Water Strider Research Articles

Water repellency of hierarchically structured legs of water-walking striders and fire ants

Some insects have the ability to walk on the surface of water due to their hierarchical leg structure and wax coating. In this study, resistance forces of water strider and fire ant legs to submersion in water, under their various orientations, were quantified using a high-sensitivity microbalance. Legs oriented parallel to the water surface could support up to ten times as much force before immersion compared to legs in a perpendicular orientation. Water pressure affected the seta structure differently at parallel and perpendicular approaches, and complete wetting was more difficult in the structure observed during parallel immersion. The wax coating on water strider legs was found to decrease adhesion force with little effect on immersion force. Overall, wax-coated strider legs, having conical setae with nanogrooves to facilitate removal of water, are natural models for legs of a biomimetic aquatic robot when oriented parallel to the water surface.

Male social plasticity influences transient dynamics in the emergence of alternative mating systems in water striders

AbstractAnimal mating systems are often studied with the goal of understanding why species, populations, or groups vary from one another in the system they display. Although these differences are often treated as basically stable, it is also known that mating systems may shift over time (e.g., from one breeding season to the next). There has been some study of how ecological factors correlate with these changes; however, few, if any, studies have investigated how the phenotypic composition of a group governs the timing and probability of these mating system transitions. Groups of stream water striders (Aquarius remigis) can experience rapid changes in mating system dynamics, with small groups often transitioning into a system in which a single, large male monopolizes mating opportunities. We asked if variation in individual- and group-level traits associated with morphology and behavior (e.g., size of the largest individual, average activity behavioral type in the group) could partially explain the variability in how rapidly groups make this transition, if they make it at all. We show that groups with males that exhibit higher social plasticity tended to take longer to transition to a mating system dominated by a single male. Our results, therefore, suggest that groups in identical ecological conditions can diverge in their mating systems based on how much individuals in the group change their behavior in response to the behavior of other members of the group.

Escalation and Morphological Constraints of Antagonistic Armaments in Water Striders

Sexual conflict may result in the escalating coevolution of sexually antagonistic traits. However, our understanding of the evolutionary dynamics of antagonistic traits and their role in association with sex-specific escalation remains limited. Here we study sexually antagonistic coevolution in a genus of water striders called Rhagovelia. We identified a set of male grasping traits and female anti-grasping traits used during pre-mating struggles and show that natural variation of these traits is associated with variation in mating performance in the direction expected for antagonistic coevolution. Phylogenetic mapping detected signal of escalation of these sexually antagonistic traits suggesting an ongoing arms race. Moreover, their escalation appears to be influenced by a trade-off with dispersal through flight in both sexes. Altogether our results highlight how sexual interactions and natural selection may have shaped sex-specific antagonistic trait coevolution.

Floating robotic insects to obtain electric energy from water surface for realizing some self-powered functions

Abstrct Microrobots that are light and agile possess unique advantages over conventional robots. Key challenges in the design of microrobots include the external power sources and the complex propulsion strategies. Here, inspired by the water strider, we realize a multi-functional self-powered microrobot that can walk on the surface of water, light up a LED and power a temperature sensor, without an external power supply. The self-powering functionality was provided by superhydrophobic wires as the artificial legs of the microrobot, which can obtain electrical energy from water surface with an output voltage of 1.38 V and an output current of 25 mA. We developed a propulsive mechanism with the dynamic coupling of a motor and shape memory alloys to paddle the side superhydrophobic legs of the microrobot, leading to a forward locomotion with an average speed of 1.45 cm/s. Our work could provide open prospects to develop self-powered microrobots in aquatic environments.

