BIOB51H3 Lecture Notes - Lecture 23: Parental Investment, Rough-Skinned Newt, Sensory System
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HYPOTHESIS #3: SEXY SONS
-In some species, we see elaborated traits in males, but find no fitness enhancing benefits
-Predictions
o1. Females choose males w/ the most elaborate trait (ornament/display)
o2. Sexy trait is heritable so sons of sexy males also have higher matting
success
othis differs from good genes, because (1) males w/ sexy trait have no
natural selection advantage, and (2) “sexy” trait is heritable
- the trait itself is preferred --> trait is heritable --> inheritance of attractiveness genes
-they have no NS advantage, but the ornament/display is heritable --> in this case:
variation in who even has these traits
But why are females choosy?
-EXMAPLE: spotted cucumber beetle
oMale stroke female w/ his antennae during copulation this is a sexy trait
oFemales are more likely to accept the spermatophore (sperm package) from
males that stroke faster (prediction #1: most elaborate trait)
-What we find: the sexy trait is heritable
(prediction #2)
oMethods: mate females w/ either fast
or slow males
oRemove the eggs form the mother’s
cage
oRear them under standard lab
conditions
ovariation among males in stroking rate
--> mated females to fast or slow
males
ocan identify genes for this trait OR
just find if this trait inherited --> reared in standard lab b/c reared in same
env. conditions (to control for the env)
-RESULTS: the sons of “sexy” fathers
(those who stroke faster) are also fast (in
terms of stroke rate) AND the sexy sons
of the sexy fasters also have a higher
mating success rate
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-thus: this is a sexy trait and it is
heritable
BUT WHY IS IT SEXY?
-For the trait to be “sexy” most
females need to have this
preference
-There is basically no survival
advantage associated with this
trait why would females have a
preference for an arbitrary trait?
oSensory Bias Hypothesis: general features of the female’s sensory system may
make females responsive to certain “arbitrary” stimuli (i.e the male’s traits are not
related to their survival)
ZEBRA FINCHES
-Mother’s cover their nests
in random white feathers
to prevent predators from
seeing them so: they
are more in tune to look
for white feathers
oIf: there was a novel white ornament introduced, would
it lead to higher mating success?
oRESULTS: they show that if there was anovel white
ornament introduced, they try to mate with that ornament
considerably more than others so: have a sensory
bias towards white feathers
SEXUAL SELECTION IN NATURE
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Document Summary
In some species, we see elaborated traits in males, but find no fitness enhancing benefits. Females choose males w/ the most elaborate trait (ornament/display: 2. Sexy trait is heritable (cid:0) so sons of sexy males also have higher matting success: this differs from good genes, because (1) males w/ sexy trait have no natural selection advantage, and (2) sexy trait is heritable. The trait itself is preferred --> trait is heritable --> inheritance of attractiveness genes they have no ns advantage, but the ornament/display is heritable --> in this case: variation in who even has these traits. -> mated females to fast or slow males: can identify genes for this trait or just find if this trait inherited --> reared in standard lab b/c reared in same env. conditions (to control for the env) For the trait to be sexy most females need to have this preference.