Abstracts (first author)


Genomic scope of adaptive mutations to different environments

Author(s): Otto S, Gerstein A


A panel of adaptive mutations was obtained by exposing Saccharomyces cerevisiae strains to harsh environmental conditions. The genomic scope of mutations allowing adaptation to these conditions was then determined by sequencing 35 different adapted lines from each of two environments. This panel was then used to measures trade-offs in different environments, as well as properties such as dominance across environments. The implications for Haldane's sieve and the role of ploidy in adaptation will be discussed.

Abstracts (coauthor)


As a consequence of environmental deterioration, a population might become maladapted and risk extinction unless it succeeds in adapting to the new conditions. How likely is it that a population escapes extinction through adaptive evolution? Modeling a population in a degrading structured habitat, we analyze the impact of several ecological factors on its survival probability and determine the relative contribution of standing genetic variation and new mutations to evolutionary rescue. We find that in the interplay of various, partially antagonistic effects, the probability of evolutionary rescue can show non-trivial and unexpected dependence on ecological characteristics. The rate of gene flow affects the fate of the population in several ways, resulting in a complex and non-monotonic relationship between migration rate and rescue probability. Counterintuitively, a harsher change or an instantaneous degradation of the total habitat can sometimes lead to a higher survival probability than a less severe or a slowly progressing change.


Helianthus petiolaris is a widespread sunflower species that usually occupies sandy soils. However, at Great Sand Dunes National Park in Colorado, populations of H. petiolaris survive in large and active sand dunes. We consider these dune populations to be an ecotype of H. petiolaris and a potential incipient species. Accordingly, there is significant phenotypic differentiation and low but significant genetic differentiation between the dune and non-dune ecotypes. For example, dune seeds are 3 times heavier than non-dune seeds. In order to better understand the extent of speciation in this system, we measured reproductive barriers between the two ecotypes. We found asymmetric immigrant inviability, in which dune seedlings emerge and survive better in both habitat types, some assortitive mating via pollen competition, and weak intrinsic post-zygotic isolation. Interestingly, in our pollen competition experiment some plants showed biased seed set while others did not suggesting that 'choosiness' is polymorphic within the ecotypes. In sum, the nature and types of reproductive barriers we found between the dune and non-dune ecotypes of H. petiolaris are consistent with those we would expect between populations at an early stage of ecological speciation. Finally, we plan to compare adaptation and speciation in this system with two pairs of sunflower sister taxa with similar habitat differences.


Independently evolving populations may adapt to similar selection pressures via different genetic changes. The interactions between such changes can then inform us about the underlying fitness landscape, allowing us to determine whether gene flow would be facilitated or hampered following secondary contact. We used Saccharomyces cerevisiae to measure the genetic interactions between independently evolved first-step mutations to the fungicide nystatin. We found that genetic interactions are prevalent, even among the first adaptive mutations. In the adaptive environment, the more beneficial mutation often masks the other, less beneficial one. This would allow a population fixed for the less beneficial allele to acquire and fix a more beneficial allele - thus continuing to climb the adaptive peak. In one case, however, reciprocal sign epistasis was observed, indicative of a fitness valley between two peaks. This is surprising given the small number of mutations combined and the relative simplicity of the adaptive environment.


Chairman: Octávio S. Paulo
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XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon


Computational Biology & Population Genomics Group