Feral chickens are a-changing: updates on the rapid evolution of Kauai's hybrid Gallus gallus

This post is by MSU research associate Eben Gering.

The author, a collaborator (Kayleigh Chalkowski), and an especially ‘domestic-like’ feral chicken in the Florida Keys

After an hour of trying to trap chickens at Hanalei Beach Park, we had only caught odd looks from locals. Finally, one bold rooster approached our buried net, cautiously tapped the spring-loaded frame, and gave an ear-splitting crow. The whole flock disappeared into the bushes, and I won a high-stakes wager with Kathyrn Fiedler, a local collaborator. “Fine,” she grumbled “they’re not so stupid after all.”

We will contemplate feral chickens’ tenacity and intelligence a bit further on. Meanwhile, if you’re curious what these animals were doing on a beach immortalized by Peter, Paul and Mary1, join the crowd. In an earlier blog entry, I described how DNA sequencing of Kauai chickens and fossils helped unravel their fascinating origins. Like the Hanalei locals, it turns out, these birds are exceptionally diverse. They are descended from both Red Junglefowl, brought to Hawaii by ancient Polynesians, and domestic chickens that arrived later, with western explorers and farmers. Recent hybridization between these ‘wild type’ and domestic chickens produced the highly variable, extremely successful, and ‘not-so-stupid’ flocks that occupy Kauai today2.

Understanding how populations came to be where they are is the central goal of biogeographical research, and it serves many purposes. Distributions of living organisms led Charles Darwin and Alfred Russel Wallace to a theory of evolution supported by countless comparative and experimental studies. Among them are studies of bacterial evolution led by Michigan State colleague Richard Lenski, who also co-founded BEACON to “illuminate and harness the power of evolution in action to advance science and technology and benefit society”.

Feral chickens inhabit most of Kauai’s scenic and variable habitats. This image from Kōkeʻe State Park highlights the mixture of wild (forest) and artificial (asphalt) elements feral chickens navigate on a daily basis.

In support of this mission, biogeographical analyses can help predict where invasive or endangered species might one day thrive.  It is not always clear though, whether and how we should apply this powerful insight. Consider the case of Kauai and its neighboring (Hawaiian) islands. There are both cultural and environmental reasons for conserving the archipelago’s heritage species, which arrived many centuries ago with Polynesian colonists. Today, these animals and plants serve a variety of useful purposes, and they are embedded in the Hawaiian ecosystem and culture. On the other hand, these non-native species also have negative impacts on native wildlife and local residents. Feral pigs, for example, are wreaking havoc on Hawaiian forests and farms. They also create breeding grounds for non-native mosquitoes, which spread human and wildlife diseases.

What about the feral chickens? Local attitudes towards these charismatic and often noisy neighbors are as variable as the chickens themselves. Kathryn, who still owes me a cocktail, is concerned they may transmit bacterial pathogens to local crops. However, as many farmers already know, chickens can also provide ecosystem services like pest control and soil improvement.

For better or worse, feral chickens’ ecological impacts have not been well studied –  this is something my collaborators and I are currently exploring. For now, let me give one fairly simple observation: it’s a pity that so many well-intentioned humans feed feral animals haphazardly. This only boosts populations to higher densities than local resources can support. In Hawaii and elsewhere, I have seen humanitarian efforts backfire, causing both unnecessary animal suffering and environmental degradation. So, if you are moved to help feral animals – please coordinate your efforts with local animal control and wildlife authorities. Thanks!

Getting back to our research update: Dr. Fielder may have lost our bet, but her research is succeeding. Her findings from Kauai will soon help guide intelligent management of feral populations, both in and beyond Kauai. But let’s get back to the apparent intelligence of the Kauai chickens themselves, and some basic questions about its recent evolution. Steven Gould, a celebrated author and evolutionary thinker, once asked what would happen if we could restart earth’s history and watch life evolve again. Would it take similar paths to produce life as we know it? Research from the Lenski lab has given us some clues. If evolution is replicated under carefully controlled conditions, adaptation to novel environments is indeed repeatable… if, and only if, a population crosses a stochastic (randomly attained) threshold of ”background’ evolutionary change.

