Regional variation in life history traits and plastic responses to temperature of the major malaria vector Nyssorhynchus darlingi in Brazil

Evolutionary adaptation under climate change: Aedes sp. demonstrates potential to adapt to warming

Climate warming is expected to shift the distributions of mosquitoes and mosquito-borne diseases, facilitating expansions at cool range edges and contractions at warm range edges. However, whether mosquito populations could maintain their warm edges through evolutionary adaptation remains unknown. Here, we investigate the potential for thermal adaptation in Aedes sierrensis, a congener of the major disease vector species that experiences large thermal gradients in its native range, by assaying tolerance to prolonged and acute heat exposure, and its genetic basis in a diverse, field-derived population. We found pervasive evidence of heritable genetic variation in acute heat tolerance, which phenotypically trades off with tolerance to prolonged heat exposure. A simple evolutionary model based on our data shows that the estimated maximum rate of evolutionary adaptation in mosquito heat tolerance typically exceeds that of projected climate warming under idealized conditions. Our findings indicate that natural mosquito populations may have the potential to track projected warming via genetic adaptation. Prior climate-based projections may thus underestimate the range of mosquito and mosquito-borne disease distributions under future climate conditions.

Population-specific thermal responses contribute to regional variability in arbovirus transmission with changing climates

Temperature is increasing globally, and vector-borne diseases are particularly responsive to such increases. While it is known that temperature influences mosquito life history traits, transmission models have not historically considered population-specific effects of temperature. We assessed the interaction between Culex pipiens population and temperature in New York State (NYS) and utilized novel empirical data to inform predictive models of West Nile virus (WNV) transmission. Genetically and regionally distinct populations from NYS were reared at various temperatures, and life history traits were monitored and used to inform trait-based models. Variation in Cx. pipiens life history traits and population-dependent thermal responses account for a predicted 2.9°C difference in peak transmission that is reflected in regional differences in WNV prevalence. We additionally identified genetic signatures that may contribute to distinct thermal responses. Together, these data demonstrate how population variation contributes to significant geographic variability in arbovirus transmission with changing climates.

Forest cover percentage drives the peak biting time of Nyssorhynchus darlingi (Diptera: Culicidae) in the Brazilian Amazon

BACKGROUND

Deforestation is an important driver of malaria dynamics, with a relevant impact on mosquito ecology, including larval habitat availability, blood-feeding behaviour, and peak biting time. The latter is one of several entomological metrics to evaluate vectorial capacity and effectiveness of disease control. This study aimed to test the effect of forest cover percentage on the peak biting time of Plasmodium-uninfected and infected Nyssorhynchus darlingi females.

METHODS

Mosquitoes were captured utilizing human landing catch (HLC) in the peridomestic habitat in field collections carried out in the wet, wet-dry transition, and dry seasons from 2014 to 2017 in areas with active malaria transmission in Amazonian Brazil. The study locations were in rural settlements in areas with the mean annual malaria parasite incidence (Annual Parasite Incidence, API ≥ 30). All Ny. darlingi females were tested for Plasmodium spp. infection using real time PCR technique. Forest cover percentage was calculated for each collection site using QGIS v. 2.8 and was categorized in three distinct deforestation scenarios: (1) degraded, < 30% forest cover, (2) intermediate, 30-70% forest cover, and (3) preserved, > 70% forest cover.

RESULTS

The highest number of uninfected female Ny. darlingi was found in degraded landscape-sites with forest cover < 30% in any peak biting time between 18:00 and 0:00. Partially degraded landscape-sites, with (30-70%) forest cover, showed the highest number of vivax-infected females, with a peak biting time of 21:00-23:00. The number of P. falciparum-infected mosquitoes was highest in preserved sites with > 70% forest cover, a peak biting at 19:00-20:00, and in sites with 30-70% forest cover at 22:00-23:00.

