Exfoliation of epithelial cells by the scallop Placopecten magellanicus : seasonal variation and the effects of elevated water temperatures

Previous studies have shown that large numbers of ciliated and nonciliated epithelial cells (diam.: 6 to 15 μm) are released by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in Newfoundland when water temperatures are at a maximum and gonads are well developed. Such exfoliation of cells could be a response to stresses associated with elevated water temperatures and/or spawning activity. In the present study an electronic particle counter/sizer was used to further investigate the factors that influence exfoliation of epithelial cells by juvenile and adult scallops throughout the year. We observed release of epithelial cells from juveniles, and from adults collected in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers of cells may be a consequence of cellular turnover and normal physiological function. Adult scallops were monitored in a second experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 °C on the frequency (proportion) and rate of cellular exfoliation. Only at the highest experimental temperature (21.0 °C) were exfoliation rates significantly higher than rates recorded at 8.5 or 14.7 °C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops were exposed to 14.7 and then to 21.0 °C for a total of 8 d. Received: 21 August 1996 / Accepted: 13 September 1996     

The economic implications of recycling exhaustible natural resources: The case for crude oil

Regardless of whether the bulk of decision-making in an economy is done by a central unit or by decentralized smaller units, the government can act to propose guidelines to individual agents. This is of particular importance when the activities of the latter cause aggregative or social problems which are not directly acted upon by the smaller agents. The purpose of this paper is to set up a model by which a central authority can make choices in the presence of two pressing social problems, namely, a diminishing domestic supply of an exhaustible resource and the contamination of the environment through discharged waste materials.The model itself takes the form of an integer-linear programming problem which runs through discrete time to a finite horizon. Besides the traditional modes of “virgin” exploration and production and/or importation from abroad, society is also given the choice of recycling. Society will choose combinations of the above three to minimize the costs of satisfying fixed (projected) oil product demands in the future. The costs include those for increasing exploration for virgin refineries; for collection, refining and transportation for refineries and for the cost to society of discharges of waste-oil into the environment. The constraints include process flow restrictions, import quotas, capacity limits and discharge restrictions as well as fixed demands.An effort was made to keep the model as general as possible. Although no numerical solution is obtained in this paper, we feel that the policy implications of some presumed solution (possible through the use of a well-known algorithm for mixed variable problems) are worth examining. They revolve around the model itself, citing the potential attractiveness of recycling as the other two alternatives become increasingly expensive, and as development of alternatives to oil progresses at an alarmingly slow rate. Also mentioned are problems relating to the potential demands for recycled versus virgin oil products, balance-of-trade problems, and the mutability of social and economic institutions in the crisis of economic adjustment that much of the world is now facing.     

Regional extent of an ecosystem engineer: earthworm invasion in northern hardwood forests.

The invasion of exotic earthworms into northern temperate and boreal forests previously devoid of earthworms is an important driver of ecosystem change. Earthworm invasion can cause significant changes in soil structure and communities, nutrient cycles, and the diversity and abundance of herbaceous plants. However, the regional extent and patterns of this invasion are poorly known. We conducted a regional survey in the Chippewa and Chequamegon National Forests, in Minnesota and Wisconsin, U.S.A., respectively, to measure the extent and patterns of earthworm invasion and their relationship to potential earthworm introduction sites. We sampled earthworms, soils, and vegetation in 20 mature, sugar maple-dominated forest stands in each national forest and analyzed the relationship between the presence of five earthworm taxonomic groups, habitat variables, and distance to the nearest potential introduction site. Earthworm invasion was extensive but incomplete in the two national forests. Four of the six earthworm taxonomic groups occurred in 55-95% of transects; however 20% of all transects were invaded by only one taxonomic group that has relatively minor ecological effects. Earthworm taxonomic groups exhibited a similar sequence of invasion found in other studies: Dendrobaena > Aporrectodea = Lumbricus juveniles > L. rubellus > L. terrestris. Distance to the nearest road was the best predictor of earthworm invasion in Wisconsin while distance to the nearest cabin was the best predictor in Minnesota. These data allow us to make preliminary assessments of landscape patterns of earthworm invasion. As an example, we estimate that 82% of upland mesic hardwood stands in the Wisconsin region are likely invaded by most taxonomic groups while only 3% are unlikely to be invaded at present. Distance to roads and cabins provides a coarse-scale predictor of earthworm invasion to focus stand-level assessments that will help forest managers better understand current and potential forest conditions and identify uninvaded areas that could serve as important refugia for plant species threatened by earthworm invasion.     

Female-biased sex allocation in peregrine falcons and other raptors

Summary The sex ratios of nestling Falconiformes in which males are smaller than females are often female biased, despite the apparent costs involved in producing very large female offspring. In Australian peregrine falcons, Falco peregrinus, this bias is most pronounced in broods produced early in the season, and the first eggs to be laid are most likely to produce females. Females that lay early are most likely to be successful breeders. Very large chicks tend to occur in female-biased broods. Collectively, these data suggest that females likely to produce large offspring produce daughters. A modified version of the Trivers/Willard hypothesis is suggested to account for this pattern.Offprint requests to: P.D. Olsen at the second address     

Genetic population structure of southern bluefin tuna (Thunnus maccoyii )

