Egg maturation strategy and survival trade-offs in holometabolous insects: a comparative approach

One of the key predictions of general life-history theory is that reproduction incurs a survival cost. Although there is a convincing body of evidence to support this prediction at the intraspecific level in insects, evidence at the interspecific level is relatively scarce, as is the case for other animals. By employing two methods of phylogenetically controlled analysis, we demonstrate the existence of a negative correlation between life-span and early life investment in reproduction, across a wide diversity of Lepidoptera. The measure of initial reproductive effort used was the 'ovigeny index', defined as the proportion of the lifetime potential egg complement that is mature (ready to lay) upon female emergence. We present a graphical model for holometabolous insects, illustrating the trade-offs that are hypothesized to occur among capital resources (soma vs non-soma and initial eggs vs storage) in relation to variation in ovigeny index. These trade-offs, for which there is some empirical support, are postulated to underlie the life-span/ovigeny index relationship observed in the Lepidoptera and also in other insect orders.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 293–302.     

Female fertility per flower and trade-offs between size and number in Claytonia virginica (Portulacaceae)

A consistent and paradoxical feature in flowering plants is the production of many more flowers than appear required for female fertility through fruit and seed production. Many mechanistic hypotheses for this observation share key assumptions about (1) limited resources available for reproduction and (b) greater female fertility benefits from larger flowering-time investment. Here I investigate these assumptions in two populations of Claytonia virginica. I also test predictions from theoretical analyses, comparing patterns of flowering allocation and fertility per flower in 18 populations of C. virginica. Results support the assumption that larger benefits accrue from greater flowering-time investment. The between-population pattern of flowering allocation and fertility per flower is also consistent with theoretical expectation, although not statistically significant. Not supported is the assumption that reproduction occurs under strong resource constraint. Possible reasons for this discrepancy are discussed.     

Seasonal polyphenism and developmental trade-offs between flight ability and egg laying in a pierid butterfly

Butterflies have competing demands for flight ability depending on, for example, mating system, predation pressure, the localization of host plants and dispersal needs. The flight apparatus, however, is costly to manufacture and therefore trade-offs are expected since resources are limited and must be allocated between flight ability and other functions, such as reproduction. Trade-offs between flight and reproduction may be difficult to reveal since they interact with other factors and can be confounded by differences in resource consumption. Previous studies have shown that adults of the summer generation of Pieris napi have relatively larger thoraxes compared with the spring generation. To study whether difference in thorax size results in a trade-off between flight ability and reproduction among the two generations, we conducted a split-brood experiment under common garden conditions. Our results show that summer generation adults have a higher dispersal capacity measured as flight duration in five different temperatures. Reproductive output differed between the two developmental pathways; spring generation females had a significantly higher output of eggs compared with summer generation females. We suggest that this is a consequence of a resource-allocation trade-off made during pupal development implemented by different demands for flight between the spring and summer generations. The significance of this finding is discussed in relation to reproduction and mobility in butterflies.     

Flower number and floral components in ten angiosperm species: an examination of assumptions about trade-offs in reproductive evolution

A common approach to modelling reproductive evolution in flowering plants includes an implicit assumption that module number and resource allocation per module follow an inverse hyperbolic trade-off. This assumption has not been thoroughly tested. In ten herbaceous and small woody species I examined phenotypic partial correlations between flower number (measured in relation to vegetative biomass) and each of three floral components: pollen number per flower, ovule number per flower, and corolla size. Significantly negative correlations between flower number and at least one of the floral components occurred in four of the ten species. These phenotypic correlations suggest the existence of true (genetically based) trade-offs, because environmental correlations are likely to be positive, but the significant negative relationships are linear except in one case. Thus, evolutionary tradeoffs involving flower number seem likely in some cases, but there is little to indicate that hyperbolic trade-offs are common. The phenotypic patterns investigated here cannot provide definitive answers about the form of trade-offs. Nonetheless, theoretical attention to the potential evolutionary consequences of trade-offs other than the implicit hyperbolic form is needed.     

