By Steven Scarpa, Associate Director of Marketing and Communications
Explorers traveling the ocean in the 18th and 19th centuries marveled at the strange beauty of Physalia, a sea creature commonly known as a bluebottle.
Observers noted common elements amongst the animals. Most obviously, they had a “sail” used to catch the wind along the surface of the sea. But they also noticed the differences. There seemed to be more than one kind of Physalia.
Modern genomic evidence confirms the sailors' suppositions.
“The differences were so screaming that people recognized it 250 years ago,” said Peabody curator Casey Dunn. “There were various scientific reasons for reducing it to one species, but our new study has changed the threshold for understanding diversity.”
By sequencing the genomes of 151 Physalia specimens from around the world, Dunn and research scientist Samuel Church have found that the bluebottle is a group of at least four distinct species, each with its form, genetics, and home location.
“We knew that there was a long debate for several centuries about whether these animals were different from each other across the world,” Church said. “As it turns out, (the explorers) were correct.”
Their study, ‘Population genomics of a sailing siphonophore reveal genetic structure in the open ocean,’ recently published in Current Biology, challenged the assumption that the open ocean supported single, well-mixed populations. Eric Lazo-Wasem, senior collections manager in invertebrate zoology, and museum assistant Lourdes Rojas are also co-authors of the paper.
The study describes Physalia physalis, P. utriculus, and P. megalista, alongside a newly identified species, Physalia minuta, found near New Zealand and Australia. Each species is further subdivided into genetically distinct subpopulations shaped by local wind and ocean currents.
“There is incredible diversity in what was thought to be a single species,” said Dunn, who is Professor of Ecology and Evolutionary Biology and Curator of Invertebrate Zoology at the Peabody. “It turns out that if you pick up one of these animals in Ireland and you pick one up in Florida, for example, it's not the same population. There’s a lot of regional variation.”
Future investigations into the natural processes that caused these variations can recalibrate science’s expectations towards open-ocean biodiversity. “We are excited about the questions this brings up,” Church said. “The open oceans are often treated like this well-mixed soup. Everything is stirred up and you can find everything everywhere. Instead, we find these Physalia populations that are very regional. It is the opposite of what people think the open oceans are doing.”
The team matched genomic lineages with four distinct physical forms identified from thousands of citizen-science images submitted to iNaturalist.org. The deep local knowledge of citizen-scientists from all over the world helped provide Church and Dunn with valuable information for their own targeted collecting trips. Passionate amateurs took photos and collected specimens. A marketing professional helped with identification. Lifeguards also tended to have deep knowledge.
“It made me feel like the world was both a bigger and smaller place,” Church said. “You are getting a wider set of visual and locational data, and then you get the animals themselves.”
“We were able to drink from this incredible local knowledge. We learned so much more by engaging and empowering the people that were already there,” Dunn said.
The researchers said future investigations into the physical, environmental, and biological processes that caused these variations can alter science’s thoughts about open-ocean biodiversity. “We are excited about the questions this brings up,” Church said.
Peabody Museum staff members played an important role in the research. Lazo-Wasem and Rojas handled the logistics of all the specimen contributions. The process included securing the chain of succession, permits, and proper transportation.
“It’s significant work. There is such responsibility in bringing something into the collection,” Dunn said.
When a new species has been described, one is the type specimen – the exemplar of the entire species. “In some ways, it is the crown jewel of the study,” Dunn said.
A specimen like this one would ordinarily become part of the Peabody’s collection. Researchers decided on a different approach. The type specimen was collected in New Zealand, so Dunn and Church offered it to the Museum of New Zealand’s natural history collection, a nod to the global scope of the investigation.
“That’s incredibly important because that is where we feel the species is going to be encountered. It’s most important that we have the resources to study it. Our mission is to understand the global diversity of invertebrates. It’s not just to build the biggest collection we can. The collection is a means to an end,” Dunn said.