Effects of food variability on growth and reproduction of Aedes aegypti

Oviposition site selection and subsequent offspring performance of Aedes aegypti in short- and long-term detritus accumulation conditions

The "oviposition preference-offspring performance" hypothesis proposes that females lay their eggs in habitats that maximize the fitness of their offspring. The aim of this study was to assess the oviposition site selection by Aedes aegypti females and the success of their larvae in habitats with different detritus accumulation times, under conditions representative of the natural spatial variability of detritus quality and quantity in the Metropolitan Area of Buenos Aires, Argentina. Two experiments were performed, one assessing oviposition site selection and the other analyzing developmental success. In both experiments, two levels of detritus accumulation time were compared, one with short-time detritus accumulation (2 weeks), and the other with long-time detritus accumulation (8 weeks). Naturally fallen detritus was used in both experiments, collected in ten sites across the Metropolitan Area of Buenos Aires. In the oviposition experiment, two contiguous ovitraps corresponding to each accumulation time were placed at each of the ten sites and the number of eggs received for each accumulation time was compared. In the development experiment, always 19 larvae were raised in containers of both accumulation times and overall performance was compared using an integrated index that considers survival, development time and female size. A large variability in the amount of detritus collected at the different sites was observed. The number of eggs was significantly higher in the long-time than in the short-time detritus accumulation containers, and approximately proportional to the amount of detritus in each ovitrap. The performance was not affected by the detritus accumulation time, but a better performance was detected in containers that received a higher amount of organic detritus, regardless of the accumulation time. Leaves were on average the most abundant type of detritus, with an average of 53 % of the total detritus collected. The amount of leaves added 2 weeks before hatching showed a positive effect on larval performance. Our results do not support the "oviposition preference-offspring performance" hypothesis, since Ae. aegypti females laid eggs in containers where larvae did not show a better performance. Moreover, at larval densities related to the number of eggs actually laid in each of the accumulation times, it is expected that the performance would be even worse in the most selected containers, due to the density-dependent effects of crowding. Since the results obtained reflect the natural heterogeneity of the environmental conditions in the region studied, they might be a fairly good indicator of what occurs in natural larval habitats.

Unexpected behavioural adaptation of yellow fever mosquitoes in response to high temperatures

Temperature is a major ecological driver of mosquito-borne diseases as it influences the life-history of both the mosquito and the pathogen harboured within it. Understanding the mosquitoes' thermal biology is essential to inform risk prediction models of such diseases. Mosquitoes can respond to temperatures by microhabitat selection through thermal preference. However, it has not yet been considered that mosquitoes are likely to adapt to changing temperatures, for example during climate change, and alter their preference over evolutionary time. We investigated this by rearing six cohorts of the yellow fever mosquito Aedes aegypti at two temperatures (24 °C, 30 °C) for 20 generations and used these cohorts to explicitly separate the effects of long-term evolution and within-generation acclimation on their thermal preferences in a thermal gradient of 20-35 °C. We found that warm-evolved mosquitoes spent 31.5% less time at high temperatures, which affects their efficiency as a vector. This study reveals the complex interplay of experimental evolution, rearing temperatures, and thermal preference in Ae. aegypti mosquitoes. It highlights the significance of incorporating mosquito microhabitat selection in disease transmission models, especially in the context of climate change.

Larval diet and temperature alter mosquito immunity and development: using body size and developmental traits to track carry-over effects on longevity

BACKGROUND

Estimating arbovirus transmission potential requires a mechanistic understanding of how environmental factors influence the expression of adult mosquito traits. While preimaginal exposure to environmental factors can have profound effects on adult traits, tracking and predicting these effects remains challenging.

METHODS

Using Aedes albopictus and a structural equation modeling approach, we explored how larval nutrition and temperature jointly affect development rate and success, female body size, and whether these metrics capture carry-over effects on adult female longevity. Additionally, we investigated how larval diet and temperature affect the baseline expression of 10 immune genes.

