A spider that feeds indirectly on vertebrate blood by choosing female mosquitoes as prey

The evolution of sanguivory in vampire bats: origins and convergences

Blood-feeding (sanguivory) has evolved more than two dozen times among birds, fishes, insects, arachnids, molluscs, crustaceans, and annelids; however, among mammals, it is restricted to the vampire bats. Here, the authors revisit the question of how it evolved in that group. Evidence to date suggests that the ancestors of phyllostomids were insectivorous, and that carnivory, omnivory, and nectarivory evolved among phyllostomids after vampire bats diverged. Frugivory likely also evolved after vampire bats diverged, but the phylogeny is ambiguous on that point. However, vampire bats lack any genetic evidence of a frugivorous past, and the behavioural progression from frugivory to sanguivory is difficult to envision. Thus, the most parsimonious scenario is that sanguivory evolved in an insectivorous ancestor to vampire bats via ectoparasite-eating, wound-feeding, or some combination of the two—all feeding habits found among blood-feeding birds today. Comparing vampire bats with other sanguivores, the authors find several remarkable examples of convergence. Further, it was found that blood-feeding has been ca. 50 times more likely to evolve in a vertebrate lineage than in an invertebrate one. The authors hypothesize that this difference exists because vertebrates are more likely than invertebrates to have the biochemical necessities required to assimilate the components of vertebrate blood.

Could species-focused suppression of Aedes aegypti, the yellow fever mosquito, and Aedes albopictus, the tiger mosquito, affect interacting predators? An evidence synthesis from the literature

The risks of Aedes aegypti and Aedes albopictus nuisance and vector-borne diseases are rising and the adverse effects of broad-spectrum insecticide application have promoted species-specific techniques, such as sterile insect technique (SIT) and other genetic strategies, as contenders in their control operations. When specific vector suppression is proposed, potential effects on predators and wider ecosystem are some of the first stakeholder questions. These are not the only Aedes vectors of human diseases, but are those for which SIT and genetic strategies are of most interest. They vary ecologically and in habitat origin, but both have behaviorally human-adapted forms with expanding ranges. The aquatic life stages are where predation is strongest due to greater resource predictability and limited escape opportunity. These vectors' anthropic forms usually use ephemeral water bodies and man-made containers as larval habitats; predators that occur in these are mobile, opportunistic and generalist. No literature indicates that any predator depends on larvae of either species. As adults, foraging theory predicts these mosquitoes are of low profitability to predators. Energy expended hunting and consuming will mostly outweigh their energetic benefit. Moreover, as adult biomass is mobile and largely disaggregated, any predator is likely to be a generalist and opportunist. This work, which summarizes much of the literature currently available on the predators of Ae. aegypti and Ae. albopictus, indicates it is highly unlikely that any predator species depends on them. Species-specific vector control to reduce nuisance and disease is thus likely to be of negligible or limited impact on nontarget predators. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Novel decorating behaviour of silk retreats in a challenging habitat

Many ecological interactions of spiders with their potential prey and predators are affected by the visibility of their bodies and silk, especially in habitats with lower structural complexity that expose spiders. For instance, the surface of tree trunks harbours relatively limited structures to hide in and may expose residents to visual detection by prey and predators. Here we provide the first detailed description of the novel retreat building strategy of the tree trunk jumping spider Arasia mullion. Using fields surveys, we monitored and measured over 115 spiders and 554 silk retreats. These spiders build silk retreats on the exposed surface of tree trunks, where they remain as sedentary permanent residents. Furthermore, the spiders decorate the silk retreats with bark debris that they collect from the immediate surrounding. We discuss the role of silk decoration in the unusual sedentary behaviour of these spiders and the potential mechanisms that allow A. mullion to engineer their niche in a challenging habitat.

Spatial acuity-sensitivity trade-off in the principal eyes of a jumping spider: possible adaptations to a 'blended' lifestyle

Jumping spiders (Salticidae) are diurnal visual predators known for elaborate, vision-mediated behaviour achieved through the coordinated work of four pairs of camera-type eyes. One pair ('principal' eyes) is responsible for colour and high spatial acuity vision, while three pairs ('secondary' eyes) are mostly responsible for motion detection. Based on its unusual capacity to visually discriminate specific prey in very low, but also under bright light settings, we investigated the structure of the principal and one pair of secondary eyes (antero-lateral eyes) of Cyrba algerina to determine how these eyes achieve the sensitivity, while maintaining spatial acuity, needed to sustain behaviour in low light. Compared to salticids that live in bright light, the principal eyes of C. algerina have a short focal length, and wide contiguous twin rhabdomeres that support optical pooling, overall favouring sensitivity (0.39 μm²), but without fully compromising acuity (12.4 arc min). The antero-lateral eye retinae have large receptors surrounded by pigment granules, providing effective shielding from scattered light. These adaptations may be beneficial for a xeric salticid species with a 'blended' lifestyle: generally living and hunting under stones in the dark, but sometimes venturing above them, in dramatically different light conditions.

