Evolutionary Biology 11

Question 1

what are the benefits from being choosy (in sexual selection)

Answer 1

Direct benefits
- material benegits (e.g. food + parental care) that increase reproductive success

Indirect (genetic) benefits
- good genes that will produce high quality offspring

Question 2

What are he direct benefits of mate choice

Answer 2

1) fertile or fecund males
2) good parenting ability
3) resources (e.g. good or nest sites)

Question 3

1) example of females choosing fertile/fecund males

Answer 3

E.G. Lemon tetra - promiscuous fish species

• external fertilisation (no parental care)
• females spawned 23 times a day
• males “should be able to keep up with this” however experiments showed male fertility declined dramatically with successive spawnings
• females 11/12 times swam near males that had not spawned recently

Question 4

Example of Male choice of fecund females

Answer 4

E.G. pipefish

• females provide eggs to males who provide parental care
• females are the larger showier, more competitive sex, during breeding season develop elaborate skin fold on ventral surface
• in experiments males prefer females with large bodies and large ventral folds = they produce more eggs

Question 5

2) Example of female choice of male parenting ability

Answer 5

E.G. Mottled scorpion

• females lay eggs in male territory (males provide parental care)
• females prefer larger males (larger males shown to hatch more eggs)

*males that are larger can waft more oxygen over eggs = females chose males on ability to raise more offspring

Question 6

3) Example of mating in exchange for resources

Answer 6

E.G. female scorpionflys swap copulations for nupital gifts

• Male zebras defend water holes at which females come to drink, gives chance to mate.

Question 7

How is sexual selection for indirect benefits maintained

Answer 7

1) Fisherian runaway models (a.k.a sexy son models)
2) chase-away models
3) good genes model (aka indicator/handicap model)
4) compatibility model

Question 8

Fisherian runaway model

Answer 8

Female selects for male trait.

• female offspring dont exhibit trait but carry on preference for it
• male offspring dont have preference , but exhibit trait
• suggests that the trait and preference genetically linked

E.g. stalk eyed fly, eye span is genetically dimorphic,
females from longspan line preferred longer span males and vice versa

Question 9

Chase-away model

Answer 9

Exaggerated male traits evolve through antagonistic co-evolution between the sexes.

- males "seduce" females with 
 trait (that is disadvantageous 
 to the female) 
- females evolve resistance to 
 trait
- males exaggerate trait to 
 "seduce" females again
-process continues 

E.g. Drosophila (Rice 1996)

• semen in males contains contains powerful substance that reduces competitive ability of other males sperm in the female
• induces female to increase egg-laying rate HOWEVER also reduces her lifespan
• as males involve increasingly toxic semen females evolve increased resistance

Question 10

Good genes model

Answer 10

• Male ornament serves as good indicator of viability/fecundity
• under GG model , we predict male traits should reflect viability of offspring.

E.G. Petrie (1994) Peacocks

• Females prefer males with many large eyespots on plumage
• experiments show fathers with larger areas of eyespots had offspring that were bigger and more likely to survive first 2 years of life.

Question 11

Compatability model

Answer 11

-Individuals choose partners with complementary MHCs to them

MHC=Major Histocompatability Complex

E.G. Humans find mates with different MHCs “smell better”
- do not aim for specific MHC combinations just different ones to promote variation.