Influence of adult nutrition on the relationship between body size and reproductive parameters in a parasitoid wasp

Abstract.  1. An important constraint upon life-history evolution in parasitoids is the limit imposed by body size on allocation of limited metabolic resources to different fitness-related physiological functions such as reproduction and survival.
2. The influence of adult nutrition on reproductive and maintenance variables was studied in the synovigenic ectoparasitoid Mastrus ridibundus , and it was determined whether resource allocation to these different functions depends on body size.
3. Over the course of adult life there was a positive relationship between body size and the number of mature eggs in adult females both in the presence and absence of food. However, only in the presence of food did egg maturation rates increase significantly with body size. Starved wasps produced significantly smaller eggs than fed ones, which has not been documented before. Moreover, starved wasps produced fewer offspring than fed wasps, and attacked fewer hosts.
4. The availability of food had a major effect on longevity, with fed females living about 10 times longer than starved ones. There was also a positive relationship between body size and longevity. In starved wasps, this relationship was the same both in the presence and absence of hosts, but in fed wasps there was a positive relationship between body size and longevity in the absence of hosts only. Allocation to initial eggs relative to lifetime progeny production did not decline with body size.
5. The data reveal that in M. ridibundus the trade-off between maintenance and reproduction varies with life expectancy.     

Differential niche modification by males and females of a dioecious herb: extending the Jack Sprat effect

Males and females of dioecious plants often differ in morphological, physiological and life‐history traits, probably as a result of their different requirements for reproduction. We found that the growth and reproductive effort of individuals of the dioecious herb Mercurialis annua depended on whether males or females had been growing in the soil previously. This suggests that males and females of M. annua differentially modify the soil in which they are growing. Our study indicates that sexual dimorphism in dioecious plants can give rise to increased environmental heterogeneity as a consequence of sex‐specific niche modification.     

Trade-offs between reproductive and somatic (storage) investments in animals: a comparative test of the Van Noordwijk and De Jong model

Classical life-history theory predicts ‘trade-offs’ between reproductive and somatic investments. However, empirical studies have shown that intraspecific phenotypic correlations between these two resource investments are often positive or nonsignificant, rather than negative as predicted. The model of Van Noordwijk and De Jong (1986) was proposed to explain these unexpected results. According to their model, positive correlations between reproductive and somatic investments will result if individual variation in resource acquisition exceeds that of resource allocation, whereas negative correlations will result if individual variation in resource allocation exceeds that of resource acquisition. To test this model, I used body storage/condition as an index of somatic investment because it is usually strongly related to level of resource acquisition. I predicted that laboratory studies should more often show negative correlations between reproductive and somatic investments than field studies, because individual variation in resource acquisition is expected to be lower in controlled laboratory environments than in variable natural environments. A literature review revealed that correlations between somatic (storage) investment and reproductive investment (estimated as clutch/litter mass, number of offspring per clutch/litter, or number of clutches/litters) among conspecific breeding female animals are more often positive (15 species) or nonsignificant (17 species) than negative (6 species). Moreover, as expected, five of six negative correlations were observed in laboratory studies, whereas 13 of 15 positive correlations were observed in field studies. It is concluded that future empirical and theoretical work on life histories should consider individual variation in both resource acquisition and allocation and the interaction between the two. This revised version was published online in July 2006 with corrections to the Cover Date.     

Egg maturation and oviposition strategy of a capital breeder,Cleorodes lichenaria,feeding on lichens at the larval stage

Abstract 1. Capital breeders rely solely on resources acquired before breeding, whereas income breeders may obtain considerable amounts of resources following the commencement of reproduction. In income breeders oviposition occurs over a longer time period with a small number of eggs ready to be laid at the start of adult life, whereas capital breeders reproduce more rapidly and contain higher numbers of mature eggs at eclosion relative to potential fecundity. 2. This study explored egg maturation and oviposition strategy of a nocturnal geometrid moth, Cleorodes lichenaria. It was predicted, based on the long larval period of C. lichenaria and the known biology of other geometrids, that this lichen‐feeding geometrid moth concentrates egg production at the beginning of its breeding period and that external nutrients have a limited role on its fecundity. 3. Approximately 46% of eggs were ready to be laid in newly hatched females and approximately 40% of their potential fecundity was realised during the first night, after which the number and the weight of eggs decreased steadily. Feeding or drinking did not increase the fecundity of females. Pupal mass correlated positively with realised fecundity and ovigeny index. 4. Reproduction of C. lichenaria is based solely on larval‐derived resources. It is suggested that females are able to resorb thoracic tissues to increase fecundity and that this ability is probably linked to relatively long lifespan and low ovigeny index of this species, characteristics rarely observed in other geometrid moths.     

