This journal frequently contains papers that report values of F-statistics estimated from genetic data collected from several populations. These parameters, FST, FIT, and FIS, were introduced by Wright (1951), and offer a convenient means of summarizing population structure. While there is some disagreement about the interpretation of the quantities, there is considerably more disagreement on the method of evaluating them. Different authors make different assumptions about sample sizes or numbers of populations and handle the difficulties of multiple alleles and unequal sample sizes in different ways. Wright himself, for example, did not consider the effects of finite sample size. The purpose of this discussion is to offer some unity to various estimation formulae and to point out that correlations of genes in structured populations, with which F-statistics are concerned, are expressed very conveniently with a set of parameters treated by Cockerham (1 969, 1973). We start with the parameters and construct appropriate estimators for them, rather than beginning the discussion with various data functions. The extension of Cockerham's work to multiple alleles and loci will be made explicit, and the use of jackknife procedures for estimating variances will be advocated. All of this may be regarded as an extension of a recent treatment of estimating the coancestry coefficient to serve as a mea-

https://www.jstor.org/stable/pdfplus/2408641.pdf

Estimating F-statistics for the analysis of population structure.

Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

Although much biological research depends upon species diagnoses, taxonomic expertise is collapsing. We are convinced that the sole prospect for a sustainable identification capability lies in the construction of systems that employ DNA sequences as taxon 'barcodes'. We establish that the mitochondrial gene cytochrome c oxidase I (COI) can serve as the core of a global bioidentification system for animals. First, we demonstrate that COI profiles, derived from the low-density sampling of higher taxonomic categories, ordinarily assign newly analysed taxa to the appropriate phylum or order. Second, we demonstrate that species-level assignments can be obtained by creating comprehensive COI profiles. A model COI profile, based upon the analysis of a single individual from each of 200 closely allied species of lepidopterans, was 100% successful in correctly identifying subsequent specimens. When fully developed, a COI identification system will provide a reliable, cost-effective and accessible solution to the current problem of species identification. Its assembly will also generate important new insights into the diversification of life and the rules of molecular evolution.

/pdf/biological-identifications-through-dna-barcodes-2m7h08avvi.pdf

Biological identifications through DNA barcodes

So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Hybridisation is a major source of evolutionary innovation. However, several prezygotic and postzygotic factors influence its likelihood and evolutionary outcomes. Differences in mating systems can have a major effect on the extent and direction of hybridisation and introgression. In plants, epigenetic mechanisms help to stabilize hybrid genomes and contribute to reproductive isolation, but the relationship between genetic and epigenetic changes in animal hybrids is unclear. We analysed the extent of a unique case of natural hybridisation between two genetically distant mangrove killifish species with different mating systems, Kryptolebias hermaphroditus (self-fertilising) and K. ocellatus (outcrossing), and the methylation patterns of their hybrids. Hybridisation rate between the species ranged between 14% and 26%. Although co-existing parental species displayed highly distinct genetic (microsatellites and SNPs) and methylation patterns (37,000 differentially methylated cytosines), our results indicate that F1 hybrids are viable and able to backcross with parental species. Hybrids had predominantly intermediate methylation patterns (88.5% of the sites) suggesting additive effects, as expected from hybridisation between genetically distant species. Differentially methylated cytosines between hybrids and both parental species (5,800) suggest that introgressive hybridisation may play a role in generating novel genetic and epigenetic variation which could lead to species diversification. We also found a small percentage of non-additive epigenetic effects which might act as an evolutionary bet-hedging strategy and increase fitness under environmental change.

/pdf/additive-and-non-additive-epigenetic-signatures-of-8k8f6n2aer.pdf

Additive and non-additive epigenetic signatures of hybridisation between fish species with different mating systems

Hybridization phenomena in anurans have traditionally been studied through mor- phological comparisons, under the assumption that various hybrids (e.g., F,'s, backcrosses) are predictably intermediate to parental species. We critically evaluate this assumption by examining morphology in genetically categorized hybrids between the treefrogs Hyla cinerea and H. gratiosa. A total of 202 frogs from a hybridizing population in Al4bama were assayed for allozyme and mitochondrial DNA genotype and for a large suite of osteological characters. Discriminant analyses demonstrated distinct morphological separation between the genetically "pure" parental species. Morphometric analyses of genetically identified hybrids showed: 1) an extreme range of phenotypic expression within F1 and backcross classes, and 2) no apparent directional parental bias on the F1 phenotype. Had morphology alone been used as a guide, over 40 percent of the individuals with known hybrid ancestry would have been misclassified as "pure" parental species, and about 25 percent of the backcross individuals would not have been distinguished from F,'s. These results exemplify the utility of joint comparisons of morphology and genotypic constitution in studies of natural hybridization, and they emphasize the limitations inherent in describing hybrid classes solely by morphological criteria.

Categories of anuran hybrids

whether cells occurred in multispecies communities or sparsely colonized, monospecific communities at tips of Cladophora filaments. This may indicate that P enrichment at location 3.2 was sufficient to reduce interspecific competition among Cladophora epiphytes. Assay of polyP bodies enabled direct assessment of one form of P stores and provided substantial insight into cells' physiological condition. PolyP body assay can be useful in determining the autecology of algal populations and provided convenient measure for assessing critical phosphorus loads.

John C. Avise

Papers

Additive and non-additive epigenetic signatures of hybridisation between fish species with different mating systems

Categories of anuran hybrids

Morphological Divergence in Fishes: Macroevolutionary Patterns

Sexual Selection and Mating Systems