Evolution and Population Genetics

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Evolution and Population Genetics I. The Modern
Synthesis II. Beyond the Synthesis III. Life
History Adaptations IV. Sex and Evolution
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature
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IV. Sex and Evolution A. Types of Sex
Determination - environmental Temperature

Manolakou et al. Reproductive Biology and
Endocrinology 2006 459  
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IV. Sex and Evolution A. Types of Sex
Determination - environmental Temperature

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IV. Sex and Evolution A. Types of Sex
Determination - environmental Temperature

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IV. Sex and Evolution A. Types of Sex
Determination - environmental Temperature

WARM Female
WARM Female
COOL Male
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IV. Sex and Evolution A. Types of Sex
Determination - environmental Temperature

Adaptive in Harem Forming Species - Lots of
daughters early maximizes fitness (theyll mate)
safe genetic investment nest egg (ha-ha)
- Males late are low cost (even if they dont
mate, the daughters mate) and potentially high
payoff if they acquire a harem take a risk when
costs are low but potential benefits are high.
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources
Jack-in-the-Pulpit - male when small -
changes to female when large
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources
Jack-in-the-Pulpit Adaptive because a small
plant can be a successful male without investing
energy in fruiting structures. So why be female?
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources
Jack-in-the-Pulpit So why be female? -
frequency dependent selection if lots organisms
in a population are one sex, then the members of
the opposite sex have lots to choose from and
will have a high probability of mating.
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources
Jack-in-the-Pulpit So why be female? -
frequency dependent selection if lots organisms
in a population are one sex, then the members of
the opposite sex have lots to choose from and
will have a high probability of mating. - also,
as a female, the plant can decide which
offspring to nurture and abort others.
Influencing offspring QUALITY.
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources Pheromonal
Inhibition
Blue-headed Wrasse
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources Pheromonal
Inhibition
Blue-headed Wrasse - males excrete a pheromone
and act aggressively this keeps the other fish
in the social group female
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IV. Sex and Evolution A. Types of Sex
Determination - environmental
Temperature Resources Pheromonal
Inhibition
Blue-headed Wrasse - males excrete a pheromone
and act aggressively this keeps the other fish
in the social group female - when male dies,
one of the females changes sex to male and
inhibits the others.
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IV. Sex and Evolution A. Types of Sex
Determination - environmental -
chromosomal
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs - only ½ genes
are passed to each offspring
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs - only ½ genes
are passed to each offspring - energy for new
structures
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs - only ½ genes
are passed to each offspring - energy for new
structures - energy for gamete dispersal,
searching for a mate, acquiring a
mate.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs - only ½ genes
are passed to each offspring - energy for new
structures - energy for gamete dispersal,
searching for a mate, acquiring a mate. -
variable offspring some will be lower quality
lower probability of survival and
reproduction
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs 2. Benefits
- variable offspring some may be high
quality high probability of surviving and
reproducing
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2. Benefits - variable offspring some may
be high quality high probability of
surviving and reproducing - this is
especially important if the environment varies
how can an environment change?
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2. Benefits - variable offspring some may
be high quality high probability of
surviving and reproducing - this is
especially important if the environment varies
how can an environment change? ABIOTICALLY
change in climate over time
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2. Benefits - variable offspring some may
be high quality high probability of
surviving and reproducing - this is
especially important if the environment varies
how can an environment change? BIOTICALLY
change in other organisms over time
Red Queen Hypothesis it takes all the running
you can do to stay in the same place!
OTHER organisms are evolving you must, too
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2. Benefits - variable offspring some may
be high quality high probability of
surviving and reproducing - because only ½ of
the genes are passed to each offspring,
deleterious alleles can be lost from the
population.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs 2. Benefits -
These are costs and benefits RELATIVE TO the
alternative asexual reproduction.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs 2. Benefits -
These are costs and benefits RELATIVE TO the
alternative asexual reproduction 3. C/B of
Asexual Reproduction - Asexual reproduction is
a more energetically and genetically efficient
way of replicating all your genes into the next
generation. All genes are passed to each
offspring.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs 2. Benefits -
These are costs and benefits RELATIVE TO the
alternative asexual reproduction 3. C/B of
Asexual Reproduction - Asexual reproduction is
a more energetically and genetically efficient
way of replicating all your genes into the next
generation. All genes are passed to each
offspring. - Beneficial if the environmental
is static success of the parental genome is
proof that the clonal offspring should ALL be
capable of survival. Selection between clones
can lead to a population dominated by an
efficient genotype.
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3. C/B of Asexual Reproduction - Asexual
reproduction is a more energetically and
genetically efficient way of replicating all your
genes into the next generation. All genes are
passed to each offspring. - Beneficial if the
environmental is static success of the parental
genome is proof that the clonal offspring
should ALL be capable of survival. Selection
between clones can lead to a population dominated
by an efficient genotype. - BUT, environments
always change. And, there is the problem of
Mullers Ratchet bad mutations accumulate in a
lineage all genes are passed to all
offspring.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs 2. Benefits -
These are costs and benefits RELATIVE TO the
alternative asexual reproduction 3. C/B of
Asexual Reproduction 4. Tests of these ideas

