Reproductive potential and lifetime potential fecundity of the freshwater amphipods Gammarus fossarunt and G. roeseli in Austrian streams and rivers

• 1 Fecundity of Gammarus fossarum populations at six stream sites (S1-S6) and G. roeseli populations at two sites (S5 and S6) was studied monthly during 1985–1988, distinguishing seven morphological stages of embryonic development. Mean survival of G. fossarum eggs was 65% (60–70%) in nature and 60% (57–63%) in the laboratory; egg survival of G. roeseli was 52% (46–58%) in nature and 41% (35–47%) in the laboratory. Regressions of egg numbers per clutch against body wet weight (WWT) decreased significantly for egg developmental stages 2 to 7 (hatching).
• 2 In stream populations, ovigerous females of G. fossarum were absent in October (six sites) and November (five sites); ovigerous G. roeseli were usually absent from October until March.
• 3 Overall mean egg volume (EV) increased significantly from 0,08 ± 0.001 mm³ and 0.075 ± 0.001 mm³ for stage 2 eggs, to 0.174 ± 0.012mm³ and 0.160 ± 0.013 mm³ for stage 6 eggs of G. fossarum and G. roeseli, respectively. The dry weights of stage 2 eggs, stage 6 eggs and neonates (stage 7) were not significantly different, within and between species; mean dry weight was 36 ± 3 μg.
• 4 Egg volumes and fecundity indices (FI, weight-specific number of eggs per clutch) were not significantly different between the same months of four successive years, so the data were pooled to give a single representative ‘year’. At most sites there were marked seasonal fluctuations in these variables. In both species, mean EV was largest for ‘winter’ eggs in December/January and smallest for ‘summer’ eggs in May, EV decreased during some months of the year when FI increased, and vice versa. Mean reproductive effort (RE = EV × FI) declined from high ‘winter’ values to low ‘summer’ values, and this difference was most marked at sites where the major foodstuff available was seasonally limited (autumn-shed tree leaves). Overall (‘annual’) mean RE was also lowest at these sites (S3 and S4) but was some 13% greater at sites where nutrients and food were present in the greatest quantifies (S5 and S6). Specific maximum potential body sizes and hence maximum potential fecundities (fifty-nine eggs for G. fossarum and eighty-seven eggs for G. roeseli) were attained only at S5 and 56. Mean RE was nearly identical for G. fossarum and G. roeseli from the same sites.
• 5 At experimental temperatures (T) in the range 3.8–20.2°C, females of the same body weight carried significantly different egg numbers per clutch. The relationship between FI and T was described by a second-order polynomial. The calculated optimum T was 12.1°C for G. fossarum and 16.3°C for G. roeseli. Interspecific differences were highly significant.
• 6 Theoretical lifetime potential fecundity was approximately 194 eggs for G. fossarum

     

Strategies of a successful new invader in European fresh waters: fecundity and reproductive potential of the Ponto-Caspian amphipod Dikerogammarus villosus in the Austrian Danube, compared with the indigenous Gammarus fossarum and G. roeseli

