Organism Displaying Retrogressive Evolutionary Trends? This finding raises intriguing questions about life's developmental paths.
Evolution isn't a straight road to improvement, as we frequently assume. It's far more complex, as shown by the unique case of the Galaapagos tomatoes. These wild-growing fruits are forsaking millions of years of evolution to revive long-lost chemical defenses.
These tomatoes are descendants of South American ancestors, possibly transported to the Galaapagos by birds. To protect themselves against the island's limited predators, the tomatoes have started manufacturing a toxin similar to those produced by nightshades such as potatoes, eggplants, peppers, and, interestingly, themselves. The compounds in question are alkaloids, which serve as a built-in pesticide to deter insects, fungi, and grazing animals.
In most cases, animals on the Galaapagos face few threats, but plants are another matter. The production of these alkaloids can help shield vulnerable species. Although low concentrations of these alkaloids are harmless to humans, high concentrations can be toxic. This is why researchers from the University of California, Riverside, took an interest in the Galaapagos tomatoes.
These tomatoes aren't just making the alkaloids, they're manufacturing the "wrong" ones, ones not seen in tomatoes since their early evolution.
"It's not something we usually expect," said Adam Jozwiak, a molecular biochemist at UC Riverside. "But here it is, happening in real time, on a volcanic island."
Contrary to popular belief, evolution isn't always a one-way journey towards greater adaptation. Sometimes it can act like a circular path where an organism regains traits similar to ones they once lost, although this is rare. However, the tomatoes appear to have accomplished this unusual reversal.
"Our group has been working hard to characterize the steps involved in alkaloid synthesis, so that we can try and control it," Jozwiak added.
The team analyzed over 30 tomato samples collected from various geological locations across the Galaapagos islands. The eastern islands' tomatoes produced the same alkaloids as modern cultivated tomatoes, while those from the western islands produced alkaloids with a chemical fingerprint similar to their ancient eggplant relatives.
The difference between these eastern and western island tomatoes comes down to stereochemistry, the arrangement of molecules in three-dimensional space. Two molecules can contain the same atoms but behave differently based on their arrangement. During their analysis, the team found that the tomatoes made the switch by changing four amino acids in a single enzyme. This simple change was enough to flip the molecule's structure from modern to ancient.
The researchers confirmed this change by synthesizing genes encoding these enzymes in their lab and inserting them into tobacco plants. As expected, the plants promptly started producing the old compounds.
This development wasn't a random event; it aligned with geography. The eastern islands are biologically diverse and stable, while the western islands are younger, and the landscape is more barren and the soil less developed. This is where the ancient alkaloids are being produced.
"It could be that the ancestral molecule provides better defense in the harsher western conditions," Jozwiak said.
Although the tomatoes have regained this surprising trait, how do we know it's due to an evolutionary reversal? To verify the direction of this change, the team conducted evolutionary modeling using modern DNA to infer the traits of long-extinct ancestors. The western tomatoes matched what the early ancestors probably produced.
So is this really a reversal? The process of evolutionary reversal has been documented in snakes, fish, and some bacteria, but it's a rare and often unclear process to study.
"Some people don't believe in this," Jozwiak explained. "But the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It occurred."
And if this change can happen in one species, it could happen in others as well.
"I think it could happen to humans," Jozwiak said. "It wouldn't happen quickly, but over time, maybe, if environmental conditions change enough."
This is theoretical, but it offers a surprising perspective on our understanding of evolution. It seems that life can sometimes find a way forward by circling back to aspects of its past.
"If you change just a few amino acids, you can get a completely different molecule," Jozwiak said. "That knowledge could help us engineer new medicines, design better pest resistance, or even make less toxic produce. But first, we have to understand how nature does it. This study is one step toward that."
The study is published in Nature Communications.
[1] Overall, evolutionary reversal in plants occurs when a trait or characteristic that was lost in a lineage re-evolves, often due to changes in environmental pressures or selection forces. This phenomenon is a form of homoplasy, where previously lost traits reappear.
- The Galaapagos tomatoes are making alkaloids that are not common in modern tomatoes, appearing to reverse a long-lost trait in their evolution.
- This unusual reversal challenges our understanding of evolution as a linear process, suggesting that life can sometimes find a way forward by circling back to aspects of its past.
- Researchers from the University of California, Riverside, are interested in the Galaapagos tomatoes due to their production of "wrong" alkaloids, ones not seen in tomatoes since their early evolution.
- In science, evolutionary modeling using modern DNA can help infer the traits of long-extinct ancestors to verify changes like those seen in the Galaapagos tomatoes.
- Understanding the mechanism behind evolutionary reversals in plants could provide insights for engineering new medicines, designing better pest resistance, or even making less toxic produce.
- The geography of the Galaapagos islands appears to influence the production of these unusual alkaloids, with the western islands producing ancient alkaloids due to harsher conditions.
- The understanding of evolutionary reversal in plants could lead to fascinating discoveries in various fields, including science, medicine, health-and-wellness, environmental-science, technology, fitness-and-exercise, and nutrition.
