Sexual specialization in phenology in dioecious Ficus benguetensis and its consequences for the mutualism.

Shang-Yang Lin,Bruno Di Giusto,Lien-Siang Chou,Anthony Bain

doi:10.1186/s40529-015-0113-7

Shang-Yang Lin, Bruno Di Giusto + Show 2 more

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https://doi.org/10.1186/s40529-015-0113-7

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Abstract

BackgroundTiming of reproductive events has become central in ecological studies linking success in pollination and seed dispersion to optimizing the probability and periods of encounters with pollinators or dispersers. Obligate plant–insect interactions, especially Ficus–fig wasp mutualisms, offer striking examples of fine-tuned encounter optimization as biological cycles between mutualistic partners are deeply dependent on each other and intertwined over generations. Despite fig flowering phenology being crucial in maintaining Ficus–fig wasp mutualisms, until now, the forces of selection shaping the phenological evolution of dioecious fig trees have received little attention. By conducting a 2-year survey of a population of Ficus benguetensis in Northern Taiwan, we assessed whether environmental factors or other selective pressures shape the phenology of male and female fig trees.ResultsConstraints by mutualistic pollinating wasps and seed dispersers, rather than climatic factors, appeared to mainly shape fig phenology and allometry in F. benguetensis. We identified a new sexual specialization in dioecious fig trees: the position of fig production. We propose that the continuous male fig production on tree trunks can enhance the survival of pollinating fig wasps through faster localization of receptive figs while reducing the mutualistic conflict between the fig and its obligate pollinators. By contrast, in female trees, fig production is massive in summer, located on the twigs of the foliar crown and seem more related to seed dispersal and germination.ConclusionsIdentifying variations in the allometry and phenology of dioecious figs provide valuable insights into how monoecious and dioecious species resolve mutualism conflicts and into the emergence of dioecy in fig trees.Electronic supplementary materialThe online version of this article (doi:10.1186/s40529-015-0113-7) contains supplementary material, which is available to authorized users.

Highlights

Timing of reproductive events has become central in ecological studies linking success in pollination and seed dispersion to optimizing the probability and periods of encounters with pollinators or dispersers
We investigated the factors affecting the phenology of Ficus benguetensis, a dioecious species involved in a constrained mutualism
Phenological census To investigate the phenology of F. benguetensis without anthropic interferences, a natural habitat was selected near Xindian District, New Taipei City, Taiwan (E121°33′55.44; N24°53′49.56)

Summary

Introduction

Timing of reproductive events has become central in ecological studies linking success in pollination and seed dispersion to optimizing the probability and periods of encounters with pollinators or dispersers. Some dioecious species exhibit intrasexual synchronized flowering phenologies (Kjellberg et al 1987; Patel 1996), where trees from one sex crop after the other In such systems, pollinators have no choice but to enter the receptive fig of whichever sex is available. Two studies (Soler et al 2011, 2012) have suggested that combined phenological synchrony and intersexual mimicry (resembling scents in receptive figs of both sexes) can reduce the ability of fig wasps to actively choose male figs These studies have supported the concept of alternative or additional adaptations to phenology allowing fig trees to “slave” their pollinators into pollinating female figs

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