E. Arevalo et al., PARAPATRIC HYBRIDIZATION BETWEEN CHROMOSOME RACES OF THE SCELOPORUS-GRAMMICUS COMPLEX (PHRYNOSOMATIDAE) - STRUCTURE OF THE AJUSCO TRANSECT, Copeia, (2), 1993, pp. 352-372
Genetic and morphological variation in the Sceloporus grammicus comple
x was examined along an elevational transect in the Sierra del Ajusco,
southwest of Mexico City. A total of 122 lizards was collected from s
ix localities beginning at 2400 m and set at every 200 m of elevation;
and a subset of 107 animals were examined for their chromosomal numbe
r, 10 morphological characters and three protein systems. A subset of
this sample was also examined for ribosomal and mitochondrial DNA rest
riction sites. Three chromosomal races were found, with 2n = 32 (LS) c
haracteristic of low elevation, 2n = 34 (F6) characteristic of interme
diate elevation, and 2n = 32 (HS) characteristic of high elevation. A
parapatric contact zone was found between locality four (F6) and five
(HS). A hybrid index score obtained with the diagnostic markers of the
se races showed a total of 42 pure F6,43 pure HS, six possible backcro
sses to F6, and two F1 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 distri
bution was very pronounced with the F6 haplotypes occurring at a frequ
ency of 0.5 at the LS locality. The rDNA markers showed symmetrical fl
ow to both sides of the F6 and HS races. Taxonomic implications of the
levels of morphological and molecular divergence are discussed, and t
he origins of the F6-HS and F6-LS contact zones are interpreted to rep
resent a secondary contact.