The evolutionary significance of wing dimorphism in carabid beetles (Coleoptera: Carabidae)

A review of data on the background of wing dimorphism in carabid beetles (Coleoptera: Carabidae) and especially of the closely relatedCalathus cinctus andC. melanocephalus is given. In bothCalathus species wing dimorphism is inherited in a simple Mendelian fashion with the brachypterous condition dominant, but inC. melanocephalus the expression of the long winged genotype is under environmental control as well. The development of long winged phenotypes in the latter species is favoured by relatively favourable environmental conditions, such as high temperatures and a high food-supply. The higher fecundity of the larger and heavier long winged females of both species may compensate for losses of long winged phenotypes by flight activities. The evolutionary significance of both types of inheritance is discussed in relation to dispersal. The ‘fixed type’ as found inC. cinctus is considered an opportunistic short term ‘between sites strategy’, whereas the ‘dynamic type’ ofC. melanocephalus represents a flexible long term ‘within sites strategy’.     

Genetic analysis of the wing-form determination of the small brown planthopper,Laodelphax striatellus (Hemiptera: Delphacidae)

Summary The mechanism of the genetic control of wing form determination of the small brown planthopperLaodelphax striatellus was analyzed by selection and crossing experiments. The selection experiment for brachypterous and macropterous forms for 13 generations showed that the wing form is under some genetic control. The crossing experiment showed that the wing form polymorphism was not a simple Mendelian character but was under polygenic control. The data from the crossing experiment were applied to the liability method for the quantitative genetics by Falconer (1981). The analysis suggested that wing form determination was a threshold character under polygenic control, and the estimated minimum number of loci concerned was 2.07. The realized heritability estimated from the data of selection experiment was 0.36 for macroptery. On the other hand, the heritability in broad sense estimated on the basis of the variance of F₁ and F₂ in crossing experiment was 0.81.     

A male fitness advantage to wing reduction in the oriental chinch bug,Cavelerius saccharivorus okajima (heteroptera: Lygaeidae)

Summary A male fitness advantage to wing reduction was investigated for the oriental chinch bug,Cavelerius saccharivorus, which is wing dimorphic. Field surveys for the frequency of matings between wing morphs showed that the mating probability was much higher in brachypterous males than in macropterous males in the early breeding season. Brachypterous males copulated with not only brachypterous females but also macropterous females in this season. This led to a considerable rate (30%) of insemination of macropterous females just before emigration even in the early breeding season. A rearing experiment for the pre-reproductive period of females revealed that females mated with brachypterous males copulated and oviposited earlier than females mated with macropterous males. These results indicate that there is a fitness advantage to wing reduction in the males ofC. saccharivorus in terms of the earlier sexual maturation.     

Journeying Toward the Nation(al): Cultural Difference at the Crossroads of Old and New Globalisations

The superimposition of new migratory flows linked to post‐Cold War global realignments upon older migratory flows marked by the global alignments of colonialism have profoundly marked contemporary Britain. Alongside policies and practices of security aimed especially at Muslims, struggles over the meaning of the plurality of cultural forms signalled by ‘multiculturalism’ have assumed a central place in government, media and popular discourse as the provenance and scope of Britishness and citizenship are debated in attempts to foster social cohesion. Against this context, and with specific reference to the British Caribbean population, this article explores the shifting subject positions and subjectivities that are constituted in the crucible of cultural difference and multiple forms of border crossing, and the anxieties these produce as they expose the instabilities inherent in the constitution of nation and national belonging.     

Genetic control and evolution of acoustic signals in planthoppers (Homoptera: Delphacidae)

Acoustic signals are part of the specific mate recognition system of planthoppers. The genetic control of acoustic signal characters was studied in the planthopperRibautodelphax imitans. Artificial selection for interpulse interval in the female call revealed a large additive genetic component for this polygenic character. Other female call characters showed a correlated response. Some male call characters also appeared to be genetically correlated with the female character selected for, despite the rather different structure of male and female calls. Parent-offspring regression provided significant heritability estimates for those male call characters that also responded to artificial selection in the female call, one of which appeared to be influenced by sex-linked genes. It is argued that the differentiation of this mate recognition system in planthopper populations and species could be the result of founder effects, enabled by the genetic plasticity of the call characters and the existence of a wing length dimorphism in these animals.     

