Do kin always make better neighbours?: The effects of territory quality

Summary The effects of territory quality on kin-biased territorial defence behaviour and fitness of juvenile rainbow trout (Oncorhynchus mykiss) were examined by manipulating food and predation risk levels in an artificial stream channel. Groups of related (full sibling) or unrelated fry were observed in the channel under one of four treatments: (1) high food-low predator (high territory quality); (2) high food-high predator; (3) low food-low predator; and (4) low food-high predator (low territory quality). Fish within kin groups always initiated fewer aggressive interactions, defended smaller territories, exhibited higher proportions of threat type territorial defence behaviours (as opposed to overtly aggressive behaviours) and had a higher mean weight increase than non-kin groups. Within both kin and non-kin groups, decreasing territory quality significantly increased the frequency of aggressive interactions, the size of territories and decreased growth. It is argued that while kin-biased territorial defence behaviours are always present, decreased availability of resources and increased predation risk serve to reduce the magnitude of this kin bias. However, even in low-quality territories, the benefit of associating with kin may increase the probability of overwintering survival (increased fitness) of the young fish by increasing body size.     

In utero development of a mediastinal teratoma: A second-trimester event

Mediastinal teratomas have rarely been discovered during the prenatal period. When seen during the neonatal period, these tumours have caused respiratory distress or hydrops fetalis. We present the sonographic and pathological findings of a rapidly developing anterior mediastinal teratoma causing hydrops fetalis and in utero demise at 27 weeks' gestation.     

Cellulose biogenesis in bacteria and higher plants is disrupted by magnetic fields

This work was supported by a grant from Johnson &; Johnson to RMB. We 5 thank Dr. M. Schülein, Novo A/S, Bagsvaerd, Denmark for providing CBH.     

Toxicological and biochemical responses of the earthworm Lumbricus rubellus to pyrene, a non-carcinogenic polycyclic aromatic hydrocarbon

The effects of the polycyclic aromatic hydrocarbon (PAH) pyrene on earthworms were investigated in contact and soil tests. In addition to measuring toxic effects on survival and reproduction, Ethoxyresorufin-o-deethylase (EROD) activity and catalase activity were also studied as possible biomarkers of toxic stress. The survival data indicated that LC₅₀ values were 0.0068 mg/ml for the contact test, and 283 mg/kg in the soil test. Cocoon production rate was significantly reduced compared to controls at 160, 640 and 2560 mg/kg in the soil test. No EROD activity could be detected in preliminary studies using control and exposed animals from the contact test, so this assay was not used to the soil test. Catalase activity was shown to be significantly lower at 640 mg/kg in the soil test compared to all other treatments and the control. When compared to toxicological data for other soil invertebrates, Lumbricus rubellus has an intermediate sensitivity in respects of survival and a lower sensitivity for reproductive effects, although the soil used in this study had a higher organic content than previous studies, meaning that the sensitivity of this species may be underestimated in comparison to previous published data for other soil invertebrates.     

Element content in tissues of four rodent species sampled in the Geysers geothermal steamfield

Liver and kidney tissue samples from four rodent species collected in the Geysers geothermal steamfield of northern California were analyzed for content of 28 elements. Element concentrations in samples from the developed region of the Geysers were compared with samples from undeveloped reference regions to determine the influence of geothermal power development on element content in small mammal tissues. Eight elements (B, Ca, Cu, Mg, Mn, P, Sr, Ti) were enriched in samples from the Geysers, 12 (Ag, Al, Co, Cr, Fe, K, Mo, Na, Ni, Pb, Si, Zn) were decreased within the Geysers, Ba and Li were inconclusive, and six (As, Be, Cd, Hg, Sn, V) were below the minimum analytical limits. The longest-lived species (Neotoma fuscipes) had the greatest occurrence of statistically significant differences in element content. Sites in grassland habitat produced more significant differences in element content than either chaparral or streamside habitats for samples from Peromyscus maniculatus. Peromyscus boylii and P. truei provided additional data, but no distinct advantages for element monitoring. The data indicate regional influences from geothermal power development on element levels in rodent tissues.     