Jumping spiders: An exceptional group for comparative cognition studies

Several non-mutually exclusive hypotheses have been proposed to explain the evolution of cognition in animals. Broadly, these hypotheses fall under two categories: those that pertain to the selective pressures exerted either by sociality or by the ecological niche in which animals live. We review these ideas and then discuss why the highly visual jumping spiders (Salticidae) are excellent models for investigating how cognitive ability evolves. With few exceptions, these behaviorally complex spiders are non-social, making them ideal candidates to explore ideas pertaining to selection based on habitat complexity and selection based on predatory behavior (foraging niche hypotheses). With the exception of Antarctica, salticids are found in all habitats on Earth, ranging from very complex to barren and simple. While many species are generalist predators, a minority also have specialized predatory behavior and prey specialization on dangerous prey, which has been proposed as an explanation for advanced cognitive ability. As this large group has a diversity of habitats in which it lives, diverse predatory behavior, as well as some "social" species, we argue that salticids are ideal candidates for comparative studies to explore the myriad selection factors acting upon a group well known for their cognitive prowess, despite having miniature brains.

Odour priming of a mosquito-specialist predator's vision-based detouring decisions

A capacity to execute long detours that are planned ahead of time has cognitive implications pertaining to reliance on internal representation. Here we investigate the detouring behaviour of Evarcha culicivora, an East African salticid spider that specializes at preying on blood-carrying mosquitoes. The findings from our experiments are the first evidence of a salticid making detouring plans based on whether the path chosen leads to more preferred instead of less preferred prey, as well as the first evidence of olfactory priming effects on motivation and selective attention in the context of detouring. Test spiders began on top of a starting platform from which, in some trials, they could view lures on top of two poles and, in some trials, the odour of blood-carrying mosquitoes was also present. When odour was present and prey were visible, significantly more test spiders took a detour and chose a pole than when only odour was present (prey not visible) or when prey were visible but odour was absent. When odour was present, test spiders also significantly more often chose the pole holding a blood-carrying mosquito instead of the pole holding another prey type.

Predation interactions among henhouse-dwelling arthropods, with a focus on the poultry red mite Dermanyssus gallinae

BACKGROUND

Analysis of the poorly explored food webs of henhouse-dwelling arthropods would improve biological control against the poultry red mite (PRM) Dermanyssus gallinae (De Geer). This study aimed to identify trophic links among native predatory arthropods, PRM, and alternative preys. In vitro predation tests were carried out to assess (i) the ability of native predators to feed on PRM juvenile and adult stages in two physiological statuses (unfed and freshly blood-fed) in the absence of any physical barrier, (ii) predator preferences between PRM and astigmatic mites, and (iii) predation interactions between PRM predators.

RESULTS

Ten arthropod taxa fed on PRM with predation rates ranging from 4% to 95% in our experimental conditions. They belonged to (i) Acari: Androlaelaps casalis (Berlese), Cheyletus spp., Macrocheles muscaedomesticae (Scopoli), M. penicilliger (Berlese), Parasitus fimetorum (Berlese), Dendrolaelaps spp. and Uroobovella fimicola (Berlese); (ii) other Arachnida: Lamprochernes nodosus (Schrank) (Pseudoscorpionida) and a linyphiid spider; and (iii) Insecta: Lyctocoris campestris (Fabricius). These predators varied in their preference for PRM stages and physiological statuses (unfed or freshly blood-fed). When given a choice, most predators preferred to feed on PRM than astigmatic mites. Bidirectional predation occurred within two pairs of PRM predators (M. penicilliger-Lamprochernes nodosus and A. casalis-Cheyletus spp.), and M. penicilliger had a 100% predation rate on A. casalis.

CONCLUSION

Our study highlights the potential of various arthropod predators occurring naturally in poultry houses for conservation and augmentative biological control of PRM. Predation interactions between these predators should be accounted for before developing biocontrol agents against PRM. © 2020 Society of Chemical Industry.

Widespread army ant aversion among East African jumping spiders (Salticidae)

Jumping spiders (Salticidae) typically prey on a variety of arthropods of similar size to themselves, but rarely on ants. Using 28 salticid species from East Africa, we first investigated vision-based aversion to ants by recording latency to enter a transparent sealed chamber flanked by chambers containing living army ants (Dorylus sp.) or tsetse flies (Glossina pallidipes) of comparable size. For all species, entry latency was significantly longer when the stimuli were ants. In another experiment, we used dead ants and tsetse flies mounted in a life-like posture as stimuli; except for Goleba puella, a species with unusual retinal ultrastructure, we again found significantly longer entry latency when the stimuli were ants. Our findings imply that these salticids express an aversion specifically to ants even when restricted to using vision alone and, except for G. puella, even when relying on solely the static appearance of the insects. Having used salticids from laboratory cultures with no prior experience with ants, our findings are consistent with vision-based aversion to army ants being innate.

