Sexual Selection Flashcards

1
Q

What is sexual selection?

A

How mate choice drives evolution - characteristics develop to attract the opposite sex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Mating systems

A

Polygamy - everyone has multiple mates

Polyandry - females have multiple mates

Polygyny - males have multiple mates

Monogomy - long standing pair bonds between individuals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is sexual dimorphism?

A

When males and females withing a species have different physical traits e.g. lion’s mane, peacock’s feathers…

Depends on mating system:

  • bonobo - polygamy = little dimorphism
  • chimps - polygyny = slight dimorphism
  • gorillas - polygyny = large difference
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are intra- and inter-sexual competition?

A

Intra-sexual competition

  • within-sex competition
  • typically males compete for access to females (male elephant seals are much bigger bc of this)

Inter-sexual competition

  • one sex tries to attract the other with ornaments and displays
  • typically females do the choosing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Ornaments

A

Used to attract the opposite sex

Evolution of male ornaments driven by aesthetic choices of females

Costly!

  • require energy to grow & maintain –> display fitness
  • can be more easily caught by predators (e.g. peacock)
  • can become too costly e.g. Irish elk’s antlers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Parental investment theory

A

Trivers (1972)

Females are the choosie ones because their costs greater than male…

  • limited egg supply
  • 9 months gestation
  • dangerous birth
  • lactation
  • years of child-rearing
  • feeding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Choosiness

A

Females pay high price for mistakes (parental investment theory)

Male choosiness increases with investment….

  • if they rear (e.g. seahorses)

Depends on mating system

  • monogamous species have similar choosiness between sexes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Ornamentation and mate choice for the long-tailed widow bird

A

Anderson, 1982

Artificially enhanced tail length - greater mating success

Shortened tail length - reduced mating success

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Fisherian runaway

A

Positive feedback between heritable ornaments and heritable preferences

  • offspring inherit parents’ ornaments and preference for it –> they spread through the species together

In humans…?

  • Stulp et al., 2015
  • height increased globally with diet and nutrition - 8” over 150yrs
  • People in Netherlands taller than UK
  • Taller men have more children (11% more on avg.)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Honest signalling

A

Hamilton & Zuk (1982)

  • Signal of quality - can’t be faked
  • improves population fitness

Loyau et al., 2005

  • measure no. antibodies in male peacocks
  • measure no. displays per hour
  • more antibodies = fewer displays

Thompson et al., 1997

  • house finches
  • high parasite load = reduced expression of sexually selected traits (bright plumage), greater reduction in males with low parasite resistance (genetic!)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Handicap principle

A

Zahavi, 1975

  • only ‘fittest’ can grow ornaments
  • spend more = more ornaments
  • high cost handicap = reduced species fitness
    • waste is necessary for ornaments, can’t be faked
  • therefore… greater ornaments = greater input = better health

Conspicuous consumption

  • time - nest building, performing songs
  • life - bright colours, useless appendages
  • resources - luxury goods
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Handicap principle in humans

A

Masculine facial features

  • require lots of T
  • T is an immunosuppressant
  • Only healthiest can “spent” T

Resources

  • luxury goods
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Sexual selection in humans

Hadza people

A

Mild dimorphism suggests some kind of competition for mates

Apicella, 2014

  • Hadza people
  • males w/ greater upper body strength reported more mating success
  • mediated by hunting success
  • more resources (food) allows access to more females
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Sexual selection in humans

Male secondary secual characteristics

A

Many have greater influence on dominance than attractiveness to women - suggests competition between males for mates

e.g.

  • full beard
  • masculine voice
  • masculine face
  • muscular/brawny

Swaddle & Reierson, 2002

  • increased facial masculinity increases perceived dominance but has no effect on attractiveness ratings from females
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Sexual selection in humans

Sexual dimorphism

A

Body fat distribution

Female fat deposits signal sexual maturity, used for development of offspring, attractive to males

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Mating mind hypothesis

A

Miller 1993

Large brains result of sexual selection?
Tripled in size in just 2M years!

If females preferred creative male minds…

  • creative males would have more children
  • offspring inherit creativity and preference for it

Lack of sexual dimorphism in mental abilities bc females have to have large brains to appreciate large brains

17
Q

Sexual selection in humans

height

A

Stulp et al., 2015

  • Netherlands are tallest people
    • Grown 20cm in 150 years – US only 8cm (NTHLDS better nutrition, lower social inequality, high-quality universal health care)
  • Taller men have 11.6% more children on avg.
  • Taller more likely to have 2nd child, have a partner/ever had one
  • Controlling for mate choice decreased effect size of fertility –> seuxual selection!
18
Q

Mechanisms of sexual selection in humans

A

Puts, 2010

  • Competition for mates
  • 2D mating environment favours competition
    • Male traits better designed for contest – size, strength, aggression, dominance signals (facial hair, masculine face, deep voice) more than attracting females
  • Female mate choice, sperm competition, sexual coercion likely shaped male traits
  • Female mating competition & traits influenced by male mate choice – attractive women obtain greater male investment