What We Don't Know About Diet-Breadth Evolution in Herbivorous Insects

Abstract

Half a million species of herbivorous insects have been described. Most of them are diet specialists, using only a few plant species as hosts. Biologists suspect that their specificity is key to their diversity. But why do herbivorous insects tend to be diet specialists? In this review, we catalog a broad range of explanations. We review the evidence for each and suggest lines of research to obtain the evidence we lack. We then draw attention to a second major question, namely how changes in diet breadth affect the rest of a species’ biology. In particular, we know little about how changes in diet breadth feed back on genetic architecture, the population genetic environment, and other aspects of a species’ ecology. Knowing more about how generalists and specialists differ should go a long way toward sorting out potential explanations of specificity, and yield a deeper understanding of herbivorous insect diversity. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 51 is November 2, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Asymmetric Evolvability Leads to Specialization without Trade-Offs

“…In the field, reciprocal transplant experiments with plant and animal species reveal highly variable costs of adaptation with only a weak signal of trade-offs (Hereford 2009). The vast number of mostly specialized phytophagous insect species has inspired a vigorous but largely unsuccessful search for trade-offs limiting niche breadth (Hardy et al 2020). These shortfalls of the trade-off hypothesis have motivated the search for alternative theories that incorporate behavior, population genetics, and macroevolution into a synthetic theory of niche limits (Poisot et al 2011;Sexton et al 2017).…”

Comparative analyses of transcriptional responses of Dectes texanus LeConte (Coleoptera: Cerambycidae) larvae fed on three different host plants and artificial diet

“…Novel plant-arthropod herbivore associations can be formed between previously geographically separated organisms or organisms that have co-existed in the same landscape 6 . These host range shifts are often attributed to low availability of natural hosts, escape from predation and/or parasitism, availability of more attractive or better quality host plants, availability of hosts that are less chemically defended, and introduction or invasion to new landscapes 8 , 9 . Plasticity of arthropod gene expression is most likely associated with the initial ability of herbivores to use and feed on novel and multiple host plants 10 – 12 .…”

Nonadaptive host‐use specificity in tropical armored scale insects

“…Yet, niche breadth varies greatly between species. Herbivorous insects are classic subjects for the study of this variation (Futuyma & Moreno, 1988; Hardy et al., 2020). Although diet specialists prevail, diet breadths vary continuously, and in some species are extremely broad (Forister et al., 2015; Normark & Johnson, 2011).…”