Exploring the role of the generalist ant Solenopsis geminata (Formicidae: Myrmicinae) on seed germination of Senna spectabilis (Fabaceae: Caesalpinioideae)

The colonization of pastures by plant species other than grasses is limited by the scarcity of primary seed dispersers and the reduced availability of suitable sites for seed germination. In pastures, generalist ants could promote secondary dispersal of trees of importance for ecological restoration by manipulating and transporting seeds to their nests. First, we evaluated in the laboratory the importance of mechanical scarification for seed germination of three tree species with potential for ecological restoration: Guazuma ulmifolia, Pithecellobium dulce and Senna spectabilis. Scarification enhanced germination of seeds of G. ulmifolia (from 5 to 37%) and S. spectabilis (from 0 to 98.5%) while decreased the germination of P. dulce (from 94 to 87%). We concluded that mechanical scarification is necessary for germination of S. spectabilis and G. ulmifolia. Then, to explore the effect of ants on seed germination, we offered non-scarified seeds of S. spectabilis to colonies of fire ant Solenopsis geminata in the laboratory. We did not observe germination with this treatment, suggesting that this ant species does not scarify mechanically or chemically the seeds, but there was no evidence of physical damage to the seeds. Finally, germination of scarified seeds of S. spectabilis in soil from S. geminata nests was compared with germination of scarified seeds in soil adjacent to the nests, both under greenhouse and field conditions. In greenhouse, germination was higher in nest soil than in adjacent soil (98% vs. 86%, respectively) whereas the opposite occurred in field (24% vs. 43%, respectively). There was no evidence that the changes in soil induced by nests of S.geminata favor the germination of S. spectabilis. We recommend assessing the contribution of soil from ant nests in post-germination stages of seedlings, their establishment, survival and growth.