Field sampling of fig pollinator wasps across host species and host developmental phase: Implications for host recognition and specificity

Abstract

Previous genetic studies of pollinator wasps associated with a community of strangler figs (Ficus subgenus Urostigma, section Americana) in Central Panama suggest that the wasp species exhibit a range in host specificity across their host figs. To better understand factors that might contribute to this observed range of specificity, we used sticky traps to capture fig-pollinating wasp individuals at 13 Ficus species, sampling at different phases of the reproductive cycle of the host figs (e.g., trees with receptive inflorescences, or vegetative trees, bearing only leaves). We also sampled at other tree species, using them as non-Ficus controls. DNA barcoding allowed us to identify the wasps to species and therefore assign their presence and abundance to host fig species and the developmental phase of that individual tree. We found: (1) wasps were only very rarely captured at non-Ficus trees; (2) nonetheless, pollinators were captured often at vegetative individuals of some host species; (3) overwhelmingly, wasp individuals were captured at receptive host fig trees representing the fig species from which they usually emerge. Our results indicate that wasp occurrence is not random either spatially or temporally within the forest and across these hosts, and that wasp specificity is generally high, both at receptive and vegetative host trees. Therefore, in addition to studies that show chemicals produced by receptive fig inflorescences attract pollinator wasps, we suggest that other cues (e.g., chemicals produced by the leaves) can also play a role in host recognition. We discuss our results in the context of recent findings on the role of host shifts in diversification processes in the Ficus genus.

Keywords: Ficus; diversification; host‐recognition; pollinators; specificity.

FIGURE 1

Expected numbers of trapped Pegoscapus pollinator individuals at different Ficus species and host developmental phases based on our hypotheses. Widths of the arrows represent the hypothesized relative attractiveness of each type of tree. Arrows with dashed lines represent pollinator choices resulting in pollinator fitness zero. If pollinators are most abundant at receptive trees belonging to the fig species from which they emerged (H1) and are attracted to other volatiles than those from receptive syconia (H2), we expect that the number of trapped pollinators increases from non‐Ficus trees, to vegetative Ficus, to receptive Ficus trees as well as from other Urostigma species to the Urostigma species from which it emerged. Parts in gray represent predictions that we do not directly address in this paper, based on the assumption that phylogenetic distance predicts similarity in fig volatile bouquets and thus to which pollinator species is more likely to be attracted.

FIGURE 2

Pegoscapus pollinator individuals trapped across three types of trees. Far more Pegoscapus individuals are trapped at receptive Urostigma trees. Significant differences based on 95% confidence intervals of the model are indicated with “*,” and non‐significant differences with “NS.” Note the pseudolog transformation; a transformation mapping numbers to a signed logarithmic scale with a smooth transition to linear scale around 0.

FIGURE 3

Pegoscapus pollinators trapped at four target Urostigma fig species. The number of trapped individuals at the non‐Ficus trees also plotted in each panel for comparison. More pollinators are trapped at vegetative Ficus trees compared to non‐Ficus controls. Significant differences, based on 95% confidence intervals calculated from the model for the number of trapped pollinators (see upper half of Table 2), are indicated with “*.” Note the pseudolog transformation; a transformation mapping numbers to a signed logarithmic scale with a smooth transition to linear scale around 0.

FIGURE 4

Species identifications of fig pollinators trapped at receptive and vegetative tree individuals belonging to 11 Urostigma fig species. The colored squares on the left side indicate the pollinator species usually emerging from these fig species. The majority of the pollinators identified at vegetative fig trees (right side) were trapped at their usual host species, and pollinators at receptive fig trees (left side) show an even higher specificity. The upper section represents six Urostigma fig species that have one associated Pegoscapus pollinator. The lower sections represent fig species that diverge from the 1‐to‐1 pattern. Note that, due to sampling bias, bar lengths are not representative of the number of trapped Pegoscapus individuals at the host trees.

FIGURE 5

Estimates of the presence of six Pegoscapus pollinator species at four types of Urostigma fig trees. Pollinator estimates are highest for receptive fig trees belonging to the Urostigma species from which they regularly emerge. Besides, there seems to be a trend of higher pollinator estimates for other receptive fig trees as well as for vegetative fig trees that belong to their usual host species compared to other vegetative trees from other species. Estimates are based on bootstraps of the results presented in Figures 1 and 3. Note that Pegoscapus gemellus A, marked with (**), is associated with two fig species. P. gemellus C was not found on receptive individuals of other Ficus species than the species it emerged from, so no estimates were possible here. Significant differences are indicated with a line, and all other comparisons are not significant. Confidence intervals can be found in Table 4.