Navigating the temporal continuum of effective population size

Abstract

Effective population size, Ne, is a key evolutionary parameter that determines the levels of genetic variation and efficacy of selection. Estimation and interpretation of Ne are essential in diverse areas of evolutionary and conservation biology, ranging from assessing the evolutionary potential or extinction risk to empowering research on the genomic basis of adaptation. The diverse applications of the Ne concept resulted in largely independent methodological developments using different Ne definitions and focusing on the estimation of either contemporary or long‐term Ne. Recently, several novel approaches appeared that allow the estimation of temporal Ne trends at various parts of the temporal Ne continuum. Here, we provide an overview of the temporal aspects of Ne, asking whether the existing methods and available data provide Ne estimates for the entire temporal continuum. We outline the apparent division into contemporary and long‐term Ne existing in the literature, review Ne estimation methods across the temporal continuum and navigate the reader through it pointing to the important biological and methodological limitations inherent to the estimation procedures. Finally, we provide examples of recent research and future perspectives. We conclude that the entire temporal Ne continuum can now be inferred using several complementary approaches, bringing together contemporary and long‐term perspectives. Further rapid progress in the field is expected from the wide adoption of machine learning and transition to haplotype‐resolved population genomic data. The expected progress notwithstanding, interpretational difficulties are likely to remain, emphasising the need for a thorough understanding of the Ne theory behind the methods, their assumptions and inherent limitations.