Reproduction and egg diapause of the oriental chinch bug,Cavelerius saccharivorus okajima (Heteroptera: Lygaeidae), in the subtropical winter season in relation to its wing polymorphism

Summary Reproduction and egg diapause of the oriental chinch bug,Cavelerius saccharivorus, in the subtropical winter season were investigated in relation to its wing polymorphism. Macropterous females collected from the southern part of Okinawa Is. in the autumn season delayed their oviposition and were less fecund early in the adult life period, but survived much longer than brachypterous females collected from the same locality. The total fecundity was not significantly different between wing morphs. The diapause of eggs laid by brachypters tended to be terminated more easily at a high temperature than that of eggs laid by macropters. This indicated that the eggs laid by macropters were more intense in their diapause than those laid by brachypters. However, irrespective of the parental wing form, diapause showed considerable variation in its intensity within and between clutches.     

Why is there so much genetic variation for wing dimorphism?

Wing dimorphism appears in general to be determined either by a single locus, 2 allele system in which brachyptery is dominant, or by the additive action of numerous loci. In the latter case studies indicate that the heritability is typically quite large. It is generally postulated that wing dimorphism is under strong selection: why then is genetic variation not eroded? In this paper I consider three possible explanations. First, genetic variation may not be exposed to selection because environmental heterogeneity effectively makes heritability zero. Because wing dimorphisms are known to evolve it seems unlikely that this is the primary factor. Second, directional selection on a threshold trait may push the population almost to monomorphism but erodes genetic variance at a very slow rate. This mechanism cannot preserve variation but makes it possible for other factors to more easily maintain variability. Finally, I demonstrate that in a heterogeneous environment spatio-temporal variation in fitness will itself maintain a genetic polymorphism for wing dimorphism. This paper is dedicated to Professor Sinzo Masaki, whose work on the evolution of wing dimorphism and diapause has been so important to our understanding of the evolution of dimorphic variation.     

Ecological significance of the wing polymorphism of the oriental chinch bug,Cavelerius saccharivorusOkajima (Heteroptera: Lygaeidae)

Summary The wing polymorphism of the oriental chinch bug,Cavelerius saccharivorus, was studied in relation to its reproductive strategy. The frequency distribution of wing form in terms of the relative wing length (R.W.L.) changed with increase in the population density from a single modality biased toward the brachypterous form to bimodality with both macropterous and more extreme brachypterous forms. Since some evidences in the field showed that fliers are limited to macropters, such a bimodality of wing form indicated thatC. saccharivorus employs a mixed strategy with some portion of adults staying on in the same habitat, whereas the rest disperse. Moreover, macropters were larger in body size than brachypters emerging in high density populations, although smaller than brachypters emerging in low density populations. Larger body size as well as the delay of ovarian maturation in macropters was considered to be a beneficial trait for migratory behaviour.     

Variability in wing form of crickets

Loss of functional hindwings is observed in most subfamilies of Japanese crickets. Habitat, behaviour, body size and phylogenetic factors might be involved, but interactions among them may obscure the general trend. Wing dimorphism is common among the relatively small-sized members of Gryllinae, and the two small-sized subfamilies, Nemobiinae and Trigonidiinae. Both environmental cues (e. g. photoperiod) and genetic factors affect the wing form. InDianemobius fascipes (Nemobiinae), the percentage macroptery was drastically changed by selection for macroptery or microptery. Crossing experiments indicated polygenic control of wing form as well asX-chromosomal and maternal effects. Neither the long-winged nor short-winged line bred true after 40 generations of selection. Full-sib families revealed a large genetic variation in frequency of macropterous forms within a population. The genetic determination of the propensity for macropterism did not seem to be directly coupled to the mechanism performing the photoperiodic time-measurement.     

Factors and consequences of a non-functional alary polymorphism inPyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

Functional alary polymorphisms have been studied rather extensively in several insect species. This review article deals with factors controlling wing polymorphism in a flightless species,Pyrrhocoris apterus (L.), and discusses its adaptive significance and mechanisms for their persistence under natural conditions. The macropterous morph is determined by a recessive allele whose penetrance depends on photoperiod and temperature. Natural populations of this species contain a small fraction of flightless macropters. The disadvantages of being a macropter (increase of development time, decrease of fecundity) are minimal, while the benefit may consist in the tendency to prereproductive arrest of ovarian development in teneral females. It prevents establishing a second generation which would mostly die during the next winter. The mechanism of alary morph regulation may be an ancestral trait linkingP. apterus with other polymorphic Heteroptera, while its decreased penetrance may be a derivative character. Variation in fitness due to alary morphs is small compared to the one associated with differences in body size. The latter is environmentally determined, and not linked to the genetic basis of wing polymorphism. In the “mosaic” of phenotypes of various size the significance of the genetic macroptery may be close to neutral.     