The Lepidoptera fauna associated with Calluna vulgaris: effects of plant architecture on abundance and diversity

Abstract .1. The effects of plant architecture on the Lepidoptera assemblage associated with heather Calluna vulgaris were studied at four locations in northern England and southern Scotland in 1992 and 1993. The study areas were Calluna vulgaris – Vaccinium myrtillus heaths, where management by rotational burning had created a mosaic of stands of different-aged Calluna . Lepidoptera were sampled in the larval stage.
2. Larval abundance was considered in relation to Calluna age, height, cover, green shoot density, and flower density. For most study areas and species, multiple regression selected Calluna height as the variable that explained most variation in larval density, although the explanatory variables were intercorrelated.
3. After compensating for the effects of different study locations, the slope of the regression between the logarithm of larval density and the logarithm of Calluna height was common to the macrolepidoptera, microlepidoptera, geometrid, and noctuid larval groups.
4. There was a significant progressive increase in larval diversity with increase in Calluna height, due to the presence of uncommon moth species in the samples from taller Calluna, and a change in the contribution of common species to the community in different height zones.
5. The significance of these results is discussed in relation to other heathland invertebrate studies and management practices.     

Effects of supplementary feeding on growth and reproduction of three carnivorous plant species in a subarctic environment

1 The effect of supplementary feeding on growth and reproduction of three carnivorous plants species was investigated over a 6‐year period. Pinguicula alpina , P. villosa and P. vulgaris populations growing at two altitudes in a subarctic environment were fed with fruit flies ( Drosophila melanogaster ).
2 Fed plants increased in size relative to control plants during the first years. Subsequently a stable size difference between feeding levels was established. The weight of the over‐wintering part was higher in fed plants than in control plants.
3 The flowering frequency (i.e. proportion of plants in a population carrying flowers) was also higher in the fed plants. The proportion of flowering plants increased in the feeding treatment compared to control plants during more‐or‐less the whole experimental feeding period (5–6 years). Seed production also increased slowly in response to feeding.
4 No feeding effect on nitrogen and phosphorus concentrations in seeds and over‐wintering parts was found.
5 In most characteristics the high‐altitude populations were less responsive than populations growing at low altitude. In the high‐altitude population reproduction failed repeatedly, suggesting that seed output may be more dependent on abiotic factors than on resource availability in cold environments.
6 Pinguicula villosa and P. vulgaris used the new resources the same summer for increased leaf rosette growth and current reproduction, showing these species to be income breeders, while the third species ( P. alpina ) allocated a larger proportion to storage and future reproduction, characteristic of a capital breeder.     

Ovicide-induced serosa degeneration and its impact on embryonic development in Manduca sexta (Insecta: Lepidoptera)

Eggs of Manduca sexta treated with the ovicide Ov. 165049 turn orange, and the embryos later die. The orange pigmentation is at first confined to the serosa, and is accompanied by pathological changes of serosal cells. Lipid vesicles aggregate and spindle-shaped electron-lucent vesicles-normally forming a single layer below the apical cell surface-greatly accumulate. The mitochondria swell considerably, and their matrices become electron-lucent. Subsequently, the serosal cells develop additional features of necrosis. They form many autophagic vacuoles which contain mostly degradating mitochondria, but also segregated rough endoplasmic reticulum (rER) and glycogen granules. The whole cytoplasm vesiculates, and the cells shrink considerably. The nuclei become less irregular in shape, the chromatin disperses rather evenly whereas the nucleoli persist. Neither chromatin condensation nor the production of apoptotic bodies was observed-further evidence, that the serosal cells die by necrosis rather than apoptosis. At some stage of development the damaged serosa ruptures, retracts from the embryo and forms a sphere beneath it. It is only after the rupture of the serosa, that the embryo also turns orange and disintegrates rapidly. This shows impressively the protective function which the serosa plays for the embryo. Our physiological tests indicate, that the orange pigmentation of the serosa induced by the ovicide results from a disturbance of the tryptophan/ommochrome pathway serving the excretion of potentially toxic metabolites of tryptophan-rich proteins. The results demonstrate first that the serosa represents an important target for ovicide pesticides and second that it plays a vital role as an excretory organ during embryogenesis.     

