Temporal patterns in the planulation of the scleractinian coral, Pocillopora damicornis (Linnaeus 1816), common on Singapore reefs were observed from August to November 1990. Widely distributed throughout the Indo-Pacific, the species is known to release planula larvae after internal fertilisation. At any one time, six colonies collected from the field were maintained in clear, sheltered outdoor aquaria and daily planula counts observed. Planulation was observed to be directly influenced by the lunar cycle, commencing 2 to 3 days before the new moon, peaking at around the new moon and ending close to the first quarter. This periodicity is similar to the planulation patterns observed in P. damicornis populations of the Central Pacific, particularly those of Palau, as well as the populations in the Great Barrier Reef during the Austral summer.

1. Mutualisms, including plant-pollinator interactions, are an important component of ecosystems. 2. Plants can avoid the costs of variation in pollinator benefit by maintaining specificity. 3. We hypothesise a novel mechanism to ensure specificity, which takes advantage of the cognitive abilities of specific pollinators to exclude non-specific flower visitors. 4. Inflorescences of the tropical vine genus Psiguria produce flowers at regular intervals, with subsequent flowers smaller than predecessors. 5. The principle pollinators, Heliconius spp., possess an excellent spatial memory. 6. Therefore, decreasing flower size may ensure specific pollination: once Heliconius individuals have learnt the location of an inflorescence they will return, but inconspicuous flowers should reduce visits by non-specific pollinators with poorer spatial memories. 7. We tested the predictions of this hypothesis with field experiments in Panama. We confirmed that flowers on inflorescences are smaller than their predecessors. 8. Paired experiments showed that larger flowers attracted more pollinators and that the presence of an initial large flower increased subsequent visitation by Heliconius spp. to small flowers, indicating learning behaviour. 9. These results suggest that learning behaviour and decreasing flower size maintain visits from specific pollinators while reducing those from non-specific pollinators. We propose this as a novel mechanism for promoting pollinator specificity and discuss its ecological significance.