Biology Reference
In-Depth Information
plausible to hypothesize that there is no correlation between nectar produc-
tion and this kind of sexual expression.
Differences are also found in species with dimorphic flowers, e.g., in the
distylous plant
Palicourea padifolia
(Rubiaceae), long-styled flowers pro-
duce a higher nectar volume than short-styled flowers (Ornelas et al., 2004).
On the other hand, in the distylous species
Turnera subulata
(Turneraceae),
no differences in volume or concentration were revealed in the two flower
forms (Schlindwein & Medeiros, 2006). A strong and fixed dimorphic
system of nectar production, probably with a genetic basis, was observed
in populations of
Prosopis glandulosa
(Fabaceae) in the Chihuahuan desert,
in which half the individuals produce nectar and the other half are nectarless
(Golubov et al., 1999). In this situation nectarless individuals would have
an advantage if they received floral visitors attracted by the individuals
having nectar, while avoiding the cost of nectar production.
8.3
Interpopulation differences
Interpopulation differences in nectar characteristics also exist. Galetto and
Bernardello (1995) report differences in sugar composition in two Argen-
tinian populations of
Lycium cestroides
(Solanaceae), while Lanza et al.
(1995) describe differences in the amino acid profile of three populations of
I. capensis
(Balsaminaceae). Large variability in amino acid concentration—
greater than in amino acid composition—was found among plants of the
same population by Gardener and Gillman (2001).
Differences in habitat may contribute to nectar variability. Early studies
by Andrejeff (1932), Hocking (1968), and Heinrich and Raven (1972) showed
that bee flowers from high elevations and latitudes produce nectars with a
greater energy content than conspecifics at lower elevations and latitudes.
On the other hand, both hawkmoth- and hummingbird-pollinated flowers in
high-elevation habitats have lower sugar concentrations than those from
lower elevations (Cruden et al., 1983).
Differences in the dynamics of nectar production, related to different pol-
lination systems, are demonstrated between populations of the columnar cactus
Pachycereus pecten-aborigenum
growing in the tropics and at northern lati-
tudes. In the tropics, nectar is only produced at night and pollination is
exclusively by bats, while in northern regions nectar is produced by day and
night and pollination is by bats and diurnal pollinators (Valiente-Banuet
et al., 2004).