CONCLUSIONS

Results of this study show empirically that degraded landscapes favour uninfected Ny. darlingi with a peak biting time at dusk (18:00-19:00), whereas partially degraded landscapes affect the behaviour of Plasmodium-infected Ny. darlingi by shifting its peak biting time towards hours after dark (21:00-23:00). In preserved sites, Plasmodium-infected Ny. darlingi bite around dusk (18:00-19:00) and shortly after (19:00-20:00).

High temperatures and low humidity promote the occurrence of microsporidians (Microsporidia) in mosquitoes (Culicidae)

BACKGROUND

In the context of climate change, a growing concern is that vector-pathogen or host-parasite interactions may be correlated with climatic factors, especially increasing temperatures. In the present study, we used a mosquito-microsporidian model to determine the impact of environmental factors such as temperature, humidity, wind and rainfall on the occurrence rates of opportunistic obligate microparasites (Microsporidia) in hosts from a family that includes important disease vectors (Culicidae).

METHODS

In our study, 3000 adult mosquitoes collected from the field over 3 years were analysed. Mosquitoes and microsporidia were identified using PCR and sequencing of the hypervariable V5 region of the small subunit ribosomal RNA gene and a shortened fragment of the cytochrome c oxidase subunit I gene, respectively.

RESULTS

DNA metabarcoding was used to identify nine mosquito species, all of which were hosts of 12 microsporidian species. The prevalence of microsporidian DNA across all mosquito samples was 34.6%. Microsporidian prevalence in mosquitoes was more frequent during warm months (> 19 °C; humidity < 65%), as was the co-occurrence of two or three microsporidian species in a single host individual. During warm months, microsporidian occurrence was noted 1.6-fold more often than during the cold periods. Among the microsporidians found in the mosquitoes, five (representing the genera Enterocytospora, Vairimorpha and Microsporidium) were positively correlated with an increase in temperature, whereas one (Hazardia sp.) was significantly correlated with a decrease in temperature. Threefold more microsporidian co-occurrences were recorded in the warm months than in the cold months.

CONCLUSIONS

These results suggest that the susceptibility of mosquitoes to parasite occurrence is primarily determined by environmental conditions, such as, for example, temperatures > 19 °C and humidity not exceeding 62%. Collectively, our data provide a better understanding of the effects of the environment on microsporidian-mosquito interactions.

Mosquito thermal tolerance is remarkably constrained across a large climatic range

How mosquitoes may respond to rapid climate warming remains unknown for most species, but will have major consequences for their future distributions, with cascading impacts on human well-being, biodiversity and ecosystem function. We investigated the adaptive potential of a wide-ranging mosquito species, Aedes sierrensis, across a large climatic gradient by conducting a common garden experiment measuring the thermal limits of mosquito life-history traits. Although field-collected populations originated from vastly different thermal environments that spanned over 1200 km, we found limited variation in upper thermal tolerance between populations. In particular, the upper thermal limits of all life-history traits varied by less than 3°C across the species range and, for most traits, did not differ significantly between populations. For one life-history trait-pupal development rate-we did detect significant variation in upper thermal limits between populations, and this variation was strongly correlated with source temperatures, providing evidence of local thermal adaptation for pupal development. However, we found that maximum environmental temperatures across most of the species' range already regularly exceed the highest upper thermal limits estimated under constant temperatures. This result suggests that strategies for coping with and/or avoiding thermal extremes are likely key components of current and future mosquito thermal tolerance.

Presence and abundance of malaria vector species in Miami-Dade County, Florida

BACKGROUND

Malaria outbreaks have sporadically occurred in the United States, with Anopheles quadrimaculatus serving as the primary vector in the eastern region. Anopheles crucians, while considered a competent vector, has not been directly implicated in human transmission. Considering the locally acquired Plasmodium vivax cases in Sarasota County, Florida (7 confirmed cases), Cameron County, Texas (one confirmed case), and Maryland (one confirmed case) in the summer of 2023. The hypothesis of this study is that major cities in the United States harbour sufficient natural populations of Anopheles species vectors of malaria, that overlap with human populations that could support local transmission to humans. The objective of this study is to profile the most abundant Anopheles vector species in Miami-Dade County, Florida-An. crucians and An. quadrimaculatus.