Polymorphic fundatrices in thimbleberry aphid — ecology and maintenance

The thimbleberry aphid,Masonaphis maxima (Mason) lives on patches of plants that support 3,4 or 5 generations depending on site and weather. The life cycle requires sexual females and males to produce overwintering eggs. The eggs hatch in the spring to produce the first ’fundatrix’ generation; subsequent generations are produced parthenogenically. Males and other morphs are produced by wingless virginoparae, but sexual females are produced by ’gynoparae’, a winged morph that is specialized to produce only sexual females. The fundatrices have no indication of the number of generations that the plants will support in the current year. There are two fundatrix types that coexist in different ratios depending on the number of generations supported by the patch the previous year. One type produces sexual females in generations 3 and 5, and males in generations 4 and 5; the other type produces sexual females in generations 4 and 5, and males in generations 3, 4 and 5. The dimorphism adapts the aphid to its heterogeneous and somewhat unpredictable environment. The role of sex in the maintenance of the dimorphism is discussed. This is the first report of fundatrix polymorphism and consequent differential sex expression in aphids.     

The dynamics of credentialism: Ireland from bust to boom (and back again)

The relationship between educational qualifications and labour market outcomes has been perhaps the dominant theme in research on school to work transitions. A range of explanations has been offered for this relationship, but such explanations have often been quite static in nature or assumed that any trend is linear. This article explores the dynamics of educational credentialism using Ireland as a case study. Using data from the national School Leavers’ Survey for the period 1984-2007, it examines the way in which two dimensions of education - level and grades - have influenced early labour market outcomes over a period shifting from high unemployment to dramatic employment growth. The analyses presented point to both long-term and short-term changes in the education-employment relationship. An increase in the proportion of young people with upper secondary qualifications is found to result in a growing gap in employment chances between the more and less qualified. Furthermore, employers are found to rely on different educational signals depending on broader economic conditions, with grades assuming a more important role in accessing employment when jobs are scarce. It is argued that the Irish example points to a more comprehensive framework for understanding the dynamics of credentialism.     

Selection and reproductive success in males of the dragonfly,Orthetrum japonicum (Odonata: Libellulidae)

Reproductive success, copulation success, and mating success were measured for a population of male dragonflies,Orthetrum japonicum. Copulation success explained the greatest variation in reproductive success. The proportion of copulations followed by oviposition was positively correlated with the number of oviposited eggs per mating. Directional selection on four morphological characters was estimated. The effect of selection on correlated traits was comparable to that of direct selection. Directional selection varied between traits and between episodes in a single trait. The probability that the observed directional selection on the four morphological traits was expected under the condition of the selective neutrality of traits was not smaller than 5%.     

Twenty years of the Journal of Homosexuality: a bibliometric examination of the first 24 volumes, 1974-1993

This study examines and evaluates the contents of the first 24 volumes of Journal of Homosexuality (JH), from 1974 to 1993. Data from each issue of JH, in terms of source articles and contributing authors, were collected and analyzed. JH is shown to be a scholarly journal, with high rates of citations per article, high levels of author education, a prevalence of scholarly methodological approaches, and a low rate of self-citation. Articles that disseminated the findings of empirical research noticeably decreased over time, while articles focusing on historical analysis noticeably increased. This trend was consonant with the change over time of JH's mission statement and editorial policy.     

Father Absence and Accelerated Reproductive Development in Non-Hispanic White Women in the United States

Girls who experience father absence in childhood also experience accelerated reproductive development in comparison with peers with present fathers. One hypothesis advanced to explain this empirical pattern is genetic confounding, wherein gene-environment correlation (rGE) causes a spurious relationship between father absence and reproductive timing. We test this hypothesis by constructing polygenic scores for age at menarche and first birth using recently available genome-wide association study results and molecular genetic data on a sample of non-Hispanic white females from the National Longitudinal Study of Adolescent to Adult Health. We find that young women’s accelerated menarche polygenic scores are unrelated to their exposure to father absence. In contrast, polygenic scores for earlier age at first birth tend to be higher in young women raised in homes with absent fathers. Nevertheless, father absence and the polygenic scores independently and additively predict reproductive timing. We find no evidence in support of the rGE hypothesis for accelerated menarche and only limited evidence in support of the rGE hypothesis for earlier age at first birth.     

