Short-term plasticity and variation in acacia ant-rewards under different conditions of ant occupancy and herbivory

Effect of Induced Mechanical Leaf Damage on the Yield and Content of Bioactive Molecules in Leaves and Seeds of Tepary Beans (Phaseolus acutifolius)

Growing interest has recently been shown in Tepary beans (Phaseolus acutifolius) because they contain lectins and protease inhibitors that have been shown to have a specific cytotoxic effect on human cancer cells. Bean lectins offer protection against biotic and abiotic stress factors, so it is possible that mechanical foliar damage may increase lectin production. This study evaluates the effect of mechanical stress (foliar damage) on lectin and protease inhibitor content in Tepary beans. Seed yield was also analyzed, and phenolic content and antioxidant capacity (DPPH and TEAC) were determined in the leaves. An experimental design with random blocks of three treatments (T1: control group, T2: 50% mechanical foliar damage and T3: 80% mechanical foliar damage) was carried out. Mechanical foliar damage increased the amount of lectin binding units (LBUs) fivefold (from 1280 to 6542 LBUs in T3) but did not affect units of enzymatic activity (UEA) against trypsin (from 60.8 to 51 UEA in T3). Results show that controlled mechanical foliar damage could be used to induce overexpression of lectins in the seeds of Tepary beans. Mechanical foliar damage reduced seed production (-14.6%: from 1890 g to 1615 g in T3) and did not significantly increase phenolic compound levels in leaves.

Scaling of indirect defences in Central American swollen-thorn acacias

Myrmecophytes may adjust the investment on ant rewards, depending on tree size and ant defence level. In swollen-thorn acacias (Vachellia collinsii), we tested whether the level of protection provided by the resident ants (defending vs. non-defending) influenced the relation between tree size and ant rewards, or between types of ant rewards (housing and food). We quantified ant rewards in trees occupied by defending and by non-defending ants. We predicted: (1) a positive relation between plant diameter and ant reward investment, with a steeper slope for defending than for non-defending ant species; and (2) that if there is any tradeoff between ant rewards, it should be aggravated (steeper slope) when inhabited by non-defending ants. We found that most structures for ants grew according to plant diameter, but contrary to our first prediction it was independent of the level of ant defence. Most ant rewards did not show a tradeoff between them, besides a weak negative relation between spine length and number of pinnules, which contrary to the prediction occurred when occupied by defending ants. The evidence shows that the interacting ants had a weaker influence on the scaling of defence structures in myrmecophytes than the habitat (location).