Lec 11 Teaching Prep: Part 2 — Price-Waldman Deep Dive + Cases 1-4

Lecture 11 Teaching Prep. Part 2. The Price Waldman Mini Deck and Cases 1-4.

Welcome back, Michael. Part 2 covers the Deep Dive on Price Waldman 2025

and then the first 4 case studies. About 25 minutes of audio for around 25 minutes of lecture time.

This is where you transition from the recap into the substantive new material of the lecture

and your single biggest risk in the stretch is over investing in the price

Waldman material and running out of time for cases. 12 minutes on the mini deck. No more.

The cases are where the framework gets ratified and you cannot skip them. Let us start with the mini

deck. After your design rule slide where you said before we go there, let us deep dive the paper

that just generated all of this. You advance into slide 6. Price Waldman 2025, what the paper tested.

This is your first mini deck slide and it lasts about 90 seconds. The slide has the figure

2A image on the left. That is the sampling diagram. 12 focal patches across 6 Tangara

Tannagers species, 6 Caratanoid patches, 6 structural patches, females and males. On the right

is a hypothesis card with four numbered hypotheses. Open with the data set. Price, Waldman and colleagues

science advances December 2025. The data set on the left is figure 2A. 12 focal patches across

6 Tangara species, 3 Caratanoid and 3 structural preside, females and males. Why Tangara? Because the

genus contains both color mechanisms in one radiation. That phylogenetic control is what makes the

comparative test rigorous. Then walk through the four hypotheses on the right card. One, are hidden

acromatic layers correlated with the visible color above them? Two, does the rule apply to both

Caratanoid and structural patches? Three, does it explain dichromatism between males and females?

Four, is it conserved across the broader colorful passerine radiation? Then deliver the methodological

point that justifies the whole mini deck. The genius of this design is that it tests the rule

across both color mechanisms simultaneously. If only the Caratanoid patches showed white

underfeathers, you might argue it is a feature of pigments that they need a backing for saturation.

If only the structural patches had black underfeathers, you might argue it is about preventing

washout. Showing both patterns in one comparative tanager radiation rules out single mechanism

explanations. Say that out loud at full energy. It is the conceptual reason students should care

about a four hypothesis paper instead of a three hypothesis paper. Then bridge. How did they test this?

Four lines of evidence. Advanced. Slide 7. Four lines of evidence. The slide is a two by two

grid showing figure one panels a through D. Confocal microscopy on top left. Schematic on top right.

Specimens on bottom left. Reflect in spectra on bottom right. Walk through the two by two quickly

about 60 seconds total. Panel A. Confocal microscopy. They imaged feather cross sections directly

and saw the acromatic backing layer in the microscope. Panel B. The schematic. The design

rule made explicit. Panel C. Specimens with the colorful tips removed. Empirical demonstration

on real birds. White layer revealed under Caratanoid patches. Black layer revealed under structural

patches. Panel D. Reflect in spectra of the acromatic layers themselves. Quantitative confirmation.

Then deliver the methodological synthesis. Microscopy plus schematic plus specimens plus spectroscopy.

One rule for converging methods. Each method could have falsified the design rule. None did. That is how

you know it is real. Drop a project pointer here. When you propose a hypothesis about your fish

this is the level of methodological convergence to aim for. Don't rest on one demo. Multiple methods,

multiple measurement scales, all converging on the same answer. That is what an A-grade analysis

looks like in this course. Now slides 8 through 11 are the four method rows in figure 3. Each one

is a 30 second slide. Walk through them briskly. The point is that the same pattern shows up in

four independent measurements at different scales. Don't dwell on the data. The pattern is the

lesson. Slide 8. Method 1. Multispectral Photography. Figure 3 row 1. Whole feather lightness and

saturation extracted across six channels. The Caratanoid case is Tangara Mexiconis belly.

The structural case is Tangara Visoria's crown. Same patch type within each species.

Different hidden acromatic layer. Measurably different brightness and saturation distributions.

Tell students. Same color mechanism. Different acromatic backing. Different visible color. That is

the pattern. We are going to see it three more times in three more methods. Slide 9. Method 2.

Micro spectrophotometry. Figure 3 row 2. Drilling down. Single feather reflectance.

Caratanoid example. Tangara Seladon Rump. Structural example. Tangara Sino-Sephalocrown.

Same comparative logic at finer measurement scale. Reflectance curves shift

identically with the acromatic backing in both cases. Same result. Different method. 30 seconds.

Slide 10. Method 3. Hyperspectral Imaging on specimens. Figure 3 row 3.

Propixel hyper spectral imaging on intact specimens. The star here is Tangara Kylensis.

The same male individual has a Caratanoid patch on the rump and a structural patch on the belly.

The acromatic layer dependent pattern shows up in one bird. Individual level effects controlled.

