Showing papers in "The American Naturalist in 1968"
TL;DR: A within-habitat analysis was made of the bivalve and polychaete components of soft-bottom marine faunas which differed in latitude, depth, temperature, and salinity, and it was indicated that species number is the more valid diversity measurement.
Abstract: In this paper a methodology is presented for measuring diversity based on rarefaction of actual samples. By the use of this technique, a within-habitat analysis was made of the bivalve and polychaete components of soft-bottom marine faunas which differed in latitude, depth, temperature, and salinity. The resulting diversity values were highly correlated with the physical stability and past history of these environments. A stability-time hypothesis was invoked to fit these findings, and, with this hypothesis, predictions were made about the diversities present in certain other environments as yet unstudied. The two types of diversity, based on numerical percentage composition and on number of species, were compared and shown to be poorly correlated with each other. Our data indicated that species number is the more valid diversity measurement. The rarefaction methodology was compared with a number of diversity indexes using identical data. Many of these indexes were markedly influenced by sample size. Good...
2,354 citations
TL;DR: Actual evapotranspiration is shown to be a highly significant predictor of the net annual above-ground productivity in mature terrestrial plant communities, and it is hypothesized that the relationship of AE to productivity is due to the fact that AE measures the simultaneous availability of water and solar energy.
Abstract: Actual evapotranspiration (AE) is shown to be a highly significant predictor of the net annual above-ground productivity in mature terrestrial plant communities. Communities included ranged from deserts and tundra to tropical forests. It is hypothesized that the relationship of AE to productivity is due to the fact that AE measures the simultaneous availability of water and solar energy, the most important rate-limiting resources in photosynthesis.
818 citations
TL;DR: The possibility that iteroparity may be an evolutionary response to uncertain survival from zygote to first maturity is examined in a competition model and a genetic model and suggests the approach may contribute to understanding the dynamics of evolution.
Abstract: The possibility that iteroparity may be an evolutionary response to uncertain survival from zygote to first maturity is examined in a competition model and a genetic model. The competition model used is an alternative to the logistic model and is based on the Ricker formulation of population growth. The genetic model is a straightforward two-allele system. Both models show clear advantage in iteroparity if there is uncertainty from zygote to first maturity. Illustrative material on marine plankton-feeding fishes suggests the modeling is realistic. Consideration of other evidence suggests the approach may contribute to understanding the dynamics of evolution.
575 citations
TL;DR: It is suggested that South American communities have a full quota of species which are optimally adapted to their current environment.
Abstract: The results of this study make possible the following generalizations. The members of avian communities resident in simple grassland habitats coexist by virtue of differences in habitat preferences and feeding behavior and in very tall vegetation by differences in feeding height. The sum of these ecological differences is constant for all communities. Using only two habitat indexes, vegetation height and its standard deviation, it is possible to predict (1) the number of species, (2) the differences in their feeding ecology, and (3) their relative habitat separation in the community which occupies this habitat. As these predictions are made for South American communities on the basis of the communities studied in North America, and as the predictions hold regardless of grazing or irrigation programs, it is suggested that these communities have a full quota of species which are optimally adapted to their current environment.
376 citations
TL;DR: It may be true that avian congeners are less likely to be able to coexist on islands than in comparable mainland areas, but it is not believed that this hypothesis receives any support from the data on the Tres Marias avifauna presented by Grant (1966).
Abstract: He believes they support his hypothesis. However, all are equally explicable on the basis of the established relation between proportion of congeners and the number of species comprising the avifauna (logarithmic series) and the known relations between the number of species and the characteristics considered. It may be true that avian congeners are less likely to be able to coexist on islands than in comparable mainland areas. I do not believe, however, that this hypothesis receives any support from the data on the Tres Marias avifauna presented by Grant (1966). I wish to thank Dr. P. R. Grant for extensive discussion on this topic, Mr. R. A. Elton for advice on statistical aspects, and Dr. L. M. Cook for criticizing an earlier draft of this letter.
