AEC 360  Ecology

Lecture 10: Sex, evolution, and behavior

I.  Why has sex evolved?
    A.  There are asexual organisms

    B.  The costs of sex
        1.  Maintaining gonads
        2.  Evolutionary cost of meiosis
            -- Only 1/2 of genes (in diploid organisms) are passed onto offspring in sexual reproduction (as compared to all genes in asexual reproduction)
        3.   Mating behavior

    C.  Benefits of sex
        1.  Dilute harmful genetic mutations
        2.  Genetically varied offspring
        3.  Keep offspring from being susceptible to parents pathogens (Red-queen hypothesis)
             - see example in Figures 9.4 and 9.5
        4.  Male parental care

II.  Mating systems among sexual organisms
    A.  Background
        1.  Different costs for males and females
            -- Females limited by the numbers of eggs they can produce and the number of offspring they can rear
            -- Males limited by number of matings, and by care in some organisms -- sperm are energetically cheap to produce

    B.  Promiscuity
        1.  Usually, males mate as many times as possible and do not provide parental care
        2.  The most common mating system among animals, and universal among outcrossing plants
        3.  No lasting pair bond between males and females

    C.  Polygamy
        1.  Single member of one sex establishes lasting pair bonds with more than one member of the other sex
        2.  Polygyny:  males mated to more than one female (typical)
        3.  Polyandry: females mated to more than one male

    D.  Monogamy
        1.  Pair bond between one female and one male, perhaps until death
        2.  Systems evolve where survival of offspring require more than one parent

III.  Sexual selection
    A.  Selection by one sex for specific characteristics in individuals of the opposite sex, usually exercised through courtship behavior

    B. Must be indicative of male quality

    C.  Must carry a cost
       - examples, including of the handicap principle

    D.  Female choice

    E.  Other examples