Influence of seeing a red face during the male-male encounters of mosquito-specialist spiders

Males of Evarcha culicivora, an East African jumping spider (Salticidae), have bright red faces. Here, we investigated how seeing a red face might influence a male's behaviour during encounters with another male. We applied black eyeliner to conceal the red on a male's face and measured the spectral properties of male faces with and without the eyeliner. Only the faces without eyeliner reflected in the long-wavelength range corresponding to red. In experiments over 2 days, where eyeliner was absent on the first day and present on the second, we compared how two groups of males responded to their mirror images. Face Group: eyeliner concealed their faces. Head Group: eyeliner was applied to the tops of the males' heads instead of on their faces. The males from both groups displayed to their mirror image as if it were a living same-sex conspecific. However, when they could see a red face, males in the face group escalated to higher levels of aggression to their mirror image and initiated displaying from farther away than when the red had been concealed. We also found that the influence of eyeliner was stronger for the face group than for the head group. These findings suggest that, when seeing a red face, E. culicivora males become more confident that the individual in view is another male.

The visual spectral sensitivity of the Chilean recluse spider Loxosceles laeta

Spiders are a large group of arthropods and nearly omnipresent in warm and temperate climates. They rely on tactile and visual information to hunt and breed, but compared with their mechanical senses, little is known about their visual systems. In this study, we analyzed the visual spectral sensitivity of the Chilean recluse spider Loxosceles laeta, a synanthropic species posing a significant threat to humans, using electroretinogram recordings of its three eye types and open field tests with localized chromatic illumination for behavioral analysis. The electroretinogram displayed two sensitivity peaks in the ultraviolet and green ranges, and no differences were observed between the three eye types and between male and female specimens. Selective chromatic adaptation reduced overall light sensitivity, but did not support the expression of more than one type of rhodopsin in photoreceptors. The open field tests revealed a preference for corners over side areas, and an increased exploration of open field areas illuminated by shorter wavelength (violet to green) light compared with non-illuminated areas, while no behavioral responses to red and near-infrared light were observed. These data suggest that L. laeta has monochromatic vision without spectral specializations in its three secondary eye pairs.

Oviposition preferences of the mosquito Aedes aegypti Linnaeus, 1762 (Culicidae): an urban environment bioassay

The establishment of an invasive species depends on reproductive success and dispersion capability in the new environment. One of the striking examples of invasion in urban environments is the mosquito Aedes aegypti Linnaeus, 1762 (Culicidae). The success of this species is primarily attributed to its ability to colonize urban environments, and some of the important adaptive strategies associated with this ability is the preference for humans as a blood source and intense occupation of residential (indoor) environments. This study evaluated the effects of location (indoor vs. outdoor) and water nutrient level (% organic matter) on the oviposition preference of A. aegypti in an urban environment. We used oviposition choice experiments to evaluate mosquito oviposition in containers holding 1:1 vs 1:0 ratios of water: organic matter placed indoors and outdoors. Eggs were sampled once per week for nine weeks. Our results revealed a strong oviposition preference for outdoor containers, with a significant preference for containers with higher concentrations of organic matter during the fifth to ninth weeks. However, mosquitoes occupying indoor environments did not prefer to lay eggs in containers with lower levels of organic matter. A better understanding of the preferences of A. aegypti regarding the nutrient level and location of oviposition containers can increase our understanding of the behavioral factors allowing mosquitoes to utilize anthropogenic environments.

Dim-light vision in jumping spiders (Araneae, Salticidae): identification of prey and rivals

Jumping spiders (family Salticidae) are known for their intricate vision-based behavior during encounters with prey and conspecific individuals. This is achieved using eyes specialized for discerning fine detail, but there has been minimal research on the capacity that salticids might have for visual performance under low ambient light levels. Here, we investigated the capacity of two salticid species, Cyrba algerina from Portugal and Cyrba ocellata from Kenya, to perform two specific visual tasks under low ambient light levels. We used lures made from spiders and midges in prey-identification experiments and mirror images (virtual conspecifics) in rival-identification experiments. These experiments were implemented under a range of ambient light levels (234, 1.35, 0.54, 0.24 cd m^-2). In most instances, C algerina and C ocellata were proficient at performing both of these visual tasks when ambient light was 234 and 1.35 cd m^-2, and a minority performed these tasks at 0.54 cd m^-2, but none succeeded when the light level was 0.24 cd m^-2 Cyrba algerina and C. ocellata showed vision-based discrimination under low ambient light levels previously associated with nocturnal species.