276 citations
TL;DR: It was possible to show that supernatants from the bacterium Escherichia coli contained an attractant for the amoebae of Dictyostelium discoideum, and now it is known that this attractant is cyclic 3', 5'-AMP.
Abstract: There has been a long search for the chemical identity of acrasin, the chemotactic substance responsible for the aggregation of amoebae in the development of cellular slime molds. With the help of ...
239 citations
TL;DR: It is proposed that evolution and specialization in the teleosts have been accompanied by loss of DNA.
Abstract: The haploid amount of DNA in teleost fishes ranges from 0.40 to 4.4 picograms. Almost all the teleost groups with low amounts of DNA per cell are considered to be evolutionally advanced. Most of the groups with large amounts of DNA per cell are more primitive and more closely related to ancestral forms. It is proposed that evolution and specialization in the teleosts have been accompanied by loss of DNA.
208 citations
TL;DR: Two features of the habitat, the variation of moisture patterns in space and the fluctuation of resources in time, appear to be correlated with most of the differences in the means and standard deviations of these distributions.
Abstract: The tendency for the lengths of adult insects of sweep samples from forest understories, considered both as species and as individuals, to fit a two-parameter lognormal distribution rather than a simple normal distribution, and a three-parameter lognormal distribution best of all, is documented for some tropical and temperate areas. Two features of the habitat, the variation of moisture patterns in space and the fluctuation of resources in time, appear to be correlated with most of the differences in the means and standard deviations of these distributions. In general, samples from drier areas or those with longer growing seasons have larger species, and samples from areas with the more uniform moisture conditions and growing seasons have the smaller standard deviations of their species' lengths.
184 citations
TL;DR: The present note considers only Levene's model in which migration is maximal, which deals with just two alleles, A and A', with gene frequencies p and q, respectively, and the change in gene frequency Aq is 1.
Abstract: Levene (1953) described sufficient conditions for at least one stable equilibrium in a model in which selection varies from niche to niche. Deakin (1966) generalized the model by allowing for partial migration between the niches and the general population. The present note considers only Levene's model in which migration is maximal. It will be shown that it is possible to state sufficient conditions for an equilibrium which are broader than those stated by Levene. The model under consideration deals with just two alleles, A and A', with gene frequencies p and q, respectively. There is random mating so that the three genotypes, AA, AA', and A'A', will be in the proportions p2 2pq and q2, respectively. These genotypes are then distributed into different niches, each characterized by its own pattern of selection. In the ith niche AA, AA' and A'A' have witnesses vi, 1.00, and wi, respectively. After selection is completed the total population undergoes random mating, and to the total population the ith niche contributes a proportion ci individuals (:cj = 1). With such a model the change in gene frequency Aq is
172 citations
TL;DR: Though the energy and nutrient values of various foods and the types of experiences affecting food preferences in predators may change in time, predictions of food preferences based on considerations of' a predator's current habitat should prove of some value.
Abstract: Environments change, often in unpredictable ways, and the selective pressures on one generation effect their changes on another. For these' reasons and others, it is impossible to know the exact conditions for which any organism has evolved an appropriate phenotype, for indeed there can be no such conditions. Nevertheless, predictions of appropriate phenotype, necessarily based on conditions specific to some given time, can still be, useful in that they represent points of maximum likelihood in collections of possibly evolved phenotypes. Thus a model predicting optimal phenotype, (i.e., that phenotype which contributes the most genes to future generations) can virtually never be quantitatively precise; nevertheless, it may suggest phenotypic trends. Inasmuch as food preferences may be at least partially controlled by genetic factors, one would assume that natural selection has favored those genotypes which predispose their owners to favor the "right" foods, that is, those that yield the most in net energy and nutrients per time' to their predators. Though the energy and nutrient values of various foods and the types of experiences affecting food preferences in predators may change in time, predictions of food preferences based on considerations of' a predator's current habitat should prove of some value. Consider all potential foods available to a given predator. Each of these' foods may be divided naturally into discrete items or artificially into units, of mass, and each such item or unit may be assigned a value. The value' with which we concern ourselves here is "food value," which in its simplest. form would be simply the calories assimilable in a given food item divided by the time required to find, capture, and devour the item. Let Fi(x) be the' number of items of food i, value x, encountered by the predator while' foraging for a time period kt. Here k denotes the fraction of its total time the predator spends foraging and feeding. F,(x) for each food can then be' plotted as a distribution curve, where the sum of the integrals under all the curves, Zifoo Fi (x)dx, represents the total net assimilable food value encountered by the predator over time t. To simplify the following discussion, I have defined all foods as belonging' to two disjoint sets. Thus only two distribution curves are considered. Two hypothetical cases one in which the variability in food values for the two foods are roughly similar and one in which items of the usually "superior" food (higher mean food value) are much less variable in value, are shown in Figure 1.
