The genetic basis of host preference and resting behavior in the major African malaria vector, Anopheles arabiensis

Malaria transmission is dependent on the propensity of Anopheles mosquitoes to bite humans (anthropophily) instead of other dead end hosts. Recent increases in the usage of Long Lasting Insecticide Treated Nets (LLINs) in Africa have been associated with reductions in highly anthropophilic and endophilic vectors such as Anopheles gambiae s.s., leaving species with a broader host range, such as Anopheles arabiensis, as the most prominent remaining source of transmission in many settings. An. arabiensis appears to be more of a generalist in terms of its host choice and resting behavior, which may be due to phenotypic plasticity and/or segregating allelic variation. To investigate the genetic basis of host choice and resting behavior in An. arabiensis we sequenced the genomes of 23 human-fed and 25 cattle-fed mosquitoes collected both in-doors and out-doors in the Kilombero Valley, Tanzania. We identified a total of 4,820,851 SNPs, which were used to conduct the first genome-wide estimates of “SNP heritability”for host choice and resting behavior in this species. A genetic component was detected for host choice (human vs cow fed; permuted P = 0.002), but there was no evidence of a genetic component for resting behavior (indoors versus outside; permuted P = 0.465). A principal component analysis (PCA) segregated individuals based on genomic variation into three groups which were characterized by differences at the 2Rb and/or 3Ra paracentromeric chromosome inversions. There was a non-random distribution of cattle-fed mosquitoes between the PCA clusters, suggesting that alleles linked to the 2Rb and/or 3Ra inversions may influence host choice. Using a novel inversion genotyping assay, we detected a significant enrichment of the standard arrangement (non-inverted) of 3Ra among cattle-fed mosquitoes (N = 129) versus all non-cattle-fed individuals. Thus, tracking the frequency of the 3Ra in An. arabiensis populations may be of use to infer selection on host choice behavior within these vector populations; possibly in response to vector control. Controlled host-choice assays are needed to discern whether the observed genetic component has a direct relationship with innate host preference. A better understanding of the genetic basis for host feeding behavior in An. arabiensis may also open avenues for novel vector control strategies based on driving genes for zoophily into wild mosquito populations

ANTI-MOSQUITO BEHAVIOR OF ADULT AND JUVENILE WHITE-FOOTED MICE (PEROMYSCUS LEUCOPUS) (TREEHOLE MOSQUITO, AEDES TRISERIATUS, EPIDEMIOLOGY)

Rodents seldom are identified as hosts for mosquitoes, based on serological analysis of bloodmeals. However, due to limited survey and lack of sensitivity in most bloodmeal analyses, host species can be misrepresented or undetected. Knowledge of behavior of a potential host species can complement results of bloodmeal analysis, because active vertebrates may prevent mosquito feeding and thus rarely serve as hosts. The objectives of this study were to characterize anti-mosquito behavior in the white-footed mouse (Peromyscus leucopus noveboracensis) and to examine effectiveness of such behavior in mice based on age, prior exposure to mosquitoes, and immediate environment. I used wild-stock Aedes triseriatus mosquitoes, reared in lab, in experiments with four groups of mice: (1) wild-caught adult males in a barren enclosure; (2) wild-caught adult males in an enclosure with seeds and nest material that could be manipulated, simulating natural activity; (3) adult males from a lab colony of P. leucopus; and (4) wild-stock, lab-reared juveniles with or without practice (prior exposure to mosquitoes). I used an electronic event recorder to monitor grooming, exploring, resting, and anti-mosquito actions. I observed each mouse without and then with mosquitoes. I then anesthetized each mouse to verify that lack of mosquito feeding success on the non-anesthetized (active) mouse was due to mouse behavior. Results indicated that the role of prior exposure to mosquitoes was minimal. Wild adult mice maintained defense while handling and eating seeds, implying that anti-mosquito behavior probably is an integral part of their activity in nature. Certain actions, such as ear-flick, occurred almost exclusively when mosquitoes were present. Juveniles usually caught, killed, and ate more mosquitoes than did adults. Individuality of mouse behavior affected the outcome of mouse-mosquito interactions. All mice, except one, had highly effective defense against mosquitoes. Therefore, P. leucopus probably rarely serves as host for mosquitoes in nature and, thus, as host or reservoir for mosquito-borne diseases

Oviposition in the blood-sucking insect Rhodnius prolixus is modulated by host odors

