Showing papers on "Genetic algorithm published in 1979"

Geographic Variation, Speciation, and Clines.

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Macroevolution, pattern and process

Abstract: In this text, the author addresses, from a palaeobiologist's perspective, the question of whether punctuated equilibria - the view, popularized by Stephen Jay Gould among others, that species remain evolutionarily static for long periods of time, with substantial genetic changes and the development of new adaptive strategies occurring only during speciation, or gradualism - the view that large-scale changes result from continual and successive small-scale changes, offers the best account of the history of life. Coming down on the side of those who favour the model of punctuated equilibria, Stanley argues that only "quantum speciation" (rapid and radically divergent), can explain the story of life revealed in the fossil record; macroevolution, he contends, cannot be attributed to microevolutionary forces such as mutation, genetic drift and natural selection. Instead, he posits a series of processes, including species selection, phyletic drift and directed speciation, to accounnt for large-scale patterns.

Testing the Context and Extent of Host-Parasite Coevolution

Abstract: Brooks, D. R. (Department of Biology, University of Notre Dame, Notre Dame, Indiana 46556) 1979. Testing the context and extent of host-parasite coevolution. Syst. Zool. 28:299307.-Coevolution is defined as a combination of two processes: co-accommodation between host and parasite with no implication of host or parasite speciation and co-speciation, indicating concomitant host and parasite speciation. Parasite speciation in general is viewed as primarily the result of allopatric speciation processes regardless of host speciation or changes in host type. The observation that co-speciation of hosts and parasites forms a predominant pattern relates to a more general principle of biotic allopatric speciation explicit in the vicariance biogeography model, more than to an assumption that host speciation somehow causes parasite speciation. The close ecological relationship between hosts and parasites, which may be depicted using a variation of the MacArthur-Wilson island biogeography model, explains their spatial proximity at any time during which an isolating event occurs and thus may be necessary in some cases, but is not sufficient to explain parasite speciation, coevolution, or parasite phylogeny. [Parasitology; coevolution; allopatric speciation; island biogeography; vicariance biogeography; speciation.] No science can free itself from its traditions; it is a difficult matter suddenly and entirely to give up doctrines which for generations have been regarded almost as axioms, even when the erroneous character of the doctrines in question can no longer be doubted. (Arthur Looss, 1911:185.) Given the name of a parasite species, a parasitologist can tell, with a great deal of consistency, the type of host and geographical locality in which the parasite occurred. Virtually any biologist, given a species of plant or animal with which he is familiar, can also predict accurately the geographical distribution and general habitat of that species, but this has assumed greater significance with parasites because their "general habitat" is another living organism. Parasitologists have assumed that, whereas free-living organisms might be free to move from one locality or habitat to another, parasites are so dependent upon their hosts that evolutionarily they have no life of their own. Historically, parasites have often been studied in an attempt to elucidate aspects of host paleobiology (phylogeny or biogeography). Only in a few cases have hosts been utilized to examine aspects of parasite phylogeny and biogeography, but the general conclusions have been the same whether one takes the host's view or the parasite's view, namely that host and parasite phylogenies and geographical distributions are highly correlated. Those conclusions led to the formulation of several "Rules" (see Inglis, 1971) concerning host-parasite coevolu-

Sympatric speciation: a simulation model

Abstract: A model of mating and population growth dependent on competition that suggests circumstances under which sympatric speciation might occur is described. The model is similar to one in a companion paper by Rosenzweig in that a heterozygote genotype, involving a new allele, is first selected by virtue of its ability to exploit a new niche and is then eliminated through competition. The superior competitor, which eliminates the heterozygote, is the homozygote for the new allele. For this process to occur the heterozygote must be sufficiently fit to exploit and invade a new niche, but not so fit that a classical polymorphism results from heterozygous advantage. This process of speciation is most likely to occur when there are vacant niches. When and where these might occur are discussed.

