Untitled

Abstract

Infrared thermal imaging has emerged as a valuable tool in veterinary medicine, in particular in evaluating reproductive processes. Here, we explored differences in skin temperature of cycling and pregnant wild chimpanzee females in Budongo Forest, Uganda.Based on previous literature, we predicted increased skin temperature when approaching peak fertility at the area of the reproductive organs of cycling females. For pregnant females, we made the same prediction, mainly because it has been argued that chimpanzee females have evolved mechanisms to conceal pregnancy, including exaggerated sexual swelling and sexually conspicuous vocal behaviour, and to encourage male mating behaviour in order to decrease their infanticidal tendencies by confusing paternity. Overall, we found only small changes in cycling females, with slight temperature increases towards the end of the swelling cycles but no overall increase in skin temperature between oestrous and non-oestrous phases. Interestingly, however, pregnant and cycling females had very similar skin temperatures. These results suggest that males cannot use skin temperature to discriminate between pregnant and non-pregnant/cycling females during maximal swelling, when ovulation is most likely to occur in cycling females.This pattern may be linked to the evolution of physiological means to conceal reproductive state in pregnant females. 10 Infrared thermal imaging has emerged as a valuable tool in veterinary medicine, in particular in 11 evaluating reproductive processes. Here, we explored differences in skin temperature of cycling 12 and pregnant wild chimpanzee females in Budongo Forest, Uganda. Based on previous literature, 13 we predicted increased skin temperature when approaching peak fertility at the area of the 14 reproductive organs of cycling females. For pregnant females, we made the same prediction, 15 mainly because it has been argued that chimpanzee females have evolved mechanisms to conceal 16 pregnancy, including exaggerated sexual swelling and sexually conspicuous vocal behaviour, 17 and to encourage male mating behaviour in order to decrease their infanticidal tendencies by 18 confusing paternity. Overall, we found only small changes in cycling females, with slight 19 temperature increases towards the end of the swelling cycles but no overall increase in skin 20 temperature between oestrous and non-oestrous phases. Interestingly, however, pregnant and 21 cycling females had very similar skin temperatures. These results suggest that males cannot use 22 skin temperature to discriminate between pregnant and non-pregnant/cycling females during 23 maximal swelling, when ovulation is most likely to occur in cycling females. This pattern may 24 be linked to the evolution of physiological means to conceal reproductive state in pregnant 25 females.