1. The Cost of Sex n Although some species reproduce asexually, the majority reproduce sexually n Therefore, it seems that sex has a selective advantage is most species n But, sex has a cost

2. The cost of sex n Consider an asexual female. Her offspring will be clones; genetically identical individuals n Now consider a sexual female. Each one of her offspring will have only 50% of her genes. n Reproductive rates differ as well. Let’s say each female produces two offspring and then dies Asexual female: 100  200  400  Sexual female: 100  100 females + 100 males  100 f + 100 m   n To compensate, it would seem that sexually produced offspring should be twice as fit as asexually produced offspring

3. n Understanding the cost of sex has been described as “the outstanding puzzle in evolutionary biology”

4. n Some argue that sexual reproduction results in greater variation for natural selection to act upon n The point is true but can’t explain the cost of sex The argument requires that individuals act for the good of the species rather than for their own good Altruism is not an adaptive behavior

5. Possible solutions to the cost of sex problem n Muller’s Ratchet: Sexual reproduction allows females to reduce the number of deleterious alleles in their offspring n The Lottery Model or the Tangled Bank Hypothesis: habitat quality varies spatially and genotypes vary in their ability to grow in different habitats - it’s better to have 100 different lottery tickets than 100 copies of the same ticket n The Red Queen Hypothesis "The most curious part of the thing was, that the trees and the other things round them never changed their places at all: however fast they went, they never seemed to passanything. "I wonder if all the things move along with us?" thought poor puzzled Alice. And the Queen seem to guess her thoughts, for she cried, "Faster! don't try to talk." Through the Looking Glass. Lewis Carroll The coevolution of parasites and hosts may produce rapid environmental change

6. The Legend of Johnny Appleseed

7. Johnny Appleseed n Born John Chapman in 1774 n Spent 49 years planting apple trees inIllinois, Indiana, Kentucky, Pennsylvania and Ohio n We know there is tremendous variation in the quality of apples arising from sexual reproduction n Most of the apples that Johnny Appleseed planted were likely none too tasty

8. Apple grafting