Application of ecological theory to determining recovery potential of disturbed lotic ecosystems: Research needs and priorities

This article summarizes the views of aquatic scientists who gathered to assess the ability of stream ecosystem theory to predict recovery from disturbance. Two views of disturbance were evident: a discrete removal of organisms vs an unusual deviation from normal. These were perceived as applying to different scales and/or objectives. Long-term information is required from both points of view to define recovery. Recovery also may be defined in different ways, but it is clear that recovery has both spatial and temporal components, and includes both physical and biological processes. Consensus was very strong that a major role (and challenge) for theory lies in the understanding of spatial aspects, temporal scales, coupling of physics and biology, and the interaction of these features in recovery processes. Some progress is evident in the articles of this volume, but among the topics identified as critical for further theoretical contributions were: homogeneous vs heterogeneous distribution of disturbance, local extent of disturbance relative to a regional context, critical vs noncritical patches (size and location) of disturbance at different spatial scales and temporal frequencies, delineation of reversible and nonreversible processes, and physical and biological constraints on the time frame for recovery. Such concepts need attention across different types of lotic ecosystems. Thus, there was strong consensus that a national monitoring system of representative lotic ecosystems within ecological regions be established. The purpose of this monitoring system would be to acquire long-term data on natural variability, to establish viable indicators of spatial and temporal aspects of recovery, and to develop and test emerging theoretical developments.     

An ecosystem perspective on potential impacts of drilling fluid discharges on seagrasses

Potential effects of oil drilling fluid discharges uponThalassia seagrass ecosystems were examined using seagrass core microcosms. Observed experimental effects, summarized in this article, included changes in both autotrophic (Thalassia and epiphyte) and heterotrophic (dominant benthic macroinvertebrates) species, and the processes of primary productivity and decomposition. The physical disturbance related to greater turbidity and sedimentation caused some effects, while others seemed a direct response to the toxic constituents of drilling fluids. Using these experimental results and the case ofThalassia and drilling fluids as a case study, we explore general methodological and philosophical issues for ecotoxicology and, furthermore, focus upon the challenge of providing a scientific basis for judging acceptability of environmental changes likely to ensue from human activities.     

Identification of a sex pheromone from a rotifer

The first isolation and characterization of a sex pheromone from a zooplankter is reported. A 29 kdalton glycoprotein on the surface of females of the marine rotifer Brachionus plicatilis acts as a contact-mating pheromone. This glycoprotein (gp29) is glycosylated with oligosaccharides containing Nacetylglucosamine, mannose, and fucose residues, and these oligosaccharides are necessary for male recognition of females. Males detect this signal by contact chemoreception with receptors located in their corona. Binding of purified glycoprotein to male receptors reduces mating attempts by 93%. An antibody to the glycoprotein binds to females, reducing male mating attempts by 86%. When purified gp29 is bound to sepharose beads, it is sufficient to elicit male mating behavior. This glycoprotein is likely to play a key role in the evolution and maintenance of reproductive isolation in rotifers.     

Mitochondrial DNA variation in the European lobster (<Emphasis Type="Italic">Homarus gammarus</Emphasis>) throughout the range

The genetic differentiation of the European lobster (Homarus gammarus) was investigated in 3,283 individuals from 44 population samples throughout its geographical distribution (Norway to Greece) by means of polymerase chain reaction restriction fragment length polymorphism analysis of a 3-kb mitochondrial DNA segment. Ninety composite haplotypes were revealed with the number of haplotypes in each population sample ranging from 4 to 31. Private haplotypes were found at very low frequencies. The global exact test of sample differentiation based on composite haplotype frequencies was statistically significant. F_ST analyses also showed significant heterogeneity among the European lobster population samples (F_ST=0.078, P<0.001). This differentiation was mainly due to the population samples from northern Norway, the Netherlands, and the Mediterranean Sea. These samples differentiated from the rest due to reduced gene diversity rather than to unique haplotypes. The relationships among these samples were illustrated with cluster analyses; four major distinct groups were evident: Mediterranean, northern Norway, Netherlands, and the remaining Atlantic samples. Based on the low degree of differentiation revealed in the European lobster and its limited capacity for dispersal, the most probable hypothesis is that all populations have been established from a common refuge after the end of the last Ice Age, that is, within the past 15,000 years. The results of this study show that mitochondrial DNA is a powerful tool for the determination of the genetic structure among lobster samples, which is important for a proper management policy designed to protect and to cultivate this species.Communicated by O. Kinne, Oldendorf/Luhe     

Influence of habitat on the reproductive biology of the deep-sea hydrothermal vent limpet <Emphasis Type="Italic">Lepetodrilus fucensis</Emphasis> (Vetigastropoda: Mollusca) from the Northeast Pacific

Habitat selection by the hydrothermal vent limpet, Lepetodrilus fucensis, in Northeast Pacific hydrothermal vent ecosystems, may influence its reproductive output, as it occupies habitats with varying physico-chemical conditions that reflect the availability of nutritional resources. Histological techniques were used to determine size at first reproduction, gametogenesis, reproductive output, and fecundity in relation to shell length (SL), through examination of the gonads of male and female L. fucensis, collected from five different hydrothermal vent habitat types with different temperature anomalies and hydrothermal fluid flow vigour: vigorous (VIG), diffuse (DIF), tubeworm bushes (TWB), peripheral (PER), and senescent areas (SEN). Both male and female L. fucensis exhibited early maturity, with the first reproductive event occurring at 3.8 and 3.9 mm shell length, respectively. All stages of gamete development were present in the gonads of males and females, suggesting continuous gametogenesis and asynchronous reproduction in this species. Gametogenic maturity of limpets did not vary among actively venting habitats (VIG, DIF, TWB, and PER), but was significantly lower in males and females from SEN habitats. Mean oocyte diameter was largest in females from VIG habitats, and smallest in females from SEN habitats, than in those from the other habitats (DIF, TWB, and PER). Females from actively venting habitats also had greater actual fecundity than those from senescent habitats. While the gametogenic pattern of L. fucensis appears phylogenetically constrained, selection of actively venting habitats by L. fucensis maximizes its reproductive output. The multiple feeding strategies of L. fucensis may allow for a constant supply of energy to be allocated to reproduction in any habitat except senescent vents. Early maturity, high fecundity, and continuous production of gametes suggest a reproductive strategy characteristic of an opportunistic species, and may be contributing to the extremely abundant populations of L. fucensis observed in the Northeast Pacific vent ecosystem.     

