Why Charles Darwin Is Smiling

Snail Kite, Pantanal, Brazil

WC suspects that Charles Darwin, wherever he is now, is smiling.

The last few months have provided wonderful examples of evolution in action. Here are two.

The Snail Kite is a threatened species. It’s primary prey is the native Apple Snail (Pomacea paludosa), but the Apple Snail is threatened by an invasive species of snail, the Island Apple Snail (Pomacea maculata), a much larger congener of the kite’s native prey.

Size Comparison: Apple Snail and Island Apple Snail

The Island Apple Snail is yet another example of a species introduced by humans that is disrupting ecosystems. The Snail Kite’s bill is specifically adapted to pull the Apple Snail’s body out of its shell. The bill is too small to pluck the Island Apple Snail out.

The much larger invasives are also hard for Snail Kites, especially fledglings, to handle. Their talons, evolved to grip the very slippery shells, cannot hold the larger shells.

But the Snail Kite, against all expectations, is adapting. It is evolving to cope with the new prey. New generations of Snail Kites have evolved longer bills, the better to extract food from those bigger shells. And the birds themselves are larger, and have evolved larger talons, to deal with the larger prey.

Researchers in Florida have documented longer bills, longer talons and bigger birds among Snail Kites living in areas with the invasive Island Apple Snail, as compared to areas not yet invaded. Evolution in action, folks.

 

a–c, Estimates (±s.e.; n = 590) of additive genetic variance (V A), environmental variance (V E) and heritability (h 2; the proportion of total variance of a trait due to additive genetic variance). Significant changes in variance components are denoted by an asterisk, and based on 95% confidence intervals for the change in the posteriors of variance components. Nature Ecology & Evolution

Researchers demonstrated that this kind of unexpected, rapid change in a top tier, slowly breeding, vertebrate predator is the result of both phenotypic plasticity, the ability of a living creature’s genes to produce different body types in response to environmental changes, and micro-evolution, changes in the genes themselves.

You want another example? It turns out that the European cousin to the Black-capped Chickadee, the Great Tit (Parus major) has a longer, heavier bill) has in Great Britain than it does in the Netherlands. That bill is also heavier and longer than it was in British specimens taken prior to the 1880s. Why? Because in Great Britain, bird feeders are popular. In the Netherlands, not so much. The Great Tits in Britain have evolved longer, heavier bills to extract seeds from bird feeders and to carry the seeds without dropping them. The researchers even tracked down the specific gene responsible for the adaptation, the collagen gene COL4A5. Even Forbes Magazine noticed the news, not exactly a science journal.

You want yet another example? For decades now, Peter and Rosemary Grant have been documenting adaptive changes in Darwin’s finches in the Galapagos Islands in reaction to seed size changes. The Grants have shown how environmental changes, mostly rainfall variation, triggers different forbs and grasses. That results in different seed sizes and seed structures. The Darwin finches, especially the Medium Ground Finch and the Cactus Finch, evolve different-sized bills to deal with the changing seeds on which they forage. The Grants are the subject of a delightful book, The Beak of the Finch: A Story of Evolution in Our Time by Jonathan Weiner, which won the Pulitzer Prize for General Non-Fiction in 1995.

Evolution is as real as a heart attack, and it’s silly to pretend otherwise. Creationists and Biblical literalists may claim a book written by stone age shepherds is more reliable, and poltroons like the Oklahoma state house may claim otherwise.

But Charles Darwin is smiling.