The reproductive cycle and physiological ecology of the mussel Mytilus edulis in a subarctic,non-estuarine environment

Mytilus edulis L. occupies a habitat in eastern Newfoundland, Canada, which is characterised by low temperatures and a lower concentration of particles in suspension than is found in estuarine locations. Gametogenesis occurs in the spring, and energy reserves from the previous year are not utilised in the synthesis of gametes. Oxygen uptake is not elevated during the winter, in contrast to most European populations, which undergo gamete development at that time. There is little seasonal variation in clearance rate. This may be attributable in part to the absence of the high particulate load which has been shown to depress feeding activity in some estuarine populations. Energy balance is positive at all times of the year, and conversion efficiency is high, suggesting that conditions are favourable. A number of physiological comparisons are made between Newfoundland mussels and those from European waters.     

Effect of food location and quality on recruitment sounds and success in two stingless bees,<Emphasis Type="Italic"> Melipona mandacaia</Emphasis> and<Emphasis Type="Italic"> Melipona bicolor</Emphasis>

It is unclear whether stingless bees in the genus Melipona (Hymenoptera, Apidae, Meliponini) can reliably encode the distance to a food source through recruitment sounds produced inside the nest, in part because the sound features correlated with distance also vary with food quality. We therefore trained marked foragers of two species, Melipona mandacaia and M. bicolor, to feeders at different distances and to different sucrose concentrations at the same distance. In both species, foragers successfully recruited to a rich 2.5-m food source and produced pulsed recruitment sounds in which pulse duration was significantly and positively correlated with distance to the rich food source. When returning from poorer food sources (0.6–1.5 m), foragers of both species decreased sound production, producing shorter sound pulses and longer sound interpulses than they did for 2.5 m food located at the same distance. Thus the temporal structure of M. mandacaia and M. bicolor recruitment sounds varies with distance and food quality. However, nestmates were not recruited by performances for poorer food sources (0.6–1.5 m), whose sucrose concentration was sufficiently low to affect recruitment sounds. Surprisingly, the interphase (the time between behavioral phases that communicate location) also increases with decreasing food quality in the closely related honeybees (Apis), suggesting a potential homology in the effect of food quality on the recruitment systems of Apis and Melipona. We explore the evolutionary implications of these similarities.Communicated by M. Giurfa     

A framework for predicting personal exposures to environmental hazards

This paper presents a general framework for constructing a predictive distribution of the exposure to an environmental hazard sustained by a randomly selected member of a designated population. The individual’s exposure is assumed to arise from random movement through the environment, resulting in a distribution of exposure that can be used for environmental risk analysis. A specialization of the general framework is that of predicting human exposure to air pollution that can be used to develop models for such things as exposure to particulate matter; practical aspects of their construction are considered. These models can help answer questions such as what fraction of the population sustained ‘high’ levels of exposure for say 5 days in a row. The immediate implementation of the above framework takes the form of a computing platform referred to as pCNEM. This provides a facility for simulating exposures to airborne pollutants and is described in detail elsewhere. This paper considers some theoretical aspects underpinning probabilistic exposure models of this type, with the ideas illustrated in developing a model for predicting human exposure to PM ₁₀.     

A first record of daytime surface swarming by Euphausia lucens in the Southern Benguela region

On 9 October, 1985 a daytime surface swarm of the euphausiid Euphausia lucens was observed and sampled in St. Helena Bay in the Southern Benguela region. The swarm was monospecific, consisted of adults in prebreeding condition and appeared to be feeding on detrital material. The swarm covered an estimated 46 ha, densities within it ranged between 4 000 and 1 500 000 individuals per cubic metre and the swarm was estimated to contain 5 000 tonnes of euphausiids. No simple explanation for the presence of the swarm was apparent.     

Tail size and female choice in the guppy (Poecilia reticulata)

Summary Under laboratory conditions, female guppies demonstrate a clear preference for males with larger tails, and this preference translates into enhanced reproductive fitness for these males. Females also prefer males with higher display rates, a behavior which appears to be linked to tail size, but which can be experimentally disassociated. This appears to be a case of female-choice sexual selection.     