160 citations
TL;DR: In a simple model case, the rates of evolution in an asexual and a sexual haploid population are compared and it is shown that, if the genetic variance of the population is generated by mutation in a uniform environment, sexual reproduction confers no advantage, but if it has arisen because selection has favored different genotypes in different environments, then sexual reproduction will accelerate adaptation to a new environment.
Abstract: In a simple model case, the rates of evolution in an asexual and a sexual haploid population are compared. It is shown that, if the genetic variance of the population is generated by mutation in a uniform environment, sexual reproduction confers no advantage. But if the genetic variance has arisen because selection has favored different genotypes in different environments, then sexual reproduction will accelerate adaptation to a new environment. These conclusions differ sharply from those reached by Crow and Kimura (1965). The difference arises because those authors treated mutations as unique events, whereas they are here treated as recurrent events.
TL;DR: Two independent experiments were conducted to compare the relative plasticity of Avena fatua and A. barbata and Avena barbata was found to be developmentally more flexible than A. fatua.
Abstract: Two independent experiments were conducted to compare the relative plasticity of Avena fatua and A. barbata. In both experiments, seed samples from a single mixed population were grown in a series of controlled environments. The within- and between-environment components of variation were estimated for a wide range of quantitative characters. Avena barbata was found to be developmentally more flexible than A. fatua. The significance of these findings is briefly discussed in relation to the adaptive strategies of the two species.
TL;DR: The assumption that the rain forest floor environment is relatively constant and predictable is re-examine, with the finding that the endless disturbance of intense rains may prevent the community from achieving the theoretical equilibrium.
Abstract: Intensive collecting carried out over an entire year in 20 square miles of lowland rain forest in Borneo yielded 72 species of amphibians and reptiles considered to be regular inhabitants of the forest floor. Thirty-eight of these species, plus 12 that are "refugees" in the sense that they do not live primarily in this habitat, were collected in 402 quadrats randomly distributed over the forest floor. The average species diversity per individual was H' = 4.26 ± 0.21 bits, using Pielou's (1966a) method for estimating H' and its standard error from individual quadrats. This much diversity is equivalent to 28.3 hypothetical "equilibrium" species having relative abundances distributed according to the "broken stick" model of MacArthur (1957, 1960). The ratio of 28.3 to 84 (72 regular plus 12 refugee species) gives an "equitability" value (Lloyd and Ghelardi, 1964) of E = 0.34. Treating frogs, lizards, and "snakes" separately, we obtain diversity values of 3.30, 3.10, and 2.86 and equitability values of 0.47, ...
TL;DR: This paper presents a third model, the "exponential" model, leading to the same numerical predictions of the average relative abundance of species that follow from MacArthur's "broken stick" model with a different set of assumptions.
Abstract: Exactly the same numerical predictions of the average relative abundance of species that follow from MacArthur's (1957) \"broken stick\" model also follow from a \"balls and boxes\" model (Cohen, 1966) with a different set of assumptions. This paper presents a third model, the \"exponential\" model, leading to the same numerical predictions. The assumptions of this third model are nearly opposite to those of MacArthur's. The numerical data which have been taken to confirm the broken-stick model in fact confirm all three models equally. Hence, this paper describes some experimental and field obervations which could discriminate among the available models.
TL;DR: The regulation of plant species diversity was studied for 14 islands, four island groups, and 10 coastal mainland areas of California and Baja California using several kinds of models to suggest area is the best single predictor of species diversity.
