Revista Chilena de Historia Natural 86 (2): 115-125, 2013
RESEARCH ARTICLE
A hybrid zone of two toad sister species, Rhinella atacamensis
and R. arunco (Anura: Bufonidae), defined by a consistent altitudinal segregation in
watersheds
CLAUDIO CORREA, MARCO A. MÉNDEZ, SERGIO ARAYA, GABRIEL LOBOS & R. EDUARDO
Delimiting the spatial extension of a hybrid zone is essential to understand its
historical origin and to identify the geographical and/or environmental factors which delimit it. Rhinella atacamensis
and R. arunco are two sister species which together inhabit Chile between 25° and 38° S. Their
distribution limits coincide at about 32° S, where recently it was reported that they hybridize in a small watershed (Pupío
creek). Although the genetic evidence suggests that these two species form a hybrid swarm, they are not mixed
homogeneously in the entire watershed, but rather are spatially segregated: R. arunco is found in the lower part
of the creek and R. atacamensis in the higher part. An extensive exploration north and south of 32° S revealed
other instances of hybridization, with the same pattern of spatial segregation within other watersheds. This study describes
the hybrid zone combining mitochondrial sequences and nuclear AFLP markers. In the northern part, the hybrid zone is a
narrow strip which crosses several watersheds and extends more than 130 km from NW-SE, so that R. atacamensis
is found at higher altitudes towards the south. However, two points south of this strip show that the hybrid zone is
more extensive and complex, and probably extends along the entire border of the mountain chains which form the
watershed of the Aconcagua River (32°30’ - 33° S). We propose an explanation for the origin of this hybrid zone considering
paleoclimatic and orographic information, and briefly discuss the taxonomic implications of these
results.
AFLP
markers, Chile, control region, hybridization, toads.