Conceptual Model and Interior Design "Water Strider" Ekranoplan

This paper deals with the computer modeling of conceptually new ekranoplan and the design of its passenger salon, from the sketch to a ready model. In this work, features of this type of transport are noted and the review of the current state of the market of small-size ekranoplan of different function is made. Publications concerning a research and model operation of the vessels using wing-in-ground effect during flight are described. The concept of a new ekranoplan on the basis of a biological prototype from the operation environment is offered and visual and graphic solutions of the developed model are provided. Outline drawings, the key operational parameters of an ekranoplan are presented and stage-by-stage three-dimensional model of design parts of the vessel is carried out. For modeling the method of a polygonal extrusion is used and the configuration of passenger salon taking into account ergonomic norms is given. Explicitly stages of modeling of a passenger seat, creation and assignment of materials when shading a scene are considered and the characteristics of sources of lighting, feature of rendering process are specified. The final scenes of realistic rendering are presented, namely the rise of an ekranoplan, an interior of passenger salon and the coastal landing module for an ekranoplan.

Alternative reproductive tactics shape within-species variation in behavioral syndromes

AbstractMultiple behaviors can correlate with each other at the individual level (behavioral syndrome), and behavioral syndromes can vary in their direction between populations within a species. Within-species variation in behavioral syndromes is predicted to be associated with alternative reproductive tactics (ARTs), which evolve under different selection regimes. Here, we tested this using a water strider species, Gerris gracilicornis, in which males employ 2 ARTs that are fixed for life: signaling males (producing courtship ripples) versus nonsignaling males (producing no courtship ripples). We measured multiple behaviors in males with both of these ARTs and compared behavioral syndromes between them. Our results showed that signaling males were more active and attempted to mate more frequently than nonsignaling males. This shaped an overall behavioral syndrome between activities in mating and nonmating contexts when we pooled both ARTs. In addition, the behavioral syndromes between cautiousness and mating activity differed significantly between ARTs. In signaling males, the syndrome was significantly negative: signaling males more eager to mate tended to leave their refuges more rapidly. However, mating activity and cautiousness were not correlated in nonsignaling males. This might be because active males, in the context of predation risk and mating, were favored during the evolution and maintenance of the unique intimidating courtship tactic of G. gracilicornis males. Thus, our findings suggest that ARTs facilitate behavioral divergence and also contribute to the evolution of tactic-specific behavioral syndromes. We also show that research on ARTs and behavioral syndromes can be harmonized to study behavioral variation.

Fluctuating selection strength and intense male competition underlie variation and exaggeration of a water strider's male weapon.

Sexually selected traits can reach high degrees of phenotypic expression and variation under directional selection. A growing number of studies suggest that such selection can vary in space, time and form within and between populations. However, the impact of these fluctuations on sexual trait evolution is poorly understood. In the water strider Microvelia longipes, males display striking trait exaggeration and phenotypic variation manifested as extreme differences in the rear leg length. To study the origin and maintenance of this exaggerated trait, we conducted comparative behavioural, morphometric and reaction norm experiments in a selection of Microvelia species. We uncovered differences both in the mating behaviour and the degree of sexual dimorphism across these species. Interestingly, M. longipes evolved a specific mating behaviour where males compete for egg-laying sites, consisting of small floating objects, to intercept and copulate with gravid females. Through male–male competition assays, we demonstrated that male rear legs are used as weapons to dominate egg-laying sites and that intense competition is associated with the evolution of rear leg length exaggeration. Field observations revealed rapid fluctuation in M. longipes habitat stability and the abundance of egg-laying sites. Paternity tests using genetic markers demonstrated that small males could only fertilize about 5% of the eggs when egg-laying sites are limiting, whereas this proportion increased to about 20% when egg-laying sites become abundant. Furthermore, diet manipulation and artificial selection experiments also showed that the exaggerated leg length in M. longipes males is influenced by both genetic and nutritional factors. Collectively, our results highlight how fluctuation in the strength of directional sexual selection, through changes in the intensity of male competition, can drive the exaggeration and phenotypic variation in this weapon trait.

