PSYC 3280 Chapter Notes - Chapter 7: Nuptial Gift, Mate Choice, Sexual Selection
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
2
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!