No evidence for acoustic mate-guarding in duetting buff-breasted wrens (Thryothorus leucotis)

There are few empirical tests of the acoustic mate-guarding hypothesis for the function of duetting in birds. This hypothesis states that when females are fertile, males initiate many songs or answer most of their mates solo songs to form duets and repel rival males seeking extra-pair copulations. We tested the hypothesis by comparing song initiation and answer rates of males and females in socially monogamous buff-breasted wrens (Throthorus leucotis) during pre-fertile and fertile periods. During pre-fertile periods, males often sang for short periods before being answered by their mates, yet first duets were formed earlier relative to dawn and more duets were given during the dawn chorus on pre-fertile than fertile mornings. Males initiated more songs during pre-fertile than fertile periods, whereas there was no difference between stages in female song initiation rates. The proportion of songs answered by individuals of both sexes did not differ between breeding stages. Other mate-guarding behaviours, such as frequent copulation and maintaining close proximity to mates when fertile, did not appear to be important in this species, as no copulations were observed and there was no difference in the time pairs spent in close proximity when females were fertile or not. Parentage analysis revealed that only 3% of 31 broods had young that were likely the result of extra-pair paternity. These findings do not support the acoustic mate-guarding hypothesis, and suggest that the low rate of extra-pair paternity in buff-breasted wrens was maintained without the use of acoustic or traditional paternity guards.Communicated by R. Gibson     

Isolation of heavy metal binding proteins from marine vertebrates

Cadmium binding proteins have been isolated from liver homogenates of marine vertebrates by ultracentri fugation and gel filtration. Liver samples of the Atlantic grey seal Halichoerus grypus and the Pacific fur seal Callorhinus ursinus contain measurable quantities of cadmium binding protein. The copper rock fish Sebastodes caurinus showed an increase in hepatic cadmium binding protein on administration of CdCl₂, in agreement with the known inducible nature of the protein isolated from terrestrial animals. The apparent molecular weights of the isolated proteins were 9000 for the grey seal, 10,000 for the fur seal, and 11,000 for the copper rock fish, as determined by gel filtration.     

Is there a relationship between soil and groundwater toxicity?

Part IIA of the Environmental Protection Act 1990 requires environmental regulators to assess the risk of contaminants leaching from soils into groundwater (DETR, 1999). This newly introduced legislation assumes a link between soil and groundwater chemistry, in which rainwater leaches contaminants from soil into the saturated zone. As the toxicity of both groundwater and overlying soils is dependent upon the chemicals present, their partitioning and their bioavailability, similar patterns of soil, leachates and groundwater toxicity should be observed at contaminated sites. Soil and groundwater samples were collected from different contaminated land sites in an urban area, and used to determine relationships between soil chemistry and toxicity, mobility of contaminants, and groundwater chemistry and toxicity. Soils were leached using water to mimic rainfall, and both the soils and leachates tested using bioassays. Soil bioassays were carried out using Eisenia fetida, whilst groundwater and leachates were tested using the Microtox test system and Daphnia magna 48 h acute tests. Analysis of the bioassay responses demonstrated that a number of the samples were toxic to test organisms, however, there were no significant statistical relationships between soil, groundwater and leachate toxicity. Nor were there significant correlations between soil, leachates and groundwater chemistry.     

Population biology of hyperbenthic crustaceans in a cold water environment (Conception Bay,Newfoundland). II.<Emphasis Type="Italic"> Acanthostepheia malmgreni</Emphasis> (Amphipoda)

Seasonal population dynamics of the gammarid Acanthostepheia malmgreni Goës in Conception Bay, Newfoundland, were examined from October 1998 to November 2000. This species exhibited a 2.5-year life span, with the reproductive cycle correlating with seasonal phytoplankton flux. Females were semelparous and died following a 5-month brooding period and the subsequent release of juveniles in April and May. The biennial life cycle of this population should result in the presence of two cohorts in the hyperbenthos at any given time. However, the cohorts alternated in strength from year to year, which affected annual density, biomass and production during the study period. Densities were 64±87 ind. per 100 m³ in 1999 and 491±492 ind. per 100 m³ (mean±SD) in 2000. Secondary production was estimated at 18–44 mg C m^–2 in 1999 and 180–311 mg C m^–2 in 2000. The annual P/B ratios were 0.89 and 2.27 in 1999 and 2000, respectively. Growth varied both among and within cohorts, with different life-history stages exhibiting variable growth rates ranging from 0 to 12 mg dry mass month^–1.Communicated by J.P. Grassle, New Brunswick