Evolutionary Biology 10

Question 1

What are some examples of sexual traits which are costly

Answer 1

1) Guppies have bright tails - more likely to be predated
2) Red deer grow new antlers every year - energy waste
3) macaws have long “graceful” tails - aerodynamically costly

Question 2

An example of natural selection vs sexual selection.

Answer 2

E.g. Marine galapagos iguanas

• studied body size across 2 populations
• larger individuals (males) had lower survival rates than smaller ones, harder to maintain body weight in harsh conditions
• both males and females eat same food resource
• only reason for increased male size is sexual selection

Question 3

Isogamy

Answer 3

same size gametes for either sex (this was the ancestral sexual state)

Question 4

Evolution of mating types can lead too:

Answer 4

1) ever increasing number of mating types
2) or reduction to just two

E.G. stylonychia mytilus has 48 different mating systems , this does NOT lead to sexual selection.

Question 5

Anisogamy

Answer 5

Existence of 2 different sized gametes

-evolution of anisogamy is a critical step on the path to sexual selection

Question 6

How did anisogamy evolve (hypothesis)

Answer 6

(Parker 1972)
- begin with a primitive isogamous sexual species

• each individual has fixed budget, either produce 1 big gamete or lots of small gametes
• note zygote size = sum of gametes and is directly related to viability of zygote
• small gametes = produce more so higher chance of encounter
• large gametes = high fitness of resulting zygote
• medium gametes = mediocre in both functions

selection for differing sizes of gametes to increase chance of encounter and increase zygote viability

disruptive selection

Question 7

benefits of small gametes

Answer 7

produce more so higher chance of encounter

Question 8

benefits of large gametes

Answer 8

high fitness of resulting zygote

Question 9

what does zygote size relate to

Answer 9

the viability of the zygote , note size is the sum of the two gametes fusing.

Question 10

Batemans principle

Answer 10

is that in most species, variability in reproductive success (or reproductive variance) is greater in males than in females.

• this is as a result of anisogamy

Question 11

How do male and female reproductive success differ with number of mates

Answer 11

Male = sucsess usually increase with no. of mates

female = dont benefit as much by increasing mate no.

Question 12

what does male- female variance in reproductive success lead to

Answer 12

It leads to competition between males, as they are constantly looking for more mates, and choosiness among females as they have to make their choice count due to higher parental investment.

• in most species females are the limiting factor for reproduction due to producing fewer gametes
• leads to sexual selection

Question 13

Anisogamy leads to

Answer 13

competition between males (intrasexual competition)

Female choice of preferred male (inter-sexual competition)

Question 14

How did sexually selected traits initially evolve

Answer 14

1) good genes theory - traits reflect the quality of the male, high quality males produce high quality traits (trait -> preference)
2) sensory exploitation theory - females have a pre-existing sensory bias for a bright or large ornament, a choice mutation in a male produces an ornament that matches the bias. nothing to do with bias. (Preference -> trait)

Question 15

which evolved first trait or preference ?

Answer 15

E.g. crested auklets

- can look at Least auklets 
 because they have not 
 evolved an ornament
- in experiment placed a 
  "crest" on some Least 
   auklets 
-  the "crested" Least auklets 
 experienced significantly 
 more courship displays 
- this proves the preference 
  was there before the trait.