Tuesday 23 June 2020

Do epigenetic changes drive corticosterone responses to alarm cues in larvae of an invasive amphibian?

Our latest cane toad paper is now online at Integrative and Comparative Biology, using our draft cane toad genome as the reference for differential methylation analysis. (Thanks to coronavirus delays, the updated cane toad genome was not quite ready for this analysis but watch this space!)

Sarma RR, Edwards RJ, Crino OL, Eyck HJF, Waters PD, Crossland MR, Shine R & Rollins LA (accepted): Do epigenetic changes drive corticosterone responses to alarm cues in larvae of an invasive amphibian? Integrative and Comparative Biology icaa082


The developmental environment can exert powerful effects on animal phenotype. Recently epigenetic modifications have emerged as one mechanism that can modulate developmentally plastic responses to environmental variability. For example, the DNA methylation profile at promoters of hormone receptor genes can affect their expression and patterns of hormone release. Across taxonomic groups, epigenetic alterations have been linked to changes in glucocorticoid (GC) physiology. GCs are metabolic hormones that influence growth, development, transitions between life-history stages, and thus fitness. To date, relatively few studies have examined epigenetic effects on phenotypic traits in wild animals, especially in amphibians. Here, we examined the effects of exposure to predation threat and experimentally manipulated DNA methylation on corticosterone (CORT) levels in tadpoles and metamorphs of the invasive cane toad (Rhinella marina). We included offspring of toads sampled from populations across the species’ Australian range. In these animals, exposure to chemical cues from injured conspecifics induces shifts in developmental trajectories, putatively as an adaptive response that lessens vulnerability to predation. We exposed tadpoles to these alarm cues, and measured changes in DNA methylation and CORT levels, both of which are mechanisms that have been implicated in the control of phenotypically plastic responses in tadpoles. To test the idea that DNA methylation drives shifts in GC physiology, we also experimentally manipulated methylation levels with the drug zebularine. We found differentially methylated regions between control tadpoles and their full-siblings exposed to alarm cues, zebularine or both treatments. However, the effects of these manipulations on methylation patterns were weaker than clutch (e.g. genetic, maternal, etc.) effects. CORT levels were higher in larval cane toads exposed to alarm cues and zebularine. We found little evidence of changes in DNA methylation across the glucocorticoid receptor gene (NR3C1) promoter region in response to alarm cue or zebularine exposure. In both alarm cue and zebularine-exposed individuals, we found differentially methylated DNA in the suppressor of cytokine signaling 3 gene (SOCS3), which may be involved in predator avoidance behavior. In total, our data reveal that alarm cues have significant impacts on tadpole physiology, but show only weak links between DNA methylation and CORT levels. We also identify genes containing differentially methylated regions in tadpoles exposed to alarm cues and zebularine, particularly in range-edge populations, that warrant further investigation.

Monday 1 June 2020

Johansson SA, Stephenson P, Edwards RJ, Yoshida K, Moore M, Terauchi R, Zubkov MV, Terry MJ & Bibby TS (2020): Isolation and molecular characterisation of Dunaliella tertiolecta with truncated light-harvesting antenna for enhanced photosynthetic efficiency. Algal Research 48:101917.


  • Liquid based screening and selection of algae with truncated light harvesting antenna
  • Selection of algae with improved photosynthetic efficiency
  • Genome independent transcriptome profiling characterises photosynthetic physiology.
  • Develops potential to exploit the natural diversity of microalgae for biotechnology


Here we report the development of a high-throughput selection protocol using random mutagenesis and live single-cell sorting to isolate cell lines from the algae Dunaliella tertiolecta with reduced chlorophyll content, with the aim to optimise the antenna size for increased photosynthetic efficiency. Two promising cell lines (lca1 and lca2) have been isolated that display a truncated light-harvesting antenna, and hence improved photosynthetic energy conversion efficiency by increasing the light intensity at which photosynthesis becomes saturated (Is). lca1 and lca2 differ significantly: the lca2 phenotype retains an ability to alter its antenna size in response to varying light intensity, whereas lca1 appears to have lost this ability and is ‘locked’ to a truncated antenna and high-light phenotype. Despite these clear differences, transcriptomic analysis shows that the expression profiles for differentially expressed nuclear-encoded photosynthetic genes is similar in both lca1 and lca2, possibly suggesting underlying mutations in the regulation of photosynthesis are causing the observed changes in phenotype rather than mutations impacting specific components of the photosynthetic apparatus. The combination of approaches presented here offer the capacity to substantially improve photosynthetic efficiency from any microalgal species irrespective of the extent to which it has been characterised genetically or the availability of molecular tools for rational engineering. It thus offers the potential to begin to exploit the huge natural diversity of microalgae for enhanced biomass production.