Explosive flowering, nectar production, breeding systems, and pollinators of New Zealand mistletoes (Loranthaceae)

  • Ladley J
  • Kelly D
  • Robertson A
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Abstract

The six New Zealand loranthaceous mis-tletoes fall into two groups based on pollination bi-ology. Four (Alepis flavida, Peraxilla colensoi, P. tetrapetala, and Trilepidea adamsii) are bird polli-nated with hermaphrodite flowers while the other two (lleostylus 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 explo-sive 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 encour-age single-visit pollination as little nectar is produced after the flowers open. However, when bird densi-ties 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 be-cause 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 Penin-sula) was 3:1 female:male, while Ileostylus at Wakefield (Nelson) was subdioecious with a 2.5:1:1 female:male:hermaphrodite ratio. Hermaphrodite lleostylus plants set seed even when pollinators are excluded, so self-pollination is possible in this spe-cies. Results suggest different species vary in their susceptibility to pollen limitation affecting reproduc-tion. The insect-pollinated species have unspecial-ised 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 special-ised 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 ex-acting pollination requirements. Long-term conser-vation of these mistletoes will require conservation of tui and/or bellbirds.

Author-supplied keywords

  • Alepis
  • Bird pollination
  • Breeding systems
  • Dioecy
  • Explosive flowering
  • Ileostylus
  • Loranthaceae
  • Nectar production
  • Peraxilla
  • Self-compatibility
  • Trilepidea
  • Tupeia

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Authors

  • Jenny J. Ladley

  • Dave Kelly

  • Alastair W. Robertson

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