Megachile rotundata overwintering nCounter gene expression

Within the United States and Canada, the primary pollinator of alfalfa is
the alfalfa leafcutting bee (ALCB), Megachile rotundata. Our previous
findings showed that overwintering conditions impacted gene expression
profile in ALCB prepupae that entered diapause early in the season.
However, ALCB are a bivoltine species, which begs the question of whether
bees entering diapause later in the season also show this trend. To better
understand the effects of the timing of diapause initiation, we analyzed
mRNA copy number of genes known to be involved in diapause regulation in
early- and late-season diapausing ALCB that were overwintered in field
conditions or using current agricultural management conditions. We
hypothesized that overwintering conditions for late diapausing bees also
affects gene expression profiles. Our results showed that expression
profiles were altered by both overwintering condition and timing of
diapause initiation, with bees that entered diapause earlier in the season
showing different expression patterns than those that entered diapause
later in the season. This trend was seen in expression of members of the
cyclin family and several targets of the insulin signaling pathway,
including forkhead box protein O (FOXO), which is known to be important
for diapause regulation and stress responses. But, of the genes screened,
the proto-oncogene, Myc, was the most impacted by the timing of diapause
initiation. Under fluctuating temperatures there was significant
differences in Myc expression between the early and late season samples in
all months except for November and February. This same general trend in
Myc expression was also seen in the laboratory-maintained bees with
significant difference in expression in all months except for November,
February, and May. These results support previous conclusions from our
research showing that the molecular regulation of diapause development in
ALCB is not a simple singular cascade of gene expression but a highly
plastic response that varies between bees depending upon their
environmental history.