It turns out evolution is also somewhat repeatable outside of the laboratory. For instance, studies of Caribbean lizards by Jonathan Losos’ group show that animals often evolve predictable forms and ways of life when they colonize similar ecosystems. Surprisingly, these evolutionary changes can occur very quickly – in just a handful of generations or less. If you’re interested in learning more, have a look at Dr. Losos’ new book, about the paradoxical predictability and capriciousness of evolution3.

By studying feral animals, my collaborators and I ask a related, but different question from Steven Gould: what happens when we reverse domestication (a human-directed evolutionary process)? Can evolution in natural environments undo behaviors, or other traits, instilled by centuries of selective breeding? Can we predict such changes, and use them to build better livestock, or protect wild populations? Feral animals abound nearly everywhere humans do, yet neither Lenski’s lab studies, nor Losos’ lizards can tell us precisely how these human-altered organisms will evolve in a human-altered landscape. This is one reason for my fascination with Kauai’s feral chickens. Now that we know where they came from, we can better understand how they are evolving.

DNA sequencing revealed that Kauai chickens are hybrid descendants of wild Red Junglefowl and domesticated breeds. It also suggested Kauai hens might inherit a gene from the Red Junglefowl that enhances their ability to raise their young in the wild. This hen’s offspring showcase the Kauai population’s impressive diversity, which was enhanced by hybridization between domesticated and wild populations.

To learn how chickens have adapted to feral environments, several European collaborators and I are now searching their genomes for signatures of recent, rapid evolution. Analyses by Martin Johnsson, a former graduate student in Dominic Wright’s lab (Linköping University, Sweden) found that genes controlling chicken reproduction and behavior are evolving quickly in the Kauai population4. We have also made progress in identifying the sources of the favored variants (i.e. versions) of the quickly-evolving genes. Care to bet where the winners came from?

You might have guessed that the Red Junglefowl gene variants would outperform the domesticated alternatives. After all, Red Junglefowl thrive in wild Asian jungles without any human help. This prediction is partially accurate: certain ‘wild-type’ (Red Junglefowl) gene variants are, indeed, over-represented in the Kauai population. And included among the genes that follow this pattern is one that critically affects brain development and maternal care behavior. Why is the domesticated chicken’s version of this gene disadvantaged in feral hybrids? We predict experiments will show this reflects their comparative inability to hatch and nurture young in the wild. Perhaps ‘wild-type’ (Red Junglefowl) versions of this gene also help hybrids build brains that can respond to dangers of the wild, such as nosy biologists’ traps. Together with Dominic Wright and Rie Henrickson, we will soon begin testing these ideas, and learn how feral brains and behaviors evolve.

In other compartments of feral chicken genomes, evolution is taking a very different path. For example, evolution has favored the domesticated version of a gene cluster affecting bone growth, comb mass, and egg production in Kauai chickens. We think this may reflect the domesticated chicken’s ability to outgrow and out-reproduce Red Junglefowl, a legacy of selective breeding for streamlined poultry production. For an educational activity exploring this idea (using data you can gather from tourist photos), have a look at our Data Nugget activity.

In this entry, I have focused on what genomic data tell us about the role of hybridization in Kauai chickens’ recent adaptive evolution. Ultimately, though, experimental studies are still needed to truly understand the environmental and social challenges that drive observed genomic changes. Fortunately, with practice and stealth, our trapping abilities have vastly improved. Unfortunately, we still get strange looks when we put them to use. Our understanding of feral chicken behavior and adaptation are also evolving quickly. Stay tuned for the next update, if you’d like to know more.

1 https://en.wikipedia.org/wiki/Puff,_the_Magic_Dragon

2 Gering E, Johnsson M, Willis P, Getty T, & Wright, D (2015). Mixed‐ancestry and admixture in Kauai’s feral chickens: invasion of domestic genes into ancient Red Junglefowl reservoirs. Molecular ecology.

3 Losos, J. B. (2017). Improbable destinies: Fate, chance, and the future of evolution. Riverhead Books.

4 Johnsson, M, Gering E, Willis P, Lopez S, Van Dorp L, Hellenthal G, Henriksen R, Friberg U, Wright D (2016). Feralisation targets different genomic loci to domestication in the chicken. Nature Communications 7: 12950.

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