1. Mating Notepacket #3
Mating Systems

2. Monogamy
Refers to TWO animals who remain sexually EXCLUSIVE with one another
Have NO outside SEXUAL partners.
May be for 1 MATING (breeding) season or their WHOLE life
Examples: DUCKS, Eagles, FOX, Geese, GIBBONS, Lynx, Swans, Mountain Lions

3. Polygamy 2 Types: Polygyny:
One Male has MULTIPLE female sexual PARTNERS during the BREEDING season.
Examples: Elk, Fur seal, Baboon

4. Polygamy
2. Polyandry
One FEMALE has MULTIPLE male sexual partners at the same time.
Examples: Jacana, Tasmanian hens, Tinamous

5. Sexual Selection
Sexual selection will often be stronger in polygynous and polyandrous systems that in monogamous systems. Why?
Because some INDIVIDULAS obtain many MATING opportunities
Some obtain NO mating OPPORTUNITIES
MONOGAMOUS systems have less VARIATION in reproductive SUCCESS

6. Promiscuity No PAIR bonds between SEXUAL partners
Each male MATES with many FEMALES, and vice versa.
Examples: Chimpanzees, Bonobos

7. Genetic Models of Female Mate Choice:
DIRECT Benefits
GOOD Genes
RUNAWAY

8. Direct Benefits Females CHOOSE mates that provide TANGIBLE resources
What is a tangible resource?
A resource that INCREASES the females child-rearing potential, their survival or both.
Example: Large PREY
Female receives TANGIBLE resource
DIRECTLY herself benefits from it.

9. Direct Benefit Examples:
Scorpion fly:
Females CHOOSE males that bring LARGE prey items during the COURTSHIP process.
HUNTING becomes very DANGEROUS for the males

10. Direct Benefit Examples:
Nuptial Gifts:
The PREY that males PRESENT to females during courtship.
LARGER gift LONGER Mating
NO gift Immediate REJECTION

11. Direct Benefit Examples:
Bad News for Males! Why?
Males CHEAT: Prey- Stealing
Increased COMPETITION between males: Dangerous

12. Direct Benefit Examples:
Why are larger nuptial gifts important to females?
Allow females to produce more EGGS
Gives female a longer LIFE SPAN because of the NUTRITION she DIRECTLY receives
Decreases the amount of TIME she must allocate to hunting.

13. Good Genes
Theory suggests that FEMALES are favored to CHOOSE mates that possess “GOOD GENES”.
“GOOD GENES” code for some FAVORABLE TRAITS
These favorable TRAITS are then INHERITED by the OFFSPRING of the female.
** Good genes models apply to mating systems in which the only benefit received by females lies in the genes residing on the male sperm.

14. Good Genes How might this model be problematic?
How can females DETERMINE which males POSSESS the “GOOD GENES”?
2. Given that females are attempting to CHOOSE males with the best GENES, wouldn’t NATURAL selection favor males that CHEAT?

15. Good Genes Handicapped Hypothesis: “HONEST advertising”
Suggests that only TRAITS that are TRUE and HONEST indicators of male genetic QUALITY should be used by FEMALES when choosing a mate.

16. Good Genes How can the Handicapped Hypothesis be accomplished?
Honest indicator TRAITS should be generally “COSTLY” to produce
The COSTLIER the trait, the more DIFFICULT it is to fake.

17. Good Genes
EXAMPLE:
Endoparasite Resistance: FEMALES choose males with strong RESISTANCE to parasites.
** Hard to FAKE
But; endoparasites can’t be seen.

18. Good Genes
How do females know which males have good genes with respect to endoparasite resistance?
Females can use TRAIT X as a PROXY for JUDGING what they really wish to LEARN.
Proxy clue: BODY COLORATION
HEALTHIER the male, the more COLORFUL he will be

19. Good Genes
Endoparasite Resistant

20. Runaway The model assumes the existence of 2 genes:
1. The gene that CODES for a particular
TRAIT in males
2. The GENE for MATING preference in
females

21. Runaway
EXAMPLE:
Imagine a population in which some fraction of the females have a heritable preference for brightly colored males, and that male coloration is itself a heritable trait.
Possibilities:
2 Groups of females Groups of males
More color
(Bright)
Less color
(Dull)
Prefer bright
colored males
Don’t prefer bright colored males

22. Runaway
Therefore, Females that mate with colorful males should produce:
Colorful MALES
Daughters that POSSESS their GENETICALLY coded preference for COLORFUL males

23. Runaway Runaway Sexual Selection states:
Over time, the ALLELES that in females code for the PREFERENCE for colorful MALES and the ALLELES that in males code for COLOR become linked.
As the FREQUENCY of one of the alleles changes, the FREQUENCY of the OTHER will.
Once this positive feedback loop is set in motion, it can, under certain conditions, “RUNAWAY”.