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U0 Biology 115 > Lecture 4 > Flashcards

Lecture 4 Flashcards

1
Q

Sexual selection was initially described by who

A

Sexual selection was initially described by Darwin

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2
Q

what does sexual selection come from

A

Arises from the observation that many animals develop features whose function is not to improve survival but to maximize their reproductive success

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3
Q

does sexual selection always increase survival

A

in some cases, the feature may actually decrease survival, while still improving fitness because it increases reproduction

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4
Q

what is Intrasexual selection (within a sex)

A

individuals intimidate, deter or defeat same-sex rivals:

territory defence
fighting or other direct competition

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5
Q

what is Intersexual selection (between the sexes)

A

individuals make themselves more attractive to the opposite sex

mate choice/mate preferences

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6
Q

In general, selection can act not just on morphology, but also on_____

A

In general, selection can act not just on morphology, but also on behaviour

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7
Q

give an example of sexual selection

A

Females preferentially mate with large clawed males
Over time (generations) this will skew the population toward larger claws
Any mutation that allows for even larger claws will thrive

Female preferences for larger claws drives an increase in claw size

Natural selection may limit increase in claw size

the crab with the claw too large will be eliminated because now they cant escape from predators, get food, dig a borrow, etc… even though the females prefer the larger claws… so they will end up eliminated
natural selection puts a limit on the distribution

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8
Q

how does sexual selection stay in line

A

sexual selection pushes against natural selection and vice versa

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9
Q

so this explains how we might end up with such elaborate traits, but it doesn’t explain how it would get started
what are some questions remaining

A

Why are there preferences?

Why does one sex tend to be choosy?

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10
Q

who is the flashy sex

A

The flashy sex: whichever sex has greater VARIANCE (or SKEW) in reproduction will evolve more elaborate traits

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11
Q

where is the mean on a graph

A

the mean is were half of the points are above and half are below (dotted line)

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12
Q

what does the variance tell us on a graph

A

the variance tells us about the width of the distribution (the width)

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13
Q

what does the skew tell us on a graph

A

the skew tells us about the shape of the distribution (the shape wont always have the normal distribution (bell curve))

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14
Q

The greater the variance, the _____ apart the extremes are

A

The greater the variance, the farther apart the extremes are

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15
Q

The greater the skew, the ______ asymmetric the distribution

A

The greater the skew, the more asymmetric the distribution(if it is sort of mushed to one side or the other… blue curve)

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16
Q

if the average reproduction success is equal (every offspring has a mother and father)
what is the reproduction skew like

A

average reproduction success is equal (every offspring has a mother and father)
reproductive skew is high for males because some males mate, some do not

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17
Q

if the average reproduction success is equal (every offspring has a mother and father)
what is the variance like

A

reproductive variance is similar because males and females form pairs, work together

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18
Q

what are the 3 situations/possibilities that sexual selection can result in

A

everyone gets to mate and variance is very small
some mate and some don’t (males) but all female mate (with only a select few males) so this is skewed so we have more variance in males (more flashy)
some mate and some don’t (females) but all males mate (with only a select few females) so this is skewed and we have more variance in females (more flashy)

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19
Q

who has more investment, typically

A

By virtue of the size and content of eggs vs. sperm, it is often thought that females have a greater investment in reproduction
There are definitely more convincing examples of females having greater investment, in particular in species where there is greater MATERNAL than PATERNAL care

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20
Q

are mammals more flashy

A

Here, I should point out that in mammals males might not be more “flashy” but rather be bigger and more aggressive and territorial

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21
Q

what did Bateman hypothesize

A

that there was a relationship between mating success and reproductive success
And that this relationship could differ between males and females

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22
Q

what does Bateman’s Gradient say

A

In species where investment might limit the reproductive output of females but not males, mating more frequently doesn’t improve reproductive success for females, but it would for males

Predicts that sexual selection will be stronger on males
In species where investment might limit the reproductive output of males
Predicts that sexual selection will be stronger on females

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23
Q

The flashy sex: whichever sex has ______-

A

Greater VARIANCE or REPRODUCTIVE SKEW (some males mate, some do not) Or, for biparental species for example, a steeper BATEMAN’S GRADIENT

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24
Q

Females that are not able to increase reproductive success with additional mating may be able to improve the quality of offspring (and therefore their reproductive success) by choosing doing what

A

Females that are not able to increase reproductive success with additional mating may be able to improve the quality of offspring (and therefore their reproductive success) by choosing a better mate

