Arrival timing and seasonal reproductive performance in a long-distance migratory landbird

The date when a landbird migrant arrives on its breeding grounds may have reproductive consequences. Generally, early arriving individuals begin breeding earlier and consequently experience greater seasonal reproductive performance. Here, we describe relationships between arrival timing and seasonal reproductive performance in the American redstart (Setophaga ruticilla), a long-distance passerine migrant, arriving at northerly breeding grounds in Michigans eastern Upper Peninsula. Evidence suggests that both males and females benefited from early arrival at the breeding grounds. Early males appeared to settle on higher quality territories and hatched nestlings sooner than later arrivals. Early females began their clutches early, produced heavier nestlings and possibly laid more eggs than later arrivals. Larger clutches and heavier offspring increase the likelihood of offspring recruiting into the breeding population. The findings of this study point to fitness consequences arising from when a bird arrives at its breeding grounds. These results also have implications for understanding how events occurring during spring migration influence reproductive performance as migratory delays likely influence arrival timing.Communicated by: W. Wiltschko     

Adsorption of crude oil on arctic terrain

Arctic terrain was divided into three layers, moss, detritus and clay, and each layer was contacted with Norman Wells crude oil. Chromatographic analysis of the crude oil extracts of the terrain layers showed that the adsorption capacity of the terrain increased with increasing organic content. The higher molecular weight n-alkanes were adsorbed to a greater extent than lower n-alkanes on the moss and detritus layers. Of the aromatics, p-xylene was adsorbed to a greater extent than benzene on all three layers of the terrain. Retention of crude oil components on Arctic terrain in the event of an oil spill would be in accord with these findings.     

A framework for allocating conservation resources among multiple threats and actions

Land managers decide how to allocate resources among multiple threats that can be addressed through multiple possible actions. Additionally, these actions vary in feasibility, effectiveness, and cost. We sought to provide a way to optimize resource allocation to address multiple threats when multiple management options are available, including mutually exclusive options. Formulating the decision as a combinatorial optimization problem, our framework takes as inputs the expected impact and cost of each threat for each action (including do nothing) and for each overall budget identifies the optimal action to take for each threat. We compared the optimal solution to an easy to calculate greedy algorithm approximation and a variety of plausible ranking schemes. We applied the framework to management of multiple introduced plant species in Australian alpine areas. We developed a model of invasion to predict the expected impact in 50 years for each species-action combination that accounted for each species’ current invasion state (absent, localized, widespread); arrival probability; spread rate; impact, if present, of each species; and management effectiveness of each species-action combination. We found that the recommended action for a threat changed with budget; there was no single optimal management action for each species; and considering more than one candidate action can substantially increase the management plan's overall efficiency. The approximate solution (solution ranked by marginal cost-effectiveness) performed well when the budget matched the cost of the prioritized actions, indicating that this approach would be effective if the budget was set as part of the prioritization process. The ranking schemes varied in performance, and achieving a close to optimal solution was not guaranteed. Global sensitivity analysis revealed a threat's expected impact and, to a lesser extent, management effectiveness were the most influential parameters, emphasizing the need to focus research and monitoring efforts on their quantification.     

Increased energy expenditure due to increased territorial defense in male lizards after phenotypic manipulation

Fitness tradeoffs are difficult to examine because many fitness variables are correlated and vary in the same direction. Phenotypic manipulation circumvents many of these difficulties, and here we used this technique to examine mechanisms for tradeoffs between increased aggression (territorial defense) and survivorship. The behavioral phenotype of male mountain spiny lizards (Sceloporus jarrovi) was manipulated with testosterone to increase territorial defense, a sexually selected trait. We previously demonstrated that increased territorial defense results in a decrease in survival caused by a lower ratio of energy intake to energy expenditure. Here we measured energy consumption of increased territorial aggression using the doubly labeled water technique in the field and compared males with and without testosterone implants (Fig. 1). In a supplementary study we measured standard metabolic rate using captive lizards given similar testosterone implants to examine if an increase in energy expenditure was a result of only an increase in standard metabolic rate (Fig. 3). Our results indicated that a primary contribution to tradeoffs between increased territorial defense and survivorship could be made by a 31% increase in energy expenditure in the field that is not due to an increase in standard metabolic rate.     

