Release Subtitle: Scientists show how day length and temperature play separate roles in the seasonal adaptation of some insects
Release Summary Text:
Most insects alter their own development or physiology to overcome
adverse conditions, such as harsh winters. Although day length and
temperature are known to regulate this change, exactly how this process
occurs is not very clear yet. In a collaborative study, a research group
from Okayama University, Tokushima University, and Pompeu Fabra
University showed how a specific insect undergoes seasonal adaptation in
its immature state.
Full text of release:
The life cycle of insects consists of specific developmental stages.
But, in response to adverse conditions, such as harsh winters, some
insects arrest their own development at a particular stage. This process
of seasonal adaptation is called “overwintering,” in which the growth
rate of the insect is either reduced or halted. This mechanism helps the
insect to cope with extreme conditions that are unsuitable for its
growth and reproduction. Overwintering usually occurs at a
species-specific developmental stage. For example, some insects, such as
silk moths, butterflies, and fresh flies, go through diapauses in the
“embryo” or “pupal” stage (developmental stages in which the insect is
still immature). In such insects, this process has been extensively
studied. But, in some insects that go through this arrest at the
“nymphal” stage (another type of stage in which the insect is still
immature), the exact details of this process have been unclear until
now.
In a study published in PNAS, a research group, led by at Dr Kenji
Tomioka of Okayama University, dug deeper into how developmental arrest
occurs at the nymphal stage. They studied this process in a species of
cricket, called Modicogryllus siamensis, in which the growth arrest
phase occurs once a year in the nymphal stage. The scientists also knew
that in this stage, the insect shows “photoperiodic” responses (meaning
that it responds to the length of days). Dr Tomioka explains, “Although
photoperiod and temperature are known to regulate this change, the
underlying mechanism remains unknown. The cricket Modicogryllus
siamensis ‘overwinters’ as nymphs, with a reduced growth rate and
increased molts.”
A nymph develops into its adult form approximately 60 days after it
hatches from the egg under long-day conditions. During its developmental
process, it undergoes about 8 molts (a process in which the insect
sheds its exoskeleton). Under short-day conditions, the nymphal period
is longer with an increased number of molts, which helps in the
overwintering process. Exactly how this happens was the question. To
begin with, the scientists wanted to see how the nymphal period of slow
growth is regulated by temperature. They found that low temperatures led
to the reduced expression of two genes, insulin-like peptide (Ms’Ilp)
and Target of rapamycin (Ms’Tor), which are part of the pathway that
promotes the growth cycle in insects (the “insulin/TOR signaling”
pathway). Interestingly, the scientists found that a suppression of
these genes leads to a slowdown of growth in the insect, without even
affecting the number of molts.
Next, the scientists focused on how day length regulates the growth
arrest in insects. They uncovered that an intracellular pathway, called
“the juvenile hormone (JH) pathway,” controls how day length affects the
growth and molting numbers of the insect. Based on these findings, the
researchers conclude that the JH signaling pathway and the
temperature-controlled insulin/TOR pathway work in tandem to regulate
nymphal development to achieve seasonal adaptation in this cricket.
These findings not only deepen our understanding on the mechanism of
seasonal adaptation in certain insects but also shed light on the
insect’s evolutionary strategy to survive in temperate areas, where day
length and temperature change seasonally. Dr Tomioka concludes, “Our
study was the first to show that nymphal development in an insect was
controlled by two distinct mechanisms. Although much remains to be known
regarding these mechanisms, we aim to gain this insight through further
research.”
Release URL: https://www.eurekalert.org/pub_releases/2020-05/ou-hsi051920.php
Reference:
Title of original paper: Photoperiod and temperature separately regulate
nymphal development through JH and insulin/TOR signaling pathways in an
insect
Journal: Proceedings of the National Academy of Sciences of the United States of America
DOI: http://dx.doi.org/10.1073/pnas.1922747117
Contact Person: TOMIOKA Kenji
E-mail: tomioka(a)cc.okayama-u.ac.jp
For inquiries, please contact us by replacing (a) with the @ mark.
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