Degradation of chemical alarm cues under natural conditions: risk assessment by larval woodfrogs

Summary. Many aquatic species use chemosensory information to assess predation risk. The cues used in such risk assessment can come either from the predator (predator odour) or from injured prey (alarm cues). The information conveyed through chemicals may, however, be inaccurate both spatially and temporally, as chemicals may persist in the environment long after the predator is gone. Thus, the level of accuracy of the cues for risk assessment may depend on the persistency of the chemicals in the habitat. Here, we investigated the persistency of alarm cues of a larval amphibian, the woodfrog (Rana sylvatica) in a ephemeral pond, their natural habitat. We introduced either alarm cues or control water in enclosed sleeves (~10 L) installed in the pond. The sleeve water was then sampled after 5 min and every two hours for eight hours. We used the behavioural response of woodfrog tadpoles to alarm cues as a bioassay to assess how long the alarm cues persisted in the environment. We found that tadpoles responded with an antipredator response to the pond water containing alarm cues 5 min after the injection of the cues in the sleeves but did not respond to that same pond water after two hours. Our results indicate that biodegradation and/or photodegradation of alarm cues in natural habitats might occur relatively quickly as the loss of a response to the cues in our experiment was independent of a dilution effect. This contrasts with previous laboratory results indicating that chemicals may be active after several hours.     

Atmospheric heavy metals in tropical South America during the past 22,000 years recorded in a high altitude ice core from Sajama, Bolivia

V, Co, Cu, Zn, As, Rb, Sr, Ag, Cd, Ba, Pb, Bi and U have been analysed by inductively coupled plasma sector field mass spectrometry in various sections of a dated snow/ice core drilled at an altitude of 6542 m on the Sajama ice cap in Bolivia. The analysed sections were dated from the Last Glacial Stage ( approximately 22,000 years ago), the Mid-Holocene and the last centuries. The observed variations of crustal enrichment factors (EFc) for the various metals show contrasting situations. For V, Co, Rb, Sr and U, EFc values close to unity are observed for all sections, then showing that these elements are mainly derived from rock and soil dust. For the other metals, clear time trends are observed, with a pronounced increase of EFc values during the 19th and 20th centuries. This increase shows evidence of metal pollution associated with human activity in South America. For Pb an important contribution was from gasoline additives. For metals such as Cu, Zn, Ag and Cd an important contribution was from metal production activities, with a continuous increase of production during the 20th century in countries such as Peru, Chile and Bolivia.     

Reproduction and growth of Euterpina acutifrons (Copepoda: Harpacticoida) under experimental conditions

Individual specimens of Euterpina acutifrons (Copepoda: Harpacticoida) taken from the mass cultures of the C.N.E.N.-EURATOM Laboratory at Fiascherino, Italy, were reared in new culture media prepared with suspensions of several species of algae in filtered and sterilized sea water. All the experiments were carried out at a temperature of 18°C±1 C°. The influence of food concentrations on adult life-span and reproductive activity of E. acutifrons was analyzed. A good correlation was found between concentration of algal suspension and egg production. Maximum life-span was observed at intermediate values of food concentration. Other experiments were carried out to determine egg fertility and duration of the various embryonic and postembryonic development stages. Embryonic development time was calculated as approximately 2 days; the adult females appeared 10 to 12 days after hatching of Nauplius I. Production of nauplii by 6 females reared under conditions of excess food supply was also studied. These conditions were achieved by supplying high concentrations of a mixture of 4 different algal species and by completely renewing the culture medium at frequent intervals. Under these conditions, each female laid an average of 12.5 sacs and produced an average of 294.3 nauplii. An average production of 355.5 eggs per female was estimated. An analysis was made of growth in size and weight of the females: the average daily egg production in terms of dry weight corresponded to about 32% of the biomass of the adult female. Birch's (1948) method was used to calculate net reproduction rate (R _o=70.89), intrinsic rate of increase (r _m=0.161) and mean generation time (T=26.5 days).This study was performed at: Laboratorio per lo Studio della Contaminazione Radioattiva del Mare, C.N.E.N.-EURATOM, Fiascherino, I-19030 La Spezia, Italy.     

Pesticide vapours in confined atmospheres. Determination of dichlorvos by SPME-GC-MS at the microg m(-3) level

A method based on SPME is described for assessing the gaseous dichlorvos concentration in confined atmospheres like a greenhouse after a pesticide application. Sampling was made by using SPME with PDMS fibres immersed into a 250 mL sampling flask into which air samples were dynamically pumped from the analysed atmosphere. Sampling duration was 40 min and samples were then analysed by GC-MS. Calibration was performed from a vapour saturated air sample and gas phase diluted samples, and this procedure afforded a curve with a regression coefficient (R2) higher than 0.98. The repeatability of these measurements was observed with an RSD of 2.5%. This analysis procedure was then applied for the determination of gaseous dichlorvos concentrations versus time, in the atmosphere of an experimental 8 m2 and 20 m3 greenhouse. The pesticide was sprayed according to real cultivation conditions and measurements were made from 2 up to 74 h after application affording observed concentrations in the range of decades and hundreds of microg m(-3) (corresponding limits of detection and quantification were found at the level of a few microg m(-3)).     