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25
Q

is Reproductive success measured only y the number of offspring

A

Reproductive success is influenced not only by the number of children a female has but also the number of grandchildren, great grandchildren, etc is influenced not only by the number of children a female has but also the number of grandchildren, great grandchildren, etc

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26
Q

so what makes a better mate

A

theories include;
Sexy Sons (also known as Fisher’s runaway selection model):
Good Genes/Immunocompetence hypothesis
Pre-existing sensory Bias and Sensory exploitation

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27
Q

what is Sexy Sons (also known as Fisher’s runaway selection model):

A

In a population, females show a preference for a particular character (and mate with males displaying that character)
The sons of those females will display that character
The daughters of those females will display the preference
Over time, the preference and the trait will become genetically coupled
And may continue to co-evolve (males produce more elaborate versions of the trait, females prefer more elaborate versions of the trait)
This hypothesis is thought to produce extreme traits that are contrary to (and eventually limited by) natural selection

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28
Q

what is Good Genes/Immunocompetence hypothesis

A

William Hamilton and Marlene Zuk, 1982:
Some males are genetically more resistant to parasites or infection
Those males would survive longer and have more offspring
AND they would be less likely to infect females
AND their offspring would also survive longer, reproduce more
Males produce a trait that signals their health or vigor
Females prefer males which display that trait
There are many steps to demonstrate this:
Parasites are costly
Heritable variation in immunity
Ornaments depend on the parasite
Females choose males with fewer parasites
But there is some support of this hypothesis in a handful of species

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29
Q

what is Pre-existing sensory Bias and Sensory exploitation

A

Michael Ryan, 1990
Females have a bias for particular types of sensory stimuli (e.g. particular colors or sounds). These biases result from the way that their brain is set up and has evolved for reasons outside of sexual selection (for example, for foraging)
Males produce a signal that stimulates that part of the female sensory system and females preferentially mate with males producing the signal

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30
Q

how is Pre-existing sensory Bias and Sensory exploitation entirely different from that of the good gene and runaway hypotheses

A

The preference and trait do not evolve in concert (no co-evolution)
The signal doesn’t indicate anything about the “quality” of the male

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31
Q

what is Phylogeny

A

a history of organismal lineages as they change through time

32
Q

how is phylogeny different from a pedigree

A

Similar to a pedigree or family tree, except that instead of marking each generation, we indicate speciation events when big changes occur

33
Q

what is the difference between a derived and ancestral trait

A

DERIVED trait is one that is more recent

34
Q

what is PARSIMONY

A

how to get to the pattern of trait expression in the descendants with the fewest changes

35
Q

give an example of parismony

A

Let’s say our green arrow indicates the appearance of a preference for chucks
No preference —> Preference for Chucks
this is the LEAST Parsimonious possibility

36
Q

One Last Question, why would ancestral females prefer chucks?

A

It has to do with the way their ears are set up
females were programmed to be biased towards the chucks
Thus, with regard to the sensory bias/sensory exploitation hypothesis
Male Tungara frogs have “exploited” an ancestral sensory bias for low frequency sounds that is present in the female auditory system

37
Q

we’ve been talking about “traits” as unitary things i.e. that females prefer a particular trait
why is this

A

This is mostly for simplicity, as clearly there are often multiple traits that appear to be selected

38
Q

Determining which traits are selected can be challenging

give an example of this

A

is all of the elaborate plumage in a peacock under sexual selection, or is there pleiotropy?

39
Q

what is Pleiotropy:

A

when a single gene influences many phenotypic traits

40
Q

what is an example of pleiotrophy

A

Frizzle trait in chickens Chickens with feathers that turn out (look “frizzled”) also have high metabolic rates and blood flow, greater digestive capacities, and abnormal body temperatures

Pigmentation and deafness in cats: Cats with white fur and blue eyes are also often deaf

41
Q

Regardless, it is important to remember that Natural Selection is not the only mechanism of evolution, what is another mechanism

A

Genetic Drift

42
Q

what did Stephen J. Gould and Richard Lewontin argue

A

They argued that too often scientists assumed that EVERY trait must be adaptations
This meant that when trying to understand the evolution of a trait, scientists would come up with one “just-so-story” after another in order to explain how that trait was adaptive
While not denying the existence of adaptations, Gould and Lewontin argued that not everything had to be an adaptation
They used as a metaphor the spandrels in the San Marco Basilica in Venice
spandrel, as they described it, is the extra space that is made when you create an arch in a rectangular space (for example the red areas below)

