Quantifying the evolutionary potential for Delta Smelt persistence in a warming habitat.

Area of Science:

• Aquatic Ecology
• Conservation Genetics
• Fisheries Science

Background:

• Long-term persistence of managed species relies on their ability to adjust to warming temperatures.
• The critically endangered Delta Smelt (Hypomesus transpacificus) is intensively managed, but its genetic variation for thermal tolerance is poorly understood.
• Understanding thermal tolerance is vital for the persistence of Delta Smelt in a rapidly warming future.

Purpose of the Study:

• To characterize genetic variation and genomic architecture for upper thermal tolerance (CTMax) in Delta Smelt.
• To investigate the effects of rearing temperatures on CTMax and its heritability.
• To assess the influence of domestication selection on thermal tolerance and plasticity.

Main Methods:

• Utilized pedigree and whole genome sequencing data to analyze genetic variation for CTMax.
• Compared CTMax across control and elevated rearing temperatures, alongside body size and hatchery ancestry.
• Employed quantitative genetics and genomic approaches to identify loci influencing thermal tolerance.

Main Results:

• Warmer rearing temperatures increased CTMax via acclimation but reduced additive genetic variation, potentially constraining adaptation.
• Larger fish exhibited reduced CTMax, an effect diminished at elevated temperatures.
• Heritability for CTMax was modest, with significant genotype-by-environment interactions; domestication influenced allele frequencies and thermal tolerance.

Conclusions:

• Rearing temperature significantly impacts thermal tolerance and its genetic basis in Delta Smelt.
• Domestication selection has influenced thermal tolerance and plasticity, with separate genetic underpinnings from CTMax.
• Knowledge of genetic variation for thermal tolerance is essential for refuge management and supplementation strategies for Delta Smelt in a warming climate.