Research published in BMC Evolutionary Biology suggests that female bonobos could have become the dominant sex in their societies by deceiving males as to when they are likely to conceive. The females’ sexual swellings, which can remain swollen up to 31 days, make it difficult for a male to monopolise and guard female mates to ensure he sires their offspring. This may reduce aggressive mate competition and male sexual coercion toward females, and results in bonobo societies being relatively peaceful.
So far the research has been covered in Science and IFL Science; El Pais and ABC.es in Spain; Eju.tv in Bolivia; and svopi.ru in Russia.
Mixed messages: wild female bonobos show high variability in the timing of ovulation in relation to sexual swelling patterns
BMC Evolutionary BiologyBMC series – open, inclusive and trusted201616:140
© The Author(s). 2016
Received: 24 February 2016
Accepted: 24 May 2016
Published: 30 June 2016
The evolution of primate sexual swellings and their influence on mating strategies have captivated the interest of biologists for over a century. Across the primate order, variability in the timing of ovulation with respect to females’ sexual swelling patterns differs greatly. Since sexual swellings typically function as signals of female fecundity, the temporal relation between ovulation and sexual swellings can impact the ability of males to pinpoint ovulation and thereby affect male mating strategies. Here, we used endocrine parameters to detect ovulation and examined the temporal relation between the maximum swelling phase (MSP) and ovulation in wild female bonobos (Pan paniscus). Data were collected at the Luikotale field site, Democratic Republic of Congo, spanning 36 months. Observational data from 13 females were used to characterise female swelling cycles (N = 70). Furthermore, we measured urinary oestrone and pregnanediol using liquid chromatography–tandem mass spectrometry, and used pregnanediol to determine the timing of ovulation in 34 cycles (N = 9 females).
We found that the duration of females’ MSP was highly variable, ranging from 1 to 31 days. Timing of ovulation varied considerably in relation to the onset of the MSP, resulting in a very low day-specific probability of ovulation and fecundity across female cycles. Ovulation occurred during the MSP in only 52.9 % of the analysed swelling cycles, and females showed regular sexual swelling patterns in N = 8 swelling cycles where ovulation did not occur. These findings reveal that sexual swellings of bonobos are less reliable indicators of ovulation compared to other species of primates.
Female bonobos show unusual variability in the duration of the MSP and in the timing of ovulation relative to the sexual swelling signal. These data are important for understanding the evolution of sexual signals, how they influence male and female mating strategies, and how decoupling visual signals of fecundity from the periovulatory period may affect intersexual conflict. By prolonging the period during which males would need to mate guard females to ascertain paternity, the temporal variability of this signal may constrain mate-guarding efforts by male bonobos.
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