1. Fecundity of a Dikerogammarus villosus population at Spitz was studied in the Austrian Danube during the 3‐year period 2002–2004. Ovigerous females were absent in October and November, and extremely scarce in December when the reproductive season started again slowly. From January to September pre‐copulatory pairs and egg‐carrying females were present. The reproductive cycle lasted for 9–10 months. 2. Various pigmentation phenotypes of D. villosus have been described in the literature. However, no significant differences were found between the reproductive variables studied here and several colour morphs. Mating was size‐assortative; mean body length of males was about 1.3 times greater than that of their potential mates, and the wet weight was approximately twice as heavy. 3. The relationship between the number of embryos per clutch and the wet weight of females was described by a 3‐parameter power equation. The population mean was 43 eggs with a range of five to 194 eggs. Eighty‐two specimens from 1359 D. villosus females had more than 100 eggs: the smallest of these females was 12 mm long (30 mg) wet weight, and the largest, which was 18 mm long (91 mg), had 194 eggs in embryonic development stage 4. 4. Numbers of embryos in developmental stages 2 (early egg stage) and 7 (newly hatched neonates) differed significantly with body wet weight of ovigerous females (P < 0.05). For an average female in the range 10–12 mm (20–30 mg) the number of juveniles in the brood pouch was 74% of the number of stage 2 eggs. This value can be interpreted as the survival rate of eggs. 5. The overall mean egg volume (EV, ±95% CL) of stage 2 eggs of D. villosus was 0.05 ± 0.001 mm³, and EV increased significantly at each stage of development. At stage 6, egg volume had increased by a factor of 2.6, and averaged 0.13 ± 0.001 mm³. In comparison, G. fossarum and G. roeseli had significantly larger eggs in all developmental stages. 6. Mean egg size of D. villosus (0.063 mm³) was maximal in January. For D. villosus (and G. roeseli) the minimum mean egg size occurred in September. In contrast to G. fossarum and G. roeseli, a second peak in egg size was not observed for D. villosus, and egg size fell more or less successively from January to September. 7. A simple index of fecundity was calculated from the number of stage 2 eggs divided by the female's wet weight. The highest values were observed in April and May, when females from the overwintering generation grew to their maximum body size. Thus the release of a large number of neonates corresponds with the availability of plentiful food and rising water temperatures for juvenile growth in the spring. The lowest value occurred in December. In June the small females of a summer generation appeared, with a naturally low fecundity. 8. The relationship between brood development time and water temperature was studied in the laboratory at a series of constant temperatures. At 16 °C, mean brood development time was 14 days for D. villosus, compared with about 3 weeks for the indigenous species. At 10 °C, mean brood development time was 24 days in D. villosus, compared with 40 days in G. fossarum and 44 days in G. roeseli. At 4 °C it was 1.8 and 3.5 times longer in G. fossarum and G. roeseli. 9. The number of offspring produced by a single clutch from a large female D. villosus is considerably higher than the total numbers produced by the indigenous freshwater gammarids, such as G. fossarum, G. roeseli and G. pulex, during their life‐spans of 1.5–2 years in seven to nine successive broods. Only one or two large ovigerous D. villosus would probably be enough to start a new population. A potentially high reproductive capacity, comparatively small eggs, optimal timing to release the maximum number of neonates per female in April/May, and a long reproductive cycle, together with rapid development of eggs, rapid growth to sexual maturation, short life span, tolerance to a wide range of environmental conditions, and exceptional predatory capabilities, all give the invasive Ponto‐Caspian gammarid an opportunity to become globally distributed in freshwater ecosystems of the temperate climate zone.     

Life history and reproductive capacity of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda) under naturally fluctuating water temperatures: a simulation study

SUMMARY 1. Mathematical functions developed in long‐term laboratory experiments at different constant temperatures were combined with daily water temperatures for 1991–93 in eight Austrian streams and rivers to simulate the complex life histories and reproductive capacities of two freshwater amphipods: Gammarus fossarum and G. roeseli. The functions describe brood development times, hatching success, times taken to reach sexual maturity, growth, and fecundity. The sex ratio was assumed to be 0.5 and an autumn–winter reproductive resting period was based on observations of six river populations. Simulations included summer‐cold mountain streams, summer‐warm lowland rivers, watercourses fed by groundwater or influenced by heated effluents, and varying amplitudes of change within each year. 2. A fortran 77 computer program calculated growth from birth to sexual maturity of first‐generation females born on the first day of each calendar month in 1991, and the numbers of offspring successfully released from the maternal broodpouch in successive broods. At the 1991–93 regimes of temperature, individual G. fossarum released 127–208 offspring and G. roeseli released 120–169 in seven or eight successive broods during life spans of less than 2 years in six rivers. Life spans extended into a third year in the relatively cool River Salzach (mean temperature 7.5 °C). They were not completed in the very cold River Steyr (mean 5.6, range 2.5–7.9 °C), where G. fossarum produced five broods (totalling 120 offspring) and G. roeseli only two broods (totalling 28 offspring) in the 3‐year period. Except in the Steyr, some offspring grew rapidly to maturity and produced several second‐generation broods during the simulation period; in the warmest rivers some third‐generation broods were also produced. Birth dates, early or late in the year, influenced the subsequent production of broods and young, depending on temperature regimes in particular rivers. Total numbers of offspring produced by the second and third generations represent the theoretical reproductive capacities of G. fossarum and G. roeseli. Minimum and maximum estimates mostly ranged from 100 to 17 300, were larger for G. fossarum except in the warmest river (March), where temperatures rose above 20 °C for 56–78 days in summer, and largest (maximum 37 600) in the River Voeckla heated by discharge from a power‐station (mean 11.5 °C). Results from the simulations agree with preliminary assessments of relative abundances for G. fossarum and G. roeseli in several of the study rivers, but in some one or both species appear to be absent. On a wider scale, the present study confirms that G. fossarum is potentially more successful than G. roeseli in cool rivers but indicates that neither species is likely to maintain viable populations in cold rivers strongly influenced by snow and ice‐melt. 3. The potential impacts of future river warming by increases of 1, 2 and 3 °C, due to climate change, vary according to river site, date of fertilisation, the extent of temperature increase, and the species of Gammarus. For Austrian rivers with mean temperatures in the range c. 7–10 °C, future warming would result in modest changes in the life histories and reproductive capacities of both G. fossarum and G. roeseli; the former would find improved temperature conditions in watercourses that are currently very cold throughout the year, and both would find warm rivers less tolerable. 4. The high potential reproductive capacity of gammarids, with rapid production of numerous successive broods when sexual maturity is finally achieved, indicates adaptation to high mortality during the relatively long period of growth to sexual maturity, and provides scope for an opportunistic strategy of emigration from centres of population abundance to colonise new territory when conditions are favourable. Rapid expansion of populations is desirable to combat the effects of environmental catastrophes, both frequent and short‐term floods and droughts, and more long‐term climatic changes that have occurred several times in glacial–interglacial periods during the current Ice Age.     

