UNIT 5 DAY 1 - DARWIN AND SEXUAL SELECTION

Question 1

Sexual dimorphism

Answer 1

• differences in features, not directly involved in copulation or in the production of eggs or sperm

Question 2

What does natural selection arise from

Answer 2

• struggle for existence that all organisms face, yields traits promoting survival

Question 3

Darwins personal factors that influenced development of sexual selection theory

Answer 3

• 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

Question 4

Sexual selection

Answer 4

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

Question 5

What made Darwin believe females pick?

Answer 5

• 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

Question 6

Sexual selection

Answer 6

• struggles between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring

Question 7

Darwins theory of sexual selection and his completed account of the origin of nature

Answer 7

• 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

Question 8

Rejection of sexual selection

Answer 8

• St. George Mivert: no female capacity for selection

Question 9

Darwins death

Answer 9

• near death of sexual selection theory

Question 10

Revival of the theory

Answer 10

• 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

Question 11

Male-male competition

Answer 11

• 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

Question 12

Females choice

Answer 12

• females constantly choose one more display over another

Question 13

Malte Anderson - female choice

Answer 13

• 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

Question 14

Long-tailed widowbirds

Answer 14

• 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

Question 15

Why aren’t male tail feathers longer than already are?

Answer 15

• 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

Question 16

Red-collared widowbirds

Answer 16

• 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

Question 17

Polygamy

Answer 17

Having multiple mates

Question 18

Polygyny

Answer 18

Males mate with many females

Question 19

Polyandry

Answer 19

Females mate with many males

Question 20

Parental investment

Answer 20

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

Question 21

How is males reproductive success limited?

Answer 21

• limited by number of fertile females he can manage to mate with, not by number of ejaculates he can produce

Question 22

how is female reproductive success limited?

Answer 22

• limited by number of eggs she can produce, not by lack of males eager to mate

Question 23

Why do females choose: 3 hypotheses (Fisher)

Answer 23

1. Direct benefits: something tangible in exchange for sex (meal, help with offspring) (eg. Male hanging flies)
2. Sensory bias: preference females already have for certain colours/scents draws them to certain males exhibiting them
3. 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

Question 24

Amotz Zahavi Handicap Theory

Answer 24

• males possessing such traits must have good genes or else wouldn’t have survived

Question 25

female choice in sticklebacks

Answer 25

• 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

Question 26

Female choice in widowbirds (bishops and widowbirds)

Answer 26

• 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

Question 27

Red-collared widowbirds

Answer 27

• 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

Question 28

Red bishop

Answer 28

• 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

Question 29

Pryke and Anderson (2005)

Answer 29

• 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

Question 30

Barber et al

Answer 30

• sticklebacks with redder feathers were less susceptible to infection —> they did a p test

Question 31

Pryke and Anderson (2002)

Answer 31

• generalised female bias for long tails in short tailed widowbird —> evidence for sensory bias because evolution has favoured selection of longer-tailed mates

Question 32

Throat sac

Answer 32

Darwins theory of natural selection that couldn’t explain it

Question 33

What part of Darwins theory of sexual selection did his contemporaries reject?

Answer 33

• female choice

Question 34

Elephant seals

Answer 34

Male-male competition for access to females