However, because selection is "intrinsic", in the sense that it depends more strongly on the local frequencies of colour pattern than on the abiotic environment, mimicry will contribute to speciation by selecting against intermediates that lie between two adaptive peaks.
This will be similar to other intrinsically selected traits such as such as chromosomal rearrangements and genes under epistatic selection. We know that selection pressures on warning colour and mimicry are intense, and that many of the same principles apply to all these traits. Closely related aposematic species often differ widely in their warning patterns, paralleling the case for chromosomal rearrangements.
Obviously, not all speciation is via warning colour, but warning colour and mimicry are good external examples of exactly those traits which normally have their hidden effects deep within the reproductive system, and do generally cause speciation.
We here cover some evolutionary oddities about the evolution of mimicry. Goldschmidt in , proposed that, while gradualistic, Fisherian multilocus evolution could explain evolution within species, speciation was due to a different process that he called "systemic mutation" - single, massive chromosomal mutations that reorganized the whole genome.
But he suggested that there were also some examples of systemic mutations within species; firstly chromosomal mutations, and secondly in mimicry. He knew that some results on Batesian mimicry showed that single loci apparently radically affected whole colour pattern, and even wing shape traits. Goldschmidt argued that these single genes were systemic mutations using pre-existing developmental genetic pathways present in the model to cause accurate resemblance in the mimic.
In other words, the mimic obtained mimicry without selection, it was a "hopeful monster" whose adaptation was created by a single mutation then preserved by selection, but not constructed by microevolutionary multi-locus selection.
Fisher and his followers took up the challenge, and many experiments were performed on mimetic butterflies in the s until the present day to attempt to refute these heretical ideas. Here, we examine the evolution of mimicry in the light of what is known about the genetics of mimicry, and try to assess how far Goldschmidt was correct.
It was quickly realized that Goldschmidt was wrong on the details. Some of the best examples come from the Asian Batesian mimic Papilio memnon , whose polymorphic females mimic a variety of unpalatable model species, also within the Papilionidae. There are loci with major effect, but there are unlinked components also. When the single major locus in Papilio memnon was carefully analysed, extremely rare recombinants within the supergene were discovered both in laboratory broods, and as rare variants in the wild.
Clarke and Sheppard were able to show that the apparent "single locus" developmental switch was in fact a "supergene" composed of a number of tightly linked elements. The recombining elements could be mapped in order in the manner shown on the overhead. Clearly, then, selection had built up the mimicry "bit by bit", and not via a single mutation. Instead of the single gene nature of the switch locus being evidence for a single locus, we can see that the mimetic polymorphism can ONLY evolve if the genes that are involved exist within a tightly linked section, i.
Here is a selective explanation for the very data that Goldschmidt used as evidence for his systemic mutation theory in mimicry. The major exception is in the narrow hybrid zones between races. Therefore, the arguments applied to Batesian mimicry, that patterns should be inherited at single locus "supergenes", do not apply. On the other hand, it is clear that mimicry is hardly based on multiple unlinked genes of individually small effect, as suggested by Fisher in his theory of evolutionary adaptation.
In this species, the major pattern changes is inherited at relatively few genes or tightly linked gene families. Are such major gene effects a result of developmental genetic constraints? Or is there a selective reason why this might be so? Sheppard and Turner have proposed a selective explanation which seems likely. A small mimetic change away from the mean for each species A or B will be selected against, since the protection will be reduced.
Only a relatively major mutation will bridge the gap. Only B will evolve, and then towards A. Mimicry provides a "rugged" adaptive landscape, with some high adaptive peaks among the possible phenotypes, but many adaptive troughs or lowlands. On the other hand, once near the adaptive peak, climbing the peak is done in the ordinary Fisherian mode, in small steps via polygenic adaptation.
In summary, mimicry is a great example of evolution by natural selection, and has been celebrated for this ever since Darwin first wrote a glowing review of Bates' paper in But there are still many puzzling aspects of mimicry that need work.
The harmless milk snake mimicking the moderately venomous false coral snake is another example of batesian mimicry a tasty treat dressed up as a venomous one. Predators associate the markings with venomousity and avoid it.
But why would a deadly snake need to mimic a less dangerous species? When a predator eats a moderately venomous species it learns that it does not want to eat that or similar prey in the future.
If the predator eats venomous prey and then dies it cannot learn that lesson. The deadly snake, thus, benefits from mimicking a moderately venomous species that its predators have already learned to avoid.
One last form of mimicry is automimicry, which occurs within a single organism. By doing this, they can trick predators into going for their tails rather their heads and avoid fatal attacks. Hairstreak butterflies also present this type of mimicry. They have a spot on the end of their hind wings, the thecla spot, which resembles an eye and little tails behind the spot which resemble antennae. When searching for these creatures, one has to look closely because they can easily be mistaken for just another extension of a tree branch.
While some insects have adpated intricate bodies to conceal their true identities, others are more simply cloaked in colors and patterns that make them easily hidden in plain sight. Grasshoppers and katydids are just two examples. The shades of green that jacket the greater anglewing katydid keep it well hidden among grasses and leafy vegetation. Grasshoppers are also similarly camouflaged to blend in with their surroundings. The appearance of some insects can be quite deceiving, and that deception is intentional and necessary for their survival.
You never know what you might uncover. Monarch Viceroy Other insects are more intricately disguised and resemble other species. Giant swallowtail caterpillar Looper moth caterpillars and walking sticks are other examples of extreme insect mimics. Contributions to an insect fauna of the Amazon valley Lepidoptera: Heliconidae. London 23, — Beccaloni G. Vertical stratification of ithomiine butterfly Nymphalidae: Ithomiinae mimicry complexes: the relationship between adult flight height and larval host-plant height.
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