Biology Reference
In-Depth Information
Mitchell (2004) postulates that floral nectaries should have more variable
nectar traits than extrafloral nectaries on the same plant. Indeed, variability
in rewards from extrafloral nectaries could reduce movements of ants within
plants, reducing defence against predators which is the commonly recog-
nized function of the association between ants and extrafloral nectaries.
A further source of variability in nectar composition is associated with
accidental pollution of nectar by foragers. Visitors may alter nectar composi-
tion, adding amino acids by direct contact, by salivation, by damaging neigh-
bouring tissues and causing cell leakage, and by dislodging pollen into the
nectar (Willmer, 1980; Gottsberger et al., 1990). Gottsberger et al. (1990)
found that contamination of nectar by pollen caused an increase in amino
acid content, especially of proline. As few as five pollen grains of
H. rosa-
sinensis
, with a mean diameter of about 200 µm, distinctly increase the
amino acid content of 20 µl of nectar. The increase in amino acid content after
nectary puncturing was caused mainly by asparagine. The authors advised
that particular care must be taken during nectar sampling for experimental
purposes: damage to nectary tissue may occur especially when using glass
micropipettes or capillaries. On the other hand, addition of
Aloe marlothii
pollen to the nectar of this species has no significant effect on nectar amino
acid concentrations (Nicolson, unpublished).
Nectar, especially when it is fully exposed to the environment and pre-
sented for a long period, may also be contaminated by airborne bacteria,
fungi (Fig. 5), or algal spores, as demonstrated by Clair-Maczulajtys and
Bory (1983) and Davis (1997). These micro-organisms may alter nectar
composition, though to what extent is not known experimentally and proba-
bly depends on nectar concentration and composition.
REFERENCES
Aizen, M.A., & Basilio, A. (1998). Sex differential nectar secretion in protandrous
Alstroe-
meria aurea
(Alstroemeriaceae): is production altered by pollen removal and receipt?
American Journal of Botany
,
85
, 245-252.
Andrejeff, W. (1932). Über Nektarien und über die Menge des Nektars einiger Gehölzarten.
Mitteilung Deutschland Dendrologie Gesellshaft
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44
, 99-105.
Arumugasamy, K., Subramanian, R.B., & Inamdar, J.A. (1990). Cyathial nectaries of
Eu-
phorbia neriifolia
L.: ultrastructure and secretion.
Phytomorphology
,
40
, 281-288.
Ashworth, L., & Galetto, L. (2002). Differential nectar production between male and female
flowers in wild cucurbit:
Cucurbita maxima
ssp.
andreana
(Cucurbitaceae).
Canadian
Journal of Botany
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80
, 1203-1208.
Baker, H.G. (1975). Sugar concentrations in nectars from hummingbird flowers.
Biotropica
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7
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