Butterfly - not as funky as the other one
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Butterfly - not as funky as the other one
Anyone have an ID? I think it is a type of swallowtail. Location: Pennsylvania
Sue Alden
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rjlittlefield
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Sue,
It's a "Red-spotted Purple", Basilarchia astyanax, or Limenitis arthemis astyanax, or Limenitis astyanax, depending on who you listen to.
Warning: arguably excessive technical detail follows!
In "How to Know the Butterflies, Paul Ehrlich 1961, astyanax was considered to be a distinct species, although Ehrlich also wrote that
The National Audubon Society Field Guide to North American Butterflies, 1981, refers to the whole genus as Basilarchia, not Limenitis, but continues to represent the relationship with arthemis as hybridization between distinct species. BugGuide.net, on the other hand, and other modern publications, have it as a subspecies of L. arthemis.
Whatever one calls the beasts, it seems clear that there's a northern population (arthemis) that looks and acts one way, a southern population (astyanax) that looks and acts another way, and a fairly narrow geographic area where those two forms come together and interbreed freely with no significant penalty to the hybrids. What causes this unusual situation is still under investigation. In a quick Google search just now, I found an abstract as recent as March 2006 addressing this question.
These butterflies occupy a special place in my heart. Back in 1973, when I was taking a college course in Evolutionary Mechanisms, I noticed that our textbook had what seemed to be a rather shaky use of the arthemis-astyanax complex to justify the author's claim that disruptive selection could not cause speciation. Investigating the literature yielded a rather nice class report, since it turned out that within the complex, at least according to data published by that time, there simply was no disruptive selection! I have no idea how the textbook got written as it did, but as an undergraduate student it was notably pleasant to essentially say "Poppycock!" to a chunk of textbook, and get a good grade as a result!
Very nice picture, by the way!
--Rik
It's a "Red-spotted Purple", Basilarchia astyanax, or Limenitis arthemis astyanax, or Limenitis astyanax, depending on who you listen to.
Warning: arguably excessive technical detail follows!
In "How to Know the Butterflies, Paul Ehrlich 1961, astyanax was considered to be a distinct species, although Ehrlich also wrote that
This species is considered by some to be conspecific with the more northern L. arthemis, with which it hybridizes in a narrow zone in southern New England, New York, northern New Jersey, Pennsylvania, Michigan and Wisconsin. The continued distinctness of the parental types in the area of overlap, however, suggests that they are best considered distinct species.
The National Audubon Society Field Guide to North American Butterflies, 1981, refers to the whole genus as Basilarchia, not Limenitis, but continues to represent the relationship with arthemis as hybridization between distinct species. BugGuide.net, on the other hand, and other modern publications, have it as a subspecies of L. arthemis.
Whatever one calls the beasts, it seems clear that there's a northern population (arthemis) that looks and acts one way, a southern population (astyanax) that looks and acts another way, and a fairly narrow geographic area where those two forms come together and interbreed freely with no significant penalty to the hybrids. What causes this unusual situation is still under investigation. In a quick Google search just now, I found an abstract as recent as March 2006 addressing this question.
These butterflies occupy a special place in my heart. Back in 1973, when I was taking a college course in Evolutionary Mechanisms, I noticed that our textbook had what seemed to be a rather shaky use of the arthemis-astyanax complex to justify the author's claim that disruptive selection could not cause speciation. Investigating the literature yielded a rather nice class report, since it turned out that within the complex, at least according to data published by that time, there simply was no disruptive selection! I have no idea how the textbook got written as it did, but as an undergraduate student it was notably pleasant to essentially say "Poppycock!" to a chunk of textbook, and get a good grade as a result!
Very nice picture, by the way!
--Rik
