CAUSES AND CONSEQUENCES OF FLUCTUATING SELECTION IN A STOCHASTIC ENVIRONMENT

I den foreliggende rapporteringsperioden nådde vi en viktig milepæl: 1. Price-Robertson ligningene representerer en av de viktigste bidragene til evolusjonsbiologien fordi de gir en metode for å beskrive evolusjonære endringer i kvantitative karakterer selv om den underliggende genetikken som koder for karakteren er ukjent. Et problem for praktisk anvendelse av disse likningene har vært at de ikke har inkludert stokastiske effekter samt at de heller ikke har behandlet effekten av svingninger i alders-sammensetning. I dette projektet har vi nå lyktes å utvikle en generalisering av Price-Robertson likningene som innebærer en vesentlig forbedring av muligheten til å estimaere seleksjon og evolusjon av fitness-relaterte karakterer i naturlige bestander. 2.Anvendelse av dette modellapparatet for å studere seleksjon på ulike morfologiske trekk hos gråspurv i et studiesystem på Helgelandskysten viste at selv under så store miljø -svingninger som i dette området kunne en stor del av den observerte variasjonen i morfologiske trekk forklares bare ut fra effekten av demografisk stokastisitet. Dette viser at genetisk drift kan ha langt større betydning for endringer i fitness-relaterte trekk enn tidligere antatt. Dette kan ha stor betydning for hvor raskt arter kan tilpasse seg endringer i de miljøbetingelsene de er påvirket av

Selection, i.e. the process by which individuals are sorted according to their differences in fitness, is the major force for causing evolution of phenotypic characters. In spite of its importance for structuring biological diversity at all organismic lev els, it is therefore surprising that we still lack understanding of factors influencing variation in the strength of selection in natural populations1. The purpose with the present project is to derive general principles for the operation of selection in natural populations of house sparrows by analysing stochastic processes acting at both ecological and evolutionary time scales using a novel theoretical framework. Such a stochastic approach is necessary because all natural populations are subject to a fl uctuating environment. Here we examine the relationship between the magnitude of environmental stochasticity and the strength of fluctuating selection in 18 island populations of house sparrows. Two alternative hypothesis are likley for such a relati onship: (1) There should be a positive relationship between the environmental variance and the strength of fluctuating selection because deviant phenotypes are more strongly selected against in flcutuating environments. (2) A negative relatioship is likel y if fluctuations in the environment produce large temporal variation in phenotype that maximizes fitness. A problem for estimating the relative contribution of fluctuating environments to ecological and evolutionary processes has been to account for flu ctuations in age structure. Here we will use a novel modelling framework based on the concept of the total reproductive value of the population, which originates back to Fisher. The advantage of this approach is that fluctuations in population size are no t inflated by transient fluctuations in the age structure. This represents an important advance because it allows to introduce stochastic fluctuations at different levels of the selection process.