The San Marco Basilica has lots of arches as well as domed ceilings so there are lots of spandrels, including some 3D ones

The spandrels all have paintings on them
So if you knew nothing about the basilica, you might imagine that spandrels were created in order to provide a place for the paintings
But Gould and Lewontin argue that would be incorrect as the spandrels actually exist just as a consequence of the architecture
Similarly, the short arms on a Tyrannosaurus Rex
Had they arisen de novo (that is, if T. Rex was the first dinosaur with arms) they might be
an adaptation
But, because they are just smaller than other arms, maybe they became small because of some other change (or adaptation) but not because selection was acting directly on them
This idea has been hotly debated ever since
In fact, there has even been considerable discussion by architects as to whether the metaphor is true architecturally

43
Q

what is a NULL hypothesis

A

our population when nothing is happening

44
Q

why would we need to know the NULL hypothesis

A

if we know what SHOULD be happening, we can see if evolution is occurring

45
Q

what is the Hardy-Weinberg Equilibrium

A

We start with a tiny, imaginary population with:
8 individuals, 2 alleles each = 16 alleles
Frequency of G = 8 / 16 = 0.5
Frequency of g = 8 / 16 = 0.5
If these individuals mate completely at random, and there is no evolution happening (no drift, no selection, no mutation, no gene flow, nothing)
We can predict the frequency of each genotype in the next generation (hint: it will be exactly the same as it is in this generation!)

46
Q

Why would you want to calculate this? (Hardy-Weinberg Equilibrium)

A

Compare the predicted frequency and the actual frequency to determine whether the population is evolving
Can also use the equation to estimate the frequency of “carriers” (heterozygotes) of rare recessive diseases

47
Q

what equation is used to calculate the Hardy-Weinberg Equilibrium

A

p^2+ 2pq + q^2= 1

48
Q

explain genetic drift: evolution by chance

A

Now, our tiny, imaginary population has
6 individuals, 2 alleles each = 12 alleles
Frequency of G = 8 / 12 = 0.66 Frequency of g = 4 / 12 = 0.33
We can calculate how it will change using: p^2+ 2pq + q^2= 1
Now, in the next generation, the number of each genotype will change

Now, our tiny, imaginary population has
5 individuals, 2 alleles each = 10 alleles
Frequency of G = 8 / 10 = 0.80 Frequency of g = 2 / 10 = 0.20
Again, we can calculate how it will change using:
p^2+ 2pq + q^2= 1
Let’s say something happens, just by chance, to our population.
Maybe the pink ones get caught in a flood
Now, in the next generation, the number of each genotype has changed And then, maybe there’s an earthquake

Current allele frequencies:
Frequency of G = 0.80
Frequency of g = 0.20
Starting allele frequencies:
Frequency of G = 0.50
Frequency of g = 0.50
Just by chance:
The flood and earthquake didn’t select against phenotypes
Those individuals were just unlucky
This is the basic idea behind genetic drift
Now, in the NEXT generation, the number of each genotype will REALLY change

a couple key points
Because effects are random, completely by chance, would be just as likely for things to go the other way. i.e. for the gray lizards to disappear.
Also, the effects of drift are stronger in small populations. That’s why we could change our tiny population so quickly.

49
Q

what are the Two Ways that genetic drift can result in big changes

A

Genetic bottleneck

Founder effect

50
Q

what is Genetic bottleneck

A

An extreme example of drift where an event results in a big decrease in:
population size
genetic diversity

51
Q

what is the founder effect

A

Similar to a genetic bottleneck except here a subset of the population “founds” a new population somewhere else, like on an island
Still results in a decrease in:
population size
genetic diversity

52
Q

what is the definition of the founder effect

A

founder effect— a founder population contains only a subset of the alleles present in the original population. I.e. there is less genetic diversity in the founder population
There is less variation for selection to act upon – influencing adaptability of the population
Allele frequencies are more susceptible to chance effects – bigger effects of genetic drift
so, just by moving to the island, there are already some changes in the allele frequencies because of the founder effect
Let’s say a mutation leads to longer claws
These individuals can climb trees
Once in the trees, there is less competition for food
Perhaps they eventually establish a tree-dwelling population
Once on the island our island population can begin to adapt to their new environment
In addition to long claws, these iguanas also evolve to be smaller
Meanwhile, the beach iguanas might also adapt to be less visible to predators
Or there could be sexual selection for increased size or ornaments

And suddenly (over millions of years) we have very different iguana populations on the island versus on the mainland

53
Q

what can separate species

A

Natural barriers can serve to separate species

54
Q

how do Natural barriers serve to separate species

A

Natural barriers can serve to separate species

they prevent gene flow between populations

55
Q

what is speciation

A

Speciation occurs when gene pools are separated, gene flow is restricted and populations diverge genetically over time
Can result from a non-adaptive evolution (genetic drift)
e.g. founder effect plus additional mutation over time
Or from natural or sexual selection
Or all of the above!