Abstract: The regulation of plant species diversity was studied for 14 islands, four island groups, and 10 coastal mainland areas of California and Baja California. Native and total species numbers for these areas were regressed on five independent variables using several kinds of models. The results suggest the following for these areas: 1. Area is the best single predictor of species diversity. 2. Curvilinear models are superior to linear models and mixed linear-curvilinear models. 3. The addition of other variables significantly contributes to the prediction of species numbers. 4. In the islands, ecological diversity, richness of the environment, and isolation contribute significantly to the regulation of species abundance. 5. For mainland areas, ecological diversity and richness of the environment contribute significantly.
TL;DR: Nine triads of species of the genus Drosophila, each triad composed of a pair of sibling species and a form closely related but morphologically distinct, were studied using electrophoretic techniques, finding that one sibling pair shared proteins with identical mobility 85% of the time.
Abstract: Nine triads of species of the genus Drosophila, each triad composed of a pair of sibling species and a form closely related but morphologically distinct, were studied using electrophoretic techniques at an average of 18 loci per species The sibling pairs, on the average, shared proteins with identical mobility 50% of the time, while a sibling and a morphologically distinct form shared proteins with identical mobility only 18% of the time One sibling pair shared proteins with identical mobility 85% of the time These findings are discussed with special reference to "the reorganization of the gene pool" during speciation
TL;DR: It is now apparent that slow growth rates are characteristic of plants from at least three types of unfavorable habitat, and it seems clear that the environmental selection of plants withslow growth rates is a frequent and simple form of adaptation to limiting levels of environmental factors.
Abstract: It is now apparent that slow growth rates are characteristic of plants from at least three types of unfavorable habitat. In discussing such growth rates as adaptations to the environment, it is necessary to bear in mind the great diversity of other adaptations to low levels of environmental resources. For example, in interspecific comparisons, different transpiration-control mechanisms may greatly complicate the relationship between growth rate and drought susceptibility. Nevertheless, it seems clear that the environmental selection of plants with slow growth rates is a frequent and simple form of adaptation to limiting levels of environmental factors. Certainly growth-rate comparisons are often a valuable way of beginning to investigate why plants grow where they do.
TL;DR: These experiments were designed to determine the degree and kind of variability in the structure of the community that one might expect under very similar ecological conditions and show that 95.5% to 98.0% of the specimens composed the same species in the eight communities.
Abstract: These experiments were designed to determine the degree and kind of variability in the structure of the community that one might expect under very similar ecological conditions. The results of these experiments show that 95.5% to 98.0% of the specimens composed the same species in the eight communities. About 5% of the specimens were in the remaining species in one series of experiments and 1% to 2% of the species in the second series. The Shannon-Weaver diversity indices and the structures of the truncated log-normal curves representing the communities in a given series were also very similar.
TL;DR: A rapid survey of the collection of the ants in the Museum of Comparative Zoology, Harvard University, and some other collections, has turned up additional cases of ants in which, judging now only from externally visible structures, the metapleural gland is absent, nonfunctional, or significantly reduced.