Fabrication of superwetting surfaces by ultrafast lasers and mechanical durability of superhydrophobic surfaces

With millions of years of evolution, nature developed various unique functional structures and intriguing phenomena, providing inexhaustible insights into design rules for biomimics. As one of those wonderful phenomena, superwetting surfaces, including superhydrophobic and superhydrophilic surfaces, have greatly excited researchers’ curiosity. By mimicking the natural superwetting structures like superhydrophobic lotus leaves, rose petals, butterfly wings, water strider legs etc. and superhydrophilic surfaces such as shark skin, nepenthes and many others, various artificial superwetting surfaces with advanced functions have been developed. It has been shown that the superhydrophobicity of a surface depends on both the low surface energy and the micro/nano scale hierarchical structures which trap air in their asperities. There are many methods to fabricate micro/nano structures, like templating, lithography, sol-gel, electrodeposition, spraying and others. But all these methods have their intrinsic limits, such as complex procedures, involving dangerous chemicals and dependence on material types. On the other hand, the development of ultrafast lasers provides a new powerful tool for micro/nano structures fabrication. As an alternative, ultrafast laser possesses a combination of excellent advantages, such as high efficiency, flexibility and controllability, non-contacting process with small heat-affected zone and high resolution, independence of material types and more, making it a great tool for superwetting micro/nano structures fabrication on solid surfaces. Although remarkable progress has been achieved on the study of superhydrophobic surfaces over the past 20 years, the commercialized practical applications are still very limited. One of the main reasons is attributed to the poor mechanical durability of the prepared superhydrophobic surfaces. Superhydrophobic surfaces are usually vulnerable and can be easily degraded by droplet impact, mechanical scratch, abrasion or vibration and so on, greatly constraining the long-term working performance of superhydrophobic surfaces, which are the hang-ups faced by the researches around the world. Hence, it is important and necessary to summarize the existing research and discuss the challenges faced in mechanical durability of superhydrophobic surfaces, and to review the ongoing research trends in the field of ultrafast laser superwetting surface fabrication. In this review, the recent advances of biomimetic superwetting surfaces fabricated by ultrafast lasers and the mechanical durability of superhydrophobic surfaces are summarized. First, the characteristics and methods of ultrafast laser fabrication are introduced. Then, some well-known natural superwetting surfaces are described. After this, different bio-inspired artificial superwetting surfaces and their potential applications are elaborated in a sequence as follows: Superhydrophobic surfaces, superhydrophobic surfaces with high transparency, superamphiphobic surfaces, superhydrophilic surfaces, hybrid superhydrophobic and superhydrophilic surfaces, smart superhydrophobic surfaces, self-healing superhydrophobic surfaces, slippery liquid-infused porous surfaces and superwetting surfaces with different adhesion and anisotropy. Subsequently, the mechanical durability of superhyrdrophobic surfaces and its testing and characterizing methods are summarized and discussed. In this section, the applicable conditions for each testing method and the methods to improve mechanical durability of superhydrophobic surfaces are discussed. In the end, the problems and challenges faced and the future development prospect in the field of ultrafast laser micro/nano fabrication are discussed. Ultrafast laser surface micro/nano fabrication is a very popular processing method. With the unknown secrets of nature being increasingly revealed and the joint efforts of all scientists and engineers, the research of bio-inspired superwetting surfaces will open a new chapter in modern technology.

Plasticity of Mating Duration in Response to Slightly Biased Operational Sex Ratios in the Water Strider (Aquarius remigis): The Effect of Cohabitation Under Standard Laboratory Conditions

In polygynandrous species, males face the trade-off between the pursuit of increased mating opportunities and securing paternity. Within such systems, males need to accurately assess the social composition of the local environment to maximize fitness. Here, we investigated this capability in the water strider (Aquarius remigis), a semi-aquatic insect known to exhibit a broad spectrum of mating behaviors and inhabit a socially diverse and changing environment. Using a combination of methodological designs to track both within- and between-subject effects, individuals remained in same-sex housing prior to being exposed to slightly biased operational sex ratios (2:1 vs. 1:2) with or without prior cohabitation to determine the effects on mating duration. Results show that males were sensitive to these subtle differences in social conditions, mating for longer periods within male-biased environments, but this was true only under conditions with prior cohabitation. In particular, when individuals could acclimate to the testing environment, mating duration dropped precipitously in female-biased conditions. These findings do not support the view that male water striders have consistent behavioral syndromes, and instead show that individuals are able to differentiate between, and adaptively respond to, small changes in the local sex ratio. In addition to improving our understanding of the plasticity of male mating behavior in this species, this study offers new insights for future laboratory research studying reproductive competition across a diverse range of polygynandrous animals.

