Mines over matter: Effects of foliar particulate matter on the herbivorous insect,Helicoverpa armigera

Coalmines, which are major contributors of particulate matter in the form of coal dust, are expanding globally into rural environments. However, ecological effects on organisms interacting with coal‐dusted foliage in mining landscapes are unknown. We tested how the behaviour, development and survival of a polyphageous insect herbivore, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is affected by consuming tomato leaves Lycopersicon esculentum laden with coal dust. We tested (a) feeding site establishment preference of neonates, (b) feeding behaviour and leaf consumption of late‐instar larvae, (c) survival of neonates and (d) survival and development of late‐instar larvae. We found that coal dust consumption increased the mortality of late‐instar larvae but did not influence their development. Despite long‐term implications for survival, late‐instar larvae did not adjust their feeding behaviour or the amount of leaf material consumed in response to foliar coal dust. Contrastingly, when neonate H. armigera were given a choice, they avoided establishing themselves on the coal‐dusted adaxial surface of leaves. Neonate mortality was 99% within 7 days, with no effect of coal dust. Our study provides the first data on the impact of coal dust on an insect herbivore. This has implications for ecological interactions in landscapes adjoining coalmines.     

Fitness Consequences of Maternal Effects in Streblospio benedicti (Annelida: Polychaeta)

SYNOPSIS. The degree to which a female partitions resourcesbetween fecundity and per offspring investment is a centralquestion in life-history theory. Maternal effects may influencethe nature of this tradeoff through their effect on per offspringinvestment and subsequent offspring fitness. The purpose ofthis study was to determine the effect of female age and sizeon brood size (number of offspring), per offspring investment,and fitness in the polychaete Streblospio benedicti. Early stageembryos were collected from brooding females of known age andsize over a period of 100 days; these embryos were counted andanalyzed for their C and N content. Female size had a positiveeffect on brood size; larger females produced larger broods.However, brood size decreased with female age (females did notincrease in size after reaching sexual maturity). Brood sizedeclined 20–46% between 60 and 160 days of age. Duringthis same age period per offspring investment, measured in termsof C and N, increased by 25%. Offspring survivorship and sizeat two weeks post-release from the female were used as measuresof offspring fitness. Offspring survivorship increased 28% between60 and 160 days of age. Increased growth in offspring from olderfemales resulted in a 23% increase in offspring size at twoweeks. Including the maternal age effect in two population modelsfor S. benedicti increased population growth rate (). Populationgrowth was increased to a greater degree when the maternal effectwas modeled by enhancing offspring survival compared to whenfecundity was increased by the same proportional amount. Thissuggests that the maternal effect may be adaptive, particularlywhen conditions for offspring survival and growth are poor.     

Sedimentation of phytoplankton populations dominated by Microcystis in a shallow lake

The sedimentary flux of phytoplankton was measured using sedimenttraps in a shallow hypertrophic lake (Lake Kasumigaura), whereMicrocystis bloomed, from June to November 1983 The sedimenttraps were set at 0.5, 1.5 and 3.0 m depth in Takahamairi Bay(3.5 m depth). Microcystis spp. (including M.aerugmosa and M.viridis)in the traps were rare until early August, but increased thereafter.Sinking rates of Microcystis were 0.0045, 0.020 and 0.24 m day^–1in June–August, September and October respectively, whichwere far lower than those of Melosira (0.2–1.7 m day^–1)and Syncdra (0.2–1.0 m day^–1). The total sedimentaryfluxes of POC and that of algal carbon during the study periodwere 283.2 and 96.7 gC m^–2 which were 59.5% and 20.3%of the gross primary production (475.8 gC m^–2) respectively.The sedimentary flux of living algae measured by algal countswas large in June but small in August and September. On theother hand, the flux of detritus obtained by subtracting totalalgal carbon from POC was small in June and July but large inAugust and September. Therefore diatoms, which appeared mostlyin June, tended to sink as live algae, while Microcystis sankas detritus after being decomposed or consumed in the waterIt was concluded from the results of carbon budget calculationsand the respiration rate of the 1- to 20-µm fraction thatthe activity of decomposers or consumers increased greatly inthe short period at the end of the bloom of Microcystis.     

