It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.

Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory

1. From Type III pneumococci a biologically active fraction has been isolated in highly purified form which in exceedingly minute amounts is capable under appropriate cultural conditions of inducing the transformation of unencapsulated R variants of Pneumococcus Type II into fully encapsulated cells of the same specific type as that of the heat-killed microorganisms from which the inducing material was recovered. 2. Methods for the isolation and purification of the active transforming material are described. 3. The data obtained by chemical, enzymatic, and serological analyses together with the results of preliminary studies by electrophoresis, ultracentrifugation, and ultraviolet spectroscopy indicate that, within the limits of the methods, the active fraction contains no demonstrable protein, unbound lipid, or serologically reactive polysaccharide and consists principally, if not solely, of a highly polymerized, viscous form of desoxyribonucleic acid. 4. Evidence is presented that the chemically induced alterations in cellular structure and function are predictable, type-specific, and transmissible in series. The various hypotheses that have been advanced concerning the nature of these changes are reviewed.

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Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III

http://aerg.canberra.edu.au/library/sex_general/2002_Devlin_Nagahama_sex_determination_in_fish_review.pdf

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

This offers the first broad treatment of the city in both its historic and its contemporary aspects. For distinction, entertainment, information, scholarship, and general human interest [this] is one of the most distinguished books (Forum). Index; photographs. "

The Culture of Cities

Hybridization may influence evolution in a variety of ways. If hybrids are less fit, the geographical range of ecologically divergent populations may be limited, and prezygotic reproductive isolation may be reinforced. If some hybrid genotypes are fitter than one or both parents, at least in some environments, then hybridization could make a positive contribution. Single alleles that are at an advantage in the alternative environment and genetic background will introgress readily, although such introgression may be hard to detect. ‘Hybrid speciation’, in which fit combinations of alleles are established, is more problematic; its likelihood depends on how divergent populations meet, and on the structure of epistasis. These issues are illustrated using Fisher’s model of stabilizing selection on multiple traits, under which reproductive isolation evolves as a side-effect of adaptation in allopatry. This confirms a priori arguments that while recombinant hybrids are less fit on average, some gene combinations may be fitter than the parents, even in the parental environment. Fisher’s model does predict heterosis in diploid F1s, asymmetric incompatibility in reciprocal backcrosses, and (when dominance is included) Haldane’s Rule. However, heterosis arises only when traits are additive, whereas the latter two patterns require dominance. Moreover, because adaptation is via substitutions of small effect, Fisher’s model does not generate the strong effects of single chromosome regions often observed in species crosses.

The role of hybridization in evolution

For everyday anglers, armchair enthusiasts, and serious students, Hubbs and Lagler's text remains the definitive work in the identification and study of the fishes of this important freshwater region. Organized by fish family, with sections on waters of the Great Lakes region, zoogeography, field study and collection, preservation of fishes for study, fish identification, anatomy, terminology, and more, "Fishes of the Great Lakes Region" is comprehensive in its scope and breadth of information-truly the classic book on Great Lakes fishes. The book also documents a half century of changes in fish population in the region that have resulted from pollution, development, and the introduction of nonnative species. This edition will thus inspire future generations of anglers and students to take a fresh look at one of our most important fauna.

Fishes of the Great Lakes Region

Fishes of the Great Lakes Region.

THE Jordan school of ichthyology, in which I was nurtured, held steadfastly to the view that the lines between fish species are almost never crossed. This mistaken idea was perhaps in part a holdover of the pre-Darwinian concept of the immutability of species, but was, more pointedly, a reaction against the tendency of some European ichthyologists to explain as hybrids specimens that proved difficult to identify. This view that there is little or no natural hybridization between fish species may be further attributed to the circumstance that systematic ichthyology in America from about 1890 to 1920 was still essentially in the exploratory and species-naming stage, and dealt chiefly with marine fishes, which, as I shall point out, hybridize much less often than do freshwater fishes. Early in my ichthyological career I encountered evidence that fish species do cross in nature, at times in considerable frequency. The analysis of such hybridization has ever since engaged my attention, in so far as other activities would allow. This report lays particular emphasis on the researches that I have conducted during the past thirty-five years, largely with the collaboration of my wife and of several students and colleagues, to all of whom I pay tribute. They might all appear as co-authors of this report. The studies continue. During the first ten years of my intensive studies of the freshwater fishes of North America, from 1919 to 1929, I gathered strong circumstantial indications that the species lines are rather often crossed in nature, and during the following fifteen years, from 1929 to 1944, I was able, with the constant aid of Mrs. Hubbs, to confirm these indications, not only by the accumulation of much more circumstantial evidence, in part subjected to critical statistical analysis, but also by breeding experiments in the aquarium of the Division of Fishes of the then new Museum of Zoology at the University of Michigan.

https://www.jstor.org/stable/pdfplus/2411933.pdf

Carl L. Hubbs

Papers

Fishes of the Great Lakes Region

Fishes of the Great Lakes Region.

Hybridization between Fish Species in Nature

Fishes of the Great Lakes Region

Fishes of the Great Lakes Region