 'Stanyon|Roscoe|R|', 'Palagi|Elisabetta|E|']
D000374:Aggression D000818:Animals D001007:Anxiety D001522:Behavior, Animal D005260:Female D007900:Lemur D008297:Male D011235:Predatory Behavior D012890:Sleep D012919:Social Behavior D011443:Strepsirhini D015000:Yawning
sexual dimorphism behavioral transitions anxiety ring-tailed lemurs sifaka