The predictability and limits of evolution in response to increased temperature: insights from a natural ‘experiment’

Therefore, knowing how currently extant populations can or have changed in response to warmer conditions would be extremely important. Here we propose to investigate how populations change with respect to their growth, physiology, and anatomy in response to long term exposure to increased temperature. We will also determine what genetic changes may have happened in addition to epigenetic changes (i.e. environmentally-induced structural alterations of the genome that affect its function but don’t change the DNA sequence), and relate these to phenotypic variation. To address this we will use a series of unique study sites in Iceland where populations of threespine stickleback live both in geothermally heated ponds and in unheated (i.e. cool) ponds in close proximity. These pairs of adjacent populations (which occur in several places) have lived at these contrasting temperatures for thousands of generations and preliminary investigation shows evidence of evolutionary divergence between them. This broad-ranging project will use both comparative and experimental approaches to quantify how the phenotype, genome, and epigenome interact when the animal experiences rising temperatures. Lab experiments will use fish from these source populations to investigate 1) population level differences between ambient (cool) and ‘warmed’ populations at the genomic and epigenomic level, 2) the inheritance of phenotypic traits (including metabolic rate, morphology and locomotor performance) and epigenomic states in sticklebacks reared under reciprocal temperature regimes, 3) alterations of development under warm conditions that could limit evolution, and 4) the genetic and epigenetic basis for variation in phenotypic traits under different temperatures. This project will be holistic through its ability to allow plasticity and heritable epigenetic effects to be assessed together with genetic variation. It will reveal whether there are consistent (and hence predictable) evolutionary and epigenetic changes when populations are exposed to warmer temperatures, and will explore the role of plasticity in shaping adaptive responses. As a result, it will provide novel information on the extent to which populations can adapt to a warming world.