Sexual Conflict Justin Hickman

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)

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

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, 1223-1236 (2003).

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

Sexual Conflict: How Does It Work? Lessells, Kate M. The Evolutionary Outcome of Sexual Conflict. Philosophical Transactions: Biological Sciences, Vol. 361, No. 1466, 301-317 (2006).

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

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)

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

Anatomical Example of Inter-locus Sexual Conflict Cimex lectularius (Bed Bugs) Males evolved traits that allow for traumatic insemination in response to female resistance http://www.pheromone.ekol.lu.se/proj2camilla.html

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

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, 1223-1236 (2003).

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

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

Reference List (1) Lessells, Kate M. The Evolutionary Outcome of Sexual Conflict. Philosophical Transactions: Biological Sciences, Vol. 361, No. 1466, 301- 317 (2006). (2) Pizzari, T., and R. Snook. Perspective: Sexual Conflict and Sexual Selection: Chasing Away Paradigm Shifts. Evolution Vol. 57, No. 6, 1223-1236 (2003).