NCSU Course ZO410 Lecture:
Reproductive Behavior and Sexual Selection

Puzzle of reproduction

Costs of sexual reproduction

1. genetic recombination
2. cost of producing males
3. cost of courtship and mating

Benefits of sexual reproduction

1. Source of variability upon which selection occurs
2. Less accumulation of deleterious mutations
3. Preadaptation to changing environments
4. Preadaptation to changes in competing species

Gametes

(Sex implies male and female):

Isogamy: gametes are the same size
Anisogamy:

Sperm = small, produced in large numbers.
Eggs = large, produced in relatively smaller numbers, energetically expensive.

Reproductive strategies differ between sexes:
Females: more invested, more discriminating
Males: attempt to mate with as many females as possible to maximize gametes

Lifetime reproductive success/ Bateman gradient

Most females reproduce, with low variance among females
In males, greater reproductive variance

Sexual Selection:

-imbalance in parental investment= sexual selection; first defined by Darwin
- M's and F's compete for mates and choose between potential partners
- generally, M's fight for mating opportunities while F's select among M's

Intrasexual vs. Intersexual Selection

- both lead to sexual dimorphism

1) INTRASEXUAL

Male/Male

- increased aggression, secondary sex characteristics
- greatest in promiscous species

-Sperm Competition/ Competition after Mating

                    -Guard Mate
                    - Remove rival sperm
                    - Mating plugs
                    - Testes Size

Female/Female

- less intense
- resources limited

2) INTERSEXUAL

Female Choice (most often)

            - male advertises, female chooses "best"
            - bowerbird example
            - can lead to runaway selection in males-- survival jeopardized by extreme traits
            - female strategies:
                1) He-man Strategy
                    - choose best quality GENES, since won't contribute anything else to female or offspring
                2) Domestic Bliss Strategy
                    - male must invest time, energy, gifts, etc. before female mates
                    - helps insure male will stay around to help with offspring (antiphilandry tactic)
                3) Mate-Choice Copying
                    - choose male because another female already chosen him

Male Choice

            - basic strategy= mate with as many F's as possible
            - defend group of F's or roam and mate as encounter F's
            - if has to invest prior to mating, more choosy about mate
            - certainty of paternity: anticuckoldry strategies

Resolution of M/F conflict

            - environmental condition, resources available
            - how F's group together, how mobile they are
            - basic gamete differences
                = species-typical mating system

HUMAN REPRODUCTIVE BEHAVIOR

Anthropology View
    -gender related to division of labor

Sociobiology
    -sexual dimorphism
    -F's and the domestic bliss strategy
    -M courtship of F
    -age (F usually younger)
    -hypergamy= basis for competition between F's
    -hidden ovulation, unlike other mammals
    - Double Standard
        -expectations of M's and F's different
        -reasons

Comparison with female primates-- control of female sexuality, etc.

Marriage

End of Lecture-Reproductive Behavior subsite. Move to: ZO 410's Course Homesite.