Topic 4 - Fundamentals of Evolution: Sexual Selection

Question 1

Sexual selection was notice by and because

Answer 1

Darwin

he noticed animals have traits that would seem to inhibit their reproductive success

but the still increase FITNESS because they allow for more reproduction

Question 2

Intrasexual selection

Answer 2

Within a sex

eg defeat/scare same-sex rivals

territory defense
fighting or other direct competition

Question 3

Intersexual competition

Answer 3

Between sex

Make themselves attractive for the other sex

Question 4

Can act on

Answer 4

behavior as well as morphology

eg fiddler crabs which both have one giant claw (morphology) and use it to signal for mates (behavior)

Question 5

Mechanism

Answer 5

Females find a trait attractive

This trait leads to increased reproductive success and therefore more individuals in the next generation with the trait

However, eventually, this trait may lead to a lack of survival which is not compensated for by an increase in reproductive success

So Natural selection acts as a buffer to stop traits being sexually selected for becoming too large or common

Question 6

Variance and skew

Answer 6

Variance is the width of the distribution (of a trait)

Skew tells us about the shape of the distribution

The greater the variance the further apart the extremes are. The greater the skew, the more asymmetric the distribution.

Question 7

Skew and distribution for flashy sex

Answer 7

Whichever sex has the biggest variance or skew in reproductive success will evolve more elaborate traits

Question 8

Which sex is choosy

Answer 8

Whichever sex has more investment will become choosy

Question 9

If the AVERAGE reproductive of the sexes is equal (as all young have a mother and father) then

Answer 9

The species with the most variation around that mean will be the flashy one.

Question 10

Investment

Answer 10

Because of size and resources in eggs vs sperm it is often said females are inherently more invested. Prof finds this oversimplified.

Sees this in terms of maternal and paternal caare

fish - often paternal
mammals - often female
brids - often biparental

Question 11

Flashy in mammals

Answer 11

may not be flashy, might be size, aggression and territorial natures

Question 12

Batemen’s gradient

Answer 12

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

In species where investment could LIMIT the reproductive output of one sex more than the other, that sex will be choosier as to increase reproductive sex does not just mean to have more kids but more grandkids too.

Hence a better mate will lead to better offspring and eventually more grandkids

Question 13

Preference for mates: Direct benefits

Answer 13

Females gain something directly from male: more or healthier offspring, more food, protection, better nesting

Eg make cardinals that are brighter red are better parents

It does not have to be a heritable trait, just has to benefit female

Question 14

Preference for mates: Good genes/immunocompetence hypothesis

Answer 14

Hamilton & Zuk, 1982

Some males more genetically resistent to parasites or infection

the survive longer and have more offspring + less likely to infect females + offspring wpuld survive longer and reproduce more

Males produce a trait that signals their health, females prefer mate that displays that

Question 15

Hoops to jump through for, good genes/immunocompetence hypothesis

Answer 15

1) that the parasites are costly
2) that there is heritable variation in immunity
3) that the males are prevented from ornamenting themselves by the parasite
4) females choose males with fewer parasites

has not been shown much

eg junglefowl

Question 16

Preference for mates: pre-existing sensory bias and sensory exploitation

Answer 16

Females have a bias for a sensory stimulus like a color or sound.

The biases result from the way their brains are set up.
This evolved for reasons other than sexual selection (eg foraging)

For example, animals that evolved to eat crickets might be attracted to the noises they make. If a male could imitate that would attract females.

Question 17

Tungera frog

Answer 17

Makes whines and chuck sounds

Chucks attract females and also bats

So number of chucks is determined by the balance sexual and natural selection

Question 18

Why do tungera frogs like chucks

Answer 18

First determined that making chucks is a DERIVED trait. One that has only recently evolved

eg not present in the ancestor but shows up after the speciation event

but then found out that ANOTHER frog likes this too even though the males of that frog never made chucks (so know the preference for chucks, if not the making of chucks comes from a common ancestor).

Most likely from the common ancestor of all 4 species.

Turns out its because the cohlea of all frogs is sensitive to low frequency sounds. This is likely an evolutionary adaptation that an ancestor made to their environment and now features in all frogs.

Only two branches make chucks. Somewhere before this speciation event, there was an ancestor who found they made chucks and female frogs were attracted. This has quickly preferred by the females (who cannot ignore it due to their cochlea and the trait spread throughout all the species.

Evolutionary, male Tungara frogs have exploited an ancestral sensory bias for low frequency sounds that is present in the female auditory system.

Question 19

Phylogeny

Answer 19

A history of organismal lineages as they change through time

Question 20

Speciation event

Answer 20

Where two species start from a common ancestor

Question 21

Parsimony

Answer 21

Get tot he pattern of trait expression in the descendants with the fewest changes.