METHODS

This study was based on high-resolution mosquito surveillance data from 2020 to 2022 in Miami-Dade County, Florida. Variations on the relative abundance of An. crucians and An. quadrimaculatus was assessed by dividing the total number of mosquitoes collected by each individual trap in 2022 by the number of mosquitoes collected by the same trap in 2020. In order to identify influential traps, the linear distance in meters between all traps in the surveillance system from 2020 to 2022 was calculated and used to create a 4 km buffer radius around each trap in the surveillance system.

RESULTS

A total of 36,589 An. crucians and 9943 An. quadrimaculatus were collected during this study by the surveillance system, consisting of 322 CO2-based traps. The findings reveal a highly heterogeneous spatiotemporal distribution of An. crucians and An. quadrimaculatus in Miami-Dade County, highlighting the presence of highly conducive environments in transition zones between natural/rural and urban areas. Anopheles quadrimaculatus, and to a lesser extent An. crucians, pose a considerable risk of malaria transmission during an outbreak, given their high abundance and proximity to humans.

CONCLUSIONS

Understanding the factors driving the proliferation, population dynamics, and spatial distribution of Anopheles vector species is vital for implementing effective mosquito control and reducing the risk of malaria outbreaks in the United States.

Mosquito thermal tolerance is remarkably constrained across a large climatic range

How mosquitoes may respond to rapid climate warming remains unknown for most species, but will have major consequences for their future distributions, with cascading impacts on human well-being, biodiversity, and ecosystem function. We investigated the adaptive potential of a wide-ranging mosquito species, Aedes sierrensis, across a large climatic gradient by conducting a common garden experiment measuring the thermal limits of mosquito life history traits. Although field-collected populations originated from vastly different thermal environments that spanned over 1,200 km, we found remarkably limited variation in upper thermal tolerance between populations, with the upper thermal limits of fitness varying by <1°C across the species range. For one life history trait-pupal development rate-we did detect significant variation in upper thermal limits between populations, and this variation was strongly correlated with source temperatures, providing evidence of local thermal adaptation for pupal development. However, we found environmental temperatures already regularly exceed our highest estimated upper thermal limits throughout most of the species range, suggesting limited potential for mosquito thermal tolerance to evolve on pace with warming. Strategies for avoiding high temperatures such as diapause, phenological shifts, and behavioral thermoregulation are likely important for mosquito persistence.

Assessing the role of family level variation and heat shock gene expression in the thermal stress response of the mosquito Aedes aegypti

The geographical range of the mosquito vector for many human disease-causing viruses, Aedes aegypti, is expanding, in part owing to changing climate. The capacity of this species to adapt to thermal stress will affect its future distributions. It is unclear how much heritable genetic variation may affect the upper thermal limits of mosquito populations over the long term. Nor are the genetic pathways that confer thermal tolerance fully understood. In the short term, cells induce a plastic, protective response known as 'heat shock'. Using a physiological 'knockdown' assay, we investigated mosquito thermal tolerance to characterize the genetic architecture of the trait. While families representing the extreme ends of the distribution for knockdown time differed from one another, the trait exhibited low but non-zero broad-sense heritability. We then explored whether families representing thermal performance extremes differed in their heat shock response by measuring gene expression of heat shock protein-encoding genes Hsp26, Hsp83 and Hsp70. Contrary to prediction, the families with higher thermal tolerance demonstrated less Hsp expression. This pattern may indicate that other mechanisms of heat tolerance, rather than heat shock, may underpin the stress response, and the costly production of HSPs may instead signal poor adaptation. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Differential expression of Phlebotomus tobbi Adler, Theodor & Lourie, 1930 (Diptera: Psychodidae) genes under different environmental conditions

