Meeting Abstract
Freeze tolerance is an extreme adaptation that is found broadly across the tree of life, including several animal lineages (both invertebrate and vertebrate) as well as in several plant species. Most studies have focused on insects and plants and relatively little is known about the mechanisms of freeze tolerance in crustaceans. Here we contrast two populations of the circumpolar and intertidal barnacle Semibalanaus balanoides, one from the southern margin of its range in British Columbia, Canada, and one from the northern edge of its range in the White Sea, Russia to elucidate potentially novel mechanisms of freeze tolerance in a poorly-understood system. We froze barnacles at -6 °C for two hours, and allowed them to recover at 10 °C in seawater, taking samples both during the freezing stress as well as after 2 h and 26 h of recovery. Using RNA-seq we first produced a transcriptome of 46,613 sequences that excluded all microbial transcripts. We then contrasted gene expression between the two populations at all three time points. Barnacles from British Columbia had a much greater transcriptomic response that continued to increase through all three timepoints, and that was dominated by downregulation of transcription. By contrast, barnacles from the White Sea had approximately equal numbers of up and down regulated transcripts, and had the greatest number of differentially regulated transcripts during the 2 h recovery window. We also found that they had significant upregulation of transcripts associated with glycerol and water transporters, signatures of intense heat shock protein upregulation, as well as potential novel antifreeze proteins. Taken together, our study shows that even short freezing exposures cause lasting changes in gene transcription and that mechanisms of freeze tolerance may be an example of convergent evolution across animal and plant life.
