Award: OCE-1559075

The three main goals of this research were to: 1) To test the simultaneous effects of temperature and CO2 under current and future conditions on life history traits, throughout the life cycle, of two keystone copepod species, Acartia tonsa (warm-adapted) and Acartia hudsonica (cold-adapted). 2) To test for adaptive capacity of both copepod species to a warmer and CO2-richer ocean. 3) To measure the genetic and epigenetic changes across multiple generations of experimental selection in future conditions in both copepod species, and identify the genes and pathways responding to selection. We were able carry out unprecedented evolution experiments in a marine metazoan, over 10 and 25 generations for the cold- and warm-adapted species, respectively, in full factorial mean current and projected (end of 21st century) temperature and CO2 conditions. We were able to measure five life history traits, egg production rate, hatching frequency, survivorship, development time, and sex ratio. These measurements allowed us to estimate the net reproductive rate and characterize adaptation and traits under selection across the generations. To link these organismal traits to their molecular underpinnings, we also measured genomic, epi-genomic, and transcriptomic responses to selection regimes. To do so we expanded the genomics resources available for these species, including a de novo transcriptome assembly and genomic capture probes for pooled sequencing of captured genomic DNA, two probes per gene, one coding and one in the putative regulatory region. We also performed opportunistic reciprocal transplant experiments between the control and greenhouse adapted selection lines to better understand the relationship between physiological plasticity and genetic adaptation in the context of global change adaptation. Intellectual merit: The research supported by this award has expanded our understanding of the capacity for and consequences of adaptation to a warmer and more acidified future ocean. Through long-term, multigeneration selection experiments and reciprocal transplants in both species, we have demonstrated that both species have the capacity to adapt to future global change conditions, though via different mechanisms and not without negative consequences. The reciprocal transplant experiments allowed us to test the interaction between plasticity and genetic adaptation, as these processes have been argued to inhibit or facilitate one another. In Acartia tonsa, for example, we showed that rapid adaptation proceeded despite the presence of plasticity. However, adaptation reduced phenotypic plasticity and eroded the adaptive genetic variation necessary to tolerate previously benign environmental stress. This work demonstrates the power of experimental evolution from natural populations to reveal the mechanisms, timescales of responses, consequences, and reversibility of complex, physiological adaptation. While plasticity facilitated initial survival in global change conditions, it eroded after 20 generations as populations genetically adapted, limiting resilience to new stressors and previously benign environments. Taken together, these results suggest that as the frequency and degree of extreme events increases due to climate change, rapid adaptation to an outlier year may reduce plasticity and result in a population that is maladapted when conditions return to previous levels. Our forthcoming work associated with this research will reveal the similarities and differences between the closely related species, the traits under selection, the molecular underpinnings of adaptation, and the relative importance of genomic, epigenomic and plastic response mechanisms. Broader impact: The outcomes of this work have societal relevance by meeting a priority area for marine ecosystem management, ?Gather and synthesize information on how systems are changing and on the drivers of these changes, especially over long time scales.? We experimentally reveal the organismal, genetic and physiological changes in two ecologically foundational marine species in response to two global change drivers, current and projected (end of 21st century) temperature and CO2 conditions. Expansions of this work are leading to models for species persistence that incorporate physiological and genetic tolerance limits in response to environmental change. The work has been shared extensively through education and outreach activities, particularly training of graduate (three students, all female) and undergraduate (ten, 9 female, two honors theses) students and one postdoc (male) at UVM. Students and the PI have shared this research using the copepods at local and international conferences, with K-12 and community college visitors, and the media (a UVM Communications article and podcast featuring student research). The work will continue to be shared with the broader research community through peer-reviewed publications and data and code are available in public repositories. Last Modified: 11/30/2020 Submitted by: Melissa Pespeni