Relative contribution of genetic and environmental factors to determination of wing morphs of the brown planthopper Nilaparvata lugens

Wing dimorphism is a fascinating feature of the ability of insects to adapt to environments. The brown planthopper (BPH) Nilaparvata lugens, a serious pest of rice, can switch between the long- and short-winged morphs. It has been known that environmental factors can affect the wing morph of BPH. However, it is still unclear whether the effect of environment is dependent on BPH genetic backgrounds or not. In the present study, we established the pure-bred lineages of short- and long-winged BPHs via multigenerational selection, and we found that survival and fecundity were similar between these 2 lineages. Wing morphs of the pure-bred lineages were almost fully dependent on genetics, but independent of the environmental factors, nymphal density and rice plant stage, 2 key factors affecting BPH wing morphs. In the unselected BPH population, short- and long-winged morphs were produced depending on those 2 environmental factors, indicating the contribution of environment to wing morph. In the wing-selected lineages, 4 developmental regulated genes of wing, NlInR1, NlInR2, NlAkt, and NlFoxo were expressed stably in the short-winged adults, but almost silenced in the long-winged adults. However, all these genes were expressed normally with a similar level in both the short- and long-winged adults in an unselected population except NlFoxo. The pure-bred lineages of long- and short-winged morphs exhibited different expression patterns of wing development-regulated genes, suggesting the genetic determination of wing morphs. Effects of environmental factors on wing morphs occurred only in the genetic mix population.     

The cost of being able to fly: a study of wing polymorphism in two species of crickets

Summary The widespread occurrence of wing polymorphisms in insects suggests that the possession of wings and ability to fly adversely affect components of the insect's life characteristics that contribute to its Darwinian fitness. This hypothesis was tested by an analysis of the differences in life history parameters of the macropterous and micropterous morphs of the two cricket species G. firmus and A. fasciatus. In both species there were no differences in development time or adult survival between the two morphs. Significant differences in head width were not consistent between the two species but in both sexes of G. firmus and females of A. fasciatus (insufficient males for analysis) long-winged individuals weighed more than short-winged individuals with the same head width. In both species egg production is delayed in macropterous females. The cumulative fecundity of the micropterous morph is greater than the macropterous morph in both species but only in G. firmus is the difference statistically significant. A. fasciatus frequently loose their wings but no such loss has been observed in G. firmus. There is a significant increase in egg production after the loss of the wings. These results are in accord with those of Tanaka (1976) for the cricket, Pteronemobius taprobanensis.Breeding experiments indicate that in G. firmus the wing polymorphism is under genetic control. The decrease in fecundity is sufficiently large that genotypes producing only macropterous offspring could only persist in highly unstable environments where continuous dispersal was imperative for survival. However, the reproductive cost of a genotype producing a small percentage of macropterous individuals is slight. The fitness that accrues to a genotype producing a few dispersing offspring is likely to offset the small reproductive cost and hence wing polymorphisms should be favoured.     

Seasonal wing length dimorphism in a tropical seed bug: ecological significance of the short-winged form

Summary Short-winged forms of the bug, Jadera aeola, were discovered during the late dry season at a study site on Barro Colorado Island, Panama. They were smaller than long-winged adults not only in elytron and hindwing sizes but also in head, thorax, rostrum and hind femur dimentions. When newly emerged adults were kept under natural photothermal conditions, short-winged females started ovipositing earlier, produced more eggs, and died earlier than did long-winged females. This was partly due to the fact that long-winged adults usually enter diapause after adult energence (Tanaka et al. 1987b). Egg size was another factor contributing to the high egg production in the short-winged form; it was significantly smaller in the short-winged form than that in the long-winged form. Wing form was apparently environmentally induced because all off-spring of short-winged adults became long-winged. No short-winged form was obtained in the laboratory when nymphs were reared on different species of seeds at different photoperiods. Although the factor(s) responsible for determination of the wing form remains unknown, the ecological significance of this short-winged form seems clear, i.e. exploitation of the food resource left in the late dry season. Wing length dimorphism in J. aeola could be a response to unpredictable availability of the food resource determined by seed production of the host plants (Sapindaceae) and by the timing of the onset of a wet season.     

