1. © Copyright 2015- all rights reserved www.cpalms.org Strange traits 2. Flashy males 1. Copulatory Suicide 4. Egg Mimics 3. Effeminate males

2. © Copyright 2015 - all rights reserved www.cpalms.org Sexual Selection and Trait Evolution

3. © Copyright 2015- all rights reserved www.cpalms.org Male Female The presence of some traits is puzzling. -Some traits cannot have evolved by natural selection, because they actually decrease survival. -Others are clearly different between males and females

4. © Copyright 2015- all rights reserved www.cpalms.org Sexual selection: selection on an organism’s ability to obtain mates

5. When does sexual selection occur? Reproduction can be more costly for one sex (usually females): Metabolic cost of eggs vs. sperm Gestation period- harder to obtain resources Parental care Unequal parental investment females more choosy when selecting a mate © Copyright 2015- all rights reserved www.cpalms.org

6. American pronghorns: females are picky when choosing a mate Females often travel great distances before choosing a mate. When females take the time to choose attractive males, their offspring grow faster and better survive the winter. © Copyright 2015- all rights reserved www.cpalms.org

7. How can males evolve to obtain more matings? 1. Outcompete other males: For example, direct combat may determine who gets to mate. © Copyright 2015- all rights reserved www.cpalms.org

8. How can males evolve to obtain more matings? 1. Outcompete other males: Or, an alternative “sneaker” male strategy may evolve. For example, in the isopod Paracerceis sculpta: These male isopods are large and aggressively try to monopolize mating with groups of females. These males mimic females and go undetected by the larger, aggressive males These males are so small that they sneak by the large males and mate with the females Female © Copyright 2015- all rights reserved www.cpalms.org

9. Alternative mating strategies – males have multiple morphologies and/or behaviors

10. © Copyright 2015- all rights reserved www.cpalms.org 2. Become more attractive to females. One way to do this is to provide direct benefits to females in the form of food or other resources

11. © Copyright 2015- all rights reserved www.cpalms.org 2. Become more attractive to females. The ultimate sacrifice is when a male sacrifices himself as food. This is called copulatory suicide.

12. © Copyright 2015- all rights reserved www.cpalms.org 2. Become more attractive to females. Good genes – males can also advertise that they have good genes through their traits or behaviors. Females choose healthier-looking males that should produce healthier offspring.

13. © Copyright 2015- all rights reserved www.cpalms.org 2. Become more attractive to females. Sensory bias – males can display something that females are naturally attracted to, even if it doesn’t indicate anything about that male. Theis A, Salzburger W, Egger B (2012) The Function of Anal Fin Egg-Spots in the Cichlid Fish Astatotilapia burtoni. PLoS ONE 7(1): e29878. doi:10.1371/journal.pone.0029878 http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029878 Egg mimics on the anal fin of Astatotilapia burtoni

14. © Copyright 2015- all rights reserved www.cpalms.org 2. Become more attractive to females. Sensory bias – males can display something that females are naturally attracted to, even if it doesn’t indicate anything about that male. Theis A, Salzburger W, Egger B (2012) The Function of Anal Fin Egg-Spots in the Cichlid Fish Astatotilapia burtoni. PLoS ONE 7(1): e29878. doi:10.1371/journal.pone.0029878 http://www.plosone.org/article/info:doi/10.1371/journal.pone.0029878

15. © Copyright 2015- all rights reserved www.cpalms.org Sexual selection can explain the evolution of many traits that are seemingly not adaptive but increase mating success. There are several different strategies that animals may evolve to get more mates. Good genes Direct benefits Alternative mating strategies Sensory bias