Elemental composition (C:N:P) and growth rates of bacteria and Rhodomonas grazed by Daphnia

The elemental composition and growth rate of Rhodomonas andheterotrophic bacteria were studied in batch cultures in thepresence and absence of Daphnia and at two different levelsof phosphorus limitation. The elemental content of single cellswas measured with X-ray microanalysis. Simultaneously, dilutionexperiments were performed in order to estimate grazing losses,growth rates and dominant nutrient sources for bacteria andRhodomonas. The phosphorus:carbon (P:C) ratios of the bacteriawere generally higher in the experiment with the stronger Plimitation of the system. High P:C ratios were taken as an indicationthat bacteria were carbon limited. The presence of Daphnia resultedin a further increase in bacterial P:C ratios and increasedspecific growth rates. Thus, grazing increased the availabilityboth of inorganic nutrients and organic substrates, stimulatingthe growth of the bacteria. P:C ratios of Rhodomonas decreasedwith increasing P limitation of the system. Only at strong Plimitation did the presence of Daphnia result in increased P:Cratios of Rhodomonas compared with the control without daphnids.This study shows that the elemental content and growth rateof heterotrophic bacteria and Rhodomonas are influenced by grazingand nutrient regeneration by daphnids. The response is dynamicand depends on the level of nutrient limitation of the system. Present address: Department of Microbiology, University of BergenJahnebakken 5, NO-5020 Bergen, Norway     

Effects of maternal age on reproductive traits and fitness components of the offspring in the bruchid beetle, Callosobruchus chinensis (Coleoptera: Bruchidae)

In many insect species, the size and number of eggs decrease with maternal age. Thus, both the size and number of eggs must be considered to know the exact cost of reproduction with maternal age. The resource depletion hypothesis was examined in the bruchid beetle Callosobruchus chinensis. The hypothesis explains why the egg size decreases with maternal age based on the decline of the female's reproductive capacity. A decrease was found in reproductive effort (= egg size × the number of eggs) and the fitness component of offspring with maternal age. The effects of the female's nutritional status on the relationship between maternal age and the reproductive effort of females with and without food and water were also examined. The results indicate that the decrease in size and number of eggs with maternal age can be explained by the resource depletion hypothesis in C. chinensis.     

Cladoceran filtration rate-body length relations: model improvements developed for a Microcystis-dominated hypertrophic reservoir

Filtering rates were measured for zooplankton species in Situon single-celled Chlorella and on four Microcystis colony sizefractions (5–20, 20–40, 40–60 and 60–100µm) in a hypertrophic reservoir. Natural-log-transformedfiltration rates of five cladoceran species, one copepod andone rotifer were included in an all-food-particle, all-speciesmultiple regression model which explained 43% of the variancein filtration rate as a function of animal body length. An additional14% and 7.6% of the variance was attributable to food type andzooplankton species respectively, with temperature accountingfor <4% of the variance. Restricting the filtration ratemodel to cladocerans alone explained 51% of the variance asa function of animal length, 16% as a function of food type,7.5% as a function of species and only 0.2% as a function oftemperature. In linear filtration rate models for each foodtype, cladoceran body length explained 70% of the variance whenfeeding on Chlorella and between 57 and 67% of the varianceon the four Microcystis colony fractions. Models describingcladoceran filtration rates on Chlorella and the 5–20µm Microcystis colony fraction were significantly differentfrom the three models on larger colonies due to cladoceran responsesto increasing food particle size. Accordingly, a combined modelfor Microcystis colonies >20 µm was developed. Inclusionof food quality factors such as cyanophyte colony size seemsjustified in models aimed at estimating clearance rates, resourceutilization and phytoplankton grazing losses in plankton orecosystem studies when applied to eutrophic or hypertrophiclakes where large cyanophyte particles are abundant.     

The influence of autotrophic and heterotrophic foods on the demography of Daphnia longispina under starved, semi-natural and enriched conditions

We tested the influence of different types of food on the fitnessof Daphnia longispina during a period of poor resources by comparingthe growth and reproduction of individuals fed on differentdiets. When Daphnia were under starvation conditions, both dissolvedorganic carbon and metabolic products enhanced bacterial growth,and the cladoceran produced 15 neonates and survived for the55 days of experiment. In the natural water, the edible foodconsisted essentially of bacteria and heterotrophic flagellates,which enabled the cladoceran to grow and reproduce. In waterenriched with Cryptomonas (an alga) or Chilomonas (a heterotrophicflagellate), the daphnid growth rates increased considerablyfrom generation to generation, but later in the time courseof the experiment with Chilomonas than with Cryptomonas. Thisalga enhanced the phosphorus:carbon ratio. The primiparous daphnidsfed with Cryptomonas were smaller than those fed with the heterotrophicflagellate and enrichment with the heterotrophic flagellatealso enhanced reproduction. In Lake Tazenat, when the algalbiomass was insufficient to support the Daphnia life cycle,the heterotrophic organisms were an essential food source. Whenfeeding essentially on bacteria, Daphnia has the capacity togrow and reproduce at very low food concentrations, and thisis important in determining its fitness under competitive conditions.     

