What cold lizards in Miami can tell us about climate change resilience


Date:
October 21, 2020
Source:
Washington University in St. Louis
Summary:
When temperatures go below a critical limit, sleeping lizards lose
their grip and fall out of trees. But when researchers collected the
scaled survivors of a record cold snap, they discovered that a Miami
lizard community responded in an unexpected way: all of them could
now tolerate cold temperatures down to about 42 degrees Fahrenheit,
regardless of their species' previous ability to withstand cold.



FULL STORY ========================================================================== [Iguana on a branch | Credit: (c) jerzy / stock.adobe.com] Iguana on a
branch (stock image).

Credit: (c) jerzy / stock.adobe.com [Iguana on a branch | Credit: (c)
jerzy / stock.adobe.com] Iguana on a branch (stock image).

Credit: (c) jerzy / stock.adobe.com Close It was raining iguanas on a
sunny morning.


========================================================================== Biologist James Stroud's phone started buzzing early on Jan. 22. A friend
who was bicycling to work past the white sands and palm tree edges of
Key Biscayne, an island town south of Miami, sent Stroud a picture of
a 2-foot long lizard splayed out on its back. With its feet in the air,
the iguana took up most of the sidewalk.

The previous night was south Florida's coldest in 10 years, at just
under 40 degrees Fahrenheit. While most people reached for an extra
blanket or a pair of socks, Stroud -- a postdoctoral research associate
in Arts & Sciences at Washington University in St. Louis -- frantically
texted a collaborator: "Today's the day to drop everything, go catch
some lizards." When temperatures go below a critical limit, sleeping
lizards lose their grip and fall out of trees. From previous research,
Stroud and his colleagues had learned that different types of lizards
in Miami can tolerate different low temperatures, ranging from about
46 to 52 degrees Fahrenheit, before they are stunned by cold. This cold
snap provided a unique opportunity to understand how they are affected
by extreme climate events.

But when the researchers collected the scaled survivors of that
coldest night, they discovered that the lizard community responded in
an unexpected way: all of them could tolerate cold temperatures down
to about 42 degrees Fahrenheit, regardless of their species' previous
ability to withstand cold. The findings are reported Oct. 21 in the
journal Biology Letters.



========================================================================== "Prior to this, and for a different study, we had measured the lowest temperatures that six lizard species in south Florida could tolerate,"
Stroud said. "We realized after the 2020 cold event that these data were
now extremely valuable -- we had the opportunity to re-measure the same
lizard populations to observe if their physiological limits had changed;
in other words, could these species now tolerate lower temperatures?"
In the days that followed the January cold snap, researchers collected representatives of as many different kinds of lizards as they could
find in the local area, rounding up small and large lizards and those
that are active during the day and at night. Then the researchers tested
their response to cold.

"A major unexpected result of this study was that all species converged
on the same new, lower level of thermal tolerance," Stroud said. "While
there was great variation in temperature tolerance before the cold event
-- some, like the large-bodied brown basilisk, were very intolerant
of low temperatures, while others like the Puerto Rican crested anole
were more robust -- we observed that all species could now tolerate,
on average, the same lowest temperature.

"Given great variation in body size, ecology and physiology, this was unexpected," he said.

Only one of the species in the study is native to the area; the rest
have been introduced to Florida over the past century, researchers noted.



==========================================================================
The results provide evidence that tropical, cold-blooded creatures --
often characterized as unable to withstand rapid changes in climatic
conditions - - can sometimes endure conditions that exceed their
established physiological limits.

"The shifts to tolerate significantly lower temperatures that we
observed were so large that we found it unclear whether natural
selection was responsible," Stroud said. "And so in our paper we discuss
other alternative processes which may also have led to this pattern."
"The results of this study are surprising and unexpected. Who would have thought that tropical lizards from places like Puerto Rico and Central
America could withstand temperatures near freezing?" said Jonathan
Losos, the William H. Danforth Distinguished University Professor and
professor of biology in Arts & Sciences and director of the Living Earth Collaborative at Washington University.

"What we now need to find out is how this was accomplished. Is this
evidence of natural selection, with those lizards that just happened
to have a lower cold tolerance surviving and others freezing to death,
or was it an example of physiological adjustment -- termed 'acclimation'
-- in which exposure to lower temperatures changes a lizard's physiology
so that it is capable of withstanding lower temperatures?" Regardless of
the underlying mechanism, the new study provides a critically important
piece of information for understanding the impacts of climate change.

Scientists expect that air temperatures will gradually become warmer
under climate change, but also that temperatures will become more chaotic.

Events that spike temperature to extremes -- both exceptionally hot
and exceptionally cold episodes -- will increase in frequency and
magnitude. As such, it is important to understand both the effects
of gradual, long-term increases in air temperatures as well as the
consequences of abrupt, short-term extreme events.

"It is widely thought that tropical and subtropical species are going
to be especially vulnerable to changes in temperature -- particularly
extreme spikes of heat or cold -- as tropical areas do not typically
have strong seasons," Stroud said. "Unlike temperate species, which are
adapted to summer highs and winter lows, tropical species have typically evolved in very thermally stable environments.

"While there is no doubt that climate change represents a major threat to species and ecosystems around the world, and deserves as much research attention as possible, this study provides fascinating insight and a
glimpse of hope," he said. "Perhaps tropical and subtropical species
can withstand more extreme climatic conditions."

========================================================================== 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. James T. Stroud, Caitlin C. Mothes, Winter Beckles, Robert J. P.

Heathcote, Colin M. Donihue, Jonathan B. Losos. An extreme cold
event leads to community-wide convergence in lower temperature
tolerance in a lizard community. Biology Letters, 2020; 16 (10):
20200625 DOI: 10.1098/ rsbl.2020.0625 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201021085119.htm

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