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Sexual Selection & Mating systems. Sexual selection overview Hypothesis Mechanisms Natural Selection v. Sexual Selection Males more affected Mating systems & sexual selection Scramble competition Mate Guarding Behavior Leks & Choruses Satellites & Interferers Sperm Competition.

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sexual selection mating systems
Sexual Selection & Mating systems
  • Sexual selection overview
    • Hypothesis
    • Mechanisms
    • Natural Selection v. Sexual Selection
    • Males more affected
  • Mating systems & sexual selection
    • Scramble competition
    • Mate Guarding Behavior
    • Leks & Choruses
    • Satellites & Interferers
    • Sperm Competition
i sexual selection overview
I. Sexual Selection overview
  • Defined as: Directional selection that acts on genetically variable phenotypic traits that affect the reproductive success of the individuals of a particular sex
  • Sexual selection can explain the persistence of conspicuous differences between females and males
a hypotheses why do females prefer certain phenotypic traits
A. Hypotheses: Why do females prefer certain phenotypic traits?
  • Direct Benefit: Certain male characters provide a direct benefit to females in terms of increased fecundity.
2 good genes
2) Good Genes

Male characters are "indicators" of "good genes",

3 sensory bias or sensory drive
3) Sensory bias or sensory drive

some aspect of the sensory world biases

females to "prefer" or notice ascertain

characters –

  • eg, if the species feeds on red prey, their visual system may be tuned to red wavelengths, therefore, females prefer males with red ornaments


  • Pre-mating sexual selection:
    • selection for species recognition (females mating w/own species) could possibly lead to elaborate secondary sexual characteristics
    • females could detect differences in the number of deleterious alleles in an male
  • Post-mating sexual selection:
    • sperm competition
    • polyandrous species have larger sperm, faster swimming sperm, more aggressive sperm
d males more affected by sexual selection than females
D. Males more affected by sexual selection than females
  • Females –
  • Males – (sperm is cheap) spend energy on mate selection ability, therefore under greater sexual selection pressure
ii mating systems sexual selection
II. Mating systems & sexual selection
  • Polygamy - single individual mates with more than one individual of the opposite sex (resource use)
  • Polyandry –

(male defense, resource defense)

  • Polygyny –

(female defense, resource defense, Lek, Scramble competition)

  • Monogamy – 1 male mates with 1 female (mate guarding/assistance)

Larval habitat affects mating strategies

Dendrobates vanzolinii

Dendrobates ventrimaculatus

a scramble competition
A. Scramble competition

Explosive breeders = Female available for short periods, spatially aggregated

  • Scramble competition = males compete to locate females as fast as possible, mate as fast as possible & with as many females as possible

Rana sylvatica

Bufo bufo,


b mate guarding behavior
B. Mate Guarding Behavior
  • If searching for mate is costly, then it may be worthwhile to invest energy in guarding her from other males
  • Monopolize the female strategy
c leks choruses
C. Leks & Choruses
  • Lek =
  • Chorus = anuran males calling from particular perches… females approach the males
d resource defense
D. Resource Defense
  • Monopolizing resources which are attractive to females gives males an advantage

Plethodon cinereus

e satellite frogs sexually interfering salamanders lizards snakes
E. Satellite frogs & Sexually interfering salamanders, lizards & snakes
  • Satellite males – don’t vocalize, but rather wait near a calling male to intercept females that are attracted to the calling male
  • Interfering males – prevent female from mating with another male

Rana clamitans


Thamnophis sirtalis parietalis – males swamp the few females that emerge…

High numbers of male garter snakes die soon after emerging from hibernation because they are attacked by crows. She-males at the center of a mating ball, however, are less exposed to predators – also remain warmer…

f sperm competition

Chiromantis xeramplina – African gray treefrog

F. Sperm Competition
  • Multiple paternity
  • Genetically superior sperm more likely to survive (better to mate with several males)