Faster Rate Of Development Research Articles

Response ofTetranychus cinnabarinus feeding on NaCl-stressed strawberry plants

The development and reproductive rates ofTetranychus cinnabarinus Boisduval (Acari: Tetranychidae), the carmine spider mite, were studied on two strawberry cultivars (Fragaria ×ananassa Duch.; ‘Camarosa’ and ‘Sweet Charlie’) at three NaCl concentrations, 1760, 2400 and 3040 mgl −1, and control. The effects of NaCl application on the contents of plant nutrients, chlorophyll, proline, peroxidase activity (POX) and proteins were assessed. On Camarosa,T. cinnabarinus had a faster development rate with applications of NaCl than without, except for female development at the highest salinity level. The total development time of females increased with the NaCl concentration, whereas total development time of males decreased. The oviposition period and female longevity on Camarosa was significantly longer in the control than with NaCl, whereas daily and total fecundity were significantly higher at all NaCl concentrations than in the control, except for total fecundity at the lowest salinity level. The total development time, oviposition period, female longevity, daily and total fecundity on Sweet Charlie did not differ significantly between NaCl salinity levels and the control. The intrinsic rate of natural increase (r m ) on Camarosa and Sweet Charlie were significantly higher with NaCl than in the control. However, the contents of Na, Cl, P, chlorophyll, proline, POX and protein in the two strawberry cultivars changed depending on NaCl concentration. On the other hand, the K and N contents were not affected significantly by NaCl salinity.

Trade-off between larval development rate and Post-metamorphic Traits in the Frog Rana latastei

Development rate early in the ontogeny is believed to correlate positively with fitness. Geographic variation in intrinsic development rate suggests the existence of trade-offs between development rate and other fitness related traits. We investigated whether these trade-offs exist between intrinsic larval development rate and post-metamorphic traits in an organism with a complex life cycle. In laboratory, we measured if the tadpoles of the frog Rana latastei with fast intrinsic development rate have a suboptimal post-metamorphic morphology, by comparing froglets from five populations. Then, we evaluated the relationship between age at metamorphosis, hindlimb length and jumping performance for frogs grown in nature in two populations. Under laboratory conditions, froglets with fast intrinsic development had shorter absolute and shorter size-adjusted tibiofibulas. We observed a strong, positive relationship between tibiofibula length and jumping performance. In nature, froglets from the last metamorphosing population had longer absolute and size-adjusted tibiofibulas, and were able to jump further. The cost of fast development could be the shorter legs of early metamorphosing frogs, and their poor jumping performance. Thus, a fast intrinsic development rate may not always be positively related to lifetime fitness, since delayed effects of larval development persist also across life history stages.

The Success Story of Peritoneal Dialysis in Romania: Analysis of Differences in Mortality by Dialysis Modality and Influence of Risk Factors in a National Cohort

This report describes the status of renal replacement therapy (RRT), particularly continuous ambulatory peritoneal dialysis (CAPD), in Romania (a country with previously limited facilities), outlines the fast development rate of CAPD, and presents national changes in a European context. Trends in the development of RRT were analyzed in 2003 on a national basis using annual center questionnaires from 1995 to 2003. Survival data and prognostic risk factors were calculated retrospectively from a representative sample of 2284 patients starting RRT between 1 January 1995 and 31 December 2001 (44% of the total RRT population investigated). The annual rate of increase in the number of RRT patients (11%) was supported mainly by an exponential development of the CAPD population (+600%); the hemodialysis (HD) growth rate was stable (+33%) and renal transplantation had a marginal contribution. The characteristics of both HD and PD incident patients changed according to current European epidemiology (increasing age and prevalence of diabetes and nephroangiosclerosis). There were significant differences between PD and HD incident populations, PD patients being significantly older and having a higher prevalence of diabetic nephropathy and baseline comorbidities, probably reflecting different inclusion policies. The estimated overall survival of RRT patients in Romania was 90.6% at 1 year [confidence interval (CI) 89.4 - 91.8] and 62.2% at 5 years (CI 59.4 - 65.0). The initial treatment modality did not significantly influence patients' survival. There was no difference in unadjusted technique survival during the first 2 years; afterwards, there was a clear advantage for HD, with more patients being transferred from PD to HD. Several factors seemed to significantly and negatively influence PD patients' survival (Cox regression analysis): male gender, lack of predialysis erythropoietin treatment, and initial comorbidities. Stratified analysis to discover the influence of these factors on patients' survival revealed that HD was associated with an increased risk of death in the younger nondiabetic end-stage renal disease population, regardless of other coexisting comorbid conditions. However, in older patients (>65 years) and in diabetics, regardless of the presence or absence of associated comorbid conditions, there was no significant difference in death rates between HD and PD patients. We report an impressive quantitative and qualitative development of CAPD in one of the rapidly growing Central and Eastern Europe countries. CAPD should be the method of choice for young nondiabetic end-stage renal disease patients. Improvement in predialysis nephrologic care and in transplantation rates is required to further ensure the ultimate success of the Romanian PD program.

