Showing papers in "The American Naturalist in 1971"
TL;DR: It is shown that the magnitude of any permanent change in the variance due to selection must decrease as the number of loci involved increases and that, when the numberof loci is large, it is likely to be much less than the temporary change due to disequilibrium.
Abstract: If a metric character is determined by an effectively infinite number of loci, selection cannot cause any permanent change in the genetic variance but will cause a temporary change which is rapidly reversed when selection ceases. This change is due entirely to the correlation between pairs of loci which is induced by selection; the correlation is negative, leading to a reduction in the genetic variance under stabilizing or directional selection, and is positive, leading to an increase in the variance under disruptive selection. When selection ceases, the correlation rapidly disappears as joint equilibrium at pairs of loci is reestablished, and the variance returns to its original value. An expression is derived for the predicted amount of change in the genetic variance due to disequilibrium in the absence of linkage. The change is likely to be small under selection intensities found under natural conditions, but it may be appreciable under intense artificial selection. This limiting result shows that the ...
874 citations
TL;DR: Paleontological evidence suggests that the mountains were colonized by a group of species during the Pleistocene when the climatic barriers that currently isolate them were abolished, and subsequent to isolation of the mountains, extinctions have reduced the faunal diversity to present levels.
Abstract: An analysis of the distribution of the small boreal mammals (excluding bats) on isolated mountaintops in the Great Basin led to the following conclusions: 1. The species-area curve is considerably steeper (z = .43) than the curves usually obtained for insular biotas. 2. There is no correlation between number of species of boreal mammals and variables which are likely to affect the probability of colonization, such as distance between island and mainland, distance between islands, and elevation of intervening passes. Apparently the present rate of immigration of boreal mammals to isolated mountains is effectively zero. 3. Paleontological evidence suggests that the mountains were colonized by a group of species during the Pleistocene when the climatic barriers that currently isolate them were abolished. 4. Subsequent to isolation of the mountains, extinctions have reduced the faunal diversity to present levels. Probability of extinction is inversely related to population size and, therefore, is influenced b...
711 citations
TL;DR: Data indicating more precise vertical habitat selection in tropical habitats are more equivocal are discussed, and suggestions of increased microspatial heterogeneity in homogeneous tropical habitats as compared with similar temperate areas, and distinctions between standing crop diversity and existence energy diversity regressed on foliage height diversity are not substantiated.
Abstract: Data on avian community structure and vegetation structure for Illinois, Panama, Texas, and Bahama study areas are discussed. Bird species diversity is linearly related to foliage height diversity and sigmoidally related to the percent vegetation cover. Under some circumstances, the volume of vegetation in addition to the layering and distribution among the layers is important as a predictor of bird species diversity. Historical factors seem to be of importance in some phases of the evolution of avian diversity. Horn's Rh, an inverse measure of overlap, applied to tropical and temperate bird and vegetation data, and other considerations indicate that horizontal habitat selection is more precise in mature tropical habitats than in temperate or less mature tropical habitats. These differences are attributed to restriction of species to narrower adaptive peaks in diverse faunas than in less diverse ones. Data indicating more precise vertical habitat selection in tropical habitats are more equivocal. Earlier ...
407 citations
TL;DR: In this article, a scale factor that expresses differences in size between comparable animals of the same shape on two or more regressions of constant α is defined, and a similarity criterion s can be extracted from the two b-values (s = [b1/b2]1/(1-α) ).
Abstract: The coefficient b of the power function y = bxa has long been misinterpreted as a measure of size-independent differences between regressions. Just the opposite is true; b is a scale factor that expresses differences in size between comparable animals of the same shape on two or more regressions of constant α. When α is invariant for two regressions, a similarity criterion s can be extracted from the two b-values (s = [b1/b2]1/(1-α)); s measures the relative difference in size at which animals on the two curves have the same shape. If this calculated difference equals the observed difference in size, then the transposition (shift of regression line without change of slope) occurred in order to maintain geometric similarity in a new size range. I present examples of geometric similarity via transposition for body shape in gulls, brain weight in felids and primates, tooth shape in canids, skull form in bovids, the evolution of Gryphaea, the growth of horses, and differences between local races of lobsters a...
283 citations
TL;DR: A case is made for plant phenolics as defensive substances by considering their structural diversity, concentration, alteration upon infection, and mode of action.