Abstract: The metapleural glands are organs characteristic of all ants (Formicidae), with the relatively few exceptions that are the main subjects of this note. Situated at the posterolateral corners of the alitrunk (thorax plus propodeum), the glands are marked externally by the presence of a bulla, which covers the atrium or collecting chamber, and a meatus in the form of a slit or pore that connects the atrium with the outside. Proximally, the atrium has a cribriform wall into which enter separately the ducts of single gland cells. The structure of this organ was beautifully worked out for Myrmica by Janet (1898), and details have been added by Tulloch (1936) for Myrmica and by Tulloch, Shapiro, and Hershenov (1962) for Myrmecia nigrocincta. During grooming, some ant species have been seen to! draw the legs, especially the tibiae and tarsi of the forelegs, repeatedly over the meatus of the gland and then to rub these leg parts over the rest of the body. One gains the impression that some substance is being spread over the integument by this means. Among various hypotheses suggested for the gland's function, one that has persisted, especially in informal conversations among ant specialists, proposes that the gland produces a "nest odor" by means of which members of one colony recognize one another. Gbsswald (1953) found the gland atrophied in the female of the aberrant workerless parasitic ant Teleutomyrmex schneideri (it is absent in the male also) and supposed that, if the gland is connected with nest odor, its loss in Teleutomyrmex would be understandable in allowing easier acceptance of the parasite by the host ant species, Tetramorium caespitum. A rapid survey of the collection of the ants in the Museum of Comparative Zoology, Harvard University, and some other collections, has turned up additional cases of ants in which, judging now only from externally visible structures, the metapleural gland is absent, nonfunctional, or significantly reduced. It should be emphasized that the presence of a well-developed bulla and meatus, where these occur, is no guarantee that the gland cells within are present and secreting a normal product. Where the meatus is fused shut, on the other hand, the gland may safely be considered as nonfunctional. Even as based on this wholly external criterion, the survey shows some interesting regularities in the occurrence of gland atrophy. Such cases fall into four classes:
TL;DR: Two clones of the hermaphroditic fish Rivulus marmoratus Poey, identified by their intraclonal histocompatibilities and interclonal histoincompatibility, were kept through successive uniparental generations, each fish in isolation to study the possible role of males in the prevalence of homozygous clones in the wild.
Abstract: Two clones of the hermaphroditic fish Rivulus marmoratus Poey, identified by their intraclonal histocompatibilities and interclonal histoincompatibility, were kept through successive uniparental generations, each fish in isolation. These hermaphrodites emit internally self-fertilized eggs incubated up to 2 1/2 days intraparentally and thereafter extraparentally. By extraparental incubation at low temperature, primary males can be produced at will from eggs otherwise yielding hermaphrodites. Secondary males originate from hermaphrodites, usually late in life, if the ovarian component of the ovotestis involutes. There are no females. Eggs from an aberrant hermaphrodite chronically emitting un-self-fertilized eggs were cross-fertilized artificially and also naturally by sperm from a primary male. A fin graft from the clone of the male parent was accepted (autograft reaction) by the interclonal hybrid, showing that amphimixis had occurred and that the clone of the graft donor is homozygous for the histocompat...
TL;DR: The breeding system of the perennial herb Lithospermum caroliniense was analyzed in a population located near Zion, Lake County, Illinois, and the low legitimate pollen loads and low chasmogamic seed-set suggest that the advantages of heteromorphic incompatibility lie not in the efficiency of cross-pollination and cross-fertilization but in its ability to generate variability via negative assortative mating.
Abstract: The breeding system of the perennial herb Lithospermum caroliniense was analyzed in a population located near Zion, Lake County, Illinois. The species is both heterostylic and functionally cleistogamic, its populations containing plants which are solely chasmogamic, solely cleistogamic, or partially cleistogamic. Heterostyly is accompanied by pollen dimorphism so that levels of legitimate pollen flow may be accurately measured by examining stigmas and noting the size of the legitimate pollen loads. Legitimate pollen flow was measured at Zion, and it was found that 63% of the pin stigmas bore legitimate grains as compared with 42% of the thrum stigmas. The average numbers of such grains on all pin and thrum stigmas were 4.88 and 2.75, respectively, the range being one to 45 in the former and one to 43 in the latter. The distribution of legitimate loads on both stigmas was markedly leptokurtic. Average pollen loads per plant were related to the proximity of legitimate pollen donor. Illegitimate loads ranged...
TL;DR: The present paper attempts to derive some generalities from the patterns observed in order to expose them to test, one of the outgrowths of a continuing study of the biology of burrowing reptiles supported by National Science Foundation grant GB 6521X.
