The Effects of Oxygen, Carbon Dioxide and Ethylene on Ethylene Biosynthesis in Relation to Shoot Extension in Seedlings of Rice (Oryza sativa) and Barnyard Grass (Echinochloa oryzoides)

Exposing dark-grown seedlings for 3 d to oxygen deficiency (0or 5 kPa) or to additions of carbon dioxide (10 kPa) or ethylene(0·1 Pa) slowed shoot extension in Echinochloa oryzoides,while in rice it was promoted by these treatments, except that5 kPa oxygen was without effect. In E. oryzoides this was dueto reduced growth of the mesocotyl, and in rice to enhancedgrowth of the coleoptile. These responses to carbon dioxideand oxygen deficiency were not consequences of increased ethyleneproduction, since this remained unchanged by carbon dioxideand depressed by oxygen shortage in both species. Furthermore,exogenous ethylene and the ethylene action inhibitor 2,5-norbornadieneeach failed to influence extension in anoxic seedlings, indicatingno regulatory role for ethylene in the absence of oxygen. However,concentrations of the ethylene precursor 1 -aminocyclopropane-1-carboxylic acid (ACC) were increased by carbon dioxide and0 kPa or 5 kPa oxygen, although after 72 h without oxygen totalACC production (i.e. changes in ethylene + ACC + MACC) was suppressedin both species. There was little effect on bound ACC [putativemalonyl-ACC (MACC)] formation. Transferring anaerobic (0 kPa)seedlings to oxygenated conditions (21 kPa) resulted in abnormallyfast rates of ethylene formation, possibly due to the accumulationof ACC under anoxia. This post-anoxic ethylene may have contributedto the faster extension by rice coleoptiles and slower extensionby mesocotyls of E. oryzoides compared with those of seedlingsmaintained continuously in air. Echinochloa oryzoides [Ard.] Fritsch, barnyard grass, Oryza sativa L, rice, oxygen shortage, carbon dioxide, ethylene biosynthesis, shoot extension, 1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC, GC-MS     

Anatomical Substrates of Behavioral Impairment Induced by Developmental Lead Exposure in Monkeys: Inferences from Brain Lesions

There is a substantial literature exploring the behavioral consequencesof developmental lead exposure in the monkey; deficits havebeen observed on a number of tasks assessing learning and memoryincluding spatial delayed alternation, discrimination reversal,matching to sample, and concurrent discrimination. Differencesin performance between control and lead-exposed monkeys havealso been observed on intermittent schedules of reinforcement.Comparison of the effects of lead with the extensive literatureon the consequences of lesions in discrete areas of brain onthe same tasks may provide insight into the possible sites ofbrain damage responsible for lead-induced behavioral impairment.Available data strongly suggest that prefrontal cortical areasare damaged by lead, based on the pattern of performance deficitsacross specific tasks. In addition, a constellation of globaldeficits including perseveration, increased distractibility,inability to change response strategy, and inability to inhibitinappropriate responding are hallmarks of both prefrontal damageand developmental lead exposure. Evidence also implicates basalforebrain structures in behavior impairment produced by leadbased on the pattern of deficits across numerous tasks, althoughthe evidence is much weaker than for prefrontal cortex. In contrast,the pattern of behavioral impairment produced by limbic systemlesions is different in many respects from that produced bylead; in addition, the scant neuropathological data availablesuggest that limbic structures are not a target of lead evenat high blood lead levels in the monkey. Comparison of the patternof damage following lead exposure with the effects of lesions,presented here, provides direction for further morphologicalor neurochemical exploration of lead-induced brain damage inthe monkey.     