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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction 1. Costs 2. Benefits -
These are costs and benefits RELATIVE TO the
alternative asexual reproduction 3. C/B of
Asexual Reproduction 4. Tests of these ideas
Some species reproduce both ways. Under what
conditions do they reproduce sexually?
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4. Tests of these ideas Some species
reproduce both ways. Under what conditions do
they reproduce sexually? ex. 1 Bacteria.
Many bacteria can genetically transform by
accepting exogenous DNA and incorporating it into
their genomes, creating variable populations. In
most cases, the ability to transform increases
when the population is stressed by new
environmental conditions (abiotic conditions or
competition).
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4. Tests of these ideas Some species
reproduce both ways. Under what conditions do
they reproduce sexually? ex. 2. Freshwater
snail in New Zealand (example from book
Potamopyrgus antipodarum) can exist as
populations of female clones or sexual
populations.
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4. Tests of these ideas Some species
reproduce both ways. Under what conditions do
they reproduce sexually? ex. 2. Freshwater
snail in New Zealand (example from book
Potamopyrgus antipodarum) can exist as
populations of female clones or sexual
populations.
In the lab, asexual populations reproduce faster
and outcompete sexual populations.
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4. Tests of these ideas Some species
reproduce both ways. Under what conditions do
they reproduce sexually? ex. 2. Freshwater
snail in New Zealand (example from book
Potamopyrgus antipodarum) can exist as
populations of female clones or sexual
populations.
In the lab, asexual populations reproduce faster
and outcompete sexual populations. The snails
have a trematode parasite with ducks as another
host. Shallow lakes with ducks and worms have
more sexual populations deep lakes without ducks
and without worms are dominated by asexual
populations.
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4. Tests of these ideas Some species
reproduce both ways. Under what conditions do
they reproduce sexually? ex. 2. Freshwater
snail in New Zealand (example from book
Potamopyrgus antipodarum) can exist as
populations of female clones or sexual
populations.
In addition, even in deep lakes, abundant clones
get hammered and there is a cycling of the
relative frequency of different clones as
abundant ones get hammered by worms adapting to
take advantage of this most abundant resource.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes?
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes?
Actually, there are lost of species with more
than 2 sexes (or mating types), such as many
protists and fungi.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes?
Actually, there are lost of species with more
than 2 sexes (or mating types), such as many
protists and fungi. More is better, but more
complicated. BETTER because a greater fraction
of the population is a suitable mat. If there
are 20 equally abundant sexes, and the only
stipulation is that you cant mate with your own
sex, then each organism can mate with 95 of the
population. Reduce search time, which is
important for small organisms.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes?
COMPLICATED because sex (fusion of gametes)
involves one sex disarming immunologically
while the other remains on. Strategies get
complex SEX 1 NEVER DISARMS SEX 2 Disarms
for sex 1, not for 2-4 SEX 3 Disarms for 1 and
2, but not for 4. SEX 4 ALWAYS DISARMS
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes?
COMPLICATED because sex (fusion of gametes)
involves one sex disarming immunologically
while the other remains on. Strategies get
complex SEX 1 NEVER DISARMS SEX 2 Disarms
for sex 1, not for 2-4 SEX 3 Disarms for 1 and
2, but not for 4. SEX 4 ALWAYS DISARMS
This works, but mistakes will be made. And they
will be made more frequently by sexes that have a
choice to make (sexes 2 and 3). So, the
reproductive success of sexes 2 and 3 should be
slightly lower than 1 and 4, and over time a
multi-sex population might degrade to a TWO SEX
SYSTEM.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes? 2. Why 5050 ratios?
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes? 2. Why 5050 ratios? Frequency Dependent
Selection Selection will favor a phenotype based
upon its frequency in the population.
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IV. Sex and Evolution A. Types of Sex
Determination B. The Costs and Benefits of
Sexual Reproduction C. Sex Ratios 1. Why two
sexes? 2. Why 5050 ratios? Frequency Dependent
Selection Selection will favor a phenotype based
upon its frequency in the population. With
respect to sex, typically the rare sex is
favored. (So, the reproductive value of sons
and daughters differs, depending on their
abundance).
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With respect to sex, typically the rare sex is
favored. Consider a population in which
females predominate. So there are lots of females
in the population, and not all of them are mating
because there arent enough males to go around.

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With respect to sex, typically the rare sex is
favored. Consider a population in which
females predominate. So there are lots of females
in the population, and not all of them are mating
because there arent enough males to go around.
A female that, for genetic reasons, produces
more sons will have her genes increase in the
population (will be selected for) because the
sons will have a higher probability of
mating.
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With respect to sex, typically the rare sex is
favored. Consider a population in which
females predominate. So there are lots of females
in the population, and not all of them are mating
because there arent enough males to go around.
A female that, for genetic reasons, produces
more sons will have her genes increase in the
population (will be selected for) because the
sons will have a higher probability of
mating. So, the frequency of females that
produce sons will increase, and the frequency of
males will increase, until the sex ratio is about
5050.