RESULTS

We found that larval development success was primarily determined by diet, while temperature and diet both affected development rate and female body size. Under a low larval diet, pupal wet weight and wing length both declined with increasing temperature. In contrast, responses of the two morphometric measures to rearing temperature diverged when females were provided higher larval nutrition, with pupal wet weight increasing and wing length decreasing at higher temperatures. Our analyses also revealed opposing relationships between adult female lifespan and the two morphometric measures, with wing length having a positive association with longevity and pupal weight a negative association. Larval diet indirectly affected adult longevity, and the time to pupation was negatively correlated with longevity. The expression of eight immune genes from the toll, JAK-STAT and Imd pathways was enhanced in mosquitoes with higher nutrition.

CONCLUSIONS

Our results highlight deficiencies from using a single body size measure to capture carry-over effects on adult traits. Further studies of larval development rate under varying environmental conditions and its potential for tracking carry-over effects on vectorial capacity are warranted.

Variable food alters responses of larval crown-of-thorns starfish to ocean warming but not acidification

Phytoplankton abundance is decreasing and becoming more variable as the ocean climate changes. We examine how low, high, and variable phytoplankton food supply affected the survival, development, and growth of larval crown-of-thorns starfish, Acanthaster sp. exposed to combined warming (26, 30 °C) and acidification (pH 8.0, 7.6). Larvae fed a low food ration are smaller, and develop slower and with more abnormalities than larvae fed a high ration. Larvae fed a variable food supply (low, followed by high ration) overcome the negative effects of low food on development rate and occurrence of abnormalities, but are 16-17% smaller than larvae fed the high ration continuously. Acidification (pH 7.6) slows growth and development and increases abnormalities regardless of the food regime. Warming slows growth and development, but these effects are mitigated by high food availability. As tropical oceans warm, the success of crown-of-thorns starfish larvae may depend on the abundance of their phytoplankton prey.

The size of larval rearing container modulates the effects of diet amount and larval density on larval development in Aedes aegypti

Mass-rearing of mosquitoes under laboratory conditions is an important part of several new control techniques that rely on the release of males to control mosquito populations. While previous work has investigated the effect of larval density and diet amount on colony productivity, the role of the size of the container in which larval development takes place has been relatively ignored. We investigated the role of container size in shaping life history and how this varied with density and food availability in Aedes aegypti, an important disease vector and target of mass-rearing operations. For each treatment combination, immature development time and survival and adult body size and fecundity were measured, and then combined into a measure of productivity. We additionally investigated how larval aggregation behaviour varied with container size. Container size had important effects on life history traits and overall productivity. In particular, increasing container size intensified density and diet effects on immature development time. Productivity was also impacted by container size when larvae were reared at high densities (1.4 larva/ml). In these treatments, the productivity metric of large containers was estimated to be significantly lower than medium or small containers. Regardless of container size, larvae were more likely to be observed at the outer edges of containers, even when this led to extremely high localized densities. We discuss how container size and larval aggregation responses may alter the balance of energy input and output to shape development and productivity.

Using body size as an indicator for age structure in field populations of Aedes aegypti (Diptera: Culicidae)

BACKGROUND

The Aedes aegypti mosquito is a vector of several viruses including dengue, chikungunya, zika, and yellow fever. Vector surveillance and control are the primary methods used for the control and prevention of disease transmission; however, public health institutions largely rely on measures of population abundance as a trigger for initiating control activities. Previous research found evidence that at the northern edge of Ae. aegypti's geographic range, survival, rather than abundance, is likely to be the factor limiting disease transmission. In this study, we sought to test the utility of using body size as an entomological index to surveil changes in the age structure of field-collected female Aedes aegypti.

METHODS

We collected female Ae. aegypti mosquitoes using BG sentinel traps in three cities at the northern edge of their geographic range. Collections took place during their active season over the course of 3 years. Female wing size was measured as an estimate of body size, and reproductive status was characterized by examining ovary tracheation. Chronological age was determined by measuring transcript abundance of an age-dependent gene. These data were then tested with female abundance at each site and weather data from the estimated larval development period and adulthood (1 week prior to capture). Two sources of weather data were tested to determine which was more appropriate for evaluating impacts on mosquito physiology. All variables were then used to parameterize structural equation models to predict age.

