When Jake Esselstyn, Professor of Biology at Louisiana State University, began his work on shrews on the island of Sulawesi in Indonesia, he wanted to investigate the ecological and evolutionary factors that might explain shrew diversity on the island.
At that time, there were six species of shrews in the genus Crocidura that had been identified there, and he thought he would be able to clarify how they had arisen on the island. “I was interested in questions about how shrews interacted with their environment, with each other, how local communities were formed.”
Although Professor Esselstyn’s research began in 2010, he soon realized that the task of analyzing ecological and evolutionary relationships was impossible because there were clearly many undescribed species present. So began ten years of field trips to collect as many shrew specimens as possible from mountain and lowland sites on the island.
“It was overwhelming because for the first several years, we couldn’t figure out how many species there were,” he said.
Shrews are small, insectivorous mammals that are most closely related to hedgehogs and moles. During Esselstyn’s field trips he and his research team collected more than 1,200 shrews using pitfall traps. All of them weighed less than an AA battery, ranging from about 3 grams (0.1 oz) to about 24 grams (0.85 oz). The largest species had an average body length of 95 mm (about 3.7 in).
While Professor Esselstyn did identify and describe a new species of shrew in 2019, the picture became clearer once the research team had examined the genetic and morphological data from the specimens they collected between 2010 and 2018, and added data from old specimens that had been collected in 1916. More than 1,400 shrews were analyzed and this resulted in the identification of 21 different shrew species on Sulawesi, 14 of them being brand new to science.
The details of the 14 new, endemic species of shrews in the genus Crocidura have been published recently in the Bulletin of the American Museum of Natural History. This discovery represents the largest number of new mammals described in a scientific paper since 1931, some 90 years ago.
“It’s an exciting discovery, but was frustrating at times,” said Esselstyn, curator of mammals at the LSU Museum of Natural Science and associate professor in the Department of Biological Sciences. “Usually, we discover one new species at a time, and there is a big thrill that comes from it. But in this case, it was overwhelming … ”
Now that he feels he has a better handle on the shrew diversity of the island, Professor Esselstyn is interested in exploring the geographic, geological and biological factors that have contributed to Sulawesi’s extraordinary shrew biodiversity. The island is shaped rather like a lower-case letter k and this shape has contributed to the radiation and diversification of shrew species, he said. “There are consistent boundaries between species … whether you’re looking at frogs or macaques or mice. It suggests some sort of shared environmental mechanisms.”
Researchers have found at least seven such zones – roughly, the island’s central mass, the three “legs” of the k, and three zones on the long, bent “neck” of the island. Genetic analysis would be crucial in understanding the evolution of this diversity of shrew species. It will enable the researchers to determine how long ago or recently similar species diverged and whether they’ve been in regular contact with each other since then.
“It’s a difficult problem. But I think we can do it now that sequencing genomes is relatively low-cost,” he said. “A few years ago, we couldn’t have done it but it’s relatively feasible now.”
“Taxonomy serves as the foundation of so much biological research and conservation effort. When we don’t know how many species there are or where they live, our capacity to understand and preserve life is severely limited. It’s essential that we document and name that diversity,” Esselstyn said. “If we can make discoveries of this many new species in relatively well-known groups like mammals, imagine what the undocumented diversity is like in less conspicuous organisms.”