Abstract
The importance and prevalence of phylogenetic tracking between hosts and dependent organisms caused by co‐evolution and shifting between closely related host species have been debated for decades. Most studies of phylogenetic tracking among phytophagous insects and their host plants have been limited to insects feeding on a narrow range of host species. However, narrow host ranges can confound phylogenetic tracking (phylogenetic tracking hypothesis) with host shifting between hosts of intermediate relationship (intermediate hypothesis). Here, we investigated the evolutionary history of the Enchenopa binotata complex of treehoppers. Each species in this complex has high host fidelity, but the entire complex uses hosts across eight plant orders. The phylogenies of E. binotata were reconstructed to evaluate whether (1) tracking host phylogeny; or (2) shifting between intermediately related host plants better explains the evolutionary history of E. binotata. Our results suggest that E. binotata primarily shifted between both distant and intermediate host plants regardless of host phylogeny and less frequently tracked the phylogeny of their hosts. These findings indicate that phytophagous insects with high host fidelity, such as E. binotata, are capable of adaptation not only to closely related host plants but also to novel hosts, likely with diverse phenology and defense mechanisms.
Highlights
Elucidating patterns of species richness and mechanisms of speciation are major goals in the study of ecology and evolution
We found that the degree of phylogenetic association between the Enchenopa binotata species complex and their host plants does not support phylogenetic tracking as the major mechanism of speciation of E. binotata
Our results suggested that host shifting dominated the evolutionary history of the E. binotata complex
Summary
Elucidating patterns of species richness and mechanisms of speciation are major goals in the study of ecology and evolution. In more than one-t hird of the studies of insect–plant interactions reviewed, the insects feed on only one plant order (or even one genus in several cases; de Vienne et al, 2013; Suchan & Alvarez, 2015) Such a narrow host range makes it difficult to distinguish phylogenetic tracking from host shifting between hosts of intermediate similarity. The intermediate hypothesis posits that the maximum probability of insect speciation occurs when alternative hosts are of intermediate similarity in resource space, as determined by the resource that is critical to the fitness of the focal insect (Nyman, 2010) Such resources may include the secondary chemical compounds, nutritional content, or phenology of a plant, depending on the specific restrictions in each insect–plant interaction (Heard, 2012; Nyman, 2010). The wide range of host plants for the E. binotata species complex provides a unique opportunity to test whether phylogenetic tracking or the intermediate hypothesis best explains insect–plant interactions. | 1956 is the difference in hatching dates caused by host plant phenology (Wood, 1980, 1993), which is phylogenetically conserved (Davies et al, 2013), we used the phylogenetic distance between host plants to represent the distance in resource space
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