Phlebotomus tobbi is a widely distributed sand fly species in Turkey and is the proven vector of Leishmania infantum and several Phleboviruses. Information regarding the genetic basis of phenotypic plasticity is crucial for managing vector-borne diseases, as the changing environmental conditions have consequences for the survival of arthropods and the disease agents they transmit. However, limited data is available on the impacts of environmental conditions on the traits associated with sand fly survival, reproduction, and vectorial competence. The present study aimed to reveal the changes in the expression levels of three selected P. tobbi genes using laboratory-reared and wild-caught populations. A nervous system protein, Cacophony (PtCac), related to the life history traits of sand flies, and two sand fly salivary protein genes, PtSP32 and PtSP38, influence the infection of the vertebrate hosts, were assessed. Sand flies were maintained at 23 °C and 27 °C in the laboratory to evaluate the relationship between temperature and the expressed phenotypes. Field collections were carried out in three climatically distinct regions of Turkey to establish the regional differences in the gene expression levels of natural P. tobbi populations. In the laboratory, PtCac expression increased with the temperature. However, PtCac expression was negatively correlated with local temperature and humidity conditions. No differences were detected in the PtSP32 gene expression levels of both laboratory-reared and wild-caught females, but a negative correlation was observed with relative humidity in natural populations. Although the expression levels of PtSP38 did not differ among the females collected from distinct regions, a positive correlation was detected in the laboratory-reared colony. The findings indicated that changes in environmental conditions could drive the expression levels of P. tobbi genes, which influence population dynamics and the transmission risk of the disease.

Variation in Pyrethroid Resistance Phenotypes in Anopheles darlingi in an Area with Residual Malaria Transmission: Warning of Suspected Resistance in French Guiana

Anopheles darlingi is the main vector of malaria in South America. In French Guiana, malaria transmission occurs inland and along the rivers with a regular reemergence in the lower Oyapock area. Control against malaria vectors includes indoor residual spraying of deltamethrin and the distribution of long-lasting impregnated bednets. In this context, the level of resistance to pyrethroids was monitored for 4 years using CDC bottle tests in An. darlingi populations. A loss of susceptibility to pyrethroids was recorded with 30-minute knock-down measured as low as 81%. However, no pyrethroid molecular resistance was found by sequencing a 170 base pair fragment of the S6 segment of domain II of the voltage-gated sodium channel gene. Fluctuation of resistance phenotypes may be influenced by the reintroduction of susceptible alleles from sylvatic populations or by other mechanisms of metabolic resistance.

Developing Wolbachia-based disease interventions for an extreme environment

Aedes aegypti mosquitoes carrying self-spreading, virus-blocking Wolbachia bacteria are being deployed to suppress dengue transmission. However, there are challenges in applying this technology in extreme environments. We introduced two Wolbachia strains into Ae. aegypti from Saudi Arabia for a release program in the hot coastal city of Jeddah. Wolbachia reduced infection and dissemination of dengue virus (DENV2) in Saudi Arabian mosquitoes and showed complete maternal transmission and cytoplasmic incompatibility. Wolbachia reduced egg hatch under a range of environmental conditions, with the Wolbachia strains showing differential thermal stability. Wolbachia effects were similar across mosquito genetic backgrounds but we found evidence of local adaptation, with Saudi Arabian mosquitoes having lower egg viability but higher adult desiccation tolerance than Australian mosquitoes. Genetic background effects will influence Wolbachia invasion dynamics, reinforcing the need to use local genotypes for mosquito release programs, particularly in extreme environments like Jeddah. Our comprehensive characterization of Wolbachia strains provides a foundation for Wolbachia-based disease interventions in harsh climates.

How will mosquitoes adapt to climate warming?