The role of juvenile hormone and juvenile hormone esterase in wing morph determination in Modicogryllus confirmatus

The role of juvenile hormone (JH) and juvenile hormone esterase (JHE) in regulating wing morph determination was studied in the cricket Modicogryllus confirmatus. JHE activities were significantly higher in nascent long-winged (LW) vs short-winged (SW) crickets during the latter half but not during the first half of the last stadium. The magnitude and direction of the activity differences were similar to those previously documented between wing morphs of the cricket, Gryllus rubens. In contrast, activities of general esterase, an enzyme or group of enzymes with no demonstrated role in regulating the JH titer in insects, showed no or only minor differences between morphs. The magnitude and direction of the JHE activity variation is consistent with a regulatory role for this enzyme in some aspect of wing dimorphism. However, the timing of the differences (exclusively during the last half of the last stadium) argue against a role in regulating wing length development per se. Single or multiple applications of juvenile hormone-III to nascent LW individuals during the first few days of the last stadium significantly redirected development from long to short wings. Multiple applications of acetone, by itself, also increased the production of short-winged adults. For most treatments, all individuals with shortened wings also had undeveloped flight muscles. These data suggest that JH may play a role in wing morph determination in M. confirmatus but that it affects a different aspect of the polymorphism from JHE.     

EVOLUTIONARY ENDOCRINOLOGY OF JUVENILE HORMONE ESTERASE: FUNCTIONAL RELATIONSHIP WITH WING POLYMORPHISM IN THE CRICKET,GRYLLUS FIRMUS

The existence, nature, and physiological consequences of genetic variation for juvenile hormone esterase (JHE) activity was studied in the wing-polymorphic cricket, Gryllus firmus. Hemolymph (blood) JHE activity was sixfold lower in nascent short-winged (SW) females, relative to nascent long-winged (LW) females during the last juvenile stadium (stage). Morph-associated genetic variation for JHE activity had two causes, variation in loci: (1) regulating whole-organism enzyme activity; and (2) controlling the degree to which JHE is secreted into the blood Reduced JHE activity in nascent SW-selected individuals was associated with reduced in vivo juvenile hormone catabolism. This suggests that variation in JHE activity during juvenile development may have important physiological consequences with respect to the regulation of blood levels of juvenile hormone and consequent specification of wing morph. This is the first definitive demonstration of genetic variation for hormonal metabolism in any insect and a genetic association between hormone metabolism and the subsequent expression of morphological variation (wing morph). However, we have not yet firmly established whether these associations represent causal relationships In contrast to the clear association between JHE activity and wing morph development, we observed no evidence indicating that variation in JHE activity plays any direct or indirect role in causing the dramatic differences in ovarian growth between adult wing morphs. Variation in JHE activity also does not appear to be important in coordinating the development of wing morph with the subsequent expression of reproductive differences between adult morphs. Finally genetic variation for the developmental profiles of JHE activity during juvenile and adult stages are remarkably similar in three Gryllus species. This suggests that genetic correlations between JHE activities during different periods of development, which underlie these activity profiles, have been conserved since the divergence of the three Gryllus species.     

昆虫翅型分化的调控及翅多型性的进化

翅多型现象普遍存在于各昆虫类群,一些学者就昆虫翅多型进行了大量的研究工作。根据昆虫翅型的分化,可划分为长翅型和短翅型,长翅型具飞行能力,而短翅型不能飞行。一些昆虫种类,如蚜虫,出现无翅个体,被称为无翅型。除飞行能力外,长翅型和短翅型在行为、生理等方面也存在差异。文章主要就环境因素对翅型分化的影响、翅多型的内分泌控制机理、翅多型的遗传机制及其进化等作一概述。     

The physiological costs of flight capability in wing-dimorphic crickets

Nutritional indices, triglyceride levels and flight muscle developmental profiles were compared between long-winged (LW) and short-winged (SW; flightless) morphs of the cricketsGryllus rubens Scudder andG. firmus Scudder. This was done to identify potential physiological costs of flight capability in adults. The LW morph of each species converted a lower proportion of assimilated nutrients into biomass (reduced ECD) than did the SW morph. This documents increased respiratory metabolism in the LW morph. Triglyceride concentration was higher in LW vs. SW adults. This suggests that the elevated respiration in the LW morph may be at least partially due to the increased biosynthesis of this high energy substance. Preliminary data indicate higher respiration rates of LW functional vs. SW vestigial flight muscles. Collectively, these data suggest that the energetic cost of flight capability in adults results from biosynthesis of triglyceride flight fuel and flight muscle maintenance but not flight muscle growth. No flight muscle growth was observed in adults.     

