Host plant shifts are central to diversification in insect herbivores. Many mechanisms can cause host shifts in insects, but one relatively unexplored mechanism is whole‐genome duplication (WGD) in the host plant. WGD, or polyploidy, is common in plants and causes spontaneous changes in physiology, morphology, and palatability that could impact the ability of herbivores to feed and develop on newly formed polyploids (neopolyploids). Here the authors tested if WGD affected the preference and performance of the specialist aphid, Acyrthosiphon pisum (pea aphids). Pea aphids seasonally form specialised lineages or ‘host forms’ on many host plant species including alfalfa and red clover. Aphid host forms on alfalfa and red clover naturally exist on different cytotypes of their respective hosts, with red clover aphids feeding on diploid clover and alfalfa aphids feeding on tetraploid alfalfa. Therefore, the authors predicted that these host forms would have a higher preference for and performance on their respective natal host cytotype. Neither host form exhibited a preference for a particular cytotype, but there were modest changes in aphid performance based on host cytotype. Specifically, aphids specialised to red clover had higher fecundity on diploid red clover than on neotetraploid red clover. Together, these results showed that both host forms were able to recognise and accept different cytotypes of the two host species, but only one host form experienced trade‐offs in performance when feeding on neotetraploids. These results suggest that WGD may act as a mechanism of host expansion in pea aphids as plants speciate via WGD.

Insect mutualisms are essential for reproduction of many plants, protection of plants and other insects, and provisioning of nutrients for insects. Disruption of these mutualisms by global change can have important implications for ecosystem processes. Here, we assess the general effects of global change on insect mutualisms, including the possible impacts on mutualistic networks. We find that the effects of global change on mutualisms are extremely variable, making broad patterns difficult to detect. We require studies focusing on changes in cost-benefit ratios, effects of partner dependency, and degree of specialization to further understand how global change will influence insect mutualism dynamics. We propose that rapid coevolution is one avenue by which mutualists can ameliorate the effects of global change.

Premise of the StudyPolyploidy, or whole genome duplication (WGD), is common in plants despite theory suggesting that polyploid establishment is challenging and polyploids should be evolutionarily transitory. There is renewed interest in understanding the mechanisms that could facilitate polyploid establishment and explain their pervasiveness in nature. In particular, premating isolation from their diploid progenitors is suggested to be a crucial factor. To evaluate how changes in assortative mating occur, we need to understand the phenotypic effects of WGD on reproductive traits. MethodsWe used literature surveys and a meta-analysis to assess how WGD affects floral morphology, flowering phenology, and reproductive output in plants. We focused specifically on comparisons of newly generated polyploids (neopolyploids) and their parents to mitigate potential confounding effects of adaptation and drift that may be present in ancient polyploids. Key ResultsThe results indicated that across a broad representation of angiosperms, floral morphology traits increased in size, reproductive output decreased, and flowering phenology was unaffected by WGD. Additionally, we found that increased trait variation after WGD was uncommon for the phenotypic traits examined. ConclusionsOur results suggest that the phenotypic effects on traits important to premating isolation of neopolyploids are small, in general. Changes in flowering phenology, reproductive output, and phenotypic variation resulting from WGD may be less critical in facilitating premating isolation and neopolyploid establishment. However, floral traits for which size is an important component of function (e.g., pollen transfer) could be strongly influenced by WGD.