Abstract: Plant phenolics are a structurally diverse group of compounds synthesized by all higher plants. The toxicity of phenolics and the products of their hydrolysis and oxidation has long been appreciated, and has implicated this group of natural products with plant defense. Unfortunately, much of the literature relating phenolics to plant defense is published in sources rarely consulted by evolutionists or ecologists. The purpose of this paper is to make a case for plant phenolics as defensive substances by considering their structural diversity, concentration, alteration upon infection, and mode of action. Correlations between ecogeographical and ecological parameters and phenolic profiles are discussed in light of the putative defensive role of phenolics, and additional correlations are predicted.
247 citations
TL;DR: A statistical method is developed for estimating the number of gene differences and evolutionary time of a pair of species from electrophoretic data on protein identity, and it is shown that the evolutionary time for a couple of nonsibling species in Drosophila is on the average three times longer than that for a Pair of sibling species.
Abstract: A statistical method is developed for estimating the number of gene differences and evolutionary time of a pair of species from electrophoretic data on protein identity This method is applied to the Drosophila data available It is shown that the evolutionary time for a pair of nonsibling species in Drosophila is on the average three times longer than that for a pair of sibling species It is also shown, under certain assumptions, that pairs of recent sibling species differ in about one to two amino acids per protein, and it is estimated that 500,000 years were required to establish such a difference
237 citations
TL;DR: An optimization model has been developed for the analysis of food selection behavior and generates hypotheses concerning conditions for "predator switching" and other predator strategies.
Abstract: An optimization model has been developed for the analysis of food selection behavior. The model determines the numbers and typed of prey species consumed given predator preferences and prey availability. Preferences are expressed as an ordinal ranking of all possible prey combinations. The model generates hypotheses concerning conditions for "predator switching" and other predator strategies.
218 citations
TL;DR: In this article, the authors examined regional, environmental, and temporal gradients of species diversity in upland forests of the western Great Lakes area and found that diversity increased across time in pioneer forests on xeric sites.
Abstract: 1. Regional, environmental, and temporal gradients of species diversity were examined for upland forests of the western Great Lakes area. Tree, shrub, and herb data for 353 stands were analyzed with emphasis given to community processes regulating diversity levels. 2. The relationship between commonly employed diversity indices was examined. Dominance was shown to be highly related to equitability diversity. Types of diversity other than species-based measures were suggested. 3. A great significance was attached to changes in diversity across time and space. Diversity increased across time in pioneer forests on xeric sites. In successional forests diversity increased through time but decreased in the climax stage. This pattern was interpreted in terms of the capability of terminal species to monopolize environmental requisites. A time-space-diversity model was developed and its implications discussed in relation to recent ecological hypotheses on diversity changes with succession and environmental stress....
194 citations
TL;DR: Working hypotheses and lines of research are pointed out in the areas of metabolism during anhydrobiosis, (2) biochemical adaptations to desiccation, (3) morphological adaptations to Desiccation.
Abstract: The reversible cessation of metabolism and growth is a unique biological state. There are two types of organisms which are normally capable of of entering this state (cryptobiosis): (1) propagules of certain organisms and (2) certain rotifers, tardigrades, and nematodes. The latter group of organisms offer a unique opportunity to study the discontinuity of life processes, uncomplicated by simultaneous developmental processes and complex endogenous factors such as those responsible for the maintenance of dormancy. Working hypotheses and lines of research are pointed out in the areas of (1) metabolism during anhydrobiosis, (2) biochemical adaptations to desiccation, (3) morphological adaptations to desiccation.
170 citations
TL;DR: Testable predictions for species with many sex loci indicate that prolonged close inbreeding should yield diploid males; that diploids in outbred lines should be extremely rare compared with haploid intersexes; and that feminized borders, due to complementation between different sex alleles, should often occur between genetically different blocks of tissue in gynoid males.
Abstract: Sex determination in haplo-diploid animals has been explained by P. W. Whiting's (1939) single-locus, multiple-allele scheme, which is applicable to two cases only, or by da Cunha and Kerr's (1957) genic-balance scheme, a more general hypothesis. I propose a general hypothesis of sex determination in haplo-diploidy, based on Snell's (1935) multiple-factor suggestion. This multiple-locus hypothesis is that, in haplo-diploid species, sex is determined by a number of loci. Females are heterozygous at one or more loci, while males are homozygous or hemizygous at all sex loci. At the molecular level, this effect might be due to female-determining properties of heteropolymers formed betwen the products of different alleles at any sex locus; homopolymers or heteropolymers between products of different loci are not formed or lack sex-determining activity. Haploid intersexes could arise from mutants that form active homopolymers or active heteropolymers with products of other loci. Diploid intersexes should be ext...
