Dataset Information

Pollination mode in fig wasps: the predictive power of correlated traits.

ABSTRACT: The over 700 species of Ficus are thought to have co-speciated with their obligate pollinators (family Agaonidae). Some of these wasp species pollinate figs actively, while others are passive pollinators. Based on direct observations of mode of pollination in 88 species, we show that mode of pollination can confidently be predicted from fig traits only (anther-to-ovule ratio) or from wasp traits only (presence of coxal combs). The presence of pollen pockets is not a predictor of mode of pollination. Data, direct and indirect, on 142 species, demonstrate numerous cases of the loss of active pollination and suggest one or few origins of active pollination. Hence, active pollination, an impressive example of the sophisticated traits that may result from mutualistic coevolution, depends on selective forces that can be overcome in some species, allowing reversions. Despite frequent loss, active pollination remains the predominant mode of pollination in Ficus.

SUBMITTER: Kjellberg F

PROVIDER: S-EPMC1088715 | biostudies-literature | 2001 Jun

REPOSITORIES: biostudies-literature

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Pollination mode in fig wasps: the predictive power of correlated traits.

Kjellberg F F Jousselin E E Bronstein J L JL Patel A A Yokoyama J J Rasplus J Y JY

Proceedings. Biological sciences 20010601 1472

The over 700 species of Ficus are thought to have co-speciated with their obligate pollinators (family Agaonidae). Some of these wasp species pollinate figs actively, while others are passive pollinators. Based on direct observations of mode of pollination in 88 species, we show that mode of pollination can confidently be predicted from fig traits only (anther-to-ovule ratio) or from wasp traits only (presence of coxal combs). The presence of pollen pockets is not a predictor of mode of pollinat ...[more]

PMID: 11375097

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Project description:Fig trees are pollinated by fig wasps, which also oviposit in female flowers. The wasp larvae gall and eat developing seeds. Although fig trees benefit from allowing wasps to oviposit, because the wasp offspring disperse pollen, figs must prevent wasps from ovipositing in all flowers, or seed production would cease, and the mutualism would go extinct. In Ficus racemosa, we find that syconia ('figs') that have few foundresses (ovipositing wasps) are underexploited in the summer (few seeds, few galls, many empty ovules) and are overexploited in the winter (few seeds, many galls, few empty ovules). Conversely, syconia with many foundresses produce intermediate numbers of galls and seeds, regardless of season. We use experiments to explain these patterns, and thus, to explain how this mutualism is maintained. In the hot summer, wasps suffer short lifespans and therefore fail to oviposit in many flowers. In contrast, cooler temperatures in the winter permit longer wasp lifespans, which in turn allows most flowers to be exploited by the wasps. However, even in winter, only in syconia that happen to have few foundresses are most flowers turned into galls. In syconia with higher numbers of foundresses, interference competition reduces foundress lifespans, which reduces the proportion of flowers that are galled. We further show that syconia encourage the entry of multiple foundresses by delaying ostiole closure. Taken together, these factors allow fig trees to reduce galling in the wasp-benign winter and boost galling (and pollination) in the wasp-stressing summer. Interference competition has been shown to reduce virulence in pathogenic bacteria. Our results show that interference also maintains cooperation in a classic, cooperative symbiosis, thus linking theories of virulence and mutualism. More generally, our results reveal how frequency-dependent population regulation can occur in the fig-wasp mutualism, and how a host species can 'set the rules of the game' to ensure mutualistic behavior in its symbionts.

Project description:Local mate competition (LMC) favours female biased clutch sex ratios because it reduces competition between brothers and provides extra mating opportunities for sons. Fig wasps seem to fit LMC model assumptions and lay female-biased sex ratios as predicted. These female biased sex ratios increase fitness greatly. In line with predictions, their sex ratios become less female-biased as the number of mothers laying in the same fig increases. However, this variation results in comparatively small fitness benefits compared to just biased ratios and data suggest substantial mismatches with LMC theory. The mismatches are due to several factors. (1) Multiple foundresses typically lay too many daughters. (2) Single foundress sex ratios are explained by sequential oviposition and ladies-last models. (3) Mortality that typically exceeds 10% may decouple the link between primary sex ratios, the focus of model predictions, and secondary sex ratios of adult wasps that are counted by researchers. (4) Model assumptions are frequently violated: (a) clutch sizes are unequal, (b) oviposition may not be simultaneous (c) cryptic/multiple wasp species inhabit the same host, (d) foundress numbers are systematically undercounted, (e) inbreeding coefficient calculations are inaccurate, and (f) male wasps sometimes disperse. These data and calculations suggest that alternative explanations must be considered seriously. Substantial data show that wasps typically lay most of their male eggs first followed by mostly female eggs require a new approach. These "slope" strategies result in more accurate sex ratios that are automatically adjusted to foundress number, own and relative clutch sizes and to sequential clutches. This effect will alter sex ratios in all species once the egg capacity of a fig is crossed or when interference reduces clutch sizes. In addition to this passive response, the females of about half the studied species have a conditional response that reduces female bias under higher foundress numbers by laying more sons. Therefore, wasps seem to use a very simple strategy that increases their fitness. Natural selection could have optimized parameters of the slope strategy and possibly the existence of the slope strategy itself. Variation in the slope strategy that is the result of natural selection is adaptive. Research should therefore focus on quantifying variables of this slope strategy. Currently, it is unclear how much of the variation is adaptive as opposed to being coincidental by-products.

Dataset Information

Pollination mode in fig wasps: the predictive power of correlated traits.

Publications

Pollination mode in fig wasps: the predictive power of correlated traits.

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