Natural populations can generally have a strong spatial structure and inhabit heterogeneous and dynamic environments which impact their ecology, genetics and evolution. However, theoretical investigations in those fields frequently neglect the importance of heterogeneity and dynamics of the environment and commonly assume a homogeneous environment.
In theoretical studies, models of migration are often used without justification even if they can have drastic consequences on the prediction of the ecology, genetic and evolution of metapopulation. When populations differ in productivity, two main models of migration type that characterizes the rate of individual exchanges between populations can be found in the literature. They are the source-sink and the balanced migration model. For the migration distance, most of theoretical models use either extreme models of isolation by distance: the stepping-stone model and island model or a restricted family of dispersal distance distributions. In order to delineate the conditions under which some metapopulation structures are more likely to emerge, the first section of this follow-up research project aims to model the evolution of migration rate and distance in a heterogeneous metapopulation considering various forms of habitats distributions, heterogeneity and fragmentation.
Environmental heterogeneity by creating gradients such as prevailing winds, ocean and river currents can modify or constrain species migration patterns. Similarly, the structure of the environment can form dendritic networks (river networks, watersheds and cave ecosystems) in which populations can be either strongly locally connected or disconnected. Studies of a variety of empirical systems have shown that island and isolation-by-distance metapopulation models with homogeneous re-colonization patterns cannot capture the dynamics, nor the genetic structure, of such metapopulations. They all directly affect the genetic forces within a metapopulation and thus the genetic diversity and the evolutionary potential of populations. The second part of this research project aims to quantify the impact of asymmetric migration pattern induced by environment heterogeneity on gene flow and the resulting genetic diversity.
During the millions years of species life-time, repeated events of disconnection and reconnection have occurred and have cyclically modified habitats and thus species distribution (isolated refugia during glaciations, the reduction of sea levels allowing migration events, fragmentation and fusion of great lake basins, periodic isolation and fusion of islands). Those short and long-term environmental cycles in which habitat alternately contracts (with fragmentation) and expands (with defragmentation) have shaped the nowadays species diversity and distributions. Nowadays anthropogenic disturbance (e.g. urbanization, agriculture) and climate change also play an important role in modifying the connectivity among populations, when some species suffer from habitat reduction and fragmentation, others experience habitat and population’s expansion. Process described above creates event of connection and disconnection that can occur cyclically. The temporal change in connectivity has been poorly explored even if they are expected to strongly contribute to the nowadays observed macro-evolutionary and macro-ecological patterns of species diversity. Thus how long and short environmental cycles can affect the genetic signature of populations remain an open question. This is the subject of the third and last part of this research proposal.
The proposed research aims to go further in the understanding and quantifying the dynamics of genes across a wide range of situations in heterogeneous landscapes. It will provide the description and the quantification of gene diversity and the fixation in neutral or adaptive environments. Results are expected to make a crucial contribution in the estimation of genetic variance in heterogeneous and dynamic environments.The expected results are directly relevant to conservation (e.g. estimation of metapopulation viability, re-colonization potential, genetic diversity), to the evolution of populations (e.g. adaptation to novel environment, coevolutionary dynamics, evolution of marginal population) and guidelines for the management and conservation of natural populations.