One bird, two patches. Same mechanism bilayer signature. This is the cleanest possible test

because the only thing varying is the patch type within one bird. Worth flagging that to students

who care about methodology. It is a beautiful design choice. Slide 11. Method 4. Optical layering model.

Figure 3 row 4. Three rows of empirical data. One row of theoretical prediction.

The simulation reproduces the observed brightness and saturation differences. Theory matches data.

Closes the loop. Then add the project pointer. When you model your fish reflectance later in the term,

the same logic applies. Model and measure. Look for convergence. That is how you make a strong inference.

Theory plus data is stronger than either alone. Then the bridge sentence. All four methods agree.

Now, does this rule explain something biology has long puzzled over? Sexual dichromatism.

Advanced. Slide 12. Dichromatism comes from the layer. Not the pigment. This is the juicy slide of the

mini deck. About two minutes. Figure 4 on the left shows three keratinoid patches across three species.

Tangara parsodaki crown. Tangara arthas crown. Tangara salad on rump. The right side has a card

explaining dichromatism and the finding. Open with the question. What is dichromatism?

Males and females of the same species differ in apparent color. The classical assumption,

going back to hill, McGraw, decades of work, was that males have more keratinoid. Better diet,

brighter pigment. Then deliver the finding with appropriate weight. Price-waltman complicate this

picture. The male female difference in these patches is not primarily in pigment composition.

It is in the architecture of the acromatic layer underneath. The hidden layer architecture is

sexually selected. The pigment chemistry isn't. Pause for two seconds. This is genuinely surprising.

Let students sit with it. Then explain why it matters. Because the acromatic layer is a developmental

and structural trait, dichromatism is reporting on a different axis of male quality, developmental

fidelity and structural integrity, then keratinoid pigment alone, which reports diet and parasite

load. Multidimensional honest signal living in different feather layers. Connect this forward to

LEC-16 when you cover sexual signaling. This is going to come back. Then deliver a project hint.

For your fish projects, if your species shows sexual dichromatism in a keratinoid patch,

do not assume more pigment in males. Test the iridipore layer underneath too. The same logic could

apply. That is a substantive new hypothesis you can hand a student doing the project. Then bridge.

So that is dichromatism in the TANager radiation. But is the design rule a TANager quirk or a deeper

signature? Advance. Slide 13. Same rule, all colorful passurines. Figure five on the left, the eight

family phylogeny. Right side, the big point card. About 90 seconds. Open with the comparative spread.

Eight families surveyed across the passurine radiation. Both major clades, subocides and

all signs. Pity. Tham no phility. Frenary ade. Piperty. Coattingity. Ecterity. Passurality. Thropody.

In every family that has both keratinoid and bar based structural plumage, the same design

rule applies. White under pigment. Black under structure. Then deliver the conservation argument.

This isn't a TANager quirk. It is a passurine wide design rule.

Conserved across 50 plus million years of independent evolution. That is the signature of a strong

selective optimum. If this were just a TANager level quirk, it could be evolutionary contingency.

Across eight families converging on the same hidden layer architecture, that tells you natural

selection has independently rediscovered the same design solution. Take home. Hidden acromatic

feather layers are themselves a phenotype with deep evolutionary history. When you analyze your

reef fish, ask the analogous question. What is the layer under the patch? The chromata force

stack from LEC9 is doing the same job in fish skin that the acromatic feather layers are doing

in bird feathers. Then transition. Okay, we have spent the recap deep diving into one paper.

Now back to today's framework. Advance. You are now leaving the mini deck. The next stop is the

roadmap. Then the framework. Then the flamingo anchor. All of which are covered in part one of your

prep. In the live lecture, you do them right here in sequence. In this prep audio, we already

rehearse them. You can mentally rejoin part one around the working definition slide if you need

to refresh. Then move on into the case studies. Block three. The case studies. This is the longest

single content stretch of the lecture. And it has the highest density of content per minute.

Eight cases plus a think-pair share in the middle. Cases one and five are the load bearing ones.

Cases two and four are convergence anchors. Cases three, six, seven, and eight are nuance.

Treat them accordingly. Case one, green parrots. This is the textbook case, and it deserves about

three minutes. Open with a hook that lands hard. Most green parrots have NO green pigment. Zero.

Their green is a mixed mechanism color produced by two layers of physics and chemistry in the same

feather barb. Pause after no green pigment. Zero. The pause is the lesson. Students assume green

animals contain green pigment. The whole lecture pivots on dislodging that assumption. Then the

recipe. Layer one is structural blue. Spungy keratin with quasi-ordered air voids in the feather barb.

Coherent scattering, broadband peak around 450 nanometers. Same family of mechanism as a blue

j feather. You can name check the blue j here. Students saw it in lec10 and it builds the bridge.

Bleach the feather with methanol. The yellow pigment dissolves. The feather appears blue.

That is one of the most striking demos in feather biology. Layer two is yellow pigment.