Effects of the removal or reduction in density of the malaria mosquito, Anopheles gambiae s.l., on interacting predators and competitors in local ecosystems

New genetic control methods for mosquitoes may reduce vector species without direct effects on other species or the physical environment common with insecticides or drainage. Effects on predators and competitors could, however, be a concern as Anopheles gambiae s.l. is preyed upon in all life stages. We overview the literature and assess the strength of the ecological interactions identified. Most predators identified consume many other insect species and there is no evidence that any species preys exclusively on any anopheline mosquito. There is one predatory species with a specialisation on blood-fed mosquitoes including An. gambiae s.l.. Evarcha culicivora is a jumping spider, known as the vampire spider, found around Lake Victoria. There is no evidence that these salticids require Anopheles mosquitoes and will readily consume blood-fed Culex. Interspecific competition studies focus on other mosquitoes of larval habitats. Many of these take place in artificial cosms and give contrasting results to semi-field studies. This may limit their extrapolation regarding the potential impact of reduced An. gambiae numbers. Previous mosquito control interventions are informative and identify competitive release and niche opportunism; so while the identity and relative abundance of the species present may change, the biomass available to predators may not.

Record breaking achievements by spiders and the scientists who study them

Organismal biology has been steadily losing fashion in both formal education and scientific research. Simultaneous with this is an observable decrease in the connection between humans, their environment, and the organisms with which they share the planet. Nonetheless, we propose that organismal biology can facilitate scientific observation, discovery, research, and engagement, especially when the organisms of focus are ubiquitous and charismatic animals such as spiders. Despite being often feared, spiders are mysterious and intriguing, offering a useful foundation for the effective teaching and learning of scientific concepts and processes. In order to provide an entryway for teachers and students-as well as scientists themselves-into the biology of spiders, we compiled a list of 99 record breaking achievements by spiders (the "Spider World Records"). We chose a world-record style format, as this is known to be an effective way to intrigue readers of all ages. We highlighted, for example, the largest and smallest spiders, the largest prey eaten, the fastest runners, the highest fliers, the species with the longest sperm, the most venomous species, and many more. We hope that our compilation will inspire science educators to embrace the biology of spiders as a resource that engages students in science learning. By making these achievements accessible to non-arachnologists and arachnologists alike, we suggest that they could be used: (i) by educators to draw in students for science education, (ii) to highlight gaps in current organismal knowledge, and (iii) to suggest novel avenues for future research efforts. Our contribution is not meant to be comprehensive, but aims to raise public awareness on spiders, while also providing an initial database of their record breaking achievements.

Ontogenetic shift in plant-related cognitive specialization by a mosquito-eating predator

Evarcha culicivora, an East African salticid spider, is a mosquito specialist and it is also a plant specialist, with juveniles visiting plants primarily for acquiring nectar meals and adults visiting plants primarily as mating sites. The hypothesis we consider here is that there are ontogenetic shifts in cognition-related responses by E. culicivora to plant odour. Our experiments pertain to cross-modality priming effects in three specific contexts: executing behaviour that we call the 'visual inspection of plants' (Experiment 1), adopting selective visual attention to specific visual targets (Experiment 2) and becoming prepared to respond rapidly to specific visual targets (Experiment 3). Our findings appear not to be a consequence of salient odours in general elevating E. culicivora's motivation to respond to salient visual stimuli. Instead, effects were specific to particular odours paired with particular visual targets, with the salient volatile plant compounds being caryophyllene and humulene. We found evidence that prey odour primes juveniles and adults to respond to seeing specifically prey, mate odour primes adults to respond to seeing specifically mates and plant odour primes juveniles to respond to seeing specifically flowers. However, plant odour appears to prime adults to respond to seeing specifically a mate associated with a plant.

Results from the Workshop "Problem Formulation for the Use of Gene Drive in Mosquitoes"

Reducing the incidence of malaria has been a public health priority for nearly a century. New technologies and associated vector control strategies play an important role in the prospect of sustained reductions. The development of the CRISPR/Cas9 gene editing system has generated new possibilities for the use of gene-drive constructs to reduce or alter vector populations to reduce malaria incidence. However, before these technologies can be developed and exploited, it will be necessary to understand and assess the likelihood of any potential harms to humans or the environment. To begin this process, the Foundation for the National Institutes of Health and the International Life Sciences Institute Research Foundation organized an expert workshop to consider the potential risks related to the use of gene drives in Anopheles gambiae for malaria control in Africa. The resulting discussion yielded a series of consensus points that are reported here.

