Drying conditions alter the defensive function of seed mucilage against granivores

Abstract

1. Environmental conditions alter the function of many plant traits that drive species interactions, producing context-dependency in the outcomes of those interactions. Seed mucilage is a common, convergently evolved trait found in thousands of plant species. When wetted, the seed coat swells into a viscid mass; when dried, the mucilage strands strongly cement the seed to whatever it is in contact with.2. This binding to the ground has been previously shown to protect seeds from granivory. Previous research found both that mucilage volume-and the correlated attachment strength-are higher in species from hot, dry, areas suggesting an environmental component of this trait's function.3. Here, we (1) quantified the effect of temperature on attachment across many species in a lab setting, (2) tested the potential mechanism behind this correlation by accelerating desiccation speed without changing temperature, and (3) tested whether these relationships introduce context dependency of the defensive function of mucilage in the field, using field trials with harvester ants. 4. We found that (1) increasing temperature during mucilage drying strongly reduced the force needed to dislodge seeds for most species, (2) drying time was likely the driving mechanism behind the loss of attachment strength at higher temperatures, not temperature per se, (3) seeds attached to substrate during higher temperatures or under accelerated drying conditions were far more susceptible to granivory. 5.Synthesis. These results show not only the mechanism behind an abiotic modification of a functional trait of seeds, but that this change majorly alters a key interaction contributing to seed survival. These results add to a small, but growing, literature on the importance of seed mucilage in seed survival and demonstrate strong and largely predictable context-dependency in this trait's defensive function.

Engineering a Macroscopic Adhesion System Inspired by Mucilaginous Seeds

“…However, plant seeds in nature are exposed to different temperature levels during spring and summer, so elevated temperatures might affect their adhesion properties. For instance, seeds from plants growing in warmer areas of the world tend to show a higher stickiness and a greater mucilage volume [52,53] . Similarly, it appears possible that samples coated with pectin C and pectin A, respectively, differ in terms of their adhesion behavior at temperature levels above Values shown represent averages together with the standard deviation as calculated from n = 3 independent samples.…”

Seed mucilage in temperate grassland species is unrelated to moisture requirements

“…Seed mucilage is largely composed of pectin and other high-energy carbohydrates that the plant could allocate elsewhere in the developing seed, so investing energy in seed mucilage presumably serves an important purpose or beneficial adaptation (LoPresti et al, 2022;. Given the high prevalence of myxospermy, seed mucilage presumably provides benefits for grassland species.…”

“…Seed mucilage is a common trait in angiosperms, and it appears to play roles in seed survival, dispersal, and germination (Fernandez-Alonso et al, 2003;LoPresti et al, 2022;LoPresti et al, 2023;Tsai et al, 2021, Western, 2012.…”

Sandy seeds: Armour or invisibility cloak? Mucilage‐bound sand physically protects seeds from rodents and invertebrates

“…Often, this is the ground, and this binding makes the seed less likely to be removed by harvester ants (Engelbrecht & García‐Fayos, 2012; Gutterman & Shem‐Tov, 1997; Pan et al, 2021; Yang et al, 2013). The mechanism behind the defensive value of physical binding to the substrate seems to be simply the force of attachment and thus the difficulty of exploitation, as seeds with greater anchorage strength were removed at lower rates (LoPresti et al, 2023; Pan et al, 2021). In areas with loose substrate, wetted mucilage binds substrate, which remains firmly bound to the seed once dry (Figure 1: top row).…”