bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic risk involved in stock enhancement of fish having environmental sex determination
Authors: Kanaiwa M. , Harada Y. 
Published: March 2003

AbstractEnvironmental sex determination is reported in various fish species, including some fishes subject to stock enhancement. We studied the influence of stock enhancement on the sex‐determining system of fish with both genotypic and environmental sex determination. We constructed and analyzed recurrence formula models for the dynamics of gene frequency in the male heterogametic (XX female and XY male) sex‐determining system of the Japanese flounder (Paralichthys olivaceus). In this species, an XX individual can develop as a phenotypic male (sex‐reversed male) depending on the conditions experienced by a juvenile. We show that the release of sex‐reversed males may result in the extinction of the Y gene that determines sex. We also studied how the risk depends on the kind of hatchery broodstock used (e.g., fish collected from the wild or fish from a lineage established in a hatchery), sex‐reversal rates in the hatchery and in the wild, and the relative contribution of released fish to reproduction in the wild. We propose some ways to reduce the risk.
Latitudinal trends in adult body size of Dolly Varden, with special reference to the food availability hypothesis
Authors: Maekawa K. , Nakano S. 
Published: March 2003

AbstractThe food availability hypothesis (FAH) predicts that the relative productivity of ocean and freshwater habitats changes with latitude, and that anadromy will evolve when ocean productivity is greater than that in neighboring freshwater habitats, or vice versa. In data sets for the anadromous salmonid species Salvelinus malma, we show that the relative body size at maturity of anadromous populations is much larger in the northern limits of their ranges than that of fluvial populations, and, conversely, that of fluvial populations is slightly smaller at the southern limits than that of anadromous populations, supporting the FAH for the evolution of migration behavior in salmonids.
Factors affecting refuge from parasitoid attack in a cynipid wasp, Aphelonyx glanduliferae
Authors: Ito M. , Hijii N. 
Published: March 2003

AbstractWe examined seasonal patterns of gall morphology, growth, and survivorship of the agamic generation of a cynipid wasp, Aphelonyx glanduliferae, and discussed its mortality factors, especially from the point of view of refuge from parasitoid attack. Although the initiation period varied greatly among individual galls, the larvae of A. glanduliferae grew rapidly and reached their maximum size within 3 weeks before pupating in late September to early October. This growth period corresponded to the period when the gall walls became thinner. Parasitoid attack, which was the principal factor in the mortality of A. glanduliferae in the tree crown, was concentrated around the pupation period of the cynipid. Gall walls were significantly thinner in galls attacked by parasitoids than in those still containing a living cynipid. Therefore, the period available to parasitoids seems to be limited by both gall wall thickness and cynipid size. Thus, the growth pattern of A. glanduliferae larvae can have significance in that it narrows the window of vulnerability to parasitoids to a particular period. Although delaying gall initiation will also shorten the exposure period to parasitoid attacks, it was likely to increase the risk of death from gall abortion caused by seasonal degradation in the quality of host plant tissues. Although many cynipids were killed by disease in the galls that fell to the ground, the falling of mature galls to the ground may be another way to a parasitoid‐free space. It is thus suggested that a trade‐off among life history traits against multiple factors operates in the refuge of A. glanduliferae from parasitoid attack.
Biodiversity and stability of herbivore populations: influences of the spatial sparseness of food plants
Authors: Yamamura K. 
Published: March 2003

AbstractReturning to the classical diversity–stability problem about population densities, we propose a hypothesis that the spatial sparseness of food plants of herbivores, which is frequently observed in diversified communities such as those in the tropics, may be a potential source of the low variability in herbivore densities. The hypothesis consists of the following components: (1) sparseness of food plants of several herbivores increases with increasing number of plant species in a given amount of area, (2) spatial sparseness of food plants reduces the dispersal rate of herbivores between food plants, (3) such a decrease in dispersal rate causes a larger spatial variance in the consumption rate of food plants, (4) such a large spatial variance in the consumption rate of food plants reduces the temporal variance in the amount of food plants, and (5) the reduced temporal variance in the amount of food plants yields a smaller variance in the temporal dynamics of herbivores. A simple mathematical model was constructed to show a theoretical basis of the fourth component of the hypothesis. To exemplify the second, third, and fourth components of the hypothesis in fields, we conducted field experiments on the interaction between butterfly larvae and cabbages, in which cabbage seedlings were planted by two levels of sparseness: 1 m apart and 0.2 m apart. The spatial variance in the amount of leaf dry weight that escaped from larval feeding was larger in sparsely planted fields, which was in accordance with the third component of the hypothesis. The variability in the mean amount of leaf dry weight was smaller in sparsely planted fields, which was in accordance with the fourth component of the hypothesis.
Spatial structure‐mediated indirect effects of an aquatic plant, Trapa japonica, on interaction between a leaf beetle, Galerucella nipponensis, and a water strider, Gerris nepalensis
Authors: Ikeda K. , Nakasuji F. 
Published: March 2003

