natural selection + sex

directional selection

stabilizing selection

disruptive selection

twofold cost of sex

the cost of males

half of the offspring are males who cannot themselves produce offspring

saying what sex doesn’t make sense

disadvantages of sex

twofold cost of sex

search cost

reduced relatedness

risk of sexually transmitted infections

advantages of sex

combining beneficial mutations

generation of novel genotypes

faster evolution

clearance of deleterious mutations

clearance of deleterious mutations

deleterious mutations can accumulate in asexual lineage rapidly (mullers ratchet) and genetic load increases

genetic load

the burden that the accumulation of mutations places on the fitness of individuals

red queen hypothesis

predicts evolutionary arms race between hosts and parasites

consequence is persistent fluctuating alleles

hosts have to constantly evolve to stay in same place

Anisogamy

sexual reproduction involving the fusion of two dissimilar gametes

larger gametes→ female

smaller gamete → males

Isogamy

sexual reproduction in which the gametes are the same size

no gametes, mating types instead

female reproductive success limited by

how many eggs she can produce and provision (=fecundity)

choosier sex

female

intersexual selection

males trying to be with females

leads to evolution of elaborate male plumage, courtship displays, and other traits used by males to gain access to females

intrasexual selection

competition between males for access to females

leads to evolution of male fighting ability, which doesnt make sense otherwise

why do males typically invest less

uncertain paternity

operational sex ratio

ratio of males to females capable of reproducing at a given time

indicates which sex experiences more sexual selection

Slower rate of reproduction by females typically leads to male-biased OSR

Male-biased OSR leads to sexual selection favoring males that can outcompete other males for access to females