Some groups of animals just don’t get enough love. The little forest mice of the genus Chilomys are such a group. They are hardly ever seen, and they all look pretty much the same at first galnce. Taxonomists have not paid much attention to them, and all specimens of Chilomys from the northern Andes of South America were lazily classified into just one or two species (depending on the taxonomist). However, in recent years there have been suggestions that there may be more species of these little mice. It is hard to know for sure, though. If all we have are a few specimens, each from different locations, how can we know that subtle differences between them are not just due to geographical variation of a single species? And if we have two slightly different specimens from a single location, how do we know that the differences between them are not simply due to individual variation (like hair color in humans)?
In order to answer these questions, we need more information. We need to look at many different individuals in a single location, and we need to look at more locations. And we have to look at many different traits, not just one or two. Then we will be able to see if the individuals can be grouped into discrete groups, with no intermediate individuals between groups. That will indicate the groups probably represent good species; DNA evidence can then be used to confirm this conclusion. (Recall that a biological species is a population that can freely interbreed , but which rarely or never breed with other populations.)
A few years ago a team of scientists led by Jorge Brito began the difficult task of trying to figure out these questions for the small rodents of Ecuador, including Chilomys. I’ve written before about the new genus of mammal that he discovered in the course of this work. This week he finally published the results of his long study of the Chilomys mice. The new publication reports the discovery of at least five new species of Chilomys mice in Ecuador! Two of them are known only from our Dracula Reserve in northwest Ecuador (province of Carchi), while a third new species is more widespread and occurs in our Naturetrek-Viscaya Reserve in east-central Ecuador (Banos area, province of Tungurahua).
One of the new species from the Dracula Reserve was named Chilomys georgeledecii after the international conservationist George Ledec. It lives at a wide range of elevations, from 1500m to more than 2300m, and it is one of the smallest members of the genus in Ecuador. It lives in the same forests as the other new species from the Dracula Reserve, which was named C. carapazi after the Olympic bicycle racing gold-medalist Richard Carapaz, who is a native of Carchi province where the species was discovered. He is a hero in Ecuador, a role model and inspiraton, and everyone in Carchi looks up to him. Jorge Brito was very pleased to be able to honor him in this way. This species is the biggest member of the genus and it was found at an elevation of 2350m.
Another of the newly recognized species is C. percequilloi, named after a Brazilian mammologist. It lives from 1600m to over 4000m on the eastern slope of the Andes in Ecuador, including our Naturetrek-Viscaya Reserve. Two other species were also discovered, C. neisi from Zamora-Chinchipe and El Oro provinces in Ecuador at 2500-2900m, and C. weksleri from the west-central Andes of Ecuador from 1600-3200m.
DNA analysis performed by the authors shows that the genus Chilomys is a relatively young genus, less than 2.5 million years old, so the species described here are probably young species which evolved due to repeated Pleistocene isolation events driven by glacial cycles. This is similar to the time scales we see in Andean orchids, but much younger than some of the frog species we have discovered, as I will report shortly.
The previously-hidden diversity of these Chilomys mice is probably not unique. Other closely related genera (Neusticomys, Microryzomys, Oreoryzomys, Neomicroxus, etc) are also apparently far richer in species than we currently believe. Surely there will be more mammal discoveries to report here soon!
Jorge Brito’s work was made possible in part by donations to EcoMinga by Rainforest Trust and the University of Basel Botanical Gardens. Our reserve guards, especially Eduardo Pena and Fausto Recalde, worked closely with Jorge’s team in the field and helped prepare the specimens. Their salaries are paid by World Land Trust’s Keepers of the Wild porgram and Humans For Abundance.
Lou Jost, Fundacion EcoMinga