Mating behaviour of a wild olive baboon population (Papio anubis) infected by Treponema pallidum
by Filipa M.D Paciência
Date of Examination:2019-11-04
Date of issue:2020-10-01
Advisor:Dr. Dietmar Zinner
Referee:Prof. Dr. Eckhard W. Heymann
Referee:Prof. Dr. Julia Fischer
Referee:Dr. Sascha Knauf
Referee:Dr. Oliver Schülke
Referee:Dr. Christian Pd Roos
Referee:Dr. Sven Bradler
Persistent Address:
http://dx.doi.org/10.53846/goediss-8232
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Abstract
English
According to the World Health Organization (2019), more than one million sexually transmitted infections (STIs) are acquired every day worldwide in the human population. These infections can have serious reproductive health consequences (e.g., infertility or mother-to-child transmission), and in nonhuman mammalian populations, are important selection agents that shape the evolution of immune defences. As such, individuals are expected to favour healthy mates instead of diseased ones. The relation between pathogens and fitness consequences in nonhuman primates has been the subject of numerous research efforts focusing on social and reproductive behaviour. My dissertation sets out to add a piece to the puzzle of the complex relation between hosts and pathogens by testing whether conspicuous disease cues prompt avoidance behaviour towards diseased individuals. Specifically, I studied the sexual behaviour of a large population (approximately 170 individuals) of wild olive baboons (Papio anubis), at Lake Manyara National Park (LMNP), in East Africa, Tanzania. Here, nonhuman primates (NHPs) are infected by Treponema pallidum (TP), a bacterium known to cause conspicuous genital ulcerations in both males and females. Since genital ulcerations are mainly found in sexually mature individuals, it is likely to be sexually transmitted. TP also affects humans, and it is responsible for different diseases such as syphilis, bejel and yaws. Interestingly, nonhuman primate TP strains, are most closely related with human yaws (a disease mainly causing facial lesions), than to syphilis (known to cause genital ulcerations). This, together with the geographic overlap of the distribution of human yaws and simian TP infection in Sub-Saharan Africa, could indicate that NHPs may function as a natural reservoir for human T. pallidum. The results of my study showed that genital ulcers have a major impact at a pre-copulatory level by influencing female mate choice. The likelihood of copulation decreased if the male mating partner had visible signs of TP infection (i.e. genital ulcers). Similarly, there was a decrease in the likelihood of copulation when females were infected (regardless of the genital health status of the male), which hints towards potential pain avoidance. No evidence has been found for male mate choice, but individuals exhibiting genital ulcers, performed less pelvic thrusts than non-ulcerated individuals. This most likely results in reproductive fitness consequences, as ejaculation can be compromised if not enough pelvic thrusts are performed. To understand whether the impact of TP-associated genital ulcerations is only restricted to the pre-copulatory level, I extended the same analyses to the female post-copulatory behaviours. I investigated whether genital ulcers would alter the frequency of female copulation calls, post-copulatory withdraw (i.e. darting) and the occurrence of post-copulatory grooming. The post-copulatory behaviour of females was not altered in relation to visible signs of disease, which means TP does play role on a pre-copulatory level but not at a post-copulatory level.This dissertation sheds light on behavioural avoidance in wild NHPs in relation to STIs and contributes to a better understanding of host-pathogen interactions and pathogen-avoidance. Additionally, it adds important data on baboon mating behaviour which is essential for comparative analyses. The close genetic relationship of simian and human TP strains, and the growing habitat encroachment of the human-NHP interface, supports the call for a more multidisciplinary approach linking humans and wildlife when investigating the impact of shared pathogens like Treponema pallidum.
Keywords: Papio anubis; olive baboon; mating behaviour; sexual behaviour; treponema pallidum; sexually transmitted infections; avoidance; diseases