RESULTS

In comparing city-specific NOAA weather data and site-specific data from HOBO remote temperature and humidity loggers, we found that HOBO data were more tightly associated with body size. This information is useful for justifying the cost of more precise weather monitoring when studying intra-population heterogeneity of eco-physiological factors. We found that body size itself was not significantly associated with age. Of all the variables measured, we found that best fitting model for age included temperature during development, body size, female abundance, and relative humidity in the 1 week prior to capture . The strength of models improved drastically when testing one city at a time, with Hermosillo (the only study city with seasonal dengue transmission) having the best fitting model for age. Despite our finding that there was a bias in the body size of mosquitoes collected alive from the BG sentinel traps that favored large females, there was still sufficient variation in the size of females collected alive to show that inclusion of this entomological indicator improved the predictive capacity of our models.

CONCLUSIONS

Inclusion of body size data increased the strength of weather-based models for age. Importantly, we found that variation in age was greater within cities than between cities, suggesting that modeling of age must be made on a city-by-city basis. These results contribute to efforts to use weather forecasts to predict changes in the probability of disease transmission by mosquito vectors.

Differential Hatching, Development, Oviposition, and Longevity Patterns among Colombian Aedes aegypti Populations

Simple Summary

Aedes aegypti is a mosquito that transmits viruses responsible for several diseases in humans, such as dengue, Zika, and chikungunya. It is crucial to study mosquito populations from different countries and regions because control of disease transmission with insecticides can be more effective if adjusted to each population’s characteristics. For this reason, we determined several features of mosquitoes captured in different cities of Colombia: Neiva, Bello, Itagüí, and Riohacha. These included the length of their lifespan, the number of eggs they lay, and the stages in which they die. We found specific patterns for each population. This knowledge will help control programs determine the optimal times to apply insecticides and make surveillance, as well as the type of insecticide used.

Abstract

Dengue, Zika, and chikungunya are arboviral diseases for which there are no effective therapies or vaccines. The only way to avoid their transmission is by controlling the vector Aedes aegypti, but insecticide resistance limits this strategy. To generate relevant information for surveillance and control mechanisms, we determined life cycle parameters, including longevity, fecundity, and mortality, of Colombian Ae. aegypti populations from four different geographical regions: Neiva, Bello, Itagüí, and Riohacha. When reared at 28 °C, Bello had the shortest development time, and Riohacha had the longest. Each mosquito population had its own characteristic fecundity pattern during four gonotrophic cycles. The survival curves of each population were significantly different, with Riohacha having the longest survival in both males and females and Bello the shortest. High mortality was observed in mosquitoes from Neiva in the egg stage and for Bello in the pupae stage. Finally, when mosquitoes from Neiva and Bello were reared at 35 °C, development times and mortality were severely affected. In conclusion, each population has a unique development pattern with an innate trace in their biological characteristics that confers vulnerability in specific stages of development.

Resource availability for the mosquito Aedes aegypti affects the transmission mode evolution of a microsporidian parasite

