Researchers have found four species of mice on Mindoro Island in the Philippines, all of which evolved from the same common ancestor in an area the size of Connecticut.

This makes the location the smallest place ever documented to have evolved new mammals.

Smallest Island To Support New Mammals

Researchers released a paper in the Journal of Biogeography which shows genetic analysis done on the mice in Mindoro Island, revealing that they all share a single common ancestor. They were determined to find the smallest island that can support diversification of new mammals. The previous record holder of the smallest island to support new mammals is the Philippine island of Luzon.

The journey to find the smallest island that can support new mammals was first posed as a thought experiment in 1980. Conservation biologist Michael Soule asked if a new species would be able to diversify in an area the size of the largest existing national parks. Scientists were looking for a place where one species diversified into multiple species.

Mindoro Island is just across the bay from Luzon. It is one-tenth the size of Luzon and about two-thirds the size of Connecticut. 

Worm-Eating Mice

Once the researchers found Mindoro Island, they came across mice whose diet mainly consisted of earthworms. DNA analysis revealed that the mice belonged to four separate species, and three were newly discovered species. All four of the species evolved from the same common ancestor.

Analysis showed that the ancestor species made its way from Luzon to Mindoro around 2.8 million years earlier. Three of the four species are found on separate mountains on Mindoro. Measurements taken of the mice also show variations across all four of the species.

Mindoro Island is also around the same size as Yellowstone National Park. This answers the original questions posed by Soule as to whether new species can diversify in an area the size of some national parks.

Lead author on the study Lawrence Heaney, Negaunee Curator of Mammals at Chicago's Field Museum, says that this research affects the way that national parks should be constructed. Instead of thinking of the area as a flat surface, he says topography should be considered when making these areas. Separation of the mice by mountains contributed heavily to the diversification of the mice into four separate species.