Abstract: One of the basic questions in the study of adaptive radiations asks what determines the success of the individual species. Attempts to answer this interesting and important question obtain impetus from the observation that diverse lines of even a small radiation differ in the number of species. The several component species again differ in terms of the geographical area each occupies, as well as in the population density within this. Number of species, area occupied, and population density may perhaps be considered indicators of a kind of evolutionary \"success,\" though only for a particular time level. Members of a given radiation will often show degrees of modification for a particular behavior pattern or mode of life-history. Frequently it is observed that those members that seemingly share the most advanced specializations have more restricted distributions than do other, seemingly more generalized, species. To this observation is related the complication that conditions which might, on a priori grounds, be described as equivalent terminal specializations in divergent sequences often have led to extremely different distributional success. Examples of each of these situations were noted during a review of the geographical distribution of the various amphisbaenians, a small but apparently very old radiation of squamate reptiles into the subterranean habitat. For references to other papers and comments on the nomenclature of the group see Gans (1967a). Table 1 gives a classification for the animals mentioned here. The present paper attempts to derive some generalities from the patterns observed in order to expose them to test. It forms one of the outgrowths of a continuing study of the biology of burrowing reptiles supported by National Science Foundation grant GB 6521X. I am deeply grateful to the many friends who have furnished specimens for study or have permitted me to cite their unpublished observations. T. Frazzetta, A. S. Gaunt, F. Gehlbach, T. S. Parsons, H. I. Rosenberg, and Miss Anne Whiting provided useful comments on the manuscript.
TL;DR: In order to substantiate evidence and explore further details of frequency dependency between third chromosome arrangements in Drosophila pseudoobscura populations, multiple-choice mating experiments involving karyotypes of Arrowhead (AR) and Pikes Peak (PP) gene arrangements were designed to measure relative mating propensity with frequencies of karyotype varied in one sex or in both sexes.
Abstract: In order to substantiate evidence and explore further details of frequency dependency between third chromosome arrangements in Drosophila pseudoobscura populations, multiple-choice mating experiments involving karyotypes of Arrowhead (AR) and Pikes Peak (PP) gene arrangements were designed to measure relative mating propensity with frequencies of karyotypes varied in one sex or in both sexes. Ten strains each of AR and PP crossed inter se as in previous experiments contrast in being fastest (75% mated) and slowest (20%) mated, respectively, in homokaryotype no-choice matings of 30 min. duration. Twenty pairs of strain-cross F1 flies, 6 days old, were introduced unetherized into small Plexiglas chambers and observed for 30 min. Flies had been marked to distinguish karyotypes by puncturing a wing on the day before the mating tests. Two contrasting types of both sexes were tested each time to measure relative propensities, total mating frequency, and any assortative mating. Ratios of karyotypes and condition...
TL;DR: The population responses of the phenotype to the environmental parameters studied are positive adaptations for a migrant insect such as Oncopeltus, which is well adapted for a rapid increase in numbers and full utilization of the habitat.
Abstract: Density, photoperiod, and temperature exert profound effects on the life history and population growth of Oncopeltus. High temperature, long photoperiod, and low density result in earlier onset of reproduction, negatively skewed egg curves, and hence greater rates of population increase. Values or r (intrinsic rate of natural increase) vary from .0861 on a 16-hr day at 27⚬C with density of 10 pairs per container to .0369 on a 12-hr day at 23⚬C and 20 pairs. When r is low, length of life increases in partial compensation for suppressed reproduction. Photoperiod and density exert their influence only after adult eclosion, while temperature acts directly at all stages of life history to regulate the rate of development. The population responses of the phenotype to the environmental parameters studied are positive adaptations for a migrant insect such as Oncopeltus. It enters an essentially empty universe in the spring, when day length is increasing and temperatures are rising. The fact that all these factors...
TL;DR: A model based on the classical Wright-Fisher random sampling formulation, but allowing general offspring number distribution and fluctuations in population size, is discussed, and the rate of approach to homozygosity is obtained with the general theory of Markoff chains.
Abstract: A model based on the classical Wright-Fisher random sampling formulation, but allowing general offspring number distribution and fluctuations in population size, is discussed With the general theory of Markoff chains, the rate of approach to homozygosity is obtained as the largest eigenvalue of a certain matrix A number of examples are considered to take account of completely random, cyclic, and some other kinds of fluctuations in the population size In the multiallelic case, the rate of loss of an allele is obtained
TL;DR: The approach differs conceptually from Haldane's in postulating that the mean fitness of the population is not affected by its genotype, but rates of substitution and selective intensities consistent with this death rate are calculated, leading to no obvious upper limit for the rate of substitution.