Using megasonic development of SU-8 to yield ultra-high aspect ratio microstructures with UV lithography

SU-8 resist is commonly used to produce high aspect ratio microstructures in MEMS field. The resist is patterned using either ultraviolet (UV) or X-ray lithography and developed to produce structures ranging from 20 microns to 1.5 millimeters in height. Three processes are currently used to develop SU-8 resist: dip development with or without stirring and dip development with ultrasonic agitation. One difficulty associated with producing high aspect ratio microstructures lies in the development of open and closed fields evenly on the same substrate. To overcome this obstacle, we have applied megasonic agitation to the developer bath, which resulted in faster development rates, uniformed development, and the ability to produce structures with higher aspect ratios. To date, this process has been used to achieve 100:1 aspect ratio open field features and 45:1 intact cylinder arrays using a broadband optical contact aligner.

Development and Kikuyu Consumption of PreimaginalHerpetogramma licarsisalis(Lepidoptera: Pyralidae) Reared at Temperatures Between 15 and 25°C

Abstract A laboratory experiment compared development and kikuyu, Pennisetum clandestinum Hochst. ex Chiov. South, consumption in preimaginal grass webworm, Herpetogramma licarsisalis (Walker), at 15, 18, 20, and 25°C. Mean developmental time from oviposition to adult emergence was 25.0 d at 25°C, 43.4 d at 20°C, 50.4 d at 18°C, and 81.4 d at 15°C. Survival decreased with decreasing temperature but not significantly. Total and daily kikuyu leaf area consumed per larva differed significantly with temperature. Leaf consumption increased exponentially with instar. Some larvae developed through six instars, rather than the usually reported five, at temperatures <25°C. Compared with five-instar H. licarsisalis, those with six instars spent longer in the egg stage, had smaller head capsule widths at all but first instar, faster developmental rates but lower kikuyu consumption for each stadium above the second, and slower egg-adult development. Developmental time from egg to adult emergence was significantly sho...