Resource quality or harem size: what influences male tenure at refuge sites in tree weta (Orthoptera: Anostostomatidae)?

Rather than seeking females directly, males in many animal species locate and defend sites that contain spatially limited resources essential for female survival and reproduction. In these cases, resident males successfully repelling conspecific rivals will mate with sexually receptive females that seek to use the resident’s resources. Theory predicts that if resources are limiting in nature, are costly to procure, and if residency at the resource site increases male reproductive success, each site should be monopolised by a single adult male. Moreover, if females aggregate at these sites, males should be sedentary and monopolise harems. This predicts that males should reside at resource sites longer than females and male tenure should be positively correlated with harem size. I address these hypotheses using a wild population of the Wellington tree weta, Hemideina crassidens, a sexually dimorphic insect in which males use mandibular weapons in fights to control resource sites (galleries in trees) required by females for diurnal refuge. In a longitudinal study using artificial galleries, I show that male tenure in a gallery is positively related to harem size and, contrary to prediction, not gallery size per se. Moreover, contrary to prediction, females are more sedentary than males: males appear to move frequently between galleries to search for novel mates. I show experimentally that galleries represent mating sites to males: males prefer galleries housing adult females whereas females prefer unoccupied galleries. Females likely avoid male-occupied galleries because they incur injuries when interacting with males.     

A dispersal model for larvae of the deep sea red crab Geryon quinquedens based upon behavioral regulation of vertical migration in the hatching stage

Behavioral responses to gravity, hydrostatic pressure, and thermoclines are described for Stage I zoeae of the deep sea red crab Geryon quinquedens Smith. Survival and rate of development as a function of temperature is presented for all larval stages. Although temperatures between 10° and 25°C have no direct effect upon survival, development time is five times longer at 10°C than at 25°C. Stage I larvae show strong negative response to gravity. Swimming rate increases with an increase in pressure up to 20 atm above ambient at 11°C, but not at 15°C. Swimming rates at 15°C are higher than those measured at 11°C at each pressure tested. Stage I larvae readily penetrate sharp thermoclines. Potential dispersal ranges of G. quinquedens larvae in the Mid-Atlantic Bight are suggested based on larval behavior, development time, and coastal hydrography. A testable recruitment model is proposed for G. quinquedens.Contribution no. 1365 of the Center for Environmental and Estuarine Studies     

Mating strategies and mating success of fallow (Dama dama) bucks in a non-lekking population

The rutting behaviour of bucks in an enclosed population was investigated between 1988 and 1990. A substantial proportion of the matings were observed. After preliminary observations in the 1987 rut we categorised bucks into one of four rutting strategies based mainly on their degree of territoriality. We investigate the effects of age, dominance and mating strategy on mating success. Territories were aggregated in an area of oak woods and mating success was highly skewed. Bucks of between 5 and 7 years old achieved the majority (over 90%) of observed matings. Mating success was highly correlated with dominance but only weakly related to fighting success. The possession of a territory was crucial to achieving high reproductive success, with a 38-fold difference between the most and least successful strategies. Bucks pursuing the different strategies also differed in the time they commenced groaning, timing of matings, mating interference and the locations where they achieved their matings. Although high-ranking males devoted considerable effort to obtaining and defending a territory only 36% of each buck's matings were achieved on his territory and males tended to abandon these sites when the tendency of females to visit them decreased.     

Can the ratio of aromatic skeletons explain cross-species responses within evolutionarily conserved Ostariophysan alarm cues?: testing the purine-ratio hypothesis

Summary. While the response to damage-released chemical alarm cues within the superorder Ostariophysi appears to be highly conserved across species, it is generally observed that the intensity of response to heterospecific alarm cues decreases with increasing phylogenetic distance. Recent studies have demonstrated that purine-N-oxides function as chemical alarm cues within Ostariophyian fishes and that the nitrogen-oxide functional group is conserved as the chief molecular trigger. According to the purine-ratio hypothesis, these cross-species differences may be due to the relative proportion of different carrier compounds associated with the nitrogen-oxide molecular trigger. To test this hypothesis, we exposed glowlight tetras (Hemigrammus erythrozonus, Characidae, Ostariophysi) to one of five synthetic stimuli (hypoxanthine-3-N-oxide (H3NO), pyridine-N-oxide (PNO) or mixed stimuli of 75 % H3NO-25 % PNO, 50 % H3NO-50 % PNO, or 25 % H3NO-75 % PNO), natural conspecific chemical alarm cue or a distilled water control. We quantified changes in shoal cohesion and vertical area use as species typical indicators of an antipredator response. As predicted, response intensity decreased as the ratio of hypoxanthine-3-N-oxide to pyridine-N-oxide decreased and the strongest response was to natural alarm cue. These results suggest that species-specific carrier compounds may account for the well-documented cross-species differences in the response to heterospecific alarm cues within phylogenetically related taxa.