ProjectEco-evolutionary consequences of forage fish stocking - Threespine Stickleback - in northern aquatic food webs
My research addresses the reciprocal interplay between evolutionary and ecological processes (Eco-Evolutionary Dynamics) in northern lake ecosystems that receive fish stocking for lake management. My project involves replicated whole lake ecosystem manipulations in which 8 Alaskan lakes have been treated with rotenone in fall 2018 by U.S. Fish & Wildlife Service to remove non-native and invasive northern pike that had become a threat to the ecological integrity of Alaskan lake ecosystems, and then restocked with threespine stickleback (Gasterosteus aculeatus) as the forage fish in spring 2019. For my M.Sc. project, I use stable isotopes and fatty acids as qualitative tracers for trophic cascades in natural lake ecosystems. More precisely, I am looking at how historical evolutionary changes influence ecological dynamics and how these eco-evolutionary dynamics are shaping the structure of the newly colonized stickleback prey communities. Different ecosystem components such as prey community composition, among others, influence the stickleback diet and the evolutionary fate of each population with distinct morphological characteristics that provide them with differential feeding efficiency. Previous studies have shown that the limnetic phenotype feeds more on zooplankton whereas the benthic phenotype feeds more on benthic invertebrates. The link between the differential diet of sticklebacks and the evolutionary trajectories of each population is that there is a difference in nutritional quality between the organisms of stickleback prey community. In this context, the present study aims to reconstruct the diet of the threespine stickleback (Gasterosteus aculeatus) in order to determine its nutritional quality. Among zooplanktonic prey, calanoid copepods are essential intermediate trophic carriers of DHA – docosahexaenoic acid, essential fatty acid in aquatic food webs – which can be limiting for fish development, reproduction, and abundance. Here, I examine the net effect of predation and excretion associated with stocked, evolutionary-divergent lineages of stickleback on calanoid copepod DHA content and abundance between stocked lakes. Second, I address the bottom-up food web feedbacks from copepod DHA availability to stickleback, and determine if this pathway can limit or facilitate stickleback lake colonization. This research project is an international collaboration between several laboratories. Among Canadian collaborators, Andrew Hendry's laboratory, McGill, is working on the Evolution portion, i.e. stickleback population genetics (Eco-> Evo), while Alison Derry's laboratory, UQAM, is working on the Ecology portion, i.e. stickleback prey community composition and environmental parameters that characterize the lake ecosystems under study (Evo-> Eco). The predictions of my study are that lakes stocked with pelagic-feeding versus benthic-feeding genotypes of stickleback will result in either phytoplankton-dominated (pelagic) or macrophyte-dominated (benthic) food webs, through the process of trophic cascade. This will create divergent eco-evolutionary feedbacks on trophic transfer of fatty acids from phytoplankton to copepods to fish. We intend to understand the implications in terms of trophic cascade of the implantation of two divergent populations – limnetic and benthic – of threespine stickleback (Gasterosteus aculeatus) whose distinct and specific to each population phenotypic characteristics influence their feeding traits. Ultimately, we seek to understand how these evolutionary changes affect the diet of sticklebacks and subsequently modify the structure and nutritional quality of zooplankton prey communities through trophic cascades. To do this, we use repeated design manipulations of whole lake ecosystems before-after control-impact (BACI) involving the experimental enrichment of lakes with divergent evolutionary lineages of sticklebacks. Sampling of zooplankton, benthic invertebrates and sticklebacks was conducted on all studied lakes in order to extract the isotopic signature of the different groups of stickleback prey community as well as stickleback fatty acid profile, being the main prey community predator. Key response variables include DHA fish tissue content derived from stickleback fatty acid profile, stickleback prey community composition and abundance, and stable isotope signal of seston and stickleback. Establishing stable isotope signals of stickleback prey community and both stickleback populations will help reconstruct the food web of the sampled lakes, while stickleback fatty acid profile will provide a more accurate understanding of the link between stickleback differential feeding strategy and nutritional quality. My project is one of the few eco-evolutionary studies conducted in nature, using replicated whole ecosystem manipulations. The results of this study are intended to provide insight of the extent to which eco-evolutionary dynamics can mediate anthropogenic disturbance on northern lake ecosystems, such as through fish stocking. The future scope of this research project is to provide useful results to aquatic wildlife managers on the eco-evolutionary dynamics affecting fish populations whose better understanding would ensure optimal management of the resource. Indeed, the ultimate goal of the U.S. Fish & Wildlife Service for stocking lakes with threespine stickleback is to eventually introduce endemic fish species feeding on sticklebacks for recreational and sport fishing. This raises the importance of stickleback nutritional quality in connection with their diet and the prey community composition, but also the concept of trophic cascade. This type of information is important in the monitoring of fish populations and the optimized management of this aquatic resource of economic and cultural values in Alaska.