Samples of southern bluefin tuna, Thunnus maccoyii (Castelnau), taken from off the coasts of South Africa, Western Australia, South Australia and Tasmania from 1992 to 1994 were analysed for six polymorphic allozyme loci (ADA ^*, GDA ^*, GPI-A ^*, MPI ^*, PGDH ^* and PGM-1 ^*, n = 595 to 733 per locus) and for mitochondrial DNA variants revealed by three restriction enzymes (Bam HI, Bcl I and Eco RI) detecting polymorphic cut sites (n = 555). No significant spatial heterogeneity was detected. There were no sex-related differences in allele or mtDNA haplotype frequencies. Juveniles (30 to 35 cm and 46 to 54 cm) from what are thought to be two temporally-separated spawning peaks showed no significant genetic differentiation. There were also no significant differences in allele or haplotype frequencies between fish smaller than 70 cm and those larger than 70 cm. These data are consistent with the null hypothesis of a single unit stock of southern bluefin tuna, with a single spawning area. This is located to the south of Java and off the north-west coast of Australia. Received: 28 August 1996 / Accepted: 30 September 1996     

Iodine in the soils of North Derbyshire

Derbyshire was one of the best known centres of endemic goitre in Great Britain. Some 160 km from the coast in the direction of the prevailing wind, topsoils in the area are generally low in iodine (mean = 5.44 mg l/kg). Weathered rocks and soils are richer in iodine than the unweathered bedrocks, with soils developed over limestones being richer than those over sandstones, shales and dolomites. Highest iodine contents in soil profiles over limestones occur in the upper horizons while over sandstones, iodine concentrates in the lower horizons. The major cause of endemic goitre in north Derbyshire is likely to be relatively low levels of iodine, while the calcium rich soils of the area may contribute by reducing plant iodine uptake.     

Mating and its effect on acoustic signalling behaviour in a primitive orthopteran,Cyphoderris strepitans (Haglidae): the cost of feeding females

Summary Males of the primitive orthopteran, Cyphoderris strepitans, provide their mates with two types of nuptial food gift during mating: 1) females feed while coupled on the fleshy metathoracic wings of the male and the resultant flow of haemolymph and 2) the spermatophore transferred by the male includes a gelatinous spermatophylax which the female eats after mating. During the peak breeding interval, virgin males secure significantly more matings than their numbers relative to non-virgin males would predict. We tested the hypothesis that non-virgin males, having lost a substantial portion of available energy through previous investment in females, call significantly less than virgin males. Reduced calling should result in the attraction of fewer females and/or a greater risk of intrusion from competing males and consequently, a lowered mating success. Calling activity of male C. strepitans of varying mating status was monitored with a sound activated relay apparatus for two consecutive nights following their capture. Males were of three experimental groups, virgin, freshly wounded males (mated on the same night of capture), and old-wound males (mated at least one night prior to capture). Our cata showed a significant short-term reduction in signalling activity as a consequence of mating. Whereas there was no difference in the time spent calling by virgins on the first and second nights following capture, freshly wounded and oldwound males called significantly less on the first night than on the second. Furthermore, the proportion of males calling on both nights was significantly greater for the virgin and old-wound groups than for freshly wounded males. When the duration over which males called on the first night was compared with that of the second, virgin males showed no difference whereas old-wound males called for significantly shorter intervals on the first night. These results indicate that the cost of a large nutrient investment in females lowers the energy level in males below the threshold required for a prolonged signalling period. After a refractory interval during which males feed and replenish their energy reserves, calling levels equivalent to those which occur prior to mating are regained. Active female choice may also contribute to the reduced mating success of non-virgins, but this possibility remains untested.     

Optimal pollution permit endowments in markets with endogenous emissions

In a permit market with endogenous emissions, both firms and citizens purchase permits. Presented here are static and dynamic models of pollution permit markets with endogenous emissions. The optimal permit endowments are characterized when the regulator faces uncertainty about damages and uncertainty about the severity of the citizens’ collective action problem. Due to the possibility of learning over time, the regulator issues a larger number of permits in the first period of the dynamic model than in the static model.     

Influences of Egg Laying Behavior on Pathogenic Infection of Amphibian Eggs

Mass mortality of developing amphibian eggs and larvae from pathogenic infection has been recently documented in some amphibian populations. For example, the pathogenic fungus, Saprolegnia ferax, has been linked with amphibian embryo mortality in the Pacific Northwest. Continued mortality in early life history stages may ultimately contribute to a population decline. We document the prevalence of S. ferax on embryos of three anuran species (   Bufo boreas, Rana cascadae, and Hyla regilla) common to the Pacific Northwest. These species differ in key aspects of their behavior and ecology, and these differences may lead to differential susceptibility to S. ferax. R. cascadae often lays its eggs communally and B. boreas usually deposits its eggs communally. We observed embryos at natural oviposition sites. Eggs laid communally had higher mortality than those laid away from other egg masses. Field experiments that manipulated both the spatial position and timing of egg laying demonstrated that eggs laid later and in closer proximity to communal masses had higher mortality. Our results suggest that eggs in communal masses are highly susceptible to infection with S. ferax.     

Provisioning rules in tree swallows

Conflict between parents and offspring may result in offspring exaggerating their needs and parents devaluing their begging signals. To determine whether this occurs, it is first necessary to establish the link between need, begging and parental response. The purpose of our study was to examine these relationships in tree swallows (Tachycineta bicolor). Parents preferentially fed nestlings that begged sooner, reached higher and were closer to the front of the nestbox (Fig. 1). Begging intensity of both individuals and entire broods increased with relatively long periods between feeding visits. Within broods, parents responded to increased begging intensity by increasing their feeding rate, although this effect was relatively weak. Large and small nestlings did not differ in their begging behavior and all nestlings, regardless of size, were fed at similar rates. Despite the overall equity in feeding, male parents preferentially fed larger nestlings while female parents fed smaller nestlings. Nestlings did not increase their begging intensity in response to begging by nestmates. Our results suggest that begging is related to need in this species and that parents respond to variation in begging intensity. Received: 4 May 1995/Accepted after revision: 17 December 1995