Allometry of maximum vertical force production during hovering flight of neotropical orchid bees (Apidae: Euglossini). (25/253)

The ability of orchid bees to generate vertical forces was evaluated using a load-lifting method that imposed asymptotically increasing loads during ascending flight, ultimately eliciting maximum forces while hovering. Among 11 orchid bee species varying by approximately an order of magnitude in body mass, the capacity to produce vertical forces expressed relative either to body weight or to flight muscle weight declined linearly with increased body mass. Allometric analysis of log-transformed data, by contrast, found maximum vertical force to scale isometrically with body mass, but also to exhibit a slightly negative allometry with respect to flight muscle mass. Maximum stroke amplitude at limiting loads averaged 140 degrees and was remarkably constant among species, a result consistent with anatomical constraints of the hymenopteran thorax on wing motions. By contrast, wing-beat frequencies during maximum performance declined with increasing body mass. Repeated lifting by individual bees reduced performance only when the number of consecutive lifts exceeded 15. Variation in linear mass density of the lifted load did not systematically alter performance estimates, although measurements on one species in two consecutive years at different thermal environments yielded significant differences in estimates of maximum force production. These findings suggest an adverse scaling of vertical force production at greater body mass even if flight muscle mass scales isometrically.  (+info)

Use of diploid male frequency data as an indicator of pollinator decline. (26/253)

Pollination deficits in agricultural and natural systems are suggestive of large reductions in pollinator populations. However, actual declines are difficult to demonstrate using census data. Here, we show census data to be misleading because many abundant pollinators exhibit high levels of production of sterile diploid males usually found only in small inbred hymenopteran populations; Euglossa imperialis exhibits high levels of diploid male production induced by low effective population sizes (Ne approximately 15), despite being the most abundant orchid bee in lowland tropical forests in Panama. We caution that although some pollinators appear abundant on the basis of census data, their long-term persistence may be highly tenuous based on genetic evidence. We propose the use of diploid male frequency data as a metric for assessing the sustainability of bee populations.  (+info)

Let your enemy do the work: within-host interactions between two fungal parasites of leaf-cutting ants. (27/253)

Within-host competition is an important factor in host-parasite relationships, yet most studies consider interactions involving only single parasite species. We investigated the interaction between a virulent obligate entomopathogenic fungus, Metarhizium anisopliae var. anisopliae, and a normally avirulent, opportunistic fungal pathogen, Aspergillus flavus, in their leaf-cutting ant host, Acromyrmex echinatior. Surprisingly, the latter normally out-competed the former in mixed infections and had enhanced fitness relative to when infecting in isolation. The result is most probably due to Metarhizium inhibiting the host's immune defences, which would otherwise normally prevent infections by Aspergillus. With the host defences negated by the virulent parasite, the avirulent parasite was then able to out-compete its competitor. This result is strikingly similar to that seen in immunocompromised vertebrate hosts and indicates that avirulent parasites may play a more important role in host life histories than is generally realized.  (+info)

Interspecific and intraspecific views of color signals in the strawberry poison frog Dendrobates pumilio. (28/253)

Poison frogs in the anuran family Dendrobatidae use bright colors on their bodies to advertise toxicity. The species Dendrobates pumilio Schmidt 1858, the strawberry poison frog, shows extreme polymorphism in color and pattern in Panama. It is known that females of D. pumilio preferentially choose mates of their own color morph. Nevertheless, potential predators must clearly see and recognize all color morphs if the aposematic signaling system is to function effectively. We examined the ability of conspecifics and a model predator to discriminate a diverse selection of D. pumilio colors from each other and from background colors. Microspectrophotometry of isolated rod and cone photoreceptors of D. pumilio revealed the presence of a trichromatic photopic visual system. A typical tetrachromatic bird system was used for the model predator. Reflectance spectra of frog and background colors were obtained, and discrimination among spectra in natural illuminants was mathematically modeled. The results revealed that both D. pumilio and the model predator discriminate most colors quite well, both from each other and from typical backgrounds, with the predator generally performing somewhat better than the conspecifics. Each color morph displayed at least one color signal that is highly visible against backgrounds to both visual systems. Our results indicate that the colors displayed by the various color morphs of D. pumilio are effective signals both to conspecifics and to a model predator.  (+info)

High seroprevalence of hantavirus infection on the Azuero peninsula of Panama. (29/253)