Ecological conditions may greatly affect the relative importance of vertical and horizontal transmission, in particular for parasites with a mixed mode of transmission. Resource availability is one important environmental factor, affecting host growth and fecundity, but also the parasite’s own development. The consequences for the potential of vertical and horizontal transmission and for the evolution of transmission mode are largely unknown. We let the mixed-mode microsporidian parasite Edhazardia aedis evolve on its mosquito host Aedes aegypti under high-food or low-food conditions, representing permissive and restricted conditions. These alter the timing of development of infected larvae and thereby the probabilities for the parasites to enter the vertical or horizontal transmission pathways. After 10 generations, evolved parasites were assayed under the two food levels. There was an ecological trade-off between transmission modes, mediated by nutrient effects on host development, resulting in a higher vertical transmission (VT) potential under high-food and a higher horizontal transmission (HT) potential under low-food test conditions. Evolution under high food increased the VT potential of the parasite, particularly if it was tested at low food. This involved higher probability of carrying binucleate spores for the emerging females, greater fecundity and a longer life compared to parasites that were tested in the same conditions but had evolved under low food. The changes are related to the developmental regulation and switch in the production of two spore types, affecting investment in VT or HT. In contrast, the HT potential remained relatively unaffected by the parasite’s evolutionary history, suggesting that, within our experiential design, the VT mode evolved independently of the HT mode. Our work illustrates the possible links between resource availability, within-host developmental processes and the evolution of parasite transmission investment. Future work, theoretical and experimental, should scale up from within-host to between-host levels, including eco-evolutionary and epidemiological dynamics.

Regional Population Structure of the European Eel at the Southern Limit of Its Distribution Revealed by Otolith Shape Signature

Given the European eel population’s marked decrease since the 1980s, it has become urgent to collect information describing its regional population structure to improve management plans. The Minho River (NW-Portugal, SW-Europe) is an important basin for the eel at the southern limit of its distribution, but the species is poorly described. Thus, we aimed to study the structure of the European eel population in the Minho River using otolith shape analysis, which has proven to be effective in discriminating fish groups experiencing different environmental conditions through ontogeny. Our results showed complete discrimination between the two main types of habitats studied (tributaries and estuaries). Otoliths of eels from the estuary were rectangular and elliptic, whereas in the tributaries they presented a more round and circular form. Eels collected in both habitats were mostly yellow-stage eels with a similar age range, but the eels from the tributaries showed smaller length-at-age and lower body condition than those collected in the estuary. Additionally, the sex ratio was skewed towards males in the tributaries and females in the estuary. This study reveals that there are at least two distinct groups of eels in this basin, likely with different development characteristics.

Transgenic refractory Aedes aegypti lines are resistant to multiple serotypes of dengue virus

The areas where dengue virus (DENV) is endemic have expanded rapidly, driven in part by the global spread of Aedes species, which act as disease vectors. DENV replicates in the mosquito midgut and is disseminated to the mosquito’s salivary glands for amplification. Thus, blocking virus infection or replication in the tissues of the mosquito may be a viable strategy for reducing the incidence of DENV transmission to humans. Here we used the mariner Mos1 transposase to create an Aedes aegypti line that expresses virus-specific miRNA hairpins capable of blocking DENV replication. These microRNA are driven by the blood-meal-inducible carboxypeptidase A promoter or by the polyubiquitin promoter. The transgenic mosquitoes exhibited significantly lower infection rates and viral titers for most DENV serotypes 7 days after receiving an infectious blood meal. The treatment was also effective at day 14 post infection after a second blood meal had been administered. In viral transmission assay, we found there was significantly reduced transmission in these lines. These transgenic mosquitoes were effective in silencing most of the DENV genome; such an approach may be employed to control a dengue fever epidemic.

Individual energy dynamics reveal nonlinear interaction of stressors threatening migratory fish populations

Migratory fish populations, like salmon, have dramatically declined for decades. Because of their extensive and energetically costly breeding migration, anadromous fish are sensitive to a variety of environmental stressors, in particular infrastructure building in freshwater streams that increases the energetic requirements of the breeding migration and food declines in the ocean.While the effects of these stressors separately are well documented, the cumulative and interactive impacts of them are poorly understood.Here, we use a bioenergetics model recently developed for fish life history to investigate the individual life history and population responses to these stressors combined.We find that food decline in the ocean can mitigate rather than exacerbate the negative effect of elevated migration costs imposed by infrastructure building in streams. This counterintuitive effect results from the highly nonlinear manner in which these stressors interact and affect the individual energetics. In particular, this effect arises from the fact that individuals growing in the ocean under higher food conditions reach larger sizes with concomitant larger migration costs but are leaner. As a consequence of their lower energy densities, they spend most of their energy reserves to transport their body upstream when migration costs are high, and little is left for reproduction, resulting in lower individual fitness.Our results highlight the need of a mechanistic understanding integrating individual energetics, life history and population dynamics to accurately assess biological consequences of environmental change. A free Plain Language Summary can be found within the Supporting Information of this article.

