DIVERSITY in NATURE If Gardeners Can Hybridise Closely Related Seeds of Young Fruit

by Dr Brett Summerell Professor George Weiblen recently visited the Royal Botanic Garden, Sydney DIVERSITY IN NATURE If gardeners can hybridise closely related seeds of young fruit. The fig is actually or P. imperialis carrying Port Jackson plants to produce a new variety, what a hollow cavity containing many small pollen. We repeated this on many figs to prevents species from intermingling in flowers, accessible by a narrow pore at one compare the fruit resulting from crosses nature? Botanists through the ages have end. Female fig wasps are expert at within and between the two species. been intrigued by this question and have navigating their way inside while also Each week, the Garden measures these asked their favourite plants for answers. delivering pollen to the flowers; males figs while awaiting the fruit. We do not My favourites are strangler figs. These never leave the fig fruit. Pollen is collected know what to expect but we’re excited to magnificent trees of tropical rainforests at birth, when female wasps are hatched, learn if the two species can hybridise. also grace gardens worldwide. Moreton mate with males of their species, then seek One reason for the experiment is to Bay fig (Ficus macrophylla) and Port new figs in which to lay eggs. The wasps understand whether some of the diversity Jackson fig (F. rubiginosa), with their are dependent on their host plants for food. in nature could be the result of fig wasps impressive aerial roots, are two popular finding new homes. Seeds from our trees. An example near the Sydney Opera HYBRID EXPERIMENT experiment can be grown to observe the House, with branches that arch almost to Fig wasps will not pollinate or feed on hybrids. A skeptical passerby asked me the ground, attracted my attention during just any fig. Although Moreton Bay and why anyone should care. I told him that a visit to the Royal Botanic Garden, Sydney. Port Jackson figs are close relatives, Port diversity in nature is the key to survival On that sunny afternoon in February, Jackson figs have a unique pollinator for many species. It certainly is for the fig only a trained eye might have noticed that named Pleistodontes imperialis. We know wasps that seem to make informed choices the green figs were teaming with tiny fig that fig wasps can make mistakes and visit about where to live and how. Perhaps our wasps known as Pleistodontes froggatti . a fig of a different species from the one in own species will learn something. Fig wasps use their stingers to lay eggs in which they were born, but we don’t know Professor George Weiblen flowers, and their offspring feed on the whether cross pollination between the two University of Minnesota species of figs could produce a new hybrid. Professor James Cook, a fig wasp expert at the University of Western Sydney, and I attempted to find out by setting up an experiment with one of the Moreton Bay figs at the Garden. First, we glued shut the opening of the fig to prevent wasps from entering. Next, we punched a hole in the fig and inserted a narrow glass tube A narrow glass tube through which we could introduce either Wasps are introduced into is inserted into the fig P. froggatti carrying Moreton Bay pollen the fig through the tube Photos: Professor David Geiser, Daniel Bishop, Jaime Plaza: © Royal Botanic Gardens and Domain Trust. Daniel Bishop, Jaime Plaza: © Royal Botanic Gardens David Geiser, Photos: Professor THE GARDENS SPRING 2014 5.

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