Abstract
BackgroundWhile the communities constituted by phytophageous insects and their parasites may represent half of all terrestrial animal species, understanding their diversification remains a major challenge. A neglected idea is that geographic phenotypic variation in a host plant may lead to heterogeneous evolutionary responses of the different members of the associated communities. This could result in diversification on a host plant by ecological speciation in some species, leading to geographic variation in community composition. In this study we investigated geographic variation of inflorescence receptacle size in a plant, Ficus hirta, and how the hymenopteran community feeding in the inflorescences has responded. Our predictions were:Inflorescence size variation affects wasp species differently depending on how they access oviposition sites.In some affected lineages of wasps, we may observe vicariant, parapatric species adapted to different inflorescence sizes.ResultsWe show that fig (the enclosed inflorescence of Ficus) wall thickness varies geographically. The fig-entering pollinating wasp was not affected, while the parasites ovipositing through the fig wall were. Two parapatric species of Philotrypesis, exhibiting strikingly different ovipositor lengths, were recorded. One species of Sycoscapter was also present, and it was restricted, like the shorter-ovipositor Philotrypesis, to the geographic zone where fig walls were thinner.ConclusionsPrevious work on fig wasps suggested that parapatric geographic ranges among congenerics were due to adaptation to variation in abiotic factors, complemented by interspecific competition. Our results show that parapatric ranges may also result from adaptation to variation in biotic factors. Within an insect community, differences among species in their response to geographic phenotypic variation of their host plant may result in geographically heterogeneous community structure. Such heterogeneity leads to heterogeneous interaction networks among sites. Our results support the hypothesis that plant geographic phenotypic variation can be a driver of diversification in associated insect communities, and can complement other diversification processes.
Highlights
While the communities constituted by phytophageous insects and their parasites may represent half of all terrestrial animal species, understanding their diversification remains a major challenge
Differences among species in their response to geographic phenotypic variation of their host plant may result in geographically heterogeneous community structure
Our results support the hypothesis that plant geographic phenotypic variation can be a driver of diversification in associated insect communities, and can complement other diversification processes
Summary
While the communities constituted by phytophageous insects and their parasites may represent half of all terrestrial animal species, understanding their diversification remains a major challenge. Since the early 1980’s the quest for understanding diversification in the communities of phytophages and their parasites associated with plants, has largely focused on the consequences of the colonisation of a new host by an insect phytophage or a parasitoid and the resulting specialisation process [1]. Large host plant ranges allow the establishment of parapatric vicariant associated insect species, adapted to different environmental conditions [8,9,10]. In this process, diversification is a response to geographic variation in abiotic factors such as minimum and maximum temperatures [11]
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