Abstract
Extreme temperature exposure can reduce stored sperm viability within queen honey bees; however, little is known about how thermal stress may directly impact queen performance or other maternal quality metrics. Here, in a blind field trial, we recorded laying pattern, queen mass, and average callow worker mass before and after exposing queens to a cold temperature (4°C, 2 h), hot temperature (42°C, 2 h), and hive temperature (33°C, control). We measured sperm viability at experiment termination, and investigated potential vertical effects of maternal temperature stress on embryos using proteomics. We found that cold stress, but not heat stress, reduced stored sperm viability; however, we found no significant effect of temperature stress on any other recorded metrics (queen mass, average callow worker mass, laying patterns, the egg proteome, and queen spermathecal fluid proteome). Previously determined candidate heat and cold stress biomarkers were not differentially expressed in stressed queens, indicating that these markers only have short-term post-stress diagnostic utility. Combined with variable sperm viability responses to temperature stress reported in different studies, these data also suggest that there is substantial variation in temperature tolerance, with respect to impacts on fertility, amongst queens. Future research should aim to quantify the variation and heritability of temperature tolerance, particularly heat, in different populations of queens in an effort to promote queen resilience.
Highlights
The queen is normally the sole reproductive female within a honey bee colony and can live up to eight years, though normally not more than three [1]
Cold stress reduces sperm viability, but laying pattern and queen mass are unaffected by heat and cold stress
We initially suspected that venom contamination could have obscured our results, because upon inspection of proteins quantified within the spermathecal fluid, we found that several proteins significantly correlating with sperm viability (5% false discovery rate), one of which was melittin precursor
Summary
The queen is normally the sole reproductive female within a honey bee colony and can live up to eight years, though normally not more than three [1]. Survey results show that over half of colonies in some operations are requeened within the first six months of being established [4], but surprisingly little is known about why queens are failing so frequently [5]. When they are about one week old, queens embark on one or more nuptial flights and store a proportion of each mate’s sperm, which must last for their lifetime since they are unable to mate again once they deplete their sperm stores.
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