The role of neuropeptides as a proximate base for (pro)social behaviour: inter- and intraspecific comparison of bonobo and chimpanzee

Understanding the evolution of behavioural differences in closely related species is one of the major challenges in modern behavioural ecology. Recently, genetics have been more and more applied to understand how these differences come about. For example variation in genes coding for neuropeptide receptors in the brain has been linked to variation in social behaviour among different species. In terms of human sociality, our two closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) offer an interesting comparative framework, as they differ in key aspect of sociality. The debate on the distinctiveness of these two species reflects recent efforts to determine more proximate causes of interspecies differences and how these evolved in early hominids. Diversity in DNA-sequences could be responsible and this could be reflected on a hormonal level. In this framework neuropeptides play a central role in modern behavioural research. Neuropeptides like oxytocin, vasopressin and dopamine are important modulators in social behaviour in humans and other mammals. This study aims to investigate the relationship between the variation in DNA-sequences and behaviour in and between bonobos and chimpanzees. We look at the variation in the oxytocin receptor gene and vasopressin receptor gene 1a in both species and a possible correlation between this variation and species-specific and individual behaviour. The RZSA is the ideal location for this research as it has both species in its collection a great collection of DNA samples available. In addition the CRC has combined many years of experience in studying bonobos with managing the breeding programme for over 20 years . Since several aspects of personality in humans and animals have been linked to the occurrence of these polymorphisms in neuropeptide receptor genes, the study also includes investigations of personality and behavioural syndromes, by combining observational and experimental data with personality ratings done by human observers. In 2012, genetic profiles were constructed for 120 bonobos and 77 chimpanzees for polymorphisms in the oxytocin and vasopressin receptor genes that will be linked to behavioural profiles and personality. Bonobos show no genetic variation in our region of interest on the oxytocin receptor gene whereas chimpanzees do, with 5 different single nucleotide polymorphisms found. For vasopressin we were not able to find the 350bp deletion, containing the microsatellite RS3 in the promotor region of the gene that occurs in chimpanzees. In our chimpanzee sample set, this short allele had a very high prevalence of ~70%, with homozygous individuals for the deletion having the highest frequency in our captive population. This is in agreement with a previous study done on chimpanzees by Donaldson et al (2008). For those bonobos and chimpanzees without the deletion, we were able to distinguish 15 alleles differing in length of the RS3 repeat. The shorter alleles appear to be less frequent in the bonobo population. Interesting here is that long alleles are correlated with more prosocial behaviour in humans and higher bonding levels in voles. As bonobos are known for their sexual and social bonding this might explain part of the variation found compared to chimps, as they have this higher prevalence of short alleles. In 2013 we finished collecting personality ratings for a total of 154 bonobos, spread over 16 groups from the EEP and SSP. Analyses on these ratings are done in collaboration with Alex Weiss (University of Edinburgh, UK). We found that bonobos have six personality components comparable to those found in chimpanzees, though some more closely resembled human personality components. These findings indicate that bonobo personality is a mosaic structure of human and chimpanzee personality, what resembles findings of this same structure by genomic studies that compared the bonobo genome to the human and chimpanzee genomes. We genotyped 110 of these bonobos and found a link between personality profiles and the RS3 microsatellite. Bonobo males with longer alleles are rated more “assertive” and “friendly” by their human raters. To validate the results from this rating approach, that uses questionnaires, we also collected behavioural data using observations and an experimental approach. With help of master students from different universities we were able to collect data for 50 adult and subadult bonobos from 6 different zoological parks in Europe. We did two rounds of data collection so that we can test for reliability and stability of the coded behaviour. For one zoo data collection of the second round will be finished early 2014. Preliminary results show that with the use of behavioural codings we are again able to construct a multidimensional personality structure and that the experimental approach provides us with extra dimensions that are harder to measure with observational data alone. Time line: PhD 2011-2015 Partners: Marcel Eens (University of Antwerp) | Jorg Massen, Annemieke Podt (Utrecht University) | Sonja Koski (Zürich University) | Leo Vorthoren (University of Nijmegen) | Alex Weiss (University of Edinburgh) | Oliver Ryder, Leona Chemnik (San Diego Zoo Institute for Conservation Research) | Funding: CRC (KMDA Dehousse)

Project type:PhD project