Abstract
BackgroundPlant-feeding insects make up a large part of earth's total biodiversity. While it has been shown that herbivory has repeatedly led to increased diversification rates in insects, there has been no compelling explanation for how plant-feeding has promoted speciation rates. There is a growing awareness that ecological factors can lead to rapid diversification and, as one of the most prominent features of most insect-plant interactions, specialization onto a diverse resource has often been assumed to be the main process behind this diversification. However, specialization is mainly a pruning process, and is not able to actually generate diversity by itself. Here we investigate the role of host colonizations in generating insect diversity, by testing if insect speciation rate is correlated with resource diversity.ResultsBy applying a variant of independent contrast analysis, specially tailored for use on questions of species richness (MacroCAIC), we show that species richness is strongly correlated with diversity of host use in the butterfly family Nymphalidae. Furthermore, by comparing the results from reciprocal sister group selection, where sister groups were selected either on the basis of diversity of host use or species richness, we find that it is likely that diversity of host use is driving species richness, rather than vice versa.ConclusionWe conclude that resource diversity is correlated with species richness in the Nymphalidae and suggest a scenario based on recurring oscillations between host expansions – the incorporation of new plants into the repertoire – and specialization, as an important driving force behind the diversification of plant-feeding insects.
Highlights
Plant-feeding insects make up a large part of earth's total biodiversity
The correlation between diversity of host use and species richness was tested with the computer program MacroCAIC [45], which applies the method of independent
A schematic illustration of the application of reciprocal sister group comparisons to evaluate questions of causation for associated traits in situations where only correlational analyses are possible, but where the correlation is not absolute. (a) Trait 1 and 2 are positively correlated across the phylogeny, so that a difference in one trait is associated with a correlated difference in the other. (b) Provided that the correlation is not perfect, there will be situations where a difference in trait 1 is not associated with a correlated difference in trait 2, and (c) where a difference in trait 2 is not associated with a correlated difference in trait 1
Summary
While it has been shown that herbivory has repeatedly led to increased diversification rates in insects, there has been no compelling explanation for how plant-feeding has promoted speciation rates. There is a growing awareness that ecological factors can lead to rapid diversification and, as one of the most prominent features of most insect-plant interactions, specialization onto a diverse resource has often been assumed to be the main process behind this diversification. Plant-feeding insects are remarkably species-rich, making up at least one-quarter of all described species, so explaining the mechanisms behind the diversification of these groups will go a long way towards understanding global biodiversity [1,2]. It has been clearly demonstrated that herbivory has repeatedly led to rapid diversification of insects, but the mechanisms behind this diversification still remain uncertain [4,5]. Insect diversification rates could conceivably be influenced by both (page number not for citation purposes)
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