|Torson, Alex - North Dakota State University|
|Rinehart, Joseph - Joe|
|Kemp, William - Bill|
|Bowsher, Julia - North Dakota State University|
Submitted to: Journal of Experimental Biology Online
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2015
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60669
Citation: Torson, A.S., Yocum, G.D., Rinehart, J.P., Kemp, W.P., Bowsher, J.H. 2015. Transcriptional responses to fluctuating thermal regimes underpinning differences in survival in the solitary bee Megachile rotundata. Journal of Experimental Biology. 218(7):1060-1068.
Interpretive Summary: Seventy percent of crops grown for human food production are dependent on pollinators. The value of this pollination service worldwide is estimated to be over 100 billion dollars annually. This value does not include agriculture products that are not directly consumed by humans such as alfalfa that is used as an input for meat and milk production. The alfalfa leafcutting bee Megachile rotundata is the primary pollinator used in the production of alfalfa seed in North America. There is growing interest in M. rotundata for pollination of various specialty crops. One of the key components making the alfalfa leafcutting bee available for these earlier season crops and to buffer against year-to-year price swings is the development of prolonged storage protocols. A storage protocol employing fluctuating thermal regime (FTR) has dramatically improved long-term survival of the alfalfa leafcutting bee during winter storage. This investigation was undertaken to clarify the physiological mechanisms responsible for this extended life expectancy during storage. Understanding the physiological mechanism of FTR will aid in the development of biomarkers that will be used to further optimize this vital storage technique.
Technical Abstract: The transcriptional responses of insects to long-term, ecologically relevant temperature stress are poorly understood. Long-term exposure to low temperatures, commonly referred to as chilling, can lead to physiological effects collectively known as chill injury. Periodically increasing temperatures during long-term chilling has been shown to increase survival in many insects. However, the transcripts responsible for this increase in survival have never been characterized. Here, we present the first transcriptome-level analysis of increased longevity under fluctuating temperatures during chilling. Overwintering post-diapause quiescent alfalfa leafcutting bees (Megachile rotundata) were exposed to a constant temperature of 6°C, or 6°C with a daily fluctuation to 20°C. RNAwas collected at two different time points, before and after mortality rates began to diverge between temperature treatments. Expression analysis identified differentially regulated transcripts between pairwise comparisons of both treatments and time points. Transcripts functioning in ion homeostasis, metabolic pathways and oxidative stress response were up-regulated in individuals exposed to periodic temperature fluctuations during chilling. The differential expression of these transcripts provides support for the hypotheses that fluctuating temperatures protect against chill injury by reducing oxidative stress and returning ion concentrations and metabolic function to more favorable levels. Additionally, exposure to fluctuating temperatures leads to increased expression of transcripts functioning in the immune response and neurogenesis, providing evidence for additional mechanisms associated with increased survival during chilling in M. rotundata.