Biology 108 - Exam 3

Sexual reproduction (sex) is the _____ .

predominant mode of reproduction in the natural world

When compared to _____ , sex ___ .

asexual reproduction, imposes a wide variety of fitness costs

Sex is favored _____ when ______ .

in the long term, selection changes over time and/or space

Competition for mates can result in ___ .

sexual selection

Sexual conflict can arise when ____ .

selection favors different alleles in males and females

Sexual reproduction (sex) is ______ in the natural world.

extremely common

Offspring have _____ .

a combination of genetic material from two genomes and later generate gametes by meiotic reduction

“outcrossing”

combination of genomes from two different individuals (vs. “selfing”)

Nearly all ____ engage in _____ .

eukaryotic organisms, sexual reproduction at least some of the time

alternative to sex

asex (asexual reproduction)

Sex imposes a wide variety of ____ .

fitness costs compared to asex

fitness costs of sex

need to find and attract a mate, mating takes time and can be risky, meiosis may take longer than mitosis, sexually-transmitted diseases, pass on only half your genes to your offspring rather than all of them

“two-fold cost of sex” or the “cost of males”

asexual genotypes (all offspring are female) will outcompete sexual genotypes (only half are female; male are dead weight)

If sex is so ___ , it must have ____ .

common, advantages

The classic argument for the evolutionary advantage of sex is _____ .

“sex generates variability, and variability is good for adaptation”

What are the problems of sex?

does not always increase genetic variability, increased genetic variability is not always “good” for adaptation

Sex produces ___ , reducing ____ .

“intermediate” genotypes, genotypic variance

_____ is ______ for adaptation.

Increased genetic variability, not always “good”

Sex creates ______ , reducing ______ !

suboptimal genotypes, mean fitness

Sex does not always _____ .

increase genetic variability

Sex is _____ , and evolves due to its ____ !

rarely directly beneficial, long-term benefits

Sex is favored when _____ .

organisms experience a different selective environment than their parents

Different combination of alleles are favored in ___ .

parents vs. offspring

Co-evolution (e.g. host-parasite) can
cause ____ .

stable evolutionary cycles

The Red Queen Hypothesis

hypothesis for the long-term benefit of sex; takes running to stay in the same place

Co-evolution (e.g.
host and parasite) can result in ____ .

a long-term benefit of sexual reproduction even given the cost of sex

Sex is advantageous because it ____ .

brings together sets of adaptative alleles and breaks apart sets of deleterious alleles

Need to wait for ____ to put ____ .

mutation, all three mutations in the same genotype

Sex/recombination can ____ into the
____ .

rapidly assemble all three
adaptive mutations, same genotype

Sex allows ___ to _____ more
quickly.

natural selection, “find” optimal
genotype combinations (adaptive peaks)

Sex also ___ sets of ____ .

breaks down, deleterious alleles

When all individuals carry some
____ , they’ll all have
____ .

deleterious alleles, similar fitness

Sex creates a ____ , some with ____ !

variety of new genotypes, NO deleterious mutations

Sex and recombination allows ____ to
be ______ , increasing
_____ .

deleterious mutations, efficiently removed, mean fitness

Sex also separates _____ .

beneficial and deleterious alleles

(McDonald et al.) Beneficial and deleterious alleles became ____ .

fixed (hitchhiking!)

(McDonald et al.) Only beneficial
alleles became ______.

fixed

(McDonald et al.) Overall improvement in fitness was much greater
for ____ .

sexual populations

McDonald et al. (2016) allowed ____ and tracked the ____ .

yeast to adapt to lab conditions with or without periodic sexual reproduction, frequencies and effects of new alleles

Sex has a variety of ___ .

important consequences for evolution and genetics (sexual dimorphism/anisogamy, sexual selection, and sexual conflict)

(Sexual dimorphism) Anisogamy

females: each gamete is relatively costly, relatively high investment in zygotes, fitness often limited by fecundity
males: each gamete is relatively cheap, relatively low investment in zygotes, fitness often limited by mating success

(Sexual dimorphism) Anisogamy is ____ .

the ultimate cause of all other sexual dimorphism, differences in phenotype between sexes in animals

(Sexual dimorphism) Anisogamy has evolved ___ .

many times

(Sexual dimorphism/Anisogamy) Genetic males and females are defined as producers of ___ .

micro-gametes (sperm) vs macro-gametes (eggs)

