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<!DOCTYPE html>
<html lang="en-US">
<head>
<title>Kevin Surya » Research</title>
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<a href="index.html">about</a>
<a href="research.html" style="color: gainsboro;">research</a>
<a href="publications.html">publications</a>
<a href="storytelling.html">storytelling</a>
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<br /><br /><br /><br /><br />
<div class="main">
<div class="title">RESEARCH</div>
<br />
DETECTING PUNCTUATED EVOLUTION IN SARS-COV-2
<br />
<img src="Surya_figure3.svg" alt="SARS-CoV-2 punctuated evolution"/>
<p>SARS-CoV-2 evolved slowly over the first year of the COVID-19
pandemic, with different mutation rates across lineages. How did this
variation arise? Using phylogenetic regression models, we show that
~13% of SARS-CoV-2 genomic evolution up to May 2020 is concentrated at
lineage branching events (i.e., punctuated evolution). This small
punctuational contribution to SARS-CoV-2 diversity is consistent with
the 'founder effect' resulting from narrow transmission bottlenecks.
Therefore, punctuation in SARS-CoV-2 may represent the
macroevolutionary consequence (rate variation) of a microevolutionary
process (transmission bottleneck).</p>
<br />
FOSSIL RECORD BIAS IN MACROEVOLUTIONARY ANALYSES
<br />
<img src="Surya_figure2.svg" alt="tetrapodomorph water-land transition"/>
<p>Fossil record bias confounds analyses of species dispersal through
space and time. Circa 400 million years ago, fish-like ancestors of
tetrapods, four-limbed vertebrates, moved from water to land. Using
this transition as a case study, Jacob Gardner, Chris Organ, and I
propose a proxy for fossil sampling bias that incorporates geographic
information. We initially found that the water-land transition occurred
in Euramerica and that cross-continent dispersals tend to be rapid.
However, these results are unreliable because they can be explained by
insufficient fossil record in all regions except Southern
Euramerica.</p>
<br />
BIRD TAIL DEVELOPMENT AND EVOLUTION
<br />
<img src="Surya_figure1.svg" alt="dinosaur tails" />
<p><i>Pygostyle</i>. The long tail of Mesozoic dinosaurs rapidly evolved
into the short, terminally-fused tail of living birds. Two fossil
specimens (<i>Zhongornis haoae</i> and the dinosaur tail preserved in
Burmese amber) exhibit a transitional tail morphology: short and
unfused. However, our study on bird tail development warrants
re-interpretation of these transitional species. Bird tail vertebrae
change radically with growth. As birds reach maturity, the last four to
six vertebrae fuse into a compound bone called the pygostyle. Vertebral
side projections mineralize long after hatching. <i>Zhongornis</i>, as
a juvenile, might not have yet formed a pygostyle, and the dinosaur
tail, also immature, might be avian.</p>
<p><i>Pygostyle Development</i>. My colleagues and I found that vertebral
fusion in bird tails is driven by sterile inflammation and resembles
bone fracture repair. This finding demonstrates a role for inflammation
in skeleton development. The immune system is involved in pathological
bone fusion, but we also found it to be a crucial contributor to normal
vertebral fusion. Evidence of necroptosis indicates that this type of
cell death can occur in post-birth development. Moreover, we documented
nucleus pulposus structures in tail discs in birds. Lastly,
corticosteroid treatment inhibits vertebral fusion, suppressing a
Cretaceous avian flight adaptation while demonstrating an unreported
effect of corticosteroids on skeletal maturation.</p>
<p><i>Spinal Nerve</i>. Ground-dwelling birds like the emu and kiwi
(paleognaths) have holes in their pygostyles. These holes are absent in
other birds' pygostyles (chicken, Chinese quail, and rock dove) or the
tail vertebrae of the brown anole and American alligator (close living
relatives of birds). What is the purpose of the holes? My colleagues
and I study the tail development in the species above and found that
the paleognath spinal nerves uniquely extend to the very end of the
tail. The holes seem to serve as exit points for these nerves. Looking
back through time, we find that these holes also exist in the Mesozoic
confuciusornithids, extinct relatives of modern birds, indicating an
ancient origin. The paleognath unique nerve configuration, combined
with other evidence such as the likely independent gain of pygostyle in
the extinct bird <i>Fukuipteryx prima</i>, spitballs yet untested
speculation: Living birds arose from more than one long-tailed
ancestors.</p>
<br />
</div>
<br /><br /><br /><br /><br />
<div class="contact">
kevin surya · montana state university · bozeman · mt
· usa · <a href="mailto:sadikin.kevin@gmail.com"
style="color: gray;
text-decoration: none";>kevinsurya@montana.edu</a>
</div>
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