This document discusses sexual selection and sexual dimorphism, specifically focusing on two methods: intrasexual selection and intersexual selection. Intrasexual selection involves competition within one sex, usually males, for access to the opposite sex for mating. Intersexual selection involves mate choice by the opposite sex, usually females choosing visually appealing traits in males like antlers, claws, or bright colors. However, these traits are not always beneficial for survival as they can make males easier for predators to spot. The document also discusses research on coloration preferences in female cichlid fish and mate choice.

2. Section 24.3
Joe Smith

3.  Often
results in sexual
dimorphism
• More intense with
males
 Formof Natural
Selection
Female

4. 2 methods
• Intrasexual
 Competition within one sex for opportunity to mate with
opposite sex
• Intersexual
 “Mate choice”
 “Cryptic Female Choice”
 Less Obvious
 These two methods can overlap

6.  Competing between members of one sex
for opportunity to mate with the opposite
 Examples
• Horns on male goats
• Antlers on male deer
• Enlarged claws on male fiddler crabs

7.  Females are picky
• Seen in Indian peafowl
• “Classic” form of
intersexual selection
 “Cryptic female
choice”
• Less obvious
• Female reproductive
tract is selective for
genetically un-related
sperm

8.  NOT always beneficial for survival
• Female guppies prefer brightly colored mates
• Bright colors are easier seen by predators
 Effects can be measured by abundance of
traits

9.  Many different hypotheses
• Related to upbringing of offspring
• Dependant on fitness
 Age is a factor

10.  Governed by same processes
• Directional
• Stabilizing
• Diversifying
• Balanced

11. Feature Investigation
Seehausen and van Alphen Found That Male Coloration in African
Cichlids Is Subject to Female Choice

12.  Cichlidae family one of largest and most
diverse
• Vary by:
 Coloration
 Body Shape
 Behavior
 Feeding Habits
• Largest population in Eastern African lakes
• Known for complex mating behavior

13.  P. pandamilia and P. nyerierei can
interbreed
 Both found in Lake Victoria
• Certain areas of the lake have interbreeding;
others do not
 Coloration valued in female choice of mate