An alternative model to explain the vectorial capacity using as example Aedes aegypti case in dengue transmission

Vectorial capacity (VC), as a concept that describes the potential of a vector to transmit a pathogen, has had historical problems related to lacks in dimensional significance and high error propagation from parameters that take part in the model to output. Hence, values estimated with those equations are not sufficiently reliable to consider in control strategies or vector population study. In this paper, we propose a new VC model consistent at dimensional level, i.e., the definition and the equation of VC have same and consistent units, with a parameter estimation method and mathematical structure that reduces the uncertainty in model output, using as a case of study an Aedes aegypti population of the municipality of Bello, Colombia. After a literature review, we selected one VC equation following biological, measurability and dimensional criteria, then we rendered a local and global sensitivity analysis, identifying the mortality rate of mosquitoes as a target component of the equation. Thus, we studied the Weibull and Exponential distributions as probabilistic models that represent the expectation of mosquitoes infective life, intending to include the best distribution in a selected VC structure. The proposed mortality rate estimation method includes a new parameter that represents an increase or decrease in vector mortality, as it may apply. We noticed that its estimation reduces the uncertainty associated with the expectation of mosquitoes' infective life expression, which also reduces the output range and variance in almost a half.

Microorganism-Based Larval Diets Affect Mosquito Development, Size and Nutritional Reserves in the Yellow Fever Mosquito Aedes aegypti (Diptera: Culicidae)

Background

Mosquito larvae feed on organic detritus from the environment, particularly microorganisms comprising bacteria, protozoa, and algae as well as crustaceans, plant debris, and insect exuviae. Little attention has been paid to nutritional studies in Aedes aegypti larvae.

Objectives

We investigated the effects of yeast, bacteria and microalgae diets on larval development, pupation time, adult size, emergence, survivorship, lifespan, and wing morphology.

Materials and Methods

Microorganisms (or Tetramin^® as control) were offered as the only source of food to recently hatched first instar larvae and their development was followed until the adult stage. Protein, carbohydrate, glycogen, and lipid were analyzed in single larvae to correlate energetic reserve accumulation by larva with the developmental rates and nutritional content observed. FITC-labeled microorganisms were offered to fourth instar larvae, and its ingestion was recorded by fluorescence microscopy and quantitation.

Results and Discussion

Immature stages developed in all diets, however, larvae fed with bacteria and microalgae showed a severe delay in development rates, pupation time, adult emergence and low survivorship. Adult males emerged earlier as expected and had longer survival than females. Diets with better nutritional quality resulted in adults with bigger wings. Asaia sp. and Escherichia coli resulted in better nutrition and developmental parameters and seemed to be the best bacterial candidates to future studies using symbiont-based control. The diet quality was measured and presented different protein and carbohydrate amounts. Bacteria had the lowest protein and carbohydrate rates, yeasts had the highest carbohydrate amount and microalgae showed the highest protein content. Larvae fed with microalgae seem not to be able to process and store these diets properly. Larvae were shown to be able to process yeast cells and store their energetic components efficiently.

Conclusion

Together, our results point that Ae. aegypti larvae show high plasticity to feed, being able to develop under different microorganism-based diets. The important role of Ae. aegypti in the spread of infectious diseases requires further biological studies in order to understand the vector physiology and thus to manage the larval natural breeding sites aiming a better mosquito control.

