NECTAR CONSUMERS - Nectaries and Nectar - page 323

systems have occurred eleven times, and shifts to lower reward systems six
times. The latter changes involve the loss of hummingbird pollination in a
few specialized species of Fuchsia , and its replacement by bee and fly polli-
nation. Pollination shifts may even involve the production of nectar in an
otherwise nectarless genus, such as Disa (Orchidaceae), in which floral nec-
tar is primitively absent but has evolved in species belonging to three
different clades and pollinated by diverse insect taxa (Johnson et al., 1998).
Of the floral traits involved in pollinator shifts, colour, and morphology have
been investigated more frequently than reward and scent (see the review of
Fenster et al., 2004). Earlier in this volume we looked at the question of
whether nectar sugar composition is determined by pollinator type or plant
phylogeny (Nicolson & Thornburg, 2007, Chapter 5 in this volume). Here I
discuss some comparative studies where species in the same genus have dif-
ferent pollinators and where multiple nectar traits have been examined, not
just sugar composition.
Southern Africa is the centre of diversity of the monocot family Iridaceae
and pollination systems in the African Iridaceae tend to be specialized
(Goldblatt & Manning, 2006). The large genus Gladiolus , with 165 species
in southern Africa, has radiated widely as a direct consequence of specializa-
tion for diverse pollinators (Goldblatt et al., 2001). Long-tongued anthophorid
bees are the ancestral pollinators of Gladiolus and the most important, but
there have been multiple shifts to diverse other pollinators: long-proboscid
flies (Nemestrinidae, Tabanidae), hopliine beetles (Scarabaeidae), a satyrid
butterfly, moths (Noctuidae and Sphingidae), and sunbirds. Nectar proper-
ties have been measured in many Gladiolus species, and while volume and
concentration tend to change with pollinator type (although substantial over-
lap remains), sugar composition is a more conservative character (Goldblatt
et al., 2001). This is clearly illustrated by 20 bird-pollinated species that have
originated in five out of seven sections of the genus (Goldblatt et al., 1999).
Gladiolus is primarily insect-pollinated and its nectar is consistently high in
sucrose, even in most of the bird-pollinated species: only one lineage of
three species has hexose-based nectar (see also Nicolson, 2002). Most of the
sunbird-pollinated species of Iridaceae retain high sucrose nectars, with the
exception of three genera with elevated hexose levels ( Chasmanthe , Klattia,
and Witsenia ) (Goldblatt et al., 1999).
The example of Gladiolus suggests that adding water may be enough to
convert a bee nectar into a bird nectar (together with increased floral size).
That is, the plant invests a similar amount of sugar but packages it in more or
less water. For example, Kaczorowski et al. (2005) studied the variation of
several floral traits with pollinators in Nicotiana species, all but one with high