The evolution of sexual dimorphism/anisogamy is ____ , and may be the result of
______ .

not fully understood, sexual cooperation, sexual conflict, or both

Sexual selection is ___ .

natural selection for the ability to acquire mates

Sexual selection is a special type of ___ .

natural selection

Sexual selection results from differences between ___ .

individuals in their ability to acquire mates

Sexual selection can cause ___ .

rapid evolution of genes and traits

Sexual selection is a major driver of _____ .

sexual dimorphism/anisogamy

Bateman’s Principle

when males have higher variance in reproductive success than females

Bateman’s Principle usually requires ___ to ____ but ___ .

multiple mating, increase male fitness, has little effect on female fitness

Comparing ____ can be used as a _____ !

variances, measure of sexual selection intensity

Sexual selection can also occur in the absence of ___ .

any anisogamy and genetically male and female individuals

simultaneous hermaphrodites

may often self-fertilize, but can also outcross

Forms of Sexual Selection

Pre-copulatory, Post-copulatory

Pre-copulatory Sexual Selection

Intra-sexual competition, Mate choice

Pre-copulatory

occurring before mating

Post-copulatory

occurring after mating

Intra-sexual competition

typically males compete to access and monopolize females

Mate choice

typically females exert preferences for some males over others

Post-copulatory Sexual Selection

Sperm competition, "Cryptic" female choice

Sperm competition

destroy, displace or outpace the sperm of other males; inhibit re-mating by females

“Cryptic” female choice

favor the sperm of some males over others

Sexual selection also occurs in ____ !

plants and fungi

Pre-Copulatory Sexual Selection in Plants

mating success depends on attracting pollinators

Post-Copulatory Sexual Selection in Plants

male gametes compete to form and elongate pollen tubes to reach an ovule

What are the outcomes of sexual selection?

secondary sexual traits, evolution of preference/choice (choosiness)

secondary sexual traits

traits not needed for reproduction, but play a role in mate competition or mate choice

Secondary sexual traits are often ____ .

sexually-dimorphic

Some secondary sexual traits become “exaggerated” due to (usually) _____ .

male-male competition – an evolutionary “arms race”

The preferred partner may:

control a larger feeding territory, offer a better “nuptial gift”, provide better offspring care or protection

Indirect benefits of preference/choice:

sire attractive offspring and provide them good genes

Sexual conflict occurs when _____ .

adaptive landscapes differ between the sexes

Examples of traits with different optima in males/females

What is one way sexual conflict can be resolved?

evolution of sex chromosomes (movement and regulation)

gene flow

movement of alleles between populations due to migration

Gene flow causes populations to become _____ , and usually _________ .

more similar in allele frequency, increases genetic diversity

Gene flow is generally higher between
_____ , causing _______ .

nearby populations, “isolation by distance”

Gene flow is extremely common in _____ .

natural populations

Gene flow can facilitate ____ .

natural selection

migration

movement of an individual from one population to another

Gene flow tends to make populations _____ over time.

more genetically similar (homogenous)

Gene flow is nearly _____ at some level, making it ____ .

always occurring, very common

It is rare for populations to be _____ from other populations.

totally isolated

Usually, organisms ______ to ______ to at least some degree.

disperse/migrate, other locations

Island Model

discrete populations of fixed size connected by bidirectional migration

The Island Model is the ____ of ___ .

simplest model, gene flow

Migration rate (m)

proportion (0.0-1.0) of individuals in each population that originate from other populations each generation

The ______ the migration rate, the _____ the populations _____ and become _____ .

higher, faster, converge, homogenized

On average, gene flow tends to _____ and _______ the effects of _____ .

increase genetic diversity, “reverse”, drift and local selection

Gene flow _____ between populations.

reduces divergence

divergence

the accumulation of genetic differences between populations by drift or selection

The ____ there is, the ____ populations are able to accumulate ____.

more gene flow, less, differences

At equilibrium, there is a direct relationship between ___ .

m and FST

FST =

1/(4Nm+1)

FST = 1/(4Nm+1) A larger m =

lower FST

FST = 1/(4Nm+1) What is the product of N and m?

number (not proportion) of migrant individuals

FST = 1/(4Nm+1) Smaller m needed to have ____ .

same FST in larger populations

FST = 1/(4Nm+1) We might expect that larger populations should require ____ than small populations.

proportionally more migrants (number of individuals)