Natures wonders: ants plant tough seeds for food (Introduction)

by David Turell , Saturday, January 14, 2017, 01:04 (2869 days ago) @ David Turell

Ants store big tough seeds, can't crack them open, so they are planted and the softer seedling provides food:

https://www.newscientist.com/article/2117953-harvester-ants-farm-by-planting-seeds-to-e...

"They’ve cracked it. Small ants carry home large seeds to eat all the time, but no one knew exactly how they managed to break through the seeds’ tough exterior.
It turns out that Florida harvester ants, Pogonomyrmex badius, have developed a clever farming strategy to do so – they plant seeds, wait for them to germinate and then eat the soft spoils.

"Some 18 genera of ants harvest seeds, and colonies of some species can store more than 300,000 seeds in their underground granaries..

"So far, scientists thought that ants must be able to break the seeds open and just ate them as they were. “The reality is a lot more interesting,” says Walter R. Tschinkel at the Florida State University.

“'There are many studies of seed choice by forager harvester ants, but none of the authors asked the question of whether the ants can open the seeds,” says Tschinkel. “This may be in part because most of these studies were done on western harvester ants whose deep nests are in hard soil, so the seed chambers are not easily excavated.”

"With his team, Tschinkel excavated and studied approximately 200 P. badius nests and found that the ants mostly open and consume small seeds, which are easier to crack. Foragers collect seeds of all sizes, so this leads to the accumulation of larger seeds, which end up forming 70 per cent of stored seeds by weight.

"In a series of lab and field experiments Tschinkel and colleagues showed that P. badius doesn’t seem to be able to open the large seeds unless they have germinated first. Even the caste of ants with large heads and mandibles thought to be specialised for seed opening can’t crack the big seeds.

"Germination, on the other hand, splits the tough husk, making the seed contents available as food for the ants. A single large seed may have nutritional value of 15 smaller seeds, so it makes sense to collect it and wait for it to crack open. Seeds from various species germinate at different times, which may give the ants a steady supply of their “crop”.

"This is the first example of ants relying on germination to consume large seeds, although some worms seem to do it, too. The only other example of ants farming plants for food is of the Fijian ant Philidris nagasau, which grows Squamellaria plants and harvests their fruit."

Comment: I think it is very probably that the ants figured this out for themselves. I imagine they brought some big seeds home, couldn't crack them, but didn't drag them out of the nest and were pleasantly surprised when the softer seedling popped up. The simply accepted it as a useful pattern of behaviour.