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parental investment

expenditure on present offspring that increases that offsprings chance of survival at the expense of future offspring.

intra-sexual selection

favors traits that affect the ability of members of the same sex to compete with each other for mates

inter-sexual selection

favors traits that attract members of the opposite sex

male-male competition

(lots of competition) strong relationship to physical attributes and the number of matings they have. Defend mating sites, defend mates, ability to avoid damage

types of defense of mating sites

emergence, foraging, and oviposition

pre-copulation mechanisms

skill in mate location, time of emergence

post-copulation mechanisms

mate concealment, mate guarding

mate concealment

remove females from area, reduce conspicuousness of courtship

post-fertilization mechanisms

induced abortion, infanticide

induced abortion

"bruce effect" pregnancy disruption in which exposure of female to a new male results in abortion


when female is with young she is not able to mate, so males will come and kill her young so she can mate.

mate guarding

last male to mate often fertilizes most eggs

sperm competition

scrappers, copulatory plugs


to remove previous males sperm

copulatory plugs

"chastity belts" closes off females area so no sperm can enter

female choice

costly to mate with bad male (reduced fitness) so they choice good males

preferential mating

rejection of members of wrong species, selection of partners with resources, selection of partners with good genes.

direct benefits

better resources, increased parental investment

indirect (genetic) benefits

increased offspring fitness

nuptial gifts

resources given to increase length of mating or decrease probability of female mating again

secondary sexual characteristics

physical or behavioral characteristic that appear in sexually mature animals, differentiate between the sexes without having direct reproductive function

fischer's runaway hypothesis

1. trait starts by conferring some advantage
2. preference for trait that confers advantage evolves
3. eventually the offspring of these matings with have genes for traint and genes for prefeering trait
4. leads to a runaway process- prefenece is given even though the exagerated trait no longer confers a fitness

handicap hypothesis

signals are costly so they information conveyed is honest and shows males genetic quality (peacocks)

hamilton and zuk

disease resistance, colorful displays often signal health and parasite Resistance

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