22 Scientific American, March 2022
mazzzur/Getty ImagesEVOLUTIONSlow and Steady
Snakes and lizards played it safe in early
evolution—outcompeting ancient cousinsEarth is crawling with lizards and snakes. More than
10,000 species of these reptiles, called squamates, have
adapted to thrive across almost every continent. But this
vast assortment took a surprisingly long time to develop,
according to University of Bristol paleontologist Jorge
Herrera-Flores and his colleagues. Instead of trying new
adaptations as quickly as possible, squamates succeeded
by evolving with a relatively slow and steady pace, the
researchers say—an idea counter to many biologists’
assumptions about how and why life generates diversity.
The researchers charted squamates’ evolution in a
new study published in Palaeontology, contrasting them
with elusive reptilian relatives called rhynchocephalians.
Today the latter are represented by just one living spe-
cies—New Zealand’s tuatara—but there were far more
in the deep past. “For many decades,” Herrera-Flores
says, “it has been questioned what was the real cause
of the decline of the rhynchocephalians.”
The researchers observed a strange pattern: the two
groups’ evolutionary trajectories were flipped. Squa-
mates evolved differences in body size slowly during
the first two thirds of the group’s existence, from about
240 million to 80 million years ago. At the same time,
rhynchocephalians were rapidly splitting into a profusion
of different sizes—until their diversity collapsed.
Until now, it had seemed that quick bursts of evolu-
tionary experimentation built long-term staying power.
Previous studies of two other reptile groups, dinosaurs
and crocodiles, proposed that fast early evolution helped
these animals shoulder out competitors and quickly dom-
inate the landscape. By that logic, rhynchocephalians’
speedy variations should have presaged greater success.
Instead, Herrera-Flores and his colleagues suggest, fast
evolution might create a kind of volatility that leads more
readily to extinction. Squamates’ slower pace resulted in
a more stable history, followed by a later burst of diversity
when tuatara relatives were already on their downturn.
Reptiles are not alone in this apparent “slow and
steady” strategy. Even though modern bony fishes are
much more diverse today, a previous study found that in
the past they were not as numerous or varied as holoste-
ans—the prehistoric relatives of today’s gar and paddle-
fish. Such studies suggest that quickly diversifying to fill
more niches is not always a route to long-term success.
And unlike its cousins, the specific rhynchocephalian
lineage that led to today’s tuatara had “exceptionally low
rates of evolution,” notes Harvard University herpetolo-
gist Tiago Simões, who was not involved in the new
study. This is what makes the tuatara stand out as a “liv-
ing fossil,” an echo of an ancient evolutionary boom that
eventually went bust. — Riley BlackBIOLOGY
Parasite Challenge
A giant, meaty flower has a fraught relationship
with its host plant
Little is known about how the parasitic Rafflesia—a genus that produces
the world’s largest and stinkiest flower—infects its host plants. Rafflesia
spends most of its life span as a tangle of strandlike cells lurking inconspic-
uously underneath the bark of a woody vine called Tetrastigma, before
emerging as drab, golf ball–sized buds. These eventually burst into fleshy
blooms that smell like rotting meat and can reach 20 pounds and three
feet across. Since 2017, Long Island University plant biologist Jeanmaire
Molina has been trying to infect Tetrastigma seedlings with Rafflesia seeds
in the laboratory, so far without success; her latest work delves further
into how some potential hosts manage to thwart this spectacular parasite.
For a new study in Planta, Molina and her colleagues extracted and
screened over 10,000 chemicals produced by infected and noninfected Tet-
rastigmacuttings from rain forests in the Philippines. The re searchers found
that noninfected cuttings contained elevated levels of benzylisoquinoline
alkaloids, a group of compounds that includes morphine and codeine.
Such substances have never been reported before in Tetrastigmaor
other creepers in the same family (which includes the common grape).
Molina says she is intrigued that Tetrastigmacan produce such biologically
potent substances, and the precise reasons it does so are not yet known.
She suspects Tetrastigmamay brandish these alkaloids preemptively to
stave off infection. Perhaps, she adds, Rafflesia’s opening gambit is to sup-
press this secretion and besiege its host.
In any case, the finding is “pretty surprising,” says Harvard University
evolutionary biologist Charles Davis, who was not involved in the study.
“Plants are incredible chemists.” He adds that the work is an important
step toward demystifying interactions between parasite and host.
Next, Molina hopes to learn how to tip the balance toward Rafflesia.
Her long-term goal is to bring some of these endangered flowers out of
their Southeast Asian habitats and make them more accessible to the out-
side world. Learning how Tetrastigma’s defenses work—and how to sub-
vert them—is a place to start.
Molina keeps a potted Tetrastigmain her university office, regularly sprin-
kling the plant with Rafflesiaseeds in the hope they will miraculously catch.
So far, nothing. But she still maintains the routine. “I think there is a way. We
just don’t know it yet,” she says. “We’ll get there somehow.” —ShiEnKim
R a ffl e s i abloom
ing in Sumatra