AbstractThe spatial structure‐mediated indirect effects of an aquatic host plant, Trapa japonica (Trapaceae), on survival of a leaf beetle, Galerucella nipponensis (Coleoptera: Chrysomelidae), with regard to predation by a water strider, Gerris nepalensis (Hemiptera: Gerridae), were investigated in an irrigation pond and under indoor conditions. Beetle density, particularly in the first‐instar stage of the larvae, became extremely low in the second generation in the pond, even though food resources were abundant. The biological check method, which excludes natural enemies by caging, suggested that a causal factor of the low density was predation by Gerris nepalensis in midsummer and thereafter. Normally growing rosettes extend their leaves horizontally on the water surface. However, some rosettes of T. japonica grew leaves vertically in the later seasons, and such overgrown rosettes were distributed patchily in the ponds. Beetle density was higher on the latter rosettes than on the former ones. The indoor experiment showed that the water strider can feed on the eggs of beetles on normally grown rosettes but not on the overgrown rosettes. Furthermore, female adults of Galerucella nipponensis preferred the overgrown rosettes over the normally grown rosettes for oviposition when water striders were present. These facts suggest that the spatial structure‐mediated indirect effects of the host plant modify the interaction between herbivore and predator.
Fixation probabilities in a spatially heterogeneous environment
Authors: Gavrilets S. , Gibson N. 
Published: March 2003

AbstractWe consider a simple model of a one‐locus, two‐allele population inhibiting a two‐patch system and experiencing spatially heterogeneous viability selection. The populaton size is finite. We use a diffusion approximation and singular perturbation techniques to find the probability of fixation of a mutant allele. We focus on situations in which each allele is advantageous in one patch and deleterious in the other patch. Our theoretical results support the previous conclusions that, under certain conditions, small populations respond faster to selection than do large populations. We emphasize that knowledge of the dependence of migration rates on population size is crucial in evaluating the effects of population size on the rate of evolution.
A model for the evolutionary dynamics of cross‐feeding polymorphisms in microorganisms
Authors: Doebeli M. 
Published: March 2003

AbstractUnderstanding mechanisms of evolutionary diversification is central to evolutionary biology. Microbes constitute promising model systems for observing processes of diversification directly in the laboratory. One of the main existing paradigms for microbial diversification is the evolution of cross‐feeding polymorphisms, in which a strain specializing on a primary resource coexists with a cross‐feeding strain that specializes on a waste product resulting from consumption of the primary resource. Here I propose a theoretical model for the evolutionary dynamics through which cross‐feeding polymorphisms can gradually emerge from a single ancestral strain. The model is based on the framework of adaptive dynamics, which has proved to be very useful for studying adaptive processes of divergence under sympatric conditions. In particular, the phenomenon of evolutionary branching serves as a general paradigm for diversification. I show that evolutionary branching naturally occurs in evolutionary models of cross‐feeding if (1) there is a trade‐off between uptake efficiencies on the primary and secondary resources, and (2) this trade‐off has positive curvature. The model also suggests that the evolution of cross‐feeding should be more likely in chemostat cultures than in serial batch cultures, which conforms with empirical observations. Overall, the model provides a theoretical metaphor for the evolution of cross‐feeding polymorphisms.
Symbiotic sympatric speciation: consequence of interaction‐driven phenotype differentiation through developmental plasticity
Authors: Kaneko K. 
Published: March 2003

AbstractA mechanism of sympatric speciation is presented based on the interaction‐induced developmental plasticity of phenotypes. First, phenotypes of individuals with identical genotypes split into a few groups, according to instability in the developmental dynamics that are triggered with the competitive interaction among individuals. Then, through mutational changes in the genes, the phenotypic differences are fixed to genes, until the groups are completely separated in genotype as well as phenotype. It is also demonstrated that the proposed theory leads to hybrid sterility under sexual recombination, and thus speciation is completed in the sense of reproductive isolation. As a result of this postmating isolation, the mating preference evolves later. When there are two alleles, the correlation between alleles is formed to consolidate speciation. When individuals are located apart in space, different species are later segregated spatially, implying that the speciation so far regarded to be allopatric may be a result of sympatric speciation. Relationships to previous theories, frequency‐dependent selection, reinforcement, Baldwin's effect, phenotypic plasticity, and resource competition are briefly discussed. Relevance of the results to natural evolution is discussed, including punctuated equilibrium, incomplete penetrance in mutants, and the change in flexibility in genotype–phenotype correspondence. Finally, we discuss how our theory is confirmed both in the field and in the laboratory, in an experiment using Escherichia coli.
Polygenic inheritance is not necessary for sympatric speciation by sexual selection
Authors: Takimoto G. 
Published: March 2003