169 citations
TL;DR: The proposal of Gadgil and Bossert (1970) to amend Cole's (1954) conclusion regarding the relative merit of perennial compared to annual reproduction is questioned.
Abstract: I would like to question the proposal of Gadgil and Bossert (1970) to amend Cole's (1954) conclusion regarding the relative merit of perennial compared to annual reproduction. Focusing on the maximum advantage of iteroparity (allowing infinite survivorship), Cole concluded that \"for an annual species, the absolute gain in intrinsic growth which could be achieved by changing to the perennial reproductive habit would be exactly equivalent to adding one individual to the average litter size.\" Gadgil and Bossert (1970, p. 11) reasoned that Cole's \"assumption of no mortality beyond age one is quite reasonable. However, the assumption of no mortality in the course of the first year is not.\" Including such a survivorship factor, they specify for an annual species, 1 =11 bi e-84, relating survivorship during the first year (11), average litter size in the first year (b1), and the intrinsic rate of natural increase (m). This is reduced from a more general formulation by Lotka (1925). Solving for the rate of increase, m = In (11 * bi). For a perennial species with no mortality after the first year and constant litter size (b1) for all ages (x),
TL;DR: A model describing the development of polygynous mating systems suggests that bigamous matings should be the commonest mating type and pair-bonding in monogamous species of birds is in keeping with this prediction.
Abstract: We have elaborated a model describing the development of polygynous mating systems. The bases of the model are measures of fertility and survival of adult females and their offspring, respectively, as functions of increasing harem size. Our data indicate that an adult female makes her greatest contribution to the next generation (is most fit) when she is monogamous. A second curve describing the fitness of the harem master with increasing harem size indicates that he is maximally fit when he maintains a harem of two or three females. Consideration of the optimal mating system for each sex leads to predictions concerning the types of behavior that would allow each sex to realize its optimal mating system. Females should react aggressively toward other females and solicit the attentions of the male. The aggressive behavior of the female should be linked with her reproductive state. Pregnant females will be more aggressive than nonpregnant females. The male, on the other hand, should actively recruit females...
TL;DR: In this paper, the authors examined the manner in which a population as a whole differentiated in time, as well as the distributional pattern of gene frequencies in the population, and found that the particular patterns of highs and lows of gene frequency over a geographic area became established quickly and persisted for a large number of generations.
Abstract: Wright's isolation-by-distance model was investigated using techniques of simulation on a digital computer. We examined the manner in which a population as a whole differentiated in time, as well as the distributional pattern of gene frequencies in the population. Both the areal and the linear isolation-by-distance models were investigated. The observed rate of increase in the inbreeding coefficient did not agree well with that predicted by the results of Wright (although the differences may be due to changes which take place in only the first few generations). It was also found that the particular patterns of highs and lows of gene frequencies over a geographic area became established quickly and persisted for a large number of generations, particularly near the periphery of the population. Implications of our results for interpreting geographic variation analyses in terms of differential selection are discussed.
TL;DR: In this article, the fertility potential of Drosophila populations endemic to Hawaii has been investigated by analyzing the ovarian development of species in their natural habitats, and three groups of species were recognized on the basis of their fecundity potential and their use of comparable ovipositing substrates: species with a low potential, breeding on flowers (pollen); species with an intermediate potential and breeding on decaying leaves (bacteria); and species with large potential and feeding on decaying stems (yeast).
Abstract: The fecundity potential of Drosophila populations endemic to Hawaii has been investigated by analyzing the ovarian development of species in their natural habitats. Species differ in mean number of ovarioles per fly and/or number of mature eggs per ovariole. This diversity is probably an adaptive response of the population to the larval food supply which is determined by the nature, abundance, and nutritional content for larval growth of the oviposition substrates. Three groups of species were recognized on the basis of their fecundity potential and their use of comparable ovipositing substrates: species with a low potential, breeding on flowers (pollen); species with a medium potential, breeding on decaying leaves (bacteria); and species with a large potential, breeding on decaying stems (yeast). Adaptive mechanisms in oviposition behavior (single egg or cluster oviposition) and in the development and function of ovarioles (alternating ovariole development or synchronous ovariole development) which coord...
