LIFESCI 15 Lecture Notes - Lecture 14: Elephant Seal, Symmetry In Biology, Mating System
2/27/18
- Physical differences in reproductive investment (constraints) lead to physical and behavioral
differences
o In females: choosiness
o In males: competition
- Sex behavior predictions
o Demand honest signals of health
o Value fighting ability
o Elicit a commitment to invest
▪ Courtship dance
▪ Nuptial gifts
- 2. Lower reproductive investment → more competition, need for paternity certainty
o 1. Competition for access
o 2. More mate guarding
o 3. Extended mating
- Sperm wars
o Observation: lots of cuckoldry
o Evolutionary response: produce more sperm
o Physical manifestation:
▪ Gorillas? (all females choose to mate with 1 male)
• Question – has there been directional selection for increased sperm size
• Looked at gorillas, all females mate with one male
• Expectation is that the male is going to have to produce sufficient sperm
▪ Chimps? (everyone has sex with dozens of partners)
• 16x larger testes than gorillas
▪ Humans? 4x gorillas, ¼ x chimps
Q: Why do males exhibit more mate guarding than females?
- THM 1: initial low reproductive investment and paternity uncertainty lead to male-male competition
for access to females, indiscriminate male mating, mate guarding, and sperm wars
Q: Can sexual selection help us understand why so few women run for political office?
- Similar to elephant seals’ males trying to be the king of the beach
- Mating system definitions:
o Polygyny: (high variance in male rs)/(low variance in female rs)
▪ One male bonds with multiple females
▪ Elephant seal males
o Polyandry: (low variance in male rs)/(high variance in female rs)
▪ One female bonds with multiple males
▪ Extremely rare
o Monogamy: low variance in both, low number of mates each
▪ One female bonds with one male
▪ Almost all bird species; peacocks
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Document Summary
Physical differences in reproductive investment (constraints) lead to physical and behavioral differences. Sex behavior predictions: demand honest signals of health, value fighting ability, elicit a commitment to invest, courtship dance, nuptial gifts. Lower reproductive investment more competition, need for paternity certainty: 1. Thm 1: initial low reproductive investment and paternity uncertainty lead to male-male competition for access to females, indiscriminate male mating, mate guarding, and sperm wars. Similar to elephant seals" males trying to be the king of the beach. Q: sexual dimorphism is considered a very good predictor of mating systems. Sexual dimorphism: is any difference between males and females. The more asymmetric the investment: the more radical the sexual dimorphism: physical, behavioral, male-male competition. Thm #2: mating systems monogamy, polygyny, polyandry describe the variance in mate number of males and females. Normal development requires: stable environment, good genes.
