Multiple sexual ornaments

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The multiple sexual ornaments concept, which is a subset of the handicap principle, states that multiple sexual preferences evolve if the cost of choosing a mate does not increase by a female using any additional biological trait in her assessment of potential males.[1]

These traits that a females assesses can included things such as a long tail in a Long-tailed Widowbird or bright colors in a King Bird of Paradise. Only a single preference is evolutionary stable if the assessment of these traits greatly increases the overall cost of choosing a male. The evolution of one preference in a way prevents the other traits from evolving as well, even if these other traits are good indicators of male quality. Thus, a female is wise if she were to narrow her choice down to one trait that was best indicator of how "sexy" the male actually is.

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[edit] Hypotheses

There are several different hypotheses that attempt to explain why a male would have multiple sexual ornaments.

[edit] Multiple messages hypothesis

The multiple message hypothesis states that each trait, or display, reflects only one aspect of the overall quality of the male.[2] Different ornaments therefore signal different kinds of properties of an individual. For instance, one ornament might reflect the amount of food is being consumed by a male if the size of the character was directly related to food intake. Another ornament could be related to overall health of the individual, like how red coloration in certain bird species shows the carotenoid content of the food.

Some ornaments represent long-term or short-term changes in overall condition. Elegant plumes in a bird or antlers in a deer grown once a year could signal the overall condition of an animal during long the period of growth; this is thus an example of a long-term change.[3] Secondary characters like the inflatable bare patches of skin on a grouse species or the colorful patches of skin in a primate species could represent short-term changes.[4]

[edit] Redundant signals hypothesis

The redundant signal hypothesis assumes that a single secondary character can only best show partial representation of overall condition.[5] Thus, a female ought to look at multiple sexual traits of a male if she wants to get an overall view of the male's quality. The reason this is important is because of the possibility that a female chooses a male that is of poor quality: if each ornament reflected the male's quality with a certain error, then mate choice based on a single trait would lead a female to select a male in poor condition rather than one in great condition.

[edit] Unreliable signals hypothesis

The unreliable signal hypothesis suggests that some signals are unreliable indicators of overall male quality.[6] Therefore a female should look at multiple traits because one trait could be misleading; it could be cheaper to produce in terms of energy usage.

[edit] Multiple receiver hypothesis

The multiple receiver hypothesis proposes that a male displays multiple traits because more than one individual of either the same species or a different species is looking at the male.[7][8] For instance, one trait that a male bird could possess is a long tail. This could be the trait that is selected by the female. In addition, this same bird could also possess a beautiful red collar, which is instead looked at by other males of the same species. The level of red on a bird could indicate how strong he is in male-on-male competition of territory. The brightest males with the longest tails therefore would have the best territories and the most females.

[edit] References

  1. ^ Iwasa, Yoh & Pomiankowski, Andrew (1994), “The evolution of mate preferences for multiple sexual ornaments”, Evolution 48 (3): 853-867 .
  2. ^ Johnstone, Rufus A. (1996), “Multiple Displays in animal communication: 'backup signals' and 'multiple messages.'”, Philosophical Transactions: Biological Sciences 351 (1337): 329-338 .
  3. ^ Moller, A. P. & Pomiankowski, Andrew (1992), “Why have birds got multiple sexual ornaments?”, Behavioral Ecology and Sociobiology 32 (3): 167-176, DOI 10.1007/BF00173774 .
  4. ^ Changizi, Mark A.; Zhang, Qiong & Shimojo, Shinsuke (2006), “Bare skin, blood, and evolution of primate colour vision”, Biology Letters 2 (2): 217-221, DOI 10.1098/rsbl.2006.0440 .
  5. ^ Jawor, Jodie M. & Breitwisch, Randall, “Multiple Ornaments in male northern cardinals, Cardinalis Cardinalis, as indicators of condition”, Ethology 110 (2): 113-126, DOI 10.1111/j.1439-0310.2003.00962.x .
  6. ^ Omland, K. E. (1996), “Female mallard mating preferences for multiple male ornaments”, Behavioral Ecology and Sociobiology 39 (6): 353-360, DOI 10.1007/s002650050301 .
  7. ^ Pryke, S. R.; Andersson, S. & Lawes, M. (2001), “Sexual selection of multiple handicaps in the red-collared widowbird: female choice of tail length but not carotenoid display”, Evolution 55 (7): 1452-1463 .
  8. ^ Cavert, Gemma; Spence, Charles & Stein, Robert E. (2004), The Handbook of Multisensory Processes, Cambridge: MITP, p. 246 .