Effect of temperature on the duration of egg development, and moulting and growth in juveniles of Crangonyx pseudogracilis (Crustacea: Amphipoda) in the laboratory

SUMMARY. The interval between moults is an extension of egg development time, increasing from birth to sexual maturity which is probably reached at instar 6 or 7. The duration of each instar increased with the animal's age. Incubation time for eggs and the intermoult interval have the same curvilinear inverse relationship with water temperature in the range 3.5–25°C. Results are expressed as degree-days above predicted threshold temperatures of 3.8°C for eggs and 3.2°C for instar 1 after birth, but inverse power-law relationships were a better fit to the results, with exponents of - 1.355 for eggs, - 1.263 for instar 1 and - 1.37 to - 1.92 for instars 2–4. Temperature — dependence apparently altered in instars 5 and 6 at 15–25°C. From a multiple regression of geometric mean moult interval (M_i, days) against mean age (A) and temperature (T, °C), M_i= 56.4 T^?0.7 e^0.016A, with mean ages of 106 days at 15°C and 85 days at 25°C after six moults. The mean number of primary flagellar segments on the antennules increased from 4.0 in instar 1 to 6.0 in instar 2 and 8.0 in instar 3. Thereafter, segments were added less regularly to give a mean of 13.2 in instar 7. In a natural population, when the sexes became distinctive they had 11–13 flagellar segments. From birth at c. 0.05 mg wet wt, individual growth rates were highly variable; mean growth rates (G_s, % wet wt day^?1) were similar in animals fed on dried, leached elm leaves and living, green leaves of Callitriche; there was a power-law relationship with temperature in the range 3.5–25°C, (G_s= 0.27 T^0.59). Faster growth rates were obtained on living leaves of Elodea. Sexual maturity is reached at c. 0.4–0.5 mg wet wt. A brief comparison is made with Gammarus pulex; C. pseudogracilis may be better adapted to warm-water habitats.     

Nomenclature,redescription, and new record from Okinawa of Cymbasoma moriiSekiguchi,1982 (Monstrilloida)

In 1990 and 1991 the distribution of the genus Gammarus was examined in the River Hunte and its tributaries (Lower Saxony, northern Germany). In contrast to data from the literature, Gammarus fossarum and G. roeseli were just as abundant as G. pulex, which had been known to inhabit rivers and brooks in northern Germany. G. pulex was most frequent (1900 at 57 out of 70 and 1991 at 37 out of 39 sampling sites) followed by G. fossarum (at 52 and 32 sampling sites, respectively), whereas G. roeseli was locally restricted (at 7 and 6 sampling sites, respectively). G. fossarum and G. pulex were distributed up to the level of the city of Oldenburg; further north their distribution is limited by tidal influences and they are replaced by G. zaddachi. The possibility of using gammarids as indicators of water quality, as it has been done in low mountain ranges, is discussed.     

Rheotaktisches Verhalten einigerGammarus-Arten bei verschiedenem Sauerstoffgehalt des Wassers

Zusammenfassung 1. Zur Untersuchung kleinerer Wassertiere wurde eine Durchflußapparatur entwickelt, die eine stufenlose Regelung einer gerichteten Strömung sowie die Einstellung einer konstanten Gaskonzentration erlaubt.2. Das rheotaktische Verhalten vonGammarus pulex, G. roeseli, G. fossarum, G. tigrinus undG. salinus wurde bei einer Temperatur von 15° C unter verschiedenen Sauerstoffkonzentrationen getestet.3. Die höchste rheotaktische Aktivität der untersuchten Amphipoden wurde bei geringen Strömungsgeschwindigkeiten (5 cm/sec) konstatiert.4. Diese Aktivität erfuhr mit abnehmendem O₂-Gehalt eine Steigerung bis zu einem Aufwanderungsmaximum, das bei einer kritischen O₂-Konzentration lag. Noch geringerer Sauerstoffgehalt bewirkte Abwanderung in Strömungsrichtung, rasche Aktivitätsabnahme und führte meist zum Tod der Versuchstiere.5. Die so definierte kritische O₂-Konzentration lag fürGammarus pulex bei 2,7 mg O₂/l fürG. roeseli bei 3,1 mg O₂/l, fürG. fossarum bei 5,3 mg O₂/l und für die BrackwasserformG. tigrinus bei 3,5 mg O₂/l. Die euryhaline ArtG. salinus hatte keine ausgeprägte Rheotaxis; lediglich die Grenze vom Auf- zum Abwandern konnte definiert werden (2,5 mg O₂/l).

