eukaryotes reproduce

sexually

hermaphrodite is

individual that produces both female and male gametes

banana slugs

hermaphrodites and can receive sperm from other slugs, deliver sperm to them, or fertilized their own eggs

parthenogenesis is a mode of

reproduction in which the female sex cells undergo meiosis but are not fertilized by sperm

in parthenogenetic species females produce

only daughters

strawberries reproduce ___ and breadmold reproduce ___

asexually, sexually/asexually

sex does not always genrate

more variable offspring

asexual linegaes multiply

faster than sexual lineages because all progeny produce offspring (sexual lineage, half males that cannot produce by themselves, halving rate of replication)

disadvantages of sex: twofold cost of sex

asexual lineages grow more rapidly each generation, sexual cannot

disadvantages of sex: search cost

males and females must locate each other in order to mate, takes time, energy, and risk of predation

disadvantages of sex: reduced relatedness

sexually reproducing organisms pass half of alleles to offspring from meiosis, halves the relatedness between parents and progeny

disadvantages of sex: risk of sexually transmitted infections

mating provides effective means of transmission for many pathogens, asexual avoid this risk

advantages of sex: combining beneficial mutations

combining alleles of genes can bring separate beneficial mutations together in a single individual faster than would be expected if they had to arise spontaneously in the same genome

advantages of sex: generation of novel genotypes

thru recombination, meiosis provide chromosomes to cross over, creating gametes with unique combinations of alleles

advantages of sex: faster evolution

offspring of sexual parents are more genetically variable than asexual. speed evolutionary response to selection (red queen effect)

advantages of sex: clearance of deleterious mutations

sexual populations can purge themselves of harmful mutations, exclude deleterious mutations. asexual cannot, they steadily accumulate mutations until extinct (Muller's ratchet)

muller's ratchet

genomes of asexual population accumulate irreversible, deleterious mutations over generations

genetic load

the burden of accumulated deleterious mutations increases over time

yeast can reproduce

either asexually or sexually

McDonald found that deleterious alleles "hitchhike" to

fixation in asexual populations but are purged from sexual populations due to recombination

the red queen effect makes

sex beneficial

red queen effect

to maintain relative fitness, coevolving populations must constantly adapt to each other.

sex evolves when selection changes over time

more readily when a species' environment changes rapidly

sex evolves when selection changes over space

can be favored when selection varies over space, as long as the genetic associations created by migration are locally disadvantageous.

sex evolves when organism are less adapted to their environment

organism both sexually and asexually tend to switch to sex under stressful conditions

sex evolves when populations are finite

with limited number of individuals in population, selection erodes and leaves only hidden variation. recombination then reveals hidden variation, improving response to selection

in the absence of sex, the only variation that remains after several rounds of selection is

hidden in the sense that plus alleles at the first site are found with minus alleles at the second site (or vice versa) (this problem is irrelevant in an infinitely large population)

anisogamy results in

differential investment in reproduction

anisogamy

sexual reproduction involving the fusion of two dissimilar gametes

limitations on reproductive success

differ for the sexes

females are limited by

fecundity (number of eggs produced)

males are limited by the

number of mates they can obtain

investment differences can

extend past fertilization

uncertain paternity may explain why

male parental care is less common

certainty of paternity

the probability that a male is the genetic sire of the offspring his mate produces

females have

certain maternity

asymmetrical parental care

alters operational sex ratio

fisher's principle

a 1:1 sex ration is an evolutionarily stable strategy

slower rat eof reprodction by females leads to male-biased operational sex ratio (OSR):

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

intrasexual selection

competition between members of the same sex (usually males) for access to mates

intersexual selection

members of one sex (usually females) choose members of the opposite sex

sexual selection

differential reproductive success resulting from competition for mates (intrasexual and intersexual selection)

sexual selection is commonly a stronger effect for

males (male biased OSR leads to males outcompete other males for access to females)

ornaments

attractive traits that incerase mating success

arnaments

weaponry used to outcompete other individuals

high variance in male reprodutive success leads to

intense sexual selection

some males compete for

territory

direct benefits

benefit the female directly

indirect benefits

benefits that affect the genetic quality of the female offspring

voluntary self sacrifice in redback spiders

male redback spiders will sacrifice their lives to copulate longer with female (higher chance in passing their genes and break the female's reproductive system)

some males display

elaborate ornaments

honest sexual signaling

level of advertisement reveals mate quality

zahavi's handicap principle proposes

females prefer males with handicaps (mating characters that reduce survival chances) because they are indicators of heritable viability

male mannikins peform in a lek

an assemblage of rival males who cluster together to perform courtship displays in close proximity

female preferences may arise from

pre existing sensory bias

arbitrary choice (fisher's positive feedback cycle)

certain male traits are advantageous not because they indicate good quality, but but simply because they are attractive to females.

good genes

elaborate or bright male ornaments signal underlying good quality (good genes)

fisher- good genes process (combination)

alleles for female preferences can coevolve with alleles influencing expression of costly indicator traits in mates

costly ornaments can be

honest signals of better health

monogamy

one male pairs with one female (sexual: exclusively, social: pair but may cheat)

polygyny

males mate with multiple females

polyandry

females mate with multiple males

pair-bonding species are not neccesarily

sexual monogamous

polyandry selects

for male traits that increase paternity rates

sperm competition

occurs when females mate multiply and ejaculates from different males overlap and compete for fertilization

sperm competition drives evolution of

larger testes in primates (males testes are larger in species where females regularly mate with multiple males)

cryptic female choice

a form of sexual selection that arises after mating, when female store and separate sperm from different males and thus determine which sperm they use to fertilize their eggs

sexual conflict

traits that confer a fitness benefit to one sex but a cost to the other (traits cevevolve antagonistically)

coevolution of male and female genitalia in waterflow has been hypothesized to occur

through sexual conflict

eviednce for antagonistic coevolution in Drosophila

Drosophila were experimentally forced to mate monogamously, had lost their defenses against seminal proteins, so females died at much higher rate when mated with normal males