Pollination ecology and speciation

Abstract: This chapter explains pollination ecology and speciation. Many of the structural changes concomitant with variation in pollination should by ordinary taxonomic judgment be considered rather insignificant, and diagnostic on the species level only. Other ones are easily considered more important, for example, the way in which filaments form an open or closed sheath in Papilionaceae. The species being considered an interbreedmg population (Poulton 1938), it is evident that the nature of breeding and pollination systems also deeply influences the speciation process. Besides specific odors or shapes and flower constancy, other characters may help set up ecological barriers promoting speciation, for instance, a pronounced daily rhythm. As a result of their preference for using floral characters, taxonomists will easily recognize speciation caused by differences in pollination systems. Pollination systems influence speciation in pollinators too.

A single locus mass-action model of assortative mating, with comments on the process of speciation

Abstract: A single locus mass-action model of assortative mating, with comments on the process of speciation

Speciation in north american field crickets: evidence from electrophoretic comparisons.

Abstract: Understanding the dynamics of the speciation process is of central importance to the study of evolution. It is of particular interest to know what changes (physiological, developmental, behavioral, ecological, chromosomal) are directly associated with the evolution of reproductive isolation, how rapidly and under what circumstances (allopatry, sympatry, etc.) such changes occur, and the relative importance of selection and stochastic factors in producing these changes. A widely accepted model of geographic speciation (Mayr, 1963a; Dobzhansky, 1970) suggests that new species arise in isolated populations through the gradual accumulation of genetic differences. It has become increasingly clear that speciation events do not always conform to this pattern (Bush, 1975b; White, 1978). Alternative models of speciation have been developed to explain observed relationships among closely related species. These include models of sympatric speciation with temporal isolation, habitat isolation, host race formation, or some combination of these (or other) factors acting to restrict gene flow (Alexander and Bigelow, 1960; Bush, 1974, 1975a; Tauber and Tauber, 1977a, b; Tauber et al., 1977). Studies of field crickets (Orthoptera: Gryllidae) have emphasized the importance of life cycle evolution in the speciation process (Bigelow, 1962; Masaki, 1965; Alexander, 1968; Harrison, 1978). From observations of closely related species of Gryllus in eastern North America, Alexander and Bigelow (1960) argued that seasonal isolation of breeding adults can provide an effective barrier to gene flow and eventually lead to speciation without geographic isolation. Here I report the results of an electrophoretic survey of genetic variation in seven species of Gryllus from North America. Relationships based on biochemical characters are significantly different from those previously established on the basis of morphology, song, distribution, and habitat. These observations provide a new framework for constructing models of speciation in the genus Gryllus.

Ecological generalism in drosophila falleni: genetic evidence.

Abstract: The idea that speciation in phytophagous insects can occur sympatrically through the formation of host races was advanced over a century ago by Benjamin Walsh (1864), who postulated that conditioned preferences for plant species may gradually become genetically reinforced. Over the years, Walsh's model has been elaborated and refined by various workers (e.g., Thorpe, 1930, 1945; Dethier, 1954; Maynard Smith, 1966; Bush, 1969, 1974; Tauber and Tauber, 1977); and sufficient conditions for sympatric speciation were formulated by Maynard Smith (1966). In Maynard Smith's model, the first step in this process is the establishment of a stable polymorphism in a heterogeneous environment in which alternative alleles are selected in different niches (Levene, 1953). If then the polymorphism is coupled with strong habitat selection and mating within the niche, sympatric speciation may occur. Despite the continued interest of evolutionists in this mode of speciation and an extensive search for evidence of its occurrence (see Mayr, 1947, 1963, and 1970 for reviews), documented cases are rare (Bush, 1974), understandably, perhaps, because the probability of witnessing speciation events is small. However, the search for species at stages preceding speciation has been more successful. Polymorphisms maintained by disruptive selection on genetically variable host plants (Hatchett and Gallun, 1970), host selection based on larval conditioning (Craighead, 1921; Cushing, 1941; Huettel and Bush, 1972; Knerer and Atwood, 1973; Wiklund, 1974; Phillips and Barnes,

Mating patterns and speciation in the fairy shrimp genus streptocephalus.

