Resistance to thermal stress in desert Drosophila

1. Four species of Drosophila are endemic to the Sonoran Desert of North America where daily and seasonal high temperatures exceed those experienced by other species in this genus. The close association between these species and their cactus hosts means that they reside only in the desert and raises the question as to whether they are better able to survive heat stress than are non-desert species of Drosophila . The tolerance of adult flies of the four desert species D. mojavensis, D. nigrospiracula, D. pachea and D. mettleri and the cosmopolitan D. simulans to acute heat stress was tested.
2. There was considerable variability among the desert endemic species with respect to survival following heat exposure. Two species, D. mojavensis and D. pachea , were more resistant at 44 °C and 46 °C than the others, with D. mettleri exhibiting similar heat stress resistance to D. simulans .
3. While there was no consistent influence of gender on heat resistance, younger flies (1-day-old) showed significantly greater survival than did older flies (7- or 14-days old).     

Wing morphology and fluctuating asymmetry depend on the host plant in cactophilic Drosophila

As in most insect groups, host plant shifts in cactophilic Drosophila represent environmental challenges as flies must adjust their developmental programme to the presence of different chemical compounds and/or to a microflora that may differ in the diversity and abundance of yeasts and bacteria. In this context, wing morphology provides an excellent opportunity to investigate the factors that may induce changes during development. In this work, we investigated phenotypic plasticity and developmental instability of wing morphology in flies on the cactophilic Drosophila buzzatii and Drosophila koepferae raised on alternative breeding substrates. We detected significant differences in wing size between and within species, and between flies reared on different cactus hosts. However, differences in wing shape between flies emerged from different cactus hosts were not significant either in D. buzzatii or in D. koepferae. Our results also showed that morphological responses involved the entire organ, as variation in size and shape correlated between different portions of the wing. Finally, we studied the effect of the rearing cactus host on developmental instability as measured by the degree of fluctuating asymmetry (FA). Levels of FA in wing size were significantly greater in flies of both species reared in non-preferred when compared with those reared in preferred host cacti. Our results are discussed in the framework of an integrative view aimed at investigating the relevance of host plant shifts in the evolution of the guild of cactophilic Drosophila species that diversified in South America.     

Resource availability and population size in cactophilic Drosophila

1. Four species of Drosophila, Drosophila nigrospiracula ( Patterson & Wheeler 1942 ) , Drosophila mettleri ( Heed 1977 ) , Drosophila pachea ( Patterson & Wheeler 1942 ) , and Drosophila mojavensis ( Patterson & Crow 1940 ) , are endemic to the Sonoran Desert of North America and breed in different species of necrotic columnar cacti. Differences in resource availability have been suggested to explain the interspecific variability in fly population biology, but resource availability for these species has not been quantitatively assessed thoroughly in either spatial or temporal terms. The resource availability was quantified quarterly at three sites for 3 years and population sizes for each Drosophila species were estimated.
2. Spatial and temporal availability of resources differed significantly among species of host cacti, with organpipe cactus ( Stenocereus thurberi ) being the least abundant and senita ( Lophocereus schottii ) the most abundant spatially.
3. Drosophila species differed significantly in population size. The largest population sizes were found for D. nigrospiracula and D. mojavensis and smallest for D. pachea . Populations of D. mettleri were intermediate to these.
4. Population size was greatest for fly species utilizing host species having the largest and longest lasting necroses.
5. Resource availability does not explain the reduction of fly populations in the summer. Necroses were most abundant when flies were absent.     

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

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

Trophic ecology of Squatina guggenheim on the continental shelf off Uruguay and northern Argentina

A total of 1280 (670 females and 610 males) Squatina guggenheim , an angel shark endemic to the south-west Atlantic, was caught during five research cruises (1995, 1997 and 1998) carried out in the Argentine-Uruguayan Common Fishing Zone (AUCFZ) at depths of 3·5–266 m. All angel sharks captured were sexed and measured. Of the 947 examined for stomach contents, 556 (58·7%) contained food and 391 (41·3%) were empty. Numerically, bony fishes were the principal dietary component (89·7%), followed by crustaceans (4·8%) and molluscs (4·4%). The most important prey species were Engraulis anchoita (58·3%), shrimps (4·4%) and Ilex argentinus (2·3%). Male and female diets were not found to differ significantly ( P  > 0·01), however, the diets of different size classes showed significant differences ( P  ≤ 0·01) (group 1, 23–44, group 2, 45–74 and group 3, 75–91 cm L _T). Low rates of cannibalism were observed. The spatial and seasonal variability in the trophodynamics of S. guggenheim is discussed.     

