Sexual conflict

Sexual conflict occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, leading to evolutionary arms race between males and females. It has primarily been studied in animals, though it can in principle apply to any sexually reproducing organism, such as plants.

This can be in two forms:

1. Interlocus sexual conflict, where male alleles have conflicting interests with females. This can be in the form of conflict over parental care, where males are more prone to abandon offspring. Another form is sexual harassment, where males harm females to gain access to matings, such as when toxins are released in sperm by male Drosophila melanogaster.
2. Intralocus sexual conflict, where the same set of alleles in males and females have different optima. i.e. they are expressed differently in the sexes. A classic example is the human hip, where females need larger hips for childbirth.

Sexual conflict may lead to sexually antagonistic co-evolution, in which one sex (usually males) evolves a "manipulative" trait which is countered by a "resistance" trait in the other sex. Some regard sexual conflict as a subset of sexual selection, while others suggest it is a separate evolutionary phenomena.

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Manifestations

There are a wide variety of manifestations of sexual conflict, occurring in a broad range of taxa. One way of sorting these is by temporal relation to a given reference point, e.g. mating or fertilization.

Infanticide

Further information: Infanticide (zoology)

Infanticide is a behavior that occurs in many species where an adult kills younger individuals, including eggs. Sexual conflict is one of the most common causes, although other cases are seen, such as male bass eating their own juvenile descendants.^[1] It is usually the males who perpetrate such behavior, though it is not unknown for females to behave in the same way.

Vertebrates have received the most research, with cases such as hanuman langurs, lions, house sparrows and mice being studied. This behavior also occurs in the invertebrates, however. One such case is the spider Stegodyphus lineatus, where males invade female nests and toss out their egg sacs.^[2] Females only have one clutch in their lifetime, and experience reduced reproductive success if they lose them. This results in vicious battles in which injuries and even death are not uncommon. Jacana jacana, a tropical wading bird, offers one example of infanticide by the female sex.^[3] Females guard a territory while males care for their young. As males are a limiting resource, females will commonly displace or kill their young. Males then mate with them and care for the young of the female which destroyed their previous offspring.

This behavior is costly to both sides, and counter-adaptations have evolved in the victim sex ranging from cooperative defense of their young to loss minimization strategies such as aborting existing offspring upon the arrival of a new male (the Bruce effect).

See also

• Chicken (game)
• Extra-pair copulation
• Genomic imprinting
• Intragenomic conflict
• Parent-offspring conflict
• Reproductive isolation
• Sex chromosome
• Sexual cannibalism
• Sexual harassment
• Sexy sons hypothesis

Notes

References

• Arnqvist, G. & Rowe, L. (2005) Sexual conflict. Princeton University Press, Princeton ISBN 0691122172
• Thierry Lodé, (2006) La guerre des sexes chez les animaux. (The war of the sexes in animal kingdom) Odile Jacob Eds, Paris