This week’s BEACON Researchers at Work blog post is by MSU postdoc Eben Gering.
Biotic invasions (the Disney version)
Some ecologists have likened invasive species to the army of enchanted brooms in Disney’s Fantasia. In the movie, Mickey Mouse portrays a sorcerer’s bumbling apprentice who uses borrowed magical powers to bring his broom to life. Once the broom has completed an epic chore (intended for Mickey), it divides into millions and millions of brooms that the apprentice is powerless to stop.
A native of Southern Asia, the small Asian mongoose (Herpestes javanicus) was introduced to Pacific and Caribbean islands in a misguided effort to control invasive rats. Image modified from Wikipedia.
Like those pernicious magic brooms, invasive species often begin as small and seemingly harmless propagules that quickly reach high densities via unchecked population growth. And while invaders usually disperse as stowaways, sometimes like Mickey’s broom, they begin as hopeful experiments.
A male and female Lesser ʻakialoa (Hemignathus obscurus), last seen in the year of Fantasia’s theatrical premier (1940). This species is one of several dozen endemic Pacific songbirds driven to extinction by introduced predators and other anthropogenic stressors. Image source: Walter Rothschild. The Avifauna of Laysan and the neighbouring islands with a complete history to date of the birds of the Hawaiian possession. London: R.H. Porter, 1893-1900).
The small Asian mongoose, for example (above), won a free trip to several remote archipelagos in order to help regulate invasive rats. Perhaps you remember the mongoose from Rikki Tiki Tavi1, in which the bold little predator massacres two cobras along with all of their eggs. This predisposition to ovivory (egg eating) came in handy for invasive mongooses2. As diurnal hunters, they seldom encountered island rats (which prefer to forage at night). So instead they ate eggs of native songbirds, many of which lacked evolutionary histories with (and defenses against) terrestrial mammalian predators.
Now cited as one of the world’s 100 worst invaders3, the mongoose has already abetted several dozen bird extinctions… each species irreplaceable, each irrevocably gone.
How the chicken crossed the sea (a case study of invasion)
Most of Hawaii’s non-native birds have faired better than native counterparts. For example, wild chickens have overrun Kauai – perhaps helped by the island’s lack of mongoose and other predators. These birds are somewhat difficult to classify (invasive? exotic? Polynesian legacies?) since neither their origins nor their ecological impacts have been established. Museum specimens indicate that Red Junglefowl (Gallus gallus; the chicken’s closest living relative), were introduced to Hawaii by ancient Polynesians, but it’s unclear if they persisted. According to many Kauai locals, modern wild chickens instead descend from livestock that went feral after recent hurricanes (see figure below). Scientific studies of Pacific chickens (both morphological and genetic) have reached similarly conflicting conclusions4,5,6.
Census data from feral chicken populations on Kauai confirm reports by Kauai locals of recent, exponential growth coinciding with hurricane events. For additional details, refer our recently published study7 (from which this figure was modified).
Our team recently completed in depth analyses of feral chicken genomes, morphologies and behaviors7. Here are our key findings:
- Some individuals’ genomes “matched” DNA sequences from ancient Kauai fossils (consistent with ancient Polynesian origins).
- Other individuals’ genomes match European breeds domesticated for food production and later distributed worldwide (consistent with recent feralisation).
- Individuals’ genomes, behaviors and morphologies exhibit tremendous variation, and show patterns consistent with hybridization between Red Junglefowl and domesticated chickens.
A feral rooster from Kauai displaying the plumage phenotype that is typical of Red Junglefowl (Gallus gallus), the ancestor of domesticated chickens. Red Junglefowl were spread throughout the Pacific by ancient Polynesians prior to European contact, and before the development of modern, food production G. gallus breeds. We found molecular, morphological, and behavioral signatures of Red Junglefowl ancestry, but also derived traits, such as yellow legs (pictured here), that are unique to domesticated breeds. These patterns are consistent with an invasion of domesticated genes into a Red Junglefowl reservoir population in the Pacific, and with the hypothesis that feralization may have contributed to the exponential growth of Kauai’s G. gallus population during the late 20th century (photo by Dominic Wright).
Kauai’s colorful modern flocks may thus descend from both intentional and accidental introductions, each originating in different places, at differen
t time points, and from different selective environments.