Mosquitoes of field and forest: the scale of habitat segregation in a diverse mosquito assemblage

Knowledge of the distribution of arthropod vectors across a landscape is important in determining the risk for vector-borne disease. This has been well explored for ticks, but not for mosquitoes, despite their importance in the transmission of a variety of pathogens. This study examined the importance of habitat, habitat edges, and the scale at which mosquito abundance and diversity vary in a rural landscape by trapping along transects from grassland areas into forest patches. Significant patterns of vector diversity and distinct mosquito assemblages across habitats were found. The scale of individual species' responses to habitat edges was often dramatic, with several species rarely straying even 10 m from the edge. The present results suggest blood-seeking mosquito species are faithful to certain habitats, which has consequences for patterns of vector diversity and risk for pathogen transmission. This implies that analysts of risk for pathogen transmission and foci of control, and developers of land management strategies should assess habitat at a finer scale than previously considered.

Convergence between a mosquito-eating predator's natural diet and its prey-choice behaviour

On the basis of 1115 records of Evarcha culicivora feeding in the field, we can characterize this East African jumping spider (Salticidae) as being distinctively stenophagic. We can also, on the basis of laboratory prey-choice experiments, characterize E. culicivora as having a specialized prey-classification system and a hierarchy of innate preferences for various categories of mosquitoes and other arthropods. Prey from the field belonged to 10 arthropod orders, but 94.5% of the prey records were dipterans. Mosquitoes were the dominant prey (80.2% of the records), with the majority (82.9%) of the mosquitoes being females, and thereafter midges were the most common prey (9.2% of the records). Preference profiles that were determined from experiments showed strong convergence with natural diet in some, but not all, instances. In experiments, E. culicivora adults appeared to distinguish between six prey categories and juveniles between seven, with blood-carrying anopheline female mosquitoes being ranked highest in preference. For adults, this was followed by blood-carrying culicine female mosquitoes and then anopheline female mosquitoes not carrying blood, but these two preferences were reversed for juveniles. Moreover, for juveniles, but not for adults, anopheline male mosquitoes seem to be a distinct prey category ranked in preference after blood-carrying culicine females and, for both adults and juveniles, preference for midges is evident when the alternatives are not mosquitoes. These findings illustrate the importance of going beyond simply specifying preferred prey categories when characterizing predators as 'specialized' and a need to make clear conceptual distinctions between a predator's natural diet, the prey categories that are relevant to the predator, and the predator's prey-choicebehaviour.

Rapid nectar-meal effects on a predator's capacity to kill mosquitoes

Using Evarcha culicivora, an East African jumping spider (Salticidae), we investigate how nectar meals function in concert with predation specifically at the juvenile stage between emerging from the egg sac and the first encounter with prey. Using plants and using artificial nectar consisting of sugar alone or sugar plus amino acids, we show that the plant species (Lantana camara, Ricinus communis, Parthenium hysterophorus), the particular sugars in the artificial nectar (sucrose, fructose, glucose, maltose), the concentration of sugar (20%, 5%, 1%) and the duration of pre-feeding fasts (3 days, 6 days) influence the spider's prey-capture proficiency on the next day after the nectar meal. However, there were no significant effects of amino acids. Our findings suggest that benefits from nectar feeding are derived primarily from access to particular sugars, with fructose and sucrose being the most beneficial, glucose being intermediate and maltose being no better than a water-only control.

Natural history and display behaviour of Servaea incana, a common and widespread Australian jumping spider (Araneae : Salticidae)

The natural history and intraspecific interactions of Servaea incana, a common jumping spider of temperate Australia, are described. S. incana inhabits the trunks of eucalypt trees, where it builds silken retreats and nests under loose bark. Like other jumping spiders, S. incana males use elaborate visual displays (Type I courtship) when they encounter females in the open. Male jumping spiders usually rely on silk-borne vibrations to communicate with females residing within retreats and nests (Type II courtship). S. incana often uses visual displays in this context, because the thin silken walls allow conspecifics to see each other. Adult males that encounter subadult females at retreats sometimes build their own retreat nearby and cohabit until the subadult female moults to maturity, copulating shortly afterwards. Adult females and immature stages of both sexes possess similar display repertoires that contain fewer display elements than the repertoire of males. We found no evidence that visual displays of S. incana contain seismic elements, in contrast to some of its closest relatives. S. incana preys upon a variety of small arthropods and, unusually amongst salticids, ants make up a large portion of the diet. Identified enemies of S. incana include spiders, a pompilid wasp and a mantispid.

