Studied by 8 peopleSexual 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)
Note
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