Early crop plants were more easily 'tamed'

Date:
April 10, 2023
Source:
Washington University in St. Louis
Summary:
Borrowing a page from what we know about animal behavior,
archaeologists say that we should reassess our understanding of
the process of plant domestication.


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FULL STORY ==========================================================================
The story of how ancient wolves came to claim a place near the campfire
as humanity's best friend is a familiar tale (even if scientists are
still working out some of the specifics). In order to be domesticated,
a wild animal must be tamable -- capable of living in close proximity
to people without exhibiting dangerous aggression or debilitating
fear. Taming was the necessary first step in animal domestication,
and it is widely known that some animals are easier to tame than others.


==========================================================================
But did humans also favor certain wild plants for domestication because
they were more easily "tamed"? Research from Washington University in
St. Louis calls for a reappraisal of the process of plant domestication,
based on almost a decade of observations and experiments. The behavior
of erect knotweed, a buckwheat relative, has WashU paleoethnobotanists completely reassessing our understanding of plant domestication.

"We have no equivalent term for tameness in plants," said Natalie
Mueller, assistant professor of archaeology in Arts & Sciences at
Washington University.

"But plants are capable of responding to people. They have a developmental capacity to be tamed." Her work with early indigenous North American
crops shows that some wild plants respond quickly to clearing,
fertilizing, weeding or thinning. Plants that respond in ways that make cultivation easier or more productive could be considered more easily
tamed than those that cannot.

"If plants responded rapidly in ways that were beneficial to early
cultivators -- for example by producing higher yields, larger seeds,
seeds that were easier to sprout, or a second crop in a single growing
season -- this would have encouraged humans to continue investing in
the co-evolutionary relationship," she said.

This capacity to express different traits and characteristics in response
to the environment is called plasticity, and not all species are equally plastic.

"Some plants respond quickly and obviously to cultivation and care,"
Mueller said. "I think ancient people would have noticed that they could
double their yields just by thinning out dense stands of plants. This
is one of the simplest and most common gardening techniques, but it
has many important effects on the development of plants." What would
an early farmer do? Mueller's study, published April 7 in PLOS ONE,
focuses on work with a plant called erect knotweed, a member of the
buckwheat family that was domesticated by indigenous farmers in eastern
North America. The domesticated sub-species is now extinct; humans don't
eat it anymore. But Mueller and others have previously uncovered caches
of seeds stored in caves, charred plant remnants in ancient hearths,
and even the seeds of erect knotweed in human feces, clear evidence that
this species was once consumed as a staple food.

Mueller, who studies lost crops, has spent years growing erect knotweed
and other crop progenitors in experimental gardens, including at
Washington University's environmental field station, Tyson Research
Center. She hasn't always been successful with growing the plants she
collects in the wild. In that way, Mueller can relate to the early farmers
who similarly experimented with plants to discover their potential.

Her efforts have often been stymied by seed dormancy, a common feature
among wild plants.

Unlike seeds you buy at the garden store, the seeds of most wild plants
will not germinate if you simply sprinkle some water on them. Their requirements for germination are diverse and shaped by their evolutionary history. For example, if a plant has evolved in a place with a winter,
like the Midwest, its seeds may not germinate unless they experience a
long cold period. This prevents them from germinating too soon in the
wild -- they are waiting for spring.

Domesticated plants have lost their diverse germination requirements.

The loss of germination inhibitors has presented a paradox to theorists
of domestication. Many of the selective pressures that could have favored
the evolution of this trait derive from planting seeds. But why would
ancient people have started planting seeds if none of them germinated?
With erect knotweed, Mueller experienced a breakthrough of sorts. Based on
four seasons of observations, Mueller determined that growing wild plants
in the low-density conditions typical of a cultivated garden (i.e. spaced
out and weeded) triggers plants to produce seeds that germinate more
easily. This makes the harvests easier to plant successfully the next
time around, eliminating a key barrier to further selection.

"Our results show that erect knotweed grown in low-density agroecosystems spontaneously 'act domesticated' in a single growing season, before any selection has occurred," Mueller said.

Think of it as the plant equivalent to that first wolf who, though still
a wild animal, sat down with its human friend around the fire. This is
a behavioral shift, rather than an evolutionary one, but it allows new evolutionary pathways to open up.

A role for plant behavior Mueller believes there is a bias in
domestication studies toward viewing this changeability, or plasticity,
as noise that is getting in the way of attempts to explain evolutionary
change. Instead, this paper argues that we need to understand the
development and behavior of wild crop relatives in order to explain the evolutionary process of domestication.

"Because we lack the practical experience with crop progenitors that
ancient people had, these effects of the environment on plant development
have gone mostly unnoticed and understudied," Mueller said.

Her findings could have applications for developing new food crops:
there is no reason why we have to be limited to the plants that our
ancestors domesticated thousands of years ago.

Some researchers have been calling for de novo domestication --
selecting wild plants with desirable characteristics and intentionally domesticating them. It may make sense to start looking to wild plants
that are easily tamed as potential crops that could be developed for
the future, Mueller said.

This paper also contributes to a growing awareness that plants are
responsive and communicative beings. Though this idea is cutting-edge and
hotly debated in biology and ecology, it is widespread in indigenous North American philosophies and probably would have been held by the people
who domesticated erect knotweed and other plants thousands of years ago.

Recent research has shown how plants warn relatives about herbivores
using chemical signaling, share resources through mycorrhizal networks
and even emit noises when they are injured or stressed.

"You can't explain plant domestication if you only consider the behaviors
of humans, because domestication is the result of reciprocal relationships between multiple species that are all capable of responding to each
other," Mueller said.

* RELATED_TOPICS
o Plants_&_Animals
# Endangered_Plants # Seeds # Botany
o Earth_&_Climate
# Grassland # Rainforests # Ecology
o Fossils_&_Ruins
# Human_Evolution # Evolution # Early_Humans
* RELATED_TERMS
o Corn o Archaeological_field_survey o Seed_predation o
Game_theory o Instinct o Mirror_neuron o Domestication o
Plant_breeding

========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Talia
Ogliore. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Natalie G. Mueller, Elizabeth T. Horton, Megan E. Belcher,
Logan Kistler.

The taming of the weed: Developmental plasticity facilitated plant
domestication. PLOS ONE, 2023; 18 (4): e0284136 DOI: 10.1371/
journal.pone.0284136 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/04/230410132158.htm

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