New study shows evolutionary breakdown of 'social' chromosome in ants


Date:
August 25, 2020
Source:
Queen Mary University of London
Summary:
Scientists have found that harmful mutations accumulating in the
fire ant social chromosome are causing its breakdown.



FULL STORY ========================================================================== Scientists from Queen Mary University of London have found that harmful mutations accumulating in the fire ant social chromosome are causing
its breakdown.


==========================================================================
The chromosome, first discovered by researchers at the University in
2013, controls whether the fire ant colony has either one queen or
multiple queens.

Having these two different forms of social organisation means the species
can adapt easily to different environments and has resulted in them
becoming a highly invasive pest all over the world, living up to their
Latin name Solenopsis invicta, meaning "the invincible." For the new
study, published in eLife, the research team performed detailed analyses
of the activity levels of all the genes within the social chromosome for
the first time to understand how it works and its evolution. They found
that damaging mutations are accumulating in one version of the social chromosomes, causing it to degenerate. The findings also showed that
most of the recent evolution of these chromosomes stems from attempts
to compensate for these harmful mutations.

Natural selection is the main evolutionary mechanism that helps to
optimise genes over generations but normally, it cannot simultaneously
optimise genes for two different types of social organisation within
one species.

To overcome this evolutionary conflict, social chromosomes group together
genes adapted to each type of social form. The results of the new study
show that this solution prevents the removal of harmful mutations from
the genome and as a result, these mutations accumulate over time and
begin to dominate the fate of the system.

The social chromosomes in fire ants are a rare example of a direct link
between genes and social behaviour. They work in a similar way to the
X and Y chromosomes in humans, which determine sex.

This discovery has wider ecological and medical implications because
genomic structures similar to social and sex chromosomes can not only
help species adapt to changing environments but also underpin diseases
such as cancer.

Dr. Marti'nez-Ruiz, lead author of the study from Queen Mary University
of London, said: "Our results show that the initial benefit of nature
combining genes into a social chromosome has a cost. One million years
later, most of the differences we see between social chromosomes are due
to the accumulation of negative mutations." "We also see that the rest
of the genome adapts very quickly in response to negative mutations,"
added Dr. Wurm, Reader in Bioinformatics at Queen Mary and senior
author of the study. "This is how evolution works, by adding patches to imperfect solutions, rather than by finding the most efficient solution." "Despite the degeneration of the social chromosomes, the fire ants are
unlikely to lose them anytime soon. This would require another major chromosomal reshuffling -- such events are rare and usually lethal,"
Dr Wurm continues.

"However, over long evolutionary timescales, anything is possible. Most
of the 20,000 species of ants either have only single-queen colonies or
only multiple- queen colonies. We are now trying to understand whether
social chromosomes are required for changes in social organisation."
The study builds on earlier research by the authors on the evolution
of social chromosomes. They have previously identified differences in
genes for chemical communication that may be responsible for perceiving
queens, showed that one social chromosome has doubled in size, and that
this social chromosome lacks genetic diversity.


========================================================================== Story Source: Materials provided by Queen_Mary_University_of_London. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Carlos Martinez-Ruiz, Rodrigo Pracana, Eckart Stolle, Carolina Ivon
Paris, Richard A Nichols, Yannick Wurm. Genomic architecture and
evolutionary antagonism drive allelic expression bias in the social
supergene of red fire ants. eLife, 2020; 9 DOI: 10.7554/eLife.55862 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825110742.htm

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