Susceptibility of Eldana saccharina (Lepidoptera: Pyralidae), Busseola fusca and Sesamia calamistis (Lepidoptera: Noctuidae) to Bacillus thuringiensis Cry toxins and potential side effects on the larval parasitoid Cotesia sesamiae (Hymenoptera: Braconidae)

Laboratory trials were conducted to determine the efficacy of four Bacillus thuringiensis (Bt) Cry toxins at five different concentrations (0.016, 0.08, 0.4, 2, 10 μg/mL) for controlling three lepidopteran stem-borer species (i.e., the pyralid Eldana saccharina and the noctuids Busseola fusca and Sesamia calamistis) as well as to evaluate their indirect effect on the braconid larval parasitoid Cotesia sesamiae. In addition, larvae from the treatments above, after having been parasitized, were either fed a contaminated (group 1) or a toxin-free (group 2) diet and compared with a control (i.e., parasitized larvae which have never fed on Bt-toxin). All Bt Cry toxins induced larval feeding inhibition. Compared with the control, significant mortality resulted at all concentrations and for all species of Lepidoptera. Cry1Ab was the most toxic with 10 days post treatment mortalities ranging from 81% in B. fusca and S. calamistis to 100% in E. saccharina. In contrast, Cry1Ac had comparatively low toxicity particularly for B. fusca and S. calamistis (e.g., respectively, 54 and 74% mortality at 10 days at the highest concentration). In the toxin-treated group 1, percentages of C. sesamiae cocoon-producing moth larvae were higher compared to group 2 and the control, whereas clutch size was higher than in group 2 but similar to the control. In both groups, 0.016, 0.08 μg/mL CrylAc yielded lower female-biased sex ratios than the control. It was suggested that paralyses of the moth larvae caused by the toxin may have facilitated parasitization leading to higher parasitism and clutch size.     

Reproductive strategies of female butterflies: variation in and constraints on fecundity

ABSTRACT.

• 1 This study first examines the reproductive strategy of female Speyeria mormonia Edwards (Lepidoptera: Nymphalidae):
• 2 Egg weight and number laid per day decrease with age.
• 3 Survival and daily egg number may be affected by temperature; mean daily egg weight is not affected by temperature.
• 4 Daily egg number is not correlated with body size. In the central range of body size, egg weight is also not correlated with body size. However, exceptionally large or small females lay respectively heavier or lighter eggs than average.
• 5 A simple trade-off between offspring size and number does not occur within females on a daily basis, or among females averaged over their lifespans.
• 6 Fat body resources are depleted at a rate independent of body size.
• 7 Females are essentially monogamous.
• 8 Age-specific fecundity data reported here for S.mormonia are next compared with data for other Lepidoptera with different adult feeding habits and egg maturation patterns, and hence different possibilities for adult feeding to play a role in egg production. Based on these comparisons, I propose that the shape of the age-specific fecundity curve for each species under optimal conditions is constrained by the potential importance of adult nutrients in egg production.

     

Effects of variation in resource acquisition during different stages of the life cycle on life‐history traits and trade‐offs in a burying beetle

Individual variation in resource acquisition should have consequences for life‐history traits and trade‐offs between them because such variation determines how many resources can be allocated to different life‐history functions, such as growth, survival and reproduction. Since resource acquisition can vary across an individual's life cycle, the consequences for life‐history traits and trade‐offs may depend on when during the life cycle resources are limited. We tested for differential and/or interactive effects of variation in resource acquisition in the burying beetle Nicrophorus vespilloides. We designed an experiment in which individuals acquired high or low amounts of resources across three stages of the life cycle: larval development, prior to breeding and the onset of breeding in a fully crossed design. Resource acquisition during larval development and prior to breeding affected egg size and offspring survival, respectively. Meanwhile, resource acquisition at the onset of breeding affected size and number of both eggs and offspring. In addition, there were interactive effects between resource acquisition at different stages on egg size and offspring survival. However, only when females acquired few resources at the onset of breeding was there evidence for a trade‐off between offspring size and number. Our results demonstrate that individual variation in resource acquisition during different stages of the life cycle has important consequences for life‐history traits but limited effects on trade‐offs. This suggests that in species that acquire a fixed‐sized resource at the onset of breeding, the size of this resource has larger effects on life‐history trade‐offs than resources acquired at earlier stages.     

Effect of a vertical object on the sex pheromone-mediated flight and landing behaviors of the male lightbrown apple moth,Epiphyas postvittana (walker) (Lepidoptera: Tortricidae)

