EVOLUTIONARY RELATIONSHIPS AMONG THE POTOOS (NYCTIBIIDAE) BASED ON ISOZYMES

Abstract

Isozyme electrophoresis was used to assess genetic variation in potoos (Nyctibiidae), a distinctive Neotropical family of caprimulgiform nightbirds. Interspecific levels of genetic differentiation among potoos are extremely high (range of Nei's D = 0.191-1.172) and are comparable to intergeneric levels of differentiation in other bird families. In addition, levels of genetic differentiation between populations of both Nyc- tibius grandis and N. griseus from east and west of the Andes are comparable to the high genetic distances found in cross-Andes comparisons in other isozyme studies of Neotropical birds. These data suggest that extant potoo lineages are quite old, and that substantial genetic diversity exists in potoos that is not conveyed in the current taxonomy, in which most potoo species lack named or described intraspecific variation, and all species share a single genus. Phylogenetic analysis of isozyme data supports the monophyly of Nyctibiidae through comparisons with outgroups from five other caprimulgiform families. Our results also support the monophyly of a clade composed of Nyctibius maculosus, N. leucopterus, and N. griseus, and confirm maculosus and leucopterus as sister taxa. The relationships of other potoos remain essentially unresolved, although there is weak support for the place- ment of N. bracteatus as the basal taxon. Relationships among caprimulgiform families are also essentially unresolved by these data, although there is some support for a clade composed of Caprimulgidae, Aegothelidae, and Eurostopodidae. The very high genetic distances from Steatornis to all other caprimulgiforms indicate that it represents the earliest branching lineage in the order. Resumen. - Electroforesis de proteinas fue usado para estudiar la variacion genetica de los nictibios (Nyctibiidae), una familia Neotropical de aves nocturnas. Los niveles de diferencia entre las especies de nictibios son altos (Nei's D = 0.191 hasta 1.172), tan alto como los niveles que se encuentran entre los generos en otras familias de aves. Los niveles de diferencia entre las dos especies con representantes en los dos lados de los Andes (el occidente y el oriente), Nyctibius grandis y N. griseus, estan de acuerdo con esos observados en otros estudios de aves de quienes los representantes ocurren en los ambos lados de las montafias. Estos resultados sugieren que los lineajes evolucionarios de nictibios son antiguos y que bastante diversidad genetica existe que no se puede reconocer con la taxonomia corriente. Un analisis filogenetico de los datos indica que los nictibios pertenecen a un grupo monofiletico y diferente de otros grupos de aves nocturnas. Los resultados tambien apoy- an la existencia de un grupo monofiletico compuesto de N. maculosus, N. leucopterus y N. griseus, en que las especies maculosus y leucopterus tienen una relacion mas cercana que con griseus. Las relaciones evolucionarias de los otros nictibios no fueron resolvadas, sin embargo los datos sugieren que N. bracteatus es la especie mas antigua. Tampoco resolvamos las relaciones entre las familias caprimulgiformas, aunque los datos sugieren que Caprimulgidae, Aegothelidae y Eurostopodidae son consanguineos. La grande dis- tancia genetica que existe entre Steatornis y otras familias en el estudio, indica que Steatornis es la familia mas antigua de las aves nocturnas. The potoos (Nyctibiidae) are an exclusively Neotropical family of nocturnal birds character- ized by their distinctive mimicry of vertical tree stubs, upon which they often perch. Mimicry is achieved by pointing their bill upward, closing their eyes, and laying their tail flat along the branch (Sick 1993). Their cryptic behavior, nocturnal habits, and tropical distribution have made them one of the most poorly known groups of birds. However, recent fieldwork in South America