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Rheotactic behaviour of someGammarus species in different oxygen concentrations of the water

An experimental vessel has been developed which makes it possible to observe the behaviour of gammarids and other aquatic invertebrates in various water current speeds and oxygen concentrations. Studies have been conducted with the following limnic and brackish-water amphipods:Gammarus pulex (L.),G. roeseli Gervais,G. fossarum Koch,G. tigrinus Sexton andG. salinus Spooner. In adequate oxygen concentrations, the gammarids tested show a moderate positive rheotaxis. Lethal and sublethal oxygen concentrations, however, lead to negative rheotaxis. The maximum degree of upstream movement is attained in the region of the critical oxygen concentration. Under the experimental conditions (15° C, water current 5 cm/sec), these maxima vary according to species. The maximum occurred at 2.7 mg O₂/l forG. pulex, 3.1 mg O₂/l forG. roeseli, 3.5 mg O₂/l forG. tigrinus, and 5.3 mg O₂/l forG. fossarum. No such maximum was found forG. salinus. Oxygen deficit causesG. salinus to move downstream at 2.5 mg O₂/l.

     

Respiratory Levels and Adaptations in Four Freshwater Species of Gammarus (Crustacea: Amphipoda)

Respiration of four freshwater species of the amphipod crustacean Gammarus: G. fossarum, G. lacustris (river and lake), G. pulex and G. roeseli were measured in a closed, stirred respirometric chamber with a micro-electrode. Oxygen consumption, expressed as weight-specific oxygen uptake (R_s) in relation to decreasing oxygen concentration, varied at air saturation from 0.86 (G. lacustris, lake) to 2.06 μl O₂ mg⁻¹ AFDW h⁻¹ (G. pulex). R_s also differed intra-specifically among the two populations of G. lacustris. G. lacustris (river), G. pulex and G. roeseli expressed moderate ability to regulate their oxygen consumption at decreasing oxygen concentrations, whereas the regulation ability was higher in G. lacustris (lake) and in G. fossarum, which maintain high oxygen uptake at oxygen levels >2 mg O₂ l⁻¹. All four Gammarus species are partial regulators in response to variations in oxygen concentration. The differences between species are considered too small to account for their natural distributions. It appears that the tolerances of Gammarus species to organic pollution depend only in part on oxygen conditions.     

Growth and maturation of a North American fairy shrimp, Streptocephalus seali (Crustacea; Anostraca): a laboratory study

SUMMARY.

• 1 We evaluated survival, growth and time to maturation of the fairy shrimp, Streptocephalus seali Ryder, in the laboratory at various combinations of temperature and water hardness.
• 2 Both independent factors affected survival and growth of S. seali. Multiple regression analysis and response surface modelling predict that after 4 days, over 80% survival is obtained at temperatures from 14 to 28°C and water hardnesses from 60 to 130 mg CaCO₃ 1-^?1.
• 3 Growth rates of larvae were often maximum at physicochemical conditions other than those which had promoted maximum rates of survival. For example, after 12 days mean total body length was almost 12 mm in larvae which had been maintained at 34°C (80 mg CaCO₃ 1-^?1): the maximum survival rate had been obtained at 19°C. Total length was directly correlated with temperature at the lowest hardness tested, but not at the other two hardnesses (100 and 120 mg CaCO₃ 1-^?1). At the latter water hardnesses, total length was significantly less at 34°C than at 32°C on all three sampling occasions (4, 8 and 12 days post-hatch).
• 4 Similarly, developmental stage of larvae correlated well with temperature but larvae reared at 34°C did not develop more quickly than those reared at 32°C. After 12 days, most larvae at the two highest temperature treatments had developed at least to Stage 14 and many were nearly mature; at 17°C most larvae were still at Stage 10.
• 5 During our study of maturation rate of females we noted that egg production was initiated after completion of fourteen or fifteen moults. Mean time to maturation at 27°C (17.3±2.8 days) exceeded that at 32°C (12.3±2.6days). The minimum time to maturation of a shrimp was 9 days at 32°C.

