WILDTYPE
BY C A R O L C R U Z A N M O R TO N
SEX LIVES OF
STRAWBERRIES
Exploring genetics and fruit
to kick off our new science column
H
i everyone! I’m Carol Cruzan Morton, your friend-
ly new science columnist at Eugene Weekly. Take a
walk with me on the WildType name. In research,
“wild type” means the normal, naturally occurring
standard for comparison to another version of the
same thing, such as a gene or another feature of a plant or
animal.
It’s a quaint old term, because there’s no such thing as
normal. A better inspiration might be Wild Type, the short-
lived cover band composed of cancer biologists who in their
day jobs shined the light of discovery for all of us dancing
in the dark.
In coming months, we’ll roam over topics from astron-
omy to zoology. For our first column, we have a yummy
genetics story about the origins of sex — at least in straw-
berries — fresh from the labs of Oregon State University re-
searchers and their collaborators at University of Pittsburgh.
The Secret Sex Life of Strawberries
We all need a break from the sex lives of Supreme Court
nominees and chief executives. In fact, at this point in the
news cycle, you may be asking yourself the same question
that has perplexed evolutionary biologists for decades: Why
two sexes? It’s risky and expensive — in politics, business
and biology.
Animal XY sex chromosomes are too old to answer this
question, so researchers turned to strawberries, which have
some of the youngest sex chromosomes among flowering
plants and animals. Using modern voyeuristic techniques
they have literally caught strawberries in the act of transi-
tioning into two sexes.
“To me, the wow-cool aspect is that this is really young
on the evolutionary time scale,” says OSU evolutionary
biologist Aaron Liston, who collaborated on the study. For
these fresh sexing things we call strawberries, “young”
means only a few million years old.
Separate sexes may seem fundamental to nature —
woman and man, hen and rooster, cow and bull — but
they’re an oddity for most plants. After all, finding a mate
is tough enough when you’re not rooted in one place. Most
flowering plants are hermaphrodites — which contain both
male and female sex organs. In other words, they complete
themselves. Only about 6 percent have split into different
sexes, but these two-sex plants are important to people, such
as garden asparagus, papaya, hops, marijuana and some
strawberries.
Liston’s Pittsburgh collaborators have been trying to pin
down the sex genes in strawberries for about 20 years. They
looked at Oregon beach strawberries and two sister species
found across the country.
Then came the first strawberry genome project (cue su-
perhero music here). That work brought the two labs togeth-
er and the results gave them a needed scientific reference
point.
In a brute force approach, they sequenced 60 strawberry
plants from three strawberry species evenly divided be-
tween males and females.
The sexual identity of wild strawberries appears to ride
on a patch of genes that has jumped between chromosome 6
versions, carrying a few more genetic neighbors each time.
What’s more, with each jump, the number of female-specif-
ic genes on the sequence increased. Those traveling “souve-
nirs” increased the difference between the sex chromosomes,
the researchers
speculate. In
humans and
other ani-
mals, such
sex-specific
differences
eventually
became ex-
treme.
I know
what you’re
thinking now: How
can they know all that
from 60 plants when it
takes 10,000 genomes
or more to look for
disease-causing
genes in people?
“Diversity,” Lis-
ton tells us. “There’s
less diversity in hu-
mans than in strawber-
ries.”
Human genomes have so much in
common, it’s hard to find culprits. Also, a lot of human dis-
eases involve complex genetics. Male and female is rela-
tively straightforward, genetically speaking.
But don’t look for the special male and female straw-
berries at your grocery stores or farmers’ markets any time
soon. In a final plot twist, the hybrid descendants of the wild
strawberries in the study have all had the sex differences
bred out of them.
Got tips, story ideas, or science events to list? Contact Carol Cruzan Morton
at WildTypeOregon@gmail.com. Note: An earlier version of the strawberry sex
story by Morton was published on the news site of the weekly journal Science.
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