The importance of genetic diversity and evolution in metacommunities.

Abstract

The evolving metacommunity framework starts from a strong conceptual framework on metacommunity ecology, but includes the impact of evolutionary dynamics. Whereas metacommunity ecology integrates migration and species sorting in response to environmental factors, evolving metacommunities research also tries to disentangle the relative importance of species and genotype sorting in determining community trait responses to environmental gradients. Studying evolving metacommunities requires not only data on species composition, but also on trait values of a whole suit of ecologically important traits of the different species in the metacommunity, and genotypic trait values of the different species in those communities, for a reasonably large set of local populations and communities.To study how evolving metacommunities work, we used zooplankton and the water flea Daphnia magna as a focal species as a model system. Zooplankton form dormant stages during winter which accumulate in the sediment to form a sort of archive, a dormant egg bank. Such egg bank is interesting as starting material for experiments since it allows large scale experiments and integrates spatial and temporal variation of a pond habitat. However, since dormant eggs are produced sexually unlike the clonally produced eggs during the growing season, we wanted to know how this difference would affect trait values. In chapter 2, we reconfirmed that there are differences between the ex-ephippial generation and the first clonal generation, but also between the first and second clonal generation. In addition, to quantify life history traits in life table experiments, we concluded from chapter 1 that it is advisable to minimize handling stress and medium renewal. These findings should be taken into account when carrying out life table experiments.In chapter 3 we studied life history traits of Daphnia magna using three treatments: the fish background and land use background of the original ponds the Daphnia populations came from, as well as exposure to fish chemicals. We found out that these three factors affect life history traits significantly: exposure to fish chemicals made the water fleas grow and reproduce faster, have larger clutch sizes and stay smaller in body size to cope with fish predation. The adaptation to fish (i.e. fish background) induced two plastic responses to fish chemicals: a smaller size at maturity and a safer vertical migration behavior. Daphnia from fishless ponds only responded with size at maturity to fish chemical exposure. Land use by agriculture had a negative impact on fecundity. In chapter 4 we combined the different levels of biological organization. We tried to assess in an integrated way the importance of local and regional processes in determining species composition, trait values and genetic variation in a natural setting of local communities in a heterogeneous landscape. We postulated that broadening variation partitioning to multiple data matrices (community structure, quantitative trait values and neutral genetic variation) and quantifying the joint and separate effects of environment and space can be informative in explaining evolving metacommunity dynamics. We advocated the new approach using two datasets of zooplankton metacommunities in two separate regions. We found pure environment to be most important in explaining community structure and trait values. For neutral variation, spatial factors are of more importance. Our analysis revealed differences in the factors driving structure in the two metacommunities, pointing to different selection regimes in both regions.In chapter 5 we studied an experimental metacommunity using outdoor mesocosms in which we inoculated Daphnia magna and zooplankton communities originating from ponds with or without fish (i.e. past selection) and subjected them to current fish selection pressure. In one third of the mesocosms, we did not apply any dispersal treatment, in one third we exchanged a proportion of the entire metacommunity and in the last third we exchanged a proportion of the D. magna individuals. Our results showed that dispersal and fish predation, both past and current, play an important role in structuring zooplankton metacommunities. In the absence of predation, dispersal increases species diversity. Fish predation directly affected the two largest species in the community depending on their local genetic adaptation to fish (i.e. fish background). We observed a fish x fish background x dispersal interaction for the amount of algal biomass, indicating that top-down control of algae by zooplankton is a function of both past and current selection pressures combined with dispersal. Understanding of the interactions between genes and traits in populations and communities combined with dispersal connecting processes to each other, is a not to be underestimated challenge in the evolving metacommunity framework. From underlying research we can conclude that population and community dynamics are impacted by the environment, including anthropogenic factors. Our data provide support for a policy to drastically reduce the collateral damage of agriculture by promoting more sustainable practices.Introduction -Ecological background: from community to metacommunity -Evolution in metacommunities -Study system -Objectives and outline of thesis -Characterization of the studied ponds Part I. Methodology Chapter 1 Effects of medium renewal and handling stress on life history traits in Daphnia Chapter 2 Ex-ephippial and clonal generations of Daphnia magna: differences in life history and behavioral traits Part II. Field survey – evolutionary ecology & evolving metacommunities Chapter 3 Genetic variation for life history and behavioral traits of the water flea Daphnia magna in response to strong environmental gradients Chapter 4 The importance of environment versus space in species, traits and genes in a metacommunity setting Part III. Experimental metacommunity analysis Chapter 5 Past and current selection and dispersal interact to determine zooplankton community impact on ecosystem functioning Part IV. General discussion Summary Samenvatting References Publicationsnrpages: 250status: publishe