Genetics and imaging to assess oocyte and preimplantation embryo health

Two major criteria are currently used in human assisted reproductive technologies (ART) to evaluate oocyte and preimplantation embryo health: (1) rate of preimplantation embryonic development; and (2) overall morphology. A major gene that regulates the rate of preimplantation development is the preimplantation embryo development (Ped) gene, discovered in our laboratory. In mice, presence of the Ped gene product, Qa-2 protein, results in a fast rate of preimplantation embryonic development, compared with a slow rate of preimplantation embryonic development for embryos that are lacking Qa-2 protein. Moreover, mice that express Qa-2 protein have an overall reproductive advantage that extends beyond the preimplantation period, including higher survival to birth, higher birthweight, and higher survival to weaning. Data are presented that suggest that Qa-2 increases the rate of development of early embryos by acting as a cell-signalling molecule and that phosphatidylinositol-32 kinase is involved in the cell-signalling pathway. The most likely human homologue of Qa-2 has recently been identified as human leukocyte antigen (HLA)-G. Data are presented which show that HLA-G, like Qa-2, is located in lipid rafts, implying that HLA-G also acts as a signalling molecule. In order to better evaluate the second criterion used in ART (i.e. overall morphology), a unique and innovative imaging microscope has been constructed, the Keck 3-D fusion microscope (Keck 3DFM). The Keck 3DFM combines five different microscopic modes into a single platform, allowing multi-modal imaging of the specimen. One of the modes, the quadrature tomographic microscope (QTM), creates digital images of non-stained transparent cells by measuring changes in the index of refraction. Quadrature tomographic microscope images of oocytes and preimplantation mouse embryos are presented for the first time. The digital information from the QTM images should allow the number of cells in a preimplantation embryo to be counted non-invasively. The Keck 3DFM is also being used to assess mitochondrial distribution in mouse oocytes and embryos by using the k-means clustering algorithm. Both the number of cells in preimplantation embryos and mitochondrial distribution are related to oocyte and embryo health. New imaging data obtained from the Keck 3DFM, combined with genetic and biochemical approaches, have the promise of being able to distinguish healthy from unhealthy oocytes and embryos in a non-invasive manner. The goal is to apply the information from our mouse model system to the clinic in order to identify one and only one healthy embryo for transfer back to the mother undergoing an ART procedure. This approach has the potential to increase the success rate of ART and to decrease the high, and undesirable, multiple birth rate presently associated with ART.

ON SEXUAL SELECTION IN FLORIDA’S PYRACTOMENA BOREALIS (COLEOPTERA: LAMPYRIDAE)

Abstract To what extent can a small animal with limited mobility use behavior to take advantage of its environment and how might this influence the population as a whole? This was examined in a firefly species Pyractomena borealis (Randall), by looking at the features of the microhabitat where larvae pupate, how developmental rates are influenced by extrinsic factors, and how the population’s spatial distribution differed according to sex. In two populations of P. borealis in Gainesville Florida, larvae pupated at the warmest locations on trees, potentially causing a faster development rate than individuals in cooler areas. In these populations males pupated sooner and in warmer areas than females, suggesting males chose their pupation locations in order to have a shorter development period and an earlier emergence date than females. This is the first evidence of protandry being experimentally linked with behavioral usage of habitat.

Genotype-by-environment interaction for salinity tolerance in the freshwater-invading copepod Eurytemora affinis.

This study examined the extent of phenotypic plasticity for salinity tolerance and genetic variation in plasticity in the invasive copepod Eurytemora affinis. Euryemora affinis is a species complex inhabiting brackish to hypersaline environments but has invaded freshwater lakes and reservoirs within the past century. Reaction norm experiments were performed on a relatively euryhaline population collected from a brackish lake with fluctuating salinity. Life history traits (hatching rate, survival, and development time) were measured for 20 full-sib clutches that were split and reared at four salinities (fresh, 5, 10, and 27 practical salinity units [PSU]). On average, higher salinities (10 and 27 PSU) were more favorable for larval growth, yielding greater survival and faster development rate. Clutches differed significantly in their response to salinity, with a significant genotype-by-environment interaction for development time. In addition, genetic (clutch) effects were evident in response to low salinity, given that survival in fresh (lake) water was significantly positively correlated with survival at 5 PSU for individual clutches. Clutches raised in fresh water could not survive beyond metamorphosis, suggesting that acclimation to fresh water could not occur in a single generation. Results suggest the importance of natural selection during freshwater invasion events, given the inability of plasticity to generate a freshwater phenotype, and the presence of genetic variation for plasticity upon which natural selection could act.

Lethal and sublethal effects of a granulovirus on the tomato moth Lacanobia oleracea.

A Scottish isolate of Lacanobia oleracea granulovirus (LoGV) was tested against larvae from a laboratory colony of L. oleracea (Lepidoptera: Noctuidae) using the peroral bioassay technique. The median lethal doses ranged from 10(1.38) occlusion bodies in first instar larvae to 10(7.45) in fifth instars. Sublethal effects on development and reproduction were observed among the survivors of virus challenge. Larvae dosed as first and second instars had faster developmental rates, and those dosed as fourth and sixth instars had reduced larval and pupal weights, compared to their respective controls. There was a 15% reduction in the number of eggs laid by adults that developed from infected larvae, but no reduction in egg viability. The F(1) generation did not show significantly greater mortality than controls, suggesting a lack of transovarial transmission. The significance of these results in terms of pest management of the tomato moth is discussed.