Background: Triatomine bugs are blood-sucking insects, vectors of Chagas disease. Despite their importance, their oviposition behavior has received relatively little attention. Some triatomines including Rhodnius prolixus stick their eggs to a substrate. It is known that mechanical cues stimulate oviposition in this species. However, it is not clear if chemical signals play a role in this behavior. We studied the role of host cues, including host odor, in the oviposition behavior of the triatomine R. prolixus. Methods: Tests were carried out in an experimental arena and stimuli consisted of a mouse or hen feathers. The number of eggs laid and the position of those eggs with respect to the stimulus source were recorded. Data were analyzed using the Mann-Whitney and Kruskal-Wallis tests. Results: Both a mouse and hen feathers stimulated oviposition. In addition, hen feathers evoked a particular spatial distribution of eggs that was not observed in the case of mouse. Conclusions: We propose that volatile chemical cues from the host play a role in the oviposition behavior of triatomines that stick their eggs. Thus, host odor would stimulate and spatially guide oviposition.Fil: Guidobaldi, Fabio. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Guerenstein, Pablo Gustavo. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentin

Aggregation Behavior of a Willow Flea Beetle, \u3ci\u3eAltica Subplicata\u3c/i\u3e (Coleoptera: Chrysomelidae)

This study examined the aggregation behavior of a specialist insect herbivore, Altica subplicata (Coleoptera: Chrysomelidae), on its host plant, Salix cordata. Mark-recapture experiments were conducted in patches of S. cordata growing along the shores of Lake Huron. Beetles aggregated on individual host plants, but did not aggregate in larger areas containing many host plants. Plants colonized by marked beetles had significantly higher abundances of unmarked beetles than did plants that were not colonized by marked beetles. Experimental manipulations of the number of beetles present on plants showed that colonization rates by marked beetles were higher on plants with conspecifics than on plants which had all beetles removed the previous day. The sex of beetles, however, did not influence colonization behavior; both male and female beetles colonized plants regardless of the sex of beetles already present on plants. These results are discussed with respect to possible explanations for aggregation, and the role of aggregation and movement in influencing insect distributions

Touch-stimulation increases host-seeking behavior in Steinernema Carpocapsae.

Previous research demonstrated that Steinernema carpocapsae infective juveniles (IJs) exposed to a host cuticle were more attracted toward certain host-associated volatile odors. We wanted to test the specificity of attraction that results from exposure to host cuticle. Host recognition behavior was analyzed after stimulating IJs by allowing them to physically interact with Galleria mellonella cuticles. The subsequent behavioral response and the proportion of the population participating in chemotaxis to multiple host odors were measured. We found that exposure to host cuticles resulted in a significantly higher percentage of the population participating in host-seeking behavior, with threefold more nematodes participating in chemotaxis. We tested whether exposure to live or dead host cuticle resulted in a different response and found that a higher percentage of IJs exposed to a live host cuticle participated in chemotaxis than IJs exposed to a dead host cuticle, but that IJs exposed to a dead host demonstrated significantly higher participation than was observed for non-stimulated IJs. To test whether the increase in IJ participation in host-seeking behaviors after exposure to a live host cuticle was specific, we exposed stimulated IJs to a known repulsive odor, a neutral odor, and two predicted attractants. We found that stimulation of IJs through physical contact with a host cuticle induces a specific enhancement of host-seeking behavior to host-specific odors rather than a general increased chemotactic response to all volatile stimuli. However, the nematodes displayed an enhanced response to multiple host-specific odors. Future work should focus on the mechanism through which contact with live host cuticle stimulates increased behavioral response.Previous research demonstrated that Steinernema carpocapsae infective juveniles (IJs) exposed to a host cuticle were more attracted toward certain host-associated volatile odors. We wanted to test the specificity of attraction that results from exposure to host cuticle. Host recognition behavior was analyzed after stimulating IJs by allowing them to physically interact with Galleria mellonella cuticles. The subsequent behavioral response and the proportion of the population participating in chemotaxis to multiple host odors were measured. We found that exposure to host cuticles resulted in a significantly higher percentage of the population participating in host-seeking behavior, with threefold more nematodes participating in chemotaxis. We tested whether exposure to live or dead host cuticle resulted in a different response and found that a higher percentage of IJs exposed to a live host cuticle participated in chemotaxis than IJs exposed to a dead host cuticle, but that IJs exposed to a dead host demonstrated significantly higher participation than was observed for non-stimulated IJs. To test whether the increase in IJ participation in host-seeking behaviors after exposure to a live host cuticle was specific, we exposed stimulated IJs to a known repulsive odor, a neutral odor, and two predicted attractants. We found that stimulation of IJs through physical contact with a host cuticle induces a specific enhancement of host-seeking behavior to host-specific odors rather than a general increased chemotactic response to all volatile stimuli. However, the nematodes displayed an enhanced response to multiple host-specific odors. Future work should focus on the mechanism through which contact with live host cuticle stimulates increased behavioral response

