Pseudocopulation of an orchid by male ants: a test of two hypotheses accounting for the rarity of ant pollination

Abstract

The orchid Leporella fimbriata is pollinated by pseudocopulation with winged males of the ant Myrmecia urens. This recently studied interaction provides a unique opportunity to examine the two current hypotheses concerning the apparent rarity of ant pollination systems worldwide. The first hypothesis requires a series of specialized growth forms and floral characteristics regarded as adaptations to ant pollination. L. fimbriata does not possess them. The second considers the pollenicidal effects of secretions from the metapleural gland of ants. These glands are absent in M. urens males and it may be that the occurrence of ant pollination requires the absence of metapleural glands in the vector.

Outcrossing in an ant pollinated clonal orchid

“…Of flights between flowers of known genotype, some 70 per cent (n = 13) were within clones. In addition, revisits to these same flowers were observed (Peakall, 1988, fig. 2(a) and Est-3 were most polymorphic at the Bickley site with 4 alleles recorded for each.…”

“…Similarly, the percentage of seed with embryos was higher for crosses but not statistically significant from self pollinated fruits (table 2). Pollinator movements in L. fimbriata have been found to be strongly localized with a mean of 314±46 m (Peakall, 1987(Peakall, , 1988. Fig.…”

“…First, to examine the clonal substructuring of patches since the orchid reproduces vegetatively by the formation of 1-3 daughter tubers which develop up to 14 cm from the parent tuber (Peakall. 1987(Peakall. , 1988.…”

“…Second, to examine the effect of pollinator movement within these patches on outcrossing rates. Third, the effect of pollinator movement was of special interest because of the unique pollination system involving pseudocopulation by winged male ants (Peakall et a!., 1987;Peakall, 1988). Ants are generally regarded as being incapable of cross-pollination (Hickman, 1974, see also review by Beattie, 1982).…”

“…Details of the pollination biology of L. fimbriata are provided in Peakall (1988 habitat are provided in Peakall (1987Peakall ( , 1988.…”