The relationship between size and longevity of the malaria vector Anopheles gambiae (s.s.) depends on the larval environment

Background

Understanding the variation in vector-borne disease transmission intensity across time and space relies on a thorough understanding of the impact of environmental factors on vectorial capacity traits of mosquito populations. This is driven primarily by variation in larval development and growth, with carryover effects influencing adult traits such as longevity and adult body size. The relationship between body size and longevity strongly affects the evolution of life histories and the epidemiology of vector-borne diseases. This relationship ranges from positive to negative but the reasons for this variability are not clear. Both traits depend on a number of environmental factors, but primarily on temperature as well as availability of nutritional resources. We therefore asked how the larval environment of the mosquito Anopheles gambiae Giles (sensu stricto) (Diptera: Culicidae) affects the relationship between body size and longevity.

Methods

We reared the larvae of An. gambiae individually at three temperatures (21, 25 and 29 °C) and two food levels (the standard and 50% of our laboratory diet) and measured adult size and longevity. We estimated the direct and indirect (via adult size) effects of food and temperature on longevity with a piecewise structural equation model (SEM).

Results

We confirmed the direct effects of food and temperature during larval development on body size, as wing length decreased with increasing temperature and decreasing food levels. While the overall relationship between size and longevity was weak, we measured striking differences among environments. At 25 °C there was no clear relationship between size and longevity; at 29 °C the association was negative with standard food but positive with low food; whereas at 21 °C it was positive with standard food but negative with low food.

Conclusions

The larval environment influences the adult’s fitness in complex ways with larger mosquitoes living longer in some environments but not in others. This confirmed our hypothesis that the relationship between size and longevity is not limited to a positive correlation. A better understanding of this relationship and its mechanisms may improve the modelling of the transmission of vector borne diseases, the evolution of life history traits, and the influence of vector control.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3058-3) contains supplementary material, which is available to authorized users.

Oviplate: A Convenient and Space-Saving Method to Perform Individual Oviposition Assays in Aedes aegypti

Aedes aegypti is the principal vector of the urban arboviruses and the blood ingestion is important to produce the eggs in this species. To analyze the egg production in Ae. aegypti, researchers frequently use small cages or Drosophila vials to collect eggs from gravid females. Although it is affordable, the setup is time- and space-consuming, mainly when many mosquitoes need to be individually analyzed. This study presents an easy, cheap, and space-saving method to perform individual oviposition assays in Ae. aegypti using cell culture plates. This new method to access fecundity rate was named “oviplate”. The oviplates are setup with 12- or 24-well plates, distilled water and filter paper and they are 78 to 88% cheaper than the traditional Drosophila vial assay, respectively. Furthermore, to allocate 72 vitellogenic females in an insectary using Drosophila vial is necessary 4100 cm³ against 1400 cm³ and 700 cm³ when using 12- and 24-well plates, respectively. No statistical differences were found between the number of eggs laid in Drosophila vials and the oviplates, validating the method. The oviplate method is an affordable, and time- and space-efficient device, and it is simpler to perform individual fecundity analyses in Ae. aegypti.

Fruit flies may face a nutrient-dependent life-history trade-off between secondary sexual trait quality, survival and developmental rate

Optimal life-history strategies are those that best allocate finite environmental resources to competing traits. We used the geometric framework for nutrition to evaluate life-history strategies followed by Drosophila melanogaster by measuring the condition-dependent performance of life-history traits, including the morphology of male secondary sexual characters, sex combs. We found that depending on their rearing environment flies faced different forms of trait trade-offs and accordingly followed different life-history strategies. High-energy, high-carbohydrate, low-protein diets supported development of the largest and most symmetrical sex combs, however, consistent with handicap models of sexual selection these foods were associated with reduced fly survival and developmental rate. Expressing the highest quality sex combs may have required secondary sexual trait quality to be traded-off with developmental rate, and our results indicated that flies unable to slow development died. As larval nutritional environments are predominantly determined by female oviposition substrate choice, we tested where mated female flies laid the most eggs. Mothers chose high-energy, high-protein foods associated with rapid larval development. Mothers avoided high-carbohydrate foods associated with maximal sex comb expression, showing they may avoid producing fewer 'sexy' sons in favour of producing offspring that develop rapidly.

