Revisiting convergence: butterfly wing designs (Introduction)

by David Turell , Monday, November 18, 2019, 23:58 (1619 days ago) @ dhw

Same design but different genes!:

https://www.smithsonianmag.com/smithsonian-institution/what-butterflies-colorful-wing-p...

"Wings start out as wing disks towards the end of the caterpillar stage of metamorphosis. Pre-patterning genes like wntA activate and communicate with different molecules and genes, more or less outlining the master plan for wing pattern. Eventually, these signals determine the identity and position of each wing scale, which develop colorless in the chrysalis at first before pigments get made. (Yellow, white and red are the first colors to emerge; black and darker pigments appear later.)

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"By disrupting the wntA gene in the mutant butterflies, researchers wanted to see how wing pattern changed. If two different species with mirror-image wings under normal conditions both had the gene knocked out, would the mutated patterns look similar across species, or would the genetic mutation lead to different end results for separate species?

"As it turned out, diverse species responded differently to the deactivated gene. Scientists noticed what Concha describes as “a boundary shifting,” often color bleeding into areas that had previously been black. Normally, Heliconius hewitsoni and Heliconius pachinus, whose habitats overlap in western Costa Rica and Panama, share three yellowish-white stripes and a central flare of red. But in the wntA mutants, H. hewitsoni had off-white coloring spread almost throughout its forewing and developed a patch of gray in its hindwing. H. pachinus, in contrast, still had a bold black stripe through its forewing and no gray.

"The discrepancy told the scientists that wntA has evolved to act differently in these distantly related species. If evolution is a maze where the exit is optimal survival, it’s like the species figured out two separate twisting-turning pathways through the genetic labyrinth to arrive at the same color pattern—a result Concha calls “a bit unexpected.” “People would more frequently expect that they would share a common pathway,” she says, especially because these creative genetic pathways cropped up in a relatively short time span; the species diverged between 14 and 10 million years ago.

"The researchers then zoomed in, using a microscope that creates close-ups 15,000 times bigger than their actual size, to look at the texture of individual scales. Different color scales have unique topography, and this closer look confirmed, Concha says, “the gene is controlling the identity of that scale.”

"In these particular butterflies, evolution had happened more speedily and less predictably than scientists tend to expect. In the Current Biology paper, Concha and her co-authors note that evolution is too complicated for generalizations. Still, she says, if evolution took two starkly different paths to pattern near-identical butterfly wings, “It could happen more than we think.”

Comment: In convergence different genes can be used to cause the same result. It must be in how the individual butterfly type expresses the gene. Perhaps a designer is at work?