Mating systems and sexual selection

what are the four types of mating systems

polygyny, monogamy, promiscuity, and polyandry

polygyny

males mate with more than one female; females mate with only one male

what do men offer or provide under polyandry

sperm only

how do polygynous males acquire their females

they will either defend territories which attract females looking for resources or they defend groups of females directly

what to females provide under polygyny

majority of parental care 

monogamy

males only mate with one female and vice versa

social monogamy

both sexes mate with multiple partners, but males help raise the offspring of their social partner (which may or may not be their own)  

does monogamy have high or low parental investment

high from both males and females

where do monogamous mating systems generally exist

in environments in which parental care from both parents Is needed to successfully raise young

are males able to capitalize on their high potential reproductive success under monogamy

no because if they do not provide parental care, none of their offspring will survive

promiscuity

males and females both mate with many individuals 

in what species is promiscuity very common in

aquatic species and all outcrossing plants

what doo males and females provide in promiscuity mating systems

males contribute only sperm and females may or may not provide any post-fertilization parental care

polyandry

females mate with more than one male; males mate with only one female

what do females provide in polyandry 

large flashy aggressive fights for territories and large eggs/ pre-fertilization investments 

t/f: polyandry is a relatively uncommon mating system

true

in which sting system would we expect the greatest variation in male reproductive success

polygyny

natural selection

allele frequency changes over time due to differences in survival AND reproductive success 

sexual selection 

allele frequency changes over time due to differences in reproductive success only 

sexual selection causes

individuals to differ in their success due to competition for mates

in sexual selection how do individuals differ and what is the effect

they differ in traits that are used to compete for mates (song, dance, color, morphological structure); if these traits increase the likelihood and individual will mate, they are favored by sexual selection

t/f: only males can have sexually selected traits 

false 

do colors, songs, and dances of peacocks and birds increase survival 

no, only reproductive success 

intra-sexual selection

direct competition among one sex for access to the other sex (usually male-male competition) competition could include signals of fighting ability, threats or actual aggression

inter-sexual selection

indirect competition among one sex to attract the other sex; involves mate choice (usually female choice)

in inter-sexual species how are male phenotypes functionally determined

by female preferences

what are the three types of intersexual selection

direct benefits, good genes, and runaway sexual selection

intersexual selection: direct benefits

females choose males based on display traits that honestly advertise (non-genetic) benefits that can directly increase the survival likelihood or reproductive success of the adult female herself and/or her offspring 

intersexual selection: good genes model

females choose males based on displays (complex songs or bright colors) that can only be produced by high quality or healthy males (i.e., those with ‘good genes”)

Under the good genes model, the beneficial alleles are inherited by

both daughters and sons and increase survival and reproductive success in both 

the good genes model of sexual selection can also apply to traits that reduce survival likelihood through

handicap principle

what is the handicap principle

only high-quality males can survive if they possess a costly or deleterious character, whereas low-quality males would be killed by the costly trait

intersexual selection: runaway (sexy sons)

females choose males based on an arbitrary preference (in females) for a genetic trait (in males). the male trait provides no information on male quality/health OR any direct benefits

what is sexual dimorphism 

when male and females of the same species look quite different than one another 

what can cause sexual dimorphism

sexual selection on one sex (typically males)