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Sexual Conflict

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

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Sexual Conflict

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  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, 1223-1236 (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, 301-317 (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 • Cimexlectularius (Bed Bugs) • Males evolved traits that allow for traumatic insemination in response to female resistance • http://www.pheromone.ekol.lu.se/proj2camilla.html

  11. Behavioral Example of Inter-locus Sexual Conflict • Sexual Cannibalism • Paratrechaleaornata(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, 1223-1236 (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, 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).

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