Physiology of a Microgravity Environment Selected Contribution: Effects of spaceflight during pregnancy on labor and birth at 1 G

The events of parturition (labor,delivery, maternal care, placentophagia, and onset of nursing) wereanalyzed in female Norway rats (Rattus norvegicus) flown oneither 11- or 9-day-long spaceflights beginning at the approximatemidpoint of their pregnancies. Each space shuttle flight landed on the20th day of the rats' pregnancies, just 48-72 h beforeparturition. After spaceflight, dams were continuously monitored andrecorded by time-lapse videography throughout the completion ofparturition and onset of nursing (days 22 and23). Analyses of parturition revealed that, compared with groundcontrols, flight dams displayed twice the number of lordosiscontractions, the predominant labor contraction type in rats.The number of vertical contractions (those that immediately precedeexpulsion of a pup from the womb), the duration of labor, fetalwastage, number of neonates born, neonatal birth weights, placentophagia, and maternal care during parturition, including theonset of nursing, were comparable in flight and ground control dams.Our findings indicate that, with the exception of labor contractions,mammalian pregnancy and parturition remain qualitatively andquantitatively intact after spaceflight during pregnancy.

     

Simulation of water-bloom formation in the cyanobacterium Microcystis aeruginosa

A mechanism for buoyancy increases in the cyanobacterium Microcystisaeruginosa and the associated formation of surface water-bloomsis presented. The mechanism is based on considering a responsetime in the rate of carbohydrate accumulation. When irradianceincreases, the Microcystis cells may require time to increasetheir rate of carbohydrate accumulation. If irradiance decreasesbefore adjustment, the maximum rate of carbohydrate accumulationis not reached. Colony buoyancy increases during mixing whenthe time scales of the light fluctuations are shorter than theresponse time. To examine the mechanism, a model of Microcystisbuoyancy that incorporates the response time has been coupledwith a hydrodynamics model that simulates mixing. The modelwas applied to a shallow lake to show that a prolonged episodeof intense mixing caused the simulated Microcystis coloniesto become excessively buoyant. Once the mixing subsided, thecolonies accumulated at the surface. Decreases in carbohydratewere reduced in large colonies as their size afforded buoyancyforces that could readily overcome the entraining forces ofthe mixing.     

Maternal consumption of non‐toxic Microcystis by Daphnia magna induces tolerance to toxic Microcystis in offspring

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Instar-dependent mortality rates of coexisting Daphnia species in Lake Vechten, The Netherlands

In Lake Vechten, population parameters were determined for twocoexisting Daphnia species, D.hyalina and D.cucullata, fromApril 23 to December 10, 1986. Daphnia hyalina is dominant inspring and D.cucullata in summer and autumn. Size frequencydistributions were converted into instar frequency distributionsby using experimental growth curves and field measurements onnewborn size and the size at first reproduction. A discreteevent computer model was used to calculate the instar mortalityrates. Relative importances of instar mortality rates for thepopulation mortality rate were calculated and discussed. Themortality of the juvenile stages was found to be more importantthan adult mortality during most of the sampling season, despiteegg mortality when egg-bearing females are killed. Only in Septemberand October was the mortality of adult instars more important.Correlation coefficients between differences in the rates ofincrease and differences in mean brood size and instar mortalitiesshow that the former are caused mainly by differences in juvenilemortality, the main factor determining the replacement of D.hyalinaby D.cucullata during early summer.     

Effects of neonate size and food concentration on the life history responses of a clone of the hybrid Daphnia hyalina × galeata to fish kairomones

1. The influence of fish kairomones on the life history parameters of a clone of the hybrid Daphnia galeata × hyalina was measured in laboratory experiments with small and large neonates at one food concentration. The influence of fish kairomones on neonates of the same size at two food concentrations was also investigated.
2. Neonate size (maternal investment per egg) changed the influence of fish kairomones on life history parameters. Daphnids that were small at birth showed greater differences between fish (kairomones present) and no-fish (kairomones absent) treatments for age at maturity and number of eggs in the first clutch than animals that were large at birth. On the other hand, animals that were large at birth differed more in size at maturity between fish and no-fish treatments than small neonates.
3. The food concentrations used in the experiments (0.25–0.75 mg C l^–1) hardly affected the influence of fish kairomones on the life history characteristics studied.
4. The effect of fish kairomones on the size of neonates from the first clutch was similar for large and small daphnids. In the no-fish treatment significant differences were found between small and large neonates for age at maturity and number of eggs in the first clutch. In the fish treatment size at maturity differed significantly between small and large neonates.
5. In life history experiments, neonate size has to be taken into account when measuring the effects of fish kairomones because size at birth influences the results.     

