Sexual Selection

1. Sexual Selection

2. How it happens… • Aka, what stressors are put on by organisms to choose the best mate • Sexual selection’s goal is to unite and pass on the best possible combination of genes • Fitness of an organism may depend on several factors, which we will discuss.

3. They are • Sexual Dimorphism • Male- Male Competition • Female Choice • Diversity in Sex Roles

4. Sexual Dimorphism • The differences between the males and females of a species • May include • body size • Coloring • Patterns • Length or size of appendages or parts of an organism ( thumbs on toads or feathers on birds)

5. Sexual Dimorphism • May be several reasons why there are differences, but all relate in that its all about finding a mate. • Body size may make a better fighter, or coloring may be flashy enough to attract a female

6. Male- Male Competition • There are a few subtopics here: • Combat • Sperm Competition • Infantcide

7. Combat • Males often possess the tools needed to fight with other males in hopes of getting the lady • This may mean a larger body size, larger antlers, longer fins, or even longer necks (giraffes) • By fighting (and winning) a male shows dominance over other males and gains the attention of the female

8. Combat • Sometimes this leads to dimorphism among males of the same species. • One is not big enough, strong enough, or armed enough to win a competition • So it uses stealth like tactics of completing the task at hand and getting out unnoticed.

9. Sperm Competition • Males of sexually reproducing species produce sperm (the gamete that holds the male’s genes) • In the case of female promiscuity (a female mating as much as possible) you often see some form of sperm competiotion

10. Sperm Competition • This may lead to many types of competition • Larger amounts of sperm • Nuptial gifts- may include amounts of food for the female or the offspring • Insertion of a copulatory plug- a literal plug inserted to block other male’s attempts at sex • Application of pheremones – decreases the attractiveness to other males • Male guarding the female, or prolonging copulation

11. Infanticide • When the male of a species consumes the offspring of a female which he has not fathered. • Most notable in lions • Goal is to pass on your own genes. • Any offspring that a male has not fathered shares no genes • Furthermore, any young males may present a challenge down the road • Best option for a male lion? • Eat all other cubs

12. Female Choice • In a lot of situations it is up to the female to find a mate • All a male can do is advertise • Say “look at me! Look at meeeeee!” • Females then can pick and choose the male they feel possesses the best set of genes. • Basically saying, most anything a male does to stand out to a female also makes him stand out to predators • But, if that male can survive, and reproduce the rest of his genes must be really good.

13. Diversity in Sex Roles • Most of the time, in most organisms, the female carries most of the cost of offspring (producing and watching over eggs, carrying babies, and/or care for the young) • Sometimes this is not the case

14. Diversity in Sex Roles • In humans, fish, some frogs, and most birds the male may take on as much of a burden (if not more) compared to the female.