Cytico-Folven. This is a parrots-specific pigment. Linear polyene similar in architecture to a

keratinoid, but synthesized an ovo by the bird rather than acquired through diet. That phrase

synthesized an ovo is worth saying because it distinguishes Cytico-Folven from keratinoids.

Keratinoids come from food. Cytico-Folven comes from the bird's own metabolism. That is a major

evolutionary innovation in parrots. They escaped the dietary dependency that constrains keratinoid

based color in songbirds. Grind the feather. The structure is destroyed, but the pigment survives.

You get yellow powder. Then the math. Blue plus yellow. Subtractive color mixing. Net result

green. Say it is a recipe. Blue plus yellow equals green. Pause. Then deliver the diagnostic.

Three independent experiments confirm the two mechanism story. Bleach yields blue. Grind yields

yellow. Tilt the intact feather. The blue component shifts angle. The yellow does not. Three

independent manipulations. Three independent confirmations. This is the cleanest mixed mechanism

biology. Both contributions are separable. Both are removable. Both are diagnosable. Tell students

to remember this case if they remember nothing else. Citations on screen. Dyke 1971. Strati

at all 2001. Magra and Nogare 2005. Acknowledge them. Move on. Don't linger. Case 2. P-cocks

2 minutes Max Rosemarie did P-cocks last Thursday. You are going one click deeper. Z-at all 2003. PNS.

Every color in a P-cocks-eye spot. Blue. Green. Yellow brown. Copper. Is made by the same

materials with different spacing. Melon and rods in a 2D hexagonal lattice with keratin matrix

between rods and air holes along the rod axis. Then the punch table. Lattice spacing 140nm

gives blue. 150 gives green. 165 gives yellow brown. 185 gives copper. One material. One molecule.

For colors. Geometry alone produces the variation. The conceptual move here is the second punch line.

Is the peacock a mixed mechanism? Yes and no. Yes, because both melanin and structure are involved.

No, because melanin in peacocks isn't acting as the chromo for. Melonin isn't selectively absorbing

visible light. Melonin is the high refractive index-filled block. The category pigmentary versus

structural begins to blur. This is your first taste of what the continuum will resolve. Say it

explicitly. In parrots, pigment and structure are separable contributions. In peacocks, the pigment

is the structural element. We will come back to this on the continuum slide at the end of class.

That forward reference is teaching architecture. Students should hear continuum three or four times

before they see the slide. Case three, butterflies, papillos swallowtails. Lucusic at all 2001,

proceedings of the Royal Society B. Two minutes. The recipe is Kighten Multi-Layer plus

papillochrome pigment. The multi-layer reflects in the blue green range. The papillochrome absorbs

UV and short wavelength blue and fluoresces yellow green. Crucially, the two contributions interact.

The structural element creates a light trap cavity. The little bit of light that gets absorbed

excites papillochrome fluorescence. The emitted yellow green light gets channeled by the multi-layer

in specific directions. Net effect, the wing looks more saturated and brighter than either pure

structural or pure pigment color would predict. This is the first synergistic, not just additive,

case in the lecture. Underline the word synergistic. The structural element changes how the pigment

radiates light. Same physics is being exploited in solar cells, LED phosphors, and photonic crystal

lasers today. Parafluorescent dye with a periodic structure, you get directional narrow band emission.

Butterflies got their 100 million years before us. That is a one line aside, not a tangent.

Say it and move on. Case four, dual beetles. Two minutes. The Presity and Satonini.

Chris Acroof full jadisima on the slide. Illetra contain five to 20 alternating layers of

chitin and melanin rich chitin. Refractive index contrast around 1.56 versus 2.0. Strong multi-layer

interference. Reflectance peaks anywhere from 400 to 700 nanometers depending on layer thickness.

The teaching beat is melanin's three jobs in one molecule. One. High refractive index,

strong interference. Two. Light absorber, prevents wash out. Three. Sclaratization of the

cuticle. Tough armor. One molecule. Three jobs. Pigment, structural element, structural protein.

Then the convergence beat. Birds use keratin plus melanin. Beetles use chitin plus melanin.

Different lineages, different proteins, same trick. Convergence on a physical principle,

not on a developmental gene. This is your second best opportunity in the lecture to see

the comparative biology insight. Don't oversell it, but do say convergence on a physical principle

out loud. The diagnostic in dual beetles is the most extreme version of mixing in the case set,

both grinding and bleaching eliminate color. There is no separable pigmentary contribution.

The pigment I ask the structure. This case will live on the far end of the continuum at position five.

End of cases one through four. Check your watch. You should be at minute 45 of the lecture. Give

or take two minutes. If you are past minute 50, accept that you will need to compress one of

cases five through eight. Cases six and seven are the most cuttable. Don't cut case five,

the tree frog, and don't cut case eight, the blue tang, because those are the project tions.

End of part two. Part three covers the first tps, the four answer cases for that tps,

the second tps, the continuum, the synthesis, and the closing. See you in part three.