Herbivory causes increases in leaf spinescence and fluctuating asymmetry as a mechanism of delayed induced resistance in a tropical savanna tree

Background and aims – Leaf spinescence is thought to be a defense against herbivory and may increase in years following high herbivory pressure (DIR – delayed induced resistance). Besides DIR, herbivory also causes plant stress, which can be assessed using fluctuating asymmetry analysis (FA – random departures from leaf bilateral symmetry). In this two-year field study we first investigated the relationships between herbivory, FA and spinescence in Solanum lycocarpum trees during an outbreak of moth caterpillars in 2010; then in 2011 we examined whether plants with intense herbivory the previous year presented changes in FA (herbivory induced stress) and spinescence.

Key results – In 2010, leaves damaged by moths were significantly more asymmetrical than undamaged leaves. In addition, moths preferentially fed on leaves with fewer and shorter spines. In 2011, plants severely attacked by moths the year before showed significant increases in FA (28%), spine abundance (21%) and spine length (84%), compared to less damaged plants.

Conclusions – Our data suggest a delayed response of S. lycocarpum to herbivory, in that plants subjected to high leaf damage the previous year maximized their display of anti-herbivore mechanisms, in this case, leaf spinescence. This is one of the few studies to show that FA increased as a response to herbivore attack. We conclude that FA can be used as an indicator of plant stress following leaf damage.