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Making the most of your pollinators: An epiphytic fig tree encourages its pollinators to roam between figs

Citation

Mohd Hatta, Siti Khairiyah; Compton, Stephen; Quinnell, Rupert; Abd Ghani, Idris (2021), Making the most of your pollinators: An epiphytic fig tree encourages its pollinators to roam between figs, Dryad, Dataset, https://doi.org/10.5061/dryad.np5hqbzrh

Abstract

Ficus species are characterised by their unusual enclosed inflorescences (figs) and their relationship with obligate pollinator fig wasps (Agaonidae). Fig trees have a variety of growth forms, but true epiphytes are rare; one example is the Ficus deltoidea of South-east Asia.  Presumably as an adaptation to epiphytism, inflorescence design in this species is exceptional, with very few flowers in female (seed-producing) figs and unusually large seeds. Figs on male (pollinator offspring-generating) trees have many more flowers. Many fig wasps pollinate one fig each, but because of the low number of flowers per fig, efficient utilization of F. deltoidea’s pollinators depends on pollinators entering several female figs. We hypothesised that it is in the interest of the plants to allow pollinators to re-emerge from figs on both male and female trees and that selection favours pollinator roaming because it increases their own  reproductive success. Our manipulations of Blastophaga sp. pollinators in a Malaysian oil palm plantation confirmed that individual pollinators do routinely enter several figs of both sexes. Entering additional figs generated more seeds per pollinator on female trees and more offspring on male trees. Pollinator offspring sex ratios in subsequently-entered figs were often less female-biased than in the first figs they entered, which reduced their immediate value to male trees because only female offspring carry their pollen.  Small numbers of large seeds in female figs of epiphytic F. deltoidea may reflect constraints on overall female fig size, because pollinator exploitation depends on mutual mimicry between male and female figs.

Methods

Study site

The study was carried out in Banting district, Selangor, West Malaysia between April and July 2017. Banting has a tropical climate with average daily minimum temperatures ranging from 24.0 to 25.2 °C, and maximum temperatures ranging between 30.9 and 32.5 °C with little seasonal variation. The average monthly precipitation is 144.3 mm. Our 2.1 ha oil palm plantation study site held about 285 oil palms that had been planted in 2001 on a peat soil.    The oil palms at Banting supported 113 epiphytic individuals of F. deltoidea var. angustifolia, with usually a single plant per trunk. Leaf and fig production was asynchronous both within plants and across the population as a whole and figs were present on the plants more or less continuously throughout the year (Mohd Hatta, 2019). The figs on female trees contained only between 3 to 6 female flowers. Although the male and female figs had a similar small size at the developmental stage when they were attractive to pollinators (around 4 mm in diameter) the male figs contain an average of 143 female flowers. In addition, the male figs also contain up to 20 or more male flowers (Mohd Hatta, 2019).

 

The specificity of the pollinators that service different varieties of F. deltoidea has not been clearly established. The only formally recognised pollinator is Blastophaga quadrupes Mayr which was recorded from an un-confirmed variety of F. deltoidea in Java. In Peninsular Malaysia the three varieties commonly present as epiphytes in oil palm plantations each have morphologically distinct Blastophaga spp. pollinators (Mohd Hatta, 2019). Here, we refer to the pollinator of F. deltoidea var. angustifolia as Blastophaga sp. Blastophaga sp. is a passive pollinator that transports pollen on its general body surface. Unusually for a Ficus species, no non-pollinating fig wasps were found in the figs of F. deltoidea at our study site and elsewhere in Malaysia (Mohd Hatta, 2019).

 

        Natural pollination rates

The behaviour of Blastophaga sp. in the plantation was recorded using 200 haphazardly-collected figs from 21 male and 10 female trees.  The figs were at early C phase (sensu Galil and Eisikowitch 1968), the stage of development when the figs contain galled ovules (male trees) or developing seeds (female trees) and the bodies and wings of foundress females that died in the figs were also present.  Seed or gall development confirmed that a foundress had entered the figs, and the presence of wings indicated that the fig had been the first one to be entered by at least one of the foundresses. Development of figs where no foundress was present indicated that one or more foundresses had entered, but had then re-emerged. When the body of a foundress was present, the position and orientation of its head was recorded. If the body was in the central cavity of the fig cavity, they had potentially laid eggs or pollinated the ovules. Foundresses in the ostioles with their heads facing towards the centre of the figs had died there before reaching the female flowers.

 

        Experimental manipulations

The behaviour of individual foundresses on male and female figs was assessed by introducing individual Blastophaga sp. females into netting bags surrounding groups of 4-15 adjacent receptive figs. The figs had been bagged earlier (at A phase sensu Galil and Eisikowitch 1968) to prevent prior entry by pollinators. One to two weeks later, mature male figs were collected locally just before the fig wasps were expected to emerge and placed in mesh-covered containers to let the female fig wasps emerge naturally. Shortly after they emerged, a single foundress was placed in each bag using a fine brush. The bag was then closed again to prevent entry by other pollinators. In total, 63 bags were placed in 11 female trees and 63 bags in 10 male trees.

 

Six weeks later, the bags were opened to record how many developing figs were present, and we recorded the numbers of fig wasp offspring and seeds they contained.  Pollinators had entered at least one fig in 30 of the bags on 6 male trees and 38 of the bags on 8 female trees. The first fig entered by each foundress was identified by the presence of the wings in the ostiole, but the precise sequence of entry by each wingless foundress into the subsequent figs could not be determined. The counts nonetheless allowed comparisons of the size of clutches or the numbers of seeds generated by a single foundress in their first and subsequent figs.

 

       Data Analysis

Statistics were performed in R (1.0.153) and SPSS Statistics 20. The frequency of figs entered by a single foundress was analysed using Chi Square Test. The total brood size for foundresses that entered different numbers of figs, total brood size of first entered and subsequent male figs and total seed production in the first and subsequent female figs entered were analysed using generalized linear models (GLM) with Poisson error distributions. If over-dispersion occurred, quasi-Poisson errors were used for those count data. Offspring sex ratios in emerged and non-emerged foundresses were analysed using generalized linear models (GLM) with a Gaussian error and offspring sex ratios in the first and subsequently entered figs were analysed using generalized linear models (GLM) with a quasi-binomial error distribution and logit link. Spearman rank correlations were used when examining the relationship between brood size and sex ratio in the experimental figs.

Usage Notes

These data are the raw data. NOT being analysed in SPSS and R yet.

Funding

Universiti Teknologi MARA