The Geography of Phytochemical Races

74 2 Examples Within Continents
Table 2.14 Variation in selected acyl sugar concentrations as a function of latitude in Lycopersicon
pennelli (from Shapiro et al., 1994)
Collection LAT S Concentrationsa 2-MP 2-MB PAG
1809b 5°0′ 2.3 62.7 56
2560 8°45′ trace 60.7 52
1657A 9°20′ 4.9 49.2 67
1376 11°0′ trace 53.9 60
1272 11°30′ trace 53.3 54
1367 11°50′ 4.2 54.5 60
1282 12°0′ trace 54.5 54
1340 12°40′ 43.8 2.7 77
1674 13°10′ 59.1 6.9 93
1732 13°10′ 54.9 4.8 94
1656 13°20′ 49.5 11.0 87
1302A 13°40′ 50.1 15.5 70
1946 15°50′ 41.6 13.0 86
1941 15°55′ 42.2 8.5 88
716 16°10′ 41.8 4.0 84
a 2-MP = Percentage of total peak area for glucose
2-methylpropionate; 2-MB = ditto for 2-methylbutanoate;
PAG = percentage acylglucoses among total acylsugars.
b Collection numbers from source paper.
Capillucas at 12°40′S. The authors also considered the possibility that acylsugar
concentration may be affected by elevation, with the longer-chain derivatives being
the more viscous of the esters, and thus providing an advantage to plants growing
in the lower, hotter sites. The only relationship of note, however, involved the
n-decanoate derivative, which showed a positive correlation with latitude (r = 0.62,
p = 0.006). No adaptive signifi cance was attributed to the differences in acylsugar
composition, which the authors felt might simply refl ect fi xation of the two forms
after differentiation and dispersal. In most cases, individuals within a sampled population
exhibited very similar acylsugar compositions.
In an earlier study, Rick and Tansley (1981) studied this species (called Solanum
pennellii in their paper) in order to determine the level of genetic variation exhibited
throughout its range. Genetic variability was measured in terms of mean number
of alleles per locus, proportion of polymorphic loci, polymorphic index, and mean
actual heterozygosity. Values for these features were highest in the central northern
part of the region, with the lowest values recorded for plants at the northern and
southern extremities of the range.
2.6.5 C 3 and C 4 Grasses in Argentina
The example from South America ranks among the most impressive searches
for variation in the literature of chemical geography. Although it does not fi t