The potential for adaptive evolution to enable species persistence under a changing climate is one of the most important questions for understanding impacts of future climate change. Climate adaptation may be particularly likely for short-lived ectotherms, including many pest, pathogen, and vector species. For these taxa, estimating climate adaptive potential is critical for accurate predictive modeling and public health preparedness. Here, we demonstrate how a simple theoretical framework used in conservation biology-evolutionary rescue models-can be used to investigate the potential for climate adaptation in these taxa, using mosquito thermal adaptation as a focal case. Synthesizing current evidence, we find that short mosquito generation times, high population growth rates, and strong temperature-imposed selection favor thermal adaptation. However, knowledge gaps about the extent of phenotypic and genotypic variation in thermal tolerance within mosquito populations, the environmental sensitivity of selection, and the role of phenotypic plasticity constrain our ability to make more precise estimates. We describe how common garden and selection experiments can be used to fill these data gaps. Lastly, we investigate the consequences of mosquito climate adaptation on disease transmission using Aedes aegypti-transmitted dengue virus in Northern Brazil as a case study. The approach outlined here can be applied to any disease vector or pest species and type of environmental change.

Water immersion tolerance by larval instars of stable fly, Stomoxys calcitrans, L1758 (Diptera: Muscidae) impairs the fitness performance of their subsequent stages

BACKGROUND

In holometabolous insects, environmental factors experienced in pre-imaginal life stages affect the life-history traits within that stage and can also influence subsequent life stages. Here, I assessed tolerance to water immersion by the larval instars of the stable fly, Stomoxys calcitrans L. (Diptera: Muscidae) and its impact on the life-history traits of their subsequent life stages.

RESULTS

After submerging the three larval instars of S. calcitrans in distilled water, I found that the first instar larvae remained active for longer as compared to the second and third instar larvae. Also, the first instar larvae took a longer period to recover from the stress-induced immobility when removed from the water and returned to ambient temperature. When I followed the development of individuals of each larval instar that survived from water immersion, I found that their developmental time, weight, pupation percentage, adult emergence percentage and adult weight were negatively affected by this stressor. However, the weight of S. calcitrans adults developed from immersed first larval instar individuals was not affected by water immersion whereas their counterparts developed from immersed second and third larval instars had lower body weight. This suggests that in S. calcitrans, water immersion stress at the earlier stage is less detrimental than that experienced at late stages.

CONCLUSION

This study provides a comparative overview of the fitness consequences associated with water immersion stress during S. calcitrans larval ontogeny. The results prove that the fitness shift induced by water immersion in S. calcitrans is stage-specific. My results illustrate the importance of considering each larval instar when assessing the impact of environmental factors on holometabolous insect performance as these may be decoupled by metamorphosis.

Flight tone characterisation of the South American malaria vector Anopheles darlingi (Diptera: Culicidae)

BACKGROUND

Flight tones play important roles in mosquito reproduction. Several mosquito species utilise flight tones for mate localisation and attraction. Typically, the female wingbeat frequency (WBF) is lower than males, and stereotypic acoustic behaviors are instrumental for successful copulation. Mosquito WBFs are usually an important species characteristic, with female flight tones used as male attractants in surveillance traps for species identification. Anopheles darlingi is an important Latin American malaria vector, but we know little about its mating behaviors.

OBJECTIVES

We characterised An. darlingi WBFs and examined male acoustic responses to immobilised females.

METHODS

Tethered and free flying male and female An. darlingi were recorded individually to determine their WBF distributions. Male-female acoustic interactions were analysed using tethered females and free flying males.

FINDINGS

Contrary to most mosquito species, An. darlingi females are smaller than males. However, the male's WBF is ~1.5 times higher than the females, a common ratio in species with larger females. When in proximity to a female, males displayed rapid frequency modulations that decreased upon genitalia engagement. Tethered females also modulated their frequency upon male approach, being distinct if the interaction ended in copulation or only contact.

MAIN CONCLUSIONS

This is the first report of An. darlingi flight acoustics, showing that its precopulatory acoustics are similar to other mosquitoes despite the uncommon male:female size ratio, suggesting that WBF ratios are common communication strategies rather than a physical constraint imposed by size.