Phthalates and the aquatic environment: Part II The bioconcentration and depuration of di-2-ethylhexyl phthalate (DEHP) and di-isodecyl phthalate (DIDP) in mussels (Mytilus edulis)

Mussels ($\text{Mytilus edulis}$) were exposed to di-2-ethylhexyl phthalate (DEHP) and to di-isodecyl phthalate (DIDP) over a period of 28 days. The bioconcentration factor (BCF) as measured by ¹⁴C analysis, reached estimated plateau levels corresponding to mean BCF values of approximately 2500 and 3500 for the DEHP and DIDP respectively. The mussels were then held in clean seawater for a further 14 days and ¹⁴C analysis showed a depuration half-life of approximately 3.5 days for both phthalates. During the whole 42 days of the experiment general observations on the health of the animals showed no evidence of any adverse effects.     

A simple method for estimating dermal absorption of chemicals in water

A semiempirical mathematical model is proposed for estimating the dermal absorption of chemicals from dilute aqueous solutions, such as bath water. Absorption depends on the concentration of the chemical in water, the area of skin exposed, the time of exposure, and a permeation coefficient that depends importantly on the relative solubility of the material in lipids and water, among other factors not so easily modeled.     

A note on environmental risk and the rate of discount

This paper examines the use of risk-adjusted discount rates to evaluate future environmental risks. It is determined that the risk-adjusted discount rate should be lower—not higher—than the risk-free rate if evaluation of future environmental risks is to point toward optimality.     

The Inefficiency of Decentralized Non-renewable Resource Extraction: The Case of Soviet Timber

This paper argues that the structure of the government in the former Soviet Union and the present Russia has led to inefficiency in harvesting non-renewable resources such as timber. It analyzes the dynamic optimization problems of the central and local authorities in choosing the path of harvesting and explains the sources and effects of inefficiency. The features of the model are compared with a hypothetical one in which the inefficiency has been removed. This hypothetical model is then applied to suggest some policies for reducing the existing inefficiency.     

The dynamic nature of antipredator behavior: prey fish integrate threat-sensitive antipredator responses within background levels of predation risk

Prey animals often have to face a dynamic tradeoff between the costs of antipredator behavior and the benefits of other fitness-related activities such as foraging and reproduction. According to the threat-sensitive predator avoidance hypothesis, prey animals should match the intensity of their antipredator behavior to the degree of immediate threat posed by the predator. Moreover, longer-term temporal variability in predation risk (over days to weeks) can shape the intensity of antipredator behavior. According to the risk allocation hypothesis, changing the background level of risk for several days is often enough to change the response intensity of the prey to a given stimulus. As the background level of risk increases, the response intensity of the prey decreases. In this study, we tested for possible interactions between immediate threat-sensitive responses to varying levels of current perceived risk and temporal variability in background risk experienced over the past 3 days. Juvenile convict cichlids were preexposed to either low or high frequencies of predation risk (using conspecific chemical alarm cues) for 3 days and were then tested for a response to one of five concentrations (100, 50, 25, 12.5%, or a distilled water control). According to the threat-sensitive predator avoidance hypothesis, we found greater intensity responses to greater concentrations of alarm cues. Moreover, in accordance with the risk allocation hypothesis, we found that cichlids previously exposed to the high background level of risk exhibited a lower overall intensity response to each alarm cue concentration than those exposed to the low background level of risk. It is interesting to note that we found that the background level of risk over the past 3 days influenced the threshold level of response to varying concentrations of alarm cues. Indeed, the minimum stimulus concentration that evoked a behavioral response was lower for fish exposed to high background levels of predation than those exposed to low background levels of predation. These results illustrate a remarkable interplay between immediate (current) risk and background risk in shaping the intensity of antipredator responses.