Fecundity in relation to wing-morph of three closely related species of the melanocephalus group of the genus Calathus (Coleoptera: Carabidae)

Summary In two successive years the fecundity of the carabid beetles Calathus (Neocalathus) cinctus, C. (N.) melanocephalus and C. (N.) mollis was studied in relation to wing-morph and temperature. Differences were found between the three species in both egg production and timing and length of the oviposition period. In all species the fecundity of laboratory bred beetles was significantly higher than that of females collected in the field. Long-winged females of both cinctus and melanocephalus had significantly higher egg production than short-winged females, and they also tended to produce eggs over a longer period. In mollis only the fecundity of the long-winged morph was established. The observed lower relative fitness of the short-winged morph in both cinctus and melanocephalus contradicts the supposed increase of the frequency of this morph in ageing, more or less isolated, populations of these species. The loss of long-winged genotypes, resulting from flight activities, is considered the most plausible cause of the increase of short-winged beetles in ageing populations. The higher fecundity of macropterous females makes them especially suited for (re)establishing populations.Communication No. 429 of the Biological Station WijsterPresent address and address for offprint requests: Kortenburg 31, NL-6871 ND Rentum     

植物病媒昆虫的翅型分化

翅多型现象是昆虫非遗传多型性的一种表现,包括不具飞行能力的短翅型或无翅型,以及可以进行长距离迁飞的长翅型或有翅型。翅多型现象常发生在可以携带病原并将其传播给植物宿主的媒介昆虫中,对植物病害的时空分布与暴发有重要影响。本文从翅型分化的遗传规律、诱导因素、分子机制和伴随翅型分化的其他生理表现4个方面,对植物病原主要传播媒介蚜虫和飞虱的翅型分化研究进行综述和梳理。昆虫翅型分化的诱导因素主要包括温度、湿度和光周期等非生物因素以及虫口密度、宿主营养、病毒等生物因素;而其内在的分子机制大多是通过胰岛素/胰岛素样生长因子信号(IIS)通路、c-Jun氨基末端激酶(c-Jun NH 2-terminal kinase,JNK)信号通路、Wingless和嗅觉受体SaveOrco等调控。翅型分化的同时伴随着生理状态的变化,表现为短翅型具有更强的繁殖能力和长翅型含有更丰富的飞行肌结构成分。目前,昆虫翅型分化的研究尚不够完善,有许多需要解答的问题,如找到胰岛素/胰岛素样生长因子信号通路中真正发挥功能的靶基因,JNK如何调控翅型分化以及虫媒病毒影响媒介昆虫翅型的分子机理。本综述可为控制虫媒病原的传播以及其他昆虫翅多型的研究提供参考。     

The effect of diet quality and wing morph on male and female reproductive investment in a nuptial feeding ground cricket

A common approach in the study of life-history trade-off evolution is to manipulate the nutrient content of diets during the life of an individual in order observe how the acquisition of resources influences the relationship between reproduction, lifespan and other life-history parameters such as dispersal. Here, we manipulate the quality of diet that replicate laboratory populations received as a thorough test of how diet quality influences the life-history trade-offs associated with reproductive investment in a nuptial feeding Australian ground cricket (Pteronemobius sp.). In this species, both males and females make significant contributions to the production of offspring, as males provide a nuptial gift by allowing females to chew on a modified tibial spur during copulation and feed directing on their haemolymph. Individuals also have two distinct wing morphs, a short-winged flightless morph and a long-winged morph that has the ability to disperse. By manipulating the quality of diet over seven generations, we found that the reproductive investment of males and females were affected differently by the diet quality treatment and wing morph of the individual. We discuss the broader implications of these findings including the differences in how males and females balance current and future reproductive effort in nuptial feeding insects, the changing nature of sexual selection when diets vary, and how the life-history trade-offs associated with the ability to disperse are expected to differ among populations.     