Anthropogenic landscape decreases mosquito biodiversity and drives malaria vector proliferation in the Amazon rainforest

Inter-relationships among mosquito vectors, Plasmodium parasites, human ecology, and biotic and abiotic factors, drive malaria risk. Specifically, rural landscapes shaped by human activities have a great potential to increase the abundance of malaria vectors, putting many vulnerable people at risk. Understanding at which point the abundance of vectors increases in the landscape can help to design policies and interventions for effective and sustainable control. Using a dataset of adult female mosquitoes collected at 79 sites in malaria endemic areas in the Brazilian Amazon, this study aimed to (1) verify the association among forest cover percentage (PLAND), forest edge density (ED), and variation in mosquito diversity; and to (2) test the hypothesis of an association between landscape structure (i.e., PLAND and ED) and Nyssorhynchus darlingi (Root) dominance. Mosquito collections were performed employing human landing catch (HLC) (peridomestic habitat) and Shannon trap combined with HLC (forest fringe habitat). Nyssorhynchus darlingi abundance was used as the response variable in a generalized linear mixed model, and the Shannon diversity index (H') of the Culicidae community, PLAND, and the distance house-water drainage were used as predictors. Three ED categories were also used as random effects. A path analysis was used to understand comparative strengths of direct and indirect relationships among Amazon vegetation classes, Culicidae community, and Ny. darlingi abundance. Our results demonstrate that Ny. darlingi is negatively affected by H´ and PLAND of peridomestic habitat, and that increasing these variables (one-unit value at β0 = 768) leads to a decrease of 226 (P < 0.001) and 533 (P = 0.003) individuals, respectively. At the forest fringe, a similar result was found for H' (β1 = -218; P < 0.001) and PLAND (β1 = -337; P = 0.04). Anthropogenic changes in the Amazon vegetation classes decreased mosquito biodiversity, leading to increased Ny. darlingi abundance. Changes in landscape structure, specifically decreases in PLAND and increases in ED, led to Ny. darlingi becoming the dominant species, increasing malaria risk. Ecological mechanisms involving changes in landscape and mosquito species composition can help to understand changes in the epidemiology of malaria.

Interpopulation variations in life history traits and reproductive tactics in Aedes aegypti: A test on populations 50 km apart

The interpopulation variation in life history traits of a species reflects evolutionary adaptation in response to a local environment regime. We examined the life history traits of Aedes aegypti populations from 2 cities in southern Taiwan separated by 50 km. Results revealed a high level of trait differentiation in immature developmental time and survival of Ae. aegypti between the 2 cities. The Kaohsiung populations exhibited total pupation of 40%-60% on day 8; this was significantly lower than that of the Tainan populations and laboratory-reared KHsm mosquitos, which exhibited a pupation rate of 70%-90%. The slow immature development of the Kaohsiung populations was reflected in the low percentage of adult emergence (22%-26%) on day 10. The prolonged immature development did not select larger adults with longer life spans because the Kaohsiung populations had a shorter life span (≈37 d) than that of the Tainan populations (≈42 d). By contrast, immature development and longevity did not differ between populations within each region, indicating weak local differentiation. Three field populations exhibited male-bias sex ratio because of differential mortality of female immatures. The effect of female size on adult life history was nonsignificant. Two reproduction tactics were detected, representing the balanced-mortality hypothesis and the bet-hedging hypothesis. Despite their differential life history strategies and reproductive tactics, these mosquito populations apparently counterbalanced any shortcomings in traits to produce similar population growth. Maintaining optimal population density is essential for Aedes mosquitos to increase the probability of encountering mates and reduce the Allee effect.

Kerteszia cruzii and extra-Amazonian malaria in Brazil: Challenges due to climate change in the Atlantic Forest

