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
16
Q
Sexual dimorphism facts
A
- Sexual selection doesn’t have to lead to sexual dimorphism
- Sexual dimorphism can arise from processes other than sexual selection
- Eg bill shape for same foods in different niches
- Reduced feeding competition between partners
17
Q
Female choice
A
- Often difficult to distinguish male- male competition and female choice
- Requires experiments controlling for differences in competitive ability between males
- Females must be given choice to reject males
- Acceptance of a partner is not proof of choice
18
Q
Do female widowbirds prefer long-tailed males?
A
- Male lekking
- Females choose a mate
- Were long tailed males better at competing or choosing longer tailed males
- Long tailed males received more mates than short and control
- Males were same level of competition , just a change in physical characteristics
- Both competition occurrence and choice can occur together
19
Q
Competition and choice depends on relative investment in offspring production
A
- Sex investing least competes
- Sex investing most chooses
- In monogamous birds both sexes invest
20
Q
Crested auklets
A
- Both sexes invest in offspring
- Both sexes have crests which is only used in breeding season
- We’d predict mutual sexual selection
- Compared crest length using models of auklets from dead birds
- Compared attractiveness between long and short crests
21
Q
Choice in crested auklets
A
- Both males and females chose longer crests birds to mate with than shorter crest birds
Male-male interactions
- 86% won by long crested birds
Female-female interactions
- 83% won by long crested birds
22
Q
Sex role reversal
A
Observation: in some species males invest more in reproduction than females
Prediction: there will be sex role reversal in species in which males invest a lot in offspring
- Females will compete and males will be choosy
23
Q
Pipefish
A
- Female provides male with a clutch of eggs that he stores and fertilises.
- He then carries them and provides nutrients till they are birthed
- Females produce more eggs to then produce more egg pouches for males
- Males are the limited sex as they have a set pouch space
- This means operational sex ratio is female biased, more females looking for males
- Males choose large females that can produce more eggs
24
Q
Nutritious spermatophores
A
- Male transfers nutrients along with his sperm
- These are spermatophores
- Other species males provide nuptial gift while male prepares to mate
- Providing gifts and spermatophores is costly, so male crickets don’t to give away large investment to any female
- Choosiness of male is linked to resource availability
- When resources are scarce, males should be more choosy
25
Q
Australian Katydid
A
- Food supply varies greatly through the breeding season
- When food is limited spermatophores are costly to produce so are very valuable
- Males then become choosy and females compete
- When food is abundant males are rarely choosy and females don’t compete
- When food is abundant males compete more
- Environmental effect on sexual selection and behaviours of males and females
26
Q
Sex role reversal: Mormon crickets
A
- Large flightless
- Males transfer a large nuptial gift as an edible spermatophore when they mate
- Males can only mate once in their lifetime
- Females can produce several clutches
- Females can mate more often, so operational sex ratio is female biased
- More females looking for males so females have to compete
- High density groups form
- Males call to attract females and females compete
- Male then chooses
- Females accepted by male are heavier and produce more eggs 48 vs 30 for rejected females
- Being choosy is therefore beneficial for the male
27
Q
Sexual selection summary
A
- Any pattern of choice and competition can occur eg male female mutual etc
- Each sex can play both roles of competing and choosing
- The environment can influence the pattern of sexual selection
