Polymorphic Natural Selection
Pervious studies focused on natural selection by predation being a strong contributing factor of polymorphic color distribution in a population. While there is some truth in this model, it may overlook the importance that sexual selection plays, as will be depicted in the following examples.
Many examples demonstrate that animals in a particular species tend to mate with individuals that share similar color patterns, in fact it is rare to see individuals with dissimilar color patterns mate. Gouldian finch, provide a good example of color morphs mating with their respective ideal mate, red with red and black with black. Those finches which may result as a hybrids due to gene flow tend to have lower fitness, which can be seen on the Z chromosome.
The low fitness seen in the hybrid helps maintain the segregated mating tradition. Other examples, such as seen in the buzzard, segregated mating by feather polymorphism are maintained due to an associated heterozygote advantage. In the Cichlids fish, we can see mating preference driven by color polymorphisms. A complex in Nicaragua harbors Midas cichlids, genetic analysis shows that each color morph has accumulated difference in genes. In Amphilophus citrinellus, a population often has 10% golden colored individuals and the other 90% will be black and white. Nearly all copulation events occur between those of the same color, leading to proportional polymorphism. Another species of cichlid, Neochromis omnicaeruleus, seems to be in conflict with color associated mating and sexual selection. Males tend to be a uniform color, while females tend to be blotchy (giving females an advantage to hide among the background). The very few males which do exhibit the blotchy pattern may have an advantage to hide, but a disadvantage when it comes to mate recognition by a female. The issue seems to be that the blotch pattern is firmly linked to a sex determining region, thus, blotch males are rare and not readily identifiable. Another interesting trait that has developed in some female species of birds is aggression towards those that look similar to them. Kind of rare to see and not widely studied, however it may maintain rare phenotypes; being that the rare phenotypes are adventitious, this shows a pattern of negative frequency dependent selection.
Many examples demonstrate that animals in a particular species tend to mate with individuals that share similar color patterns, in fact it is rare to see individuals with dissimilar color patterns mate. Gouldian finch, provide a good example of color morphs mating with their respective ideal mate, red with red and black with black. Those finches which may result as a hybrids due to gene flow tend to have lower fitness, which can be seen on the Z chromosome.
The low fitness seen in the hybrid helps maintain the segregated mating tradition. Other examples, such as seen in the buzzard, segregated mating by feather polymorphism are maintained due to an associated heterozygote advantage. In the Cichlids fish, we can see mating preference driven by color polymorphisms. A complex in Nicaragua harbors Midas cichlids, genetic analysis shows that each color morph has accumulated difference in genes. In Amphilophus citrinellus, a population often has 10% golden colored individuals and the other 90% will be black and white. Nearly all copulation events occur between those of the same color, leading to proportional polymorphism. Another species of cichlid, Neochromis omnicaeruleus, seems to be in conflict with color associated mating and sexual selection. Males tend to be a uniform color, while females tend to be blotchy (giving females an advantage to hide among the background). The very few males which do exhibit the blotchy pattern may have an advantage to hide, but a disadvantage when it comes to mate recognition by a female. The issue seems to be that the blotch pattern is firmly linked to a sex determining region, thus, blotch males are rare and not readily identifiable. Another interesting trait that has developed in some female species of birds is aggression towards those that look similar to them. Kind of rare to see and not widely studied, however it may maintain rare phenotypes; being that the rare phenotypes are adventitious, this shows a pattern of negative frequency dependent selection.