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Keynote presentations

  1. Nicolas Bierne
  2. Nicolas Galtier
  3. Andreas Hejnol
  4. Marjorie Oleksiak
  5. Cynthia Riginos
  6. Frédérique Viard

From speciation genes/islands to the architecture of species barriers, the two tales of speciation genomics

Nicolas Bierne
Institute des Sciences de l'Évolution Montpellier (ISEM), University of Montpellier, France

Identifying barrier loci that restrict gene flow between incipient species has sometimes been argued as one of the principal aims of speciation genomics. This objective echoes the quest for the loci of adaptation within species; a quest that has often been criticized to result in focusing on Mendelian traits and in distracting us from our ultimate goal of understanding and predicting adaptation. However, speciation genomics has obtained outstanding successes. Genes involved in hybrid lethality and sterility have been identified and have supported the well-known Dobzhansky-Muller model of hybrid incompatibility. Genome sequences have revealed large genome regions of high genetic differentiation, the so-called genomic islands, in accordance with the expectation that barrier loci restrict gene flow in these regions. Finally genomic islands are sometimes shared between repeated events of parallel speciation, suggesting a common pathway to speciation under shared environmental pressures. Building on these successes it was easy to conclude that speciation is distinct from within-lineage evolutionary change and proceeds to sieve a few large effect loci. I was one of those who were easily inclined to embrace this view, until recently. I will present some studies of segregation distortions and population genomics we conducted in mussels and other marine and terrestrial species. I will show that a general multigenic model of hybrid fitness can account for a large number of empirical patterns. Without denying that large effect genes, gene clusters and supergenes exist, closer inspections of empirical patterns together with theoretical and molecular evolution arguments suggest that species barriers are mainly a side-effect of genome-wide divergence. 

Comparative population genomics in animals: genetic diversity, adaptive rate, species barrier

Nicolas Galtier
Institute des Sciences de l'Évolution Montpellier (ISEM), University of Montpellier, France

The molecular evolutionary literature in animals has been dominated
during decades by just two taxa, namely hominids and drosophilids.
Here, taking a comparative approach across ~100 species from 35 distinct
families and eight phyla of animals, I investigate the relationship
between species traits and population genomic processes. I show that
the genetic diversity, but not the rate of adaptive evolution, is
remarkably well predicted by species life history traits.

Comparative developmental biology and its relationship to genomic and morphological evolution

Andreas Hejnol
Sars International Centre for Marine Molecular Biology, Norway

Life evolved in the sea and also main animal lineages originated in the oceans. The study of marine animals thus provides a fascinating resource to understand in depth the origin of major animal organs systems before they diversified into highly specialised organs found in terrestrial animals including humans. The improved resolution in the animal tree and advancements in technology such as novel sequencing, microcopy and molecular tools allow to investigate a much broader number of marine animals and their embryos than ever before. This opens the opportunity to strategically sample many species to test previous hypotheses and develop new ones. Genomic changes can be now correlated with evolutionary changes in morphology providing to ask novel questions. I will provide using the example of gut evolution new insights that change previous ideas about how animal evolved.

Adaptation: from among to within populations

Marjorie Oleksiak
Rosenstiel School of Marine & Atmospheric Science, University of Miami, USA

How fast and at what scale does adaptive divergence occur in natural populations? Adaptive divergence within populations has typically been studied over tens of thousands of years. However, with the pace of rapid environmental change, adaptive change on ecologically relevant time scales will be increasingly important. To explore the potential for ecologically relevant evolutionary adaptation, my research focuses on the teleost Fundulus heteroclitus. F. heteroclitus populations have extensive standing genetic variation and exhibit adaptive divergence across different time periods and spatial scales. Time scales range from the last glaciation (10,000 mya) to a few seasons, and spatial scales range from 1,000s of kilometers to within the same population and even within the same individual (between nuclear and cytoplasmic genomes). This rapid pace of adaptive change means that much evolution must result from standing genetic variation, which can be redeployed in constantly changing environments. Additionally, rapid adaptation is more likely when there are many different polymorphic genes, and selection for a few of these genes creates a more fit phenotype (a polygenic trait). These two parameters (standing genetic variation and polygenic traits) explain the rapidity of adaptive divergence in F. heteroclitus populations

