Sexual conflict

Drosophila melanogaster (shown mating) is an important model organism in sexual conflict research.

Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females.[1][2] In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females due to the anatomical differences of that species.[3] Sexual conflict underlies the evolutionary distinction between male and female.[4]

The development of an evolutionary arms race can also be seen in the chase-away sexual selection model,[5] which places inter-sexual conflicts in the context of secondary sexual characteristic evolution, sensory exploitation, and female resistance.[1] According to chase-away selection, continuous sexual conflict creates an environment in which mating frequency and male secondary sexual trait development are somewhat in step with the female's degree of resistance.[1] It has primarily been studied in animals, though it can in principle apply to any sexually reproducing organism, such as plants and fungi. There is some evidence for sexual conflict in plants.[6]

Sexual conflict takes two major forms:

  1. Interlocus sexual conflict is the interaction of a set of antagonistic alleles at one or more loci in males and females.[7] An example is conflict over mating rates. Males frequently have a higher optimal mating rate than females because in most animal species, they invest fewer resources in offspring than their female counterparts. Therefore, males have numerous adaptations to induce females to mate with them. Another well-documented example of inter-locus sexual conflict are the seminal fluid proteins of Drosophila melanogaster, which up-regulate females' egg-laying rate and reduces her desire to re-mate with another male (serving the male's interests), but also shorten the female's lifespan,[8] reducing her fitness.
  2. Intralocus sexual conflict – This kind of conflict represents a tug of war between natural selection on both sexes and sexual selection on one sex. An example would be the bill color in zebra finches. Ornamentation could be costly to produce, but it is important in mate choice. However, it also makes an individual more vulnerable to predators. As a result, the alleles for such phenotypic traits exist under antagonistic selection. This conflict is resolved via elaborate sexual dimorphism thus maintaining sexually antagonistic alleles in the population. Evidence indicates that intralocus conflict may be an important constraint in the evolution of many traits.[9]

Sexual conflict may lead to antagonistic co-evolution, in which one sex (usually male) evolves a favorable trait that is offset by a countering trait in the other sex. Similarly, interlocus sexual conflict can be the result of what is called a perpetual cycle. The perpetual cycle begins with the traits that favor male reproductive competition, which eventually manifests into male persistence. These favorable traits will cause a reduction in the fitness of females due to their persistence. Following this event, females may develop a counter-adaptation, that is, a favorable trait that reduces the direct costs implemented by males. This is known as female resistance. After this event, females' fitness depression decreases, and the cycle starts again.[5] Interlocus sexual conflict reflects interactions among mates to achieve their optimal fitness strategies and can be explained through evolutionary concepts.

Sensory exploitation by males is one mechanism that involves males attempting to overcome female reluctance. It can result in chase-away selection, which then leads to a co-evolutionary arms race. There are also other mechanisms involved in sexual conflict such as traumatic insemination, forced copulation, penis fencing, love darts and others.

Female resistance traditionally includes reducing negative effects to mechanisms implemented by males, but outside the norm may include sexual cannibalism, increased fitness in females on offspring and increased aggression to males.

Some regard sexual conflict as a subset of sexual selection (which was traditionally regarded as mutualistic), while others suggest it is a separate evolutionary phenomenon.[10]

  1. ^ a b c Danchin, Étienne; Giraldeau, Luc-Alain; Cézilly, Frank (2008). Behavioural Ecology. Oxford: Oxford University Press. ISBN 978-0-19-920629-2.[page needed]
  2. ^ Parker, G. A. (2006). "Sexual conflict over mating and fertilization: An overview". Philosophical Transactions of the Royal Society B: Biological Sciences. 361 (1466): 235–59. doi:10.1098/rstb.2005.1785. PMC 1569603. PMID 16612884.
  3. ^ Cite error: The named reference reducing cost was invoked but never defined (see the help page).
  4. ^ Gissis, Snait B.; Lamm, Ehud; Shavit, Ayelet (2018-01-12). Roughgarden, Joan (ed.). Landscapes of Collectivity in the Life Sciences. MIT Press. p. 228. ISBN 978-0-262-34266-7.
  5. ^ a b Holland, Brett; Rice, William R. (1998). "Perspective: Chase-Away Sexual Selection: Antagonistic Seduction Versus Resistance". Evolution. 52 (1): 1–7. doi:10.2307/2410914. JSTOR 2410914. PMID 28568154.
  6. ^ Lankinen, Åsa; Green, Kristina Karlsson (2015-01-01). "Using theories of sexual selection and sexual conflict to improve our understanding of plant ecology and evolution". AoB Plants. 7: plv008. doi:10.1093/aobpla/plv008. PMC 4344479. PMID 25613227.
  7. ^ Chapman, Tracey; Arnqvist, Göran; Bangham, Jenny; Rowe, Locke (2003). "Sexual conflict" (PDF). Trends in Ecology & Evolution. 18 (1): 41–7. doi:10.1016/S0169-5347(02)00004-6.
  8. ^ Cite error: The named reference fruit flies ACPs was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference arnq was invoked but never defined (see the help page).
  10. ^ T Lodé "la guerre des sexes chez les animaux" Eds O Jacob, Paris, 2006, ISBN 2-7381-1901-8[page needed]