Reproductive Hormones And Reproductive Success In Yellow Baboons (Papio Cynocephalus) And Yellow-Olive (Papio Anubis) Hybrids In The Amboseli Ecosystem, Kenya

Abstract

Several baboon species in the genus Papio exhibit distinct ranges across Africa. Where those ranges meet, hybridization occurs, contributing to genetic diversity and structuring in these species. Hybridization between yellow (P. cynocephalus) and olive (P. anubis) baboons is common, though previous studies on these species reported strong effects of hybrid ancestry on males. However, information on hybrid females is lacking. The present study investigated the link between yellow-olive baboon admixture and female reproductive success in the Amboseli ecosystem in Kenya. It leveraged new data as well as multidecade data from this long-term population study. The study hypothesized that miscarriage rates, birth rates, and estrogen and progesterone levels do not differ between pure female baboons (P. cynocephalus) and hybrid female baboons. The main objective was to examine differences in the reproductive hormones and reproductive success of the female P. cynocephalus baboons and hybrids between P. cynocephalus and P. anubis. To achieve this objective, female baboons were observed for cycling, pregnancy, post implantation loss, births as well as duration of lactation. Fecal samples were collected from 48 adult females with known admixture, preserved in 95% ethanol and transported to the Reproductive Biology Unit laboratory at the University of Nairobi for further processing through evaporation of ethanol, freeze-dried and sifted. Fecal estrogen and progesterone levels were determined using enzyme immunoassay technique at the School of Biological Sciences laboratory, University of Nairobi. Long-term data were extracted from the Amboseli Baboon Project’s online relational database to evaluate each subject’s number of miscarriages, interbirth intervals, and multi-year steroid hormone profiles as well as several covariates (hybrid score, maternal age, maternal parity, maternal rank, group size, xv habitat quality, infant sex, daily maximum temperature and daily rainfall). These data were analyzed using Generalized Linear Mixed Models and Linear Mixed Model packages in the R statistical environment. Results showed influence of hybridity on estrogen with higher levels (P=0.0155) for females with more P. anubis genetic background. Cycling duration was longer for females with more P. anubis ancestry (P=0.0215), while postpartum amenorrhea was shorter for females with more P. anubis ancestry (P=0.0147). However, hybridity did not predict progesterone levels, miscarriage rates, or birth rates among Amboseli female baboons, indicating that admixture does not influence these measures of reproductive biology. It is concluded that hybrid and non-hybrid female baboons experience equal reproductive success and are therefore both evolutionary fit. In addition, hybridization has likely increased genetic diversity in Amboseli although its frequency is low and may not permit hybrid speciation.