Abstracts (first author)


Fluctuating temperature leads to evolution of thermal generalism and pre-adaptation to novel environments


Author(s): Ketola T, Mikonranta L, Zhang J, Saarinen K, Friman V, Örmälä A, Mappes J, Laakso J


Climate change scenarios do not only expect elevated temperatures but also increased temperature fluctuations. Environmental fluctuations are suggested to select for low levels of plasticity in fitness that is also hypothesized to increase organisms’ ability to invade novel environments and affect virulence of pathogens. We tested these hypotheses and show that across a range of temperatures, opportunistic bacterial pathogen Serratia marcescens that evolved in fluctuating temperature (daily variation between 24 and 38 °C, mean 31 °C), outperforms strains that evolved in constant temperature (31° C) across all measured temperatures. Their better growth was also evident in novel environments with parasitic viruses and predatory protozoans. However, the strains from fluctuating environment were less virulent to Drosophila melanogaster host. Therefore, whilst supporting the hypothesis that evolution in fluctuating environments is paired with tolerance to several novel environments, our results show that adapting to fluctuating environments can also be costly in terms of reduced virulence. Together these results suggest that thermal fluctuations driven by the climate change could affect not only species thermal tolerance but also species’ invasiveness and virulence.

Abstracts (coauthor)


Opportunistic pathogens generally face two vastly different environments - within the host and outside host. One mechanism allowing for adaptation to alternating environments is switching between phenotypes (phenotypic plasticity). The opportunistic fish pathogen Flavobacterium columnare can be found from natural waters and from fish farms and it exhibits two reversible colony morphologies; a non-virulent “rough” and a virulent “rhizoid” morphology. As compared to natural waters, fish farms can be considered as extreme environments in terms of available host resources, but also in terms of stress caused by chemical and antibiotic treatments. Fish farms could thus be expected to impose higher selection pressures for coping between the within and outside host environment, and to select for increased phenotypic plasticity. To test these ideas we measured growth parameters of rhizoid and rough colony morphotypes of F. columnare isolates both from natural waters and from disease outbreaks at fish farms in different resource concentrations and temperatures, and tested their virulence with a zebrafish challenge model. We found that the non-virulent “rough” morphotypes had a higher growth rate and lower virulence than the “rhizoid” morphotypes, but only if the isolate was originating from the fish farms. This suggests that phenotypic plasticity between two morphotypes of opportunistic pathogen and their characteristic traits is clearly selected for in fish farms rather than in the natural environment.


Fluctuating temperature is predicted to select for generalist genotypes that are capable of performing well across a wide range of temperatures. Although theories particularly predict fast fluctuations in selecting for thermal generalists, such experiments are scarce. Our aim was to find out whether fluctuating temperature selects for temperature generalists and test how uniform the temperature induced evolutionary changes are across different bacterial species. We set up a factorial experiment where ten replicate populations of nine different bacterial species were propagated separately either in a constant temperature (30 ºC) or in a rapidly fluctuating temperature (2 h 20 ºC - 2 h 30 ºC - 2 h 40 ºC, mean 30 ºC). After 2.5 months we isolated altogether 720 bacterial clones from experimental populations and measured growth rate and yield (growth efficiency) in three constant temperatures (20, 30 and 40 ºC). Meta-analysis of all of the species over all of the temperatures indicated that clones from the fluctuating temperature treatment had higher overall growth efficiency compared to clones from the constant environment. Moreover, the selection was found to be asymmetric, selecting more profoundly the tolerance of hottest temperatures. Generality of the results across studied species gives a strong support for the theories of evolution of thermal generalism but also indicates that evolutionary consequence of fluctuating temperature is especially strong in hot temperatures where the fitness consequences of increased or decreased heat are much more profound than in cold temperatures.


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