Abstract: Maximum rates of gene substitution are calculated, showing that Haldane's estimate (1957) of one completed gene substitution per 300 generations may be much too low. The approach differs conceptually from Haldane's in postulating that the mean fitness of the population is not affected by its genotype. The rate of death is assumed to be set by density-dependent factors, and rates of substitution and selective intensities consistent with this death rate are calculated. This formulation leads to no obvious upper limit for the rate of substitution. Rates of one completed substitution per generation or more are by no means excluded. The selective value consistent with a given death rate or set of fitness differentals is not independent of the rate of substitution but is approximately inversely proportional to it. The result is little affected by the degree of dominance or by the initial gene frequency.
TL;DR: It is concluded that different patterns of interspecific pollen-style compatibility relationships are highly specific and are mainly controlled by different forms of S alleles which have arisen from mutation of various genetic elements comprising the primitive S-gene complex.
Abstract: Interspecific hybridization between 17 species of Nicotiana, including those of both South American and Australian origins, revealed a complex but highly systematic pattern of unilateral incompatibility behavior. A critical review of the earlier observations on unilateral incompatibility and S-gene polymorphism and a detailed consideration of the present data have led the author to conclude that different patterns of interspecific pollen-style compatibility relationships are highly specific and are mainly controlled by different forms of S alleles which have arisen from mutation of various genetic elements comprising the primitive S-gene complex. Unilateral incompatibility owes its origin primarily to the mutational independence of the pollen and stylar controlling elements of the S complex. It is argued that the supremacy of the S gene in the determination of compatibility behavior is dependent upon the maintenance of the native polygenic background in which it normally acts. A hybrid or disturbed geneti...
TL;DR: The genetic component of the variation in Ranunculus flammula results from selection toward some "optimum" carpel number consistent with the amount of food reserve that can be accumulated by the plant for endosperm tissue in the environment in which this selection occurs.
Abstract: The variation in carpel number in Ranunculus flammula was analyzed. Both genetic and environmental components of variance were observed and discussed. Significant correlations between length of growing season and carpel number were observed. It was concluded that the genetic component of the variation results from selection toward some "optimum" carpel number consistent with the amount of food reserve that can be accumulated by the plant for endosperm tissue in the environment in which this selection occurs. The plasticity of individuals for carpel number allows for annual fluctuations in environment. An analogy is made with clutch size regulation in birds.
TL;DR: Observations of territorial behavior of Calidris melanotos, a sandpiper which breeds on arctic tundra, support the suggestion that noncolonial birds breeding at high density hold territories which should be polyhedral in shape.
Abstract: Where there are relatively uniform, structurally simple, habitats, noncolonial birds breeding at high density hold territories which should be polyhedral in shape. Observations of territorial behavior of Calidris melanotos, a sandpiper which breeds on arctic tundra, support this suggestion. Some territories were certainly angular and not circular. Calculations of angles between pairs of boundaries held in common with two adjacent neighbors. indicate an approach to a hexahedral (hexagonal) shape.
TL;DR: Electrophoretic serum protein analysis reveals that the gynogenetic species Poecilia formosa possesses two albumin bands that are identical with those of laboratory-produced hybrids of its two sympatric species, P. latipinna and P. mexicana.
Abstract: Electrophoretic serum protein analysis reveals that the gynogenetic species Poecilia formosa possesses two albumin bands that are identical with those of laboratory-produced hybrids of its two sympatric species, P. latipinna and P. mexicana. The presumed parental species possess single albumins that are different in electrophoretic mobility. Studies involving the mixing of P. formosa, P. latipinna, P. mexicana, and the hybrid P. mexicana x P. latipinna in various combinations demonstrate the electrophoretic identity of the two albumins of P. formosa with those of its presumed parental species. These results substantiate the conclusion, based on morphological and reproductive evidence, that P. formosa arose by hybridization of P. latipinna and P. mexicana.