TL;DR: It is suggested that two major adaptive alterations in the basic alarm-defense system have occurred within the higher Formicinae and are causally linked to the development of a strongly aggressive form of alarm communication.
Abstract: 1. The higher formicine ants base their chemical alarm-defense systems primarily on a limited array of acyclic terpenes discharged from the mandibular glands, and alkanes and ketones discharged from Dufour's gland. All of these substances appear to be utilized in defense, and most, especially those at the lower end of the range of molecular weight (C9-C13), also function as alarm pheromones. The active space of the pheromones reaches over a distance of centimeters and is relatively short-lived. The alarm response of the various species can be classified roughly as either "panic" or "aggressive" in nature. 2. Two major adaptive alterations in the basic alarm-defense system have occurred within the higher Formicinae. In the genus Acanthomyops, the mandibular gland has been enlarged and made the site of storage of unusually large quantities of citronellal and two isomers of citral. We suggest that the changes are causally linked to the development of a strongly aggressive form of alarm communication. The res...
TL;DR: The evolutionary potentials of large animals with low reproductive rates are evaluated and demographic factors which contribute to the process of megafaunal extinction are examined.
Abstract: This paper applies demographic methods devised by Leslie (1966) to the population biology of the California condor. The methods permit evaluation of the population's potential for growth and of its capacity to withstand exploitation. For condors, the potential for growth must always remain low unless the frequency of reproduction can be increased. Any degree of exploitation would pose a threat to the population's persistence, which must have been marginal, even in the Recent prehistoric and Pleistocene. Such life history modifications as changing developmental time or permitting renesting after a nesting failure would have a very small impact on the population biology of this species. Besides its game management implications, this paper evaluates the evolutionary potentials of large animals with low reproductive rates and examines demographic factors which contribute to the process of megafaunal extinction.
TL;DR: Dioclea megacarpa (Leguminosae), a large woody vine in Costa Rican deciduous forest, loses most of its seeds and seedlings to predation by squirrels, bruchid beetles, and moth larvae.
Abstract: Dioclea megacarpa (Leguminosae), a large woody vine in Costa Rican deciduous forest, loses most of its seeds and seedlings to predation by squirrels (Sciurus variegetoides), bruchid beetles (Caryedes brasiliensis), and moth larvae (Noctuidae, Erebinae) Squirrels take 0%-43% of the seeds in a crop while in the "milk stage," but leave a large absolute number of uneaten seeds; they are probably prevented from eating larger numbers by a toxic amino acid, canavanine, in the seeds The bruchids kill from 13% to 100% of a given seed crop; the mortality percentage appears to be proportional to the number of females that find the crop Caryedes brasiliensis may act as a density-dependent population regulator of D megacarpa adults Both squirrels and bruchids effectively lower the carrying capacity of the habitat for D megacarpa by reducing the seed crop size Noctuid larvae that normally feed on the crown of the adult vine are a severe threat to seedlings growing beneath the adult; these predators cause the dea
TL;DR: A maximization principle relating gene frequency changes and population growth is formulated for a simple model of density-regulated selection, where the selective value of each genotype is altered by density in a way analogous to logistic population growth.
Abstract: A maximization principle relating gene frequency changes and population growth is formulated for a simple model of density-regulated selection. The selective value of each genotype is altered by density in a way analogous to logistic population growth. The growth of the population as a whole is logistic, its maximal rate of increase being a weighted arithmetic mean of the genotypic rates, and its carrying capacity a weighted harmonic mean of the genotypic carrying capacities. A stable genetic polymorphism occurs at a maximum, and an unstable equilibrium at a minimum, of the mean genotypic carrying capacity.
TL;DR: The interplay between density-independent (r) and density-dependent (K) components of selection is investigated using models of Mendelian populations with breeding at discrete intervals and overlapping generations to investigate the effects of environmental variation on the interaction between r- and K-selection.
