PSYC 3280 Chapter Notes - Chapter 7: Nuptial Gift, Mate Choice, Sexual Selection

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Chapter 7- Sexual Selection
Sexual Selection depends on the advantage which certain individuals
have over others of the same sex, in exclusive relation to reproduction
Intrasexual Selection- members of one sex compete with each other for
access to the other sex
Intersexual Selection- individuals of one sex choose which individuals of
the other sex to take as mates (mostly females pick the males)
o Bateman’s Principle-
Females should be choosier in selecting a mate because
eggs are expensive/limited to produce
Females choosiness in males should translate into greater
variance in the productive success of males
o In species with internal gestation, females devote much energy
to offspring before they are born so they must pick mates that
will produce healthy offspring
Epigametic Sexual Characteristics- secondary sexual traits that play a
role in attracting mates (ornamental plumage, bright colours)
There is greater variation in reproductive success (stronger sexual
selection) inn polygamous and polyandrous systems
Evolutionary Models of Mate Choice
Direct Benefits
Sexual selection favors females that have a genetic predisposition to
choose mates that provide them with resources that increase the
fecundity (food, shelter)
Scorpion Fly- females choose males that bring them large prey items as
nuptial gifts
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o The size of the nuptial gift determines the copulation time,
which in turn, determines how much sperm is transferred during
the mating
o Males will often sample, and discard prey that are too small to
result in long copulation
o Makes may steal large prey from one another by mimicking the
behaviour of a female, and stealing the prey brought to them by
other males
Good Genes
Females choose males with genes/genetic quality best suited to their
particular environment (indirect benefit to the mother because the
offspring will also receive some of those good genes)
Honest Indicators- focus on these traits when choosing a mate can help
females overcome the male cheater problem (males giving the
impression that they possess good genes even if they don’t)
o The costlier the trait is to produce, the more difficult it is to fake
Parasite Resistance- body coloration indicates that a male does not have
endoparasites, therefore, females choose the most colourful mate
Major Histocompatibility Complex (MHC)- Genes involved in disease
resistance, but has genetic variability (few individuals have the same
MHC allele)
o Females prefer mating with others with a dissimilar MHC to
allow the offspring the possibility of an even stronger immune
system
o Females use odors to determine if another individual is a good
MHC match, and use perfume to magnify their own MHC odors
o Rather than choosing a mate with dissimilar MHC alleles, female
stickleback fish will select males with many MHC alleles (2-8
alleles)- THERE IS AN OPTIMAL NUMBER!
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