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In order of appearance: 

  1. Roger Butlin
  2. Marina Rafajlovic
  3. Henrik Pavia
  4. Adam Jones
  5. Emily Rose
  6. Hunter Fraser
  7. Ryosuke Kita
  8. Felicity Jones
  9. Alexander Eiler
  10. Anja Westram
  11. Silva Uusi-Heikkilä

The wonderful world of clines 

Roger Butlin
Molecular Ecology Laboratory, University of Sheffield, UK & Department of Biological and Environmental Sciences, University of Gothenburg, Sweden

One way to detect the operation of natural selection in the wild is through consistent patterns in genotypes or phenotypes that would not be expected to result from other processes. A cline is one such pattern. A rich theory exists for narrow clines, maintained by a balance between gene flow and natural selection. Using this theory, it is possible to estimate the strength of selection on genes and phenotypes, often in cases where direct measurement would be very difficult. I will try to illustrate this potential with results from contact zones between ecotypes of the marine snail Littorina saxatilis and other study systems.

The dynamics of local adaptation of small partly isolated subpopulations

Marina Rafajlovic
Dept Physics, University of Gothenburg, Sweden


Linking demography of long-lived size-structured seaweeds to phenotypic selection in stochastic environments

Henrik Pavia
Dept Biological and Environmental Sciences, University of Gothenburg, Sweden

This study compare the pattern of phenotypic selection on quantitative morphological as well as chemical traits in two natural populations of a perennial brown seaweed from areas with different levels of environmental variability. Demographic data, including morphological and physiological traits, were collected annually from 300 tagged individuals during four years in the two study areas. A stage structured stochastic matrix model was used as the underlying demographical model and individual fitness was calculated as the sensitivity of the stochastic population growth rate to the removal of one individual from the data set. Analyses of yearly phenotypic selection were calculated by correlating individual traits to the fitness value (the Lande-Arnold method). The most consistent pattern was selection for larger size in the area with less environmental variability while it was a stabilizing selection on the same trait in the other area. The pattern of selection was generally more complex in the area with larger environmental variability where variance and correlation selection were more frequent and slightly stronger. In the same area selection on defense chemicals and individual growth suggested the possibility for evolution of two morphs; 1) individuals with lower annual growth, a large number of fronds and high levels of phlorotannins, and 2) individuals with higher annual growth and lower levels of phlorotannins. Our study demonstrates that population modeling is a useful tool also when looking at individual performance as it facilitates the analyses of selection in long-lived organisms.

Confronting Challenges in the Measurement of Sexual Selection 

Adam Jones
Ecology and Evolutionary Biology, Texas A&M University, USA

Sexual selection is a potent mechanism of evolution, and many species possess conspicuous traits that only make sense in light of sexual selection. However, to understand sexual selection, we also need to understand the evolution of mating preferences, which have proven very difficult to study. In fact, the targets of the preferences can be very difficult to diagnose. Here, I discuss how we can make progress in sexual selection research even when we do not know the traits upon which mating preferences act. One useful approach is to measure genetic mating systems, which provide real constraints on the intensity of sexual selection, to identify populations and species in which sexual selection is likely important. Another potential approach is to study overall attractiveness, a highly complex trait, and use information on attractiveness to make inferences about the nature of mating preferences in natural and artificial populations. Regardless, we need to find new ways to characterize mating preferences that account for the multivariate nature of sexually selected traits and preferences.

The effects of synthetic estrogen on total selection in the sex-role-reversed Gulf pipefish

Emily Rose
Ecology and Evolutionary Biology, Texas A&M University, USA

To determine total selection in the sex-role-reversed Gulf pipefish we simultaneously quantified premating and postmating episodes of selection by using a microsatellite-based analysis of parentage in experimental populations. We exposed half of the replicates to a synthetic estrogen 17α-ethinylestradiol, EE2, to determine the effect of estrogen exposure on total selection. Exposure to low levels of EE2 did not affect the strength of selection, likely due to the unusual sex-role-reversed mating system found in this species. In both treatments for males, the variance in relative fitness arose mainly from the number of eggs received per copulation and a small number of males who failed to mate. Female pipefish exhibited an opportunity for selection (I) of 1.64 in the control and 1.59 in the EE2 treatment, which was considerably higher than that of males (0.35, control; 0.39, EE2). Decompositions of I and the selection differential (s) on body size showed that over 95 percent of the selection on females arose from the premating phase in both treatments. We found evidence for a tradeoff between selection phases in control females, where multiply mating females had significantly lower offspring survivorship compared to singly mated females. However, multiply mated females exposed to EE2 produced more eggs with higher embryo survivorship than non-exposed females. Thus, short-term exposure to low concentrations (2.0 ng/L) of EE2 in Gulf pipefish enhanced female reproductive success. However, higher EE2 concentrations (5.0 ng/L) caused complete reproductive failure in Gulf pipefish males. Overall, our study exemplifies a general approach for the decomposition of total selection into premating and postmating phases to better understand the interplay of natural and sexual selection and also calls for more work on the long-term effects of EE2 exposure in Gulf pipefish in artificial and natural populations.