Image Stability and Performance of a New Silver Halide Color Paper for Digital Printers: Crystal Archive Paper type One

FUJICOLOR CRYSTAL ARCHIVE PAPER TYPE ONE is a silver halide color paper designed for digital printers, and is capable of yielding high-image-quality digital prints, especially when it is used with the Digital Minilab Frontier. This color paper allows the attainments of enhanced suitability to high-intensity laser exposure, excellent image stability, brilliant whiteness, and consistent processing result. These features were brought about by the following technologies.(1) APC (Advanced Photoelectron Controlling) TechnologyThis technology is to control the behavior of photoelectrons created by high-intensity laser exposure in order to provide high-image-quality digital prints without deterioration of latent image stability by enhancing the concentration of latent image formation.(2) HDS (Hybrid Dye-image Stability) TechnologyThis technology enhances the stability of the anti-fading agent to produce unparalleled image permanence.(3) WE (Whiteness Enhancing) Technology and RR (Resistance to Radiation) TechnologyThe development of WE technology brings about brilliant whites by retarding the formation of residual dyes during processing. This technology also provides brilliant whites, which do not change among batches by suppressing fog formation due to environmental radiation.(4) PS (Process Stabilizing) TechnologyThis technology depends on new chemical sensitization technology, which makes it possible to achieve the required level of sensitivity with smaller silver halide grains than before, and provides more consistent results with faster rate of development than before even when exhausted solutions are used.

Evaluation of alternative development process for high-aspect-ratio poly(methylmethacrylate) microstructures in deep x-ray lithography

The development of very thick commercial sheets of poly(methyl methacrylate) (PMMA) resist patterned by deep x-ray lithography was investigated. The development characteristics were explored, with the alternative methyl-iso-butyl-ketone (MIBK)-based developer systems, MIBK and MIBK/ iso-propyl-alcohol (IPA) 1:3, being compared with the “GG” developer system (2-butoxyethoxy-ethanol, morpholine, 2-aminoethanol, and water) more generally used. In particular, the influence of various parameters were studied: PMMA characteristics (resist thickness, pre-exposure thermal treatment), exposure conditions (x-ray incident energy, dose at the bottom of the resist, rate of dose deposition, distribution of dose inside the resist), development conditions (temperature, megasonic-assistance, length of cycle into developer and rinse baths), postexposure treatments (storage, thermal treatment), etc. The study also focused on surface finish of the parts corresponding to different exposure and development conditions. Using MIBK/IPA megasonic assisted development and postexposure treatment at 40 °C resulted in the best conditions, faster development rate, as well as smoother developed surfaces.

Growth, photosynthesis and water-use efficiency of two C4Sahelian grasses subjected to water deficits

Growth, photosynthesis and water use efficiency of two Sahel dominant C4grasses:Schoenefeldia gracilis Kunth and Dactyloctenium aegyptium (L) P. Beauv were studied under well-watered and drought conditions. D. aegyptium had a faster rate of development than S. gracilis and responded to water-deficits by decreasing leaf area in the earlier stages of development. However, under water-stress the overall reduction of leaf area suffered by S. gracilis was greater than in D. aegyptium. The decrease in net photosynthesis observed under water-deficits resulted mainly from stomatal closure. Analysis of correlation between long-term water-use efficiency and several physiological, structural and growth characteristics shows that long-term water-use efficiency in D. aegyptium was positively correlated with relative growth rates. The reduction in growth resulting from water-deficits was compensated by an increase in the short-term water-use efficiency associated with stomatal closure. In S. gracilis, the long-term water-use efficiency under moderate water-deficits increased but was not positively correlated with relative growth rate; it was associated with a high allocation to non-photosynthetic (support and vascular) tissues. The possible implications of this behaviour for the different ‘strategies’ for plant survival in the arid climate of the Sahel are discussed.

