AbstractsBiology & Animal Science

Predicting evolutionary outcomes and reconstructing past evolutionary transitions are among the main goals of evolutionary biology. Ultimately, understanding the mechanisms of evolutionary change will also provide answers to the timely question of whether and how organisms will adapt to changing environmental conditions. In this thesis, I have investigated the relative roles of natural selection, random genetic drift and genetic correlations in the evolution of complex traits at different levels of organisation from populations to individuals. I have shown that natural selection has been the driving force behind body shape divergence of marine and freshwater threespine stickleback (Gasterosteus aculeatus) populations, while genetic drift may have played a significant role in the more fine scale divergence among isolated freshwater populations. These results are concurrent with the patterns that have emerged in the published studies comparing the relative importance of natural selection and genetic drift as explanations for population divergence in different traits and taxa. I have also shown that body shape and armour divergence among threespine stickleback populations is likely to be biased by the patterns of genetic variation and covariation. Body shape and armour variation along the most likely direction of evolution the direction of maximum genetic variance reflects the general patterns of variation observed wild populations across the distribution range of the threespine stickleback. Conversely, it appears that genetic correlations between the sexes have not imposed significant constraints on the evolution of sexual dimorphism in threespine stickleback body shape and armour. I have demonstrated that the patterns of evolution seen in the wild can be experimentally recreated to tease out the effects of different selection agents in detail. In addition, I have shown how important it is to take into account the correlative nature of traits, when making interpretations about the effects of natural selection on individual traits. Overall, this thesis provides a demonstration of how considering the relative roles of different mechanism of evolutionary change at different levels of organisation can aid in an emergence of a comprehensive picture of how adaptive divergence in wild populations occurs. Evoluutiobiologian keskeisimpiä tavoitteita on lajien evolutiivisen historian selvittäminen ja tulevaisuudessa tapahtuvan evoluution ennustaminen. Näiden tavoitteiden saavuttamisen tarkoitus on puolestaan antaa vastaus yhteen biologian tärkeimmistä ja ajankohtaisimmista kysymyksistä kuinka organismit sopeutuvat muuttuvaan ympäristöön? Ympäristö määrittelee, minkälaiset luonnonvalintapaineet lajeihin kohdistuvat, ja geeniperimä sen, kuinka voimakkaasti luonnonvalinta voi lajeja muuttaa. Populaatiossa täytyy olla geenien erilaisia muunnelmia, jotta evoluutiota voisi tapahtua. Lajien evoluutiota voi kuitenkin tapahtua ilman luonnonvalintaa, jos jotkut geenien muodot yleistyvät populaatiossa…