While we know that temperature matters, ecologically, and we've gotten a little closer to explaining why mucilage volume and attachment strength is higher in hotter areas, we still don't know exactly why this temperature relationship exists. Our best guess, which we are testing in the lab now, is that it reduces the area of attachment of the seed.

So, why? Madi Stessman, another undergrad in the lab, figured that we could isolate the effect of temperature from drying speed by using vacuum desiccators - so, she tested accelerated drying via increases in temp and vacuum and found that it was the accelerated drying, not the high temperature alone, that caused the reduction in attachment force. Then Madi, Kathy, and I went to the field and found that the reduction in attachment strength made them more susceptible to harvester ant predation.

To back up - 1000's of plant species have seed mucilage, a layer of polysaccharides on the outside of the seed that swells up into a sticky mess when wetted. Then, after drying, it cements the seed onto whatever it is contact with (sometimes takes >1kg of force to remove seed!). However, as Sara Warren, an undergrad in the lab, clearly demonstrated, with 9999 seed dislodgement measurements (!), the force is highly dependent on drying temperature. At high temperatures, seeds stick badly...