Abstract
IntroductionIn the past decade ecological speciation has been recognized as having an important role in the diversification of plant-feeding insects. Aphids are host-specialised phytophagous insects that mate on their host plants and, as such, they are prone to experience reproductive isolation linked with host plant association that could ultimately lead to species formation. The generality of such a scenario remains to be tested through macroevolutionary studies. To explore the prevalence of host-driven speciation in the diversification of the aphid genus Cinara and to investigate alternative modes of speciation, we reconstructed a phylogeny of this genus based on mitochondrial, nuclear and Buchnera aphidicola DNA sequence fragments and applied a DNA-based method of species delimitation. Using a recent software (PhyloType), we explored evolutionary transitions in host-plant genera, feeding sites and geographic distributions in the diversification of Cinara and investigated how transitions in these characters have accompanied speciation events.ResultsThe diversification of Cinara has been constrained by host fidelity to conifer genera sometimes followed by sequential colonization onto different host species and by feeding-site specialisation. Nevertheless, our analyses suggest that, at the most, only half of the speciation events were accompanied by ecological niche shifts. The contribution of geographical isolation in the speciation process is clearly apparent in the occurrence of species from two continents in the same clades in relatively terminal positions in our phylogeny. Furthermore, in agreement with predictions from scenarios in which geographic isolation accounts for speciation events, geographic overlap between species increased significantly with time elapsed since their separation.ConclusionsThe history of Cinara offers a different perspective on the mode of speciation of aphids than that provided by classic models such as the pea aphid. In this genus of aphids, the role of climate and landscape history has probably been as important as host-plant specialisation in having shaped present-day diversity.
Highlights
In the past decade ecological speciation has been recognized as having an important role in the diversification of plant-feeding insects
In agreement with predictions from scenarios in which geographic isolation accounts for speciation events, geographic overlap between species increased significantly with time elapsed since their separation
Sequence data The final matrix contained 56 morphological ingroup species, six specimens for which identification keys did not lead to any known species and four outgroups, representing a total of 246 individuals and 4076 bp (COI + cytochrome b gene (Cytb) = 1418 bp, Aph = 257 bp, Elongation Factor (EF) = 1135 bp, His = 719 bp, and GroEL = 547 bp)
Summary
In the past decade ecological speciation has been recognized as having an important role in the diversification of plant-feeding insects. Aphids are host-specialised phytophagous insects that mate on their host plants and, as such, they are prone to experience reproductive isolation linked with host plant association that could lead to species formation. The generality of such a scenario remains to be tested through macroevolutionary studies. Aphids (Hemiptera, Aphididae) are considered as model systems for the study of ecological speciation favored by adaptation to different host plants These insects are often host specific and always mate on their host plants which make them good candidates for host driven speciation. Other studies have shown that Aphis gossypii Glover, 1877 consists of several host-associated populations or races with a world-wide distribution [16,17]
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