The Accidental Grain - How Rye Evolved Its Way Into Our Diet

Humans have been altering the genomes of plants for a very long time. Nowhere is this more apparent than in the crops we grow. These botanical mutants are pampered beasts compared to their wild congeners. It is easy to see why some traits have been selected over others, whether it be larger leaves or fruit to munch on, smaller seeds to keep them out of our way, or tough rinds to make shipping easier. However, not all of our crops have been consciously bred for our consumption. Just as many weed species are adapting to herbicides today, some species of plant were able to adapt to the more archaic methods of early farming, which allowed them to avoid the ever watchful eye of the farmer.

This concept is known as Vavilovian mimicry (sometimes referred to as crop mimicry) and it is named after the Soviet botanist and geneticist Nikolai Vavilov (who was later imprisoned and starved to death by Stalin because of his firm stance on basic genetic principles). The idea is rather simple. At its core it involves artificial selection, albeit unintentional. A wild plant species finds certain forms of agriculture appealing. It becomes an apparent weed and the farmer begins to deal with it. Perhaps this plant is a close relative and thus looks quite similar to the crop in question. As the farmer weeds out plants that look different from the crop, they may be unintentionally selecting for individual weeds that more closely resemble the crop species. Over enough seasons, only those weeds that look enough like the crop survive and reproduce, sometimes to the point in which the two are almost indistinguishable.

Rye is an interesting example of this idea. Wild rye (Secale montanum) was not intentionally grown for food. It was a weed in the fields of other crops like wheat and barley. Both wheat and barley are annual plants, producing their edible seeds at the end of their first growing season. Wild rye, however, is a perennial and does not produce seed until at least its second season. Therefore, most wild rye plants growing in wheat or barely fields are killed at the end of the season when the field gets tilled. However, there are some mutant rye plants that occasionally pop up and produce seeds in their first year.

It is believed that these mutant annual rye were harvested unintentionally and reseeded season after season. Over time, other traits likely developed to help push rye into the spotlight for these early farmers. Like many wild grasses, wild rye has weak spindles (the part that holds the seed to the plant). In the wild, this allows for efficient seed dispersal. On the farm, this is not a desirable trait as you end up quickly losing the seeds you want to harvest. Again, by accidentally selecting for mutants that also had thicker spindles and thus held on to their seeds, farmers were unintentionally domesticating rye to parallel other cereal crops. It is believed that oats (Avena sterilis) also originated in this manner.

Photo Credit: Lotte Grønkjær (http://bit.ly/1xMEfVw)

Further Reading: [1] [2]

Shhhh... Let Him Finish

Sexual deception is rampant in the orchid family. Orchid genera all over the world produce flowers that trick sexually charged male insects into failed mating attempts. The orchids go to great lengths to resemble females both in appearance and smell. Indeed, many sexually deceptive orchid species emit odors that precisely mimic the pheromones of specific insect species. 

In many instances, the orchids ruse is so powerful that male insects will often preferentially visit the flower over an actual female. For many of the sexually deceptive orchids, all that is required is the male to pay a visit. No attempt at copulation is necessary, though that doesn't stop vigorous attempts. Because of this, it is easy to see how the minute cost incurred to the insects is not enough to drive evolution away from deception. However, there is a group of tongue orchids (genus Cryptostylis) from Australia that seem to throw a wrench into this finely tuned system.... or do they?

The tongue orchids rely on deceiving male wasps in the genus Lissopimpla into mating with their flowers. As mentioned above, the males simply cannot resist the attempt. However, unlike many other reported cases, the male wasps actually mate to completion, depositing their sperm onto the flower. This should be disastrous for the wasps since males not only prefer flowers to wasp females, but they also waste their precious few mating attempts. How could this have evolved?

Most sexually deceptive orchids rely on bees and wasps (family Hymenoptera) for their pollination. Thus, the answer to this evolutionary conundrum lies in the mating system of these insects. Queens are genetically haplodiploid. I will spare you the details on that but basically what it means for Hymenoptera is that female offspring are produced via fertilized eggs whereas male offspring are produced via unfertilized eggs. 

The orchids have (unknowingly of course) tapped into this system to their benefit. If by mating with the flower and not a female wasp meant that no offspring were produced, this system surely would not have evolved to the level that it has. Instead, female wasps that have not been mated with or received less sperm than usual end up producing a higher amount of male offspring.

The orchids are effectively skewing the sex ratio of their pollinators! "How is this a sustainable system?" you may be asking. Well, by causing female wasps to produce more males, the orchids are ensuring that there will be more naive males in the population the next time they are in bloom. Also, by skewing the sex ratio towards males, there are now fewer females to mate with so that males become less choosy and more readily mate with orchids. Finally, with more sexually charged males flying around, each female has a greater chance of being fertilized. Because of the unique mating system that has evolved in Hymenoptera, the orchids have thus been able to evolve this pollination strategy with little harm to the pollinators.

Photo Credit: photobitz

Further Reading:
http://instructional1.calstatela.edu/kfisher2/BIOL360/classroom.activities/species_interact._casestudies/orchid.sex.pseudo.II.pdf