Sunday, April 4, 2010
Sensory-Bias
On page 166, Coyne uses the term sensory-bias model. He says these models explain sexual dimorphism. From class we already know that sexual dimorphism is the difference in characteristics (i.e. size, color) between different sexes. What are some examples of sensory-bias models and how do you think that sensory-bias models are, as Coyne says, "by-products of natural selection?"
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Coyne cites many explanations for sexual dimorphism and the third one he lists is the sensory-bias model. Coyne notes that "these models assume that the evolution of sexual dimorphisms is driven simply by preexisting biases in a female's nervous system" (166). The sensory bias theory proposes to explain two phenomena: First, it has been used as a hypothesis about signal design, that is, that males evolve traits that stimulate female sensory systems. Second, sensory bias has been used as a hypothesis for the evolution of female preference itself, that is, to explain why females exhibit particular preferences.
ReplyDeleteHowever, the importance of sensory bias as an explanation for the evolution of female preferences remains to be determined (http://cat.inist.fr/?).
Recently, this model has been tested in the cardueline finch (family Fringillidae). This could be cited as an example of the sensory-bias model. The scientists tested the model relative to elongated tail feathers, a widespread sexually selected trait in birds (www.sciencedirect.com). Coyne himself brings up the example of a visual preference for red color because that preference may be beneficial in locating fruits and berries. He also notes that female grassfinches appeared to favor white - possibly in connection to eggs and feathers camoflage.
Now, sensory-bias models are by products of natural selection because often times the traits that females are previously biased towards are traits that help them function in some other aspect of survival. Coyne cites the example of finding food. For example, the preference for red color on males in reference to ripe fruits. Thus, natural selection dicates that the most selectively advantageous traits remain, and in an effort to find an emulation of these traits, females demonstrate sensory bias.
Clearly, this relates to the theme of evolution. Sensory bias models propose that natural selection may often "create preexisting preferences that help animals survive and reproduce", which may demonstrate that certain aesthetic traits seem to be more attractive evolutionarily. However, Coyne notes that in the sensory bias model, the females derive no benefits. However, evolutionarily, certain traits may be demed more selectively advantageous.
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ReplyDeleteSensory-bias models is simply when females have an irrational preference of how a male looks based off of his ability to hold their attention or a pre-existing notion related to their survival that the male displays.
ReplyDeleteAn example of sensory-bias is if a male has larger eyes than the average male of that species and holds a female's attention for longer because of this abnormality. Another example is if a male has a spot of color that the female has associated with survival, thus the female will show sensory-bias.
This is a by-product of natural selection because the females see this variation, which held their attention longer or they associated with survival. This variation can correlate with having offspring that have a better chance of survival, so even if the males make no contribution to raising the offspring, the offspring will naturally have better genes.
Agreeing with Connie, I believe too that although these traits that attracted them to the males have no "evolutionary benefit" the traits appear to yield offspring that have more selective advantages.