Parapatric Hybridization between Chromosome Races of the Sceloporus grammicus Complex (Phrynosomatidae): Structure of the Ajusco Transect

Abstract

ric contact zone was found between locality four (F6) and five (HS). A hybrid index score obtained with the diagnostic markers of these races showed a total of 42 pure F6, 43 pure HS, six possible backcrosses to F6, and two F, individuals. Different levels of introgression were found for the different marker systems. Two different classes of markers, allozyme and mtDNA, showed asymmetrical gene flow from the F6 into the LS. The asymmetrical flow of the F6 mtDNA into the LS distribution was very pronounced with the F6 haplotypes occurring at a frequency of 0.5 at the LS locality. The rDNA markers showed symmetrical flow to both sides of the F6 and HS races. Taxonomic implications of the levels of morphological and molecular divergence are discussed, and the origins of the F6HS and F6-LS contact zones are interpreted to represent a secondary contact. Se examin6 variaci6n genetica y morfol6gica en el complejo Sceloporus grammicus a lo largo de un transecto elevacional en la Sierra del Ajusco, al suroeste de la ciudad de Mexico. Un total de 122 lagartijas se colectaron en seis localidades empezando a los 2400 m y establecidas a cada 200 m de altitud, y una submuestra de 107 animales fue examinada en cuanto a su numero cromos6mico, diez characteres morfol6gicos y tres sistemas de proteinas. Una selecci6n de esta muestra