Linking Global Warming, Metabolic Rate of Hematophagous Vectors, and the Transmission of Infectious Diseases

Climate is under constant change. In addition to its natural variability, there is plenty of evidence suggesting persistent changes overtime produced by external forces, such as anthropogenic activities. These changes are observed on patterns of precipitation and temperature, among others (Crowley, 2000). Carbon dioxide levels in the atmosphere have been recorded since the beginning of the twentieth century. The hypothesis that changes in CO 2 concentration of the atmosphere could be responsible for climate deviations, first propose

Machine-learning model led design to experimentally test species thermal limits: The case of kissing bugs (Triatominae)

Species Distribution Modelling (SDM) determines habitat suitability of a species across geographic areas using macro-climatic variables; however, micro-habitats can buffer or exacerbate the influence of macro-climatic variables, requiring links between physiology and species persistence. Experimental approaches linking species physiology to micro-climate are complex, time consuming and expensive. E.g., what combination of exposure time and temperature is important for a species thermal tolerance is difficult to judge a priori. We tackled this problem using an active learning approach that utilized machine learning methods to guide thermal tolerance experimental design for three kissing-bug species: Triatoma infestans, Rhodnius prolixus, and Panstrongylus megistus (Hemiptera: Reduviidae: Triatominae), vectors of the parasite causing Chagas disease. As with other pathogen vectors, triatomines are well known to utilize micro-habitats and the associated shift in microclimate to enhance survival. Using a limited literature-collected dataset, our approach showed that temperature followed by exposure time were the strongest predictors of mortality; species played a minor role, and life stage was the least important. Further, we identified complex but biologically plausible nonlinear interactions between temperature and exposure time in shaping mortality, together setting the potential thermal limits of triatomines. The results from this data led to the design of new experiments with laboratory results that produced novel insights of the effects of temperature and exposure for the triatomines. These results, in turn, can be used to better model micro-climatic envelope for the species. Here we demonstrate the power of an active learning approach to explore experimental space to design laboratory studies testing species thermal limits. Our analytical pipeline can be easily adapted to other systems and we provide code to allow practitioners to perform similar analyses. Not only does our approach have the potential to save time and money: it can also increase our understanding of the links between species physiology and climate, a topic of increasing ecological importance.Centro de Estudios Parasitológicos y de Vectore

Oxygen Reperfusion Damage in an Insect

The deleterious effects of anoxia followed by reperfusion with oxygen in higher animals including mammals are well known. A convenient and genetically well characterized small-animal model that exhibits reproducible, quantifiable oxygen reperfusion damage is currently lacking. Here we describe the dynamics of whole-organism metabolic recovery from anoxia in an insect, Drosophila melanogaster, and report that damage caused by oxygen reperfusion can be quantified in a novel but straightforward way. We monitored CO2 emission (an index of mitochondrial activity) and water vapor output (an index of neuromuscular control of the spiracles, which are valves between the outside air and the insect's tracheal system) during entry into, and recovery from, rapid-onset anoxia exposure with durations ranging from 7.5 to 120 minutes. Anoxia caused a brief peak of CO2 output followed by knock-out. Mitochondrial respiration ceased and the spiracle constrictor muscles relaxed, but then re-contracted, presumably powered by anaerobic processes. Reperfusion to sustained normoxia caused a bimodal re-activation of mitochondrial respiration, and in the case of the spiracle constrictor muscles, slow inactivation followed by re-activation. After long anoxia durations, both the bimodality of mitochondrial reactivation and the recovery of spiracular control were impaired. Repeated reperfusion followed by episodes of anoxia depressed mitochondrial respiratory flux rates and damaged the integrity of the spiracular control system in a dose-dependent fashion. This is the first time that physiological evidence of oxygen reperfusion damage has been described in an insect or any invertebrate. We suggest that some of the traditional approaches of insect respiratory biology, such as quantifying respiratory water loss, may facilitate using D. melanogaster as a convenient, well-characterized experimental model for studying the underlying biology and mechanisms of ischemia and reperfusion damage and its possible mitigation

Assessment of nectar flow rate and memory for patch quality in the ant Camponotus rufipes

Ants as central place foragers are known to visit repeatedly renewable patches such as extrafloral nectaries, yet the criteria workers use to evaluate their quality, as well as the rules used to decide when to leave the patch, have not been identified. We examined the assessment of nectar flow rate by nectar-feeding ants, Camponotus rufipes. Single workers from a laboratory colony were trained to visit an artificial feeder providing 20% sucrose solution either ad libitum or at controlled flow rates (0.118–2.36 l/min). These flow rates simulate the conditions faced by workers when visiting plant extrafloral nectaries. Ants adjusted their visit times to the different flow rates, so that the time spent at the feeder decreased with increasing nectar flow rates. The volume of nectar collected increased with increasing nectar flow rates, and workers were observed to return to the nest with partially filled crops. To investigate the rules used by ants to decide when to depart from the patch, we confronted experienced workers on their fifth visit with a depleted patch, and recorded the time spent there before leaving. The time depended on the previously experienced flow rate, even though ants always found a depleted patch, indicating that ants arrive at the patch with an expectation about the nectar flow rate, and use as a departure rule an estimate of time that depends on the flow rate previously experienced

