By Meredith Swett Walker
What do the United States Navy, the famous naturalist Alfred Russel Wallace, and bizarre genitalia have in common? They are all part of the story of a newly discovered genus of fleas from Indonesia.
In the latest issue of the Journal of Medical Entomology, David K. Mardon and Lance A. Durden describe a new stivaliid genus of fleas, Musserellus, containing five new species. Four of the species were collected on the island of Sulawesi and the fifth was collected in the Indonesian province of West Papua on the island of New Guinea. Mardon and Durden’s discovery provides a window on the history, both prehistoric and recent, of Indonesia and illustrates the importance of scientific collections.
According to Dr. Durden of Georgia Southern University, male flea genitalia is arguably “the most complex genitalia of any organism and consists of a bedazzling array of uniquely shaped plates, rods, and spines that connect with the female of the same species during mating like a three-dimensional jigsaw puzzle.” It is this complex anatomy that led to Mardon and Durden’s discovery.
The fleas described in their paper had certain genital features not found in any known genera, prompting the authors to define a new genus they named Musserellus in honor of Dr. Guy Musser. Musser is a mammologist and curator emeritus of the American Museum of Natural History who collected some of the flea specimens during a three-year expedition to Sulawesi in the 1970s. The newly described species include Musserellus vanpeeneni, Musserellus wattsi, Musserellus whitei, Musserellus marshalli, and Musserellus dunneti.
In addition to the fleas collected by Dr. Musser, some of the specimens described were collected by co-author Lance Durden and other members of Project Wallace, a collaboration between the Royal Entomological Society and the Indonesian Institute of Sciences. Additional specimens were collected by the U.S. Naval Medical Research Unit No. 2 (NAMRU-2) during expeditions led by P.F. Dirk Van Peenen, for whom the species M. vanpeeneni was named.
Collecting fleas may seem an odd job for the Navy, but NAMRU-2 was founded during World War II to study infectious diseases in the region that might affect military operations. The fleas were collected as part of an investigation of parasites in the area. The unit is now based in Phnom Penh, Cambodia and is still collecting insects. Its current activities include mosquito mass trapping, monitoring drug resistant malaria, and assisting U.S. regional partners with infectious disease surveillance and response.
The famous British naturalist Alfred Russell Wallace also collected specimens in this part of the world. A contemporary of Charles Darwin, Wallace independently developed the theory of evolution at about the same time Darwin did. He is also considered by many to be the father of biogeography — the study of the distribution of organisms in geographical space and geologic time. Mardon and Durden discuss how Musserellus fleas could give us insight on the “Wallace Line,” a biogeographical boundary running through Indonesia that divides an area with species of Asian origins from “Wallacea,” an area with species originating from both Asia and Australia.
The island of Sulawesi, which is part of Wallacea and sits at the junction of two tectonic plates, has a complex and incompletely understood geological history. There is evidence that emergent land masses from New Guinea broke off and moved toward Sulawesi in the last 3-15 million years. The distribution of the genus Musserellus, with four species occurring on the island of Sulawesi and one species occurring on the island of New Guinea, is a faunal link between the two islands that supports this idea.
All of the Musserellus flea specimens were collected at least 30 years ago in the 1970s and 1980s. Why did it take so long for them to be described and classified? Sadly, this kind of delay is not uncommon. As Ed Yong wrote recently in The Atlantic, “…the average specimen languishes for 21 years before it’s formally described…” There is frequently not enough time, money, or expertise available to describe all of the specimens at the time of their collection.
The Musserellus flea specimens faced an additional challenge because they had been “cleared” of soft tissue by immersion in potassium hydroxide. That was standard practice in the 1970s and 1980s as it helped preserve the specimen and made it easier to see anatomical structures under the microscope. Unfortunately, potassium hydroxide also denatures DNA. DNA amplification and sequencing techniques had not been developed at that time, so preserving DNA was not a concern. But it is today. According to Durden, these days “it is virtually impossible to garner external funding for species descriptions unless a major molecular component is included in the project.”
The story of the Musserellus fleas is another illustration of the value of natural history collections. And it’s not just new species or genera that can be discovered in these collections. A recent paper in Transactions of the American Entomological Society describes how entomologists used information from museum collections to rediscover a species of grasshopper endemic to Georgia’s sandhills that had not been recorded in 60 years. As stated in the Entomological Society of America’s Position Statement on the Importance of Entomological Collections, these collections “offer a lens into the past, a snapshot of the present, and a means for predicting the future.”
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Meredith Swett Walker is a former avian endocrinologist who now studies the development and behavior of two juvenile humans in the high desert of western Colorado. When she is not handling her research subjects, she writes about science and nature. You can read her work on her blogs http://picahudsonia.com and https://citizenbiologist.com or follow her on Twitter at @mswettwalker.