Heat resistance of Cronobacter species (Enterobacter sakazakii) in milk and special feeding formula

Aim:  To determine D - and z -values of Cronobacter species ( Enterobacter sakazakii ) in different reconstituted milk and special feeding formula and the effect of reconstitution of powdered milk and special feeding formula with hot water on the survival of the micro-organism.
Methods and Results:  Five Cronobacter species (four C. sakazakii isolates and C. muytjensii ) were heated in reconstituted milk or feeding formula pre-equilibrated at 52–58°C for various times or mixed with powdered milk or feeding formula prior to reconstitution with water at 60–100°C. The D -values of Cronobacter at 52–58°C were significantly higher in whole milk (22·10–0·68 min) than in low fat (15·87–0·62 min) or skim milk (15·30–0·51 min) and significantly higher in lactose-free formula (19·57–0·66 min) than in soy protein formula (17·22–0·63 min). The z -values of Cronobacter in reconstituted milk or feeding formula ranged from 4·01°C to 4·39°C. Water heated to ≥70°C and added to powdered milk and formula resulted in a > 4 log₁₀ reduction of Cronobacter .
Conclusions:  The heat resistance of Cronobacter should not allow the survival of the pathogen during normal pasteurization treatment. The use of hot water (≥70°C) during reconstitution appears to be an effective means to reduce the risk of Cronobacter in these products.
Significance and Impact of the Study:  This study supports existing data available to regulatory agencies and milk producers that recommended heat treatments are sufficient to substantially reduce risk from Cronobacter which may be present in these products.     

Detection of infectious rotavirus in naturally contaminated source waters for drinking water production

Aims:  To assess chlorine susceptibility of Legionella pneumophila grown from two amoebic hosts, Acanthamoeba castellanii and Hartmannella vermiformis .
Methods and Results:  After being released from amoebae, Leg. pneumophila were chlorinated at 2 and 5 mg l⁻¹ for 5 min–24 h. Bacterial culturability and cytoplasmic membrane deterioration were quantified by culture assay on BCYEα agar and BacLight stains coupled with a fluorescent microscope, respectively. Chlorination reduced the culturability of Leg. pneumophila by 2·93–4·59 log CFU ml⁻¹ and damaged cellular membrane by 53·8–99·2%. Moreover, cells released from H. vermiformis exhibited significantly lower degrees in culturability reduction ( P  = 0·0008) and membrane deterioration ( P  < 0·0001) when compared with those from A. castellanii . The amoebic genus is the most significant parameter affecting cytoplasmic membrane integrity of chlorinated Legionella ( P  < 0·0001), followed by free chlorine concentration ( P  = 0·042).
Conclusions:  Legionella pneumophila replicated from H. vermiformis possess greater chlorine resistance than the cells from A. castellanii .
Significance and Impact of the Study:  This study shows the heterogeneity of amoebae-grown Leg. pneumophila in chlorine susceptibility, which should be considered in the control of legionellae proliferation, particularly in the systems where H. vermiformis is dominant, e.g. hot water plumbing.     

The vectoring of cactophilic yeasts by Drosophila

Summary At two locations in the Sonoran Desert, yeasts were sampled from species of Drosophila, the flies' cactus hosts, and other neighboring sources of cactophilic yeasts to determine the relation between the yeasts vectored by the fly and the yeasts found in their breeding sites. D. mojavensis, D. nigrospiracula, and D. mettleri vectored yeast assemblages significantly more similar to the yeast species found on the rot from which the flies were collected than to the yeasts found on other rots from the flies host cactus or other rotting cactus at the same site. Rots with Drosophila had fewer yeast species than those without flies, suggesting that flies were associated with younger rots. Rots with flies and the Drosophila also had more yeast species with the capability to produce ethyl acetate than rots without flies. The results support the contention that cactophilic Drosophila feed on a subset of the yeasts available in an area, and may act to maintain differences among the yeast communities found on different species of cactus.     