56
Q

what is a species

A

a population whose members can interbreed to produce viable (can live after birth) and fertile (can reproduce) offspring

57
Q

what is Reproductive Isolation

A

mechanisms that prevent gene flow between members of different species

58
Q

what are the 2 types of reporductive isolation

A

pre-zygotic or post-zygotic

59
Q

what is a Zygote:

A

cell formed by the joining of two gametes (i.e. sperm and egg)

60
Q

what is Pre-zygotic mechanisms

A

prevent formation of a zygote

they do so by preventing interactions, mating, or the actual union of gametes
There are a lot of pre-zygotic isolating mechanisms

61
Q

wat is Post-zygotic mechanisms

A

occur after the formation of a zygote
the zygote either doesn’t survive or cannot reproduce
Why are there more pre-zygotic than post-zygotic mechanisms

62
Q

how is mating costly

A

Finding and attracting a mate takes time and energy

Producing eggs and offspring can require even more time and energy

63
Q

who should selection favour

A

Selection should favour individuals that are better at identifying and mating with their own species

64
Q

what happens to Individuals who mate outside their species

A

Individuals who mate outside their species will produce fewer offspring, their alleles will be less represented in the next generation

65
Q

what is allopatric speciation

A

Reproductive isolation is often set up by some sort of physical isolation (e.g. on an island)
This is called allopatric speciation

66
Q

what is sympatric speciation

A

this is when species arise in the absence of some sort of physical isolation or barrier (long debate wether this even exists)
i.e. species arise even though individuals live in the same place
difficult to prevent gene flow when there aren’t physical barriers between individuals

THIS RARELY OCCURS

67
Q

what is parapatric speciation

A

parapatric speciation is when species live immediately adjacent to each other and only share a small contact zone
You can think of it as being somewhere between allopatric (no overlap) and sympatric (complete overlap)

68
Q

what does parapatric speciation result in

A

It results in really interesting patterns of species distribution that we call ring species

69
Q

what is a ring species

A

In biology, a ring species is a connected series of neighboring populations that can interbreed with relatively closely related populations, but for which there exist at least two “end” populations in the series that are too distantly related to interbreed

70
Q

what is the definition of Allopatric speciation–

A

new species result when populations are physically separated –most common

71
Q

what is the definition of Sympatric speciation

A

—new species arise when populations are in overlapping ranges –less common, difficult to prevent gene flow when there aren’t physical barriers between individuals

72
Q

what is the definition of Parapatric speciation

A

Parapatric speciation– new species arise sequentially when populations only overlap in a small contact zone.
The species at the start and end of the sequence are very different –also less common but creates really interesting patterns

73
Q

Before Darwin and Wallace, one theory of evolution was proposed by who

A

Jean-Baptiste Lamarck

74
Q

what did Jean-Baptiste Lamarck propose

A

Over a single lifetime, a giraffe would stretch to reach higher leaves, making its neck longer
These use-dependent changes would be passed down to the offspring

75
Q

what are epigenetics

A

Heritable changes in gene expression and function without alterations in the DNA sequence
For example: DNA is usually wrapped around histone proteins
keeps DNA compact
regulates gene expression

76
Q

what is Histone modification

A

Changes in the attachment of methyl groups to histone proteins or DNA influence which genes are expressed and which are not

77
Q

give examples of epigenetics

A

Daphnia that have been exposed to a predator grow spines
spine expression persists over many generations, even in the absence of predators
Agouti mice overeat and become obese (and have a number of obesity related diseases)
And they have kids that overeat and become obese (and have a number of obesity related diseases)
Agouti moms fed food rich in methyl donors have slimmer, healthier offspring
Baby rats with attentive moms tend to be brave and calm (for rats, anyway)
High nuturing mothers raise high-nuturing offspring
Offspring of high-nuturing mothers have different methylation patterns in the brain than baby rats whose moms were less attentive

U0 Biology 115 (23 decks)

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