Studies of intercellular invasion in vitro using rabbit peritoneal neutrophil granulocytes (PMNS). I. Role of contact inhibition of locomotion.

Intercellular invasion is the active migration of cells on one type into the interiors of tissues composed of cells of dissimilar cell types. Contact paralysis of locomotion is the cessation of forward extension of the pseudopods of a cell as a result of its collision with another cell. One hypothesis to account for intercellular invasion proposes that a necessary condition for a cell type to be invasive to a given host tissue is that it lack contact paralysis of locomotion during collision with cells of that host tissue. The hypothesis has been tested using rabbit peritoneal neutrophil granulocytes (PMNs) as the invasive cell type and chick embryo fibroblasts as the host tissue. In organ culture, PMNs rapidly invade aggregates of fibroblasts. The behavior of the pseudopods of PMNs during collision with fibroblasts was analyzed for contact paralysis by a study of time-lapse films of cells in mixed monolayer culture. In monolayer culture, PMNs show little sign of paralysis of the pseudopods upon collision with fibroblasts and thus conform in their behavior to that predicted by the hypothesis

Modeling microevolution in a changing environment: The evolving quasispecies and the Diluted Champion Process

Several pathogens use evolvability as a survival strategy against acquired immunity of the host. Despite their high variability in time, some of them exhibit quite low variability within the population at any given time, a somehow paradoxical behavior often called the evolving quasispecies. In this paper we introduce a simplified model of an evolving viral population in which the effects of the acquired immunity of the host are represented by the decrease of the fitness of the corresponding viral strains, depending on the frequency of the strain in the viral population. The model exhibits evolving quasispecies behavior in a certain range of its parameters, ans suggests how punctuated evolution can be induced by a simple feedback mechanism.Comment: 15 pages, 12 figures. Figures redrawn, some additional clarifications in the text. To appear in Journal of Statistical Mechanics: Theory and Experimen

Behavior out of control: experimental evolution of resistance to host manipulation

Many parasites alter their host's phenotype in a manner that enhances their own fitness beyond the benefits they would gain from normal exploitation. Such host manipulation is rarely consistent with the host's best interests resulting in suboptimal and often fatal behavior from the host's perspective. In this case, hosts should evolve resistance to host manipulation. The cestode Schistocephalus solidus manipulates the behavior of its first intermediate copepod host to reduce its predation susceptibility and avoid fatal premature predation before the parasite is ready for transmission to its subsequent host. Thereafter, S. solidus increases host activity to facilitate transmission. If successful, this host manipulation is necessarily fatal for the host. I selected the copepod Macrocyclops albidus, a first intermediate host of S. solidus, for resistance or susceptibility to host manipulation to investigate their evolvability. Selection on the host indeed increased host manipulation in susceptible and reduced host manipulation in resistant selection lines. Interestingly, this seemed to be at least partly due to changes in the baseline levels of the modified trait (activity) rather than actual changes in resistance or susceptibility to host manipulation. Hence, hosts seem restricted in how rapidly and efficiently they can evolve resistance to host manipulation

Universal behavior of dispersive Dirac cone in gradient-index plasmonic metamaterials

We demonstrate analytically and numerically that the dispersive Dirac cone emulating an epsilon-near-zero (ENZ) behavior is a universal property within a family of plasmonic crystals consisting of two-dimensional (2D) metals. Our starting point is a periodic array of 2D metallic sheets embedded in an inhomogeneous and anisotropic dielectric host that allows for propagation of transverse-magnetic (TM) polarized waves. By invoking a systematic bifurcation argument for arbitrary dielectric profiles in one spatial dimension, we show how TM Bloch waves experience an effective dielectric function that averages out microscopic details of the host medium. The corresponding effective dispersion relation reduces to a Dirac cone when the conductivity of the metallic sheet and the period of the array satisfy a critical condition for ENZ behavior. Our analytical findings are in excellent agreement with numerical simulations