Kp. Han et De. Lincoln, THE EVOLUTION OF CARBON ALLOCATION TO PLANT SECONDARY METABOLITES - AGENETIC-ANALYSIS OF COST IN DIPLACUS-AURANTIACUS, Evolution, 48(5), 1994, pp. 1550-1563
Diplacus aurantiacus contains large amounts of a leaf phenolic resin,
an important deterrent to a leaf-eating caterpillar, Euphydryas chalce
dona. The resin can also retard water loss during drought. Furthermore
, the leaf resin content differs among plants and populations. This st
udy investigates the existence of heritable variation (h(2)) in resin
production and tests for a genetic correlation (r(G)) between carbon a
llocation to secondary metabolites and growth rate, as well as with th
ree other vegetative traits. Nine dam and 10 sire plants were chosen r
andomly at a field site and used to generate 78 full-sib families (19
half-sib families) by crossing all males to all females in a factorial
design. Heritability was estimated in two ways, and genetic correlati
ons were estimated by three methods. We found: (1) the heritability of
resin production estimated by the regression of offspring on sires wa
s significantly greater than zero (h(s)(2) = 0.32, P < 0.01); (2) the
maternal variance in resin content was significantly greater than zero
(21.3% of total phenotypic variance); (3) significant negative geneti
c correlation between resin content and growth rate was observed from
two of three methods and was consistent with the phenotypic correlatio
n; and (4) the cost of resin could be assessed quantitatively. The gen
etic cost of 1 mg in resin is equivalent to 25 mg of dry shoot-biomass
growth, but the phenotypic cost is only 2.1 mg. This study indicates
that carbon allocation to these secondary metabolites may respond to n
atural selection, and the phenotypic cost of resin production has a ge
netic basis in D. aurantiacus. This trade-off suggests that once selec
tion occurs, increased phenolic resin production may result in decreas
ed growth, or vice versa.