Birth-sex ratios and local resource competition in roe deer, Capreolus capreolus

We investigated variation in the primary sex ratio within andbetween 14 populations of roe deer (Capreolus capreolus) inrelation to maternal body condition. The sex ratio was increasinglymale biased as average maternal body weight decreased. Thisrelationship did not vary according to the population consideredand was not affected by the litter size produced. This relationshipwas also apparent within populations. These results indicatethat, where environmental conditions are limiting, roe doestend to produce male-biased litters. Dispersal is more commonand occurs at an earlier age among male juveniles in this species,particularly as density increases and resources become increasinglyscarce. Thus, we suggest that where females experience environmentalstress, they tend to produce male kids to avoid potential futurelocal resource competition posed by female offspring. [BehavEcol 7: 461–464 (1996)]     

Effects of neonate size and food concentration on the life history responses of a clone of the hybrid Daphnia hyalina × galeata to fish kairomones

1. The influence of fish kairomones on the life history parameters of a clone of the hybrid Daphnia galeata × hyalina was measured in laboratory experiments with small and large neonates at one food concentration. The influence of fish kairomones on neonates of the same size at two food concentrations was also investigated.
2. Neonate size (maternal investment per egg) changed the influence of fish kairomones on life history parameters. Daphnids that were small at birth showed greater differences between fish (kairomones present) and no-fish (kairomones absent) treatments for age at maturity and number of eggs in the first clutch than animals that were large at birth. On the other hand, animals that were large at birth differed more in size at maturity between fish and no-fish treatments than small neonates.
3. The food concentrations used in the experiments (0.25–0.75 mg C l^–1) hardly affected the influence of fish kairomones on the life history characteristics studied.
4. The effect of fish kairomones on the size of neonates from the first clutch was similar for large and small daphnids. In the no-fish treatment significant differences were found between small and large neonates for age at maturity and number of eggs in the first clutch. In the fish treatment size at maturity differed significantly between small and large neonates.
5. In life history experiments, neonate size has to be taken into account when measuring the effects of fish kairomones because size at birth influences the results.     

Hyperscums of the cyanobacterium Microcystis aeruginosa in a hypertrophic lake (Hartbeespoort Dam, South Africa)

It is proposed that surface scums of densely packed planktoniccyanobacteria (blue-green algae) which exist for weeks to months,measure several decimeters in thickness and are covered by acrust of photo-oxidized cells, be called hyperscums. Hyperscumsof Microcystis aeruginosa formed during prolonged periods ofcalm weather in wind-protected sites in a hypertrophic lakesubject to low wind speeds (Hart beespoort Dam, South Africa).A hyperscum that extended over 1–2 hectares and persistedfor 103 days during winter 1983 was studied. Chlorophyll a concentrationsranged from 100 to 300 mg l^–2 Microcystis cell concentrationsreached 1.76x10⁹ cells ml^–1 or 116 cm³l^–1. The hyperscumenvironment was anoxic, aphotic, with a fluctuating temperatureregime and low pH values. The densely packed Microcystis cellssurvived these conditions for more than 2 months. This was shownby comparing the potential photosynthetic capacity of Microcystisfrom the hyperscum with that of Microcystis from the main basinof the lake. However, after 3 months the hyperscum algae losttheir photosynthetic capacity and decomposition processes prevailed.The hyperscum gradually shrank in size until a storm causedits complete disintegration.     

Life history shifts in response to different levels of fish kairomones in Daphnia

Life history parameters, such as age and size at maturity, neonatesize and number of eggs in the first clutch, of a clone of thehybrid Daphnia galeata x hyalina were determined at six levelsof fish kairomones. It was found that the age and size at maturitydecreased gradually with increasing kairomone level, while thenumber of eggs in the first clutch increased linearly. At thesame time, neonate size decreased linearly with increasing kairomonelevel. In a starvation experiment, newly born neonates of mothersnot cultivated in the presence of kairomones survived the longest.These results show that Daphnia is able to adjust its life historytraits to different levels of kairomones, and thus to differentfish densities.     