丽斗蟋翅二型雌虫飞行肌和卵巢发育间的资源分配差异

丽斗蟋Velarifictorus ornatus具有明显的翅二型现象, 长翅型与短翅型雌虫的卵巢和飞行肌存在着生理权衡。本研究分别应用蒽酮比色法、 硫代磷酸香草醛法、 考马斯亮蓝染液对羽化后10 d内两型雌虫飞行肌与卵巢内糖原、 总脂及蛋白质含量进行了定量分析。结果表明： 成虫羽化后10 d内, 两型雌虫体重无明显差异(P>0.05), 但短翅型雌虫怀卵量明显多于长翅型雌虫, 而人工脱翅能够促进长翅型雌虫怀卵量增加(P<0.05)。短翅型雌虫飞行肌内蛋白质、 糖原及总脂含量在成虫羽化后10 d内无明显变化, 但长翅型雌虫飞行肌内蛋白质在成虫羽化后3 d时达到最大值564.4±87.5 μg/♀, 糖原与总脂含量分别于羽化后第5天达到最大值85.2±21.7 μg/♀和5 284.7±1 267.4 μg/♀。然后开始下降, 各实验处理天数内, 长翅型雌虫飞行肌内蛋白质、 糖原及总脂含量都显著多于短翅型雌虫(P<0.05)。相反, 各处理天数内, 短翅型雌虫卵巢内蛋白质、 糖原及总脂含量则明显多于长翅型雌虫(P<0.05), 同时虫龄对蛋白质、 糖原及总脂在两型雌虫飞行肌与卵巢内分配也产生明显影响(P<0.05)。人工脱翅能够促进长翅型雌虫卵巢内蛋白质、 糖原及总脂含量增加, 同时诱导飞行肌内蛋白质、 糖原及总脂含量降低, 其中总脂含量在脱翅后10 d时降为2 394.9±1 461.8 μg/♀, 只有最大值的一半, 而与短翅型雌虫相似(P>0.05), 表明总脂为丽斗蟋飞行的主要能源物质。外用保幼激素Ⅲ能够促进长翅型雌虫卵巢内蛋白质、 糖原及总脂含量增加(P<0.05), 但对飞行肌内三者含量无明显影响(P>0.05), 外用早熟素Ⅰ对短翅型雌虫卵巢内蛋白质、 糖原及总脂含量亦无明显影响(P>0.05)。上述结果表明, 丽斗蟋长翅型雌虫首先将获得的资源用于发育飞行所需的飞行肌, 短翅型雌虫则首先将所获得的资源用于发育繁殖所需的卵巢, 但长翅型雌虫飞行肌与卵巢间的资源分配方式受保幼激素的影响。     

Cryptic female choice predicated on wing dimorphism in decorated crickets

Male decorated crickets, Gryttodes sigllatus, normally lackbind wings and are incapable of flight (short-winged males),but occasionally exhibit fully developed hind wings that makerudimentary flight possible (long-winged males). Long-wingedmales bear a cost of flight in the form of decreased inseminationsuccess, which arises as a consequence of two interrelated factors:(1) long-winged males exhibit a lower reproductive investmentrelative to short-winged males, as measured by the mass of amale's spermatophore and reproductive organs and (2) the postcopulatorybehavior of females favors males that maximize their reproductiveinvestment. Of particular importance to male mating successis the spermatophylax, a large gelatinous mass forming partof the spermatophore and consumed by the female after mating.Consumption of the spermatophylax keeps the female preoccupiedwhile sperm are discharged from the remaining portion of thespermatophore (sperm ampulla) into her repro ductive tract.The spermatophylax of long-winged males is significantly smallerthan that of short-winged males and consequently requires lesstime to consume. As a result, the sperm ampulla of long-wingedmales is frequently removed before its complete evacuation andsignificantly sooner than that of short-winged males. Becausethe spermatophore-removal behavior of females mediates the relativeinsemination success of short-winged and long-winged males,it can be considered a form of cryptic female choice     