Life stage specific variation in the occupancy of ponds by Litoria aurea,a threatened amphibian

Breeding aggregations are a reproductive strategy to increase mate finding opportunity. However, because aggregations skew the distribution of mature animals through conspecific attraction, rather than resource availability, the distribution of breeding sites may be reduced, so that not all suitable breeding sites are used. To examine the relationship between landscape and reproductive strategies of a threatened frog, Litoria aurea, we studied its distribution at Sydney Olympic Park over two breeding seasons. We aimed to: (i) determine the distribution and predictors of breeding ponds; and (ii) assess the significance of dispersal in the juvenile age‐class. We found that the distribution of the calling males was highly skewed and occurred in large, well‐connected ponds. Despite this, breeding ponds were not aggregated; pond size was the single factor explaining the distribution of breeding ponds. Juvenile frogs dispersed from breeding ponds and were not associated with a specific pond characteristic. Less breeding occurred in the second season during which fewer ponds were used for breeding including many different ponds from the previous year. These changes suggest that breeding effort and breeding pond choice are dynamic and therefore knowledge of the factors that drive breeding events will be a powerful tool in managing species, particularly in light of changing climatic regimes.     

Scaling environmental change through the community-level: a trait-based response-and-effect framework for plants

Predicting ecosystem responses to global change is a major challenge in ecology. A critical step in that challenge is to understand how changing environmental conditions influence processes across levels of ecological organization. While direct scaling from individual to ecosystem dynamics can lead to robust and mechanistic predictions, new approaches are needed to appropriately translate questions through the community level. Species invasion, loss, and turnover all necessitate this scaling through community processes, but predicting how such changes may influence ecosystem function is notoriously difficult. We suggest that community‐level dynamics can be incorporated into scaling predictions using a trait‐based response–effect framework that differentiates the community response to environmental change (predicted by response traits) and the effect of that change on ecosystem processes (predicted by effect traits). We develop a response‐and‐effect functional framework, concentrating on how the relationships among species' response, effect, and abundance can lead to general predictions concerning the magnitude and direction of the influence of environmental change on function. We then detail several key research directions needed to better scale the effects of environmental change through the community level. These include (1) effect and response trait characterization, (2) linkages between response‐and‐effect traits, (3) the importance of species interactions on trait expression, and (4) incorporation of feedbacks across multiple temporal scales. Increasing rates of extinction and invasion that are modifying communities worldwide make such a research agenda imperative.     

Stable isotopes, mesocosms and gut content analysis demonstrate trophic differences in two invasive decapod crustacea

1. Improving our understanding of dietary differences among omnivorous, benthic crustacea can help to define the scope of their trophic influence in benthic food webs. In this study, we examined the trophic ecology of two non‐native decapod crustaceans, the Chinese mitten crab (Eriocheir sinensis) (CMC) and the red swamp crayfish (Procambarus clarkii) (RSC), in the San Francisco Bay ecosystem to describe their food web impacts and explore whether these species are functionally equivalent in their impacts on aquatic benthic communities. 2. We used multiple methods to maximise resolution of the diet of these species, including N and C stable isotope analysis of field data, controlled feeding experiments to estimate isotopic fractionation, mesocosm experiments, and gut content analysis (GCA). 3. In experimental enclosures, both CMC and RSC caused significant declines in terrestrially derived plant detritus (P < 0.01) and algae (P < 0.02) relative to controls, and declines in densities of the caddisfly Gumaga nigricula by >50% relative to controls. 4. Plant material dominated gut contents of both species, but several sediment‐dwelling invertebrate taxa were also found. GCA and mesocosm results indicate that CMC feed predominantly on surface‐dwelling invertebrates, suggesting that trophic impacts of this species could include a shift in invertebrate community composition towards sediment‐dwelling taxa. 5. Stable isotope analysis supported a stronger relationship between CMC and both algae and algal‐associated invertebrates than with allochthonous plant materials, while RSC was more closely aligned with terrestrially derived detritus. 6. The trophic ecology and life histories of these two invasive species translate into important differences in potential impacts on aquatic food webs. Our results suggest that the CMC differs from the RSC in exerting new pressures on autochthonous food sources and shallow‐dwelling invertebrates. The crab's wide‐ranging foraging techniques, use of intertidal habitat, and migration out of freshwater at sexual maturity increases the distribution of the impacts of this important invasive species.     

