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New Paper Excited to have our new paper on butterfly dichromatism out in @EvolLetters! We ask: why do male and female butterflies differ in color?
Resolving a 150 year old argument between Darwin & Wallace, using modern methods.
https://onlinelibrary.wiley.com/doi/full/10.1002/evl3.199
A
(1/10)
An Old Argument:
To explain why male birds and butterflies often have different colors than females, Darwin argued that choosy females drives males to become more sexy & conspicuous.
Darwin: Dichromatism occurs when males evolve away from females by sexual selection. (2/10)
To explain why male birds and butterflies often have different colors than females, Darwin argued that choosy females drives males to become more sexy & conspicuous.
Darwin: Dichromatism occurs when males evolve away from females by sexual selection. (2/10)
Wallace disagreed. He argued that brooding on nests and flying around with heavy eggs puts extra predation pressure on females, causing them to become more camouflaged than males.
Wallace: Dichromatism occurs when females evolve away from males by natural selection. (3/10)
Wallace: Dichromatism occurs when females evolve away from males by natural selection. (3/10)
These are claims about evolutionary history; both mechanisms end at the same point (males and females are different), but got there through different mechanisms.
It turns out that in birds, Wallace's model is usually better supported than Darwin's! What about butterflies? (4/10)
It turns out that in birds, Wallace's model is usually better supported than Darwin's! What about butterflies? (4/10)
We used scanned images from a field guide to model the evolutionary history of male and female color of all European butterflies.
The first thing we found is that male color evolves faster. But is this faster evolution actually linked to evolving dichromatism? (5/10)
The first thing we found is that male color evolves faster. But is this faster evolution actually linked to evolving dichromatism? (5/10)
Instead of looking at the average evolutionary rate across the whole tree, we relate the rates to the level of dichromatism along the same branch.
Male and female rates are the same when there is little dichromatism, but males evolve (much) faster in dichromatic clades. (6/10)
Male and female rates are the same when there is little dichromatism, but males evolve (much) faster in dichromatic clades. (6/10)
But is this faster male evolution simply _within_ dichromatic clades, or is it responsible for dichromatism evolving in the first place?
To answer this, we use the direction of color evolution to estimate the male and female contribution to changes in dichromatism. (7/10)
To answer this, we use the direction of color evolution to estimate the male and female contribution to changes in dichromatism. (7/10)
This works by taking the evolutionary vector in 3d color space, and projecting it on the direction of dichromatism. This means we can calculate the evolutionary rates along the axis of dichromatism.
We find that males contribute ~2x as much as females to dichromatism (8/10).
We find that males contribute ~2x as much as females to dichromatism (8/10).
Males evolve faster, especially in dichromatic clades, and specifically along those branches where dichromatism changes most. These results all point in the same direction.
Butterfly dichromatism primarily evolved via Darwin's, not Wallace's, model. (9/10)
Butterfly dichromatism primarily evolved via Darwin's, not Wallace's, model. (9/10)
Thanks a ton to my wonderful co-authors, @Dirk_Zeuss, @ChazotNicolas, @Kallekarlhugo, @LepPhylo, Christer Wiklund, John Fitzpatrick & especially @ChrisWWheat.
Code and data on github: https://github.com/Ax3man/vdBijl_etal_EvolLett_2020
Code and data on github: https://github.com/Ax3man/vdBijl_etal_EvolLett_2020
