THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Evolution and measurement of species diversity

A high number of tree species, low density of adults of each species, and long distances between conspecific adults are characteristic of many low-land tropical forest habitats. I propose that these three traits, in large part, are the result of the action of predators on seeds and seedlings. A model is presented that allows detailed examination of the effect of different predators, dispersal agents, seed-crop sizes, etc. on these three traits. In short, any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents. Either event will lead to more space in the habitat for other species of trees, and therefore higher total number of tree species, provided seed sources are available over evolutionary time. As one moves from the wet lowland tropics to the dry tropics or temperate zones, the seed and seedling predators in ...

Herbivores and the Number of Tree Species in Tropical Forests

The primary rationale for the use of phylogenetically based statistical methods is that phylogenetic signal, the tendency for related species to resemble each other, is ubiquitous. Whether this assertion is true for a given trait in a given lineage is an empirical question, but general tools for detecting and quantifying phylogenetic signal are inadequately developed. We present new methods for continuous-valued characters that can be implemented with either phylogenetically independent contrasts or generalized least-squares models. First, a simple randomization procedure allows one to test the null hypothesis of no pattern of similarity among relatives. The test demonstrates correct Type I error rate at a nominal α = 0.05 and good power (0.8) for simulated datasets with 20 or more species. Second, we derive a descriptive statistic, K, which allows valid comparisons of the amount of phylogenetic signal across traits and trees. Third, we provide two biologically motivated branch-length transformat...

/pdf/testing-for-phylogenetic-signal-in-comparative-data-3lvcin7t3t.pdf

Testing for phylogenetic signal in comparative data: behavioral traits are more labile.

The genetic effects of pleistocene ice ages are approached by deduction from paleoenvironmental information, by induction from the genetic structure of populations and species, and by their combination to infer likely consequences. (1) Recent palaeoclimatic information indicate rapid global reversals and changes in ranges of species which would involve elimination with spreading from the edge. Leading edge colonization during a rapid expansion would be leptokurtic and lead to homozygosity and spatial assortment of genomes. In Europe and North America, ice age contractions were into southern refugia, which would promote genome reorganization. (2) The present day genetic structure of species shows frequent geographic subdivision, with parapatric genomes, hybrid zones and suture zones. A survey of recent DNA phylogeographic information supports and extends earlier work. (3) The grasshopperChorthippus parallelusis used to illustrate such data and processes. Its range in Europe is divided on DNA sequences into five parapatric races, with southern genomes showing greater haplotype diversity — probably due to southern mountain blocks acting as refugia and northern expansion reducing diversity. (4) Comparison with other recent studies shows a concordance of such phylogeographic data over pleistocene time scales. (5) The role that ice age range changes may have played in changing adaptations is explored, including the limits of range, rapid change in new invasions and refugial differentiation in a variety of organisms. (6) The effects of these events in causing divergence and speciation are explored usingChorthippusas a paradigm. Repeated contraction and expansion would accumulate genome differences and adaptations, protected from mixing by hybrid zones, and such a composite mode of speciation could apply to many organisms.

https://www.fc.up.pt/mestr_biodiv/aulas/hewitt_1996.pdf

Some genetic consequences of ice ages, and their role in divergence and speciation

The origin and evolution of species and host racesl in certain phytophagous insect groups have long been a source of disagreement among evolutionary biologists. The rapid establishment of new host races by some stenophagous insects on introduced plants, as well as various other aspects of their biology and distribution, has led several biologists to suggest that new host races and species may arise sympatrically (Brues, 1924; Thorpe, 1930; Smith, 1941; Haldane, 1959; Alexander and Bigelow, 1960; Bush, 1966). Others regard geographic isolation as a prerequisite for speciation in all groups of sexually reproducing animals (for examples see Mayr, 1963). The difficulty in resolving whether either one or the other, or both, modes of speciation may occur in these insects stems directly from the paucity of detailed studies of wild stenophagous insects. Our information on these insects has been derived primarily from studies made over the past hundred years on a few economically important plant pests. One such group that has received particular attention is the Holarctic and Neotropical genus Rhagoletis whose larvae feed within the developing fruits of many plant species such as cherries, blueberries, apples, currants, rose hips, walnuts, and tomatoes. The objective of this paper is to point out how the biological attributes of these flies may have permitted new forms to arise rapidly in the absence of geographical barriers to gene flow.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1969.tb03508.x

Sympatric host race formation and speciation in frugivorous flies of the genus rhagoletis (diptera, tephritidae).

