Recent observations on rates of mutation, recombination, and random genetic drift highlight the dramatic ways in which fundamental evolutionary processes vary across the divide between unicellular microbes and multicellular eukaryotes. Moreover, population-genetic theory suggests that the range of variation in these parameters is sufficient to explain the evolutionary diversification of many aspects of genome size and gene structure found among phylogenetic lineages. Most notably, large eukaryotic organisms that experience elevated magnitudes of random genetic drift are susceptible to the passive accumulation of mutationally hazardous DNA that would otherwise be eliminated by efficient selection. Substantial evidence also suggests that variation in the population-genetic environment influences patterns of protein evolution, with the emergence of certain kinds of amino-acid substitutions and protein-protein complexes only being possible in populations with relatively small effective sizes. These observations imply that the ultimate origins of many of the major genomic and proteomic disparities between prokaryotes and eukaryotes and among eukaryotic lineages have been molded as much by intrinsic variation in the genetic and cellular features of species as by external ecological forces.

Genetic management of fragmented populations involves the application of evolutionary genetic theory and knowledge to alleviate problems due to inbreeding and loss of genetic diversity in small population fragments. Populations evolve through the effects of mutation, natural selection, chance (genetic drift), and gene flow. Large outbreeding sexually reproducing populations typically contain substantial genetic diversity, while small populations typically contain reduced levels. Genetic impacts of small population size on inbreeding, loss of genetic diversity and population differentiation are determined by the genetically effective population size, which is usually much smaller than the number of individuals.

A major aim of evolutionary biology is to explain the respective roles of adaptive versus non-adaptive changes in the evolution of complexity. While selection is certainly responsible for the spread and maintenance of complex phenotypes, this does not automatically imply that strong selection enhances the chance for the emergence of novel traits, that is, the origination of complexity. Population size is one parameter that alters the relative importance of adaptive and non-adaptive processes: as population size decreases, selection weakens and genetic drift grows in importance. Because of this

Abstract Fisher’s mechanism is central to sexual selection theories, where mate choice generates a genetic correlation between male trait and female preference alleles, driving the coevolution of the trait and preference with positive feedback. However, how Fisher’s mechanism operates in finite populations remains unclear, as sexual selection can interact with genetic drift, influencing both trait-preference correlation and allele frequencies. By using population genetic models, this study addresses the gap in our understanding of interactions between fundamental evolutionary forces. We show that more frequent recombination increases trait-preference correlations in infinitely large populations, unless a positive correlation initially exists. In finite populations, interactions between sexual selection and drift elevate trait-preference correlation when the male trait is rare but reduce the correlation when the trait is common, potentially making it negative when recombination is rare or population size is small. Also, these interactions tend to slow the spread of the male trait while promoting the evolution of preferences. These results differ from the Hill-Robertson effect under natural selection due to two key factors: mate choice generates positive linkage disequilibrium, and the strength of indirect selection on preferences increases with linkage disequilibrium. The fixation of trait and preference alleles is positively correlated. This correlation peaks at intermediate

mobility, that occur in fragmented habitats, where there are long distances between populations, and when there are small population sizes. Mobility plays In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent allele frequencies and therefore can be considered a single effective population. It has been shown that it takes only "one migrant per generation" to prevent populations In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent allele frequencies and therefore can be considered a single effective population. It has been shown that it takes only "one migrant per generation" to prevent populations from diverging due to drift. Populations can diverge due to selection even when they are exchanging alleles, if the selection pressure is strong enough. Gene flow is an important mechanism for transferring genetic diversity among populations. Migrants change the distribution of genetic diversity among populations, by modifying allele frequencies (the proportion of members carrying a particular variant of a gene). High rates of gene flow can reduce the genetic differentiation between the two groups, increasing homogeneity. Gene flow has been thought to constrain speciation and prevent range expansion by combining the gene pools of the groups, thus preventing the development of differences in genetic variation that would have led to differentiation and adaptation for this reason. In some cases dispersal resulting in gene flow may also result in the addition of novel genetic variants under positive selection to the gene pool of a species or population (adaptive introgression. ) There are a number of factors that affect the rate of gene flow between different populations. Gene flow is expected to be lower in species that have low dispersal or mobility, that occur in fragmented habitats, where there are long distances between populations,…