Evo. Biology Chpt 16: Sex and Sexual Selection

what are the three models that favor sexual reproduction?

1. high environmental probability

2. high niche number

3. high parasite load

what is the red queen hypothesis?

the frequency of sexual reproduction will be related to the level of parasitic infection

what are the two types of asexual reproduction?

1. apomixis

2. automixis

what is apomixis?

an unfertilized gamete undergoing a single mitosis-like cell division, producing two daughter cells; each daughter cell is genetically identical to its mother

what is automixis?

haploid gametes produced via meiosis, but diploidy is usually restored among fusion of these from the same meiosis; producing offspring that are genetically different from parent and sibling

what is amphimixis?

sexual reproduction; alternating phases of meiosis and syngamy (gamete fusion)

list and describe the three steps of amphimixis

1. recombination: crossover between homologous chromosomes

2. gamete production: production of haploid gametes from diploid individuals via meiosis

3. gamete fusion: haploid gametes fuse to produce diploid offspring

how can we use genetics to distinguish between sexual and asexual reproduction?

by observing the presence/absence of reproductive genes

how can we use phylogenetic trees to distinguish between sexual and asexual reproduction?

• Mt DNA only from mother

• nuclear DNA from both parents

• in an asexual reproduction tree, Mt and nuclear DNA trees are more congruent with one another

do asexually reproducing vertebrates exist?

yes

do sexually or asexually reproducing vertebrates tend to go extinct more quickly?

asexual

what is the one taxa that is entirely composed of asexual species?

rotifers

where are asexual species thought to have evolved from?

sexually reproducing ancestors

describe how asexual females are related to their offspring in comparison with sexual females?

asexual females are twice as related to their offspring as are sexual females

what is the 2-fold cost of sex?

asexual females avoid the cost of also producing males by producing offspring that do not need to be inseminated in order to reproduce

do asexual or sexual populations increase more quickly? why?

asexual will increase twice as quick as sexual as a consequence of anisogamy

what is anisogamy?

the production of two different kinds of gametes

what is isogamy?

each parent produces mid-sized gametes

what are favorable gene combinations?

an allele at one locus is favored when in the presence of an allele at another locus

list the four costs of sexual reproduction

• breaking up favorable gene combinations

• time and energy

• during courtship, often less vigilant for predators

• risk parasitic infection

list the two main benefits of sexual reproduction

1. can purge deleterious mutations

2. generates genetic variation that is favored by natural selection

what is muller’s ratchet?

the process of deleterious mutations increasing and a shift in which individual would be considered “best class”; not equivalent to a deleterious mutation becoming fixed

does the y chromosome undergo recombination?

no

what is epistasis?

the interactions between the effects of alleles at different loci

what are synergistic mutations?

two mutations occurring together having more of a detrimental effect than either would on their own

what deleterious mutation rate per diploid genome per generation value makes it so that sexual reproduction is favored?

>1

what is the fisher-muller hypothesis?

recombination allows natural selection to operate at a quicker rate than is possible in asexual species

what are the three predictions of the red queen hypothesis?

1. oscillations in the relative frequency of asexual lineages when parasites are present

2. time lags between new mutations

3. correlation between parasite load and sexual reproduction

what is bet hedging?

maximizing the chance that an offspring will survive to reproduce

how does variability reduce competition among offspring?

by allowing for the possibility for offspring to go on to specialize in different niches

what is cyclical parthenogenesis?

the process of being able to reproduce both asexually and sexually depending on environmental conditions

list the three cues that can initiate sexual reproduction in cyclical parthenogens

1. predator presence

2. decreased food

3. environmental changes

what happens in regards to selection after both sexual reproduction and anisogamy are present?

selection begins to favor different traits in males and females; EX: competition among members of the same sex, gamete size

what are the two reasons that allow variation among male reproductive success high?

1. low cost of sperm production

2. differences in reproductive success

what are the two reasons that allow variation among female reproductive success to be low?

1. high cost of egg production

2. choosier sex

what is sexual dimorphism?

a difference in how the same trait manifests itself in males and females

what are the three types of sexual selection?

1. intersexual selection

2. intrasexual selection

3. mutual mate choice

what is intersexual selection?

when individuals of one sex select among individuals of the other sex as mates

what is intrasexual selection?

members of one sex, most often males, compete with each other for mating access to the opposite sex

what are the four evolutionary model of female mate choice?

1. direct benefits

2. good genes

3. fisherian runaway selection

4. sensory bias

what does the direct benefits model state?

selection favors females who have a genetic predisposition to choose mates that provide them with resources above and beyond sperm that increase survival/fecundity; EX: safety from predators

what does the good genes model state?

that females will exhibit a preference for ornaments that are a sign of good, healthy genes that will allow offspring to go on to produce successful children

what is the handicap principle hypothesis?

that costly ornaments/behaviors function as reliable signals; EX: peacock tail is a handicap as it is a cost to maintain, but signals that the male is healthy

what does the fisher process of sexual selection state?

that some females simply express a preference for an ornament; linkage disequilibrium arises as selection favors the male ornament and female preference for it

what does the sexy son mechanism for female choice state?

that females benefit from mating with extravagant males because by doing so they are more likely to produce sons who are colorful and preferred by females

what is runaway sexual selection?

genetic correlation between trait and preference results in a positive feedback loop; will produce increasingly exaggerated traits

what is the sensory bias hypothesis?

the a preference for a certain trait predates a mating trait that correlates with said preference, initiating a response from the female nervous system

does the sensory bias hypothesis address the origin or the maintenance of female preference for certain traits?

the origin

describe how competition between the three male morphs of bluegill sunfish are an example of more subtle competition?

• parental males: highly territorial, much energy into caring for offspring

• sneaker males: when see a parental male mating, they will swim up and shed sperm

• satellite male: look like females, so they can swim between spawning pairs and release sperm

what is postcopulatory sexual selection?

sexual selection acting on traits that affect a sperm’s ability to reach and fertilize an egg

in increasing order of testes to body size ratio, list the different bluegill sunfish morphs

parentals, satellites, sneakers

compare the number and quality of sperm produced by the parental and sneaker morphs

parental: high quality, but fewer

sneakers: lower quality, but more

what is sexual conflict?

when traits in one sex can be detrimental to individuals in the other sex

in what scenario would a male dunnock bird have the most reproductive success? least?

most: polgyny (multiple females, one male)

least: polyandry (one female, multiple males)

in what scenario would a female dunnock bird have the most reproductive success? least?

most: polyandry (one female, multiple males)

least: polygyny (multiple females, one male)