Genetic and biochemical analysis of brown eye mutation in Drosophila nasuta nasuta and Drosophila nasuta albomicans.

By analyzing the progeny of crosses involving brown eye mutants and the wild types in two members of Drosophila nasuta subgroup namely D. n. nasuta and D. n. albomicans we could show that the mutant gene is recessive, located in the chromosome 2 and the alleles of this gene are present at different loci. A study of fitness in the eye color mutants in comparison with the wild types revealed that D. n. nasuta mutant has higher viability at both 25+/-1 degrees C and ambient temperatures; while D. n. albomicans mutant has faster rate of development only at 25+/-1 degrees C. Quantitative analysis of eye pigments in the mutants revealed that there is biosynthesis of both pteridines and xanthommatins unlike in bw/bw of D. melanogaster, where only xanthommatins are synthesized. In both the species, the pteridine quantities in mutants are similar; whereas xanthommatin quantity in bw(n)/bw(n) is 10 times higher than that of bw(a)/bw(a). Further, the F1 progeny of intraspecific crosses (wild type X mutant) are found to have high amounts of pteridine, even when compared with parental wild type.

Egg quality, larval growth and phenotypic plasticity in a forcipulate seastar

The present study provides the first clear evidence of larval developmental plasticity in forcipulate seastars and a relationship between egg size and developmental plasticity. Adult Pisaster ochraceus were collected from Point Caution (a wave-protected site) and Mar Vista (a wave-exposed site) on the San Juan Islands. Seastars from the wave-exposed site were larger and had larger pyloric caeca while those from the wave-protected site were smaller with smaller pyloric caeca. Bigger females produced smaller eggs with a low biochemical content/egg and smaller females produced bigger eggs with a high biochemical content/egg. Egg quality and larval food had a significant effect on larval growth, development and survival. Bipinnariae from large eggs were initially bigger with faster developmental rates than those from small eggs. When starved, the numbers of bipinnariae surviving later on in development were higher for those from large eggs than for those from small eggs. When fed, the numbers of larvae surviving was higher for those from small eggs. This suggests that for this species large and small eggs might have equivalent fitness depending on the environmental conditions in which the offspring develop. All bipinnariae responded to food scarcity by changing their form, with those from smaller eggs responding to food scarcity later than those from larger eggs. Starved early bipinnaria stages were longer and wider and fed bipinnariae were narrower and shorter. Wider bipinnariae with larger mouths and stomachs were able to progress to more advanced stages while those with smaller internal structures could not. Thus for this species the mere increase in bipinnaria length and width might be insufficient to ensure continued larval development under food-limiting conditions; changes in internal morphology such as increase in the size of the digestive tract might be necessary.

Genetic regulation of preimplantation mouse embryo survival

The preimplantation period of mammalian development is characterized by cleavage of a one-cell embryo to a blastocyst stage embryo. During preimplantation development, 15%-50% of the embryos die as a result of factors that are largely unknown. Two parameters of preimplantation development, a fast rate of development and a low degree of fragmentation, are indicative of good embryo quality. There is mounting evidence that genes control both rate of development and degree of fragmentation. We have discovered a gene, Ped (preimplantation embryo development), which controls the rate of preimplantation embryonic cleavage. The Ped gene is encoded by two similar genes, Q7 and Q9, in the Q region of the mouse major histocompatibility complex (MHC). The Ped gene product is an MHC class Ib protein, the Qa-2 antigen. The mechanisms by which the Ped gene controls rate of embryonic cleavage division are being explored. In order to understand genetic mechanisms underlying the second criterion of embryo quality, degree of fragmentation, we have begun to assess expression of the genes that could potentially regulate apoptosis in preimplantation embryos. We have shown that staurosporine can induce apoptosis in mouse blastocysts. By using RT-PCR, we have shown that genes encoding protein in the two major gene families that regulate apoptosis, the Bcl-2 and caspase gene families, are present in preimplantation embryos. We hypothesize that there is a homeostatic mechanism by which genes that regulate cell survival and those that regulate cell death determine the overall viability of preimplantation embryos.

Role of the Ped gene and apoptosis genes in control of preimplantation development.