     

Effects of diet, body size, age and temperature on growth rates in the amphipod Gammarus pulex

SUMMARY. Increase in body wet weight of Gammarus pulex fed on decaying elm leaves was followed to senescence and death. Growth in juveniles was approximately exponential; from birth to death it conformed to a logistic growth curve, with maximum absolute increments in weight about half-way through a life span of 350–450 days at 15°C. Some individuals lived longer, for up to 640–700 days. The instantaneous or specific growth rate was maximal near birth, at c. 5–6% wet wt day^?1, and declined exponentially with increasing size and age. Over the range 4.7–14.8°C there was a log-log relationship between temperature and specific growth rate. Growth was maximal at 20°C in newborn animals and at 15°C in 6–9-mg animals. The specific growth rate of young individuals was fastest on decaying leaves of elm with a well developed flora of fungi and other microorganisms. Leached elm leaves without this flora supported growth at a lower rate. The latter diet was sufficient for survival and growth of newborn individuals; detritus, faeces or other food items were not needed. Isolated specimens grew as fast as those kept in groups. Growth was generally slower on leached leaves of oak and sycamore. In newborn animals fed on the fine roots of aquatic plants (Veronica, Rorippa and Glyceria), growth was as fast as on decaying elm leaves; growth on the green living leaves of the plants was slower, as on detritus from two streams and on a pure culture of an aquatic fungus. Consumption of leached elm leaves was related to leaf thickness. In a full gut the wet weight (1.34–1.37 mg) and volume (3.8–4.1 mm³) (for 20-mg animals) was independent of leaf thickness but dependent on animal size, increasing 4-fold over the range 2–50 mg body wt. Daily consumption (dry wt) was approximately equivalent to 50% body dry wt at 5 mg and 20% at 50 mg body wet wt. Individuals fed on thick leaves ingested 50% more dry weight per day and absorbed more in the gut than when fed on thin leaves, but the relative efficiency of absorption was the same at 36–59% for 10–20-mg animals. Weight-specific absorption in the gut was highest in juveniles and decreased with increasing body weight; relative efficiency of absorption was generally lower in the larger individuals. Assuming an energy value of 5 cal mg^?1 dry wt for elm leaves, daily mean energy intake by absorption in thegutof G. pu/ex was2.2 cal mg^?1 animaldry wt (9.2 J mg^?1) in individuals of 0.4 mgdry wt (2 mg wet wt), decreasing to 0.3 cal mg^?1 (1.3 J mg^?1) at 10 mg dry wt (50 mg wet wt). Growth in Gammarus is briefly reviewed in the hght of work on other animals and it is emphasized that all aspects of feeding, growth and metabol-ism should be specifically related to size and age of the individuals, using well defined diets.     

Feeding and growth of Asellus aquaticus (Isopoda) on food items from the littoral of Windermere, including green leaves of Elodea canadensis

SUMMARY. In the laboratory, Asellus aquaticus devoured intact green leaves from growing shoots of the aquatic macrophyte Elodea canadensis. In four collections of A. aquaticus on Elodea in a lake (Windermere), c. 20% of the specimens contained in their guts fragments of green Elodea leaves; this material and pieces of oak (Quercus) were identified from characteristic leaf hairs. Some specimens had also eaten the filamentous alga Oedogonium. Fluorescence microscopy is a useful aid for screening invertebrates that may have eaten living plant tissues. Immature A. aquaticus, with an initial mean body length of c. 3 mm, wet weight c. 1 mg, were grown through sexual maturity over a 49-day period at 15°C in a series of twenty-two experiments (six to twelve isolated specimens in each experiment) comparing growth rates on different foods, including instances where no food was given. Animals were fed on a variety of items collected from the littoral of Windermere, plus some laboratory cultures of algae and bacteria. The highest mean specific growth rate (5.8% day^?1) was obtained on young Elodea leaves mechanically shaken to remove epiphytes. Other diets yielding fast growth rates (3.7–5.3% day^?1) were young growing leaves of Elodea with few epiphytes and older green and brown living leaves covered with a thick growth of epiphytic algae, epiphytic algae removed from Elodea, plastic imitation Elodea immersed in the lake until covered with attached algae, epilithic algae on stones, Oedogonium, and decaying oak leaves. Slower growth (1.3–2.2% day^?1) and poorer survival was obtained on the following: a pure culture of the bacterium Sphaerotilus natans; cultured bacteria from lakewater; the filamentous algae Cladophora and Stigeoclonium both with and without epiphytes; faecal matter from Asellus; freshly killed Asellus; lake sediment. Some growth (mean = 0.7% day^?1) and 50% survival for 21 days occurred in ‘starved’ animals kept in filtered, sterilized lakewater. Better survival and slightly faster growth (1.0–1.5% day^?1) occurred in ‘starved’ animals kept in filtered and unfiltered lakewater. Growth of A. aquaticus was also experimentally determined from birth in animals fed on young green Elodea leaves and on decaying oak leaves. On both diets, growth was curvilinear and approximately exponential from birth to sexual maturity reached at c. 2mg wet weight in 46–60 days at 15°C. In older specimens the relative growth rate gradually fell over a period of 50 days, representing a more linear phase of growth during sexual maturity.     

