Announcements Monday, March 12 - review 2 Wednesday, March 14 - exam 2 Friday, March 16th - no class Film screening: Thursday, 7pm English Building 160 Life in the Undergrowth - social insects

Darwin (1871), The Descent of Man, and Selection in Relation to Sex Sexual Selection: “the advantage which certain individuals have over others of the same sex and species, in exclusive relation to reproduction.”

Sexual Selection occurs in two forms Intrasexual: Male-male competition Intersexual: Female choice

Male-male competition How do males get mates / increase reproductive success? Scrambles, endurance contests, fights, avoidance of fights, sperm competition, mate guarding, infanticide… …any way they can

Male-male competition Alternate male strategies: Monogamy Polygyny Sneaker or satellite males

Male-male competition Alternate male strategies: Monogamy -one mate (season, lifetime) parental investment territorial (area)

Male-male competition Alternate male strategies: Polygyny -many mates low parental investment sexual dimorphism territorial (area or harem)

Elephant seals among seal species

Male-male competition Alternate male strategies: Sneaker or satellite males less investment in territory / aggression often use deception

BBC Wednesday, 19 January, 2005 Cuttlefish wimps 'dress as girls’ Size is everything in the world of the Giant Australian Cuttlefis. Diminutive Giant Australian Cuttlefish males have taken to pretending to be female to elbow out larger love rivals. With males outnumbering females four to one, smaller cuttlefish stand little chance of getting close to a mate. But they have been spotted changing colour to mimic females and hiding their masculine fourth arms. Scientists say they were then able to trick their way past male consorts to make their move, often successfully.

Sperm competition (postcopulatory competition) When females mate with more than one male, competition for fertilizations does not end with securing a mating event.

Sperm competition Adaptations for sperm competition include: Mate guarding (the last male to mate often fertilizes most eggs)

Blue milkweed beetle

Seychelles Warbler

Sperm competition Adaptations for sperm competition include: Nuptial gifts (to increase length of mating or decrease probability of female mating again) hanging fly

The ultimate nuptial gift…

Australian redback spider ( Latrodectus hasselti ) - males actively 'encourage' females to cannibalize them while they mate. -males 'somersault' onto the female's mouthparts during copulation - males are able to transfer sperm while they are being consumed. -males that are consumed reap a two- fold paternity advantage relative to males who survive. Maydianne Andrade - Univ. Toronto Scarborough

Sperm competition Adaptations for sperm competition include: Postcopulatory mate choice (active choice by females in which sperm to use)

Sperm competition Adaptations for sperm competition include: More elaborate mating structures “scrubbers” to remove previous males sperm

Sperm competition Adaptations for sperm competition include: More elaborate mating structures increase sperm production

Sperm competition Adaptations for sperm competition include: More elaborate mating structures elaborations for pleasure? (increase copulatory duration) Primate penises females mate with one male females mate with more than one male

examples of “role reversal”