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

Extreme inbreeding is expected to reduce the incidence of hybridization, serving as a prezygotic barrier. Mangrove rivulus is a small killifish that reproduces predominantly by self-fertilization, producing highly homozygous lines throughout its geographic range. The Bahamas and Caribbean are inhabited by two highly diverged phylogeographic lineages of mangrove rivulus, Kryptolebias marmoratus and a 'Central clade' closely related to K. hermaphroditus from Brazil. The two lineages are largely allopatric, but recently were found in syntopy on San Salvador, Bahamas, where a single hybrid was reported. To better characterize the degree of hybridization and the possibility of secondary introgression, here we conducted a detailed genetic analysis of the contact zone on San Salvador. Two mixed populations were identified, one of which contained sexually mature hybrids. The distribution of heterozygosity at diagnostic microsatellite loci in hybrids showed that one of these hybrids was an immediate offspring from the K. marmoratus x Central clade cross, whereas the remaining five hybrids were products of reproduction by self-fertilization for 1-3 generations following the initial cross. Two hybrids had mitochondrial haplotypes of K. marmoratus and the remaining four hybrids had a haplotype of the Central clade, indicating that crosses go in both directions. In hybrids, alleles of parental lineages were represented in equal proportions suggesting lack of recent backcrossing to either of the parental lineages. However, sympatric populations of two lineages were less diverged than allopatric populations, consistent with introgression. Results are discussed in terms of applicability of the biological species concept for isogenic, effectively clonal, organisms.

Extensive hybridization and past introgression between divergent lineages in a quasi-clonal hermaphroditic fish: Ramifications for species concepts and taxonomy.

In the Light of Evolution: Volume VI: Brain and Behavior

Mangrove killifishes of the genus Kryptolebias have been historically classified as rare because of their small size and cryptic nature. Major gaps in distribution knowledge across mangrove areas, particularly in South America, challenge the understanding of the taxonomic status, biogeographical patterns and genetic structuring of the lineages composing the self-fertilizing "Kryptolebias marmoratus species complex." In this study, the authors combined a literature survey, fieldwork and molecular data to fill major gaps of information about the distribution of mangrove killifishes across western Atlantic mangroves. They found that selfing mangrove killifishes are ubiquitously distributed across the Caribbean, Central and South American mangroves and report 14 new locations in South America, extending the range of both the "Central clade" and "Southern clade" lineages which overlap in the Amazon. Although substantial genetic differences were found between clades, the authors also found further genetic structuring within clades, with populations in Central America, north and northeast Brazil generally showing higher levels of genetic diversity compared to the clonal ones in southeast Brazil. The authors discuss the taxonomic status and update the geographical distribution of the Central and Southern clades, as well as potential dispersal routes and biogeographical barriers influencing the distribution of the selfing mangrove killifishes in the western Atlantic mangroves.

Filling the gaps: phylogeography of the self-fertilizing Kryptolebias species (Cyprinodontiformes: Rivulidae) along South American mangroves

https://www.cell.com/trends/genetics/pdf/S0168-9525(02)02646-X.pdf

Captivating Life: A Naturalist in the Age of Genetics

One of the fundamental assumptions in the multi-locus approach to phylogeographic studies is that unlinked loci have independent genealogies. For this reason, congruence among gene trees from unlinked loci is normally interpreted as support for the existence of external forces that may have concordantly shaped the topology of multiple gene trees. However, it is also important to address and quantify the possibility that gene trees within a given species are all inherently constrained to some degree by their shared organismal pedigree, and thus in this strict sense are not entirely independent. Here we demonstrate by computer simulations that gene trees from a shared pedigree tend to display higher topological concordance than do gene trees from independent pedigrees with the same demographic parameters, but we also show that these constraining effects are normally minor in comparison to the much higher degree of topological concordance that can routinely emerge from external phylogeographic shaping forces. The topology-constraining effect of a shared pedigree decreases as effective population size increases, and becomes almost negligible in a random mating population of more than 1,000 individuals. Moreover, statistical detection of the pedigree effect requires a relatively large number of unlinked loci that far exceed what is typically used in current phylogeographic studies. Thus, with the possible exception of extremely small populations, multiple unlinked genes within a pedigree can indeed be assumed, for most practical purposes, to have independent genealogical histories.

/pdf/does-organismal-pedigree-impact-the-magnitude-of-topological-477i4oiz8s.pdf

John C. Avise

Papers

Extensive hybridization and past introgression between divergent lineages in a quasi-clonal hermaphroditic fish: Ramifications for species concepts and taxonomy.

In the Light of Evolution: Volume VI: Brain and Behavior

Filling the gaps: phylogeography of the self-fertilizing Kryptolebias species (Cyprinodontiformes: Rivulidae) along South American mangroves

Captivating Life: A Naturalist in the Age of Genetics

Does organismal pedigree impact the magnitude of topological congruence among gene trees for unlinked loci