week 5 + 6 - sexual selection

Question 1

sexual selection
intra and inter sexual

Answer 1

• Males can develop traits that enable them to be more successful either via intra or inter sexual selection and often via both at the same time

Question 2

secondary sexual characteristics

Answer 2

• Features not directly part of the reproductive system that develop during sexual maturity
• Often result in sexual dimorphism
  o Differences between the sexes (to some degree)
• Purpose: to give an individual a selective advantage

Question 3

competition

Answer 3

direct

indirect

Question 4

competition
direct

Answer 4

o E.g. weapons, size
o Narwhal

Question 5

competition
indirect

Answer 5

o E.g. ornaments
o peacock

Question 6

conflict between males
(intrasexual)

Answer 6

• Direct competition/interference
  o E.g. fighting
• Indirect competition
  o E.g. sperm competition
   Chasity belts
   Anti-aphrodisiacs
• Cuckoldry/EPP
  o Extra pair paternity

Question 7

conflict between males
intrasexual
example

Answer 7

RED DEER CONFLICT
- Breeding season – the rut
- Dominant males compete to take each others’ harems
- Multiple stages to assess each others’ strength and fighting ability
- Minimise chance of actual fighting and thus injury

Question 8

conflict between males
sperm competition

Answer 8

Defensive tactics
- Mate guarding
o Consortship in primates
o (chimp)
- Mating/copulatory plugs
o Gelatinous secretion that harden in the female genital tract
- Toxic seminal substances
o ACPs (accessory gland proteins): anti aphrodisiac
Offensive tactics
- Physical removal of sperm

CASE STUDY: twisting tubes
- mascovy duck

Question 9

conflict between males
cuckoldry

Answer 9

‘males who unwittingly invest parental effort into offspring that are not their own ‘
- Different morphs in fish
o Parental: males prepares the area for eggs and guard eggs
o Sneaker: try and deposit their sperm on someone else’s eggs and zip off
o Satellite: disguise themselves as females and then do the same as sneaker
- Morphs developed as ways to compete with other males
o Sneaker have many short-lived lower quality sperm
o Parentals have fewer high quality sperm
- All result in success and so persist via sexual selection

Question 10

female mate choice

Answer 10

• Invest more in initial gamete production, but even more if there is internal gestation, but also beyond (e.g. lactation)
• Females have more to lose
  o Therefore need to make their choices carefully
  o E.g. mating with the wrong male could cost a female frog her entire years supply of eggs, whereas the male could go on to mate with a different female the next day
  Not just female
• For example st Andrews cross spider uses up his lifetime of sperm in one go
• He has to choose his female carefully

Question 11

evolutionary models: why might a female choose a particular male

Answer 11

• Four classes
  o Direct benefits
  o Good genes
  o Runaway selection
  o Sensory exploitation
  The evolution of a particular sexually selected trait might be best explained by one, or a combination of two or more models

Question 12

evolutionary models: why might a female choose a particular male
- good genes

Answer 12

• Good genes code for favourable traits
  o Depends on the environement
• Males would prefer to ‘cheat’ – give the impression that they posses favourable genes
• Sexual selection pressure on females will lead them to use traits that cant be cheated:
  o Honest indicators
   E.g. parasite resistance or more efficient metabolism
• The costlier the trait to produce the more difficult it is to fake

Question 13

evolutionary models: why might a female choose a particular male
- direct benefits

Answer 13

• Additional resource benefit
  o Access to food
  o Shelter/protection
  o Parental care
  o Nuptial gifts
   E.g. nutrients in spermatophore, prey or even male body parts
   But are these a direct benefit or a tool of manipulation ./ distraction

Question 14

evolutionary models: why might a female choose a particular male
- parasite resistance

Answer 14

• Hamilton-Zuk hypothesis
  o Females that choose males worth strong resistant to parasites may be mating with males that have good genes
• Females use a trait that correlates with parasite resistance
  o E.g. carotenoids based body colouration

Question 15

evolutionary models: why might a female choose a particular male
parasite resistance
CASE STUDY

Answer 15

• In blackbirds infection by parasites slows carotenoid assimilation in the blood
• Birds without parasites have brighter colured bills
• Only birds with a carotenoid-rich diet can cope with parasites
  Baeta et al, 2008

Question 16

evolutionary models: why might a female choose a particular male
runaway sexual selection

Answer 16

• Evolution of exaggerated male ornamentation
  o Look like thay have a cost to fitness
  o Non adaptive?
• Peacock tail: paradox of natural selection
• Non adaptive triat that is selected for
• Assumption: Loci for both male colour and female preference are found in both male and females but alleles are only switched on in appropriate sex
• When a female mates with a colourful male:
  o Colourful sons
  o Daughters prefer colourful males
• Positive feedback loop
  o Causing the evolution of these traits

Question 17

evolutionary models: why might a female choose a particular male
sensory exploitation

Answer 17

• Preference for a male trait emerges because it elicits a neurobiological response in females that initially is not related to mating preference
  o E.g. red in primates
• Some primates have trichromatic vision
• Red skin arises randomly in males
• Females’ nervous system predisposed to be attracted to red
• Red males attract more females = greater success
• Over time red faces selected for via sexual selection