A small (2.5-cm-wide) vertical (10-cm-high) white object influenced the sex pheromone-mediated flight and landing behaviors of maleEpiphyas postvittana. When the vertical object was positioned on a horizontal surface to the side (3–5 cm) and upwind of a pheromone source (in the middle of the surface), the distribution of landing positions of males on the surface was different from that when the object was not present; males tended to land in positions skewed toward the side of the source that the object was on. The closer the object was positioned to the source, the greater the number of males that landed on the object (rather than on the horizontal surface). This difference in landing positions (when the object was present) corresponded with changes in the flight tracks; the tracks of males flying to the surface with an object were skewed toward the object and had higher amplitude intertrack reversal distances than the tracks of males flying to a surface without a vertical object. Positioning of a vertical object progressively upwind of the source resulted, apparently, in decreased effects on the landing (and presumably flight) behavior of males. The effect of the vertical object on the flight and landing behaviors of males corresponded largely with changes in pheromone plume structure (visualized with smoke) induced by the extra turbulence in the airflow over the source. Thus it appears that the vertical object influences the behavior of maleE. postvittana largely through the olfactory sensory modality. However, when a clear, Mylar object, in place of the white object, was placed on the surface, more males landed on the Mylar object (than did on the white object), suggesting that the vertical object may also influence the behavior of males through the visual modality.     

Cataclysta lemnata Linnaeus, 1758 (Lepidoptera: Crambidae) expanded its host range feeding on invasive aquatic ferns,species of Azolla Lamarck, 1783 (Hydropteridales: Azollaceae): fitness factors and costs

Cataclysta lemnata Linnaeus, 1758 is a semi-aquatic moth that feeds on Lemnaceae and few of other aquatic plants. In recent years, this moth has been seen feeding on Azolla Lamarck, 1783 Lamarck, J.B. (1783), Encyclopedie methodique: botanique, 1, Paris: Panckouche. 752 pp. [Google Scholar] in Iran in high numbers. The effect of the host plant on preference and performance of the moth was assessed under laboratory conditions. Despite the high survival rate of the young larvae, due to high mortality of the late instars and pupa on Lemna Linnaeus, 1753, the total survival rate on Azolla was higher. Feeding on Azolla increased the development time by almost a week and reduced fertility to half. However, by consuming more food, regulating the egg laying dynamic, and increasing emergence period, the moth retrieved most of the losses and adapted to feed on Azolla. A week before pupation, feeding activity increased between 2 and 8 times in all treatments and on Azolla, the larvae growth rate was slightly higher.     

黄钩尺蛾在四个茶树无性系品种上的生长和存活(英文)

在实验室条件下, 对食叶害虫黄钩尺蛾Hyposidra infixaria Walker在4个茶树Camellia sinensis无性系品种（TV1, TV9, TV25和Teen ali 17）上的生长和存活进行了研究, 以确定其最适合寄生的茶树无性系品种。结果表明： 在TV25上的黄钩尺蛾幼虫期 (15.78 d)比在TV1 (18.14 d), TV9 (18.00 d)和Teen ali 17 (17.00 d)上显著缩短。黄钩尺蛾按幼期龄数分为5龄型和6龄型两类。6龄型幼虫在TV25上的发生率显著高于其在其他3个无性系品种上的发生率。在TV25上黄钩尺蛾幼虫和蛹的体重也显著高于在其他3个无性系品种上的。同样地, 以TV25为食的黄钩尺蛾未成熟阶段的存活率显著高于其以其他3个无性系品种为食的存活率。基于生长参数和存活率, 我们发现TV25是黄钩尺蛾最适合寄生的茶树无性系品种。     

转sck+cry1Ac基因水稻对二化螟及二化螟绒茧蜂存活和生长发育的影响

在实验室研究了转sck+cry1Ac基因水稻（MSB）对二化螟Chilo suppressalis (Walker)生长、存活以及经寄主对二化螟绒茧蜂Apanteles chilonis (Munakata)生物学特性的影响。连续取食转sck+cry1Ac基因水稻的二化螟, 体重下降、死亡率上升,从第2天开始,其体重显著低于取食明恢86的对照组;从第6天开始,死亡率极显著高于对照组。二化螟取食MSB 36 h后移至对照水稻上继续取食3、6、9、12天后,死亡率与对照差异都不显著;但体重均低于对照,其中第3天的体重差异达显著水平。二化螟绒茧蜂分别以取食MSB一定时间的3、4、5龄二化螟幼虫为寄主时,寄生率均低于以对照组,其中对4龄幼虫的寄生率差异显著;结茧率与对照差异均不显著;寄生在取食MSB的5龄二化螟幼虫体内的蜂、蛹期显著长于对照,而所结茧的茧长显著短于对照;但卵 幼虫历期、每茧块茧数、羽化率、雌性率、成蜂寿命和前翅长与对照无显著差异。结果表明转sck+cry1Ac基因水稻不仅对二化螟生长和存活有显著影响, 而且可经寄主二化螟影响到二化螟绒茧蜂的一些生物学特性。