Following in Darwin's Footsteps

More than 150 years ago, Charles Darwin’s
fascination with genetics and domestication catapulted the scientific world
into new territory as scientists started to ask: How did a species evolve to be
this way?

In a study published in Plants People
Planet, a team led by Virginia Tech researchers discovered that in its 200
years of being cultivated and domesticated, florist’s gloxinia, Sinningia
speciosa, has reached tremendous levels of phenotypic, or physical, variation
and originates from a single founder population.

“The hallmark here is that, with early
stages of domestication, we see increased phenotypic variation but an overall
decrease in genetic variation. So it’s a paradox — and we’ve made it even more
of a paradox because we’re showing that all of this phenotypic variation came
from a single founder population,” said Tomas Hasing, lead author.

Florist’s gloxinia, a species originally
documented by Darwin himself, was introduced to England in the 18th century.
Since then, plant breeders have cultivated hundreds of strains by intentionally
selecting for desired traits. Within 200 years — a mere blink of an
evolutionary eye —florist’s gloxinia reached the same levels of phenotypic
variation as snapdragons, Antirrhinum spp. Snapdragons, however, have been
cultivated for 2,000 years.

“Florist’s gloxinia presents a clear
domestication syndrome and rich phenotypic diversity. We already knew that it
had a small, simple genome, but the complexity of its origin was a mystery that
we needed to solve before we started to use it as a model,” said Aureliano
Bombarely, a former assistant professor in the School of Plant and
Environmental Sciences. In 2014, he proposed the use of this species as a model
to study genomic evolution during domestication.

To account for the plant’s major aesthetic
changes in such a short period of time, the team expected florist’s gloxinia to
have been cross-bred with other species at some point during its history. They
used reduced representation sequencing of the genome to trace the origins of
the plant back to its native home of Rio de Janeiro, Brazil, but found no
evidence of hybridization, indicating that most varieties of florist’s gloxinia
come from a single founder population just outside of the city.

The discovery of the single founder
population explains why florist’s gloxinia has such low genetic variation —
cultivating plants in captivity allows breeders to select for different
physical traits like color, shape, or size and purge unwanted genetic variation
from a population. When beneficial mutations arise, breeders can increase a
mutation’s frequency by breeding it into the population. Ultimately, the
accumulation of small changes from mutations led to the plant’s high levels of
phenotypic diversity.

“Most studies conducted on domesticated
plants are focused on food crops, but studying how ornamental crops are
domesticated expands our understanding of plant genetics and patterns. This
ultimately benefits agriculture as a whole,” said David Haak, assistant
professor in the School of Plant and Environmental Sciences.

The commercial cultivation of flowers,
known as floriculture, was recently named the ninth highest-grossing sector of
Virginia’s top 20 agricultural products by generating $146 million annually. An
increased understanding of plant genetics will allow floriculturists to grow
and harvest flowers more efficiently and generate more income.

With the new-found discovery of this
alternate evolutionary route to plant domestication, Bombarely, Haak, and their
research teams are looking forward to continuing their work on plant genomics
and studying its implications for agriculture.

Reference

Hasing et al. (2019) Extensive phenotypic
diversity in the cultivated Florist’s Gloxinia, Sinningia speciosa
(Lodd.) Hiern, is derived from the domestication of a single founder population.
Plants, People, Planet. DOI: https://doi.org/10.1002/ppp3.10065

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