The Geography of Phytochemical Races

6.2 The Hawaiian Islands 257
fl avonoids of individual plants revealed that hybrid plants of several generations
existed in the area, some clearly fi rst generation, others that appear to have arisen
through backcrossing with one of the parental species. Unfortunately, there were
too few individuals available in the fi eld to allow us to pursue the study. Ideally,
one would have liked to study the fl avonoid profi les of individuals obtained from
controlled backcrosses.
6.2.6 Vaccinium (Ericaceae)
Vaccinium is represented on the islands by three endemic species, V. calycinum, V.
dentatum, and V. reticulatum. Following the discovery of a high level of withinpopulation
variation in the fl avonoids of Bidens, as noted, above, an examination
of other Hawaiian taxa was undertaken to see if similar patterns (or lack thereof) of
variation were characteristic of island endemics. Analysis of extensive collections
of V. calycinum and V. reticulatum from several islands for fl avonoids and condensed
tannins (Bohm and Koupai-Abyazani, 1994) revealed qualitatively identical
profi les. Some quantitative variation was evident, but no efforts were made to determine
if this were caused by local environmental factors or refl ected genetic differences.
The profi les observed were of the same general sort seen in North American
species of blueberry, in agreement with observations, based on DNA sequences,
that the island species are most likely related to mainland blueberries (Powell and
Kron, 2002). The DNA study revealed that the island species very likely resulted
from a single colonization event. Diversifi cation into the three current species has
not affected the species’ fl avonoid biosynthetic apparatus.
6.2.7 Zanthoxylum
In a study of insecticidal properties of Zanthoxylum (Rutaceae) endemic to the
Hawaiian Islands, Marr and Tang (1992) noted a good deal of variation among individuals
of the three species available to them, Z. dipetalum H. Mann, Z. hawaiiense
Hillebr. and Z. kauaense A. Gray, as well as among the species themselves. Signifi
cant differences in toxicity (based upon egg hatch assay using Dacus dorsalis
Hendel, the oriental fruit fl y) were observed among the species, 12 of 47 individuals
of Z. kauaense yielded toxic extracts, whereas only one of 12 individuals of
Z. dipetalum was toxic. Twenty-one individuals representing Z. hawaiiense were
tested but none of them was toxic.
Variation within a species was examined by looking at the chemistry of
Z. dipetalum specimens collected from sites on three islands, Hawaii, Kauai, and
Oahu. Of the seven compounds detected in this comparison, only two, caryophyllene
[542] and humulene [543] (see Fig. 6.5 for structures 542–546), were present
in all individuals. Trees from a site on Oahu were unique in their possession of