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You could study…. Birds in Costa Rica Bats in Israel Squirrels in Canada Monkeys in Ethiopia Pronghorn in Montana www.animalbehavior.org. Sexual selection. Sex (the basics). Asexual and sexual organisms Sex and gender Sexual selection Selection affecting access to gametes.

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You could study
You could study…

  • Birds in Costa Rica

  • Bats in Israel

  • Squirrels in Canada

  • Monkeys in Ethiopia

  • Pronghorn in Montana

  • www.animalbehavior.org



Sex the basics
Sex (the basics)

  • Asexual and sexual organisms

  • Sex and gender

  • Sexual selection

    • Selection affecting access to gametes

http://www.micrographia.com/specbiol/cnidari/hydrozo/hydr0100/hydra-01.htm

http://flickr.com/photos/billwalker/2521121709/


Sex is a mixed bag
Sex is a mixed bag

  • Costs of sex

    • Cost of meiosis

    • Breakup gene combinations

    • Mate acquisition

    • STDs

  • Benefits of sex

    • Adapt to changing environment

      • Abiotic

      • Biotic

http://porpax.bio.miami.edu/~cmallery/150/life/meiosis.pics.jpg


Hermaphroditism
Hermaphroditism

  • Pathological in tetrapods

  • Simultaneous

    • Earthworms, gastropods, hamlet fish

    • Self fertilization is rare

    • Costs: Double the sex organs

    • Benefits: When optimal sex for relative size of mates changes

  • Sequential

    • Teleosts

    • Usually a one way ticket

    • Female  male in reef fish

      • When harem male dies

      • Only large males can defend a territory

    • Male  female in sea bass

      • Female reproductive output increases with size

http://www.fsbio-hannover.de/oftheweek/196/800px-Mating_earthworms.jpg

http://throughthestatic.wordpress.com/category/idiots/


Anisogamy
Anisogamy

  • The evolution of Anisogamy

    • Females and males

  • Consequences of anisogamy

    • Unequal parental investment

    • Unequal variance in fitness

      • Ornamented males

      • Choosy females

        • Easy males

http://www.microscopy-uk.org.uk/thedark/eggbigx.jpg


Kinds of sexual selection
Kinds of sexual selection

  • Intra-sexual selection

    • Interference competition

      • Armaments (displays)

      • Size

      • Badges of status

  • Inter-sexual selection

    • Scramble competition

      • Locomotion and mate seeking

    • Mate choice

      • Ornamentation (displays)

      • Alternative tactics (e.g, coercion, female mimicry)

  • Sperm competition



The evolution of size dimorphism
The evolution of size dimorphism

  • Given interference competition

    • Directional selection for male size, armaments

    • Decrease in males’ mean viability

    • Evolutionary “arms race”

    • Distribution of male size as costs balance benefits

    • Mean investment is proportional to number of defended females (reproductive variance)

http://www.innatmorrobay.com/elephant_seals_color.jpg


Caveats on size dimorphism
Caveats on size dimorphism

  • Male size vs. male trait size

  • Shrinking females

  • Alternative strategies

  • Small male advantage

http://crawford.tardigrade.net/journal/album/lillivatia.jpg

From Legrand and Morse 2000 Biol. J. Lin. Soc. 71:643-664


Precopulatory guarding
Precopulatory guarding

  • Amplexus

    • Female receptivity is limited, cyclic, asynchronous

    • Males are available to reproduce almost continuously

  • Mate guarding in birds

http://www.treknature.com/gallery/Middle_East/Turkey/photo164737.htm

From Birkhead 1979 Anim. Behav. 27:866-874



Which sex chooses
Which sex chooses?

  • The importance of the question

  • The operational sex ratio (OSR)

  • The potential reproductive rate (PRR)

  • The differential cost of reproduction

    • Covaries with OSR and PRR

From Amundsen & Forsgren 2001 PNAS 98:13155-13160


Direct benefits
Direct benefits

  • Definition

  • Kinds

    • Fertilization success

    • Protection

    • Resources

      • Territories

      • Parental care

      • Nuptial gifts

        • Nutritious ejaculates

        • Sexual cannibalism

http://www.biology.au.dk/trine.bilde.htm


Indirect benefits
Indirect benefits

Photograph by Medford Taylor


Fisher s runaway model
Fisher’s runaway model

Benefit of trait

Male cost

Different genes promoting trait / preference

Genetic linkage

Trait size

Female preference

Generations


Quantifying the runaway model
Quantifying the runaway model

  • Lande’s version

    • Quantitative genetic

    • Runaway when B / G > (v2 / w2 ) + 1

    • In other words, when CVA (B) is high relative to VA of trait (G) with low variance in female preference (v2), weak utilitarian selection on trait (high w2)

  • Requires initial preference!

    • Natural selection

    • Drift

    • Sensory exploitation


Testing for runaway
Testing for runaway

  • P1: Additive genetic variance for trait and preference

    • Generally supported

    • Traits are influenced by several loci

  • P2: Genetic co-variation between trait and preference

    • Method 1: Select for trait, see if preference also changes

      • Generally supportive

    • Method 2: Is there covariation among traits in brothers and preferences in sisters?

      • Supported in sticklebacks and crickets