Genes and collective behavior

Date:
October 13, 2021
Source:
University of Konstanz
Summary:
The targeted manipulation of individual genes in zebrafish larvae
changes their behavioral responses to visual stimuli and thus
affects the collective behavior of the animals.



FULL STORY ========================================================================== Individual zebrafish (Danio rerio) exhibit predictable behavioural
responses to certain visual stimuli that are sufficient to explain the collective behaviour of the animals -- even in their larval stage. Genetic mutations associated with neurological disorders in humans alter these behavioural responses and, as a consequence, the group behaviour of
the larvae. These are the results of a study conducted by Konstanz neurobiologist Dr Armin Bahl and his collaborators at Harvard University
that was recently published in Science Advances. The research shows
that genetic changes in individuals can not only alter the behaviour
of groups, but can also provide a methodological approach for testing
existing models of collective behaviour experimentally.


========================================================================== Collective behaviour of zebrafish A large proportion of today's fish
species display collective behaviours, at least in certain stages of
their lives. This is when a large number of individuals remain in close proximity to each other for social reasons or swim together in the
same direction. The potential advantages of these behaviours are many
and range from simplifying the search for partners to providing greater protection for individual fish from predation and making the search for
food more effective.

Zebrafish, too, are known for these forms of collective behaviour. The
species has long been used as a model organism in genetic, evolutionary
biology and neurobiology research. Until now, however, it has never been systematically examined when zebrafish start exhibiting such collective behaviour, which genes play a role in the process and which sensory
information the fish use for this purpose.

"Especially to neuroscientists like me, these questions are of importance.

Since the bodies and brains of zebrafish larvae are almost entirely transparent, my group can use high-resolution, non-invasive microscopy techniques to observe in real time how nerve cells react to different
stimuli and how the behaviour of the zebrafish changes in response to
them. Since the wiring of the larvae's brains is less complex than in
adult animals, these techniques make it possible for us to investigate
the neural basis of collective behaviour with high precision," Armin
Bahl explains the advantage of zebrafish larvae for his research. Since September of last year, Armin Bahl has led the Emmy Noether research team "Neural Circuit Computation and Behaviour" in Konstanz. In the summer
of this year, he was offered the professorship of zoology/neurobiology
at the University of Konstanz.

Even zebrafish larvae react to each other The research team thus
examined the group behaviour of zebrafish during different stages of
their development -- seven days and 21 days after egg fertilization. The researchers showed that even seven-day old larvae respond to their
peers by orienting their movements in the same direction while,
at the same time, actively avoiding close proximity to others. The
21-day old zebrafish oriented their movements even more strongly in
the same direction as their peers but, instead of avoiding each other,
the animals in this stage sought close proximity to each other, like in
swarm formation.

Based on further behavioural experiments in this study as well as existing knowledge, the researchers suspected that the behaviour observed in
zebrafish larvae is based on two relatively simply behavioural responses:
One system in the larval brain measures the general amount of objects in
its surroundings, while a second system analyses motion stimuli. "Both behavioural responses are visuomotor reflexes. This means that, in the
animals, a certain type of visual information causes a set behavioural
reaction in the form of a movement," Armin Bahl states.

To test their assumption, the researchers used a computer model to
simulate the movements of small groups of fish. The model used only
the two stated visuomotor reflexes as "decision rules" to determine
the behaviour of individual virtual fish. "The simulated groups of fish
behaved exactly like the real zebrafish larvae. This clearly indicates
that the collective behaviour of the animals can indeed be explained
using these relatively simple behavioural responses," says Armin Bahl.

Targeted mutations change the group behaviour of the larvae In order
to also find out which role the individual genetic make-up plays in
the group behaviour of zebrafish, the researchers used the CRISPR-Cas9 technique to edit specific genes in individual larvae. In doing so,
they were able to show that mutations of the genes scn1lab and disc1
altered the individual behavioural responses of the mutated animals to
visual stimuli and, consequentially, the behaviour of the group. These
genetic mutations are respectively linked to specific forms of epilepsy
and autism in children or to schizophrenia. The zebrafish larvae with
the scn1lab mutation kept a greater distance between themselves and
others than their peers without the mutation.

By contrast, the zebrafish larvae with the disc1 mutation stayed closer together than their wild-type peers.

As before, the behaviour of the mutated animals could be simulated and reproduced by the computer model. "Our approach of using modern genetic techniques and behavioural experiments with zebrafish in combination
with computer simulations gives us the unique opportunity to specifically influence social behaviour and then test models of the collective animal behaviour. With the various molecular-genetic and microscope tools that
already exist for zebrafish and that we are currently establishing in
Konstanz, we will soon be able to also analyse the neural foundations
for this fascinating behaviour in great detail," Armin Bahl concludes.

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


========================================================================== Journal Reference:
1. Roy Harpaz, Ariel C. Aspiras, Sydney Chambule, Sierra Tseng,
Marie-Abe`le
Bind, Florian Engert, Mark C. Fishman, Armin Bahl. Collective
behavior emerges from genetically controlled simple
behavioral motifs in zebrafish. Science Advances, 2021 DOI:
10.1126/sciadv.abi7460 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211013104619.htm

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