Developmental events used in this study
(1 = onset of ciliary driven rotation, 2 = onset of cardiac function, 3 = foot
attachment and onset of muscular crawling, 4 = onset of radula function). (A)
Lymnaea stagnalis (B) Radix balthica (C) Physella acuta. Locations of
developmental events recorded are indicated: h = cardiac function, f = foot
attachment, r = radula function. In Physella acuta, attachment of the foot on
the wall of the egg capsule occurs before the onset of cardiac function.
Credit: Frontiers in Physiology (2023). DOI: 10.3389/fphys.2023.1237022
Scientists
have made a major breakthrough in the study of species evolution, and provided
further evidence that state-of-the-art visual technology can be used to track
the tiniest changes in different organisms' development.
New research used a combination of
robotic video microscopes and computer vision to measure all of the observable
characteristics of embryos of three different species.
These measurements were recorded as
spectra of energy and, through this, scientists were able to compare shifts
between species alongside previously documented differences in the timing of
discrete developmental events.
A detailed analysis of these so-called
Energy Proxy Traits (EPTs) has provided researchers with the first evidence
that traditionally measured timings of developmental events are associated with
far broader changes to the full set of an embryo's observable characteristics.
They also found huge changes in an
embryo's observable characteristics before and after the onset of each
developmental event.
Writing in Frontiers in Physiology, the study's authors say that applying lessons from the research has the potential to advance how development and evolution is studied, by enabling greater depth in the assessment of biological development and the ability to combine data across a wide range of species.
By measuring timelapse videos of embryos—such as
this one of a developing snail—showing a number of key developmental events,
researchers can capture complex differences in how species grow and develop.
Credit: University of Plymouth
This is something, they add, that
is particularly crucial at a time when climate and other environmental changes
are having a significant—and in many cases harmful—impact on many parts of the
natural world.
The study was led by scientists
from the University of Plymouth's EmbryoPhenomics Research Group, in the School
of Biological and Marine Sciences, and builds on its 15-plus years of
groundbreaking research into ways of monitoring embryo development.
Dr. Jamie McCoy, a postdoctoral
researcher and the study's lead author, said, "The advances highlighted in
this paper are critical to addressing the fundamental question of how species
differ in the way that they develop. Measuring differences in the timings of
development is one of the main ways in which researchers investigate how
changes in development may drive evolution."
"But the results from our
study suggest that measuring the timings of developmental events is just the
tip of the iceberg in terms of how we measure and analyze evolutionary changes.
By assessing EPTs across three different species, we have seen how they could
provide us with an alternative approach to understanding how development leads
to evolutionary change."
The EPT method uses timelapse video
of animals during their earliest and most dynamic life stages.
Each video is composed of a series
of individual pixels, whose brightness fluctuates from one frame to the next as
objects—such as a beating heart, muscle contractions, or spinning of the whole embryo
driven by tiny hairs—move.
Researchers can exploit these
fluctuations in pixel values and convert them into frequency data, allowing
them to track a huge breadth of different aspects of the biology of the animal
as it develops.
The resulting visuals mean that
rather than choosing individual parts of the animal to measure, scientists can
capture all of its traits—such as changes in heart rate or movement—and interrogate the resulting
frequency data to capture a greater breadth of its biological response.
Dr. Oliver Tills, senior author on
the study, has been pioneering studies into embryo phenomics since 2007 and was
in 2020 awarded a UK Research and Innovation Future Leaders Fellowship to
advance his work.
He added, "Our current
understanding of biology is limited by the technologies available to observe
it, and we need a new technology-enabled approach to understanding the most
complex period of an organism's life history. This study has broad implications
for advancing our understanding of the nexus between biological development and
evolution, and marks a significant step forward in how we might monitor the
development of lifeforms all over our planet."
Two decades of expertise in developmental biology
The EPT method used in the current
study builds on pioneering work started almost 20 years ago using manual
measurements.
That work was led by Dr. Jennifer
Smirthwaite and colleagues at the University of Plymouth and the Technical
University of Munich, and documented a number of heterochronies—changes in the
timings of developmental events between species—in a number of species of
freshwater snail.
EPTs were applied to three species of freshwater snail from that study, and aimed to understand whether these evolutionary changes in the timings of development were associated with more high-dimensional changes to the phenotype.
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