Sexual selection mating systems
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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 traits?

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

3 sensory bias or sensory drive
3) Sensory bias or sensory drive traits?

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 traits?

  • 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 traits?

  • 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 traits?

Dendrobates vanzolinii

Dendrobates ventrimaculatus

A scramble competition
A. Scramble competition traits?

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 traits?

Bufo bufo,


B mate guarding behavior
B. Mate Guarding Behavior traits?

  • 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 traits?

  • Lek =

  • Chorus = anuran males calling from particular perches… females approach the males

D resource defense
D. Resource Defense traits?

  • 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 lizards & snakes – 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 lizards & snakes – African gray treefrog

F. Sperm Competition

  • Multiple paternity

  • Genetically superior sperm more likely to survive (better to mate with several males)