Nitrogen and phosphorus content of some temperate and tropical freshwater fishes

The nitrogen and phosphorus content of two temperate fishes, Rutilus rutilus and Perca fluviatilis , and six tropical fishes, Oreochromis niloticus , Cichla monoculus , Serrassalmus rhombeus , Plagioscion squamosissimus , Prochilodus brevis and Hoplias malabaricus , were investigated to test the hypothesis that variation in body P content and N:P ratio is related to body size. Regressions of %P and N:P ratios against fish size (length and mass) confirmed the hypothesis for P. fluviatilis and P. squamosissimus , suggesting that body size is an important factor driving body P content and N:P ratios in some fishes. Moreover, significant increases in %N and N:P ratio with body size was found for H. malabaricus , a common piscivorous fish of the Neotropics. Interspecific variation in %P and N:P ranged two-fold and significant differences ( P < 0·05) were found among the tested species. The mean ± s . d . elemental content across all fishes ( n = 170) was 10·35 ± 1·29% for N and 3·05 ± 0·82% for P, while the N:P ratio was 8·00 ± 2·14. Data on fish body nutrient content and ratio will improve parameterization of bioenergetics and mass balance models and help clarify the role of fishes in nutrient cycles in both temperate and tropical freshwaters.     

Insect invasion sequences: systematic or stochastic?

Abstract. 1. This study examined the invasion sequence of Drosophila species arriving at decomposing strawberries.
2. It was found that the age of fruit affected the likelihood of Drosophila arrival, flies preferring relatively fresh fruit. However, there were no repeatable trends in invasion sequence of Drosophila species, different species responding in a similar manner to changes in fruit age.
3. Although no systematic trends in invasion sequence were observed, species tended to be temporally separated due to stochastic differences in their arrival at the fruit.
4. It is suggested that stochastic, as well as repeatable, temporal separation of species can have an important influence on subsequent community development.     

Effects of simulated N deposition on understorey vegetation of a boreal coniferous forest

1. We report the short-term effects of simulated nitrogen (N) deposition on the understorey of a boreal forest in northern Sweden. Doses of ¹⁵N double-labelled NH₄NO₃ (0·5, 12·5, 25·0 and 50·0 kg N ha^–1) were applied to 1 m² plots in the summer of 1995 and plants were harvested the following autumn.
2. No significant treatment effects were found in either above- or below-ground biomass which was distributed as follows: the ericaceous shrub Vaccinium myrtillus contributed 76%, the grass Deschampsia flexuosa 4%, and the bryophytes Dicranum majus and Pleurozium schreberi 20%.
3. The recovery of applied N in these species was 24, 27, 27 and 32% of the 0·5, 12·5, 25·0 and 50·0 kg N ha^–1 applications, respectively, and thus the recovery increased with the N dose.
4. In the 0·5 kg N ha^–1 treated plots, the highest concentrations of fertilizer-derived ¹⁵N were found in the bryophytes, while in plots given the three higher N applications, leaves of D . flexuosa had the highest concentrations.
5. N application resulted in elevated concentrations of free amino acid N, which indicate increased storage of N in plant tissues. Furthermore, the N application resulted in increased damage to V . myrtillus by natural enemies. The severity of disease caused by two foliar parasitic fungi showed a clear numerical response to N treatment, as did the amount of herbivory as a result of Lepidoptera larvae.     

Survival and growth of Cronobacter species (Enterobacter sakazakii) in wheat-based infant follow-on formulas

Aims:  To determine the survival and growth characteristics of Cronobacter species ( Enterobacter sakazakii ) in infant wheat-based formulas reconstituted with water, milk, grape juice or apple juice during storage.
Methods and Results:  Infant wheat-based formulas were reconstituted with water, ultra high temperature milk, pasteurized grape or apple juices. The reconstituted formulas were inoculated with Cronobacter sakazakii and Cronobacter muytjensii and stored at 4, 25 or 37°C for up to 24 h. At 25 and 37°C, Cronobacter grew more (>5 log₁₀) in formulas reconstituted with water or milk than those prepared with grape or apple juices ( c. 2–3 log₁₀). The organism persisted, but did not grow in any formulas stored at 4°C. Formulas reconstituted with water and milk decreased from pH 6·0 to 4·8–5·0 after 24 h, whereas the pH of the formulas reconstituted with fruit juices remained at their initial pH values, c. pH 4·8–5·0.
Conclusions:  Cronobacter sakazakii and C. muytjensii can grow in reconstituted wheat-based formulas. If not immediately consumed, these formulas should be stored at refrigeration temperatures to reduce the risk of infant infection.
Significance and Impact of the Study:  The results of this study will be of use to regulatory agencies and infant formula producers to recommend storage conditions that reduce the growth of Cronobacter in infant wheat-based formulas.     