Intricate predatory decisions by a mosquito-specialist spider from Malaysia

Paracyrba wanlessi is a southeast Asian jumping spider (Salticidae) that lives in the hollow internodes of fallen bamboo and preys on the larvae, pupae and adults of mosquitoes. In contrast to Evarcha culicivora, an East African salticid that is also known for actively targeting mosquitoes as preferred prey, there was no evidence of P. wanlessi choosing mosquitoes on the basis of species, sex or diet. However, our findings show that P. wanlessi chooses mosquitoes significantly more often than a variety of other prey types, regardless of whether the prey are in or away from water, and regardless of whether the mosquitoes are adults or juveniles. Moreover, a preference for mosquito larvae, pupae and adults is expressed regardless of whether test spiders are maintained on a diet of terrestrial or aquatic prey and regardless of whether the diet includes or excludes mosquitoes. Congruence of an environmental factor (in water versus away from water) with prey type (aquatic versus terrestrial mosquitoes) appeared to be important and yet, even when the prey were in the incongruent environment, P. wanlessi continued to choose mosquitoes more often than other prey.

Innate pattern recognition and categorization in a jumping spider

The East African jumping spider Evarcha culicivora feeds indirectly on vertebrate blood by preferentially preying upon blood-fed Anopheles mosquitoes, the vectors of human malaria¹, using the distinct resting posture and engorged abdomen characteristic of these specific prey as key elements for their recognition. To understand perceptual categorization of objects by these spiders, we investigated their predatory behavior toward different digital stimuli - abstract ‘stick figure’ representations of Anopheles constructed solely by known key identification elements, disarranged versions of these, as well as non-prey items and detailed images of alternative prey. We hypothesized that the abstract images representing Anopheles would be perceived as potential prey, and would be preferred to those of non-preferred prey. Spiders perceived the abstract stick figures of Anopheles specifically as their preferred prey, attacking them significantly more often than non-preferred prey, even when the comprising elements of the Anopheles stick figures were disarranged and disconnected from each other. However, if the relative angles between the elements of the disconnected stick figures of Anopheles were altered, the otherwise identical set of elements was no longer perceived as prey. These data show that E. culicivora is capable of making discriminations based on abstract concepts, such as the hypothetical angle formed by discontinuous elements. It is this inter-element angle rather than resting posture that is important for correct identification of Anopheles. Our results provide a glimpse of the underlying processes of object recognition in animals with minute brains, and suggest that these spiders use a local processing approach for object recognition, rather than a holistic or global approach. This study provides an excellent basis for a comparative analysis on feature extraction and detection by animals as diverse as bees and mammals.

Cross-modality effects of prey odour during the intraspecific interactions of a mosquito-specialist predator

One of the predictions from evolutionary game theory is that individuals will increase their willingness (i.e., become primed) to escalate aggression when they detect the presence of a limiting resource. Here we test this prediction in the context of prey odour priming escalation decisions during vision-based encounters by Evarcha culicivora. This East African jumping spider (Salticidae) feeds indirectly on vertebrate blood by actively choosing blood-carrying female mosquitoes as preferred prey. Unlike many salticid species, it also expresses pronounced mutual mate choice. As predicted, we show here that, in the presence of odour from their preferred prey, both sexes of E. culicivora escalate during vision-based same-sex encounters. This is further evidence that the odour of blood-carrying mosquitoes is salient to this salticid. For both sexes of E. culicivora, this particular prey may be a resource that matters in the context of intrasexual selection.

Role in diuresis of a calcitonin receptor (GPRCAL1) expressed in a distal-proximal gradient in renal organs of the mosquito Aedes aegypti (L.)

Evolution of anthropophilic hematophagy in insects resulted in the coordination of various physiological processes for survival. In female mosquitoes, a large blood meal provides proteins for egg production and as a trade-off, rapid elimination of the excess water and solutes (Na(+), Cl(-)) is critical for maintaining homeostasis and removing excess weight to resume flight and avoid predation. This post-prandial excretion is achieved by the concerted action of multiple hormones. Diuresis and natriuresis elicited by the calcitonin-like diuretic hormone 31 (DH(31)) are believed to be mediated by a yet uncharacterized calcitonin receptor (GPRCAL) in the mosquito Malpighian tubules (MTs), the renal organs. To contribute knowledge on endocrinology of mosquito diuresis we cloned GPRCAL1 from MT cDNA. This receptor is the ortholog of the DH(31) receptor from Drosophila melanogaster that is expressed in principal cells of the fruit fly MT. Immunofluorescence similarly showed AaegGPRCAL1 is present in MT principal cells in A. aegypti, however, exhibiting an overall gradient-like pattern along the tubule novel for a GPCR in insects. Variegated, cell-specific receptor expression revealed a subpopulation of otherwise phenotypically similar principal cells. To investigate the receptor contribution to fluid elimination, RNAi was followed by urine measurement assays. In vitro, MTs from females that underwent AaegGPRcal1 knock-down exhibited up to 57% decrease in the rate of fluid secretion in response to DH(31). Live females treated with AaegGPRcal1 dsRNA exhibited 30% reduction in fluid excreted after a blood meal. The RNAi-induced phenotype demonstrates the critical contribution of this single secretin-like family B GPCR to fluid excretion in invertebrates and highlights its relevance for the blood feeding adaptation. Our results with the mosquito AaegGPRCAL1 imply that the regulatory function of calcitonin-like receptors for ion and fluid transport in renal organs arose early in evolution.

