Understanding the evolutionary history of a high Andean endemic: the Ecuadorian hillstar (Oreotrochilus chimborazo)

Abstract

Geographic isolation has been proposed as the factor driving subspecific diversity of the Ecuadorian hillstar (Oreotrochilus chimborazo), a highland species restricted to the naturally fragmented paramos of Ecuador and southern Colombia. Current taxonomy recognizes three subspecies: O. c. chimborazo (from the Chimborazo volcano), O. c. soderstromi (from the Quilotoa volcano), and O. c. jamesonii (along the paramos of Ecuador and southern Colombia). To understand the origin of this morphological diversity, we explored the genetic variation along the species range based on analyses of two mitochondrial genes (ND2 and ND4), and one nuclear intron (MUSK). Subspecies O. c. soderstromi was not included in the analysis, as it was not registered at or around its type locality, the Quilotoa volcano. Instead, only O. c. jamesonii was encountered in that area. We found no evidence of genetic structure corresponding to subspecies or physiographic units, aside from some inconclusive evidence in putatively isolated populations. Ecological niche modeling predicted continuous and homogeneous environmental space between the two volcanos, and field expeditions showed evidence of a potential contact zone between O. c. jamesonii and O. c. chimborazo. Also, our data suggest that the only specimen described as O. c. soderstromi may have been an intergrade. We discuss our results in the light of possible range shifts in the past, resulting from climatic fluctuations around the Pleistocene–Holocene transition.