By Lawrence J. Winship Gazette Contributing Writer
Who in Amherst has not heard of the tunnels that allow the gorgeous yellow-and-black spotted salamanders to cross safely under Henry Street on their way to vernal pools where they mate and lay eggs? Or of the scores of enthusiasts who wait expectantly for the first warm wet night in spring when the call goes out, “The salamanders are migrating!” and then rush to the tunnels to watch and help? Or that these marvelous amphibians are the “mascots” of the Hitchcock Center for the Environment?
Well, now we can engage in a little more local pride: These same salamanders may be partners in a symbiotic relationship with green algae living inside the animal—the first such partnership discovered that involves a vertebrate species. Maybe we could think of them as solar-powered amphibians!
Call it serendipity or curiosity that led researchers in Nova Scotia and Indiana to take a closer look recently at the algae that live inside clutches of bright yellow-green salamander eggs. These tiny plants occupy the jelly around the embryo, where they grow on sunlight and the waste nitrogen given off by the eggs. (The algae’s chlorophyll gives the egg masses their color.) The scientists weren’t surprised to see the algae outside the embryo—naturalists have known for more than 100 years that algae grow around salamander eggs. Indeed, the scientific name for these kinds of algae, Oophilia, means “egg loving.” They also knew how this external symbiosis works. In the 1980s researchers found that salamander embryos develop more quickly and fully with the algae than without them. Likewise, if the algae were cultured separately from the embryos, they grew better in water that had previously been exposed to the embryos. These two organisms really were helping each other—a true symbiosis between two distinct, separate organisms. So far, this was not surprising.
And then, evolutionary-developmental biologist Ryan Kerney, the leader of the research team, tried something different, just for fun.
He put an egg mass under a fluorescent microscope. Blue light shining on the eggs revealed little spots of red fluorescent light, the tell-tale sign of algal chlorophyll. Not only were the red dots in the jelly; they were also inside the cells of the embryos. Molecular evidence confirmed that the algae were actively growing and dividing.
This opened up a host of new questions, which will likely take some time to answer fully. Have they discovered a new, genuine internal symbiosis? Could the algae inside the embryo really help it grow? Do the algae actually move between salamander generations inside salamander cells or are the salamander cells colonized during embryo growth? Kerney also found algae inside the oviducts of mature female salamanders, suggesting that perhaps the salamander mothers pass the algae down to their offspring’s jelly sacs as the eggs are made.
Quite apart from the excitement about discovering this new relationship is the fact that it opens up a previously unheard-of pathway in vertebrate evolution. It’s been many years since UMass geosciences professor Lynn Margulis and others demonstrated that chloroplasts—the components of plant cells that allow all green plants to photosynthesize—evolved from a symbiotic relationship with green algae. But no one thought that algal cells could live and grow inside the cells of a vertebrate, because foreign invaders are usually quickly destroyed. This keeps the animal safe from disease. Now that assumption no longer holds.
Beyond evolutionary and molecular biology, this story is a testimony to the sheer delight of inadvertent discovery, of simple luck and taking time to really look. After reading Kerney’s work, my students and I ran right out to find frog eggs in a local vernal pool and, sure enough, they were a beautiful green. Under our microscope, we too could see chlorophyll glowing red, but not inside the embryos—different species perhaps. We also saw a thousand other microscopic living things, a universe in a jelly jar, perhaps known to science, but new to us!
Who knows what might yet be discovered, if we are only wise enough to first take delight in the beautiful, strange world all around us, and then to change our lives so that we consciously share that world with all living things. This story serves as a reminder to me: We don’t need to travel to exotic distant locations to make startling new discoveries. We just need vernal pools. And salamander tunnels!
Lawrence J. Winship, a member of the Hitchcock Center board, is a professor of botany in the School of Natural Science and director of the Southwest Studies Program at Hampshire College.
Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 845 West Street, Amherst, appears every other week. For more information, call 413-256-6006, or write to us.Click here to return to full list of Earth Matters articles.