The properties of the mouse Ped gene and the genes that mediate apoptosis in mediating preimplantation embryonic survival were reviewed. Preimplantation mouse oocytes and embryos were evaluated microscopically and biochemically for rate of development, degree of fragmentation, and gene expression to correlate these characteristics with embryo mortality, Biochemical assays included PCR for DNA analysis, RT-PCR for mRNA analysis, immuno-PCR for protein analysis, and TUNEL assay for assessment of apoptosis. Using the mouse as a model system we have identified a gene that controls the rate of development, the Ped gene. The Ped gene product is a class Ib major histocompatibility complex protein called the Qa-2 antigen. Research to understand the molecular mechanisms of Ped gene action and to identify the human homologue of the Ped gene is under way. We have also shown using the mouse model, that fragmented embryos show the morphological and biochemical characteristics of apoptosis. Genes in the two major gene families that regulate apoptosis, the caspase and Bcl-2 families, are expressed in mouse oocytes and preimplantation embryos. Preimplantation embryonic survival depends on two major morphological parameters: rate of development and degree of fragmentation. A fast rate of development and a low degree of fragmentation lead to a better chance of producing live offspring. Both rate of development and degree of fragmentation are genetically controlled, the former by the Ped gene and the latter most likely by genes that mediate apoptosis. It seems probable that regulation of apoptosis will prove to be a major mechanism that mediates oocyte and preimplantation embryonic survival.

Effect of food quality on rate of growth and development of the pelagic copepod Pseudocalanus elongatus (Copepoda, Calanoida)

Rates of body growth, development and egg production of Pseudocalanus elongatus were measured in the laboratory, in relation to the taxonomy and physiology of algal food. Four types of experiments were performed to measure the copepod's response to (1) 7 algal species of similar size and shape, but different taxonomic groups, (2) inferior food species that were offered with good food as a check of toxicity, (3) nitrogen limitation and the growth rate of food species, and (4) highly unsaturated fatty acids that were supplied with inferior food to test for lack of essential fatty acids. Grazing was measured to check that the offered food was really ingested. The best food species proved to be Rhodomonas sp., whlch induced a fast rate of development, good somatic growth and egg production and low mortality. The development rate was almost equally fast 1~1th Thalassiosira weissflogi~, Gyrnnodinium simplex and Tetraselmjs suedca, but the rates of somatic growth or egg production were lower and mortahty generally higher than with Rhodornonas sp. Three algal species, Dunaljella sp , Amphidinium sp, and Chrysochrornulina polylepjs, were poor food; copepod development was not completed, the rates of somatic growth and egg production were low and mortality was high. Ingestion was equally high with most of the species; only C. polylepis was not eaten No clear toxic effects were found when the 3 poor-food species were offered in mixtures w ~ t h Rhodomonas sp. N-limited Rhodomonas sp. did not reduce the rate of copepod development in comparison to a N-replete culture; however, N-limited T weissflogii reduced the development rate to the low level of poor-food species. No effect of different growth rates of Dunaliella sp. was found. Lipids rich in highly unsaturated fatty acids supplied with DunalieUa sp. did not substantially improve the slow development and low egg production observed with this species. The weight-specific somatic growth rate was always higher than the weight-specific egg production rate, especially with less optimal food, which seems to hamper the estimation of the secondary production of copepods based on egg production alone. It is concluded that large differences in the food quality of different algal species are due to differences in digestibility or in mineral and biochemical composition.

THE EFFECTS OF WINTER LENGTH ON THE GENETICS OF APPLE AND HAWTHORN RACES OF RHAGOLETIS POMONELLA (DIPTERA: TEPHRITIDAE).

