New Zealand Journal of Botany abstract
B96066
Received 31 October 1996; accepted 9 April 1997
Explosive flowering, nectar production, breeding systems, and pollinators of
New Zealand mistletoes (Loranthaceae)
JENNY J. LADLEY
DAVE KELLY*
Department of Plant and Microbial Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
ALASTAIR W. ROBERTSON
Department of Ecology
Massey University
Private Bag 11222
Palmerston North, New Zealand
*Author for correspondence
Abstract The six New Zealand loranthaceous mistletoes fall
into two groups based on pollination biology. Four (Alepis flavida,
Peraxilla colensoi, P. tetrapetala, and Trilepidea
adamsii) are bird pollinated with hermaphrodite flowers while the other two
(Ileostylus micranthus and Tupeia antarctica) are dioecious or
sub-dioecious and insect pollinated. We provide data on the pollination biology
of the five extant species (Trilepidea is extinct).
The two Peraxilla species and Trilepidea have recently been
shown to have explosive flowers. Here we show that Alepis has weakly
facultatively explosive flowers. The world distribution of explosive mistletoe
flowers suggests that the syndrome has arisen a number of times independently
within the family, and is found in about half the putatively ancestral genera.
The principal avian visitors to the bird-pollinated species were tui and
bellbirds; introduced species are numerically unimportant as pollinators. The
nectar production schedules of Alepis and Peraxilla encourage
single-visit pollination as little nectar is produced after the flowers open.
However, when bird densities are high, buds of Peraxilla may be forced
open prematurely, encouraging multiple visits.
Alepis is highly self-compatible and its flowers achieve good seed set
in the field even when all pollinators are excluded by mesh bags, partly
because pollen contacts the already-receptive stigma before the bud opens.
Unvisited Peraxilla buds do not open, but their morphology allows a low
level (11-22%) of self-pollination in the bud.
The sex ratio of Tupeia at Wainui (Banks Peninsula) was 3:1
female:male, while Ileostylus at Wakefield (Nelson) was subdioecious
with a 2.5:1:1 female:male:hermaphrodite ratio. Hermaphrodite Ileostylus
plants set seed even when pollinators are excluded, so self-pollination is
possible in this species.
Results suggest different species vary in their susceptibility to pollen
limitation affecting reproduction. The insect-pollinated species have
unspecialised pollination syndromes and are probably adequately pollinated by
native and/or introduced insects; Ileostylus is also self-compatible.
The bird-pollinated species are more susceptible with specialised pollination
systems depending principally on endemic birds, but the effect is reduced in
Alepis as its flowers can open themselves and it achieves good seed set
even when pollinators are excluded. Peraxilla spp. seem most at risk
with obligately-explosive flowers and only low seed set without pollinators.
Historical declines in the North Island have been greatest in the species with
the most exacting pollination requirements. Long-term conservation of these
mistletoes will require conservation of tui and/or bellbirds.
Keywords Loranthaceae; Peraxilla; Alepis;
Tupeia; Ileostylus; Trilepidea; bird pollination;
self-compatibility; dioecy; breeding systems; explosive flowering; nectar
production
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