Leaf shape variation and herbivore consumption and performance: a case study with Ipomoea hederacea and three generalists

Abstract

The effect of leaf shape variation on plantherbivore interactions has primarily been studied from the perspective of host seeking behavior. Yet for leaf shape to affect plant-herbivore coevolution, there must be reciprocal effects of leaf shape variation on herbivore consumption and performance. We investigated whether alternative leaf morphs affected the performance of three generalist insect herbivores by taking advantage of a genetic polymorphism and developmental plasticity in leaf shape in the Ivyleaf morning glory, Ipomoea hederacea. Across four experiments, we found variable support for an effect of leaf shape genotype on insects. For cabbage loopers (Trichoplusia ni) and corn earworms (Helicoverpa zea) we found opposing, non-significant trends: T. ni gained more biomass on lobed genotypes, while H. zea gained more biomass on heartshaped genotypes. For army beetworms (Spodoptera exigua), the effects of leaf shape genotype differed depending on the age of the plants and photoperiod of growing conditions. Caterpillars feeding on tissue from older plants (95 days) grown under long day photoperiods had significantly greater consumption, dry biomass, and digestive efficiency on lobed genotypes. In contrast, there were no significant differences between heart-shaped and lobed genotypes for caterpillars feeding on tissue from younger plants (50 days) grown under short day photoperiods. For plants grown under short days, we found that S. exigua consumed significantly less leaf area when feeding on mature leaves than juvenile leaves, regardless of leaf shape genotype. Taken together, our results suggest that the effects of leaf shape variation on insect performance are likely to vary between insect species, growth conditions of the plant, and the developmental stage and age of leaves sampled.

Response of Leaf Functional Traits of Cerasus yedoensis (Mats.) Yü Li to Serious Insect Attack

“…Conversely, this negative relationship is not consistent with previous results [32]. As one of the most variable plant characteristics affecting major physiological properties that enable plants to adapt to numerous environmental conditions [9,33], such as defense against pathogens [23] and herbivores [9], leaf shape index was positively correlated with petiole diameter, leaf length, leaf thickness, ratio of leaf length to petiole length, ad single leaf wet and dry weight, but negatively correlated with leaf moisture. Therefore, leaf shape index may be affected by leaf length, leaf thickness, allocated biomass in leaf lamina relative to leaf petiole (the ratio of leaf length to petiole length), a single leaf wet and dry weight (although leaf shape index was calculated as the ratio of leaf length to the corresponding leaf width).…”

“…For instance, plants adapt to multivariate environments by changing morphological characteristics and growth mechanisms [2,6,[8][9]. One of the most commonly regarded key traits of plant development strategies is SLA (trade-off between resource capture and conservation); SLA is also a critical trait in carbon fixation of plants [7,8,[10][11].…”

“…Leaves exhibit phenotypic plasticity in response to changes in environmental factors to help plants improve fitness; with phenotypic plasticity, plants can utilize a successful ecological strategy in changing environments during life processes [2,[7][8][9]. In addition to phenotypic plasticity, specific leaf area (SLA, defined as investment per unit of light capture surface deployed) can indicate the adaptability of plants to different habitats; as such, SLA is a key functional trait reflecting the trade-off between resource capture and conservation (e.g., high SLA can indicate high resource acquisition and use efficiency with low investment in leaf construction and protective tissues according to the leaf economic spectrum) [7][8][10][11].…”

Testing potential selective agents acting on leaf shape inIpomoea hederacea: predictions based on an adaptive leaf shape cline

“…Insect herbivores impose differential leaf damage to the two homozygous leaf shape genotypes of I. hederacea, suggesting that insects could be an important selective agent on leaf shape variation in I. hederacea (Campitelli et al. ). Latitudinal gradients in insect herbivory have been reported (e.g., Adams and Zhang ; Moles et al.…”

Morning glory as a powerful model in ecological genomics: tracing adaptation through both natural and artificial selection

“…Is resistance to herbivory determined by a few major effect loci, or several loci of smaller effect? Are the effects of polymorphism in Mendelian traits (flower color, leaf shape: Simms and Bucher, 1996;Campitelli et al, 2008) on herbivory due to the pleiotropic effects of those genes, or closely linked genes? Are molecular signatures of balancing selection detected on genes where classical ecological genetics suggests selection is maintaining stable polymorphisms?…”