AbstractThe theoretical possibility of sympatric speciation by sexual selection has been demonstrated by a number of mathematical models. Although these models assumed that sexually selected traits are additively determined by many genes, recent empirical studies suggest that many sexually selected traits are determined by major gene inheritance. Thus, using a mathematical simulation model, this article examines whether sympatric speciation by sexual selection can occur when sexually selected traits are determined by major gene inheritance. The model reveals that speciation can occur with major gene inheritance of sexually selected traits. Simulations show that speciation from an initially monomorphic population occurs via two successive Fisher's runaway processes of sexual selection. The first runaway causes the unidirectional evolution of male secondary sexual character toward one extreme in the trait space and of female mate preference for such a character. The second runaway then drives the male character and female preference of a part of the population toward the other extreme in the trait space, splitting the population into two reproductively isolated subgroups. The current results reinforce the plausibility of sympatric speciation by sexual selection.
Dispersal distance of heterogeneous populations
Authors: Yamamura K. 
Published: March 2003

AbstractHeterogeneity among individuals in a population is one of the important factors that influence the rate of population spread. To incorporate the population heterogeneity into dispersal rate, we assume that the traveling duration varies following a gamma distribution with a shape parameter k, where (1/k) indicates the heterogeneity in the traveling duration. The resultant distribution of the traveling distance, which is called dispersal function, is then expressed by using a modified Bessel function of the second kind of order (k − 1). It is shown that the front of the distribution spreads with time in an accelerated manner during an early phase of expansion if the heterogeneity is sufficiently large, which is consistent with the results from previous studies of biological invasions. By using the data obtained from mark–recapture experiments using traps, we can obtain the maximum likelihood estimates of three parameters: heterogeneity in the traveling duration, which is defined by (1/k); the mean dispersal ability, which is defined by the product of the diffusion coefficient and the mean traveling duration; and the trap efficiency. The usefulness of this model is shown by using the data of mark–recapture experiments with the common cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae).
Population dynamics of a thistle‐feeding lady beetle Epilachna niponica (Coccinellidae: Epilachninae) in Kanazawa, Japan. 1. Adult demographic traits and population stability
Authors: Koji S. , Nakamura K. 
Published: March 2003

AbstractPopulation dynamics of a thistle‐feeding univoltine lady beetle, Epilachna niponica Lewis (Coleoptera: Coccinellidae), was studied from 1996 to 1999 in Yuwaku, Kanazawa, Japan. The lady beetles often reached such a high density level that food was depleted. The Jolly–Seber method was used for adult marking, release, and recapture data to estimate population parameters of adult number, daily resident rate, longevity, reproductive rate (R, the number of new adults produced per overwintered adults), and survival rate of new adults to the reproductive seasons (Sw). These estimates were compared with those of the Asiu, Kutsuki (A and F), and Kyoto populations, which were previously studied with similar methods and have similar intensities. Asiu and Kutsuki F populations remained at a rather low density with a low R, while Kutsuki A and Kyoto populations reached a high density where food depletion occurred with a high R value. The Yuwaku population often reached a food‐depleting level as in the Kutsuki A and Kyoto populations. It also shared the short life span of overwintered adults (13.5 days) of other high‐density populations; however, it showed much shorter longevity of new adults (36.6 days), much lower R (1.0–2.5), and higher Sw (43%–53%). In some traits the Yuwaku population was similar to the Asiu population: low R, high Sw, and low population variability (SD of log densities; 0.103 and 0.115 for overwintered and new adults, respectively, which were lowest among the populations).
Long‐term responses in arctic ungulate dynamics to changes in climatic and trophic processes
Authors: Forchhammer M. C. , Post E. , Stenseth N. C. , Boertmann D. M. 
Published: March 2003

