1. Sexual Conflict
Justin Hickman

2. Sexual Conflict: How It Relates to Sexual Selection
The traditional view of sexual selection
Genes that have reproductive advantage for males translate simultaneously into fitness gains for females reproducing with these males
Sexual conflict theory is an alternative view of sexual selection
Suggests reproductive traits can evolve in response to conflicts between sexes over reproductive decisions(2)

3. Sexual Conflict: “The Battle of the Sexes”
Occurs when two sexes have conflicting optimal fitness strategies for reproduction
Often leads to the evolution of harmful strategies
However, not all strategies are harmful
Sexual conflict theory implies reciprocal selection
Leads to antagonistic co-evolution

4. Sexual Conflict: “The Battle of the Sexes”
As one sex evolves a strategy to increase its reproductive fitness, the other sex’s fitness decreases
Each evolutionary gain by one sex provokes a counteracting evolutionary response by the opposite sex
Male
Female
Traditional Sexual Selection
Male
Sexual Conflict Theory
Female
Pizzari, T., and R. Snook. Perspective: Sexual Conflict and Sexual Selection:
Chasing Away Paradigm Shifts. Evolution Vol. 57, No. 6, (2003).

5. Sexual Conflict: How Does It Work?
Definitions
Palliative adaptations- reduce harm without influencing the gene over which there is conflict—not sexually antagonistic (1)
Example: Spermalege in bed bugs
An organ that evolved in females to reduce infection at the site of traumatic insemination by males
Cooperative adaptations- changes in the adaptation/counter adaptation cycle that are in the interest of both sexes—not sexually antagonistic (1)
Example:
If original conflict led to bi-parental care, both sexes may gain through role specialization

6. Sexual Conflict: How Does It Work?
Lessells, Kate M. The Evolutionary Outcome of Sexual Conflict. Philosophical
Transactions: Biological Sciences, Vol. 361, No. 1466, (2006).

7. Sexual Conflict: Two Types
Intra-locus
Arises when sex-specific optima for a trait is expressed in both sexes
The same set of alleles have different optima in males and females
Example
The human hip

8. Sexual Conflict: Two Types
Inter-locus (main focus)
Male and female alleles at different loci conflict
Occurs when there is sexually antagonistic selection on a trait so that the optimal trait value differs between the sexes(1)
Results in selection on each sex to manipulate this trait toward its own optimum and resist manipulation by the other sex(1)

9. Inter-locus Sexual Conflict Continued
Rules for resistance to manipulation
Will only evolve once the manipulative behavior has evolved
Initial evolution of manipulation depends only on the costs and benefits of the manipulation, NOT on the costs and benefits of resistance

10. Anatomical Example of Inter-locus Sexual Conflict
Cimex lectularius (Bed Bugs)
Males evolved traits that allow for traumatic insemination in response to female resistance

11. Behavioral Example of Inter-locus Sexual Conflict
Sexual Cannibalism
Paratrechalea ornata (Gift-giving Spider)
The cannibalistic behavior thought to have evolved in females due to parental investment
Females eat males to receive increase in quality offspring
Males provide gifts to females to avoid being eaten

12. Why is Sexual Conflict Feasible?
Counter-intuitive process
Manipulation by male increases his fitness, but decreases female fitness
Female manipulation brings her fitness back up thereby decreasing male fitness
When there is sexual conflict over a trait, manipulation and resistance of that trait bring fitness benefits by reducing conflict load(1)
Reciprocal selection seems lead to an overall increase in the fitness of each sex
Male
Female
Traditional Sexual Selection
Male
Sexual Conflict Theory
Female
Pizzari, T., and R. Snook. Perspective: Sexual Conflict and Sexual Selection:
Chasing Away Paradigm Shifts. Evolution Vol. 57, No. 6, (2003).

13. Summary How sexual conflict relates to sexual selection
The reciprocal nature of sexual conflict
The two types of sexual conflict
Why sexual conflict theory seems to explain certain behaviors

14. Sexual Conflict and Human Behavior
Could the theory of sexual conflict give us insight into human sexual behaviors?

15. Reference List
(1) Lessells, Kate M. The Evolutionary Outcome of Sexual Conflict. Philosophical Transactions: Biological Sciences, Vol. 361, No. 1466, (2006). (2) Pizzari, T., and R. Snook. Perspective: Sexual Conflict and Sexual Selection: Chasing Away Paradigm Shifts. Evolution Vol. 57, No. 6, (2003).