Abstract: According to a recent paradigm of the speciation process presented by Ayala (1975), geographic speciation often occurs in two stages. In the first stage isolated populations accumulate genetic differences which may reduce the genetic compatibility between populations. In the second stage the isolated populations regain sympatry. If hybrids have reduced fitness, selection favors the development of premating isolating mechanisms which prevent wasteful hybridization. This isolating mechanism is often ethological or sexual in nature (Mayr, 1963). This paradigm of the speciation process should be appropriate for many groups of organisms, but the relative importance of changes occurring in each of the two stages may differ considerably between species groups. For many pond and lake dwelling crustaceans, for example, stage two, the sympatric development of premating isolating mechanisms following geographic separation, appears to be rare. The degree to which populations differentiate during stage one of geographic speciation depends on the amount of gene flow between populations and on the differences in the selective regimes encountered by different populations. The disjunct nature of ponds and lakes should facilitate the genetic differentiation of aquatic populations by restricting gene flow and by offering many different selective regimes (Hebert, 1974). Studies of population differentiation suggest that gene flow between aquatic populations may be quite restricted. Baldi (1946), for example, found morphological differentiation between closely situated populations of both calanoid and cyclopoid copepods;

Stylidium in Arnherm Land: New Species, Modes of Speciation on the Sandstone Plateau, and Comments on Floral Mimicry

Abstract: The northeastern portion of Northern Territory, Australia, is known as Arnhem Land. Arnhem Land can be defined in various ways, but the geographical feature I wish to use is the sandstone plateau, often termed the sandstone scarp. Areas very close to the sandstone scarp are also discussed in this paper. The plateau can be said to form a large triangle lying within Oenpelli on the northwest, Nhulunbuy (Gove Peninsula) on the northeast, and Mataranka (south of Katherine) on the south. The borders of the plateau are not easily definable, because isolated tablelands away from the main scarp are numerous in places and because the lower northeastern portions of the plateau may rise only a little above the lowlands. Although cut by dramatic gorges—most notably Katherine Gorge and the gorge of the East Alligator River—the plateau generally lies at only about 300 m (or 1,000 ft). Thus it is not climatically distinct from the lowlands, as are other sandstone plateaus in the world (the Guayana highlands of South America: the mountains of Cape Province, South Africa). Reasons why the Arnhem Land sandstone plateau is nevertheless interesting with respect to speciation in angiosperms are given below.

Theoretical Models of Speciation

Abstract: Some population genetical models bearing on the question of speciation are reviewed, and a new kind of model dealing with resource competition between animals in partially reproductively isolated populations is introduced.

A graphical model of disruptive selection on offspring size and a possible case of speciation in freshwater gobies characterized by egg-size difference

Abstract: The graphical technique devised bySmith andFretwell (1974) to construct a model of the optimal offspring size was applied to the case where disruptive selection might work on offspring size. On this basis, a possible case of speciation in freshwater gobies characterized by egg-size difference was discussed.

Considerations on the evolution of qualitative multistate traits

Abstract: Simple models for the evolution of qualitative multistate traits are considered, in which the traits are permitted to evolve in time-dependent versus speciation-dependent fashion. Of particular interest are the means and variances of distances for these traits in evolutionary phylads characterized by different rates of speciation, when alternative characters are neutral with respect to fitness, and when the total number of observable characters is limited to small values. As attainable character states are increasingly restricted, mean distance (D) in a phylad decreases, regardless of whether evolution is a function of time or of rate of speciation. The ratio of mean distances in species-rich and species-poor phylads of comparable evolutionary age (DR/DP) remains near one when differentiation is proportional to time, even when attainable character states are severely restricted. DR/DP also nears one as a result of restricting character states when differentiation is proportional to rate of speciation, but the effect is not severe unless the number of character states is very small and the probability of change per speciation very large. These and other results are discussed with reference to available data sets on qualitative multistate traits.

Speciation Patterns and What They Mean

Abstract: Systematics is a multipurpose endeavour and is constantly becoming more complex. No longer are we solely concerned with describing the diversity of nature but, among, other things, we have the responsibility (and, increasingly, the capability) of organizing this data base for use by other biologists. This demand for organization requires that we interpret our data in an attempt to reconstruct a reasonable approximation of evolutionary history and relationships.