Otters! Who doesn’t love ‘em? From the fluffy and adorable sea otter to the giant Amazonian river otter; there’s an otter for every occasion! Most are fairly social, but the Asian small-clawed otter (Aonyx cinerea) beats all the others out when it comes to gregariousness. It is the most social of all the world’s 13 otter species, forming lifelong pair bonds that lead to extended family groups of as many as 15 or even 20 individuals. In addition to being a family oriented otter, it’s also the chattiest; you have to be to communicate with your many relatives. Along with the classic mustelid trait of scent marking, sound is one of the primary ways in which this animal discusses the intricacies of life. Small-clawed otters are known to use a repertoire of at least 12 different kinds of vocalization including chirps, squeals, barks, and shrieks. They’re like a group of excited tweens who won’t shut up about whatever boy band is popular with the kids these days. Unlike tween girls, though, the small-clawed otters’ company is actually enjoyable because they’re so darn cute and fuzzy!
Native to southern and eastern Asia, these little rascals thrive near clean freshwater streams and rivers with lots of vegetation. Occasionally, they can be found in rice paddies or along the coast near saltwater. Although small-clawed otters need a water source, they are happy to spend time on land as well. Their paws are only partially webbed due to this more terrestrial lifestyle and they use them to search for and capture prey both in the water and on land. Just like raccoons, small-clawed otters hold whatever they are eating in their delightful little hands. Sometimes they can be a nuisance in rice paddies because they will pull up rice plants while on the hunt. As mustelids, otters are playful and mischievous by nature after all.
Unfortunately, their numbers are currently on the decline because of habitat destruction caused by land development and competition with humans for food resources. The favorite foods of these otters, which include crabs, mussels, and clams, are also harvested by people and can be overexploited. In addition to reduction of food biomass, there is more frequent chemical contamination of these food sources from human activity. Since small-clawed otters are considered to be a vulnerable species, they are protected throughout much of their range. This is a good start, but areas that were once home to these otters have still seen them disappear.
One such case comes from Singapore. Small-clawed otters were historically common there, but are now only visitors from its offshore islands rather than permanent residents. Fortunately, though, Singapore has not remained an otter free zone. Thanks to pollution cleanup efforts in local waterways, smooth-coated otters (Lutrogale perspicillata) have recently made a return. These much larger cousins of the small-clawed otter now number over 60 individuals and can often be seen and photographed by locals and tourists alike… or so it was thought! Recent research indicates that these water weasels are not actually smooth-coated otters. As it turns out, they are a hybrid between smooth-coated and small-clawed otters. This is the first recorded observation of a wild otter hybridization.
The story behind these fuzzy hybrids is even more interesting. The research team, led by Beatrice Moretti, came up with several reasons why this union occurred and settled on the “sexual selection hypothesis” as the most likely. Years ago when small-clawed and smooth-coated otter populations overlapped in Singapore’s waters, there may have been a dearth of small-clawed males. The smooth-coated otter was more common in this region, so small-clawed females likely would have interacted with them. Initially, these females may have rejected the smooth-coated males while they searched for males of their own species. Upon being unsuccessful, the females might have settled for the smooth-coated males instead. So why were the frisky locals seen today mistaken for smooth-coated otters in the first place? Well, it’s because they look exactly like smooth-coated otters. The initial objective of the study mentioned above was to learn about smooth-coated otter populations around the world, not phylogeny and hybridization. So naturally, the researchers were confused. They thought the samples collected from their smooth-coated otters might have been contaminated by small-clawed otters swimming by for a visit! After rerunning tests and making sure that no mistakes had been made, they realized that what they found was genuine and set out to figure out why and how. This hybridization happened so many generations ago that the offspring of the first few couples who bred ended up back-crossing with smooth-coated otters. The otters that now live in Singapore contain small-clawed DNA, but superficially appear to be smooth-coated otters because of the continued back-crossing with that latter species.
Examples like this prove that even when we think we know something, nature always has surprises for us hidden up its sleeves. Perhaps with continued conservation efforts and habitat restoration, small-clawed otters will return to the waters of Singapore to frolic with their not so distant cousins.
1.Hamman, David. “Aonyx Cinerea.” ADW, Animal Diversity Web, 2004, animaldiversity.org/site/accounts/information/Aonyx_cinerea.html.
2.Wright, L., et al. “Aonyx Cinereus” IUCNRedlist, The IUCN Red List of Threatened Species, 2015, http://www.iucnredlist.org/details/44166/0. Wright, L., de Silva, P., Chan, B. & Reza Lubis, I. 2015. Aonyx cinereus. The IUCN Red List of Threatened Species 2015
3.Scheifele, Peter M., et al. “Vocal Classification of Vocalizations of a Pair of Asian Small-Clawed Otters to Determine Stress.” The Journal of the Acoustical Society of America, vol. 138, no. 1, 2015, doi:10.1121/1.4922768.
4.Hong, Jose. “Surprising Branch in Singapore’s Otter Family Tree.” The Straits Times, 14 Jan. 2018, www.straitstimes.com/singapore/surprising-branch-in-otter-family-tree?xtor=CS1-10.
5.Moretti, Beatrice, et al. “Phylogeography of the Smooth-Coated Otter (Lutrogale Perspicillata): Distinct Evolutionary Lineages and Hybridization with the Asian Small-Clawed Otter (Aonyx Cinereus).” Scientific Reports, vol. 7, 27 Jan. 2017, doi:10.1038/srep41611.