Evolution of the endangered Perdido beach mouse. Illustration showing the eight subspecies of the beach, or oldfield, mouse (Peromyscus polionotus) and their distribution in the southwestern USA. Five subspecies inhabit the Gulf Coasts of Alabama and Florida. From left to right these are the Alabama beach mouse (Peromyscus polionotus ammobates), the Perdido Key beach mouse (Peromyscus polionotus trissyllepsis), the Santa Rosa Island beach mouse (Peromyscus polionotus leucocephalus), the Choctawhatchee beach mouse (Peromyscus polionotus allophrys) and the Saint Andrews beach mouse (Peromyscus polionotus peninsularis). Three subspecies inhabit Florida’s Atlantic coast. From top to bottom these are the Anastasia Island beach mouse (Peromyscus polionotus phasma), the pallid beach mouse (Peromyscus polionotus decoloratus) and the southeastern beach mouse (Peromyscus polionotus niveiventris). Apart from the Santa Rosa Island beach mouse, all these subspecies are threatened or endangered, largely due to habitat loss.