Unit 3 : Sexual Selection, Mate Choice, and Mating Systems

BIOL1003

gender

social, cultural, psychological, political construct

sex

gamete size

sexual reproduction

the mixing of genomes through the fusion of gametes (requires two different individuals)

isogamy

gametes that are equal in size (different, NOT the same)

anisogamy

gametes different in size

zygote

egg and sperm fused together (fertilized egg)

large gamete

• large zygote

• advantage : nutrient rich

• disadvantage : slow moving, a lot of energy, less created

small gamete

• small zygote

• advantage : fast moving, little energy, many created

• disadvantage : low nutrients

dissimilarity

some species have two sexes (males and females), but they look dramatically different

similarity

some species have two sexes (males and females), but they look almost identical

parental investment

sum of gamete investment + care of offspring

• bi-parental

• female-only or male-only

• no parental care

choosiness

an individual's fitness (# of offspring) will be highest if they mate with the highest quality mates

sexual conflict

males and females have opposing interests

competing sex (often male)

low to no parental investment, selection for traits that increase mating frequency

choosy sex (often female)

higher parental investment, selection for traits that resist poor quality mating

sexual selection

traits that help individuals find, attract, choose and fertilize mates will be favored

*sexual selection and natural selection can oppose each other

secondary sex traits

traits that aid in the process of sexual reproduction by allowing individuals to gain access to mates

ornaments/sexual signals

traits that are subject to selection via mate choice

• olfactory, auditory, vibratory signals

mate choice (intersexual selection)

individuals of one sex choosing among members of the opposite sex based on the attractiveness of certain traits that those individuals possess

*inter = between sexes

mate competition (intrasexual selection)

involves individuals of one sex competing with members of the same sex for access to mates

*intra = within sexes

sexual dimorphism

an elaborate secondary trait

direct benefits

mates provide material resources (food, shelter, parental care) which is an immediate benefit

indirect benefits

 increase fitness of potential offspring, a mate that helps make an offspring healthy

sexy son hypothesis

the trait happens to be attractive to the choosy sex and therefore preferred

*preference is passed down to the offspring and maintained through future generations

*the display does not have anything to do with other genetic traits

good genes hypothesis

 the ornamental trait indicated genetic quality because genetic quality correlates with display attractiveness

*the display trait is therefore an honest signal that the mate has better alleles (stronger, faster) and is healthier

runaway sexual selection

 traits can become absurdly “sexy” (and costly)

pre-copulatory

individuals selection potential mates before mating occurs

• physical traits

• behavioral displays

• other attributes

post-copulatory

 individuals select potential mates during and after mating occurs

• cryptic female choice

• sperm competition

cryptic female choice 

females exert control over male mating success within the reproductive tract by selectively using sperm to fertilize their eggs

sperm competition

sperm from different males inside the female reproductive tract compete to fertilize eggs

sneaker male

steal mating activity from another same sex individual

*alternative mating strategy

satellite male

one sex mimics the other sex in its behavior, morphology, or chemical signaling

mating pattern

the general pattern in which females and males pair up within a species

polyandry

two individuals pairing together for at least one breeding

• one parent can provide enough parental care

• males and/or resources are aggregated within a habitat and therefore defensible

• fertility may not matter

polygyny

one male mates with multiple females over a lifetime

• one parent can provide enough parental care

• females and/or resources are aggregated within a habitat and therefore defensible

• females are fertile for a long time, female fertility is detectable, females are fertile at different times (asynchronous)

monogamy

two individuals pairing together for at least one breeding season

• two parents are required for parental care

• females and/or resources are dispersed and mostly unable to be defended

• females are fertile for a short period of time. female fertility is hidden. females are synchronous in their fertility

promiscuity

individuals of both sexes mate with multiple individuals of the opposite sex

• for some species, little parental care is needed. for other species, group parental care is needed

• resources are distributed and unable to be defended. in some species, males and females live in large social groups

• in large social groups, females are synchronous in their fertility

aggregated (clumped) resources

members of the opposite sex can defend and monopolize those potential mates

*polyandry or polygyny

dispersed (spread out) resources

there is a limit to how large of a territory an individual can inhabit and defend

*monogamy or promiscuity

detectability 

can an individual detect a fertile individual 

• detectable = polygyny

• hidden = monogamy 

duration

length of duration of fertility

• long = polygyny

• short = monogamy

timing

synchronous : all females fertile at the same time = polygyny

asynchronous : females fertile at different times = monogamy