Chemical Plume Tracing

Environmental Fluid Mechanics -     

Feeding responses of the bivalves Crassostrea gigas and Mytilus trossulus to chemical composition of fresh and aged kelp detritus

The chemical composition of kelps (e.g. polyphenolics) deters grazing by herbivores, but kelp detritus is potentially a source of nutrition for suspension feeders. The effects of kelp detritus derived from two species [Agarum fimbriatum Harvey and Costaria costata (Turner) Saunders] on feeding of oysters, Crassostrea gigas Thunberg, and mussels, Mytilus trossulus Gould, were examined in feeding experiments. Fresh and aged kelp particles were sequentially presented in combination with the microalga Rhodomonas lens at an initial total concentration of 5᎒^-4 ml^-1. Aging of kelp particles for 4 days in seawater significantly reduced the concentration of polyphenolics without changing the total carbon or nitrogen content. Clearance rates of both mussels and oysters were significantly lower in the presence of fresh versus aged kelp particles, and clearance rates declined overall with declining polyphenolic concentrations. Video endoscopy was used to examine feeding selectivity at the level of the gill in oysters in the same food treatments used in the clearance rate experiments. Comparison of particle composition in the water versus the pseudofeces in both oysters and mussels was also used as a measure of feeding selectivity. When presented with R. lens in combination with fresh and aged kelp particles selectivity for R. lens tended to be greater against fresh than aged particles, and there was some indication that this was stronger for A. fimbriatum than for C. costata particles. The ability to select was lower at very high polyphenolic concentrations, which may reflect poisoning of sensory binding sites. These data suggest that bivalves distinguish among particles of varying chemical composition and respond by changing their clearance rates and their selectivity.     

Territorial defense in the bannertail kangaroo rat (Dipodomys spectabilis): footdrumming and visual threats

Summary Footdrumming and visual displays associated with territorial defense in the bannertail kangaroo rat (Dipodomys spectabilis) were studied in the field in Arizona. We predicted that foot-drumming functioned like bird song in territorial advertisement. Rats were tested in their territories for their responses to the presentation of four different stimuli: a playback of airborne footdrumming patterns (audio); a stuffed and mounted kangaroo rat in an aggressive posture (visual); a combination of both (audio-visual); and a playback of cricket stridulation as a control. Kangaroo rats investigated all experimental stimuli equally by becoming alert, approaching, and retreating (Fig. 2). Rats, therefore, seemed to assess the amount of threat and footdrummed at higher rates and sooner in response to the more threatening visual stumulus of a stuffed rat than to the apparently less threatening ones of a airborne footdrumming playback or cricket stridulation (Fig. 1). We conclude that rats footdrum at long ranges to repel a potential intruder and also at close ranges when territories are threatened by a persistent intruder. Chase and attack, as in territorial birds, are the final lines of defense.     

Influence of marine microalgal metabolites on the feeding behavior of the blue mussel Mytilus edulis

Effects of microalgal ectocrines on the feeding behavior of the blue mussel Mytilus edulis L., collected from Delaware Bay, Lewes, USA, were studied. Unialgal cultures of six species of marine microalgae were grown to the end of their exponential growth phase. Cells were removed by gentle filtration, leaving dissolved microalgal ectocrines in culture filtrates. Filtrates were then tested in filtration rate and particle selection bioassays. In filtration rate bioassays, dissolved ectocrines were delivered to mussels in a flow-through apparatus and removal of beads (6 m) used to determine rates. Filtration rates were significantly reduced by dissolved ectocrines from two of the microalgal species tested (Olisthodiscus luteus Carter and Dunaliella tertiolecta Butcher). None of the microalgal filtrates stimulated filtration rates of mussels. In particle selection bioassays, ectocrines were adsorbed onto either reverse phase (lipophilic) or normal phase (hydrophilic) microparticles (10 m) and delivered to mussels with an equal concentration of control treated particles. Mussels showed significant selection, either rejection or preferential ingestion, for ectocrine treated spheres depending upon microalgal species and sphere type used. This research shows that pre-ingestive chemical cues from microalgae can influence mussel feeding behavior. We suggest that epicellular ectocrines are more important in mediating this behavior than dissolved ectocrines.     