Adaptive evolution of gene expression 

Hunter Fraser
Dept Biology, Stanford University, USA

Linking selection on gene expression and fitness across diverse yeast strains

Ryosuke Kita
Dept Biology, Stanford University, USA

Despite a great deal of investigation, the role of gene expression in the evolution of life remains obscure. Although a handful of examples of evolutionary adaptation by gene expression regulation have been found, the relationship between gene expression and the fitness landscape is unknown. We measured fitness and genome-wide gene expression across 85 diverse strains of the yeast S. cerevisiae to explore the connection between natural selection on gene expression and fitness across a wide range of environments.


Felicity Jones
Max Planck Institute Tübingen, Germany

The marine - freshwater transition in streamlined bacteria 

Alexander Eiler
Department of Ecology and Genetics, Uppsala University, Sweden

The most common bacteria in many environments, in particular aquatic systems, are now considered to have very small and compact genomes. This genomic streamlining is predicted to restrict evolutionary radiation but is challenged by the successful leap from marine to fresh waters reported for the alphaproteobacterial clade SAR11. Here, we reveal overall similarities in genome architecture and the metabolic adaptations that occurred during the marine-freshwater transition in SAR11 by comparing ten partial single cell genomes from freshwaters and genomes from sequenced marine isolates. Freshwater and marine SAR11 resembled each other in streamlined genomic features and shared a large number of orthologous genes, yet had widely distinct local gene synteny and formed distinct monophyletic groups in phylogenetic trees. In addition to expected adaptation in osmoregulation, freshwater SAR11 were missing several carbon degradation pathways when compared to the repertoire present in their marine siblings. Auxotrophy for several vitamins were shared whereas glycine and serine biosynthesis genes were present in freshwater SAR11 contrary to most marine SAR11 genomes. Evolutionary reconstruction suggest that most of these genes do not represent innovations specific for freshwater SAR11 as they were already gained by gene duplication and recombination events in the ancestor marine populations. This suggests that homologous recombination plays an important role in the initialization of transitions due to reshuffling of the pangenome, followed by gradual emergence of barriers to gene flow where populations become disconnected from the original gene pool. Thus, maintaining high genotypic diversity facilitates the evolvability of streamlined genomes and represents an evolutionary strategy to increase the chances of finding and fixing an adaptive genotype.

Little evidence for similar genetic changes underlying repeated ecotype divergence in Littorina saxatilis 

Anja Westram
Molecular Ecology Laboratory, University of Sheffield, UK

Anja M. Westram(1), Juan Galindo(2), Magnus Alm Rosenblad(3), John W. Grahame(4), Marina Panova(5), Roger K Butlin(1,5)

(1)Animal and Plant Sciences, University of Sheffield, Sheffield S102TN, United Kingdom. (2)Departamento de Bioquímica, Genética e Inmunología, Facultad de Biología, Universidade de Vigo, 36310 Vigo, Spain. (3)Chemistry and Molecular Biology, University of Gothenburg, SE-405 30 Gothenburg, Sweden. (4)School of Biology, University of Leeds, Leeds LS2 9JT, United Kingdom. (5)Department of Biological and Environmental Sciences - Tjärnö, University of Gothenburg, SE-452 96 Strömstad, Sweden.

Parallel speciation is strong evidence for the role of divergent selection in speciation and has been demonstrated in multiple systems. However, it is often not clear whether the genetic basis of divergence is similar across locations. Our project aimed at identifying the relative contribution of globally and locally selected genetic variation to divergence in the snail Littorina saxatilis, which is split into two ecotypes (adapted to crab predation vs. wave exposure) on rocky shores across Europe. We performed an RNA-sequencing experiment using snails from Spain, Sweden and the United Kingdom. Analysing the resulting allele frequency data, we found that within all three countries, ecotypes were genetically distinct. In each country, we identified loci potentially under divergent selection as those with the highest level of differentiation. Most outlier loci appeared only locally (i.e. within one of the countries). When two countries were compared, only about 15% of outliers were shared. However, the proportion of shared outliers was greater than the chance expectation. Our results suggest that the genetic basis of divergence largely differs between countries (at least for expressed genes). We discuss possible explanations for this result, including a polygenic basis of divergent traits and axes of selection differing among countries.

What Can Selection Experiments Teach Us? 

Silva Uusi-Heikkilä
Environmental and Marine Biology, Åbo Akademi University, Finland


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