Genetic correlation of wing polymorphism between females and males in the oriental chinch bug,Cavelerius saccharivorus Okajima (Heteroptera: Lygaeidae)

Summary Genetic correlations of the wing form and the relative wing length between females and males were estimated in the oriental chinch bug,Cavelerius saccharivorus, by calculating the correlation between the sexes of the proportion macropterous or the mean relative wing length in full-sib families obtained from different wing forms of parents emerged in a high density population. There was a significantly positive genetic correlation between the sexes in both the proportion macropterous and the mean relative wing length. However, the appearance rate of macropters tended to be much lower in males than in females under the rearing conditions which promote the appearance of macropters. This was evident especially in the offspring of brachypterous parents. These indicated that inC. saccharivorus the wing polymorphism of males is not a simple result of the genetic correlation of wing morphology between the two sexes. It was considered that both of the female and male fitness advantages to wing reduction, as well as the genetic correlation between the sexes, would influence the evolution of wing polymorphism in this species.     

Nonmarket networks among migrants: evidence from metropolitan Bangkok,Thailand

This paper examines the nonmarket interactions among migrants in the urban labor market of Bangkok, Thailand. We test whether the population size and the labor-market performance of previous migrants have externalities to new migrants who have moved from the same province of origin. Our empirical results, which control origin fixed effects, time fixed effects, and origin- and year-specific correlated shocks, show that (1) the relative population size of previous migrants in the market decreases the employment probability of new migrants (substitution effect), (2) the employment probability of previous migrants increases that of new migrants (positive externalities), and (3) when the employment probability of previous migrants is high, however, the scale effect becomes positive, which demonstrates a threshold in the informational scale economies. The results imply that positive informational scale effect dominates negative substitution effect when the efficiency of previous migrants is sufficiently high in the destination labor market.

Correlations,causes and heuristics in surveys of life satisfaction

Satisfaction with life domains is more highly correlated with interpersonal than with intrapersonal comparisons (Emmons and Diener, 1985). The hypothesis of the present studies is that the high correlations reflect inferences of social comparison from global satisfaction. Paradoxically, such inferences are most likely in private domains (love life, friends), where social information is scarce and relatively unimportant as a determinant of satisfaction. Study I replicates the Emmons-Diener findings, but also finds that subjects judge recent changes more important than social standing as a determinant of life satisfaction, especially in private domains. Study II examines an order effect in judgments of satisfaction. As hypothesized the correlation between social comparison and global satisfaction is higher (in private domains only) when global satisfaction is judged first than when the order of judgment is reversed.     

Negative population growth: how to go about it? (Letter to the editor)

It proves an interesting exercise to try to determine the effects of a national policy of government control developed on the basis of the need to conserve scarce resources, lessen environmental pollution, and to reduce the U.S. population to 1/2 of the 1970 figures within 100 years without increasing the risks of death. Let it additionally be assumed that in order to minimize the required reduction of fertility that there be no net migration. At the end of the reduction process, the stationary state in stable equilibrium might hopefully be achieved. If these are the goals, the process would include 1) reduction of the annual stream of births immediately to the number that would ultimately be required to sustain a population 1/2 as large as the present number and 2) smooth decline of the totals but with constituent age groups shifting drastically as the sharply reduced stream of births spreads upward through the span of life, with those 65 years and older making up 12% of the population. To obtain a fixed annual stream of births from sharply changing numbers of women of childbearing age would require rapid and drastic changes in the rates of childbearing. The same reduced population could be obtained from a system involving less drastic changes in the age composition, but these means would not be positive ones for older individuals. Both fertility and age distribution could move more smoothly if the mortality risks increased or with considerable emigration of the aged. Other means of reducing the population to 1/2 the present size within 100 years would create even more turbulence in the age distribution and rates of childbearing than those just discussed.     

A new method to control houseflies,Musca domestica, at waste disposal sites

Summary Investigation was carried out from 1976 to 1979 to establish a new control system against the houseflies,Musca domestica, at a sea-filling waste disposal site in Osaka Bay, Japan. Field surveys showed that the garbage was favorble for the fly breeding for 20–30 days after being disposed, while the sewage sludge and the ash from incinerated refuse were unfavorable. Comparing the fly density at the site to the reported cases of the public complaints in the urban area near to the site, a complaint threshold density of the flies at the site was estimated. Then, a control threshold density was assumed from the complaint threshold density and the reproductive rate of the housefly population. Several insecticides, as well as a surface active agent, polyoxyethylene lauryl ether (PEL), were found effective for the temporary suppression of the fly density. Based on the results obtained, the following control system was worked out. 1) Refuse is disposed onto the same area as other inorganic wastes to deteriorate the capacity of breeding sources. 2) The fly density is examined on newly disposed refuse almost everyday by landfill operators. 3) PEL is sprayed when the density slightly exceeds the control threshold density. If the density increases rather higher, insecticide should be used. 4) The disposed refuse is covered with soil or other inorganic wastes on every weekend or every other weekend by 15 cm thickness. Success in both fly control and reduction of the amounts of insecticides sprayed was achieved by a field application of this new control system.