Transgenerational plasticity in the purple sea urchin, Strongylocentrotus purpuratus
Given the pace of climate change, an important research priority in marine science is to understand the mechanisms with which organisms can respond to rapidly changing ocean conditions. Transgenerational effects, in which the experience of the parental generation can shape the phenotype of their offspring, may serve as such a mechanism. Alternatively, transgenerational plasticity may be disadvantageous if there is a negative parental response or if a rapid environmental change causes the offspring to experience conditions very different than what their parents prepared them for. Failing to consider the parents' environmental history may lead to inaccurate predictions of how organisms will respond to current and future ocean stressors.
Adult purple urchins, Strongylocentrotus franciscanus, were conditioned to static treatments that reflected conditions measured either during upwelling events (i.e., upwelling conditions of combined low temperature and low pH) or between upwelling events (i.e., non-upwelling conditions of average temperature and pH). Offspring were then tested to determine if different parental environments influenced their response to different pH levels during development. In a follow-up study, offspring were tested by raising them in either the same or the reciprocal treatment as that of their parents. Possible mechanisms of transgenerational plasticity include maternal provisioning and epigenetic mechanisms.
Physiological and transcriptomic differences
The offspring whose mothers experienced simulated upwelling conditions during gametogenesis tended to be larger in size than those whose mothers experienced non-upwelling conditions. This pattern was primarily evident during embryological stages, but was not apparent by the pluteus larvae stage. Differential conditioning of the adults also had an effect on the gene expression patterns of the offspring. Maternal conditioning to simulated upwelling intensified the transcriptomic response of offspring raised under low pH levels.
Maternal provisioning and changes in DNA methylation
Female urchins acclimated to non-upwelling conditions produced eggs that were more variable in size, while female urchins acclimated to upwelling conditions produced eggs with a slightly higher lipid content. Different conditions experienced by the mothers were also associated with differentially methylated genes in the offspring. Thus, the observed transgenerational plasticity may be due to differences in maternal provisioning, epigenetic inheritance, or both.
Marie E. Strader, Logan C. Kozal, Terence S. Leach, Juliet M. Wong, Jannine D. Chamorro, Maddie Housh, and Gretchen E. Hofmann (2020) Examining the role of DNA methylation in transcriptomic plasticity of early stage sea urchins: Developmental and maternal effects in a kelp forest herbivore. Frontiers in Marine Science 6(205). https://doi.org/10.3389/fmars.2020.00205.
Juliet M. Wong, Logan C. Kozal, Terence S. Leach, Umihiko Hoshijima, and Gretchen E. Hofmann (2019) Transgenerational effects in an ecological context: Conditioning of adult sea urchins to upwelling conditions alters maternal provisioning and progeny phenotype. Journal of Experimental Marine Biology and Ecology 517: 65-77. https://doi.org/10.1016/j.jembe.2019.04.006.
Marie E. Strader, Juliet M. Wong, Logan C. Kozal, Terence S. Leach, and Gretchen E. Hofmann (2019) Parental environments alter DNA methylation in offspring of the purple sea urchin, Strongylocentrotus purpuratus. Journal of Experimental Marine Biology and Ecology 517: 54-64. https://doi.org/10.1016/j.jembe.2019.03.002.
Juliet M. Wong, Kevin M. Johnson, Morgan W. Kelly, and Gretchen E. Hofmann (2018). Transcriptomics reveal transgenerational effects in purple sea urchin embryos: Adult acclimation to upwelling conditions alters the response of their progeny to differential pCO2 levels. Molecular Ecology 27(5): 1120-1137. https://doi.org/10.1111/mec.14503.