Losing flight had huge benefits for ants

Date:
October 19, 2020
Source:
Okinawa Institute of Science and Technology (OIST) Graduate
University
Summary:
Researchers have taken detailed scans of worker ants to examine
the hypothesis that the loss of flight is directly connected to
the evolution of strength.



FULL STORY ==========================================================================
Ants are one of the most successful groups of animals on the planet,
occupying anywhere from temperate soil to tropical rainforests, desert
dunes and kitchen counters. They're social insects and their team-working abilities have long since been identified as one of the key factors
leading to their success. Ants are famously able to lift or drag objects
many times their own weight and transport these objects back to their
colony. But with previous research having focused on the social aspects of
an ant colony, looking at an individual ant has been somewhat neglected.


==========================================================================
Now, researchers at the Okinawa Institute of Science and Technology
Graduate University (OIST) and Sorbonne University in Paris have
investigated why individual worker ants are so strong by taking X-ray
images and creating 3D models of their thorax -- the central unit of
their bodies -- to analyze their muscles and internal skeleton. Their
study, published in Frontiers in Zoology, examines the hypothesis that
loss of flight in worker ants is directly connected to the evolution of
greater strength.

"Worker ants evolved from flying insects," said Professor Evan Economo,
who leads OIST's Biodiversity and Biocomplexity Unit. "We've always
assumed that losing flight helped to optimize their bodies for working
on the ground, but we have much to learn about how this is achieved."
Being able to fly might be a common dream amongst people but the reality
of flight is that it puts strong constraints on the build of a body. In
flying insects, the wing muscles occupy a major part of the thorax --
sometimes more than 50%. This means that other muscles, which are used
to support and move the head, legs, and abdomen are constrained and
squeezed up against the exoskeleton.

But once the constraints of flight are removed, all that space in the
thorax is open, which, the researchers surmised, would allow the remaining muscles to expand and reorganize.

Previous research in this area had focused on the external structure of
ants but, with the technology available at OIST, the researchers were
able to gain a highly detailed picture of what was going on inside the
thorax. The aim was to analyze the general features common across all
ants, rather than focus on the specialization of certain species. To do
this, the researchers did a detailed analysis of two distantly related
ant species, including both the wingless workers and the flying queens,
and confirmed their findings across a broader sample of species.

They used advanced X-ray technology to scan the internal and
external anatomy, like CT scans used in a hospital, but at much higher resolution. From these scans, the researchers mapped all the different
muscles and modeled them in 3D.

The result was a comprehensive image of the inside of the thorax. They
then compared findings from these two species to a range of other ants
and wingless insects.

As predicted, the researchers found that loss of flight had allowed
for clear- cut reorganization of the thorax. "Within the worker ant's
thorax, everything is integrated beautifully in a tiny space," said
the late Dr. Christian Peeters, lead author of this paper, who was a
research professor at Sorbonne University. "The three muscle groups
have all expanded in volume, giving the worker ants more strength and
power. There has also been a change in the geometry of the neck muscles,
which support and move the head. And the internal attachment of muscles
has been modified." Interestingly, when looking at wingless wasps,
the researchers found that these insects had responded to the loss of
flight in a completely different way.

Wingless wasps are solitary and consume food as they find it. On the
other hand, ants are part of a colony. They hunt or scavenge for food
that then needs to be carried back to the nest for the queen and younger nestmates, so it makes sense that there was a selection pressure to
promote carrying ability.

Ants have been studied for centuries in terms of their behavior, ecology,
and genetics but, the researchers emphasized, this story of strength
has, so far, been somewhat overlooked. The next step is to develop more detailed biomechanical models of how different muscle groups function,
do similar research on the mandible and legs, and explore the diversity
seen between ant species.

"We're interested in what makes an ant an ant and understanding the key innovations behind their success" explained Professor Economo. "We know
that one factor is the social structure, but this individual strength
is another essential factor."

========================================================================== Story Source: Materials provided by Okinawa_Institute_of_Science_and_Technology_(OIST)
Graduate_University. Original written by Lucy Dickie. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Christian Peeters, Roberto A. Keller, Adam Khalife, Georg Fischer,
Julian
Katzke, Alexander Blanke, Evan P. Economo. The loss of flight in
ant workers enabled an evolutionary redesign of the thorax for
ground labour.

Frontiers in Zoology, 2020; 17 (1) DOI: 10.1186/s12983-020-00375-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019082912.htm

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