Why we are crowing about feral chickens
While feral chickens pose significant threats to agriculture and human health, Kauai’s G. gallus seem fairly benign (e.g. compared to mongoose). Chickens have even been adopted by locals as their island’s unofficial mascot, which enjoys limited regulatory protections on public land. Perhaps someday our team’s data will prove useful for revisiting local management priorities. Meanwhile though, we have broader (and exciting!) motivations to continue our studies:
- Advancing invasion biology. When we left off with Mickey Mouse (above), he was inundated by monsters of his own making. Fortunately his skilled mentor arrives in time to intervene, and easily puts the brooms to bed. One can hope, Fantasia suggests, that by understanding our errors we obtain the power to correct them. But even if that’s so, we are leagues from understanding population biology well enough to mitigate invasions8. If invasive species are analogous to Mickey’s demonic brooms, then today’s ecologists are well-meaning apprentices at best, fumbling against nature’s complex interdependencies.
- Biosecurity. There are more than 20 billion chickens on earth right now, which comprise humanity’s leading source of animal protein. In contrast, the Red Junglefowl has disappeared throughout its native range due to habitat loss and “contamination” of gene pools by hybridization. It is crucial that we identify and conserve the genetic variation that still remains in the Red Junglefowl. This variation could soon be essential for the improvement and/or evolutionary rescue of commercial chicken breeds. Recent years found chicken producers combating both rapidly evolving pathogens, and fertility issues believed to be products of inbreeding. An exciting new collaboration between MSU and UT biologists will use Kauai’s feral birds to obtain insight to these issues, combining molecular, biophysical and evolutionary approaches.
- Studying evolution in action. Darwin drew heavily from his studies of domesticated species to develop his theory of evolution9. He did this because domesticated taxa display many traits that are readily apparent as product of artificial selection regimes. Broiler chickens are 3x larger than Red Junglefowl, yet somehow mature 2x as fast. Hens from certain egg-laying varieties exceed 300 eggs/year, while Red Junglefowl females produce only a dozen. In Kauai, hybrid G. gallus can potentially inherit both domestication-related enhancements to growth and fecundity, and ancestral abilities to survive and compete in complex natural and social environments. We are eager to learn which combinations of genes and traits are emerging from this ‘evolutionary experiment,’ and to see whether our findings can translate to gains in the sustainability or efficacy of egg and poultry production.
Disney’s Fantasia was based on an 18th century poem by Goethe (German poet, naturalist, philosopher and statesman). The plots of Der Zauberlehrling and of the derivative scenes from Fantasia are basically the same… except for one detail. Whereas Goethe’s sorcerer is unruffled by his pupil’s mistake, his Disney counterpart becomes enraged when he stumbles upon Mickey’s magic mess. Here are two wild guesses as to the reason for that discrepancy: 1) By the time Fantasia was made (1940), we better understood what can happen when people like Mickey muck with nature expecting simple outcomes. 2) While growth of human knowledge and experience might have made us more cautious, it has also produced newer, better, and more idiot-friendly tools for the mucking-inclined. Or maybe, like me, something about Mickey Mouse just irritated him. We stand as little chance of knowing this as we do of deciding if the chicken preceded its egg. My parting gift is this: if anyone ever asks you which came first? and you happen to be standing on Kauai, then you can answer with reasonable conviction: Red Junglefowl did.
1Ricki-Tikki-Tavi is one of the stories from The Jungle Book. It was not included in the Disney version.
2mongooses is, indeed, the plural form of mongoose
3http://www.issg.org/database/species/search.asp?st=100ss
4Condon T (2012). Morphological detection of genetic introgression in red junglefowl (Gallus gallus). MS Thesis, Georgia Southern University.
5 Storey AA, Ramırez JM, Quiroz D et al. (2007) Radiocarbon and DNA evidence for a pre-Columbian introduction of Polynesian chickens to Chile. Proceedings of the National Academy of Sciences, 104: 10335–10339.
6 Thomson VA, Lebrasseur O, Austin JJ et al. (2014) Using ancient DNA to study the origins and dispersal of ancestral Polynesian chickens across the Pacific. Proceedings of the National Academy of Sciences, 111, 4826–4831.
7Gering 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.
8Bock, Dan G., Celine Caseys, Roger D. Cousens, Min A. Hahn, Sylvia M. Heredia, Sariel Hübner, Kathryn G. Turner, Kenneth D. Whitney, and Loren H. Rieseberg. (2015) “What we still don’t know about invasion genetics.” Molecular ecology
9Darwin C. (1871). On the origin of species by means of natural selection. Murray. London.
For more information about Eben’s work, you can contact him at geringeb at msu dot edu.