Potential Reproductive Advantage of Short-over Long-Winged Adult Males of the Cricket <Emphasis Type="Italic">Velarifictorus ornatus</Emphasis>

A trade-off between flight capability and reproduction is well known in adult females of the wing-dimorphic cricket Velarifictorus ornatus, but it is not clear whether such a trade-off exists in adult males of the species. In the present study, we investigated sexual maturation time, mating frequency, and the fertilization success of spermatophores after sequential mating in long-winged (LW) and short-winged (SW) adult males of V. ornatus to evaluate the potential reproductive advantage of the SW over the LW male morph. We found that the SW males of V. ornatus attained sexual maturity earlier and produced heavier spermatophores during the early stage after adult emergence than their LW counterparts. Additionally, within a 24-h mating period, the SW males showed a higher mating frequency, greater spermatophore weight, and shorter intermating time interval compared with their LW counterparts. Although females copulated with the two male morphs produced eggs of similar size, fertilization success by SW males was significantly higher than by the LW males. These results provide support for a trade-off between dispersal capability and reproduction success in wing-dimorphic males of V. ornatus.     

Differential allocation of protein resources to flight muscles and reproductive organs in the flightless wing-polymorphic bug, <Emphasis Type="Italic">Pyrrhocoris apterus</Emphasis> (L.) (Heteroptera)

Differences in the growth of dorsolongitudinal flight muscles and gonads in 1–28 days old long-winged (macropterous) and short-winged (brachypterous) adults of the firebug (Pyrrhocoris apterus L.) and the resource allocation to these organs were studied by means of total protein analysis. We found predominant allocation of food resources to flight muscles compared to reproductive organs in both macropterous males and females during the first 5 days of adult life. Subsequent histolysis of developed flight muscles coincided with increased total protein content in some reproductive organs. Initiation of intensive food intake after starvation or application of higher dose of methoprene on macropterous adults changed the resource allocation in favour of growth of reproductive organs and induced precocious histolysis of flight muscles. It indicates an involvement of juvenile hormone in wing morph-related differential allocation of resources in the bug. Increased total protein contents in the ovaries and accessory glands of starved macropterous females and males treated with methoprene, respectively, indicate that proteins derived from the methoprene-induced histolysis of the flight muscles are re-utilized for the growth of the reproductive organs. It is the first report of persistence of differential resource allocation to flight muscles and reproductive organs in the wing-polymorphic insects with non-functional macropterism.     

Diversities in morphological characteristics and seed germination behavior in fruits ofSalsola komarovii Iljin

Two different types of dispersal units (called fruits in this study) were observed inSalsola komarovii Iljin. One is a fruit which has dark brown lignified tepals with long wings and a green seed and falls easily from the mother plant (long-winged type). Another has light brown lignified tepals with short wings and a yellow seed and attaches tightly to the mother plant (short-winged type). This difference of fruit type appeared independently from maturity of fruit. Seeds in the short-winged fruits were in dormancy for a longer period of time than those in the long-winged fruits. The germination rate was significantly higher in the seeds of long-winged fruits. The dormancy in seeds of the long-winged fruits was effectively terminated by reducing the temperature but the effect of chilling was very weak in seeds of the short-winged fruits. It was concluded from these observations that there exists a dimorphism in the fruits of, or a heterocarpy in,S. komarovii. The plants grown under water stress produced mostly short-winged fruits and those grown under well-watered conditions bore fruits of both types. Exogenously applied abscisic acid (ABA) tended to produce the short-winged fruits, suggesting that the heterocarpy was, at least partly, regulated by ABA.     

