Abstracts (first author)

Talk 

Adaptive divergence in two coexisting stickleback species

Author(s): Raeymaekers JAM, Chaturvedi A, Konijnendijk N, Maes G, Volckaert F

Summary:

Natural populations are at least partially adapted to local environmental conditions. The level of adaptation is promoted by divergent selection on ecologically relevant traits, but hampered by gene flow. The relative strength of both forces depends on genomic architecture as well as dispersal abilities, both of which might differ between species. In this study, we tested for divergent selection and gene flow in two coexisting and phylogenetically related species, the three- and nine-spined stickleback. Populations occur across very similar environmental clines in biotic and abiotic conditions (salinity, oxygen concentration, predation, parasites and prey), and were sampled within exactly the same spatial matrix. In each species we assessed gene flow between populations from contrasting environments and determined divergence in ecologically relevant traits (body shape, armour, spleen size, and trophic morphology). An analyses of genome-wide differentiation was used to identify the genomic basis of adaptation. Based on these data we compared the relative strength of divergent selection and gene flow in both species, as well as the biological functions of the genes under selection. We discuss how these relationships explain how both stickleback species maintain partially overlapping habitats.



Abstracts (coauthor)

Host dispersal shapes host-parasite co-evolutionary dynamics in cichlid fishes

Author(s): Hablützel, PI, Grégoir AF, Roose AK, Volckaert FAM, Raeymaekers JAM

Summary:

Parasite communities have been proposed to drive adaptation and reproductive isolation of their hosts mediated by the pleiotropic role of immunogenes in both parasite defence and assortative mating. Parasite communities themselves are shaped by the abiotic environment, the availability of intermediate hosts, and live history traits of the host species. The degree to which parasites drive the evolution of their hosts hence may directly rely on intrinsic host traits. Here, we tested the hypothesis whether host dispersal can drive parasite community structure and investigated how this influences the degree local immunogenetic adaptation of the host. We compared parasite communities and Mhc (major histocompatibility complex) allele frequencies in two sympatric cichlid fish species with contrasting dispersal patterns along the shoreline of Lake Tanganyika. We found that allopatric and genetically diverged colour morphs of philopatric blunt-headed cichlids (Tropheus spp.) are infected by contrasting parasite communities and are immunogenetically adapted to them. We could not detect such a pattern in the closely related, but non-philopatric cichlid fish species Simochromis diagramma. This suggests that the presence of migrants among isolated host populations homogenises their respective parasite communities in Lake Tanganyika and ultimately affects immunogenetic adaptation. Therefore we conclude that host-parasite co-evolutionary dynamics are the main driver of diverging parasite communities among allopatric host populations. The proposed pleiotropic role of the Mhc in parasite defence and assortative mating lets us speculate, whether contrasting parasite communities could drive speciation in colour morphs of philopatric blunt-headed cichlids.

Summary:

Our ability to find signatures of selection in the genome is rapidly increasing. As a consequence we now know that strong selection leading to local adaptation can affect many regions in the genome. However, not all local adaptations result in structural gene changes. Changes in regulation of existing genes might be at least as important. To what extend this happens and whether selection only affects genes directly related to the focal trait, or also other gene classes is for many cases unknown. Host-parasite systems are very suitable for testing the importance of gene expression alterations in local adaptation. Selection is often strong due to the fact that parasites can have a big impact of fitness of the individual, making it probable we can pick up alterations in expression. Start and finish of changes in gene expression are much easier to predict than for many other (somatic) traits and temporal an spatial fluctuations in parasite abundance are common in nature, which may favor changes in gene expression rather than genetic changes as they are much easier to reverse. We used the F2 generation of two populations of stickleback fish that differ in host resistance, in order to identify which genes are involved in resistance and to understand whether heritable differences in resistance across populations are linked to differential gene expression. We infected naive fish with Gyrodactylus gasterostei, a parasitic flatworm and tracked the infection by counting parasites on the skin over time. Targeting the beginning and peak of the infection, we used microarrays to identify differential gene expression across the genome. We will present whether differences in host resistance result in differential expression patterns among populations and whether infection only affects immune related genes or a wider set of genes, thereby contributing to a better understanding of the role of gene expression alterations in host adaptation to parasites.

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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