Advantages and a disadvantage of large size for male gammarus pulex (Crustacea: Amphipoda)

Summary The breeding system of the freshwater amphipod Gammarus pulex includes a precopulatory guarding phase by a male. The length of this guarding phase is investigated with respect to a male's size and the number and size of his competitors. As the absolute number of competitors increases, so does the guarding time but as the absolute number of available females increases, the guarding time decreases. Takeovers of the females by unpaired males are more frequent in longer precopulas (Table 2). In contests for females, larger males have two advantages over smaller males; they are better able to make a takeover (Table 2) and better able to resist takeover attempts while paired (Table 3). Males increase the length of the guarding phase as the mean size of their competitors increases (Table 4). When not paired males are usually searching for available females, perhaps in the stream current. Females are unaffected by current speed but increasing current causes decreased male survivorship (Table 5) and increased precopula duration (Table 5). Searching in currents is more dangerous for larger males than smaller ones. It is proposed that the male size distribution observed is the result of selection pressure to increase size from male-male competition balanced by selection against large size while searching for females in the current.     

Olfactory cues,genetic relatedness and female mate choice in the agile antechinus (<Emphasis Type="Italic">Antechinus agilis</Emphasis>)

Females show mate preferences for males that are genetically dissimilar to themselves in a variety of taxa, but how females choose these males is not clearly understood. In this study, we examined the effects of olfactory stimuli and genetic relatedness on female mate choice in a small carnivorous marsupial, the agile antechinus (Antechinus agilis), during two breeding seasons. Captive female antechinus in oestrus were provided with a combination of male urine and body scent from two novel males, one more genetically similar and one more dissimilar to the females, in a Y-maze olfactometer. Genetic relatedness between females and pairs of males was determined using highly polymorphic, species-specific, microsatellite markers. Females consistently chose to visit the scents of males that were genetically dissimilar to themselves first, spent significantly more time near the source of those scents and showed more sexual and non-exploratory behaviours near those scents. These data demonstrate that chemosensory cues are important in mate choice in the agile antechinus and that females prefer males that are genetically dissimilar to themselves.     

Four years' experience of maternal alpha-fetoprotein screening and its effect on the pattern of antenatal care

Estimation of alpha-fetoprotein (A.F.P.) in maternal serum was used as a screening method for the detection of fetal neural tube defect (N.T.D.) in 7315 women over a four year period. Of these, 5668 pregnancies were tested between 15 and 21 weeks. Action was advised in 129 patients (2·3 per cent). In 74 patients, the only action required was reviewing the notes, including the report of any ultrasound examination, and repeating the blood A.F.P. Detailed ultrasound including scanning the fetal spine was requested in 47 patients and amniocentesis was advised in 19 of these (0·33 per cent). In practice the incidence of amniocentesis was 0·28 per cent as three patients declined our advice. The programme gave detection rates between 15 and 21 weeks of 100 per cent and 75 per cent respectively for anencephaly and open spina bifida. A high fetal mortality was associated with persistently elevated blood A.F.P. levels whether amniocentesis was performed or not.     

Perceived barriers to and drivers of community participation in protected‐area governance

Protected areas (PAs) are a frequently used conservation strategy, yet their socioeconomic impacts on local communities remain contentious. A shift toward increased participation by local communities in PA governance seeks to deliver benefits for human well‐being and biodiversity. Although participation is considered critical to the success of PAs, few researchers have investigated individuals’ decisions to participate and what this means for how local people experience the costs and benefits of conservation. We explored who participates in PA governance associations and why; the perceived benefits and costs to participation; and how costs and benefits are distributed within and between communities. Methods included 3 focus groups, 37 interviews, and 217 questionnaire surveys conducted in 3 communities and other stakeholders (e.g., employees of a nongovernmental organization and government officials) in PA governance in Madagascar. Our study design was grounded in the theory of planned behavior (TPB), the most commonly applied behavior model in social psychology. Participation in PA governance was limited by miscommunication and lack of knowledge about who could get involved and how. Respondents perceived limited benefits and high costs and uneven distribution of these within and between communities. Men, poorer households, and people in remote villages reported the highest costs. Our findings illustrate challenges related to comanagement of PAs: understanding the heterogeneous nature of communities; ensuring all households are represented in governance participation; understanding differences in the meaning of forest protection; and targeting interventions to reach households most in need to avoid elite capture.