Lorna Little

Floral biology and flower visitors on subantarctic Campbell Island

Abstract Island plants often show reduced floral pigmentation and display size compared with mainland relatives, which is commonly thought to relate to a lack of specialized pollinators. Some species on New Zealands subantarctic islands have spectacular, highly pigmented inflorescences, yet the depauperate insect fauna provides little apparent opportunity for biotic pollination. We document breeding systems and floral visitors for six Campbell Island species. All species tested had lipid-rich rather than starchy pollen and some produced nectar. Pleurophyllum hookeri appeared to be self-incompatible, but P. criniferum, Veronica benthamii and Damnamenia vernicosa were all capable of selfing. Daytime floral visitors were predominantly small Diptera and the flightless Muscid, Coenosis filipennis. The nocturnal wētā, Notoplectron campbellensis (Orthoptera), visited V. benthamii flowers and carried pollen between male and female plants of Anisotome latifolia and Bulbinella rossii. Biotic pollination might be more important in the subantarctic than previously thought and wētā are possibly key flower visitors.

Leaf and floral heating in cold climates: do sub-Antarctic megaherbs resemble tropical alpine giants?

High latitude and altitude floras are characterized by low-statured, small, wind-pollinated plants, which mainly reproduce by self-pollination or asexual reproduction. However, at odds with this are some sub-Antarctic islands that have plant species with giant growth forms and large, brightly coloured flowers which require insect visitation for pollination. The size, colour and shape of the inflorescences and leaves of these megaherbs suggest thermal benefits similar to giant tropical alpine plants of equatorial Africa, South America and Hawaii. We evaluated whether heating occurs in sub-Antarctic megaherbs, and to what extent it is related to environmental variables. We measured leaf and inflorescence temperature in six sub-Antarctic megaherb species on Campbell Island, latitude 52.3°S, New Zealand Biological Region. Using thermal imaging techniques, in combination with measurement of solar radiation, ambient air temperature, wind speed, wind chill and humidity, we assessed environmental influences on leaf and floral heating. We found that leaf and inflorescence temperatures of all megaherbs were higher than simultaneously measured ambient temperatures. Greatest heating was seen in Pleurophyllum speciosum, with observed leaves 9°C higher, and inflorescences nearly 11°C higher, than ambient temperature. Heating was highly correlated with brief, unpredictable periods of solar radiation, and occurred most rapidly in species with hairy, corrugated leaves and darkly pigmented, densely packed inflorescences. This is the first evidence that floral and leaf heating occurs in sub-Antarctic megaherbs, and suggests that leaf hairiness, flower colour and shape could provide thermal benefits like those seen in tropical alpine megaherbs.