Abstract: The interplay between density-independent (r) and density-dependent (K) components of selection is investigated using models of Mendelian populations with breeding at discrete intervals and overlapping generations. Selection within each genotype is age-specific, while the contribution of each genotype to population growth is logistic. The interaction between the r- and K-characteristics of the genotypes, in conjunction with the initial population structure, determines the patterns of population growth and gene frequency change. Moreover, these patterns may be strikingly different from the sigmoid curves obtained with simpler models. In a constant environment, K-characteristics alone determine the ultimate outcome of selection. Heterozygote advantage with respect to K is necessary for a balanced genetic polymorphism. The situation is different if the environment varies. We have investigated the effects of two kinds of environmental variation on the interaction between r- and K-selection. In the first of th...
TL;DR: The observed pattern of functional diversity allows a prediction of intergeneration selection or intrageneration differential mortality, where heterozygotes are at an advantage at higher environmental temperatures and homozygotes at lower environmental temperatures, as well as a significant amount of differential genetic mortality occurring within populations.
Abstract: Electrophoresis on starch gel of muscle homogenates of the freshwater fish, Notropis stramineus, indicated two regions of esterase heterogeneity. The most anodal group (Es-I) consisted of several closely associated minor bands while the more cathodal group (Es-II) exhibited a clear pattern of variation attributable to three codominant alleles segregating at an autosomal locus. A two-allele polymorphism was also detected at a lactate dehydrogenase locus (Ldh). Temperature-dependent activity of the esterase isozymes separated by column chromatography indicated: (1) there is a correlation of Es-I activity at various temperatures with Es-II genotype, and (2) a difference in temperature-dependent activity between the homozygotes and the heterozygote. The Es-I isozymes from Es-II heterozygotes exhibited a maximum activity at temperatures higher than those from Es-II homozygotes. Population samples during 3 years, ranging over more than 300 miles of the Kansas River mainstream, indicated both temporal and spatia...
TL;DR: The potential for local differentiation is enhanced by autogamy and retarded by heteromorphic incompatibility, dioecy, and apomixis, the latter being the case in spite of the fact that apomixedis is the best method for perpetuating superior genotypes.
Abstract: Neighborhood size and area, and equations for their calculation, have been treated in relation to reproduction under diverse reproductive methods. With allogamy via homomorphic incompatibility as the standard system, consideration has been given to the effect of autogamy, allogamy via heteromorphic incompatibility and dioecy, and apomixis upon the neighborhood parameters of colonies. It has been shown that neighborhood size contracts under autogamy, as it does under dioecy or heteromorphic incompatibility if the sex or morph ratios are disproportionate. Neighborhood size may expand under heteromorphic incompatibility or dioecy through enhanced pollen carry-over if the sex ratio is 1:1 and if the plants are insect-pollinated. Because of the formation of clones which are incompatible inter se, it also expands if apomixis is an adjunct to allogamy. As an expansion of neighborhood size may be equated with enhanced outbreeding and a contraction with reduced outbreeding, it is evident that heteromorphic incompa...
TL;DR: The evidence supports the hypothesis that genes responsible for the production of unpalatability gain their advantage in part by having individuals carrying genes identical by descent nearby, so that a predator attacking one of these individuals will learn subsequently to avoid attacking other related individuals in the same area.
Abstract: The relative palatabilities of seven species of heliconiine butterflies from Trinidad studied by Brower, Brower, and Collins (1963) correlate with variables directly related to individual dispersal and presumably inbreeding. The more unpalatable a species, the greater the number of geographic races and the higher the probability that populations will form site-specific roosting aggregations indicative of home-range behavior and inbreeding. These correlations are expected if kin selection has been important in the evolution of unpalatability in the Heliconiinae, but not if individual selection has been of overriding importance. The evidence supports the hypothesis that genes responsible for the production of unpalatability gain their advantage in part by having individuals carrying genes identical by descent nearby, so that a predator attacking one of these individuals will learn subsequently to avoid attacking other related individuals in the same area.
TL;DR: The cost of gene substitution can be defined as the reproductive excess necessary to prevent extinction when the population is at a low density, which makes it independent of the exact mode of population size regulation.
Abstract: If gene substitution is a response to unfavorable changes in the environment, there will be a lag in the population's response to those changes. The cost of gene substitution can be defined as the reproductive excess necessary to prevent extinction when the population is at a low density. Two simple derivations of the cost in a haploid population are presented. The cost is a function of the initial gene frequency of the favored alleles and the rate of occurrence of the environmental changes. The exact expression obtained is compatible with Haldane's (1957) result. The occurrence and substitution of favorable mutants in the absence of environmental change does not impose any cost, but makes the population better able to bear the cost. It is argued that this definition of the cost makes it independent of the exact mode of population size regulation. Too high a cost leads, not to a slowing of substitution, but to extinction. Models of natural selection by truncation are discussed, as are limits on the rate o...
