Molecular species delimitation of a symbiotic fig-pollinating wasp species complex reveals extreme deviation from reciprocal partner specificity.
BACKGROUND
Symbiotic relationships have contributed to major evolutionary innovations, the maintenance of fundamental ecosystem functions, and the generation and maintenance of biodiversity. However, the exact nature of host/symbiont associations, which has important consequences for their dynamics, is often poorly known due to limited understanding of symbiont taxonomy and species diversity. Among classical symbioses, figs and their pollinating wasps constitute a highly diverse keystone resource in tropical forest and savannah environments. Historically, they were considered to exemplify extreme reciprocal partner specificity (one-to-one host-symbiont species relationships), but recent work has revealed several more complex cases. However, there is a striking lack of studies with the specific aims of assessing symbiont diversity and how this varies across the geographic range of the host.


RESULTS
Here, we use molecular methods to investigate cryptic diversity in the pollinating wasps of a widespread Australian fig species. Standard barcoding genes and methods were not conclusive, but incorporation of phylogenetic analyses and a recently developed nuclear barcoding gene (ITS2), gave strong support for five pollinator species. Each pollinator species was most common in a different geographic region, emphasising the importance of wide geographic sampling to uncover diversity, and the scope for divergence in coevolutionary trajectories across the host plant range. In addition, most regions had multiple coexisting pollinators, raising the question of how they coexist in apparently similar or identical resource niches.


CONCLUSIONS
Our study offers a striking example of extreme deviation from reciprocal partner specificity over the full geographical range of a fig-wasp system. It also suggests that superficially identical species may be able to co-exist in a mutualistic setting albeit at different frequencies in relation to their fig host's range. We show that comprehensive sampling and molecular taxonomic techniques may be required to uncover the true structure of cryptic biodiversity underpinning intimate ecological interactions.
School of Biological Sciences, University of Reading, Reading, RG6 6AS, UK. cdarwell@syr.edu.|Department of Biology, Syracuse University, 107 College Place, Syracuse, NY, 13244, USA. cdarwell@syr.edu.
Clive T
CT
Darwell
Royal Horticultural Society, Wisley Garden, Woking, Surrey, GU23 6QB, UK. sarahalbeidh@rhs.org.uk.
Sarah
S
al-Beidh
School of Biological Sciences, University of Reading, Reading, RG6 6AS, UK. james.cook@reading.ac.uk.|Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW, 1797, Australia. james.cook@reading.ac.uk.
James M
JM
Cook
D000818:Animals; D001315:Australia; D045303:Cytochromes b / Q000235:genetics; D017753:Ecosystem; D003576:Electron Transport Complex IV / Q000235:genetics; D019143:Evolution, Molecular; D030681:Ficus / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D054817:Pollination; D016415:Sequence Alignment; D013045:Species Specificity; D013559:Symbiosis / Q000235:genetics*; D014863:Wasps / Q000235:genetics* / Q000502:physiology*
D045303:Cytochromes b; D003576:Electron Transport Complex IV