INTRODUCTION - Nectaries and Nectar - page 13

interest in its non-sugar components, such as proteins which inhibit micro-
bial growth, amino acids which contribute to taste and the nitrogen balance
of pollinators, and alkaloids and phenols which deter certain pollinators but
not others. The water component in nectar, greatly affected by microclimatic
conditions, is an important factor in pollinator drinking rates and water bal-
ance.
The molecular biology of nectar is a relatively new area of research.
Chapter 6 describes the developmental processes that change the Nicotiana
floral nectary from a non-secretory organ into a secretory one. There is a
dramatic decline in levels of starch in the nectary to produce sugar for nectar
production. A general analysis of gene expression in nectaries is included,
with special reference to proteins with a defence function against microbial
attack.
Nectar consumption and ecology (Chapters 7 and 8)
Flowers differ in size by orders of magnitude, and so do their nectaries and
the volumes of nectar produced for nectar-consuming animals, which range
from 10 mg flies to 30 g bats. Nectar, especially in more open and accessible
flowers, is also consumed by nectar robbers, which provide no benefit to the
plant. The most numerous nectar consumers are found in three of the four
largest insect orders (Diptera, Lepidoptera, and Hymenoptera), and nectari-
vorous birds and bats provide reliable pollination services in warmer parts of
the world. Nectar feeding has physiological implications for all these ani-
mals in terms of water, energy, and nitrogen balance, but many are able to
utilize nectars of varying composition and concentration. As stressed by
Galetto and Bernardello (2003), “success in attracting pollinators is a relative
matter”, depending on alternative nectar sources available, so animal visitors
should not be too particular. The ability of flower-visiting animals to deal
with all kinds of nectar seems appropriate in view of the broad generalization
apparent in many plant-pollinator relationships.
Most of the individual studies on nectaries, nectar, and nectar consumers
included in this topic concern a few plant species (either sympatric or re-
lated) and a few animal species that visit them. The final chapter takes a
much broader approach, examining nectar resources at the community level
in Mediterranean habitats. The information is derived from a unique data set
including extensive analyses of nectar sugars and amino acids, combined
with a complete survey of insect visitors. It has enabled consideration of
several hypotheses about the evolutionary ecology of nectar production in
Mediterranean environments, where summer drought is common, flowers