Exam 3: Sexual Selection Flashcards
Sexual selection
A type of natural selection, where members of the sexes develop strategies reproductive success. It can result in the secession acquiring distinct traits and characteristics
Mate choice
members of one sex house mates with particular features that may indicate traits important for reproductive success
Mate competition
in the competition for mates among males or females, those with certain traits succeed in getting mating partners
Mate choices
- When one individual chooses to mate with a partner who is compatible and who potentially carries good traits for survival of offspring
- Need to determine
- Need to be the same species so they use color and how they look to determine mating
- Females tend to put a lot of work into making the choices
- Males do still have some mate choice
Indicator traits
traits that are attractive are linked to “good genes” and thus may result in higher quality offspring
Sexual selection: secondary sexual traits
- Features that distinguish the sexes but are not directly related to reproduction. We have seen this before with sexual dimorphism
- Sexual swellings with females is an example
- Indicate a very clear difference with male and females
- This has been going on for a while when looking at the fossil record
- likely the result of sexual selection
Female secondary sexual traits: signs of sexual state
- If there is, then that means that males have some say as well
- 14% of primate species advertise sexual reproductivity with sexual swellings or some other visual cue
- Tend to mirror menstrual cycle
- Sexual swellings become largest (or most brightly colored) just prior to ovulation—when conception is most likely
Female genitalia: external signs of sexual state
- Take measurements of the butts
- They are thus seen as “honest signals” about fertility
- Males will mate with females at the max time of swelling
- Adult males are most attracted when swelling is at its highest
Females are affecting each other
- Female chimps will do a copulation call when mating towards the end and reduce it?
- Chimps females adjusted their calling behavior in flexible ways, potentially to avoid aggression from other females
Function of sexual swellings?
- Found primarily within multi-male social groups
- Increase mate competition among males (best male is successful)?
- May be fertility “cue” selected for by males
- Attract many males to mate with to confuse paternity to avoid infanticide? Females won’t reproduce when they’re taking care of a baby so they try to kill the babies?
Primate sexual displays
- Females and males both do it
- A number of haplorrhine primates have faces with both naked skin and red facial color
- Advertise their health status to females
- Advertise hormone levels such as testosterone to other males
Primate sexual displays - rhinopithecus (sub nosed monkey)
- The color of the mouth changes
- Reproductive male: lips swell and reddens in the mating season
- Subadult and juvenile bachelor males: the lips become paler
Sexual selection - mate competition can affect biology: sperm competition
- Sperm competition is the physical competition between the sperm of two or more individual males to fertilize the eggs of a single female
- The sperm itself can fight itself to fertilize
- Correlates with the size of the testes
- Part of the competition is becoming faster
There’s a difference in sperm speed depending on the primate
- Gorillas are the slowest
- -One male multiple female social organization
- Chimps and macaques are the fastest
- -Multi male multi female social organization
- Humans are between
Sperm speed
- the first ones to make it to the egg succeeds
- Faster speed in multi-male, multi-female social groups. —More potential competition among males here
- Sperm competition: tested/body weight
- Correlates with the number of males a female mates with
- Suggests that we came more from a monogamous
- At any given body size, males have larger testes (more sperm) in species where females mate with multiple males
- Human values link to smaller groups with fewer or only one male mating
Human secondary sexual traits?
- Not very sexually dimorphic species
- Gibbons are the closest
- Humans have breasts that stay swollen
- Male humans have beards
- -Sexual trait
Sexual selection may be affected by culture in humans
- Changes in female body type has changed throughout time
- Male physique has also changed throughout time
- There were Fat Men’s Club’s existed since it was a sign of wealth
- 1930s for becoming the hunks
- Hollywood has always had a large influence on societies
- Humans are affected by what we see on television
Female Mating Strategies: Female mate choice?
- To avoid inbreeding is the main one - not mate with someone closely related to them
- Mating with someone close by themselves produce genetic defects
- To mate with males with better traits, e.g. using high rank as a measure of “good or compatible genes”
Female Mating Strategies: Direct female mate choice
- Agree to mate with a male or not
- Direct: choosing a mate or refusing to mate with a particular male
- Females may use visual and even odor cues
- Stone throwing as sexual display by female capuchin monkeys
Female Mating Strategies: Direct female mate choice: Uakari
- Important to use visual to show whether or not they’re healthy
- Males are dichromatic but females are both dichromatic and trichromatic
- Trichromatic females can see the red faces and may use it to determine the health of the male (whiter faces associated with malaria)
Female Mating Strategies: Indirect female mate choice
- Choosing which males gets to join females in one male groups e.g. mandrills, geladas, pastas or
- Which male group to join, e.g. gorillas
Female Mating Strategies: Female-female competition
In gorillas females use “post-conceptive mating” by already pregnant females to reduce other female’s successful reproduction
Male Mating Strategies
In most cases males have to move out of the group they’re born in
Male Mating Strategies: Transfer
- Males have to move out of their natal group
- They look for another group
Male Mating Strategies: Stay (chimps)
- Rare and remain in the community and they still need to compete
- Only one alpha male in the group
Male Mating Strategies: Join bachelor group
- It’s not safe to be alone so they gather together
- Doesn’t work very well in reproduction
Male Mating Strategies: Become a lurker - hang out on the fringe
Stay away from the alpha male but stay close to the group
Male Mating Strategies: Visit during mating season then leave
- Males come in during estrous period and hangout to mate
- They leave afterwards mating
Male Mating Strategies: Types of Competition
- Direct competition
- -Males fighting each other
- Disrupting over male’s mating attempts (e.g. male coalitions)
- -Short mating periods could mean disruption
- Develop special relationships with females
- -Getting to know each other before mating
- Sperm competition
Male mate choice: Why?
Distribute mating to ensure fertilization. They can do this by:
- Mating with females most likely to conceive and have a record of being able to raise offspring. To adulthood
- -Older females and ability to become good mothers - Mating with females who prefer them; e.g. developing friendships
- -Forced mating is very rare
- Because mating agonist can be intense and dangerous, males should “decide” when it’s worth it
Same-sex specula behavior in primates
- Originally thought to be abnormal result of captivity. . . But
- Observed among 33% of all primate species
- Appears to reflect a normal part of the sexual behavior of primates
- It’s fluid especially among haplorrhine primates
- It’s highly variable in frequency of expression
- It’s observed among all age classes
- It’s typically demonstrated by both sexes
- The closer the social bond between two animals, the more intrusive and risky the greeting when they meet
Same sex sexual behavior
genetical contact, genetically manipulation or both between same sex individuals
Hypotheses for same-sex sexual behavior in primates
- Tension-regulation, reduce agonist, maintain social order
- Alliance formation and friendships
- E.g. bonobos, macaques, and baboons
Sexual behavior in haplorrhine primates is thus very fluid
- Exclusive same-sex pair bonds have not been seen in non-human primates
- Only two species have been observed showing a same-sexy preference for life, even when partners of the opposite sex are available: humans and male Ovis Aries domestic sheep
- Appears to be part of the continuum of primate social relationships reflecting not just reproduction but also friendship