Considering the seascape context in population genomic studies

Cynthia Riginos
School of Biological Sciences, University of Queensland, Australia

The question of how spatially arrayed environmental and habitat features influence microevolutionary processes has a long history in evolutionary biology. Our newfound ability to query genomic variability in natural populations has reinvigorated enthusiasm for discovering correlations between such features and genetic variants and, subsequently, drawing inferences regarding how drift, migration, and selection shape intraspecific genetic variation. In our exuberance, however, fundamental attributes of spatial geographic features have been largely overlooked, especially with respect to inherent correlational structures of such data. For marine species, life in flowing water brings additional challenges for attempting to relate spatial genetic variation to underlying processes, as environmental attributes can be highly dynamic, and dispersal could be episodic, asymmetric, and collective. I will discuss these issues and suggest some strategies and potentially fruitful avenues for research. Then, I will focus on the specific issue of asymmetric dispersal and ask whether oceanographic-based dispersal models can serve as adequate spatially explicit hypotheses of migration, using a case study of Acroporid corals on the Great Barrier Reef, Australia.

Documenting the extent and variability of planktonic larval dispersal remains a persistent challenge in marine biology. Despite substantial recent progress in determining mean dispersal distances for focal species, how dispersal varies across seascapes and whether specific seascape attributes can effectively predict relative dispersal levels remains largely unknown. Biophysical models provide compelling and detailed spatial hypotheses of dispersal across seascapes, and inferences from such models are increasingly being used to support spatial planning for conservation and fisheries. How well biophysical models provide accurate spatial summaries of dispersal history, however, is unresolved. At large geographic scales, intraspecific spatial genetic structure provides an observable, albeit murky, outcome of past generations of dispersal, but is limited both by the high variance of evolutionary genetic processes and constrained sampling efforts. Here, we focus on a foundational coral from the Great Barrier Reef, Acropora tenuis; we draw upon a customized biophysical dispersal model and a spatially extensive microsatellite data set (43 populations, 1928 distinct multilocus genotypes) to test for correlations between independent estimators of dispersal and diversity derived from biophysical models, reef configuration, and genetics.

Improving our understanding of biological invasion processes with DNA-based studies: a brief overview and a case study

Frédérique Viard
Station Biologique Roscoff, France

Non-indigenous species provide excellent case studies to explore important eco-evolutionary processes. In this context, DNA-based studies have been extensively used in the past thirty years. A brief overview of what we had been learnt from such studies (e.g. little evidence of founder events) will be provided. An illustration will then be provided regarding an important issue of marine biological invasion studies: the outcome of secondary contacts between native and introduced species that diverged in allopatry. The outcomes of such secondary contacts may be diverse (e.g. adaptive introgression of the introduced species, establishment of hybrid zones that may stop propagation of the introduced species etc.) but are not yet well examined. We investigated the fate of such a human-mediated secondary contact between two tunicates, namely Ciona intestinalis and C. robusta, in the English Channel. Field surveys documented that the two species are found in syntopy, mature at the same period and display similar life-cycle in the study area. In addition, despite an ancient divergence (ca. 4 Mya) they were shown to be only partially reproductively isolated under laboratory conditions. And yet, using 312 SNPs developed from full-transcriptomes, we showed that the introgressions, observed in the wild, are the outcome of historical gene flow (spread afterwards at a worldwide level) rather than contemporary hybridization. We then investigated the mechanisms that may explain the lack of hybridization between the two species. Post-zygotic ecological effects alone are unlikely to be effective against hybridization. The analyses of F2 hybrid and backcross progenies with ddRaq-sequencing finally suggested that genetic incompatibilities are the most likely mechanisms preventing hybridization between the introduced and native species in the English Channel. This case study illustrates that combining field work, experimental crosses and high-throughput sequencing-based studies can help improving our understanding of eco-evolutionary processes associated with biological introductions.


Page Manager: Eva Marie Rödström|Last update: 5/12/2018

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