What Protects Lonchocarpus (Leguminosae) Seeds in a Costa Rican Dry Forest?

Abstract

The seeds of the six native species of Lonchocarpus (Leguminosae) trees in the tropical dry forest of Santa Rosa National Park in northwestern Costa Rica are rejected by all species of vertebrate seed predators. Liomys salvini (Heteromyidae) mice, the primary vertebrate seed predators in this habitat, were found to die of starvation rather than eat Lonchocarpus seeds in captivity; in contrast, some of the species of Lonchocarpus seeds are preyed upon by the larvae of host-specific bruchid beetles (Ctenocolum spp.). Lonchocarpus costaricensis seeds were found to be rich in at least four nonprotein amino acids and a polyhydroxypyrrolidine alkaloid. However, when this potentially toxic alkaloid, and thus potential deterrent to the mice, was added to a laboratory chow diet at concentrations approximating that in the seeds, the mice consumed the adulterated chow with no effect or only slight effect. The L. costaricensis seeds also contained seven kinds of flavonoids. When these potentially toxic molecules were added to lab chow as single compounds or in pairs, at concentrations approximating those found in the seeds, the mice readily consumed the adulterated laboratory chow. However, when a mix of flavonoids that represented the entire flavonoid profile of an intact seed in concentration and kind was added to laboratory chow, this diet was absolutely rejected by the mice until death by starvation. The flavonoids, rather than the peculiar small nitrogenous molecules in the L. costaricensis seeds, are at least one basis for seed rejection by (and thus, protection from) the mice. However, there is still the opportunity for other as yet unrecorded secondary compounds in the seed to also be a basis for seed rejection by the mice.