Adaptive divergence of scaling relationships mediates the arms race between a weevil and its host plant

Abstract

Coevolution of exaggerated morphologies between insects and plants is a well-known but poorly understood phenomenon in evolutionary biology. In the antagonistic interaction between a seed-predatory insect, the camellia weevil (Curculio camelliae), and its host plant, Japanese camellia (Camellia japonica), we examined the evolutionary trajectory of an exaggerated offensive trait of the weevil (rostrum length) in terms of scaling relationship. Sampling throughout Japan revealed that the ratio of the rostrum length to overall body size was correlated with the ratio of the pericarp thickness to overall fruit size across the localities. We found a geographical interpopulation divergence in a parameter pertaining to the allometric equation of rostrum length (the coefficient a in yZax b , where y and x denote rostrum and body lengths, respectively), and the pattern of geographical differentiation in the allometric coefficient was closely correlated with the variation in the pericarp thickness of Japanese camellia. Our results provide a novel example of a geographically diverged scaling relationship in an insect morphology resulting from a coevolutionary arms race with its host plant.

Conservative whole‐organ scaling contrasts with highly labile suborgan scaling differences among compound eyes of closely related Formica ants

“…At the whole‐eye level, changes in static allometric scaling relationships are restricted to grade shifts, with slope shifts entirely absent. This supports previous claims based on comparisons among closely related species or artificial selection experiments that allometric scaling relationships can evolve but that grade shifts are easier to achieve than slope shifts (Bolstad et al., 2015; Emlen & Nijhout, 2000; Frankino et al., 2005, 2007; Pélabon et al., 2014; Tobler & Nijhout, 2010; Toju & Sota, 2006; Voje et al., 2014). …”

Complex selection on life-history traits and the maintenance of variation in exaggerated rostrum length in acorn weevils

“…The same analysis was used to compare head capsule width between the larvae of both species. To detect any interspecific difference in the scaling relationship between adult rostrum length and body size, we compared females of both species, adapting the methodology used by Toju and Sota (2006a) for intraspecific population analyses. We carried out these analyses only on females, as their rostrums are longer, used for drilling oviposition holes, and thus susceptible to a stronger selection pressure.…”

“…In beetles, high species richness is frequently associated with phytophagy and diversity of host plants (Farrell and Mitter 1998;Kergoat et al 2005;Hunt et al 2007). Host plantherbivore interactions may result in differences in allometric shape or in body size in response to specialized feeding, which may lead to species diversification (e.g., Farrell and Mitter 1998;Kergoat et al 2005;Toju and Sota 2006a; see Strauss and Zangerl 2002 for a review).…”

“…The plant and the insect are involved in a coevolutionary race in which thick seed coats promote the development of longer rostrums and vice versa (Toju and Sota 2006b). The pressure on rostrum length is strong, as evident from the disproportionally enlarged rostrum relative to body size in populations feeding on seeds with thick seed coats (Toju and Sota 2006a).…”

Sistemática e biogeografia de besouros curculionídeos (Curculionoidea; Coleoptera) associados a figueiras (<i>Ficus</i>; Moracae)

“…For the genus Curculio, it has been shown that the imbalance between the length of the rostrum and the thickness of the host fruit wall determine the strength of local selection (Toju & Sota, 2006a), which in a long term evolution would have contributed to the increase of species diversity. The huge polymorphism of Curculio, especially in relation to rostrum length, provides an unambiguous example of adaptive radiation Toju & Sota, 2006b), for which two major routes have been pointed out: the Afrotropical species of Curculio are believed to have radiated on tropical fig trees while a second lineage radiated on temperate Fagales (Perrin, 1992). The African fig feeding species of Curculio are suggested to be a sister group of all seed feeding species .…”