Interactive effects of previous and current thermal conditions on gene expression in Manduca sexta

High temperatures can negatively impact performance and survival of
organisms, particularly ectotherms. While an organism’s response to high
temperature stress clearly depends on current thermal conditions, its
response may also be affected by the temporal pattern and duration of past
temperature exposures. We used RNA sequencing of Manduca sexta larvae fat
body tissue to evaluate how diurnal temperature fluctuations during
development affected gene expression both independently and in conjunction
with subsequent heat stress. Additionally, we compared gene expression
between two M. sexta populations, a lab colony and a genetically related
field population that have been separated for more than 300 generations
and differ in their thermal sensitivities. Lab-adapted larvae were
predicted to show increased expression responses to both single and
repeated thermal stress, whereas recurrent exposure could decrease later
stress responses for field individuals. We found large differences in
overall gene expression patterns between the two populations (across all
temperature treatments), as well as population-specific transcriptomic
responses to temperature; most differentially expressed genes were
upregulated in the field compared with lab larvae. Developmental
temperature fluctuations alone had minimal effects on long-term gene
expression patterns, with the exception of a somewhat elevated stress
response in the lab population. Fluctuating rearing conditions did alter
gene expression during exposure to later heat stress, but this effect
depended on both the population and the particular temperature conditions.
This study contributes to increased knowledge of molecular mechanisms
underlying physiological responses of organisms to temperature
fluctuations, which is needed for the development of more accurate thermal
performance models.