The spotted salamander isn't a jailbird, but for a vertebrate it has an unusual cell mate nonetheless: algae.
For more than a century, scientists have known that a certain species of alga, Oophila amblystoma, grows in association with spotted salamanders' eggs. The alga's scientific name even means “egg-loving.”
Earlier research had found that eggs developed faster in the presence of algae and that algae grew better in water that had contained embryos. But they didn't know the algae actually grew within the eggs.
In fact, this is the first time algae have been found living symbiotically within the cells of any vertebrate animal.
"It raises the possibility that more animal/algae symbioses exist that we are not aware of," said Indiana University at Bloomington biologist Roger Hangarter in a press release from that school. It is also nice to know that vertebrates can take photosynthetic advantage of plant life growing in their skin. Invertebrate animals, like nudibranchs, a.k.a. sea slugs, keep algae as cell mates and, like photovoltaic cells on a rooftop, utilize the energy they produce.
"Since other salamanders and some frog species have similar algae/egg symbioses, it is possible that some of those will also have the type of endosymbioses we have seen in the spotted salamander," Hangarter said.
Endosymbiosis is when one organism lives inside the cells of another. In the case of the algae and the salamanders, it seems to be a case of mutualism, by which both species benefit, though scientists haven't figured out exactly how yet.
It took a century to find the algae within the eggs because the algae are not easy to see within the cells. But a new visualization technique, known as fluorescence in-situ hybridization, allowed the scientists to find the salamander's long hidden photosynthetic friends.
They also looked within the embryos for evidence of a specific gene (18S rRNA) from the algae.
"With the ability to use gene-specific probes, it is now possible to determine the presence of organisms that may not be easily visible by standard light microscopy," Hangarter said. "In the past, researchers looking with simpler light microscopy techniques than are available today failed to see any algae in the salamanders."
This discovery was waiting right under researchers' noses. The spotted salamander is common in North America.
"We were particularly excited to discover this association in spotted salamander embryos, because this species was a model organism for early experimental embryology research and is a locally common salamander in eastern North America," one of the study's co-authors, Ryan Kerney of Dalhousie University, said in an Indiana University press release.
"We hope that this study will highlight biodiversity research on common North American species, which can easily be overlooked or even considered over-studied," said Kerney.
"We would like this work to draw attention to a fascinating yet common backyard salamander, and hope that it will both raise awareness of the species and promote the preservation of their fragile breeding habitat," Kerney said.
"I think it is important for people to realize that you do not need to go to exotic locations to make interesting scientific discoveries,” added Hangarter.
“The vernal ponds that the salamanders mate in are also essential for many other amphibians and other organisms, but such ponds are often among the first things destroyed when humans develop in wooded areas. One 500-square-foot pond might service several thousand mating salamanders and frogs that might inhabit an area of a few acres of woodland," Hangarter said.
IMAGE 1: Salamander embryos grow inside egg capsules that are covered with and usually infiltrated by a type of green algae. (Courtesy of Roger Hangarter)
IMAGE 2: Spotted salamanders are the first known vertebrate to have an endosymbiont. The salamanders are found throughout eastern North America. (Courtesy of Roger Hangarter)