Adaptation and drift in the deep sea - investigating the evolution of diversity in a 'uniform' environment

点击翻译按钮获取中文摘要

The conservation of biodiversity is necessary to provide natural populations with the potential to respond to a changing environment, and to prevent the loss of fitness associated with lost diversity. An understanding the underlying processes is necessary to promote effective transferable management strategies. This is especially important in the marine environment where there are few obvious boundaries to gene flow. Biodiversity is lost within populations by drift & directional selection, and retained among populations by the same processes. The size of insular populations helps to determine the dominant process, since drift is stronger than selection in small populations. It is known that much natural diversity is divided among conspecific populations by these processes, but the fragmented structure of this diversity is often cryptic, especially in poorly understood environments like the deep sea. We typically define populations a priori by geographic distance and according to apparent physical boundaries. However, in addition to spatial factors, environmental characteristics can affect patterns of connectivity by affecting the rate and direction of gene flow, and this influence will vary as environments change over time. Environmental characteristics also drive local selection, and selection can maintain differences among populations even with continuing gene flow. Without knowledge about how local populations may have adapted to local environments, we remain unable to incorporate that type of biodiversity into conservation strategy, and to address its potential importance to the long-term survival of species. Understanding the function and value of biodiversity requires a better understanding of the interacting processes of selection and drift leading to its evolution and loss. While much of the relevant theory is well established, empirical data are required to test theory and determine how environmental factors interact with evolutionary processes in natural systems. In this study we will employ second generation sequencing technologies to investigate how environmental factors are associated with the evolution of population structure and speciation in the deep sea, at both neutral and functional loci. The particular focus will be on habitat depth and isolation by distance, however other environmental factors will be quantified at collection sites based on data collected from the same sites during the recent ECOMAR consortium study (during which samples for the proposed study were collected). The study species will be fish in the genus Coryphaenoides, a specious genus of deep demersal fishes, some of which are commercially important fisheries species (including the primary focal species in this study, C. rupestris). Initial studies have shown phylogenetic lineage division correleted to habitat depth. Other work has indicated selection at genes associated with adaptation to pressure in some of these species. Two focal Coryphaenoides species will be investigated in a comparative population genomics study. These species, C. rupestris and C. brevibarbis are sympatric, but the former is found at shallower depths than the latter. We will test hypotheses about how habitat division by depth or other characteristics (e.g. current systems or geographic distance) may determine the evolution of intra- and inter-specific diversity (including among multiple habitat-specialist species in the genus using an extended phylogenetic assessment) both by drift (through differential environmental pressures associated with dispersal) and by selection. Greater connectivity is predicted in the abyssal habitat, which may lead to larger effective population sizes and facilitate adaptive evolution. Taken together these data will provide novel insight into the interactive role of drift and selection during the evolution of diversity, and transferable inference about how diversity is structured in the deep sea.