AbstractFollowing predictions from climatic general circulation models, the effects of perturbations in global climate are expected to be most pronounced in the Northern Hemisphere. Elaborating on a recently developed plant–herbivore–climate model, we explore statistically how different winter climate regimes and density‐dependent processes during the past century have affected population dynamics of two arctic ungulate species. Our analyses were performed on the dynamics of six muskox and six caribou populations. In muskoxen, variation in winter climate, mediated through the North Atlantic Oscillation (NAO), explained up to 24% of the variation in interannual abundance, whereas in caribou up to 16% was explained by the NAO. Muskoxen responded negatively following warm and snowy winters, whereas caribou responded negatively to dry winters. Direct and delayed density dependence was recorded in most populations and explained up to 32% and 90% of variations in abundance of muskoxen and caribou, respectively.
The role of antipredator behavior in an experimental community of jumping spiders with intraguild predation
Authors: Okuyama T. 
Published: March 2003

AbstractThe role of direct and indirect interactions in intraguild predation (IGP) was investigated in a laboratory study. The study system contained two spider species, Phidippus audax and Phidippus octopunctatus, and the fruit fly, Drosophila melanogaster. P. audax and P. octopunctatus eat D. melanogaster. P. audax (top predators) also eat P. octopunctatus (intermediate predators). Thus, P. audax and P. octopunctatus compete for the shared resource and also interact as predator and prey. Experiments consisted of two treatments: risk‐IGP and full‐IGP. In the risk‐IGP treatments, I examined the effects of trait‐mediated indirect effects generated by antipredator behavior of P. octopunctatus on the survival of fruit flies. P. audax chelicerae were waxed so that P. audax could not attack a prey. The result indicated a significant positive indirect effect of P. audax on the survival of D. melanogaster due to the antipredator behavior of P. octopunctatus (a trait‐mediated indirect effect). In the full‐IGP treatments, P. audax chelicerae were not restricted, so that it could attack prey; this resulted in decreased survival of D. melanogaster. Because of predation of P. audax on P. octopunctatus, even stronger positive interactions occurred between P. audax and D. melanogaster in full‐IGP than in risk‐IGP.
Resilience Among Urban African American Male Adolescents: A Study of the Protective Effects of Sociopolitical Control on Their Mental Health
Authors: Zimmerman Marc A. , Ramírez-Valles Jesus , Maton Kenneth I. 
Published: March 2003

AbstractResilience refers to the notion that some people succeed in the face of adversity. In a risk‐protective model of resilience, a protective factor interacts with a risk factor to mitigate the occurrence of a negative outcome. This study tested longitudinally the protective effects of sociopolitical control on the link between helplessness and mental health. The study included 172 urban, male, African American adolescents, who were interviewed twice, 6 months apart. Sociopolitical control was defined as the beliefs about one's capabilities and efficacy in social and political systems. Two mental health outcomes were examined—psychological symptoms and self‐esteem. Regression analyses to predict psychological symptoms and self‐esteem over time were conducted. High levels of sociopolitical control were found to limit the negative consequences of helplessness on mental health. The results suggest that sociopolitical control may help to protect youths from the negative consequences of feelings of helplessness. Implications for prevention strategies are discussed.
Adjustment Problems and Emerging Personality Characteristics from Early to Late Adolescence
Authors: Ge Xiaojia , Conger Rand D. 
Published: March 2003

AbstractThis 6‐year longitudinal study extended earlier findings of contextual influences on adolescent adjustment problems by examining relationships between adolescent emotional and behavioral problems and late adolescent personality among more than 400 youths who were followed from 7th grade to the last year of high school. Results suggest that psychological distress and behavioral problems experienced during the adolescent years (7th–10th grades) are significantly related to personality structure during the final year of high school (12th grade). Psychological distress in adolescence was primarily related to the Multidimensional Personality Questionnaire (MPQ) superfactors of negative and positive emotionality, whereas delinquency and substance use problems were primarily related to the MPQ superfactor of constraint. These relationships remained significant even when personality characteristics in 9th grade were taken into account. That is, emotional and behavioral problems predicted change in personality traits during the adolescent years. Moreover, both initial level and change in distress and problem behaviors were predictive of late adolescent or early adult personality. This finding suggests that personality formation is a dynamic process, dependent on the growth or decline, as well as the magnitude of earlier developmental problems. Because earlier research has shown that these developmental problems are affected by both distal and proximal environmental contexts as well as by the formative nature of adolescence, intervention efforts aimed at the reduction of maladjustment and the enhancement of healthy personality development should target early adolescent social contexts. Other theoretical implications of the findings also are discussed.