Differential allocation of resources underlies the dispersal-reproduction trade-off in the wing-dimorphic cricket,Gryllus rubens

The cricket, Gryllus rubens (Orthoptera, Gryllidae), exists in natural populations as either a fully-winged (LW), flight-capable morph or as a short-winged (SW) morph that cannot fly. The SW morph is substantially more fecund than the LW morph. In this study we report on the physiological basis of this trade-off between flight capability and fecundity. Results from gravimetric feeding trials indicate that LW and SW morphs are equivalent in their consumption and digestion of food. However, during the adult stage, the LW morph is less efficient in converting assimilated nutrients into biomass. This may be a consequence of the respired loss of assimilated nutrients due to the maintenance of functional flight muscles in the LW morph. In both morphs the gross biomass devoted to flight muscles does not change significantly during the first 14 days of adult growth while there is a significant biomass gain in ovarian tissue mass during the same period. SW morphs have vestigial flight muscles and gain substantially more ovarian mass relative to the LW morphs. These data are consistent with a trade-off between flight muscle maintenance in the LW morph and ovarian growth in the SW form. This is the first evidence for a life-history trade-off that has a physiological basis which is limited to the allocation of acquired and assimilated nutrients within the organism.     

Genetic variation in developmental times among four pure lines exhibiting specific wing form and body color in the brown planthopper, <Emphasis Type="Italic">Nilaparvata lugens</Emphasis> (Hemiptera: Auchenorrhyncha)

Developmental times were compared among four pure lines of wing-dimorphic Nilaparvata lugens generated by successive selections for the following designated characteristics: blackish short-winged (BS), blackish long-winged (BL), yellowish brown short-winged (YS) and yellowish brown long-winged (YL). When the nymphs were reared on rice seedlings at low density, the developmental time was in the order of BS = BL < YS = YL, while with an increase in rearing density, the time lengthened markedly in long-winged lines but only slightly in short-winged lines, rearranging the order to BS < BL = YS < YL. Among F₁ progeny of BS × YL, the developmental time in short-winged phenotypes was the same as those of BS lines at any of the densities tested, but the long-winged phenotypes emerged as adults at intermediate time between BS and YL lines at high density. This method of inheritance of developmental time and the differences in the duration observed among the four pure lines suggest that the genes regulating wing form and body color expression are also involved in the regulation of developmental time.     

Mate choice by male water striders (Gerris lacustris): expression of a wing morph preference depends on a size difference between females

Natural selection maintains wing polymorphism in populationsof water striders. Long-winged females benefit from being ableto migrate because they avoid the risk of pool evaporation,but early in the season their fecundity is lower than that ofshort-winged females. We tested preferences of 18 long-wingedmales and 29 short-winged males in spring. Males preferred long-wingedfemales, and there was no difference between the two male morphs.The preference was only observed when the long-winged femalewas heavier; when the short-winged female was larger, the malesshowed no preference. There was a positive relationship betweenlong-winged female weight and number of eggs laid per day, andthe males behaved as if they were taking into account that large,long-winged females are more fecund. We suggest that males preferredlong-winged females because this preference increases the proportionof long-winged individuals in the autumn F2 generation.     

Ladies last: diel rhythmicity of adult emergence in a parasitoid with complementary sex determination

Protandry, the earlier adult emergence of males, is explained as either an adaptive strategy maximizing male mating opportunities at the same time as minimizing female pre‐reproductive mortality, or as an incidental by‐product of sexual dimorphism fuelled by selection for other life‐history traits. Adult emergence sequences are monitored of broods of the gregarious larval endoparasitoid Cotesia glomerata L. (Hymenoptera: Braconidae) undergoing pupal development under different temperature regimes. As a haplodiploid species with single‐locus complementary sex determination, gender in C. glomerata is determined by the genotype at one sex locus. Haploids are always male, whereas diploids are female when heterozygous but male when homozygous at the sex locus. Sibling mating promotes homozygosity and thus the production of diploid males. Diploid males are produced at the expense of females, and impose a genetic burden on individuals and populations, despite their exceptional fertility in C. glomerata. Emergence of broods is typically completed within 2 days. Irrespective of temperature, males emerge earlier and within a shorter time interval than females, and a majority of the males in a cluster emerge before the first female. The implications of an incomplete temporal segregation of the sexes on the incidence of inbreeding in C. glomerata are discussed in the light of its sex determination mechanism and its patterns of mating, host exploitation and natal dispersal.