Assessment of nectar flow rate and memory for patch quality in the ant Camponotus rufipes

Ants as central place foragers are known to visit repeatedly renewable patches such as extrafloral nectaries, yet the criteria workers use to evaluate their quality, as well as the rules used to decide when to leave the patch, have not been identified. We examined the assessment of nectar flow rate by nectar-feeding ants, Camponotus rufipes. Single workers from a laboratory colony were trained to visit an artificial feeder providing 20% sucrose solution either ad libitum or at controlled flow rates (0.118–2.36 l/min). These flow rates simulate the conditions faced by workers when visiting plant extrafloral nectaries. Ants adjusted their visit times to the different flow rates, so that the time spent at the feeder decreased with increasing nectar flow rates. The volume of nectar collected increased with increasing nectar flow rates, and workers were observed to return to the nest with partially filled crops. To investigate the rules used by ants to decide when to depart from the patch, we confronted experienced workers on their fifth visit with a depleted patch, and recorded the time spent there before leaving. The time depended on the previously experienced flow rate, even though ants always found a depleted patch, indicating that ants arrive at the patch with an expectation about the nectar flow rate, and use as a departure rule an estimate of time that depends on the flow rate previously experienced

Energetics of locomotion and load carriage in the nectar feeding ant, Camponotus rufipes

To investigate if there is an energetic constraint influencing a nectar feeding ant’s decision to come back to the nest with partial loads, the energetic costs of running and carrying a load in the ant Camponotus rufipes are measured. Metabolic rates of individuals are measured in a running tube respirometer while they are unladen and laden at 25 °C. Workers voluntarily collect a load of 6 µL of a 30 % sucrose solution (mass = 6.8 mg), which results in an internal load of about 50% of the ant mass and is close to a full load for ants within this size range. The gross cost of unladen running is 264 J kg-1 m-1, while that of laden running is 225 J kg-1 m-1. The mass used to calculate the cost of laden running includes body mass of ant and load carried. Load carriage cost in C. rufipes foragers is calculated to be about 60% as much as body carriage per unit mass. Internal load carriage in C. rufipes is energetically cheaper compared with external carriage in other ant species. Such low carriage costs make it unlikely that the collection of partial crop loads in C. rufipes foragers is based on a minimization of foraging costs, as suggested for honeybees

Energetics of locomotion and load carriage in the nectar feeding ant, Camponotus rufipes

To investigate if there is an energetic constraint influencing a nectar feeding ant’s decision to come back to the nest with partial loads, the energetic costs of running and carrying a load in the ant Camponotus rufipes are measured. Metabolic rates of individuals are measured in a running tube respirometer while they are unladen and laden at 25 °C. Workers voluntarily collect a load of 6 µL of a 30 % sucrose solution (mass = 6.8 mg), which results in an internal load of about 50% of the ant mass and is close to a full load for ants within this size range. The gross cost of unladen running is 264 J kg-1 m-1, while that of laden running is 225 J kg-1 m-1. The mass used to calculate the cost of laden running includes body mass of ant and load carried. Load carriage cost in C. rufipes foragers is calculated to be about 60% as much as body carriage per unit mass. Internal load carriage in C. rufipes is energetically cheaper compared with external carriage in other ant species. Such low carriage costs make it unlikely that the collection of partial crop loads in C. rufipes foragers is based on a minimization of foraging costs, as suggested for honeybees

Respirometry recordings from: Diatomaceous earth as insecticide: physiological and morphological evidence of its underlying mechanism

Open-flow RespirometryRespirometric measurements were performed in two groups of insects. One that we called “DE” that was previously treated with diatomaceous earth, and the other called “Control”, which was not exposed to diatomaceous earth. For the DE group we used a concentration of half gram of Diatomaceus earths per kg of wheat grain (0.5 g kg-1). After the two days treatment, 14 replicates of DE and 13 of Control group of 30 individuals each were placed inside the respirometric chamber for measurement. Insect's water and carbon dioxide emission rate were measured at real time using a high-resolution TR-2 Stable System International's open flux respirometry setup (SSI, Las Vegas, NV, USA). Insects are placed inside a respirometric chamber (RC-M; internal volume ≈13ml; SSI), which is connected to an open circuit of air flow, generated and controlled by a flow controller (SS4 sub-sampler, SSI). The setup has a set of analyzers and modules that enables us to measure carbon dioxide and water emission of the insects inside the chamber, as well as ambient temperature, chamber temperature and insect's activity (movement), in high resolution and real time. The analog outputs from the analyzers were connected to an A/D converter (UI-2; SSI) and stored in a computer by ExpeData data acquisition software (SSI) at a frequency of 1 Hz.</p