What Can Marmots Teach Us About Plastics?
At the Rocky Mountain Biological Lab in Gothic, just over the Maroon Bells from Aspen, a number of long-term field studies are pumping out reams of scientific data. In part two of our report on the laboratory, science reporter Ellis Robinson looked at a study on marmots that raises questions about the abundance of plastics in human society.
UCLA professor Dan Blumstein is leading a massive long-term study of yellow-bellied marmots. The field study at Rocky Mountain Biological Lab has been going on for 53 years. Recently, something his team uncovered about marmots has given him pause.
“This was a wake-up call to me.”
Over the span of a decade, Blumstein and his team found that female marmots born in mostly male litters, had very different lives from those born into female-dominated litters. He says, this worries him.
To understand why, let's start with one of the most basic measurements that marmot scientists make: “The ano-genital distance.”
Ano-genital distance is what marmot scientists use to distinguish a marmot’s sex. “The distance between their anus and their genital papilla. If it’s a male, it’s a greater distance, and if it’s a female the distance is smaller.”
Blumstein and his team know every marmot that lives near Gothic by name and have been doing this measurement for years.
“We discovered males in female biased litters tend to have a smaller ano-genital distance,” meaning they are feminized, “and females in male-biased litters tend to have a larger ano-genital distance,” meaning they are “masculinized.”
The reason for this, Blumstein says, is leaky hormones. Male marmots produce testosterone in the womb. And when there are a lot of male marmots, there is a lot of testosterone. This can leak into the neighboring female marmot's bloodstream.
“We then said OK, what are the consequences of this? People can do these studies in the lab, but it sort of ends there. But in the field it continues.”
The next step was tracking the life histories of these masculinized female marmots, and asking “What does it mean in life to be born a masculinized female marmot?”
“Well they’re less likely to survive their first year. Fifty percent of marmot pups born in a given year will not make it to the next year, but if you’re a masculinized female you’re less likely to make it.”
Even if the masculinized females do survive, the cards are still stacked against them.
“Females can breed as two year olds. But if you’re masculinized, you’re less likely to breed as a two year old. Age at first reproduction has a profound effect on how many descendants you can leave. So here are all of these really life-long consequences.”
It was only at the end of this study that Blumstein had his major wake-up call. But it wasn't about marmots. It was about us.
“I’d been reading about BPA, a chemical in plastics that are an estrogen mimicker. I’d been reading about phthalates, which are a chemical in plastics to make them soft, which is a testosterone mimicker. There’s a whole literature on endocrine disrupting chemicals.”
Now, marmots at RMBL are not exposed to many plastics. But Blumstein’s research shows their lives are drastically affected by natural fluctuations of hormones in the womb. And if that’s true, he asks, what does it mean for us humans, as we expose ourselves to such enhanced levels of hormone-like chemicals in our everyday environments through plastics?
“An endocrine-disrupters is some kind of chemical that can interfere with your bodies hormone system. ”
That’s Linda Birnbaum, director of the National Institute for Environmental Health Sciences. She says our bodies, can mistake chemicals like BPA that can masquerade as hormones.
They also can "produce effects that can be on the development, or reproduction, or the nervous system, or the immune system, and these effects might occur not only in humans but in wildlife.”
And so, back to the marmots:
“I don’t think our marmot study shows that estrogen-mimicking chemicals influence human behavior in these ways. But to me, this is a natural benchmark. If these systems are so exquisitely sensitive to natural variation? Let’s think a little more clearly about what we’re exposing ourselves to with our industrial society.”
From studying marmots high up in the Elk Mountains, for a decade, we learn something that, in Blumstein’s opinion, should give us pause.
For Aspen Public Radio, I’m Ellis Robinson