Effects of Hg2+ and Cu2+ on the cytosolic Ca2+ level in molluscan blood cells evaluated by confocal microscopy and spectrofluorimetry

In the present work the effect of Hg²⁺ and Cu²⁺ on the level of cytosolic Ca²⁺ in mussel (Mytilus edulis L.) haemolymph cells were investigated by confocal microscopy and spectrofluorimetry utilizing the fluorescent dye Fluo3. In the blood cells of marine molluscs, exposure to Cu²⁺ and Hg²⁺ in the nanomolar and micromolar range causes a time-and concentration-dependent increase in the cytosolic Ca²⁺ level. Both the presence of a low-calcium containing medium and pretreatment of the cells with the channel blocker Verapamil greatly reduced the effects of higher (50 M) Hg²⁺ concentrations, this indicating that Hg²⁺ enhances the influx of extracellular Ca²⁺ partly through activation of voltage-dependent Ca²⁺ channels. Low concentrations of Hg²⁺ (1 M) and also of Cu²⁺ (0.5 M), an essential element, were able to induce a sustained increase in cytosolic Ca²⁺, which was not affected either by Verapamil pretreatment or by lowering the extracellular calcium concentration. These data indicate that in mussel haemocytes heavy metal cations impair Ca²⁺ homeostasis not only by affecting Ca²⁺ channels, but also by interfering with other mechanisms of calcium transport across cellular membranes, such as the Ca²⁺-ATPases. The resulting increase in cytosolic Ca²⁺ could activate Ca-dependent processes which may be involved in many of the biochemical and physiological alterations observed in the cells of metal-exposed mussels. Specimens used in these experiments were collected from the river Linker near Plymouth, U.K. in June 1991.     

Graded recruitment in a ponerine ant

Summary (1) The giant tropical ant, Paraponera clavata, exhibits graded recruitment responses, depending on the type, quantity, and quality of a food source. More ants are initially recruited to a large prey or scavenge item than to a large quantity of sugar water. (2) Individual ants encountering prey items gauge the size and/or unwieldiness of the item, regardless of the weight, when determining whether to recruit. (3) The trail pheromone of this species is often used as an orientation device by individual ants, independent of recruitment of nestmates. (4) It is proposed that the foraging behavior of P. clavata represents one of the evolutionary transitions from the independent foraging activities of the primitive ants to the highly coordinated cooperative foraging activities of many higher ants.     

Lysosomal responses to experimentally injected anthracene in the digestive cells of Mytilus edulis

Experimentally injected anthracene (10 to 100 g mussel^-1) has been shown to induce dose-dependent lysosomal destabilisation and release of hexosaminidase in the digestive cells of Mytilus edulis after 24 h. This destabilisation was accompanied by cytological evidence of cytolysis of the digestive cells. The destabilising effect of 100 g of injected anthracene persisted for 96 h with a return to the control condition by 168 h. These results are discussed in the context of environmental contamination by polycyclic aromatic hydrocarbons.     

Long-term storage of sediments: Implications for sediment toxicity testing

A study using open-top chambers ventilated with ambient or charcoal-filtered air in the vicinity of Lahore, Pakistan, has demonstrated a reduction of 46.7% and 34.8% in the grain yield for two cultivars of winter wheat (Triticum aestivum L.). The 6-h daily mean O(3) concentrations were 25-45 nl litre(-1) and on the basis of experience in North America and Europe, reductions in yield in the present study are substantially greater than might be predicted. The reasons for this discrepancy are discussed, together with implications for the suitability of a simple, relatively cheap, open-top chamber system for developing-country studies on the effects of air pollution on crops.