The value of three cereal aphid species as food for a generalist predator

The value of the cereal aphid species Metopolophium dirhodum (Wlk.), Sitobion avenae (F.) and Rhopalosiphum padi (L.) as prey for the linyphiid spider Erigone atra (Bl.) was assessed. Fecundity of females was determined for spiders fed on eight experimental diets: three single‐species aphid diets, a mixed diet of all three aphid species, three mixed diets with each aphid species in combination with fruit flies Drosophila melanogaster (Meig.), and pure D. melanogaster as a high quality comparison diet. The development and survival of first‐instar juveniles fed on three diets of single aphid species, and on a diet of Collembola were compared with those subjected to starvation. Prey value for adult females was assessed by egg production, hatching success and offspring size. In pure diets all three aphid species were of low value to the spiders, causing a rapid decline in egg production and supporting no growth of significance of first‐instar juveniles. No difference in value of aphid species of single‐species aphid diets was found in the fecundity experiment, while a ranking of aphid species of M. dirhodum > R. padi > S. avenae was revealed in the survivorship experiment. A mixed‐aphid diet was not found to be advantageous compared with single‐species aphid diets, and no advantage of including aphids in mixed diets with fruit flies was found. Metopolophium dirhodum and R. padi were neutral in mixed diets, while a diet of S. avenae and fruit flies caused reduced egg production compared with the pure diet of fruit flies, revealing a toxic effect of S. avenae on the spider. The value‐ranking of aphid species in mixed diets was similar to that of single‐species diets. A similar ranking of aphid species was found for different fitness parameters (fecundity of adult females and development of juveniles). A ranking of aphids by offspring size of mothers on aphid‐only diets was S. avenae > M. dirhodum > R. padi. All aphid‐fruit fly diets resulted in larger offspring than a diet of only D. melanogaster, with the overall largest offspring being produced on the diet of M. dirhodum and fruit flies.     

Essential fatty acid content and the phosphorus to carbon ratio in cultured algae as indicators of food quality for Daphnia

1. A series of experiments examined growth of Daphnia magna on three algal diets ( Rhodomonas minuta , Scenedesmus acutus and Synechococcus sp.) at varying physiological states [nitrogen and phosphorus (P) limitations] to test whether variation in algal fatty acid and/or elemental composition can predict Daphnia growth.
2. These algae differed widely in their essential fatty acid (EFA) composition while phosphorus (P) or nitrogen limitation had only a small influence on their ω3-polyunsaturated fatty acid (PUFA) content.
3. Individually, algal ω3-PUFA content explained 69% of the variation in the normalised growth of D. magna, while algal phosphorus content explained 11% of the variation. Quantitative models for D. magna growth used both algal ω3-PUFA content and algal C : P ratio as food quality indices. Together, algal ω3-PUFA content and C : P ratio explained 70% of the variation in the normalised growth rate of D. magna .
4. Our results indicate that EFA influenced algal food quality much more strongly than P. The EFA and mineral P impacts appear to be independent.     

Effects of aggregation pheromone on individual behaviour and food web interactions: a field study on Drosophila

Abstract.  1. The effects of an aggregation pheromone on individual behaviour and food web interactions were investigated in two ecological communities, using Drosophila melanogaster and D. simulans as focal species.
2. Fruit substrates with aggregation pheromone were significantly more attractive to adult D. melanogaster and D. simulans than control fruit substrates, and the response was positively dose dependent. Competing species and natural enemies were also significantly attracted to substrates with the aggregation pheromone of D. melanogaster and D. simulans .
3. Significantly more eggs were deposited on pheromone-treated fruits than on control fruits, and the microdistribution of eggs within fruits was correlated to the microdistribution of the pheromone. The aggregation pheromone induced more females to share the breeding site.
4. The extremely high densities of fruit flies in the large aggregations appeared to reduce the oviposition rate of females. Physical interactions with conspecific and heterospecifics were frequently observed in the aggregations, and often led to patch leaving of the fruit flies.
5. Competition for food among larvae occurred at high densities and parasitism was density dependent. Aggregation pheromones can be directly responsible for these patterns through their effects on the con- and heterospecific behaviour.
6. The combined results show that aggregation pheromones affect a multitude of aspects in the ecology of interacting animals. The importance of incorporating the communication signals in ecological theory of aggregations is discussed.     

