UNIT 5 DAY 1 - DARWIN AND SEXUAL SELECTION Flashcards
1
Q
Sexual dimorphism
A
- differences in features, not directly involved in copulation or in the production of eggs or sperm
2
Q
What does natural selection arise from
A
- struggle for existence that all organisms face, yields traits promoting survival
3
Q
Darwins personal factors that influenced development of sexual selection theory
A
- marriage with his cousin Emma
- Darwin had natural selection urges, viewed loss of time as a con of marriage
- married Emma due to wealth, familiar connections and desire for wife
4
Q
Sexual selection
A
Favours strength and size in males to fight females and “charms”
- Darwin viewed women as the weaker sex, physically and intellectually, superior in moral values and religion, unfit to seek males
5
Q
What made Darwin believe females pick?
A
- frigated birds: females prefer showy males
- pigeons: females choose bizarre varieties of birds, like breeders do
- Victorian fashion: female Victorian women adore themselves in gaudy dresses, couldn’t mate birds do the same
6
Q
Sexual selection
A
- struggles between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring
7
Q
Darwins theory of sexual selection and his completed account of the origin of nature
A
- if natural selection is the source of adaptive complexity of the wings, beaks and eyes, the sexual selection is the source of colour, ornament, song and dance
—> sexual selection and female choice was rejected by his peers and ignored for an entire century
8
Q
Rejection of sexual selection
A
- St. George Mivert: no female capacity for selection
9
Q
Darwins death
A
- near death of sexual selection theory
10
Q
Revival of the theory
A
- Fisher tried to retrieve with ‘The Genetical Theory of Natural Selection’
- not until the 1970s, did research verify Darwins theories, made them more widely accepted
- previously held beliefs are somewhat oversimplified —> females can be aggressive too
11
Q
Male-male competition
A
- occurs when females resources clumped in space and males can fight/defend females against other males
- not always violent, “displays of prowess”, threatening looks can do the job
- Elephant Seals
- polygynous, on male mates with many females
- single male could reproduce 100-250 pups but females could produce 10-12
- males fight with other males, shorter lifespan, increased weight
12
Q
Females choice
A
- females constantly choose one more display over another
13
Q
Malte Anderson - female choice
A
- examined long-tailed widowbirds, males only carry during breeding season
- 3 hypotheses posed examining long-tailed feathers
1. Could be products of natural selection
2. May intimidate other males in territorial disputes, thus product of sexual selection by male-male competition
3. May be preferred by females in choosing mates, products of sexual selection by choosing female choice
14
Q
Long-tailed widowbirds
A
- outside of breeding season, short tails (7cm)
- breeding season —> males replace with coats of velvety black feathers and grow long (nuptial feathers) —> 50cm
- defend large territories —> fly slowly with nuptial feathers, spread display that is visible to females
- polygynous
- females visit succession of males before choosing
- successful males can host several females at same time
- mapped territories of 36 birds in Kenya and clipped tail feathers
15
Q
Why aren’t male tail feathers longer than already are?
A
- weapons and ornament favoured by sexual selection, require energy to build and maintain —> impede daily life and increase vulnerability to predators
- disfavoured by natural selection even as favoured by sexual selection
- size and cost, Darwin and Fisher reasoned will strike a balance between benefits confer in mating and costs they impose in decreased survival
16
Q
Red-collared widowbirds
A
- Pryke and Anderson studied cost of nuptial tails
- similar to long-tailed widowbirds in appearance and habits but smaller
- male nuptial feathers in breeding season long but not as long as long-tailed widowbirds
- male (long nuptial tails) gained more mates than did males with shortened tails
- cost —> male body condition declines, declines faster with normal tails
17
Q
Polygamy
A
Having multiple mates
18
Q
Polygyny
A
Males mate with many females
19
Q
Polyandry
A
Females mate with many males
20
Q
Parental investment
A
Amount of energy each expands by one parent on producing and raising offspring
—> because females usually invest more in their offspring than males, they are the sex in short supply
21
Q
How is males reproductive success limited?
A
- limited by number of fertile females he can manage to mate with, not by number of ejaculates he can produce
22
Q
how is female reproductive success limited?
A
- limited by number of eggs she can produce, not by lack of males eager to mate
23
Q
Why do females choose: 3 hypotheses (Fisher)
A
- Direct benefits: something tangible in exchange for sex (meal, help with offspring) (eg. Male hanging flies)
- Sensory bias: preference females already have for certain colours/scents draws them to certain males exhibiting them
- Good genes: natural selection will favour females who choose superior males, not because it brings immediate benefit to their offspring; females can avoid being folded by males by selecting a costly trait that actively handicaps the male because only males with superior genes can survive possession of handicaps
24
Q
Amotz Zahavi Handicap Theory
A
- males possessing such traits must have good genes or else wouldn’t have survived
25
female choice in sticklebacks
- threespine sticklebacks, small fish
- males display a bright red throat during breeding season, females mate with males with reddest throat
- polygynous: successful male can entice multiple females
- sensory bias: intrinsic preference for red, visual systems sensitive to red as carotenoid-rich food items essential to diet are red
- carotenoids are honest indicator of male quality
- condition-dependent handicap Becca uses makes males more conspicuous to predators
- sexual selection
—> selection due to sensory bias in females
—> selection by females for good parenting ability in males
—> selection by females for genes that make males resistant to parasites
26
Female choice in widowbirds (bishops and widowbirds)
- once nuptial tails evolved, more often evolved in direction of greater length rather than shorter
- nuptial feathers evolved independently twice (convergent evolution)
- when a new species branches off an ancestral one, nuptial tails in new species are usually longer than ancestor
27
Red-collared widowbirds
- natural selection favours investing energy into feathers, bone, muscles and immune system —> all necessary to reproduce
- sexual selection by female choice favours growing a long tail as a honest indicator of genetic quality
- sexual selection by male-male competition favours in investing in bright red collar and cap as honest indicator that other males can use to accessing to fighting
28
Red bishop
- natural selection favours investing energy into feathers, bone, muscles and immune system —> all necessary to reproduce
- sexual selection by female choice based on colour and fighting ability
- sexual selection by male-male competition favours really bright feathers (carotenoids) = male strength
29
Pryke and Anderson (2005)
- short-tailed males spend more time displaying territories
- short-tailed males, more time active on territories
- longer-tailed control males nearly 3 times as many nesting females
- longer tails of red-collared widowbirds condition-dependent handicap that females can use to reliable judge male quality
- longer tails attracted to more and viable males
30
Barber et al
- sticklebacks with redder feathers were less susceptible to infection —> they did a p test
31
Pryke and Anderson (2002)
- generalised female bias for long tails in short tailed widowbird —> evidence for sensory bias because evolution has favoured selection of longer-tailed mates
32
Throat sac
Darwins theory of natural selection that couldn’t explain it
33
What part of Darwins theory of sexual selection did his contemporaries reject?
- female choice
34
Elephant seals
Male-male competition for access to females
