On the uniquely fragmented distribution of a rare Panamanian snake, Dipsas nicholsi (Colubridae: Dipsadinae)

Abstract

Dipsas nicholsi has been known from a handful of specimens collected during the final threequarters of the 20th century. All came from a restricted lowland area (60-150 m) in central Panama, in the upper drainage of the Rio Chagres. A recently identified specimen, the first known juvenile and only the second female, was found in 1997 in the Darie'n highlands (Serrania de Jingurudo, 855 m) of extreme eastern Panama, about 250 km from the clustered lowland localities in central Panama. It differs from central Panamanian specimens in some scutellation characters and especially in details of dorsal color pattern. The species' rarity makes it impossible to determine whether differences reflect geographic isolation or unknown aspects of ontogenetic, sexual, or individual variation. Distributional disruptions are commonplace in the Panamanian herpetofauna, although difficult to verify in the case of rare species. However, in the absence of a present-day habitat corridor, the Darien specimen of Dipsas nicholsi clearly represents a population widely separated and discontinuous from the one in central Panama. The Serrania de Jingurudo population, apparently a distributional relict, slightly closes the wide geographic gap between Dipsas nicholsi and its likely sister species, D. andiana, of western Ecuador. Commentary is provided on the cartographic names of several eastern Panamanian highlands. The Serrania de Jingurudo' takes its name from a river, as shown by the Embera's suffix-do. This highland was known for nearly half a century as the Sierra or Serrania de `Jungurudo', probably a confused combination of a still-older map name (Sierra de ``Jungururo'') and the Rio Jingurudo