Host plant-associated fitness trade-offs are central to models of sympatric speciation proposed for certain phytophagous insects. But empirical evidence for such trade-offs is scant, which has called into question the likelihood of nonallopatric speciation. Here, we report on the second in a series of studies testing for host-related selection on pupal life-history characteristics of apple- (Malus pumila L.) and hawthorn- (Crataegus mollis L. spp.) infesting races of the Tephritid fruit fly, Rhagoletis pomonella (Walsh). In particular, we examine the effects of winter length on the genetics of these flies. We have previously found that the earlier fruiting phenology of apple trees exposes apple-fly pupae to longer periods of warm weather preceding winter than hawthorn-fly pupae. Because R. pomonella has a facultative diapause, we hypothesized that this selects for pupae with more recalcitrant pupal diapauses (or slower metabolic/development rates) in the apple-fly race. A study in which we experimentally manipulated the length of the prewintering period for hawthorn-origin pupae supported this prediction. If the period preceding winter is important for apple- and hawthorn-fly pupae, then so too should be the length (duration) of winter; the rationale for this prediction is that "fast developing" pupae that break diapause too early will deplete their energy reserves and disproportionately die during long winters. To test this possibility, we chilled apple- and hawthorn-origin pupae collected from a field site near Grant, Michigan, in a refrigerator at 4°C for time periods ranging from one week to two years. Our a priori expectation was that longer periods of cold storage would select against allozyme markers that were associated with faster rates of development in our earlier study. Since these electromorphs are typically found at higher frequencies in hawthorn flies, extending the overwintering period should favor "apple-fly alleles" in both races. The results from this "overwinter" experiment supported the diapause hypothesis. The anticipated genetic response was observed in both apple and hawthorn races, as allele frequencies became significantly more "apple-fly-like" in eclosing adults surviving longer chilling periods. This indicates that it is the combination of environmental conditions before and during winter that selects on the host races. Many tests for trade-offs fail to adequately consider the interplay between insect development, host plant phenology, and local climatic conditions. Our findings suggest that such oversight may help to explain the paucity of reported fitness trade-offs.

Developmental rates for Chromatomyia fuscula (Zett.) (Dipt., Agromyzidae) at five constant temperatures

AbstractThe median developmental rates for all immature stages of Chromatomyia fuscula (Zett.) increased linearly between 9 and 21 °C. An exponential and a Cobb‐Douglas model was tested, but gave only as good as or slightly better fits than the linear regression model. The lower thermal developmental thresholds for all stages were 3.0 ± 0.5 °C. Both sexes required 400 degree‐days above 3.0°C for the total development from egg to adult emergence. At the relatively low temperatures investigated, C. fuscula had a fast developmental rate, especially in the pupal stage, and low thermal thresholds compared to other agromyzids. The possible reasons for this are discussed. Introduction of a dichotomous variable for sex in the regression model for egg to adult emergence indicated an elevated mortality below 15 °C. Also, the introduction of a dichotomous variable proved the sex ratio 1 male: 1.3 females to be significantly different from 1:1. The thermal sums calculated indicated that C. fuscula theoretically could have two generations per year in a large part of its range. The reasons why it is still univoltine must be sought elsewhere.

Life history variation in plants: an exploration of the fast-slow continuum hypothesis

Several empirical models have attempted to account for the covariation among life history traits observed in a variety of organisms. One of these models, the fast-slow continuum hypothesis, emphasizes the role played by mortality at different stages of the life cycle in shaping the large array of life history variation. Under this scheme, species can be arranged from those suffering high adult mortality levels to those undergoing relatively low adult mortality. This differential mortality is responsible for the evolution of contrasting life histories on either end of the continuum. Species undergoing high adult mortality are expected to have shorter life cycles, faster development rates and higher fecundity than those experiencing lower adult mortality. The theory has proved accurate in describing the evolution of life histories in several animal groups but has previously not been tested in plants. Here we test this theory using demographic information for 83 species of perennial plants. In accordance with the fast-slow continuum, plants undergoing high adult mortality have shorter lifespans and reach sexual maturity at an earlier age. However, demographic traits related to reproduction (the intrinsic rate of natural increase, the net reproductive rate and the average rate of decrease in the intensity of natural selection on fecundity) do not show the covariation expected with longevity, age at first reproducion and life expectancy at sexual maturity. Contrary to the situation in animals, plants with multiple meristems continuously increase their size and, consequently, their fecundity and reproductive value. This may balance the negative effect of mortality on fitness, thus having no apparent effect in the sign of the covariation between these two goups of life history traits.