Kerteszia cruzii is a sylvatic mosquito and the primary vector of Plasmodium spp., which can cause malaria in humans in areas outside the Amazon River basin in Brazil. Anthropic changes in the natural environments are the major drivers of massive deforestation and local climate change, with serious impacts on the dynamics of mosquito communities and on the risk of acquiring malaria. Considering the lack of information on the dynamics of malaria transmission in areas across the Atlantic Forest biome, where Ke. cruzii is the dominant vector, and the impact of climate drivers of malaria, the present study aimed to: (i) investigate the occurrence and survival rate of Ke. cruzii based on the distinct vegetation profiles found in areas across the coastal region of the Brazilian Atlantic Forest biome; (ii) estimate the extrinsic incubation period (EIP) and survival rates of P. vivax and P. falciparum parasites in Ke. cruzii under current and future scenarios. The potential distribution of Plasmodium spp. was estimated using simulation analyses under distinct scenarios of average temperature increases from 1 °C to 3.7 °C. Our results showed that two conditions are necessary to explain the occurrence and survival of Ke. cruzii: warm temperature and presence of the Atlantic Forest biome. Moreover, both Plasmodium species showed a tendency to decrease their EIP and increase their estimated survival rates in a scenario of higher temperature. Our findings support that the high-risk malaria areas may include the southern region of the distribution range of the Atlantic Forest biome in the coming years. Despite its limitations and assumptions, the present study provides robust evidence of areas with potential to be impacted by malaria incidence in a future scenario. These areas should be monitored in the next decades regarding the occurrence of the mosquito vector and the potential for malaria persistence and increased occurrence.

Evidence for family-level variation of phenotypic traits in response to temperature of Brazilian Nyssorhynchus darlingi

BACKGROUND

Nyssorhynchus darlingi (also known as Anopheles darlingi) is the primary malaria vector in the Amazon River Basin. In Brazil, analysis of single nucleotide polymorphisms (SNPs) previously detected three major population clusters, and a common garden experiment in a laboratory setting revealed significant population variation in life history traits. Increasing temperatures and local level variation can affect life history traits, i.e. adult longevity, that alter vectorial capacity with implications for malaria transmission in Ny. darlingi.

METHODS

We investigated the population structure of Ny. darlingi from 7 localities across Brazil utilizing SNPs and compared them to a comprehensive Ny. darlingi catalog. To test the effects of local level variation on life history traits, we reared F1 progeny from the 7 localities at three constant temperatures (20, 24 and 28 °C), measuring key life history traits (larval development, food-starved adult lifespan, adult size and daily survival).

RESULTS

Using nextRAD genotyping-by-sequencing, 93 of the field-collected Ny. darlingi were genotyped at 33,759 loci. Results revealed three populations (K = 3), congruent with major biomes (Amazonia, Cerrado and Mata Atlântica), with greater FST values between biomes than within. In the life history experiments, increasing temperature reduced larval development time, adult lifespan, and wing length in all localities. The variation of family responses for all traits within four localities of the Amazonia biome was significant (ANOVA, P < 0.05). Individual families within localities revealed a range of responses as temperature increased, for larval development, adult lifespan, wing length and survival time.

CONCLUSIONS

SNP analysis of several Brazilian localities provided results in support of a previous study wherein populations of Ny. darlingi were clustered by three major Brazilian biomes. Our laboratory results of temperature effects demonstrated that population variation in life history traits of Ny. darlingi exists at the local level, supporting previous research demonstrating the high plasticity of this species. Understanding this plasticity and inherent variation between families of Ny. darlingi at the local level should be considered when deploying intervention strategies and may improve the likelihood of successful malaria elimination in South America.

Minimal genetic differentiation of the malaria vector Nyssorhynchus darlingi associated with forest cover level in Amazonian Brazil

The relationship between deforestation and malaria in Amazonian Brazil is complex, and a deeper understanding of this relationship is required to inform effective control measures in this region. Here, we are particularly interested in characterizing the impact of land use and land cover change on the genetics of the major regional vector of malaria, Nyssorhynchus darlingi (Root). We used nextera-tagmented, Reductively Amplified DNA (nextRAD) genotyping-by-sequencing to genotype 164 Ny. darlingi collected from 16 collection sites with divergent forest cover levels in seven municipalities in four municipality groups that span the state of Amazonas in northwestern Amazonian Brazil: São Gabriel da Cachoeira, Presidente Figueiredo, four municipalities in the area around Cruzeiro do Sul, and Lábrea. Using a dataset of 5,561 Single Nucleotide Polymorphisms (SNPs), we investigated the genetic structure of these Ny. darlingi populations with a combination of model- and non-model-based analyses. We identified weak to moderate genetic differentiation among the four municipality groups. There was no evidence for microgeographic genetic structure of Ny. darlingi among forest cover levels within the municipality groups, indicating that there may be gene flow across areas of these municipalities with different degrees of deforestation. Additionally, we conducted an environmental association analysis using two outlier detection methods to determine whether individual SNPs were associated with forest cover level without affecting overall population genetic structure. We identified 14 outlier SNPs, and investigated functions associated with their proximal genes, which could be further characterized in future studies.

