Abstracts (first author)

Talk 

Genetic signature of local adaptation of MHC genes to varying parasite pressures

Author(s): Eizaguirre C, Lenz TL, Kalbe M, Milinski M

Summary:

Although crucial for the understanding of adaptive evolution, genetically resolved examples of local adaptation are rare. To maximize survival and reproduction in their local environment, hosts should resist their local parasites and pathogens. The major histocompatibility complex (MHC) with its key function in parasite resistance represents an ideal candidate to investigate parasite-mediated local adaptation. Using replicated field mesocosms, stocked with second-generation lab-bred three-spined stickleback hybrids of a lake and a river population, we show local adaptation of MHC genotypes to population-specific parasites, independently of the genetic background. Furthermore, the multi-locus specificity of MHC genes revealed that increased individual allele divergence of lake MHC genotypes allows lake fish to fight the broad range of lake parasites, whereas more specific river genotypes confer selective advantages against the less diverse river parasites. Such results demonstrate that not only the presence of given alleles is important for local adaptation but also that the combinations of alleles on the different duplicated loci are crucial for host-parasite coevolution.



Abstracts (coauthor)

Genomic islands of divergence: a comparison of five parapatric lake-river population pairs of three-spined sticklebacks

Author(s): Feulner, PGD, Chain FJJ, Panchal M, Huang Y, Eizaguirre C, Kalbe M, Lenz T, Samonte I, Stoll M, Bornberg-Bauer E, Reusch T, Milinski M

Summary:

Sticklebacks have recently colonized various freshwater habitats and have since undergone recurrent phenotypic divergence. Here, we sample five geographically distinct lake-river population pairs of the three-spined stickleback for investigating patterns of population divergence at varying stages of ecological speciation. Using 60 whole genome sequences (15x coverage each) we identify genomic islands of divergence between parapatric lake-river ecotypes. This allows us to evaluate the number, size and distribution of genomic islands of divergence between several population pairs and to assess the extent of population differentiation across our samples. We identify different genes and genomic regions potentially associated with ecological differentiation in the five lake-river comparisons. This suggests that divergence patterns between lakes and rivers can involve multiple molecular pathways. Interestingly, we find some associations between genomic structural variations and islands of divergence. This is based on our extensive set of structural variations including deletions, copy-number variations, inversions, and translocations. Combined with estimates of the recombination rates across the genomes, we provide insights into the relevance of the genomic architecture and the role of genomic islands during adaptive divergence.

Summary:

Besides traditional genetic inheritance, the phenotype of an individual can be influenced by its parents’ phenotypes and environment. Whether those environmentally-induced parental effects are adaptive though remains elusive. To address this question, we focused on paternal effects of exposure to a nematode parasite in the three-spined stickleback. We experimentally investigated how parasite infection affects adult stickleback males and their offspring’s early life history traits and parasite resistance. By means of in vitro fertilization, we produced over 50 maternal half-sibships sired by pairs of infected and uninfected brothers. We first present evidence for sperm deficiency in infected fathers compared to uninfected fathers (reduced velocity and fertilizing ability). We then show that although offspring of infected fathers suffered from low hatching success and survival rates, when exposed to the same parasite, they achieved higher body condition than their counterparts from uninfected fathers. These results highlight that the adaptive potential for paternal effects is only expressed in the presence of the paternal environmental stressor. We thus discuss the likelihood and potential consequences of sperm-mediated transgenerational effects under stable or predictable environments.

Summary:

Invasion of new habitats is an important natural process known to require phenotypic plasticity of migrating individuals to cope with their new environments. It is poorly understood though how the potential for plasticity among individuals changes during an invasion. Increased trait variation among phenotypes of individuals experiencing a new environment could indicate the use of different strategies for coping with stress and a disruption of previously adaptive patterns. On the other hand, more uniform patterns in groups subjected to environmental changes would suggest a homogenizing effect of high stress levels. We investigate this question with a particular focus on immunity and immune related genes. The three-spined stickleback (Gasterosteus aculeatus) is known for its repeated and parallel invasion of different freshwater habitats from marine environments throughout the Northern hemisphere. In a lab-based study, we mimic transition from brackish water to freshwater and vice versa. Taking into account multiple biological levels as well as standing genetic variation and phenotypic plasticity, we explore the effects and patterns of variation caused by habitat invasion. Furthermore, we subject fish to experimental infection with the monogenean parasite Gyrodactylus gasterosteus and investigate differences in parasite susceptibility entailed by the mimicked invasion.

