Fight or flight? How birds are helping to reveal the mysteries of
evolution
A blend of natural and sexual selection sent birds skyward

Date:
February 24, 2022
Source:
University of Massachusetts Amherst
Summary:
New research uncovers the negative link between flight-worthiness
and fight-worthiness in birds. Evolutionary pressure demanded
that birds could either fly or arm themselves -- but not
both. Furthermore, the new research suggests that developing wings
and not bony spurs involved both sexual and natural selection. This
insight helps us better understand how the enormous diversity of
life and earth came to be.



FULL STORY ==========================================================================
New research from the University of Massachusetts Amherst uncovers
the negative link between flight-worthiness and fight-worthiness in
birds. Evolutionary pressure demanded that birds could either fly or arm themselves -- but not both. Furthermore, the new research suggests that developing wings and not bony spurs involved both sexual and natural
selection. This insight helps us better understand how the enormous
diversity of life and earth came to be.


========================================================================== Beetles do it, deer do it, even crabs in the sea do it. But birds
don't. Carry weapons that is. "It's kind of puzzling," says Joa~o
C. T. Menezes, graduate student in the Organismic and Evolutionary Biology Program at UMass Amherst and lead author of the new paper, published
recently in Ecology Letters. "Birds have such spectacular songs, plumage
and dances, but they mostly don't have specialized weapons. It's strange because dancing, singing, fancy feathers and fighting are all ways of successfully obtaining a mate, and often go together." To understand why, Menezes and his co-author, Alexandre V. Palaoro of Clemson University,
went searching for two things: a dependable estimate of how many species
of birds do in fact carry weapons, and a way of measuring how much,
and how well, different species fly.

It turns out that, although the vast majority of birds are unarmed,
a small percentage, 1.7% do pack weapons in the form of bony spurs on
their legs. To measure different species' flight aptitude, the researchers relied on the hand- wing index, or HWI, an enormous dataset that evaluates
more than 10,000 species of birds and which lets researchers compare
how efficiently different birds are at taking wing.

Menezes and his coauthor then compared the two sets of data and found a striking correlation: "the best fliers tend to lack spurs," says Menezes,
"and the most heavily armed fighters tend to struggle in the air." All
of which immediately begged the question, why? To answer that, the
researchers ran a number of simulations and models, which showed that
bony spurs could impose a heavy evolutionary cost. While it's true that weapons, like plumage, dancing and the ability to sing helps attract a
mate and so are an advantage in sexual selection, the spurs make flying a
more energy-intensive activity. Though it's remarkably difficult to pin
down exactly how this affected the course of evolution, it seems likely
that spurs decreased an individual's ability to fly fast, far and takeoff easily. This is where natural selection should kick in: spurs might make
birds more likely to get eaten or require more food to meet their daily
energy requirements, while their unspurred counterparts can get away,
eat less and live to breed another day.

"This helps explain why birds have an amazing range of plumage, song
and dance, while almost totally lacking in the weaponry department,"
says Menezes.

========================================================================== Story Source: Materials provided by
University_of_Massachusetts_Amherst. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Joa~o C. T. Menezes, Alexandre V. Palaoro. Flight hampers the
evolution
of weapons in birds. Ecology Letters, 2022; 25 (3): 624 DOI:
10.1111/ ele.13964 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220224091129.htm

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