Tackling the species problem: theory and application in plant -feeding insects

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Biological diversity and evolutionary success are often measured in terms of species numbers, but for many groups of organisms, it is difficult to determine where one species ends and another begins. This uncertainty has its origins in the evolutionary processes that create those species in the first place. The research programme will address both theoretical and practical aspects of the “species problem”, examining the processes that create species and developing methods to circumscribe and describe them.******Insects account for more than half of all described life on Earth. As with other insects, sap-feeding, host specialist aphids, diversified with the radiation of angiosperm plants. One of the most diverse aphid groups is an exception, however, having switched from angiosperm onto conifer hosts. Whereas most species of this group feed on woody parts of their hosts, those of four other groups feed exclusively on pine needles. Sharing the same ecological niche, these needle-feeding lineages represent evolutionary replicates of host- and niche-specialization and diversification. Did these independent lineages diversify in similar ways? Did the similar environmental pressures experienced by each group lead to evolutionary convergence, or did each lineage evolve in its own way? Answering these questions will shed light on the processes that led to the incredible diversification of the insects. The first objective of the research is to use DNA sequence and ecological data to compare the relative importance of plant host, bacterial symbiont, and geographic factors to the speciation of these aphids.******In aphids, host plant association is often used both to discover new species and to identify them, a problematic circularity because host plants are known to affect aphid development and what they look like. The second objective of the research is to use modern genetic methods to thoroughly delimit the conceptual boundaries between species. Different groups will be examined and compared to see if the same methods can be applied across all aphids.******For the third objective, the project will make sure the species we examine are properly and fully described and catalogued online. Novel computer methods will speed up the descriptive process, including the publication of museum specimens digitally imaged in three dimensions. They will form a virtual reference collection, providing researchers and insect identifiers an unprecedented research tool.******Aphids are among the most economically devastating pests of agriculture. Considerable resources are expended trying to understand the biology of different species and to discriminate pest and non-pest species. The proposed project will dramatically accelerate our capacity to understand aphid species and bring new understanding to the nature of species in general and insect species in particular.