Abstract
The effects of allelochemical stress on genetic variations in the specific activities of gypsy moth digestive enzymes (trypsin and leucine aminopeptidase) and relative midgut mass (indirect measure of food consumption), as well as variability in their plasticity, were investigated in fifth instar gypsy moths originating from two populations with different trophic adaptations (oak and locust-tree forests). Thirty-two full-sib families from the Quercus population and twenty-six full-sib families from the Robinia population were reared on an artificial diet with or without supplementation with tannic acid. Between population differences were observed as higher average specific activity of trypsin and relative midgut mass in larvae from the Robinia population. Significant broad-sense heritabilities were observed for the specific activity of trypsin in the control state, and for specific activity of leucine aminopeptidase in a stressful environment. Significantly lower heritability for relative midgut mass was recorded in larvae from the Robinia population reared under stressful conditions. Significant variability of trypsin plasticity in larvae from both populations and significant variability of leucine aminopeptidase plasticity in larvae from the Robinia population point to the potential for the evolution of enzyme adaptive plastic responses to the presence of stressor. Non-significant across-environment genetic correlations do not represent a constraint for the evolution of enzyme plasticity.
Highlights
The complex and variable chemical composition of host plants is an aspect of plant defense and represents a challenge for insect feeding
The rearing of gypsy moth larvae from Quercus and Robinia populations on a tannin-supplemented diet decreased the specific activity of trypsin, while for the specific activity of leucine aminopeptidase, a trend of increase in enzyme activity in response to dietary tannin was noticed (Mrdaković, 2010, submitted, and this study)
Local adaptation has been shown for Quercus and Robinia populations (Perić Mataruga et al, 1997; Lazarević et al, 2002, 2003; Mrdaković et al, 2013), we did not detect significant “population x treatment” interactions, i.e., analyzed traits reacted in a similar way to dietary tannin regardless of population origin
Summary
The complex and variable chemical composition of host plants is an aspect of plant defense and represents a challenge for insect feeding. Phytophagous insects have evolved counter-adaptations to the defensive mechanisms of their host plants (Mello and Silva Filho, 2002). As a component of a plant’s “quantitative” defense, tannins play an important role in defense against phytophagous insects by deterrence and/or toxicity. Tannin structural heterogeneity causes variations in their biological activity, which depends on insect gut pH, surfactants and permeability of the peritrophic membrane. In insects with high gut pH (e.g. larvae of Lepidoptera), tannins are prone to oxidize and form semiquinone radicals, quinones and other reactive oxygen species. Their toxicity results from the production of high ROS levels (Barbehenn and Constabel, 2011). Higher levels of tannins in leaves or its high concentration in an MARIJA MRDAKOVIĆ ET AL
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