The Role of the Environment in the Evolution of Tolerance and Resistance to a Pathogen

Defense against parasites can be divided into resistance, which limits parasite burden, and tolerance, which reduces pathogenesis at a given parasite burden. Distinguishing between the two and understanding which defense is favored by evolution in different ecological settings are important, as they lead to fundamentally different evolutionary trajectories of host-parasite interactions. We let the mosquito Aedes aegypti evolve under different food levels and with either no parasite, a constant parasite, or a coevolving parasite (the microsporidian Vavraia culicis). We then tested tolerance and resistance of the evolved lines on a population level at the two food levels. Exposure to parasites during evolution increased resistance and tolerance, but there were no differences between the lines evolved with coevolving or constant parasites. Mosquitoes that had evolved with food restriction had higher resistance than those evolved with high food but similar tolerance. The mosquitoes that had restricted food when being tested had lower tolerance than those with normal food, but there was no difference in resistance. Our results emphasize the complexity and dependence on environmental conditions of the evolution and expression of resistance and tolerance and help to evaluate some of the predictions about the evolution of host defense against parasites.

How Metamorphosis Is Different in Plethodontids: Larval Life History Perspectives on Life-Cycle Evolution

Plethodontid salamanders exhibit biphasic, larval form paedomorphic, and direct developing life cycles. This diversity of developmental strategies exceeds that of any other family of terrestrial vertebrate. Here we compare patterns of larval development among the three divergent lineages of biphasic plethodontids and other salamanders. We discuss how patterns of life-cycle evolution and larval ecology might have produced a wide array of larval life histories. Compared with many other salamanders, most larval plethodontids have relatively slow growth rates and sometimes exceptionally long larval periods (up to 60 mo). Recent phylogenetic analyses of life-cycle evolution indicate that ancestral plethodontids were likely direct developers. If true, then biphasic and paedomorphic lineages might have been independently derived through different developmental mechanisms. Furthermore, biphasic plethodontids largely colonized stream habitats, which tend to have lower productivity than seasonally ephemeral ponds. Consistent with this, plethodontid larvae grow very slowly, and metamorphic timing does not appear to be strongly affected by growth history. On the basis of this, we speculate that feeding schedules and stress hormones might play a comparatively reduced role in governing the timing of metamorphosis of stream-dwelling salamanders, particularly plethodontids.

Larval environment influences vector competence of the malaria mosquito Anopheles gambiae

Background

While environmental factors such as temperature can influence the vector competence of mosquitoes directly, for example by affecting the longevity of the mosquito and the development of the malaria parasite they may also have an indirect impact on the parasite's transmission. By influencing larval development, they may affect the adult traits that are important for the parasite's development and transmission. We studied the influence of two larval environmental factors, food availability and temperature, on the probability that mosquitoes infected with the malaria parasite survived to harbour sporozoites in their salivary glands.

Materials and methods

Anopheles gambiae larvae were reared at 21ºC, 25ºC or 29ºC, and fed either a standard larval diet or half of it. Adults could blood feed on mice harbouring the infectious gametocytic stage of Plasmodium berghei ANKA transformed with green fluorescent protein (GFP). Survival was assessed every 24 hrs up to 21 days post infection, when surviving mosquitoes were dissected to check the salivary glands for sporozoites with a fluorescent microscope sensitive to GFP. Using a binomial GLM we analysed 'vector competence', i.e. if mosquitoes survived until dissection and harboured sporozoites in their salivary glands.

Results

Vector competence dropped by about a third if we fed larvae half the standard food regime. The effect of temperature during the larval period depended strongly on the food regime. At low food, increasing temperature from 21ºC to 29ºC increased vector competence from about 0.18 to 0.48, whereas at standard food, vector competence dropped from about 0.67 at 21ºC to 0.56 at 29ºC.

Conclusions

Thus, perceptions and models about the role of environmental change on the transmission of malaria should include how the environment changes adult life-history by influencing larval development.