ANT211H5 Lecture Notes - Lecture 4: Cuckold, Extra-Pair Copulation, Amotz Zahavi
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žANT211: Intra sexual Competition: How males and females compete for
Any investment by the parent in an individual o"spring that increases the
o"spring’s chance of survival (and hence reproductive success) at the cost of
the parent’s ability to invest in other o"spring” (Trivers)
Female Reproductive Eorts
žLarge parental investment
žMore discriminating mate selection
Since females invest more energy and time into parenting, then it would
make sense that they would be choosier when it comes to selecting a mate
(must pick the mate with the best traits/genes, so that it would be worth her
time to raise his o"spring)
- Once a female becomes pregnant, she cannot become pregnant again
until she gives birth or miscarries
- Both alternatives require a large time and energy investment
How are females selective in their reproductive e"ort?
Females would be choosy in 2 ways:
(1) More selective towards a male with higher genetic quality as their
(2) More likely to choose males that can procure more resources that they
can invest into their o"spring
žThe Nurturing Female
Cost of internal fertilization – Parental investment
Females have a greater parental investment as they:
žGreater energy to nurture each ovum (trade o" between fecundity &
Decreasing # of o"spring – so more energy and time is invested in
o"spring to ensure survival –for them to reach sexual maturity
žFemale’s are limited by their physiology
oGestation – impregnating, carrying/protecting the fetus until it is
ready for birth
oPlacentation –nurturing the baby within mothers body
oLactation – milk production as a source of nutrients for their
o"spring during <rst years of life
Female – Female Competition
Females = choosier sex
They don’t have to compete with each other with regards to
selecting which males they want to mate with
How do females compete then? Do they actually compete?
žFemales compete for limited resources vs males compete with each other
for access to fertile females.
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A female should pick the male with the best gamete to contribute to her
Di"erent strategies for competing for resources depending on the
(1) Female coalitions with each other- dispersal of resources with other
(2) Indirectly – Didn’t discuss this? Relative investment of males. Females
will compete for males if they <nd males are making a large parental
investment in o"spring.
If males make a large parental investment in their o"spring then competition
between females will increase attract high genetic quality, parental investing
In species such as humans, our o"spring consume so many resources that it
requires males to also invest parentally in order for their o"spring to reach
sexual maturity and survive.
Diamond asks the question (readings): Can females actually detect the
genetic quality of a male?
- Higher testosterone levels may be an indication of a “higher quality”
genetic male, and during di"erent times of a females menstrual cycle
are attracted to di"erent kinds of males
- Recall from the <lm: females (during ovulation- high fertility stage) can
detect higher testosterone levels in males (more prominent secondary
sex characteristics are indicative of higher testosterone levels, hence
higher quality genome)
- Relation to chimps (who live in a high promiscuity population), if
there’s going to be a short term dating strategy, in which males are not
going to give male parental assessment, then high testosterone
markers may be a signal for females as a which males are more fertile
When females are looking for a long term sexual partners, or males who will
invest more resources into their o"spring, then they do not tend to
necessarily look at high testosterone markers. They often go for males who
have more feminine qualities suggesting that those qualities are indicative of
a high parental investment in that male.
Civic vs porche lol
Is male quality heritable?
Runaway Selection Model (Fisher)
- Certain traits in males that are selected to attract females become
greater over generations because of the increase reproductive success
of those males
- Ex – Male peacock. Males with the largest of tails will be the most
reproductively successful within that species. Females tend to choose
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