Thermal tolerance experiments help establish survival probabilities for tilapia, a group of potentially invasive aquatic species

1. Estimating the probability of establishment is an important step toward managing ecological risk posed by natural or intentional introductions. Species introductions in certain geographic areas may pose less of a threat when environmental conditions are unlikely to promote long-term establishment. Species commonly referred to as 'tilapia' have become widespread in certain areas of the southeastern United States, yet concerns remain regarding their potential spread to other areas.
2. We created a model to predict the survival of tilapia in Georgia (U.S.A.) based on individual 'thermal experience'. Laboratory experiments were conducted to measure the duration of survival of two strains of tilapia, Oreochromis nilotica and O. nilotica  ×  O. aureus hybrids, exposed to a variety of temperature regimes with three minimum temperatures and two rates of temperature decline.
3. We used Mayfield hierarchical logistic regression (MHLR) to describe the daily probability of survival as a function of the rate of temperature decline, average sustained temperature, tilapia strain and mass–length ratio.
4. Tilapia generally survived constant minimum temperatures over 12 °C but survival rate was mediated by the rate of decline, mass–length ratio and strain. For every 1 °C increase in minimum temperature, tilapia were 2.76 times more likely to survive. Fish exposed to rapid temperature decline were less likely to survive than those exposed to slowly decreasing temperature. More robust fish (higher mass–length ratio) were more likely to survive, and strain had a minimal effect despite being supported by the best MHLR model.
5. Our model can be used to estimate survival probability for tilapia under known surface water temperature regimes. Using MLHR in conjunction with experimental tolerance data may be useful for estimating the likelihood of establishment of potentially invasive species.     

Ionotropic Nucleation of Calcium Carbonate by Molluscan Matrix

The hydrophilic, sulfated fraction of the organic matrix foundin molluscan shells appears to be involved in crystal nucleation.It is located primarily at the sites of initial nucleation.The hydrophilic fraction favors in vitro formation of calcifieddeposits, when it is fixed in place on the hydrophobic fraction.Calcium is bound by the hydrophillic fraction with high affinityand selectivity. Enzymatic desulfation reduces the calcium binding.However, the binding stoichiometry of one calcium for everytwo ester sulfates is not altered. The calcium binding induceslocal anion binding, which induces secondary calcium binding.This coordinated ion binding is known as ionotropy. The resultantlocal high concentration of ions is thought to bring about nucleation.     

Nutrient regulation in the pea aphid Acyrthosiphon pisum: application of a novel geometric framework to sugar and amino acid consumption

Abstract. A recently developed framework was applied to investigate the responses of newborn pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), to simultaneous variations in dietary suerose and amino acid levels. The location of functional 'targets' for intake and growth were determined experimentally using performance criteria. Behavioural rules employed by insects to approach these targets were investigated by reference to the geometry of arrays of intake and growth across a range of diets. First-instar aphids were fed one of thirty-one chemically-defined diets ranging in sucrose concentration from 200 to 1000 mM and amino acid concentration from 25 to 250 mM. Insect survivorship, dry weight, protein- and carbohydrate-derived growth were high for all diets except those with the lowest nutrient levels. Peaks in final dry weight and protein content identified the intake target as the point reached by larvae fed the 600 mM sucrose, 75 mM amino acid diet. Aphids regulated sucrose primarily by consumption (i.e. behaviourally), whereas amino acids were regulated post-ingestively (i.e. by physiological mechanisms).     

Grasshopper sexual pheromone: a component of the defensive secretion in Taeniopoda eques

ABSTRACT. Both male and female Taeniopoda eques (Burmeister) emit a defensive secretion from their thoracic spiracles. The secretion from mature females was found to act as a sex pheromone, eliciting mating behaviour in males. Females became chemically attractive to males about 16–18 days after eclosion. The antennae are shown to be the site of pheromone reception in males. Feeding upon natural host plants was not a prerequisite for pheromone production.     

Ammonia volatilization from a seasonally and spatially variable grazed grassland: Yellowstone National Park

We measured ammonia volatilization at three topographic positions(hilltop, mid-slope, slope-bottom) on three grassland landscapes at threetimes during 1995 (April, May, July) on the northern winter range ofYellowstone National Park that supports large herds of native ungulates.Percent ammonia-N lost from all sites during the study ranged 1–24%of urea-N applied. Volatilization among sites was negatively related tosoil cation-exchange capacity (r = –0.85) and rates were highest inJuly. We used the relationship between soil CEC and percent Nvolatilized from urea-amended plots to estimate annual ammonia-Nvolatilization from 5 sites for which annual ungulate urine inputs werepreviously determined (Frank et al. 1994). Estimated mean annualammonia-N volatilized from those sites was 1.4 kg/ha/yr, which wasless than a previously reported regional atmospheric deposition rate (2kg/ha/yr; Swank 1984). Results indicate the need to understand theinteraction between (1) spatially heterogeneous patterns of soilprocesses, and 2) nonuniform patterns of ungulate use of landscapes todetermine rates of ecosystem-level N-gaseous loss. Findings alsosuggest that ammonia-N volatilized from urine patches should not leadto a decline in soil N in this ecosystem.     

Effects of the fungus Aspergillus penicillioides on the house dust mite Dermatophagoides pteronyss'mus: an experimental re-evaluation

Abstract. In this report the widely-held view that house dust mites benefit from fungal contamination of the dietary substratum is re-examined. The performance of Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) is documented over two successive generations in the presence or absence of the xerophilic fungus Aspergillus penicillioides (Hyphomycetales: Moniliaceae). This fungus reduced survival, development rate, adult length and fecundity of D.pteronyssinus. Detrimental effects of A.penicillioides were proportional to the fungal density. Despite the antagonistic effects of A.penicillioides, a requirement for the fungus was indicated by the poor performance of fungus-free mites in the second generation; sustained culture of D.pteronyssinus in the absence of fungi is probably not possible. It is suggested that fungi may alter the particulate nature of the substratum to the detriment of house dust mites, but also provide micronutrients deficient in the diet.