Selection experiments and sequencing to identify mechanisms of thermal adaptation in a splash pool copepod

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Heat tolerance is an important trait, because it influences where a species can live, and whether it will survive in a warming climate. Heat tolerance varies among species, but little is understood about the genetic differences that make some animals and plants more heat tolerant than others. This research will use the small marine crustacean, Tigriopus californicus, as an experimental model to investigate the genetic changes lead to increased heat tolerance. The researchers will conduct a series of evolution experiments, where they will artificially select for increased heat tolerance in Tigriopus in the laboratory. At the end of the experiments they will sequence the genomes of the experimental populations to examine which genetic changes led to greater heat tolerance. Then they will compare these genetic changes to differences among northern and southern populations of Tigriopus, which naturally differ in their heat tolerance, to test whether the same changes are responsible for increased heat tolerance in the lab and in nature. This research will contribute a greater understanding of why some species are more heat tolerant than others, leading to an improved ability to predict which species will be more vulnerable to climate change. An understanding of the genetic changes that lead to greater heat tolerance could also be used in aquaculture and in conservation breeding programs, to identify which strains of a given species are the most likely to be resilient to warming.Thermal tolerance traits govern the abundance and distribution of organisms across environments and shape organismal responses to climate change. However, mechanisms determining variation in thermal tolerance are poorly understood for most species. The splash pool copepod Tigriopus californicus exhibits divergent thermal tolerance traits across populations, and is easily crossed and reared in the lab. As a result, it is an excellent model for examining mechanisms of temperature adaptation. The researchers will perform three selection experiments, each targeting a different aspect of thermal performance that differs among Tigriopus populations: (A) upper lethal limits, (B) plasticity of thermal limits, and (C) thermal optima. They will combine these experiments with physiological measurements, transcriptome profiling, and whole-genome resequencing to identify mechanisms underlying each aspect of thermal adaptation. Finally, they will compare results of laboratory experiments to population resequencing data for two Tigriopus species distributed over parallel temperature gradients in North and South America. Results of this project will provide a comprehensive map of the genetic and physiological bases of temperature adaptation in this species, and shed light on key questions, including the role of gene regulation vs. protein coding changes in physiological divergence among populations, the proportion of the genome involved in temperature adaptation, the costs and trade-offs imposed by the evolution of increased thermal breadth, and the repeatability of adaptation across parallel environmental gradients.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.