Lecture 22—2/24/2015 (TUES)
The Evolution of Mate Choice
Four types of Mate choices
Pure epigamic selection
Epigamic= attracting opposite sex at breeding time
1. Good looks
2. Good Genes
Boils down to PI & direct benefits! (increase fitness)
Direct benefits—female choice leads to increased fecundity (more offspring)
3. Good Parents
4. Good Resources
How do females use to assess the direct benefits from males?
(Focus on good parents and good resources)
Honest signals or traits are used by females to access the potential of direct benefits
(e.g. signals or traits that may indicate whether a mate will provide material gain to female)
Honest signals or traits may indicate direct benefits such as
Access to good food or territory
Be in the form of Nuptial gifts (e.g. Mormon cricket: nutritious-rich protein component)
Parental effort or ability
Direct benefits: nuptial gifts (Good resources?)
E.g. Hanging flies—Prey that male presents female during courtship
Hanging flies dangle prey to entice female to feed and mate
Release a pheromone to attract females
Video: hanging flies
The quality the gift may be a good indication…
Give gift to female, when female consuming the gift, he mates with it= =
Direct benefits: parental effort or ability
Signal or trait may indicate male parental effort (health, good foragers…)
May produce better signals
Foraging ability is benefit in caring for young
E.g. In sedge warbler: Female prefer males with larger song repertoires
Male with larger repertoires are better providers for chicks
Can produce chicks with heavier body weight
Question: Why do females show preferences for males that provide no parental care for males that provide no parental care or material benefit other than just sperm?
(Focus on good looks and good genes)
Video: Sexual selection, mate choice and Evolution (Why sex?)
Peacock’s tail: take a lot of energy to grow, so heavy, slow down the energy
Darwinian Theory can’t explain…. Why can it be adaptive?
Darwin is convinced that there has to be an evolutionary explanation and natural selection!
Mate selection! Have to attract opposite sex and male
Male usually fight for access to female
Seduction from sexual display
Female invest more!!! Should be choosier!
Experiment with Peacock (how is it related to natural selection)
Only strong, and healthy peacock can afford to grow that tail
They can attract their mate….
When you cut some of their tail…. No one wants to mate with them (lonely mating season!)
Six theories for why females show preferences for males that provide no parental care or material benefit
1. Healthy mate
2. Good genes
3. Handicap principle
4. Runaway selection
5. Sensory Exploitation
6. Chase away selection
#1 Healthy mate theory
Females prefer traits that are indicative of male health
Adaptive value: females (& offspring) avoid contagious diseases and parasites
Example: Male satin bowerbirds provide females with multiple signals that are indicators of their health and physiological condition
E.g. Bower’s quality and its decoration, and also the male appearance are the indicator of feather growth, body size (mostly correlated), blood parasites, Ectoparasite load….. body size and Ectoparasite load is direct correlated with bower quality!!!!
#2 Good genes theory
Females prefer courtship displays and ornaments (traits) that are indicative of male viability
Adaptive value—offspring may inherit the viability advantages of the father
Female choice with for indicators of health, which may also be related to good genes
Example: strong immune response correlated with song rate in male starlings
The greater the swelling, the higher the song rate!
Case study: Many large eyes make for a sexy peacock
Do the male ornaments signal good genes??
Females prefer males with large tails with many “eyes”
Offspring of males with larger eyespots show higher survival
But why doesn’t selection favor males that “cheat”?
E.g. Why don’t males with relatively poor genes…