TL;DR: Sex ratios of newly recruited and resident members of Microtus ochrogaster and M. pennsylvanicus populations have been analyzed from live trapping data and the population sex ratio seems to be 1:1 as Fisher's hypothesis predicts.
Abstract: Sex ratios of newly recruited and resident members of Microtus ochrogaster and M. pennsylvanicus populations have been analyzed from live trapping data of 1965-1969. The resident trappable population of these voles usually showed a deficiency of males at any given instant, while the total number of recruits obtained over a long time period showed an excess of males. A computer simulation model was used to test the influence of differential recruitment, survival, movement, trappability, and growth on the sex ratios. Male voles survive less well than females but grow more rapidly and move about more. Increased male recruitment lowered population growth, and differential survival reduces the proportion of males in the resident population. Differential growth greatly influenced the sex ratios of newly caught animals in the three age categories. Male movement is probably important in determining the high sex ratio of newly caught M. pennsylvanicus. However, a slight excess of males at birth could also produce ...
TL;DR: There is need for additional work on Payne's most significant points-his attempt to provide evidence for the adaptiveness of the polymorphism in egg color found in the parasitic African diederik cuckoo (Chrysococcyx caprius), as there is some doubt as to whether Payne's data prove this point.
Abstract: In a recent paper in this journal, Payne (1967) made several important contributions to the study of brood parasitism by analyzing various aspects of this phenomenon in terms of natural selection. However, there is need for additional work on one of Payne's most significant points-his attempt to provide evidence for the adaptiveness of the polymorphism in egg color found in the parasitic African diederik cuckoo (Chrysococcyx caprius). The major hosts of this parasite are of the genera Passer, Ploceus, and Euplectes (family Ploceidae). These hosts lay a wide range of egg types which are reflected in the types laid by the cuckoo. It is commonly suggested that the matching of host and parasite eggs would be of selective advantage to the cuckoo because the hosts reject eggs unlike their own. Payne claimed to have shown that individual cuckoos usually parasitize those hosts which lay eggs that match their own. However, there is some doubt as to whether Payne's data prove this point; I suggest that an experimental approach is desirable. Payne's argument for selective egg deposition by C. caprius is based on observations made on naturally parasitized host nests. The various parasitic egg morphs were found in nests with similar-appearing host eggs more often than would be expected on a hypothesis of random placement. But this is what one should expect to find if cuckoos laid their eggs at random and the hosts removed cuckoo eggs that did not mimic their own eggs. Payne's data can thus be used only to prove that the C. caprius eggs which people generally find in nests match those of the hosts; not that C. caprius parasitizes nests in such a way that the eggs laid match those of the host. Unless it is known that a host species accepts parasite eggs of any type, data from nature on the percentage of nests found parasitized are of little value in indicating the actual incidence of parasitism which that species suffers. Swynnerton (1916, 1918) was aware of this problem after he conducted a small number of experiments on egg recognition in birds of southern Africa. His data strongly suggest that at least some ploceid hosts of C. caprius do eject eggs unlike their own. I can testify to the reality of this problem because I have, in effect, played the part of a brood parasite. From 1966 to 1969 I investigated the
TL;DR: It is shown that, by means of selection over a period of some 70 generations, ethological isolation can be constructed where none had existed previous to initiation of selection for it.
