The Geography of Phytochemical Races

82 2 Examples Within Continents
Most of the protein profi le groups clustered as geographical units, which can be
represented broadly as occurring in the following areas: California, southern Arizona,
northern Arizona, Utah, eastern New Mexico, northeastern New Mexico, and
Wyoming. In general, populations from nearby localities exhibited the highest levels
of similarity. Two exceptions to this generalization require comment. A population
in northeastern New Mexico seems to be out of place since it was shown to link
most closely with two populations from southern Wyoming. No explanation was
offered for this unexpected pairing since there is little similarity between the habitats
in the two areas. The second exception involves a population from northeastern
New Mexico, which was found to be most closely related to several populations
from eastern New Mexico. In this situation, all populations were growing in pinyon
pine-juniper woodlands. It seems reasonable to suggest that the New Mexico population
arose from the chance combination of a propagule and an appropriate niche.
Overall, it was suggested that the occurrence of C. fremontii likely became successful
owing to the evolution, and successful establishment, of several local races
throughout its range.
Additional evidence suggesting that C. fremontii is genetically more homogeneous
than its morphology would suggest came from a study of allozyme profi
les. Collections involving over 1100 plants from 40 populations were assayed for
glutamate-oxaloacetate transaminase (GOT) and leucine aminopeptidase (LAP),
while over 600 plants from 22 populations were assayed for phosphoglucoisomerase
(Crawford and Wilson, 1977). Sampling was expanded to include populations
from Colorado and Nebraska in addition to the states listed above. These collections
include a wider range of the species than was studied in the seed protein study,
which presents some problems in making direct comparisons of specifi c sites.
Nonetheless, the overall geographic patterns that emerged from the allozyme study
agreed with observations drawn from the earlier data set. The most obvious result
is the observation that the Californian populations were fi xed for an allele of GOT
not seen in any other population. This is in line with the unique seed-storage protein
profi le observed and, as we shall see below, with the existence of a fl avonoid race
restricted to the Californian populations.
Other than the Californian situation with regard to GOT alleles, the distribution
pattern can be reckoned as consisting of, to a reasonable degree at least, a northern
“race” found in populations from Nebraska, northern and western Colorado,
Utah, and Wyoming. The southern “race” occurs in Arizona, central and southern
Colorado, and New Mexico. Three populations from northeastern New Mexico,
however, exhibited the highest level of variation seen in the study with 11 of the 13
heterozygous plants observed being from this region. The authors offered two possible
explanations for the observed allelic arrays: (1) this area represents a zone of
gene exchange; or (2) this area may represent a center of diversity. Efforts to study
the possibility of hybridization between the two GOT races failed owing to technical
problems with pollination.
The third paper in the Chenopodium fremontii study involved an investigation
of the species’ fl avonoids (Crawford and Mabry, 1978). Twenty-two populations
were sampled representing much of the range of the species. Four fl avonoid races