Nav: Home

Glowing millipede genitalia help scientists tell species apart

April 18, 2019

Sometimes, it's really easy for scientists to tell species of animals apart--they'll be obviously different shapes or colors. Other times, different species will look nearly identical to the naked eye. In those cases, scientists need to turn to techniques like DNA analysis to tell them apart. Or, like researchers at the Field Museum discovered when studying some near-identical millipedes, you can sometimes just shine a blacklight on them, and under the ultraviolet light, parts of the different species' genitals will glow different colors.

"This paper is reviewing and mopping up and synthesizing what we know about these species of North American millipedes," says Petra Sierwald, an associate curator at the Field and the lead author of a paper describing the findings in the Zoological Journal of the Linnean Society, along with co-authors at the Field, Virginia Polytechnic Institute, and the University of California, Davis.

Millipedes are arthropods, relatives of centipedes and distant cousins of spiders and insects. They have a lot of legs, but nowhere near the "thousand" implied by their name--the ones in this paper, in the genus Pseudopolydesmus, have around 70. "Arachnids like spiders are all predators, but millipedes are mulch-munchers, they're in waste management," explains Sierwald. The species in this study are found all over the eastern United States, from Canada for Florida, where they live in dead leaves on the forest floor, but they're not very flashy-looking: they're half an inch long, and their exoskeletons are brown. Their genitals, though, are a little more special.

Male millipedes' sperm comes out from an opening behind their second pair of legs. Their seventh pair of legs are called gonopods, and they're specially adapted for transferring sperm to a female millipede's vulvae, which are behind her second pair of legs. "We think, he dips his gonopods into his ejaculate, which is kind of a blue-ish liquid, and then he goes in search of a female, walking around with his sperm on his gonopods," explains Sierwald. "The males' gonopods have all these special features, little knobs and things. Some of them look like the bristles on a toothbrush." And the differences between the different gonopods are even more vivid under UV light.

The idea to look at the millipedes under UV light came from previous studies showing that other arthropods glow under similar conditions. When the animals are exposed to UV light, the energy from the light interacts with special proteins in the animals' exoskeletons, causing them to emit light in a process called fluorescence. "We discovered that a lot of the millipedes' genital parts fluoresce under UV light, so we developed an imaging method to capture it," says Sierwald.

Taking a picture of glowing millipede genitals is easier said than done. "These millipedes are really small, and their genitalia are even smaller," says Sierwald. One way to get images of tiny specimens is to use a scanning electron microscope, but that wasn't ideal in this case--that technique involves coating the specimen in a thin layer of gold so that electrons bounce off of it, and then a detector puts together a picture showing where the electrons were deflected. Since many of the millipede specimens used in this research were very old (the oldest was collected in 1887) and scientifically valuable, the researchers had to find a new way to study the specimens without damaging them. Instead, Sierwald's co-author, Stephanie Ware, a research assistant at the Field Museum, developed a new way to take detailed pictures of very tiny things.

"We have a camera on a motorized lift that allows us to move the camera towards the specimen in tiny, tiny amounts. With every movement, a different part of the specimen comes into focus while most of the rest of it is out of focus and a picture is taken, " says Ware. "At the end, we have anywhere from 10 to 70 pictures and we use special software that picks out what is in focus in every picture and stitches it all together into one image where the entire specimen is in focus. You get highly detailed images and you don't have to damage the specimens at all."

Ware photographed the millipedes' gonopods under UV light, and in the resulting images, it's much easier to see details. Some species' genitals glowed in different colors; in others, the UV lighting made differently-shaped parts stand out more.

It's not clear why the millipedes have evolved glowing genitalia--as far as we can tell, they can't really see the glow. "Millipedes don't see well at all, they don't see images. I don't know if they see any color," says Sierwald. "I think the fluorescence is an artifact or byproduct of the cuticle, the covering of the gonopod. Maybe it makes the cuticle stronger, but that is something we don't really understand."

But while reason behind the glowing gonopods remains a mystery, scientists are already able to use them to tell species apart. Analyzing Ware's photographs, Sierwald and her colleagues were able to sort the specimens into eight separate species--four fewer than scientists had previously recognized. "In some ways, it's the opposite of describing a new species--we were able to put some back together that shouldn't have been separated," says Sierwald.

Being able to properly tell species apart--even species of animals as unassuming as millipedes--is important for scientists. "One of the benefits of millipede research is we can use them as environmental indicators," explains Sierwald. "By collecting them and seeing where the different species are distributed over time, we can learn about climate and environmental change. And millipedes are important to their ecosystems--they're decomposers that release nutrients trapped in rotting leaf litter back to the soil."

And beyond these applications, says Sierwald, "We do this research because it tells us something about how the world works."
This study was contributed to by co-authors Derek Hennen and Paul Marek at Virginia Polytechnic Institute and Paul Marek at the University of California, Davis.

Field Museum

Related Millipedes Articles:

ESF lists Top 10 new species for 2017
A spider and an ant with names drawn from popular books, a pink katydid and an omnivorous rat made the College of Environmental Science and Forestry's list of the Top 10 New Species for 2017.
Paleontologists identify new 508-million-year-old sea creature with can opener-like pincers
Paleontologists have uncovered a new fossil species that sheds light on the origin of mandibulates, the most abundant and diverse group of organisms on Earth, to which belong familiar animals such as flies, ants, crayfish and centipedes.
Vision, not limbs, led fish onto land 385 million years ago
A Northwestern University and W.M. Keck Science Department of Pitzer, Claremont McKenna and Scripps colleges study suggests it was the power of the eyes and not the limbs that first led our aquatic ancestors to make the leap from water to land.
Low level of oxygen in Earth's middle ages delayed evolution for 2 billion years
A low level of atmospheric oxygen in Earth's middle ages held back evolution for 2 billion years, raising fresh questions about the origins of life on this planet.
Intensification of land use leads to the same species everywhere
In places where humans use grasslands more intensively, it is not only the species diversity which decreases -- the landscape also becomes more monotonous, and ultimately only the same species remain everywhere.
New species of extremely leggy millipede discovered in a cave in California
Ninety years ago, a world record-breaking 750-legged millipede was discovered in California.
Tracing the ancestry of dung beetles
One of the largest and most important groups of dung beetles in the world evolved from a single common ancestor and relationships among the various lineages are now known, according to new research by entomologist Dr T.
Dragons out of the dark: 6 new species of dragon millipedes discovered in Chinese caves
Six new species of Chinese dragon millipedes, including species living exclusively in caves, are described as a result of an international cooperation of research institutes from China, Russia and Germany.
Millipede research 2.0
Thousands of new species are identified every year, and new and efficient methods are needed to document this diversity and to make information about new species available to other scientists and to the interested public.
Underground gourmet: Selected terrestrial cave invertebrates and their meal preferences
Doubting whether cave invertebrates feed on just anything they can find in the harsh food-wise environment underground, Dr.

Related Millipedes Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#529 Do You Really Want to Find Out Who's Your Daddy?
At least some of you by now have probably spit into a tube and mailed it off to find out who your closest relatives are, where you might be from, and what terrible diseases might await you. But what exactly did you find out? And what did you give away? In this live panel at Awesome Con we bring in science writer Tina Saey to talk about all her DNA testing, and bioethicist Debra Mathews, to determine whether Tina should have done it at all. Related links: What FamilyTreeDNA sharing genetic data with police means for you Crime solvers embraced...