Lecture 15 - Primate Sexual Signals Flashcards
What is the criteria for sexual selection
Sexual dimorphism in signals (sounds and size). Variation in dimorphic traits within a population - individuals needs to differ to ensure selection can act.
Conspecific discrimination of differences, for example Wait et al., 2013 found a correlation between redness of face and testosterone/high social status, suggesting a benefit for women to choose individuals with redder faces.
Expression of preference must be related to sexual motivation and conception. For example, lactating female baboon friendships with males show the males response to screams of their female friend more if the infant is alive, possible to protect from infanticide and secure future mating opportunities.
Outcome of differential mating and reproductive success - sexual swelling advertises reproductive value. Larger swelling = earlier sexual maturity, more offspring, higher proportion of offspring survival.
Discuss vocal signals as part of primate sexual signals
Numerous species present sexually dimorphic calls. But there is a lack of evidence of female preference and differential outcome of these calls.
Barbary macaques demonstrate female copulation calls, wherby males discriminate between females calls at different stages of the oestrous cycle. Calls in late oestrus has more elements, were longer and had a higher dominant frequency. Females whose calls were played mated sooner than control females.
Discuss visual signals as a sexual signal used by primates
Sexual swelling in female. Females with normal ovarian cycle undergo changes in skin swelling, and males are more likely to mate with females during the swelling period. Copulation declines rapidly 2-3 days before a decline in swelling.
A study tested to see if this was a visual signal, or if there were some underlying mechanisms going on. They injected oestrogen into a female, who then demonstrated normal swelling (out of noraml oestrus) an males mated with the females after the injection and display of swelling anyway. Males who can see this swelling but not access it show increased masturbation in correlation with swelling size. However, the more oestrogen injected, the larger the swelling and the larger the male response.
When males could not see the swelling but could potentially smell, there were still no repsonses. Suggesting the swelling has no odour or behavioural cues, and is simply a visual signal. Males also responded when females wore prosthetic swelling.
Discuss chemical signals in sexual signals in primates
Several exmaples of scent-marking and other olfactory behaviour is demonstrated in primates. fMRI studies show increased activation of brain areas involved in sexual arousal, with both experiences and virgin males presenting the same response.
Discuss the use of multimodal signals in sex
In most species, signals and cues are multimodal. Whereby there is often more than one mechanism happening at once. For example in mandrills scent marking abilities. Odour profiles differ by sex but those og young males resembles those of females (which may be related to testosterone). But females show preferences for males that are genetically dissimilar to themselves.
Calls can demonstrate fitness, social ranking and dominance.
Discuss sexual selection and learning
There are multiple cues and signals from multiple sensory modalities, whereby there may be a role of learning and context.
