The Geography of Phytochemical Races

2.3 Europe 29
involved probably the largest sampling program to be met in this review (and likely
any where else!). It has been known for some time that European populations of
L. corniculatus are usually polymorphic for keel petal color, which can be either
“light” referring to yellow pigmentation, or “dark” involving deposition of anthocyanin
glycosides toward the tip of the petal. The compounds involved have been
identifi ed as cyanidin and delphinidin [personal communication from P. Kakes to
T. J. Crawford and Jones (1988, p. 175)]. Previous studies revealed that pigmentation
is determined by a pair of alleles at a single locus, and that presence of the pigments
represents the dominant situation (Hart and Wilsie, 1959).
The presence of the petal pigment polymorphism prompted Jones and Crawford
(1977) to undertake a more systematic examination of the phenomenon. Although
no clear-cut pattern emerged from the study, dark-keeled plants seemed to occur
more commonly near the Atlantic and North Sea coasts of Europe. Limited sampling
in the same study in Great Britain revealed that the darker morph was more
common in plants found growing in northern England and Wales than in more
southern areas. Additional information on pigment variation in Scotland came from
a study by Abbott (1981), who found the color morph to occur more frequently in
eastern populations than in western ones. Crawford and Jones (1986) found that
the cline reported in Scotland also was evident in northern England, namely, an
increase in the frequency of the colored keel feature in populations in the east. This
study also recorded extremes in the appearance of the trait with the virtual absence
of pigmented keels in collections made in the vicinity of Morecambe Bay (map
reference: Lancaster, 54°03′N, 2°48′W) in the west to frequencies nearing 100%
in the vicinity of Flamborough Head (Fig. 2.15). The authors noted that interpretation
of these results was complicated by the fact that there was a steep increase in
frequency of the trait over the initial 30 km of the transect, followed by a slower
increase in frequency as samples were taken farther along the transect to the east.
It was not possible to determine whether this refl ected the “coastal” effect, as noted
Fig. 2.15 Morecambe Bay to Flamborough Head transect in study of keel color morph in Lotus
corniculatus