The effect of life-history genes on eco-evolutionary dynamics (EcoEvoGene)

Genetic change may have large effect on the ecology of an organism. Traditionally, genetic changes – that is, evolution – have been regarded as a slow process that is not relevant on timescales shorter than hundred years. In later years, however, scientists have realized that evolution can be very fast, and strongly influence ability for organism to adapt and survive human induced environmental change. Knowledge of genes with large effect on important biological traits make it possible to study fast contemporary evolution in the wid. However, such knowledge exists only for a few species. In Atlantic salmon, we know about two genes that have large influence for the number of years an individual spends at sea before it returns to its natal river to spawn. Vi do not know the exact position of these genes in the Atlantic salmon genome, but we think that one of them is SIX6 on chromosome 9 and the other is VGLL3 on chromosome 25. The reason that SIX6 and VGLL3 are particularly interesting to study is their effect on adult body size. An Atlantic salmon that spends one year at sea is typically 1-3 kg, two years at sea gives a body size of 3-7 kg, while three or more years at sea gives a body size of more than 7 kg. The longer an Atlantic salmon is at sea, the lower is its survival probability, but it gains fecundity if it survives. A large female has many more eggs than a small, while a large male has better fighting ability compared to a small male and gains access to more females on the spawning ground. In the EcoEvoGene project we have shown that declined waterflow following river regulation increases the advantages of being a small salmon. We do not know exactly why this is the case, but somehow the late maturing salmon must have lost some of the advantages it had of a large body size when there was much water in the river, and survival at sea has become more important than size. This change in optimal body size led to a change in SIX6 and VGLL3. The alleles associated with small body size became more frequent and the Atlantic salmon became smaller. This evolutionary change was fast. It took only 6 salmon generation (a little over 30 years) before the salmon had adapted to the new level of waterflow. Vi have also shown that capelin fishing, which is a prey species for Atlantic salmon, leads to a benefit for the salmon that stays shorter time at sea and increased frequency of the alleles associated with small body size. A different human influence that has large effect on wild salmon is genetic interaction with escaped farmed salmon. Some escaped farmed salmon find their way to the rivers and spawn with the wild Atlantic salmon. This alters the genetic composition of the wild Atlantic salmon population. We show that offspring that have farmed genetic ancestry have faster growth, stays shorter time in the river before migrating to sea and matures at an earlier age compared to Atlantic salmon that are not genetically influenced by escaped farmed salmon. These changes were not due to SIX6 or VGLL3, and must therefore be due to other genetic differences between wild and farmed Atlantic salmon.

Hovudleveransen til prosjektet er vitskaplege publikasjonar og auka forståing av grunnleggjande prosessar i økologi og evolusjon. I tillegg har prosjektet bidra til forvaltningsrelevant kunnskap for laks, gjennom studiar av laksen sin evne til å tilpasse seg eit miljø i ending og genetiske effektar av rømt oppdrettslaks på villaks.

A primary goal in evolutionary biology and ecology is to understand the interplay between evolutionary and ecological processes in contemporary time. This knowledge is the key to predict the ability of populations and species to adapt and persist in a changing environment. A growing body of studies on eco-evolutionary dynamics has shown that evolutionary and ecological processes reciprocally affect each other. However, this research has not taken advantage of the increasing knowledge on the genetic basis of phenotypic traits in natural populations, and is held back by the lack of statistical tools that can quantify the effect of variation in genetic markers on eco-evolutionary dynamics. The EcoEvoGene project will develop a statistical framework that combines genetic and demographic processes, and use this framework to analyse the eco-evolutionary dynamics that has played out over more than 40 years in a daily monitored Atlantic salmon population. This innovative approach will allow us to estimate how the optimal allele frequencies at specific loci have changed over time, how the allele frequencies at the same loci have tracked their optima, and how this has affected life-history evolution, population dynamics and extinction probability. These estimates provide answers to a range of questions fundamental for understanding how rapidly populations can adapt to environmental change and escape extinction. EcoEvoGene represents a novel attempt at quantifying the reciprocal effects of genotypes, phenotypes and population dynamics as they have played out in real time, and provides a quantitative framework for analysing the genetic basis of eco-evolutionary processes in wild populations.