To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and drift, we estimated rates of speciation and rates of chromosomal evolution in 225 genera of vertebrates. Rates of speciation were estimated by considering the number of living species in each genus and the fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were one-fifth those in mammalian genera. Genera with high karyotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution, and strong individual territoriality (e.g., some rodents). This is consistent with the above hypothesis regarding the evolutionary importance of demes.

https://www.pnas.org/content/pnas/74/9/3942.full.pdf

Rapid speciation and chromosomal evolution in mammals.

Benjamin Walsh (174) was probably the first to seriously consider the status of insects that morphologically resemble one another so closely that they can only be distinguished on the basis of subtle biological traits such as preference for or the ability to survive on different hosts. Most of Walsh's "phytophagic varieties" now fall under the rubric "biotype," a term employed primarily by applied biologists to distinguish populations of insects and other organisms whose differences are due to a very wide range of underlying causes. The significance of biotypes for both evolutionary and applied fields is not general­ ly appreciated. Our objective is to integrate the current concepts used by evolutionary biologists to describe various patterns and levels of differentiation in insects with the views of the applied biologist. A classification system of insect biotypes, based on the mechanisms underlying their differentiation, is outlined below. We also consider the significance of biotypes in adaptation, speciation, and pest management.

An Evolutionary and Applied Perspective of Insect Biotypes

Recent research on natural host races and sympatric sister species, comparative phylogenetic analyses, laboratory experiments and theoretical models has greatly strengthened the case for sympatric speciation. Traits evolving in response to divergent selection experienced by subpopulations adapting to different habitats provide sufficient intrinsic premating isolation for sympatric speciation to occur. The initiation of speciation through a habitat shift in animals which mate within a preferred habitat (such as many phytophagous and parasitic invertebrates and some vertebrates, including birds) requires few genetic changes.

/pdf/sympatric-speciation-in-animals-new-wine-in-old-bottles-4xug01j2d7.pdf

Sympatric speciation in animals: new wine in old bottles.

It has been proposed that true fruit flies in the Rhagoletis pomonella species group speciate sympatrically (that is, in the absence of geographic isolation) as a consequence of shifts to previously unexploited host plants1,2. Because Rhagoletis larvae are host-specific fruit parasites and mate selection in these flies is directly coupled to host-plant recognition3–5, variation for larval survivorship and host preference traits can act as genetically based barriers to gene flow. This reduction in gene flow results in the sympatric divergence of fly populations adapted to alternative hosts. The shift of R. pomonella from its native host hawthorn (Crataegus spp.) to domestic apples (Mains pumila) in eastern North America in the past 200 years6 provides an opportunity to determine whether host specialization is sufficient to differentiate populations without earlier periods of geographic isolation. We report finding genetic differentiation between co-occurring hawthorn and apple populations of R. pomonella at a field site near Grant, Michigan. The result confirms that hawthorn and apple flies represent partially reproductively isolated 'host races' and is consistent with a sympatric mode of divergence for these flies.

/pdf/genetic-differentiation-between-sympatric-host-races-of-the-8zldi3z8a6.pdf

Guy L. Bush

Papers

Sympatric host race formation and speciation in frugivorous flies of the genus rhagoletis (diptera, tephritidae).

Rapid speciation and chromosomal evolution in mammals.

An Evolutionary and Applied Perspective of Insect Biotypes

Sympatric speciation in animals: new wine in old bottles.

Genetic differentiation between sympatric host races of the apple maggot fly Rhagoletis pomonella