Announcements

Monday, March 12 - review 2Wednesday, March 14 - exam 2

Friday, March 16th - no class

Film screening: Thursday, 7pmEnglish 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 mateslow parental investmentsexual dimorphismterritorial (area or harem)

Elephant seals

among seal species

Male-male competition

Alternate male strategies:

Sneaker or satellite malesless investment in territory / aggressionoften use deception

BBCWednesday, 19 January, 2005Cuttlefish 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.

http://www.utsc.utoronto.ca/~mandrade/somersault.html

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 competitionAdaptations for sperm competition include:

More elaborate mating structuresincrease sperm production

Sperm competitionAdaptations for sperm competition include:

More elaborate mating structureselaborations for pleasure? (increase copulatory duration)

Primate penises

females mate with one male

females mate with more than one male

examples of “role reversal”