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SoCal Scientist Makes Remarkable Rainforest Discovery

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Terentia hairstreak among Apodantia flower buds | Photo: Aaron Pomerantz / Rainforest Expeditions

This story starts as so many stories do: a scientist trudged through a rainforest and stopped to inspect a curious-looking plant. "Huh, that's weird," said Aaron Pomerantz, to no one in particular.

The LA-based entomologist took a step closer to inspect the specimen.

He found himself looking at hundreds of tiny yellow bulbs protruding out of a tree trunk. At first he thought the bulbs were part of a fungus growing on the planet, or maybe some sort of strange fruit. He didn't think much of it until a closer look revealed caterpillars, happily munching away on the yellow knobs.

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An even closer look showed that ants accompanied the caterpillars. It's not really that unusual to find caterpillars and ants spending time together in the tropics. The symbiotic relationship between the two even has a name. "Mymecophily" literally means that the caterpillars are "ant loving."

Ants really like sugar, and that's something that many tropical plants have evolved to exploit. They offer up small growths called extrafloral nectaries, supplies of nutrients outside of flowers, to the ants. The ants slurp up the sugary nectar and in exchange, they keep parasites and predators at bay. It's a win-win situation.

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Caterpillar, ant, and flower buds | Photo: Aaron Pomerantz / Jeff Cremer
 

Caterpillars in the family Lycaenidae have come up with a similar strategy. They evolved something called a dorsal nectary organ. The ants drum on the caterpillars' backs, and the caterpillars release a concoction of sugars and amino acids for the ants to sip. In return, the ants act as caterpillar bodyguards.

"While I had little idea at the time what I was looking at, my background in entomology was telling me one thing. This was something cool," Pomerantz says.

That's when he noticed something fluttering in the corner of his eye. "I could immediately identify it as a lycaenid and it had a distinct yellow spot on its hind wing that looked remarkably like the yellow bulbs," he wrote in a blog post about the discovery. "Was this the adult of the caterpillars?"

What Pomerantz had was the makings of a scientific mystery. What were these strange yellow plants? Were the caterpillars related to the adult butterfly he saw? Did the adult evolve a wing pattern to match the plant? And how do the ants fit in to the puzzle?

Thanks to contacts back in the States, Pomerantz learned that the yellow projections were not fruits or fungi. They were instead flower buds of a rare parasitic plant, possibly one called Apodanthes caseariae.

The parasite lives inside of the tree, but every year around October its yellow flowers break through the bark and bask in the jungle air where they become food for hungry caterpillars. By January the buds fall off, leaving the tree pockmarked with holes, as if several hundred woodpeckers had found their way to Peru. Pomerantz says that his observations, conducted through his work as a biologist and science communicator for a Peruvian ecotourism company called Rainforest Expeditions, "appear to be the first record of an insect utilizing Apodanthes as a host plant."

The butterfly meanwhile turned out to be a critter first described nearly 150 years ago in 1868: a lycaenid called Terenthina terentia, or the Terentia hairstreak.

The Amazon rainforest is home to roughly one in every ten species found on our planet, and new ones are being discovered all the time. According to a WWF survey, 441 new species there were described by scientists between 2010 and 2013, including 258 plants, 84 fish, 58 amphibians, 22 reptiles, 18 birds, and one mammal. That's nearly three every week.

But describing a species is not the same as really understanding it. Knowing what a particular plant or animal looks like is far different from knowing how it lives its life. The Terentia hairstreak may have been described a century and a half ago, but until now nobody knew much about its life cycle. Where does it lay its eggs? How do the caterpillars survive? How might the butterflies' coloration have evolved?

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Pomerantz documents the ecological relationship | Photo: Rainforest Expeditions
 

"By observing its behavior in the wild, we have insight into why the butterfly has this striking yellow wing spot and can start to delve deeper into why it uses this host plant, how it finds it, what purpose the yellow spot serves, and so on," Pomerantz says. "Describing a new species is just the first step. Picking apart its life and behavior is far more interesting."

By doing so, Pomerantz has uncovered a mini-ecosystem in the jungle, a complex relationship between two plants and two insects, four species that appear to have evolved alongside each other for a very, very long time. The truth is that anybody can make an exciting discovery like this one if they keep their eyes open. And he should know: unlike many folks making new scientific discoveries, Pomerantz isn't a PhD-wielding doctor. He received his master's degree in entomology and molecular biology in 2014 from the University of Florida.

"There are still so many discoveries people can make just by observing organisms in nature, no matter what your educational background or where you are," he says. And as Angelenos know well, you don't have to be in the tropics to do it. After all, a band of citizen scientists in LA helped researchers last year discover more than thirty new species of flies in their very own backyards.