Mortality during dispersal and the cost of host-specificity in parasites: how many aphids find hosts?

1. For a full assessment of explanations for the evolution of host-specificity it is necessary to estimate the probability that a dispersing parasite finds a host. We develop a method of estimating this success rate from samples of dispersing parasites and populations resident on hosts.
2. Applying this method to data on the bird cherry-oat aphid, Rhopalosiphum padi (L.), from southern Scotland in 1984–92, we estimate that 0·6% of the autumn migrants find hosts.
3. With such a low success rate, there should be selection for a broadening of host range, to include any host on which the colonist's fitness is more than about 0·6% of that on the normal hosts. We argue that neither nutrition nor the need for 'enemy-free space' are sufficient explanations of the host-specificity of this animal, and propose instead that it is the host's role as a rendezvous for mating that constrains the migrants to their costly host-specificity.
4. We also discuss the implications of this low success rate for the hypothesis that aphids speciate sympatrically through the formation of host races.     

Seed size and shape are not related to persistence in soil in Australia in the same way as in Britain

1. Previous studies have shown that among British species, seeds that persist in the soil tend to be small and compact compared with non-persistent seeds. We tested whether or not this pattern is repeated among 101 Australian species, from a range of habitats.
2. Seed mass was plotted against variance of seed dimensions, across all species. Species with persistent seeds were found across the whole range of seed mass (0·217–648·9 mg) and variance (0·0000–0·2497), providing no evidence for a critical mass or variance which separated persistent from transient seeds.
3. We tested whether or not divergence within individual clades between persistent and transient seeds was associated with increased seed mass or seed dimension variance, using phylogenetically independent contrasts (PICs). There was no consistent tendency found.
4. Thus for Australian species, persistent seeds were not smaller or more compact than transient seeds when compared across all species or when compared using PICs. Presumably the natural history of burial and disturbance operates differently in British and Australian habitats.     

Modelling the growth of Weissella cibaria as a function of fermentation conditions

Aims:  To investigate the effect of pH, water activity ( a _w) and temperature on the growth of Weissella cibaria DBPZ1006, a lactic acid bacterium isolated from sourdoughs.
Methods and Results:  The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (4·0–8·0), a _w (0·935–0·994) and temperature (10–45°C) in a rich medium. The growth curve parameters (lag time, growth rate and asymptote) were estimated using the dynamic model of Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int J Food Microbiol 23, 277–294). The effect of pH, a _w and temperature on maximum specific growth rate (μ_max) were estimated by fitting a cardinal model. μ_max under optimal conditions (pH = 6·6, a _w = 0·994, T  = 36·3°C) was estimated to be 0·93 h⁻¹. Minimum and maximum estimated pH and temperature for growth were 3·6 and 8·15, and 9·0°C and 47·8°C, respectively, while minimum a _w was 0·918 (equivalent to 12·2% w/v NaCl).
Conclusions:  Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread.
Significance and Impact of the Study:  This is the first study reporting the modelling of the growth of W. cibaria , a species that is increasingly being used as a starter in sourdough and vegetable fermentations.     

Natural hybridization between endangered and introduced species of Pseudorasbora, with their genetic relationships and characteristics inferred from allozyme analyses

From 25 populations of Pseudorasbora in Japan, polymorphism at 22 allozyme loci indicated that the level of genetic differentiation between Pseudorasbora parva and Pseudorasbora pumila ( D  = 0·421–0·517) was greater than that between the two subspecies of P. pumila , P. pumila pumila and P. pumila subsp. ( D  = 0·164), consistent with morphological differences. While P. parva displayed genetic variation ( H  = 0·003–0·100) similar to other freshwater fishes, P. pumila pumila and P. pumila subsp. populations showed no genetic variation. In five of the 15 populations collected from the contact zone between P. parva and P. pumila pumila , hybrids were detected by allozyme analyses. All hybrids were presumed to represent the F₁ generation, because they were heterozygous at all 12 loci diagnostic between P. parva and P. pumila pumila . Although four populations were characterized by high frequencies of F₁ hybrids ( c . 40%), only one of the parental species was observed in each case. The results indicated that the two species have hybridized easily under natural conditions, but cannot coexist in the long-term. It is suggested that continued invasion of P. parva would hasten the extinction of P. pumila pumila .