L8 Flashcards
1
Q
Darwin’s Natural selection
A
- The fittest individuals will survive and reproduce
- Succeeding generations will become adapted to their environment
2
Q
Darwin’s problem
A
- Natural selection can’t explain costly traits that lower an individual’s survival
- Peacocks tail increases predation chance, is costly to produce, carry and fly with
- Must lower peacocks chances of survival
- Argued if males were willing to suffer increase cost of traits they must be getting something important in return
- Eg increased mating with females
3
Q
Sexual selection
A
- Males compete with each other by fighting or displaying
- Intrasexual selection
- Female choice
- Intersexual selection
- Choice, by one sex, of mates of the other sex
- In Victorian times female choice was looked upon with suspicion as it suggested the course of evolution could be determined by females
- Mechanisms of choice were therefore poorly understood
4
Q
Secondary sexual characters
A
- Not characters for reproduction eg genitalia, these evolved by natural selection
- These involve size, behaviour, colours etc
- Only males have these traits, sexual dimorphism
5
Q
What is the basis for sexual selection
A
- Differences in gamete size
- Anisogamy is a difference in gamete size across genders, sexual selection acts differently eg male vs female sperm production
6
Q
Experimental study
A
- 5 males and females into pots and identified who produced what offspring
How did reproductive success vary with amount of copulation?
Females
- Offspring produced didn’t alter significantly after first copulation - One copulation fertilised all offspring
Males
- Reproductive success increased almost linearly with increasing copulations - More copulation = more offspring - Male have higher reproductive potential than females
7
Q
Females are limited by?
A
The number of eggs they can produce
8
Q
How does sexual dimorphism occur?
A
Males compete and females choose
Males aim for quantity and females aim for quality
9
Q
Sexual Dimorphism
A
- No selection pressure on females to evolve ornaments
- May be selection to keep them plain to protect offspring when rearing young
10
Q
How does sexual dimorphism arise?
A
Intrasexual competition
11
Q
Intrasexual competition in seals
A
- Males compete for harems of females by roaring matches proceeding to fighting
- Winners become beachmasters
- Other males get few or no mating’s
12
Q
Seals study
A
- Higher the dominance rank the more copulations
- DNA analysis shows more mating’s = more offspring produced
- Selection pressure to grow large as biggest males copulate more
- If males cannot monopolise many females dimorphism will not occur
- Doesn’t occur in water as it is harder to monopolise females
- Some males stay small and sneak copulations from females In the sea
13
Q
Most important criterion to male success
A
Weight/ size
- Large males often displace smaller males when they are attempting to mate with a female - Small males sometimes manage to hold on - In cases where the initial male is large they can hold on when smaller males try and copulate - Small males never displaced large males - Large size exerts a huge effect on reproductive success - The relationship between success and size is more positive more males than females - This leads to size sexual dimorphism - We would expect in species with more competition there would be more dimorphism
14
Q
Body size and Harem size in Pinnipeds
A
- As sexual dimorphism increases so does harem size
- Sexes are of similar size in species where males are monogamous
- This is because there is little male-male competition
- Where there is more competition there is more size dimorphism
15
Q
Body size does not always determine success
A
- Association between polygyny and degree of sexual dimorphism in structures eg size etc
- Antlers longer in polygynous species than monogamous ones
- Monogamous species have smaller bodies, but proportionally have smaller antlers even for body size