Plasmodium infection in Kerteszia cruzii (Diptera: Culicidae) in the Atlantic tropical rain forest, southeastern Brazil

In Southeastern Brazil, Kerteszia cruzii (former Anopheles cruzii), a bromeliad mosquito species, is considered an efficient human Plasmodium spp. vector. In this region, recent studies showed asymptomatic or sub-patent Plasmodium falciparum infection. In areas of the Atlantic coast in Rio de Janeiro, Plasmodium simium infection was recently reported in both human and howler monkey. Considering that (1) few malaria cases are reported each year in areas across the tropical Atlantic rain forest in southeastern Brazil; (2) malaria elimination in Atlantic forest is challenged by circulation of P. falciparum and P. simium in humans; (3) the complexity of malaria epidemiology in this region; and (4) the public health importance of Kerteszia cruzii as a sylvatic vector; the major goal of this study is to evaluate Plasmodium infection in Ke. cruzii. Mosquito sampling collections were conducted in Esteiro do Morro and Sítio Itapuan, in Cananeia municipality, and Tapiraí municipality in Ribeira Valley, southeastern São Paulo state, Brazil. Influence of climate and landscape factors in Plasmodium infection in Ke. cruzii was addressed. Among the 1719 mosquitoes tested, 3 females collected in Sítio Itapuan and three from Tapiraí were found infected with either P. vivax or P. simium. Results of statistical analyses did not demonstrate association between Plasmodium infection in mosquito and the landscape. Mosquito infection was found in two landscape clusters, with Plasmodium detected in forest fringe mosquitoes. This finding shows that Ke. cruzii can facilitate transmission among human and non-human primates. Plasmodium falciparum was not identified in the samples analyzed. Spatiotemporal variation in local malaria incidence, low prevalence of Plasmodium, variations in humidity and temperature can explain the absence of mosquitoes infected with P. falciparum in the study.

Amazon deforestation drives malaria transmission, and malaria burden reduces forest clearing

Deforestation and land use change are among the most pressing anthropogenic environmental impacts. In Brazil, a resurgence of malaria in recent decades paralleled rapid deforestation and settlement in the Amazon basin, yet evidence of a deforestation-driven increase in malaria remains equivocal. We hypothesize an underlying cause of this ambiguity is that deforestation and malaria influence each other in bidirectional causal relationships-deforestation increases malaria through ecological mechanisms and malaria reduces deforestation through socioeconomic mechanisms-and that the strength of these relationships depends on the stage of land use transformation. We test these hypotheses with a large geospatial dataset encompassing 795 municipalities across 13 y (2003 to 2015) and show deforestation has a strong positive effect on malaria incidence. Our results suggest a 10% increase in deforestation leads to a 3.3% increase in malaria incidence (∼9,980 additional cases associated with 1,567 additional km² lost in 2008, the study midpoint, Amazon-wide). The effect is larger in the interior and absent in outer Amazonian states where little forest remains. However, this strong effect is only detectable after controlling for a feedback of malaria burden on forest loss, whereby increased malaria burden significantly reduces forest clearing, possibly mediated by human behavior or economic development. We estimate a 1% increase in malaria incidence results in a 1.4% decrease in forest area cleared (∼219 fewer km² cleared associated with 3,024 additional cases in 2008). This bidirectional socioecological feedback between deforestation and malaria, which attenuates as land use intensifies, illustrates the intimate ties between environmental change and human health.