Love is in the air: olfaction-based mate-odour identification by jumping spiders from the genus Cyrba

Jumping spiders (Salticidae) are known for having good eyesight, but the extent to which they rely on olfaction is poorly understood. Here we demonstrate for the first time that olfactory pheromones are used by two species from the salticid genus Cyrba (C. algerina and C. ocellata). Using a Y-shape olfactometer, we investigated the ability of adult males and females of both species to discriminate between mate and non-mate odour. A hidden spider or a spider’s draglines (no spider present) were used as odour sources. There was no evident response by females of either Cyrba species to any tested odour. Males of both species chose odour from conspecific females, or their draglines, significantly more often than the no-odour control, but there was no evident response by males to any of the other odours (conspecific male and heterospecific female). Our findings demonstrate that C. algerina and C. ocellata males can make sex- and species-specific discriminations even when restricted to using olfaction alone. Also, by showing that draglines can be a source of olfactory pheromones, our findings illustrate the difficulty of ruling out olfaction when attempting to test for chemotactile cues.

The discerning predator: decision rules underlying prey classification by a mosquito-eating jumping spider

Evarcha culicivora is an East African jumping spider that feeds indirectly on vertebrate blood by choosing blood-fed female Anopheles mosquitoes as prey. Previous studies have shown that this predator can identify its preferred prey even when restricted to using only visual cues. Here, we used lures and virtual mosquitoes to investigate the optical cues underlying this predator's prey-choice behaviour. We made lures by dissecting and then reconstructing dead mosquitoes, combining the head plus thorax with different abdomens. Depending on the experiment, lures were either moving or motionless. Findings from the lure experiments suggested that, for E. culicivora, seeing a blood-fed female mosquito's abdomen on a lure was a necessary, but not sufficient, cue by which preferred prey was identified, as cues from the abdomen needed to be paired with cues from the head and thorax of a mosquito. Conversely, when abdomens were not visible or were identical, spiders based their decisions on the appearance of the head plus thorax of mosquitoes, choosing prey with female characteristics. Findings from a subsequent experiment using animated 3D virtual mosquitoes suggest that it is specifically the mosquito's antennae that influence E. culicivora's prey-choice decisions. Our results show that E. culicivora uses a complex process for prey classification.

Evarcha culicivora chooses blood-fed Anopheles mosquitoes but other East African jumping spiders do not

Previous research using computer animation and lures made from dead prey has demonstrated that the East African salticid Evarcha culicivora Wesolowska & Jackson (Araneae: Salticidae) feeds indirectly on vertebrate blood by actively choosing blood-carrying female mosquitoes as prey, and also that it singles out mosquitoes of the genus Anopheles (Diptera: Culicidae) by preference. Here, we demonstrate that E. culicivora's preference is expressed when the species is tested with living prey and that it is unique to E. culicivora. As an alternative hypothesis, we considered the possibility that the preference for blood-fed female anopheline mosquitoes might be widespread in East African salticids. When live-prey choice tests were carried out in 19 additional species, there were no instances in which blood-carrying mosquitoes were chosen significantly more often than other prey. Combined with the findings of previous work, these results suggest that it is possible that specialized predators play a role in the biological control of disease vectors.

Evolution of stenophagy in spiders (Araneae): evidence based on the comparative analysis of spider diets

Stenophagy (narrow diet breadth) represents an extreme of trophic specialization in carnivores, but little is known about the forces driving its evolution. We used spiders, the most diversified group of terrestrial predators, to investigate whether stenophagy (1) promoted diversification; (2) was phylogenetically conserved and evolutionarily derived state; and (3) was determined either by geographical distribution and foraging guild. We used published data on the prey of almost 600 species. Six categories of stenophagy were found: myrmecophagy, araneophagy, lepidopterophagy, termitophagy, dipterophagy, and crustaceophagy. We found that the species diversity of euryphagous genera and families was similar to stenophagous genera and families. At the family level, stenophagy evolved repeatedly and independently. Within families, the basal condition was oligophagy or euryphagy. Most types of stenophagy were clearly derived: myrmecophagy in Zodariidae; lepidopterophagy in Araneidae; dipterophagy in Theridiidae. In contrast, araneophagy was confined to basal and intermediate lineages, suggesting its ancestral condition. The diet breadth of species from the tropics and subtropics was less diverse than species from the temperate zone. Diet breadth was lower in cursorial spiders compared to web-building species. Thus, the evolution of stenophagy in spiders appears to be complex and governed by phylogeny as well as by ecological determinants.

