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Department of Biological Sciences

The LoPresti lab published a new study in Oecologia

Many seeds are consumed by granivores despite numerous adaptations to prevent detection or exploitation. Seed mucilage is a sticky coating that binds imbibed seeds to substrates and lessens exploitation by granivores. Mucilage prevents seed predation in several ways. Mucilaginous seeds can be unwieldy for insect granivores to handle when imbibed. Dried mucilage can bind substrate to the seed, making collection and processing difficult or unwieldy, or it can anchor the seed to the substrate, again making collection and processing difficult. A mucilage-bound seed may require hundreds of grams of force to dislodge, many thousands of times the body mass of small granivores (i.e. ants). Therefore, it is unsurprising that seeds more tightly bound to the ground are generally better protected from insect granivores. However, the strength of attachment is also affected by external factors acting during the drying period.

Understanding the mechanisms by which environmental factors modify defensive efficacy is important for understanding spatial patterns of granivory and seed recruitment. In their new study titled "Seed mucilage as a defense against granivory is influenced by substrate characters", lab technician Madi Stessman, undergraduate student Ashlesha Sharma, and their mentor Dr. Eric LoPresti investigated whether whether particle size of substrate affects mucilage binding strength and subsequent interactions with granivores. Using seeds of plant species from five different families (representing independent evolutionary origins of seed mucilage), they tested attachment strength across substrate textures in the laboratory and how that affects exploitation by granivorous ants in the field. They found that small differences in substrate grit lead to differential mortality in mucilaginous seeds due to alterations in attachment strength. They also observed strikingly different relationships across species when examining dislodgement force across a wider range of particle sizes, suggesting that mucilage chemical and physical characters may likely play large roles in determining the more specific species effects. 

Picture of seed mucilage and predation by ant.
Left: Wetted seed mucilage of Mirabilis nyctaginea ((Wild Four O'Clock). Right: Harvester ant, Pogonomyrmex barbatus, struggling with a bound Salvia azurea (Pitcher sage) seed.

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