Invasive plant population and herbivore identity affect latex induction

Abstract

Latex functions as a physical and chemical defence against herbivores that may vary in their responses to latex quantity and chemical composition. In their introduced ranges, many exotic plants experience reduced herbivore regulation, especially from specialist herbivores, which may lead to differences in defences among native and invasive populations. Here, we compared latex produced by seedlings from native and invasive populations of tallow tree (Triadica sebifera) when damaged by a native specialist or generalist caterpillar. We measured the growth of caterpillars fed leaves of plants from native and invasive populations that had latex washed from the leaves or were unwashed controls. We found that constitutive latex mass, tannins and flavonoids of plants from invasive and native populations were similar. The masses of caterpillars fed leaves from native and invasive populations were comparable regardless of leaf washing. We also found that the specialist induced more latex production than the generalist did, especially for plants from invasive populations. Tannins increased and flavonoids decreased when plants were damaged by the generalist caterpillar but neither changed when plants were damaged by the specialist caterpillar. Our results suggest divergent selection on the physical and chemical properties of latex in the introduced range. The quantity of latex produced was more sensitive to herbivore identity in the introduced range but the specificity of the latex chemical response was retained.