Week Nine Flashcards
Why is testosterone suggested to be a handicap, and an honest signal of genetic quality?
T has been suggested to have immunosuppressant effects.
- High T men who are in good health are therefore advertising good genes.
- Healthy individuals can afford to suppress their immune system by raising their testosterone levels, which also augments secondary sexual traits and displays.
- Women showed preference for men that had higher levels of T.
What does the good genes immunocompetence hypothesis in humans rely upon?
1) female prefer masculine faces.
2) Masculine faces indicate higher testosterone
3) Testosterone imposes metabolic costs
4) Males who can afford such metabolic costs are high quality individuals
5) high quality males sire high quality offspring.
What did Mills et al. show about antagonistic alleles for testosterone in voles?
F1 male offspring had greater fitness and females had decreased fitness when selected for T.
F1 male offspring had decreased fitness and females had increased fitness when the lines were selected against T.
What is sensory exploitation?
It is a term by MJ Ryan; it is evolution based on arbitrary biases.
- The key to identifying sensory exploitation is showing that the preference for the trait precedes the evolution of the trait itself.
- There are many examples of females finding traits of other species attractive (traits not yet evolved in their own species)
What did Kirkpatrick and Ryan conclude about the Tungara frog?
Regarding female preference, there is a preexisting bias for enhanced calls “chucks”.
-Artificially enhanced male calls were used in the experiment.
What did Helen Rodd et al. suggest about guppy females?
Food color drive hypothesis:
Guppy females like orange (AND RED) male spots because they resemble fruits eaten by females.
- A markedly different explanation from good genes (a signal of male condition, prowess in acquiring carotenoids, parasite load).
What colors do guppies use for their bower decorations?
Males use colours least appetizing in their bower decorations.
-Suggest ancestral bowerbirds used inedible objects in decoration
BLUE, VIOLET
What is the chaseaway hypothesis?
Reproductive interests of two sexes conflict in mating rate.
- Males will often have a stronger fitness interest in frequent mating
- But if mating carries a cost for females, then the sexes are in conflict over mating rate.
- -Wrong time, too frequent, physically injurous….
What is the arms race that Holland and Rice envisioned over mating signals?
Female sensory bias –> Rudimentary male trait –> female fitness depressed –> female resistance increases –> Male attractiveness declines –> Male trait exaggeration –> female fitness depressed
When does the chaseaway stop?
What do Rice and Holland think?
When trait exaggeration reaches a naturally-selected limit.
- Traits are at the point where males are max’d out, but they are stuck producing the trait.
- Rice and holland saw this as a case in sexual conflict where females can ‘win’.
- Males stuck producing expensive characters that not longer create variation in mating success (you’ve got to have the long tail to be a suitor, but normal variation in tail length no longer matters)
What is the evidence that females have “won” sexual selection in wolf spiders?
Some species have tufts on pedipalps used in sexual selection.
- Exposure of non-tufted species to highly tufted males (with artificial or normal tufts) suggests strong sensory bias to tufts
- HOWEVER; females form species with tufts are not impressed by tufts anymore; perhaps they use other characters to discriminate male quality.
- Perhaps they have developed resistance.
What did Pryke et al. find about male breeding success in red-collared widowbird?
Male breeding success is unrelated to collar carotenoids.
-The day of first egg is negatively correlated with tail length. You want eggs as early as possible so offspring can take advantage of available resources.
What is the significance of relative differences as traits become more extreme?
It’s hard to tell the difference between two long tails with 3cm difference. But it’s easier to tell the difference between two small tails with 3cm difference.
-Larger structures demand larger absolute differences to create the same relative effect.
How is the chaseaway hypothesis a different dynamic from evolution by good genes SS, runaway or simple sensory bias?
Females are harmed if there are too many matings…allocation of energy, etc.
- More resistant females will have higher fitness.
- Like runaway, selected display trait and resistance to the trait coinherited and coevolving as a feedback loop.
(Chaseaway) Won’t females benefit from mating with males with ‘harming’ genotypes through their sons?
This depends upon the ratio of direct harm to indirect benefits - something only convincingly measured in fruit flies so far (harm > benefit)
What are the predictions of chaseaway? (1)
Attraction to a given male trait will diminish over time.
-Other models predict static (sensory bias) or increased female attraction (runaway) with time
What are the predictions of chaseaway? (2)
Females will suffer a fitness reduction from attraction
-Other models predict benefits (direct or via good genes) or no effect
What are the predictions of chaseaway? (3)
Females can ‘win’ the battle of the sexes
-Males stuck with inventions that only worked for a short period of time. A “graveyard” of sexually selected traits.
How do closely related species differ?
Typically more different for reproductive characters than other parts of morphology.
Why might sexual selection be a driver of speciation?
- Sexual selection involves selection on reproductive traits; traits likely to affect isolation.
- SS often operates on otherwise arbitrary traits; means potential for mutation and drift in allopatry to steer different trajectories is great
- SS leads to assortative mating
- Helps promote fission of once continuous gene flow
- Allows favourable gene-gene combinations to cosegregate, reinforcing natural selection.
Why were jumping spiders morphologically different in such a small geographic location?
They were confined to different mountain tops of varying size.
-Males adapted and isolated by mountains, little gene flow.
-They are morphologically different in sexually-selected characters.
-FEMALES WERE SIMILAR THROUGHOUT - mtDNA evolved slowly
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How is mate choice maintained, if all successful traits are expected to become fixed in the population, and benefits to mate choice decline?
Genic Capture
Sexual Conflict
What is Genic Capture?
How would mate choice be maintained?
The supposition that the fitness phenotype is made up of the contributions of many genes.
-Exhaustion of fitness variation is unlikely because the elaborate traits employed by males are subject the effect of hundreds or thousands of genes.
What conclusion did Agrawal and Siller independently and simultaneously arrive at about males and males and mutations?
If mutations are frequent enough and hurt males more than females, then males could be a kind of sieve for removal of harmful variation.
-In promiscuous species, the advantage of reduced mutation load could actually pay for the 2-fold cost of sex.
