John Pfeiffer first forayed into natural history collections work during his undergrad at Northern Michigan University. At the time, he was unaware that his professional journey would lead to a position as the new Curator of Bivalves at the Smithsonian National Museum of Natural History.
Pfeiffer’s beginnings
As an ambitious undergraduate at a small university nestled on the south shore of Lake Superior, Pfeiffer developed his fascination with freshwater mussels and decided to take a stab at collections-based research. With specimen donations from the Illinois Natural History Survey and his own local collecting efforts, Pfeiffer built the school’s first collection of freshwater mussels, focused on species distributed across the Midwestern United States. Today, the school still proudly displays the exhibit Pfeiffer built to document the freshwater mussel diversity in the region. This simple exhibit with neatly labeled shells delicately fastened to the display foreshadowed the bright future of a talented researcher.
Unlike many scientists who follow a winding path to their final discipline of study, Pfeiffer found freshwater mussels and stuck with them. “How they infect their host was really what sold me on freshwater mussels,” explained Pfeiffer as he dove into the evolutionary tale of their wriggling lures and parasitic larvae. Freshwater mussels evolved from a marine ancestor and managed to traverse into the rivers and lakes of the world against the downstream flow that characterizes most freshwater habitats. Given the limited mobility of these bivalves, this movement against the flow was a marvelous feat. For their marine ancestors to climb into freshwater habitats, mussel larvae evolved to attach to freshwater fish which dispersed them upstream. To infect their hosts, adult freshwater clams go fishing.
Poring over videos of mussel appendages that resemble the prey of their larvae’s host fish, Pfeiffer explains how freshwater mussels attract their hosts in the same way humans use bait or tackle when fishing recreationally. Instead of buying fishing supplies at a store, freshwater mussels had to rely on evolution. In a beautiful representation of natural selection, this “fishing” tactic became so specialized in some mussel species that their lures look almost identical to the prey of a single host species.
Often times, a part of the mussel’s mantle (the fleshy structure that is responsible for exuding the shell in bivalves) mimics the shape, coloring, and movement of a prey type enjoyed by the target host fish. When the host fish nibbles on the suspected snack, it ruptures a structure filled with larval mussels and sucks in a bunch of babies that attach to the fish’s gills and body. These adorable parasites hang on for a few days to weeks until they mature enough to drop off and settle on the riverbed.
Scouring the rivers of Thailand and beyond
Having always enjoyed time on the water, fishing and relaxing with a cold one in the great outdoors, Pfeiffer found the perfect counterpart in freshwater mussels. “They live in the river, they drink all day, and they do a little fishing,” joked Pfeiffer as he delved into his research and his plans as the new bivalve curator at the Smithsonian.
As a master’s student at the University of Alabama, Pfeiffer was more completely introduced to biodiversity science and looked into the evolutionary history of lesser-known freshwater mussel species in Southeast Asia, primarily in Thailand. Still interested in the parasitic life cycle of freshwater mussels, Pfeiffer focused his research on the evolution of different larval morphologies. As part of his master’s research Pfeiffer discovered that an endemic radiation of mussels in southeast Asia had evolved an unusual adaptation that caused the parasitic larvae to have asymmetrical shells. Pfeifer reconstructed the evolution of this trait and hypothesized about how it may be used to infect the fins of its host fish.
Pfeiffer continued his research on tropical freshwater mussels during his Ph.D. at the University of Florida and the Florida Museum of Natural history. There, he worked to uncover the evolutionary history of species in Mesoamerica and Southeast Asia. The species-level diversity between temperate and tropical freshwater mussels is comparable, but lack the same level of documentation as to their North American counterparts. Eliminating this disparity is one of Pfeiffer’s main goals.
Freshwater mussel conservation
While the evolution of mussels lured Pfeiffer into his current research, he now also dedicates much of his work to conservation. “A lot of my conservation work,” he says, “has to do with understanding species boundaries. In order to protect a critter, you have to understand where its found, how that range has changed over time, and how you might expect it to change in the future due to certain threats.”
To better understand the diversity and distribution of freshwater mussels, Pfeiffer and his colleagues often use DNA tests to help identify particular lineages or groups. The goal of this work is to establish conservation priorities. By drawing a detailed map of species ranges, scientists can determine potential threats to each distinct species and the urgency of that threat.
As a newly appointed Smithsonian researcher, Pfeiffer hopes to reveal some secrets about other poorly studied mussel species housed here at the National Museum of Natural History. ‘One thing that I think we can do better in regards to better understanding mussel evolution is to more completely include endangered and extinct species in our reconstructions’, states Pfeiffer.
Many of these rare specimens are here in the museum and Pfeiffer hopes to use historical DNA techniques to pull out genealogical information to help build a more robust picture of freshwater mussel evolution across the globe. With a better understanding of evolution and biodiversity for these organisms, Pfeiffer hopes to inform conservation efforts to help maintain their stunning diversity. The Department of Invertebrate Zoology could not be more excited to have him on board.
BY Raven Benko and Jaimee-Ian Rodriguez
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