Seasonal spatial dynamics and causes of nest movement in colonies of the invasive Argentine ant (Linepithema humile)

Abstract.  1. Colony organisation and movement behaviour of the Argentine ant ( Linepithema humile ) was studied over 3 years in field populations in California and in captive colonies in the laboratory. This invasive species is highly polydomous and unicolonial; colonies consist of expansive and fluid networks of nests and trails. The spatial and temporal organisation of colonies may contribute to ecological dominance.
2. Argentine ant nests and inter-nest trails shift in size, abundance, and location, so that colony networks are spatially contracted in the winter and expanded spring to autumn. Colonies occupy permanent sites; ants migrated to and from the same winter nest locations year after year, and occupied 30% of the same nests repeatedly during seasonal migrations.
3. Nests were moved on average 2–3 m. Forty-two per cent were occupied less than 1 month, 4% the entire study, and the other 54% lasted 3.9 ± 2.3 months (mean ± SD).
4. Nests were located within 2–4 m of woody plants, in warm sites in the winter and cool sites in the summer. Both humidity and food availability influenced nest-site choice in laboratory colonies. However, when faced with a trade-off between factors, the ants chose humid nest boxes over nest boxes near food, and ants moved nests only in response to changes in humidity and not distance to food.
5. The results indicate that L. humile colonies are seasonally polydomous, and that nest movements are driven by changes in microclimate. Colony organisation maintains high local density and increases food supply, which may improve the competitive ability of L. humile colonies and reduce opportunities for species coexistence.     

Comparative size,biomass, elemental composition (C,N, H), and energy concentration of caridean shrimp eggs

Summary

In the evolution of decapod crustaceans, interspecific variation in egg size is considered as an important life-history trait that is linked with the duration of embryonic and larval development, the number and type of larval stages, and with juvenile size. Aiming to provide a quantitative characterization of reproductive traits in related decapod taxa differing in lifestyle (freshwater, estuarine, marine) and geographic-climatic distribution (tropical-temperate), we compared size, biomass, and elemental composition of eggs of caridean shrimps from three families: seven species of Palaemonidae (three congeners of Macrobrachium: M. olfersii, M. carcinus, M. acanthurus; four species of Palaemon: P. northropi, P. pandaliformis, P. elegans, P. adspersus), two Atyidae (Potimirim potimirim, Atya scabra), and one Pandalid (Pandalus montagui). Egg size was measured as larger and smaller diameter (D₁ D₂), volume was calculated from D₁ and D₂, and biomass was measured as dry mass (W), carbon (C), nitrogen (N), hydrogen (H), and energy (E, estimated from C) contents. The smallest size and lowest biomass were found in the eggs of two freshwater atyids (both originating from Brazil); the largest size occurred in a marine species, P. montagui (from the North Sea); and intermediate values in freshwater, estuarine, and marine palaemonid species (from Brazil and the Baltic Sea, respectively). Among the Palaemon species, the most limnic (P. pandaliformis) showed a significantly larger egg size and volume (P<0.001) than the estuarine and marine congeners, P. elegans, P. adspersus and P. northropi. This suggests that the generally postulated relationship between egg size and lifestyle (freshwater vs. estuarine or marine) may appear at a generic but not at the family level. On the other hand, individual biomass (in μg or Joules per egg) of early eggs was significantly higher in P. elegans and P. adspersus, indicating interspecific variability in biomass and energy concentration (in μg or Joules per unit volume, mm³). Generally lower biomass concentrations in early eggs of freshwater shrimps may be caused by a higher average water content. Eggs in late embryonic stages were generally larger than earlier eggs of the same species, reflecting an increase in the water content, while an increasing D₁:D₂ quotient indicated an increasingly elongated egg shape. The biomass per egg decreased during embryonic development due to metabolic degradation of organic reserves. As a consequence of inverse ontogenetic changes in size and organic biomass of developing eggs, the mass-specific biomass values (C, N, H in percent of W; E in Joules per mg W) and volume-specific concentrations (μg or Joules per unit volume) decreased. This change was consistently stronger in the C, H, and E contents than in other measures of biomass (W, N). In consequence, the C:N mass ratio also decreased, suggesting that lipid degradation rather than protein utilization was the principal fuel for embryonic development. Our results indicate high intra- (mainly developmental) and interspecific variation in reproductive traits of closely related species. While volume-specific biomass and energy concentrations of early eggs appear to be associated with variation in habitat salinity (freshwater, brackish, marine), individual egg size and biomass may be related more with the climatic-geographic distribution (temperate, tropical) of different taxa.