Genome evolution and structural variation in sticklebacks across different stages of divergence

Author(s): Chain, FJJ, Feulner PGD, Panchal M, Huang Y, Eizaguirre C, Kalbe M, Lenz TL, Samonte IE, Stoll M, Bornberg-Bauer E, Reusch TBH, Milinski M

Summary:

Deciphering the genetic architecture underlying population differentiation and adaptation is crucial for better understanding the process of ecological speciation. To reveal patterns of genome evolution across different stages of population divergence, we characterized genetic variation in three-spined sticklebacks using 66 whole genomes (15x coverage each) from geographically and ecologically distinct populations. This fish species has recently colonized freshwater habitats and undergone substantial and recurrent phenotypic divergence associated with their habitat. We have evaluated the relative importance of several types of genetic variation (SNPs, INDELs, CNVs, inversions and translocations) in the differentiation of genomes across populations and ecotypes. Structural variations cover a larger proportion of the genome than the ~10 million single nucleotide variants. Whereas the majority of variants are shared across several populations, we detect genomic regions of high differentiation between closely related populations. Lineage-specific genes and RNA genes often differ in copy number between individuals and between populations, suggesting a potential role of structural variation such as CNVs in ecological adaptations. We also investigate the relationship between CNVs and different categories of duplicate genes, and evaluate the molecular rates of gene evolution using interspecific data. Taken together, our findings demonstrate extensive genomic differentiation within only a few thousand generations and support a mechanism for the birth and death of new genes via duplication, highlighting the dynamic nature of genomes. Due to our population sampling design we are able to shed some light on the interplay of ecological and genomic features of populations during adaptive evolution and at different stages of ecological speciation.

Dispersal and evolution of the European eel shaped by variations of North Atlantic drift currents

Author(s): Baltazar-Soares, MA, Biastoch A, Harrod C, Hanel R, Marohn L, Prigge E, Evans D, Bodles K, Behrens E, Böning CW, Eizaguirre C

Summary:

For open ocean broadcast spawners, environment-dependent dispersal is a crucial but critical life phase. The yearly recruitment fluctuations and cryptic adult population structure commonly observed in these species are assumed to reflect both the temporal and the spatial environmental conditions that early stages are exposed to. With a long-lasting ocean-dependent dispersal, the European eel (Anguilla anguilla) poses as perfect model organism to study the role of the environment in the evolutionary ecology of a broadcast spawner. To this end, we compared predictions made on dispersal, recruitment and population genetics by 45 years of high-resolution North Atlantic drift modeling with natural recruitment and population genetics at European coasts. We identify atmospherically-driven current variations in the Sargasso Sea as a key factor for a successful dispersal. We also demonstrate how unexpected findings of population structuring are consistent with contemporary recruitment levels, and with cryptic female philopatric behaviors within the Sargasso Sea. We suggest this strategy to be an evolutionary consequence of the unpredictable oceanic environment in the Sargasso Sea.

MHC Evolution in Neotropical Cichlids (Amphilophus sp.)

Author(s): Hofmann, MJ, Bracamonte SE, Eizaguirre C, Barluenga M

Summary:

The Major Histocompatibility Complex (MHC) is a key component of the adaptive immune system of all vertebrates. Considerable evidence has accumulated suggesting that parasite-mediated selection acting on MHC genes may ultimately lead to speciation. The Midas cichlid species complex of the crater lakes of Nicaragua is an ideal model system for the study of speciation, because it has recently colonized several isolated crater lakes where it has independently diverged into sympatric sister species. We evaluate the hypothesis that host parasite interactions might be contributing to the speciation process in this system. To this end we have characterized and sequenced the MHC class IIB of individuals from different putative species of this cichlid species complex.

Contacts

Chairman: Octávio S. Paulo
Tel: 00 351 217500614 direct
Tel: 00 351 217500000 ext22359
Fax: 00 351 217500028
email: mail@eseb2013.com

Address

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
Portugal

Website

Computational Biology & Population Genomics Group 
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