Lecture 15 Flashcards
Mate choice
- Any trait (behavior, morphology) of one sex that biases the mating success of other sex toward preferred type
- No implied sense of beauty
Tail length experiment
- N: Natural tail length
- R: Reduced tail length
- L: Elongated tail length
- S: Sham surgery
- Mating success predictions: L > N = S > R
- Results(Prior to treatment): L > N > S > R. All not significantly different
- Results(After treatment): L > N > S = R. L is significantly different
- Study asked if tail length impacted male-male competition. No, tail length only influenced female choice
Female choice and acoustic cues: complex calls in Tungara frog
- Females consistently prefer complex calls when given choice between two synthetic calls
- Frog eating bats also prefer complex calls: Increase mating success for frogs, but decrease survival(predation)
Relative strength of sexual vs natural selection varies across environments
- Stronger competition for mates in urban environments
- Stronger predation from bats in forest environments
Urban vs forest frog calls
- Urban Tungara frogs make more complex calls than forest frogs and all females prefer them
Why are elaborate traits and behaviors common
- They are preferred by mates
- Selection for elaboration
Hypotheses for choice
- Direct benefits: involve direct natural selection on individual making choice. Chooser produces more offspring
- Indirect benefits: Involve genetic benefits to the offspring of individual making the choice. Chooser produces offspring that are of higher genetic quality
Direct benefits
- Choosiness based on resources (parental investment) rather than apparent male attributes
- Male trait is an indicator or badge of those resources
Female preference for males that provision resources
- Prey: Hanging fly
- Nutritious spermatophores: Sperm, protein
- Provisioning larger resources leads to increased copulation duration -> increased copulation leads to more sperm transferred/eggs fertilized
Selection for male traits as indicators of resource provisioning or other direct benefits
- Territory quality
- Defense
- Parental care
- Lack of parasites (STIs)
Indirect benefits
- Females prefer male traits that indicate high genetic quality
- If indirect benefits exist, then offspring from matings with preferred males should have higher fitness
Is peacock display size an indicator of good genes
- Females prefer to mate with males that have more eyespots
- Males with more eyespots produce offspring that survive better
How do alternative reproductive strategies influence female choice
- Parental males offer a direct benefit to females: defend nests, provide care to young
- Satellite and sneaker males offer indirect benefit to females: “good genes” leads to offspring growing faster, surviving better
Experiment: In vitro fertilization of eggs with sperm from either parental or sneaker/satellite male
- Offspring of sneaker and satellite males are larger
- Larger offspring size means less likely to be eaten by a predator
Parental males adjust level of care when they sense offspring have been sired by other males
Female bluegill sunfish face trade-off in mate choice: parental offer direct benefit, good care. satellite offer indirect benefit, good genes
Parental investment theory
- Sexes of some species differ in their reproductive investment
- Members of sex that invest little in offspring will compete among themselves to mate with members of sex that invest more in offspring
Broadening view of parental investment
- When males invest a lot relative to females, then predict male choice, female/female competition
Pipefish sex roles and mating system
- Male reproductive success limited by size of brood pouch
- Female reproductive success limited by access brood pouch of males
- Females compete for males
- Sexual selection on female size and ornamentation
Do males exercise mate choice?
- Males will prefer large, highly fecund females
- Results: Males prefer large body length and large female fold size
Relative investment can be influenced by environmental factors
- Food abundant for katydids: Males can make food, more receptive to mating. Females less interested in mating
- Food scarce: Males less receptive to mating, females have more interest in mating
Environmental effects on relative PI and mate choice in Katydids
- As ambient resource levels decline:
- Potential reproductive rate of males decline
- Females have incentive to increase reproductive rate(benefit of resources of males increases)
- Changes operational sex ratio
- Predictions at low resources
- Male choice
- Female-female competition
Results
- Food abundant
- Calling males: 6.6
- Matings per female: 0.7
- Male choice: <0.1
- Female competition: 0
- Food scarce
- Calling males: 0.4
- Matings per female: 1.3
- Male choice: 0.4
- Female competition: 0.2
