Fruit flies adapt activity to 'white nights'
Internal clock: Research team shows why a naturally occurring gene
variant in fruit flies is spreading northwards

Date:
March 31, 2022
Source:
University of Mu"nster
Summary:
Fruit flies with a new variant of a 'clock gene' are spreading
northwards. Neurobiologists have now found an explanation for
this phenomenon.



FULL STORY ========================================================================== Evolution takes place constantly, everywhere in nature. Nevertheless,
it is always exciting for biologists to observe evolution "in real
time." One such opportunity for observation is currently being presented
by the internal clock, i.e. the innate sleep-wake rhythm, of the fruit
fly Drosophila melanogaster. In fruit flies, a certain variant of a
"clock gene," which presumably first appeared in southern Europe 300
to 3000 years ago, is spreading northwards, for example to and within Scandinavia. Researchers have observed this phenomenon but have not yet
been able to fully explain it. Based on laboratory studies, a team led
by the neurobiologist Prof Ralf Stanewsky from the University of Mu"nster (Germany) are the first to offer an explanation for this phenomenon.


==========================================================================
The study, which has now been published in the journal Nature
Communications, focused on a clock gene called "timeless." Together
with a second clock gene ("period"), it controls the circadian rhythm
of the fruit fly, which lasts about 24 hours. This rhythm is permanently synchronised with the environment using external zeitgebers such as light
and temperature. The researchers investigated why a special variant of
the timeless clock gene, namely the ls- tim allele, has spread so rapidly.

"Like humans, Drosophila originated in sub-Saharan Africa and spread
North, up to the Arctic Circle," explains first author Ange'lique
Lamaze. "There, the flies experience long summer days or even almost
constant light, so-called white nights." Constant lighting disrupts
the function of the internal clock because it triggers the permanent degradation of the clock protein TIMELESS via a molecular reaction
chain. Thus, the circadian rhythm is lost.

However, temperature cycles can overcome the effects of constant
illumination.

Our experts have demonstrated that flies with the recently evolved ls-tim allele synchronise their circadian rhythm with the ambient temperature
under light and temperature conditions that mimic a Scandinavian summer
day. One indicator was the insects' level of active movement. With
constant lighting and a daily temperature cycle between 16 and 25 degrees Celsius, the flies with the ls-tim allele were particularly active in
the second half of the warm phase. In contrast, when there was constant lighting and temperature, there was no behavioural rhythm. Unlike the
ls-tim flies, those fruit flies carrying only the original gene variant
(s-tim) showed no behavioural adaptation -- neither with temperature
cycling nor a constant temperature.

New gene variant increases reproductive success "From an evolutionary
biology point of view, the behavioural adaptation can be well explained," emphasizes Ange'lique Lamaze. "Summer is the insects' reproductive
season. Animals that are synchronised in their behaviour and ready
to mate at the same time of day have a better chance of meeting and reproducing. As ls-tim allows such synchronization even under extremely
long summer days, this is most likely an important factor contributing to
its ongoing northward spread and could explain its evolutionary success. "
The research team also proved that even a single copy of the ls-tim allele
is sufficient to enable synchronisation in "Scandinavian conditions,"
which is further supporting the spreading of this allele. Like humans,
for example, fruit flies possess two, either identical or similar,
copies of each gene - - one copy from each parent.

The new gene variant produces a protein that deviates slightly from
the original form, which is particularly stable under illumination and, therefore, interferes with the molecular reaction cascade that otherwise triggers the degradation of the clock protein TIMELESS. This, the team concluded, is a prerequisite required for the temperature cycle to
restore the circadian rhythm of fruit flies under continuous illumination.

The neurobiologists used a combination of behavioural experiments as well
as modern genetic and immunohistochemical methods in their study. Among
other things, they compared fly strains with different genetic make-ups investigating their behaviour during simulated Scandinavian summer nights
and the activity of their clock genes in different brain neurons.


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


========================================================================== Journal Reference:
1. Angelique Lamaze, Chenghao Chen, Solene Leleux, Min Xu, Rebekah
George,
Ralf Stanewsky. A natural timeless polymorphism allowing circadian
clock synchronization in "white nights". Nature Communications,
2022; 13 (1) DOI: 10.1038/s41467-022-29293-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220331134229.htm

--- up 4 weeks, 3 days, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)