Abstract: Natural selection acts to build and reinforce barriers to gene exchange between populations whose hybridization results in reproductive wastage (Dobzhansky 1970). This has been demonstrated experimentally by Koopman (1950), Wallace (1954), Knight, Robertson, and Waddington (1956), Kessler (1966), and most recently, by Dobzhansky and Pavlovsky (1971). These last authors have shown that, by means of selection over a period of some 70 generations, ethological isolation can be constructed where none had existed previous to initiation of selection for it. Wallace's experiment warrants more detailed description, since his results were similar to those of Knight et al. (1956), while his technique was similar to Koopman 's (1950) and that of Dobzhansky and Pavlovsky (1971). He employed the straw and sepia Drosop7hila mnelanogaster mutants and practiced 73 generations of selection against the wild-type progeny produced between them. After that time, mating was significantly nonrandom: One type of female, sepia, gave a 9 :1 ratio of homogamic (sepia X sepia) to heterogamic (sepia X straw 6 ) matings while straw females still mated as often heterogamically (straw 9 X sepia S ) as homogamically (straw X straw). With this experiment in mind, in December 1970 Professor Wallace sent me three replicates of two strains of Drosop7tila melanogaster from another study. My aim was to test for the possible existence and magnitude of sexual isolation between these strains; they had been reared together in half-pint culture bottles since January 1968, at Cornell University. Each set of two consisted of a mutant and wild-type strain, with the latter originating from a single gravid female captured at Ceres, New York. The genotype was constructed in such a way that heterotypic matings would produce no progeny. The genetically marked compound autosome strain was synthesized in Prof. E. B. Lewis's laboratory at California Institute of Technology in Pasadena and may be designated C(2L)P b el rd\" pr px/so2 b; C(2R) P px, all with reference to the second chromosome. Here, C refers to the compound second chromosome in which one part consists of two left arms while the second, independent, part contains two right arms; the vertical slash separates mutant genes carried by the two L/L arms -of the left-armed compound; and P '-Pasadena. Of the other genetic symbols, b -black (II, 48.5); el= elbow (II, 50.0); rd= reduced scraggly (II, 51.2);
TL;DR: Some serious shortcomings were found in Pimentel's mathematical model of population regulation by the genetic feedback mechanism, and the models proposed so far for genetic feedback appear to be untenable.
Abstract: Some serious shortcomings were found in Pimentel's mathematical model of population regulation by the genetic feedback mechanism: (1) the chain of events postulated by the model is unlikely to occur in ecosystems; (2) this difficulty can be avoided, but the basic assumption of the model-the uniform distribution of animals among plants, whether conditions for their reproduction are favorable or not-is implausible in terms of the theory of natural selection; and (3) Pimentel's second model, including genetic variability of net reproductive rates of animals, seems irrelevant to the problem of population regulation. The models proposed so far for genetic feedback appear to be untenable.
TL;DR: It is found that moderately large DNA amounts in mesopelagic myctophoid lanternfishes may serve their highly specialized life-style, including frequent vertical migrations between the warm, productive surface waters and the cold, impoverished depths, and additional DNA, which may have accumulated slowly by tandem duplications in one-armed chromosomes, may encode multiple enzyme systems for acclimation to different bathymetric climes.
Abstract: The primitive teleostean superorder Protacanthopterygii and the derived Paracanthopterygii contain many deep-sea fishes, which inhabit the cold, dark, and impoverished oceanic depths, and which have shallow-marine relatives typical of more diverse and productive environments. Genome sizes, as estimated by DNA amounts per diploid nucleus, vary widely among members of both superorders. We investigated genome sizes and karyotypes of deep- and shallow-living representatives of relatively primitive and advanced protacanthopterygian orders and of an advanced paracanthopterygian order to see if DNA amount is somehow correlated with depth of habitat. DNA amounts almost quadruple between shallow-marine and bathypelagic (deep oceanic) representatives of the primitive paracanthopterygians (Salmoniformes: Argentinoidei). This may have been caused by "saltatory replications," mostly in large two-armed chromosomes. Gradual tandem duplication of genes seems incapable of producing the huge DNA increases. Polyploidy, whic...
TL;DR: A general conclusion is that a preponderance of positive competitive effects is required for stable equilibria, which are entirely a function of these competitive effects.
Abstract: General procedures are developed for finding equilibrium and maximum/minimum mean compositions for a population of autogenous components competing in a pairwise manner among individuals. The procedures, involving elementary matrix techniques, are easy to apply for any specific competitive model. Necessary and sufficient conditions are developed for the mean to be a maximum and for the equilibrium composition to be stable. The problem of a maximum mean reduces to that of evaluating a quadratic form which must be negative definite, and is easily accomplished for a specific competitive model. Stability of equilibrium depends on the eigenvalues of a first-order transition matrix relating deviations of component frequencies from their equilibrium frequencies in successive generations. For stability, all of the eigenvalues must vanish in time. These conditions, sometimes difficult to find, are illustrated for a three- and four-component model. The eigenvalues also provide considerable information about the dyna...