Lecture 17 Notes

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7 Jun 2011
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BIO120H1
LECTURE 17: ORGANISMAL REPRODUCTIVE DIVERSITY
Why did sex evolve?
Costs and benefits of reproducing: inbreeding and outbreeding
Reproductive Modes examples:
Daphnia:
oReproduces sexually in warmer water
oReproduces asexually in cooler water
Water Hyacinth
oWorlds worst water weed
oReproduces through sexual and clonal reproduction
Sexual reproduction: 50% les genetic transmission
Asexual reproduction: 100% genetice transmission
Costs: break up genetic combos
Researchers working on sex in Canada
Sarah Otto:
Aneil Agrawal:
Graham Bell:
Twofold cost of meiosis: number of gene copies
More individuals produced by asexuals, genes spread faster by females because of cost of
producing males
Transmission bias favours asexual
Advantages of sex:
Sex brings together favourable mutations; asexuality takes longer
Relatively few winners in the environment; each individual replaces itself- high mortality levels;
lottery-
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oSpatially hetero environments TANGLED BANK:
Sex is adaptive
oTemporally hetero environments: RED QUEEN
Individuals adapt at different rates
Things are changing all the time
Temporal variability
Fisher and muller: first to say sex brings together favourable mutations
Example: heterogenous genotypes most favourable;
oABC is the fittest genotype
In experiment with rotifer:
Two different homogenous environements; condition with combo of both environments
oLet rotifer evolve
oSex remained at high level at combo environment;
oAsexual reopduction dominated in homogenous
^TANGLED BANK
Asexuality is sporatically distributed
Many perennial plants reproduce asexually
Parthenogenesis
Clonal propagation
In phylogenies, asexual species are at the tips of the trees
oAssociated with low genetice variability
oCannot adapt to changing environments
oAsexual species should be short lived
Evening primrose experiment
oReconstruct phylogeny
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