“Evolution is chance caught on the wing.” Henry Walter Bates and Batesian Mimicry – Bates collected 14,712 different animal species during his 11 years on the Amazon. Returned to England just prior to publication of Darwin’s The Origin of Species. In one of his first letters to Darwin, Bates stated, “ – Bates studied insects, especially butterflies, where protection from predators was provided by __________________________________ _________________________________________________________ Bates observed that birds found certain butterflies to be edible and others noxious. Birds learned to distinguish between the two types based only on a few experiences. ___________________________________________________________________ 1

– Bates wrote, “... On these expanded membranes nature writes, as on a tablet, the story of the modification of species, so truly do all changes of the organization register themselves thereon.” 2

– “As the laws of nature must be the same for all beings, the conclusions furnished by this group of insects must be applicable to the whole organic world... “ – The butterfly wing served as a canvas for the evolution of thousands of color patterns. – __________________________ __________________________ ____________________________ 3

The Coloration of Butterfly Wings... Pure chance or could it be... 4 In current times the observations begs the question “what are the genetic and developmental mechanisms for making these coloration patterns?” ___________________________________

The Ground Level Plan For Butterfly Wing Pattern Stichophthalma camadeva 5 Taenaris macrops A different degree of representation of the ground plan

What Did Butterflies Invent? 1)Wing Scales 2)Coloration 3)Geometrical Patterning System 6

1)Scales – Greek, lepis, meaning scale or flake; ptera, winged creation: Lepidoptera – One scale is produced by a single cell. Scales have been found to evolve as modifications of the sensory bristles on insects. They flattened and widened. ________________________________ 7

– Tool Kit Genes 8

2)Coloration -Each scale is a particular color, which can be seen at high magnification. -Individual scales may be entirely different hue than their neighbors. -_______________________________ _______________________________ 9

3)Geometrical Patterns on the Wings There are developmental pathways that organize the pattern. Eyespots: concentric rings of scales of different colors. Proposed role: to where are “you,” the predator, attracted? Or to what part of the butterfly are you attracted? How did all these pattern elements get made or evolve? 10

Making Eyespots: Teaching Old Genes New Tricks – It All Begins In the Caterpillar Each wing forms from a flat disc of cells that grows a lot during larval development. – Then you have the chrysalis... And just before the butterfly emerges the final color pattern is filled in. 11

– The position of the eyespots is decided in the caterpillar. Concentric ring patterns of the eyespots are induced by an “organizer,” which is at the center of the developing eyespot. 1980: Fred Nijhout of Duke Univ. killed a tiny patch of cells and no eyespot formed. When this group of cells was isolated from the developing butterfly wing in the first day of the chrysalis stage and transplanted to a site elsewhere in the wing, a new eyespot now appeared. Only cells at the future center of the eyespot had this property... Called the “focus.” – So what are the genes responsible for this organizer??? 12

Finding the Eyespot Organizer’s Gene: The Questions 13

How Could They Ever Find A Starting Place? – They knew a lot about fruit fly wings. Insect wings evolved only once so what they knew about the tool kit genes of insect wings should apply to their counterparts of the butterfly wing. – They compared Buckeye butterfly tool kit genes and fruit fly tool kit genes that were homologous. That is, they were both involved in the building and patterning of wings. – But just because their genes were there... 14

They needed to prove that the genes were actually involved.. Active... Being transcribed.. for the purpose of wing patterning and at the time when patterns were actually being set up. 15

Their Experiments – Location of Expressed Genes ______________________________________________________ Some Results – All of the butterfly genes were expressed in parts of the butterfly wing disc that corresponded to the same geographical region where they were expressed in the fruit fly. So that is a “good” sign. Conclusion: the butterfly wing had common geography to the developing fruit fly wing. – Top, bottom, front, rear of each wing and the wing edges were all delineated by the same genes in both species. – Conservation of an ancient wing design. 16

– But there were some patterns of gene expression in the butterfly wing that had no counterparts in the fruit fly. Aha!!! A difference! There were spots in the caterpillar discs precisely where the eyespots would appear 1 week later in development. And these spots were made by just one of several genes. It was named Distal-less or Dll. – Significance? Well, it wasn’t simply finding the gene’s function but that this particular gene had other functions in other organisms... building fruit fly limbs and arthropod limbs. » _______________________________________________ _______________________________________________ » Dll turned out to be deployed in the distal parts of butterfly limbs, limbs of crustaceans, spiders and centipedes. » _______________________________________________ – __________________________________________________ __________________________________________________ __________________________________________________ 17

» When mutated, Dll caused the distal parts of fly limbs to be lost. » Dll turned out to be deployed in the distal parts of butterfly limbs, limbs of crustaceans, spiders and centipedes; vertebrates and invertebrates. » It played a role throughout arthropod limb formation. » In completely unrelated species, chicken’s legs, fish fins, tube feet of sea urchins, all have a Dll gene and it is associated with things that stick out of animal’s bodies. – This was a tool-kit gene involved in building very different structures that only share, at most, the common feature of projecting away from the main body. 18

How did Distal-less or Dll learn the new trick of making spots in the wing? – Dll retained its old job but this tool kit of genes and the spots of Dll expression were a new trick. – So the role of Dll is at another time and place in wing spot development and it controls a different pattern and all this has to do with predator / prey relationships... Fitness... Natural selection... Being around or not being around. 19

How did Distal Less “Learn” This New Trick of Making Spots In the Wing? – ___________________________ – The gene acquired a new switch that coordinates the longitude and latitude on these spots on cells. – ____________________________ ____________________________ ____________________________ ____________________________ ____________________________ ____________________________ ____________________________ 20

Is That All There Is? – No, there were other proteins, tool kit proteins, involved in making these concentric rings. – So somehow each ring of scales receives different instructions. That’s pretty darn complicated!! – Could signals from the “focus” induce the surrounding cells to be different colors???? And different instructions at the different distances?? Ah, come on. 21

Two more took kit proteins – Spalt and Engrailed – Both are expressed, spalt in a spot and engrailed in a ring, in the African species, Bicyclus anynana. – Spalt tool kit protein pattern precisely marked the future black ring. – Engrailed pattern did the same for the gold ring. – The genes for spalt and engrailed are both “old.” So the new role in butterflies is due to a new genetic switch controlling each gene thus provided a new job. 22 Bicyclus anynana: the eyespot has a white center, surrounded by the black ring which in turn is surrounded by a gold ring.

The Distal-less gene switches. – _________________________________________________________ ____________________________________________. ________ // ________// _______________ – In butterflies, however, a new switch, S, has evolved that controls the expression in eyespots. ________//________//______//__________ 23 gene ELW WLES embryo wing leg embryo leg wing eyespots

How Do Butterflies Change Their Spots? – The Distal-less eyespot switch, S, can be modified. – Environmental changes in rainfall or temperature may affect hormone presence or absence and the hormones will affect the genetic switches. – Within the genetic switch there are specific places where tool kit proteins bind. These specific places or signature sequences can also change with time. 24 Dry SeasonWet Season

How Do Butterflies Change Their Spots? – Within the genetic switch there are specific places where tool kit proteins bind. These specific places or signature sequences can also change with time. 25

Mimicry and Color Pattern Evolution – We’ve basically said that the difference in appearance between species or between individuals of the same species, is due to different spatial patterns of pigment synthesis and scale structural colors. – How have these differences, slight or large, affected the evolution of mimicry and its role in natural selection? ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ The goal is to ascertain the connection between fitness, genes and the forms of the colorful patterns. 26