Quantifying food limitation of arthropod predators in the field

A method for quantifying food limitation of arthropod predators in the field is presented and applied to species of ground beetles (Carabidae) and sheet-web spiders (Linyphiidae) from a cereal field. Food limitation is expressed quantitatively as accumulated hunger (=starvation) by transforming 24-h food consumption at 20°C of animals newly collected in the field into days of starvation at 20°C. This is done by means of a reference curve relating 24-h food intake at 20°C to starvation periods (days) at 20°C. Such a reference curve was obtained for the carabid beetle Agonum dorsale in the laboratory. For other species the reference curve was modified with species-specific data. The procedure makes it possible to compare the feeding conditions of different species populations that are part of the same community. Hunger levels in the field for females of A.␣dorsale were equivalent to c. 15 days of starvation in early spring, c. 5 days in June, increasing to c. 10 days in late summer. Two ground beetles occurring during summer also showed increasing hunger levels from June to July, probably the result of a dry summer. Two spider species experienced a hunger level in the range of 4–8 days of starvation. Received: 15 August 1997 / Accepted: 22 January 1998     

Post-harvest age-induced seed dormancy of Acer ginnala and its alleviation by growth regulator and low temperature treatments

One-month-old fruits of Acer ginnala with winged pericarp attached gave 44% germination and this was not increased by cold treatment at 4°C for 0, 10, 20, or 30 days, gibberellic acid treatment at 0, 1, 10, 100 or 1000 mg litre^-1, or ethephon treatment at 0, 2, 20, 200 or 2000 mg litre^-1. After 6 months of storage at 20–25 °C, germination of untreated fruits fell to 5% but could be restored to that of 1-month-old fruits by incubation at 4 °C for 30 days. After 9 months storage, no germination occurred in untreated fruits. Cold treatment (30 days at 4 °C partially restored germination (26%). Treatment with either gibberellic acid (1000 mg litre^-1) and 30 days at 4 °C (40%) or ethephon (100 mg litre^-] and 30 days at 4 °C improved germination (69%). The combination of all three treatments, i.e. 100 mg litre^-1 gibberellic acid, 100 mg litre^-1 ethephon and 30 days at 4 °C, optimised germination (86%). Thus, dormancy of A. ginnala developed during storage but could be reversed by a combination of treatment with low temperature and growth regulators. The highest germination (86%) was achieved after low temperature and growth regulator treatment of stored fruit.     

Interference competition among native and invader amphipods

Aquarium experiments were used to study indications of interference competition, such as substratum choice shifts, swimming activities and mortality of invasive and indigenous gammarids in each other's presence. The more recent invaders Gammarus tigrinus and Dikerogammarus villosus were more likely to prefer stone substratum, whereas the native Gammarus pulex and an earlier invader Gammarus roeseli were found more frequently in the water layer. Sand was the least likely substratum to be chosen by any of the species. G. pulex and G. roeseli did not alter their substratum preference in each other's presence. In the presence of D. villosus, G. pulex shifted towards smaller stones and increased its swimming activities, whereas D. villosus did not change its behaviour in the presence of G. pulex. These shifts may indicate interference competition, with D. villosus being the stronger competitor. The greatest shifts in substratum preference arose when one species had occupied a substratum before the other one was introduced, especially when D. villosus was already present before G. pulex was introduced, possibly indicating pre-emptive competition. Swimming activities of G. pulex increased in the presence of D. villosus, whereas D. villosus spent little time swimming. Mortality was comparable between the different experiments without any indication of predation. The effect of Intra Guild Predation (IGP) may not be reflected adequately by short-time experiments as moults occurred seldom during the experiments. Although no IGP was observed during our experiments, habitat shifts occurred, which may indicate that competitive interactions are apparent before IGP starts. Such shifts may serve to avoid intraguild competition.     