Retention of acquired predator recognition among shy versus bold juvenile rainbow trout

The ability to acquire information about predators allows prey to better balance threat-sensitive tradeoffs by responding only to ecologically relevant predation threats. However, predation risk is highly variable through time and responding to predators that no longer represent a threat would likely prove costly to prey. While a wealth of studies have examined the way in which prey learn, little attention has been paid to retention of acquired information. Recent studies suggest that retention is indeed plastic and shaped by a suite of intrinsic factors such as strength of initial conditioning and individual growth rate. Here, we investigated if the duration of retention of acquired information is influenced by individual behavioral tactics (i.e., ‘personality’). We recorded latency to escape an opaque acclimation chamber of juvenile rainbow trout (Oncorhynchus mykiss) as a measure of behavioral tactic. We then immediately conditioned individual trout to recognize pumpkinseed (Lepomis gibbosus) and tested for recognition 24 h or 8 days postconditioning. Our results demonstrate that while shy versus bold trout exhibited no difference in the strength of conditioned response to pumpkinseed odor during conditioning trials or when tested for recognition 24 h postconditioning, there was a significant effect of individual behavioral tactic on the retention of learned predator recognition. While shy trout continued to exhibit a learned response to pumpkinseed odor when tested 8 days postconditioning, bold trout were not different from our pseudoconditioned controls. These data suggest that the behavioral tactic employed at the time of conditioning influences the ‘memory window’ of acquired information.     

The effect of acute hypoxia on swimming stamina at optimal swimming speed in flathead grey mullet <Emphasis Type="Italic">Mugil cephalus</Emphasis>

Flathead grey mullets Mugil cephalus are commonly found in Mediterranean lagoons, which are regularly subject to high environmental variations. Oxygen is one of the factors that shows extremely high variation. The objective of this study was to test the effects of acute hypoxia exposure at two experimental temperatures (i.e. 20 and 30°C) on the stamina (time to fatigue) in M. cephalus swimming at the minimal cost of transport (i.e. optimal swimming speed; U _opt). At each temperature, a relationship was established between swimming speed and oxygen consumption (MO₂). This allowed estimation of U _opt at 45 cm s⁻¹ (~1.12 Body Length s⁻¹). Independent of temperature, stamina at U _opt was significantly reduced in severe hypoxia, i.e. at 15% of air saturation (AS). In these conditions, oxygen supply appears therefore to be insufficient to maintain swimming, even at the low speed tested here. After the stamina test, MO₂ measured in fish tested at 15% AS was significantly higher than that measured after the test in normoxia. Therefore, we suggest that in hypoxia, fish used anaerobic metabolism to supplement swimming at U _opt, leading to an oxygen debt. Since flathead grey mullet is a hypoxia-tolerant species, it is possible that hypoxic conditions less severe than those tested here may reduce stamina at low speed in less tolerant species. In addition, we suggest that testing stamina at these speeds may be relevant in order to understand the effect of hypoxia on behavioural activities carried out at low speed, such as food searching.     

An Upper Limit Analysis of Carbon Monoxide Monitoring in the United States

In performing carbon monoxide (CO) studies, the question is invariably raised as to whether available monitoring data are truly representative of the highest ambient 8-hr average CO levels experienced in major cities. The most practical means for such a determinate is to inventory the critical characteristics of monitor siting. The authors catalogued such data for the worst station in eight of the 12 counties measuring the highest number of CO violations in the nation.     

Evaluation of surface water quality in aquatic bodies under the influence of uranium mining (MG, Brazil)

The quality of the water in a uranium-ore-mining area located in Caldas (Minas Gerais State, Brazil) and in a reservoir (Antas reservoir) that receives the neutralized acid solution leaching from the waste heaps generated by uranium mining was investigated. The samples were collected during four periods (October 2008, January, April and July 2009) from six sampling stations. Physical and chemical analyses were performed on the water samples, and the data obtained were compared with those of the Brazilian Environmental Standards and WHO standard. The water samples obtained from waste rock piles showed high uranium concentrations (5.62 mg L^?1), high manganese values (75 mg L^?1) and low average pH values (3.4). The evaluation of the water quality at the point considered the limit between the Ore Treatment Unit of the Brazilian Nuclear Industries and the environment (Consulta Creek) indicated contamination by fluoride, manganese, uranium and zinc. The Antas reservoir showed seasonal variations in water quality, with mean concentrations for fluoride (0.50 mg L^?1), sulfate (16 mg L^?1) and hardness (20 mg L^?1) which were low in January, evidencing the effect of rainwater flowing into the system. The concentrations for fluoride, sulfate and manganese were close or above to the limits established by current legislation at the point where the treated mining effluent was discharged and downstream from this point. This study demonstrated that the effluent discharged by the UTM affected the quality of the water in the Antas reservoir, and thus the treatments currently used for effluent need to be reviewed.