In a new study published in Trends in Plant Science , Dr. Robert Spengler examines these evolutionary responses and theorizes that all of the earliest traits to evolve in the wild relatives of modern domesticated crops are linked to human seed dispersal and the evolutionary need for a plant to spread its offspring. Many of the earliest traits of domestication in plants are similar across different crop species, a phenomenon evolutionary biologists refer to as parallel evolution.
For example, in all large-seeded grass crops -- e. Likewise, in all large-seeded legumes, such as peas, lentils, fava beans, and kidney beans, the earliest trait of domestication is a non-shattering pod. Archaeobotanists studying early plant domestication agree that the evolution of tougher rachises in cereal crops was a result of humans using sickles to harvest grains.
During a harvest, the specimens with the most brittle rachises lost their seeds, whereas the plants with tougher rachises benefited from having their seeds protected and saved for the following year. Humans then cleared away competitive plants weeding , tilled soil, sowed seeds, and maintained the crops until the next harvest.
We can assume that the same process occurred for legumes. For nearly a century, scholars have been aware of the fact that this parallel evolution was the result of similar selective pressures from people in different centers of domestication around the world, leading to what many researchers call "domestication syndrome. Archaeobotanists have studied seed-dispersal traits in the wild relatives of cereal and legume crops, but few have discussed how the wild relatives of other crops dispersed their seeds.
In this manuscript, Spengler steps away from the heavy focus on these few plants and looks at the wild seed-dispersal processes in other crops. Spengler notes that before the last Ice Age, megafaunal mammals, including humans, were key for the evolution of larger fruits in the wild.
While some plants have mechanical methods of seed dispersal, the most common way plants spread their seeds is by recruiting animals to do it for them. Bright red cherries, for example, have evolved to entice birds with red-green color vision. The birds consume the sugary fruit, then fly to a new area and deposit the seed from the cherry. When an animal chews the seeds rather than swallow them whole, dispersal fails as the seeds are killed.
In our native woodlands, badgers help spread the seeds of yew trees Taxus baccata to more open areas in their poo.
These black-and-white creatures swallow the yew berries but only digest the fruit pulp, leaving the seeds to pass through their digestive system intact and grow into new trees. Did you know? Some invertebrates that are big enough to swallow seeds, like crickets, slugs and snails, may ingest and disperse them, but this is not common. Secondary seed dispersal happens when a predator devours another animal that has eaten the seeds, such as birds of prey that feed on small seed-eating lizards.
This increases the distance the seeds are carried before they are finally deposited. But the seeds have to be tough enough to survive digestive tracts, twice over. The most important benefit of seed dispersal through animal poo is distance. This is also why large-bodied animals are important seed dispersers — they eat a lot and travel far! Being dispersed further away from the parent plants means the seeds are carried to an environment with less competition with parents and siblings, better light conditions, avoidance of predators and pathogens, and an opportunity to colonise new habitats.
The Milkweed plant, which is very important to the monarch butterfly, also uses wind to disperse its seeds. Ballistic: Seeds from the oxalis, the shamrock, and the Artillery Fern are bursting to get out! These plants produce their seeds in pods and capsules. As the seed matures in the fruit, the pod swells. In nurseries and greenhouses, the oxalis plant is known to hop from pot to pot using this bursting method. A coconut can travel for days and 3, miles! Thanks to the grey squirrel, 32 different species of oaks continue to grow in North America!
Birds consume fruits and berries leading to seeds being distributed many miles away.
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