Sexual Selection

Sexual Selection BasicsSexual selection – differential reproduction as a result of variation in the ability to obtain mates (Futuyma 2004)

Sexual dimorphism – males and females of the same species have a different appearance.

Can you think of an example of sexually dimorphic animals? (hint think Virginia)

Sexual Selection Examples

• Male widow-birds grow exceptional long tail feathers, females lack tail feathers

• Males make low flights over grasslands making loops

Do females prefer longer tailed males? WHY?

Sexual Selection Basics

Malte Anderson –

Tails were cut and glued to birds with naturally short tails

Artificially longer tails had significant more matings than normal males

Why Long Tails?

It is very costly to grow and maintain a long tail

Indicates strong and vigorous genes

What would it take to grow a long tail?

Sexual Selection vs. Predators

Being attractive can attract predators

Far Side 1992

Females prefer males with bright spots

Male guppy (Poecilia reticulata)

Sexual Selection vs. Predators

More spots = More mating = Spreading your genes

Crenicichla (cichlid) preys on guppies

How do predators and females both influence male phenotypes?

Sexual Selection vs. Predators

Endler (1980) – Classic experiment

Results = Predators keep number of spots lower

(Futuyma 2004)