Oxygen consumption and ammonia excretion rates in Octopus maya,loligo forbesi and Lolliguncula brevis (Mollusca: Cephalopoda)

Oxygen consumption and ammonia excretion rates were investigated in young Octopus maya (hatching to 139 days old; 0.11–81.23 g wet body weight, BW; 22.5–23.9°C), young squids of Loligo forbesi (hatching to 45 days old; 9.4–115.3 mg BW; 12.3–13.1°C) and young squids of Lolliguncula brevis (2.00–39.98 g BW; 23.8–24.7°C). Except at hatching, oxygen consumption and ammonia excretion rates on an individual basis (M) of these three cephalopods increased linearly with increasing body weight (BW) expressed as M = aBW^b . Values of b for oxygen consumption were 0.900, 0.910 and 0.848 and for ammonia excretion were 0.744, 0.809 and 0.751 for O. maya, L. forbesi and L. brevis, respectively. Among the three species the value a varied widely, while b was similar for both oxygen consumption and ammonia excretion rates. Based upon these data, metabolism for hatchlings of O. maya and L. forbesi was estimated to be relatively lower than that of older juveniles. The O/N ratios for hatchlings of O. maya and L. forbesi were relatively high and indicate an apparent dependence upon lipids in the immediate post‐hatching period, followed by standard protein energy utilization thereafter.     

Confrontation of cryptic diversity and mate discrimination within Gammarus pulex and Gammarus fossarum species complexes

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Comparison of cold hardiness and sugar content between diapausing and nondiapausing pupae of the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract. To understand overwintering of the cotton boll worm Helicoverpa armigera, cold hardiness and sugar content are compared between diapausing and nondiapausing pupae. Diapausing and nondiapausing pupae reared at 20 °C under short and long photoperiods are acclimatized with a reduction of 5 °C per 5 days to 0 °C. When the acclimation temperature reaches 0 °C, the survival of diapausing pupae is assessed. The survival gradually decreases as the period of treatment progresses and approximately half survive for 112 days. However, nondiapausing pupae survive only 14 days after exposure to 0 °C. The surpercooling points of nondiapausing, diapausing and acclimatized pupae are approximately −17 °C. The major sugars contained in pupae are trehalose and glucose. Even though trehalose contents in diapausing pupae (initial level: 0.6 mg 100 mg⁻¹ fresh weight) increase significantly during cold acclimation and continue increasing until 58 days after exposure to 0 °C (maximum level: 1.8 mg 100 mg⁻¹), glucose is maintained at low levels (0.02 mg 100 mg⁻¹) for 56 days at 0 °C. However, glucose contents increase (maximum level: 0.8 mg 100 mg⁻¹) with decreasing contents of trehalose 84 days after exposure to 0 °C. Glycogen content gradually decreases during cold acclimation. When nondiapausing pupae are acclimatized with a reduction of 5 °C per 5 days to 5 °C from the beginning of pupation until the eyespots move, trehalose content increases (maximum level: 1.0 mg 100 mg⁻¹). Glucose contents in nondiapausing pupae increase before eclosion (0.09 mg 100 mg⁻¹). From these results, diapausing pupae of H. armigera can overwinter in regions where average winter temperatures are higher than 0 °C, but nondiapausing pupae cannot.     

Temperature effects on egg and larval development and phenological forecasting of the smaller fruit tortrix,Grapholita lobarzewskii

The effects of temperature on egg and larval development of Grapholita lobarzewskii Nowicki (Lepidoptera: Tortricidae) were studied under controlled conditions to complement the basis for phenological forecasting and thus to optimize the timing of monitoring and control measures with respect to sustainable pest management. Egg development lasted on average 28.1 days at 12.7 °C and 5.5 days at 26.1 °C. Egg mortality was generally low, varying between 12 and 14% within a temperature range of 12.7–22.0 °C, but slightly increased to 20% at 26.1 °C. For egg development, a lower thermal threshold of 9.7 °C and a thermal constant of 90.6 degree days were established. Larval development took on average 76.0 days at 12.7 °C and 21.5 days at 26.1 °C. Larval mortality was 51% at 12.7 °C but only 6–12% at temperatures above 17 °C. The lower thermal threshold and the thermal constant for larval development were 7.6 °C and 389.2 degree days, respectively. Final larval weight increased with temperature from 18.6 mg at 12.7 °C to a maximum of 23.9 mg at 22.0 °C. Based on mortality rates, the optimal temperature range was between 12.7 and 22.0 °C for egg development and between 17.1 and 22.0 °C for larval development, which was confirmed based on the weight of fully grown larvae. These biological parameters of egg and larval development enabled us to parameterise a phenology model for G. lobarzewskii, which was incorporated into an existing decision support system for fruit pests. Precise forecasts of pest phenology facilitate the optimal timing of monitoring and control measures, improve their efficiency, and thereby contribute to sustainable crop protection.     

