Macroevolution of insect-plant associations: the relevance of host biogeography to host affiliation

Abstract

Identifying the factors that have promoted host shifts by phytophagous insects at a macroevolutionary scale is critical to understanding the associations between plants and insects. We used molecular phylogenies of the beetle genus Blepharida and its host genus Bursera to test whether these insects have been using hosts with widely overlapping ranges over evolutionary time. We also quantified the importance of host range coincidence relative to host chemistry and host phylogenetic relatedness. Overall, the evolution of host use of these insects has not been among hosts that are geographically similar. Host chemistry is the factor that best explains their macroevolutionary patterns of host use. Interestingly, one exceptional polyphagous species has shifted among geographically close chemically dissimilar plants.

Figure 1

Feeding associations of Blepharida beetles on Bursera hosts. Both phylogenies were reconstructed by using the nucleotide sites of the nuclear ribosomal DNA internal transcribed spacer sequences. For clarity, the hosts of polyphagous B. alternata are not indicated (but see Fig. 4 for its host plants). Asterisks indicate outgroups, and the numbers above branches are bootstrap percentages.

Figure 2

Dendrogram of Bursera on the basis of similarity of geographical ranges (biogeogram). Letters and color coding indicate the five main biogeographical groups of plants.

Figure 3

Bursera’s main biogeographic areas in Mexico according to our cluster analyses. Letters and colored areas indicate the geographic distribution of species groups in the biogeogram.

Figure 4

The five main groups of the biogeogram are traced onto Blepharida’s phylogeny. All polytomies indicate multiple host use by a single beetle species except for the polytomy that includes B. lineata, which is unresolved. The chemical, phylogenetic, and biogeographic groups of the hosts are color coded in squares above the branch tips as per Insets and Fig. 2.