Induction time and reversibility of changes in Daphnia life history caused by the presence of fish

Two experiments were run, to demonstrate how Daphnia life historychanges in the response to fish kairomone, depending on at whichontogenetic stage the simulated presence of fish appears ordisappears. Exposures of Daphnia, starting from different ontogeneticstages, to the fish kairomone showed that the period betweenthe initiation of phenotypic changes induced by the presenceof fish and their adaptive expression in Daphnia varies fromone instar (2–3 days) in the case of size at first reproductionto five instars (about 7 days) in the case of age at first reproduction.Removing the fish kairomone in different ontogenetic stagesshowed, in turn, that if a proximal factor that induced an anti-predatormechanism disappears and is not detected for at least four instars,Daphnia may withdraw from former changes (e.g. maturation whenlarger). It is suggested that the moment of the final ‘decision’regarding size at first reproduction cannot be attributed toa specific instar, but rather to a given moment in the Daphnialife cycle that is not related to any particular developmentalinstar but rather to the instantaneous level of resources thatcan be allocated to the reproduction.     

Photosynthesis and primary production of Microcystis aeruginosa Kutz. in Lake Kasumigaura

Seasonal changes in the photosynthesis and primary productionof Microcystis aeruginosa Kütz. were investigated in LakeKasumigaura during 1981–1982. Microcystis always showeda light-saturated photosynthesis-light curve. Both P_max andthe initial slope of the photosynthesis-light curve of Microcystisin early summer were very high, so it was concluded that Microcystisutilized both low and high light intensities efficiently. TheP_max of Microcystis was found to be a function of the watertemperature except in August and September. The linear regressionon the temperature-P_max relationship discontinued at 11°C,where the P_max value dropped; Microcystis did not photosynthesizebelow 4°C. The initial slope of the curve was also descendingbelow 11°C. It is suggested that Microcystis changes itsphysiological properties below 11°C. The highest value ofgross production calculated for M. aeruginosa was 5.4 gC m^–2d^–1 in July; the annual gross production was estimatedto be 300 gC m^–2year^–1 (i.e., 40% of the total primaryproduction in this lake).     

Inter- and intra-instar food consumption in the German cockroach, Blattella germanica

Food consumption was measured in an insecticide-susceptible (Orlando) and-resistant (Village Green) strain of German cockroach, Blattella germanica (Dictyoptera: Blattellidae), throughout each stadium. All instars exhibited a similar pattern of consumption over the course of the instar; consumption was low to moderate at the beginning of each instar, climbed steadily to a maximum near the middle, declined progressively from the mid-instar maximum, and ceased or was minimal several days before the next molt. Consumption ceased or was minimal during the final two to four days of each instar. Cumulative consumption for the six instars was significantly greater in the Village Green strain as compared with the Orlando strain. Village Green nymphs consumed 79.6±0.7 mg of rat chow while Orlando nymphs consumed 63.7±3.4 mg. Total consumption by instar increased significantly with each successive instar in the Village Green strain. In addition, Village Green sixth instar females consumed significantly more food than sixth instar males. A similar trend was observed for the Orlando strain; consumption tended to increase in each successive instar. Relative consumption rate (food consumed/cockroach/instar divided by the mean weight of the instar) was highest in the first two instars and decreased in subsequent instars.     

Egg size and clutch size in two Daphnia species grown at different food levels

The effect of three different Scenedesmus food concentrations(0.04, 0.2 and 1 mg C l^–1) on maternal investment wasstudied in two cladoceran species of similar size, Daphnia pulicariaand D.hyalina. It was observed that as food concentration decreased(between 1 and 0.2 mg C l^–1), there was an increase insize, protein content, lipid content, carbon and mass of theegg, while, at the same time, the clutch size of the femalesbecame smaller. Such an increase in ‘per offspring investment’was reflected in an increase in body length, body carbon andbody mass of neonates as the food available for females decreased.However, in D.pulicaria this tendency was not maintained downat 0.04 mg C l^–1 in which there was a decrease of theegg characteristics mentioned above. Although, there are notavailable all the egg and neonate parameters of D.hyalina at0.04 mg C l^–1, the body length of the neonates was largerthan at 0.2 and 1 mg C l^–1. These results show that, asfood diminishes, these two cladoceran species are able to respondby decreasing clutch size, but increasing the size of egg, therebyincreasing the probability of neonate survival. This tendencyis probably maintained until the food concentration is too lowand the females have to reduce the energy allocated for reproduction.