Mating Notepacket #3 Mating Systems

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

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

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

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

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

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

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.

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

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

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

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.

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.

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?

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.

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.

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

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

Good Genes Endoparasite Resistant

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

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 2 Groups of males More color (Bright) Less color (Dull) Prefer bright colored males Don’t prefer bright colored males

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

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”.