The first outbreak of hantavirus pulmonary syndrome (HPS) in Central America was documented on the Azuero peninsula of Panama in late 1999 and 2000. Reverse transcriptase-polymerase chain reaction evidence implicated only Choclo virus in symptomatic HPS with a mortality rate of 20%, although two rodent-borne hantaviruses (Choclo virus and Calabazo virus) were identified in the peridomestic habitat. Neighborhood serosurveys around case households found seroprevalence rates as high as 30%, the highest in the Americas except for western Paraguay. We report here population-based serosurveys for 1,346 adults and children in four communities, three on the Azuero peninsula and one in adjacent central Panama. Overall seroprevalence ranged from 33.2% in a population engaged in farming and fishing on Isla de Canas, to 16.3% and 21.2% in two mainland agricultural communities, to 3.1% in central Panama, with a modest male predominance of 1.2:1. Nine percent of children 4-10 years old were seropositive, and seroprevalence increased with age in all communities, with highest levels of 52% in those 41-50 years old cohort on Isla de Canas. Univariate analysis identified correlations between seroprevalence and multiple agricultural and animal husbandry activities. However, stepwise logistic regression models identified only raising animals (cows, pigs, goats, poultry) and fishing as significant independent variables. Human infection with hantavirus on the Azuero peninsula, either with Choclo virus or combined with Calabazo virus, is frequent but rarely results in hospitalization due to respiratory illnesses resembling HPS.  (+info)

Error propagation and scaling for tropical forest biomass estimates. (30/253)

The above-ground biomass (AGB) of tropical forests is a crucial variable for ecologists, biogeochemists, foresters and policymakers. Tree inventories are an efficient way of assessing forest carbon stocks and emissions to the atmosphere during deforestation. To make correct inferences about long-term changes in biomass stocks, it is essential to know the uncertainty associated with AGB estimates, yet this uncertainty is rarely evaluated carefully. Here, we quantify four types of uncertainty that could lead to statistical error in AGB estimates: (i) error due to tree measurement; (ii) error due to the choice of an allometric model relating AGB to other tree dimensions; (iii) sampling uncertainty, related to the size of the study plot; (iv) representativeness of a network of small plots across a vast forest landscape. In previous studies, these sources of error were reported but rarely integrated into a consistent framework. We estimate all four terms in a 50 hectare (ha, where 1 ha = 10(4) m2) plot on Barro Colorado Island, Panama, and in a network of 1 ha plots scattered across central Panama. We find that the most important source of error is currently related to the choice of the allometric model. More work should be devoted to improving the predictive power of allometric models for biomass.  (+info)

Suction feeding in orchid bees (Apidae: Euglossini). (31/253)

Energy flux during nectar feeding is maximized at an intermediate sugar concentration, the value of which depends on the morphology of the feeding apparatus and the modality of fluid feeding. Biomechanical models predict that a shift from capillary-based lapping to suction feeding will lead to a decrease in this optimal sugar concentration. Here, I demonstrate that the four major genera of orchid bees (Apidae: Euglossini) are suction feeders and provide experimental evidence that the feeding optimum for one species, Euglossa imperialis, falls below the optimum for bee taxa that lap.  (+info)

Thermal stability and muscle efficiency in hovering orchid bees (Apidae: Euglossini). (32/253)

To test whether variation in muscle efficiency contributes to thermal stability during flight in the orchid bee, Euglossa imperialis, we measured CO2 production, heat loss and flight kinematics at different air temperatures (Ta). We also examined the relationship between wingbeat frequency (WBF) and Ta in five additional species of orchid bees. Mean thoracic temperature (Tth) for Eg. imperialis hovering in a screened insectary and in the field was 39.3+/-0.77 degrees C (mean +/- 95% C.I.), and the slope of Tth on Ta was 0.57. Head and abdominal temperature excess ratios declined with Ta, indicating that Eg. imperialis were not increasing heat dissipation from the thorax at high Ta. Elevation of Tth above Ta was correlated with WBF, but Tth alone was not. Estimates of heat production from both respirometry and heat loss experiments decreased 33% as Ta rose from 24 to 34 degrees C. Mean muscle efficiency over this temperature range was 18% assuming perfect elastic energy storage and 22% assuming zero elastic energy storage. Both efficiency estimates increased significantly as Ta rose from 24 to 34 degrees C. In all six species examined, WBF declined significantly with Ta. These data indicate that hovering orchid bees regulate heat production through changes in wingbeat kinematics and consequent changes in energy conversion by the flight motor. Temperature-dependent variation in elastic energy storage or muscle contraction efficiency or both may contribute to the observed trends.  (+info)