The effect of light on oxygen consumption in two amphipod crustaceans–the hypogean Niphargus stygius and the epigean Gammarus fossarum

The effects of light on the metabolic rates of the hypogean amphipod Niphargus stygius and the epigean amphipod Gammarus fossarum were compared by measuring oxygen consumption and respiratory electron transport system (ETS) activity. They were exposed to light intensities of 720 and 4700?lx at 10°C. Oxygen consumption increased significantly in N. stygius exposed to both low and high intensities of light, but no significant increase was observed in G. fossarum at either intensity. The increase of oxygen consumption in N. stygius was significantly greater at the higher light intensity. This indicates a stress response in which exploitation of half the metabolic potential for energy production in N. stygius during exposure to high light intensity constitutes an adverse effect on its metabolism, since this species usually uses less than 25% of its total metabolic potential for standard metabolic demands.     

Développement endoparasitaire et croissance pondérale larvaire du parasitoïdeLixophaga diatraeae [Dip.: Tachinidae] dans un hôte de substitution:Galleria mellonella [Lep.: Pyralidae]

Résumé L'étude du développement endoparasitaire deLixophaga diatraeae (Towns.) dans un h?te de substitutionGalleria mellonella L. a été effectuée par dissections d'h?tes hébergeant des parasito?des d'age connu. Les résultats mentionnés sont obtenus avec en movenge 2.6 parasito?des par h?te. Les élevages ont lieu à 22.5±0.5°C et 85±5 % H.R. avec une photophase de 12 h pourL. diatraeae et à 28±1°C à l'obscurité pourG. mellonella. La croissance pondérale larvaire suit une loi exponentielle et correspond à un temps de doublement du poids de 0,65 j pour les stades 1 et 2 et environ 0,8 j pour le stade 3. Le développement larvaire complet requiert 7,5 j en moyenne. Les stades 1,2 et 3 durent en moyenne respectivement 2,9, 2,5 et 2,1 j. La mue larvaire L₁–L₂ intervient vers 0,23 mg et la mue L₂–L₃ vers 3,2 mg. La larve nouvelle née pèse 12,3 μg et la croissance larvaire représente un facteur multiplicatif maximum d'environ 2 500 fois. Le poids moyen des pupes obtenues est de 14,2 mg.

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Summary Endoparasitic development ofLixophaga diatraeae (Towns.) reared in a substitution hostGalleria mellonella L. was studied by dissections of hosts containing known aged parasitoids. The exposed results are obtained with an average of 2,6 parasitoids per host. Rearing ofL. diatraeae was performed at 22.5±0.5°C and 85±5% R.H. with 12 light hours and rearing ofG. mellonella at 28±1°C in darkness. The larval weight growth is exponential and exhibits a doubling time of 0.65 day for the 1st and 2nd stages and around 0.8 d. for the 3rd stage. Mean complete larval development time is 7.5 days. The 1, 2 and 3 stages last respectively 2.9, 2.5 and 2.1 days. Larval moulting 1–2 happens around 0.23 mg and moulting 2–3 around 3.2 mg. New hatched larva weights 12.3 μg and during larval growth multiplicates its weight by about 2,500. The mean pupal weight is 14.2 mg.

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Nous remercionsColette Ogier pour sa collaboration technique,P. Laviolette etG. Bonnot pour leur lecture critique du manuscrit.     

Experiments on feeding and growth of the amphipod Gammarus pulex (L.) related to its distribution in the River Duddon

Individuals of Gammarus pulex were kept at 15°C for periods of 23–70 days on diets comprised of elm or oak leaves, Tricladium and Clavariopsis (Hyphomycete fungi), Molinia (grass), Zygogonium (alga), Nardia (liverwort). Both the mean interval between moults (m_i), and daily increments in body wet weight, were related to diet. The lowest value for m_i was 14·6 days on a diet of naturally decaying elm and oak leaves. The largest weight gains also occurred on this diet; the average daily gain in weight (D_w) = 130·8 μg/day, the mean specific gain in weight (G_w) = 1·69 μg %/day. On green Molinia and fungi diets D_w ranged from nil to 60·7 μg/day, and m_i= 17·4–18·4 days was significantly (P<0·01) longer than m_i on leaf diets. Survival and growth were poor on brown Molinia. Nardia did not support growth or survival. A mixed diet of Tricladium, Zygogonium, Nardia and decaying grasses was not sufficient to promote an increase in body weight, and m_i= 21·8 days. This diet represents the commonly available food materials in Mosedale Beck, an acid stream in the upper Duddon catchment. Survival and growth of G. pulex on fungi and leaf diets in media containing low concentrations of potassium ions are also described and discussed briefly in relation to the distribution of G. pulex in the upper catchment of the R. Duddon.