Salticid predation as one potential driving force of ant mimicry in jumping spiders

Many spiders possess myrmecomorphy, and species of the jumping spider genus Myrmarachne exhibit nearly perfect ant mimicry. Most salticids are diurnal predators with unusually high visual acuity that prey on various arthropods, including conspecifics. In this study, we tested whether predation pressure from large jumping spiders is one possible driving force of perfect ant mimicry in jumping spiders. The results showed that small non-ant-mimicking jumping spiders were readily treated as prey by large ones (no matter whether heterospecific or conspecific) and suffered high attack and mortality rates. The size difference between small and large jumping spiders significantly affected the outcomes of predatory interactions between them: the smaller the juvenile jumping spiders, the higher the predation risk from large ones. The attack and mortality rates of ant-mimicking jumping spiders were significantly lower than those of non-ant-mimicking jumping spiders, indicating that a resemblance to ants could provide protection against salticid predation. However, results of multivariate behavioural analyses showed that the responses of large jumping spiders to ants and ant-mimicking salticids differed significantly. Results of this study indicate that predation pressure from large jumping spiders might be one selection force driving the evolution of nearly perfect myrmecomorphy in spiders and other arthropods.

Olfaction-based anthropophily in a mosquito-specialist predator

Evarcha culicivora is an unusual salticid spider because it feeds indirectly on vertebrate blood by choosing blood-carrying mosquitoes as preferred prey. Its preferred mosquitoes are Anopheles, the genus to which all human malaria vectors belong. Here, we show that human odour, which is known to be salient to malaria vectors, is also salient to the adults and juveniles of E. culicivora. Test spiders spent more time in the vicinity of a source of human odour (previously worn socks) when the alternative was unworn socks.

Establishment of a self-propagating population of the African malaria vector Anopheles arabiensis under semi-field conditions

Background

The successful control of insect disease vectors relies on a thorough understanding of their ecology and behaviour. However, knowledge of the ecology of many human disease vectors lags behind that of agricultural pests. This is partially due to the paucity of experimental tools for investigating their ecology under natural conditions without risk of exposure to disease. Assessment of vector life-history and demographic traits under natural conditions has also been hindered by the inherent difficulty of sampling these seasonally and temporally varying populations with the limited range of currently available tools. Consequently much of our knowledge of vector biology comes from studies of laboratory colonies, which may not accurately represent the genetic and behavioural diversity of natural populations. Contained semi-field systems (SFS) have been proposed as more appropriate tools for the study of vector ecology. SFS are relatively large, netting-enclosed, mesocosms in which vectors can fly freely, feed on natural plant and vertebrate host sources, and access realistic resting and oviposition sites.

Methods

A self-replicating population of the malaria vector Anopheles arabiensis was established within a large field cage (21 × 9.1 × 7.1 m) at the Ifakara Health Institute, Tanzania that mimics the natural habitat features of the rural village environments where these vectors naturally occur. Offspring from wild females were used to establish this population whose life-history, behaviour and demography under semi-field conditions was monitored over 24 generations.

Results

This study reports the first successful establishment and maintenance of an African malaria vector population under SFS conditions for multiple generations (> 24). The host-seeking behaviour, time from blood feeding to oviposition, larval development, adult resting and swarming behaviour exhibited by An. arabiensis under SFS conditions were similar to those seen in nature.

Conclusions

This study presents proof-of-principle that populations of important African malaria vectors can be established within environmentally realistic, contained semi-field settings. Such SFS will be valuable tools for the experimental study of vector ecology and assessment of their short-term ecological and longer-term evolutionary responses to existing and new vector control interventions.

Olfactory search-image use by a mosquito-eating predator

By choosing blood-carrying mosquitoes as prey, Evarcha culicivora, an East African salticid spider, specializes at feeding indirectly on vertebrate blood. It also has an exceptionally complex mate-choice system. An earlier study revealed that search-image use assists E. culicivora in finding prey and mates when restricted to using vision alone. Here we show that search-image use assists E. culicivora in finding prey and mates when restricted to using olfaction alone. After being primed with prey odour or mate odour (control: not primed with odour), spiders were transferred to an olfactometer designed to test ability to find a prey-odour or mate-odour source that was either 'cryptic' (i.e. accompanied by a masking odour source, Lantana camara) or 'conspicuous' (no L. camara odour). When tested with conspicuous odour, the identity of the priming odour had no significant effect on how many spiders found the odour source. However, when tested with cryptic odour, significantly more spiders found the odour source when primed with congruent odour and significantly fewer spiders found the odour source when primed with incongruent odour.