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ANTC23H3 Lecture Notes - Sifaka

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Joyce Parga

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Announcements: Midterm in 2 weeks
Sexual Selection
How many copulations v. How many viable
offspring produced
Mating Success v. Reproductive Success
Male RS is limited by access to mates
Females typically don't have a problem
finding mates
Problem is having resources to go
through pregnancy, childbirth, etc.
Female RS is limited by access to resources
(food, water, etc.)
Females limited by gestation and
Males limited by number of females
available for insemination
Males have a higher potential reproductive
rates than females
Unequal partitioning of RS among
individuals in a population - Reproductive
Some males sire many offspring, some
sire none
Males show greater reproductive variability in
RS than females [Reproductive Skew]
Females typically show less reproductive skew
Reproductive variability
Within the sex; male/male or
female/female competition
Can result in secondary sexual
characteristics relating to competition for
mates (ie. Body size, tooth size,
weaponry) and primary sexual
characteristics relating to competition for
mates (ie. Shape, size, etc. of
reproductive organs, sperm count,
copulatory plugs)
InTRA-sexual selection [typically physical,
always direct competition]
Between the sexes; mate choice
Courtships, aesthetics, etc.
Anything that isn't aiding direct
competition between same-sex
Also called Epigamic selection
InTER-sexual selection [typically aesthetic or
social, non-direct competition]
Can be a combination of both; if they are,
typically are the traits most selected for
Sexual Selection is: a form of natural selection acting
on variation in the ability of individuals to compete
with others of their own sex and to attract members
of the opposite sex
In cases where there is more male
investment (either because of parental
care or because of low sperm production)
there is some 'choosiness' in mate choice,
but female mate choice tends to be more
Females are considered to be more selective
than males because of their greater parental
investment; don't want to waste the energy of
gestation, labour, lactation, etc. on a sub-par
Mate Choice
Mating Strategies
The show or threat of force that
makes a female more likely to mate
with a male when she is fertile at
some cost to the female
Example: neck-biting with
Hamadryas baboon, aggression by
chimpanzees and gorillas,
An extreme form of sexual
coercion in which an
individual is forcibly mated
Orangutans, forced
copulation is performed by
both unflanged and flanged
males (not just by those who
cannot get mates)
Patas monkey, spider
monkey, bonnet macaque,
orangutan, and other species
on occasion
Forced Copulation
Except: rape
tends to not be
sexually or
procreative in
nature; when
men rape on a
constant basis,
they tend to
actually be
attractive and
If this is the case, then
the males expected to
use this strategy would
be males unsuccessful
in competition for
Sexual coercion and forced
copulation as human male
mating strategies?
Sexual Aggression in humans
Believed to indicate genetic
quality ("good" genes) - what
does "good" genes mean?
Aren't valued genes always
Often leads to mating success
for males
Applies to MM/MF
groups where males
have a dominance
Attempts to describe
which males get to
mate and in what order
Alpha male gets
priority of mating with
females if female
estrus periods don't
If more than one
female is in estrus,
then other males get to
mate in order of
Rank reversals, or
change in the
Female mate-
choice for non-
dominant males
mating strategies
(ie. Sneak
Priority of access hypothesis
Male dominance ranks
Sexual Coercion
Male Mating Strategies
Patas monkey females will sometimes sneak away and mate
with extra-group males
Japanese macaque females will sneak away from high-ranking
mate-guarding males to male with subordinate males
Sneak copulations
Close, temporary association between a male and an estrous
Frequent grooming, resting together in contact; high frequency
of affiliative behaviour
Mate Guarding
Particular of baboons
Males cooperate to collectively mate-guard females, to disrupt
consortship of another male
Male Coalition formation
An act by an individual that makes a direct or significant
contribution to the immediate or imminent death of a
conspecific young
A lot in Hanuman Langurs
Males kill infants that are not their own
Infanticide should shorten the mother's interbirth
interval; stop lactational amenorrhea
Male makes it more likely that the next offspring she
produces will be his offspring
Examples: capuchin monkeys, chimpanzees, patas monkey,
ring-tailed lemurs, gorilla, colobus monkey, sifaka, howler
monkeys, etc.
By-product of inter-group aggression
Social pathology due to overcrowding
Some do not believe it is sexually selection
Infanticide (Sexually Selected)
Human Sexual Jealousy
Supported by physiological tests in the laboratory
Men and women show sexual jealousy, men are more bothered by
sexual infidelity, women more bothered by emotional infidelity
Men against having an unfaithful partner and losing RS
Women against losing their mate's investment to another
Protects what is important to men and women
Sexual jealousy may be adaptive
Female Counter-Strategies to infanticide by males
Mating with many males to 'confuse paternity' ("multiple mating")
Formation of 'friendships' with males who aid in the protection of
Typically directed at immigrant males
Female coalitions to cooperatively defend infants from infanticidal
Sexual Selection and Mating Strategies
1:01 PM
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