2 Sexual Selection Flashcards
Sex in vertebrates is determined by
many strategies implying genetic, environmental influences, or both
Biological Sex Definition
Gamete Size (larger = female)
Sexual selection
A form of natural selection that occurs when individuals differ in their ability to compete with others for mates or to attract members of the opposite sex
Limits on offspring for males (2)
females
1 male fathers most children - imbalance = competition
Limits on offspring for females
increase RS by increasing offspring survival
Intrasexual selection….
leads to…
competition for mates within a sex
sexual dimorphism and traits that increase fighting ability, endurance, sperm
Distribution of females determines
Results of both (2)
type of competition (contest or scramble)
contest = hierarchies, weapons, mate guarding
scramble = no hierarchies, scramble and sperm competition
relative testes size is
larger in primates when females have multiple partners
sperm competition (2)
decrease inter-ejaculatory intervals
increase sperm plugs
Anisogamy:
the form of sexual reproduction that involves the union of 2 gametes, which differ
in size and/or form. The smaller gamete is called the sperm cell, whereas the larger gamete is called the egg cell.
Gamete:
a haploid cell that fuses with another haploid cell during conception, gametes are sex
cells (ovum, sperm).
Gonad:
reproductive gland that produces the gametes (testicle produces sperm, ovary produces
egg)
Genitals:
external sex organs; visible parts of the body that are involved in sexual reproduction
(penis, vulva)
Sex chromosomes:
chromosomes that are involved with determining the sex of an individual. In
humans, each cell nucleus contains 23 pairs of chromosomes, a total of 46 chromosomes. The first 22 pairs are called autosomes. The chromosomes of the 23rd pair are called allosomes often consisting of 2 X chromosomes or 1 X chromosome and 1 Y chromosome.
allosomes
chromosomes of the 23rd pair
Hormone:
chemical messenger, how one part of your body to communicates with another part
of your body.
Sex steroids:
a type of hormones that are produced by gonads (although they can be produced
elsewhere too).
Androgens:
testosterone, dihydrotestosterone, androstenedione
Estrogens:
estradiol
Secondary sexual characteristics:
sexually dimorphic phenotypic traits that are not directly related to the reproductive system and that appear as an individual reaches sexual maturity.
Intersex:
A category that describes a person whose reproductive, genetic, genital, or hormonal
configuration doesn’t seem to fit the traditional definitions of male or female. The term “hermaphrodite” is considered outdated and offensive. Intersex is frequently confused with transgender but the 2 are completely distinct.
Transgender:
an adjective used to describe a
person whose gender identity does not match the biological sex they were assigned at birth.
Covariation:
If 2 traits covary, then they vary together and if you know one trait, you can
successfully predict the other trait.
the 3 Gs
(genitals, gonads, and gametes)
covary, to a certain extent
mate choice + traits (4)
competition to be chosen by the opposite sex as a mate
ornamentation, courtship, services, friendship
sexual conflict = traits (3)
competition by each sex for control over mating and reproduction
vaginal tract, estrus synchrony, sexual coercion
male reproductive lifespan is….
short = extreme strategies
Infanticide purpose + 3 conditions
by killing an infant a male will gain a reproductive advantage provided that:
- he is not related to the infant he kills
- death of unweaned infant shortens subsequent interval b/t births for mother
- killer increases his chance if mating with the mother and siring her next infant
Female counterstrategy to infanticide
confuse paternity
Sexual Selection occurs in…
both sexes
alternative mating tactics
different behavioral strategies/morphologies