Hox genes mediate the escalation of sexually antagonistic traits in water striders.

Sexual conflict occurs when traits favoured in one sex impose fitness costs on the other sex. In the case of sexual conflict over mating rate, the sexes often undergo antagonistic coevolution and escalation of traits that enhance females' resistance to superfluous mating and traits that increase males' persistence. How this escalation in sexually antagonistic traits is established during ontogeny remains unclear. In the water strider Rhagovelia antilleana, male persistence traits consist of sex combs on the forelegs and multiple rows of spines and a thick femur in the rear legs. Female resistance traits consist of a prominent spike-like projection of the pronotum. RNAi knockdown against the Hox gene Sex Combs Reduced resulted in the reduction in both the sex comb in males and the pronotum projection in females. RNAi against the Hox gene Ultrabithorax resulted in the complete loss or reduction of all persistence traits in male rear legs. These results demonstrate that Hox genes can be involved in intra- and inter-locus sexual conflict and mediate escalation of sexually antagonistic traits.

Notes on the morphology and histology of the ovarioles of Gerris lacustris (L.) (water strider) (Insecta: Hemiptera: Heteroptera: Gerridae)

The morphology and histology of the female reproductive system of Gerris lacustris water strider (Linnaeus 1758) (Heteroptera: Gerridae) are described using both light and scanning electron microscopy (SEM). Based on histomorphology, the adult female reproductive system of G. lacustris consists of a pair of ovaries, a pair of lateral oviducts, a common oviduct. The ovaries are connected to a genital aperture by oviducts. Each adult ovary is composed of four telotrophic meroistic type ovarioles. A peritoneal sheath is a thin membranous layer surrounding the entire ovariole. The ovarioles are attached to the dorsal wall of the anterior prothorax by terminal filaments. Each ovariole is divisible into four different regions: the thread like terminal filament followed by the germarium containing nurse cells (trophocytes) and the primordial oocytes, vitellarium containing oocytes at different developmental stages and pedicel (ovariolar stalk, calyx). A long vitellarium is developed composed of a series of oocytes in their folicular sheath. The vitellarium becomes progressively large towards the distal end and the pedicel, in which the mature eggs are lodged before passing into the short lateral oviduct. It opens to the common oviduct.

The achaete-scute complex contains a single gene that controls bristle development in the semi-aquatic bugs.

The semi-aquatic bugs (Heteroptera, Gerromorpha) conquered water surfaces worldwide and diversified to occupy puddles, ponds, streams, lakes, mangroves and even oceans. Critical to this lifestyle is the evolution of sets of hairs that allow these insects to maintain their body weight on the water surface and protect the animals against wetting and drowning. In addition, the legs of these insects are equipped with various grooming combs that are important for cleaning and tidying the hair layers for optimal functional efficiency. Here we show that the hairs covering the legs of water striders represent innervated bristles. Genomic and transcriptomic analyses revealed that in water striders the achaete–scute complex, known to control bristle development in flies, contains only the achaete–scute homologue (ASH) gene owing to the loss of the gene asense. Using RNA interference, we show that ASH plays a pivotal role in the development of both bristles and grooming combs in water striders. Our data suggest that the ASH locus may have contributed to the adaptation to water surface lifestyle through shaping the hydrophobic bristles that prevent water striders from wetting and allow them to exploit water surface tension.

The genome of the water strider Gerris buenoi reveals expansions of gene repertoires associated with adaptations to life on the water

BackgroundHaving conquered water surfaces worldwide, the semi-aquatic bugs occupy ponds, streams, lakes, mangroves, and even open oceans. The diversity of this group has inspired a range of scientific studies from ecology and evolution to developmental genetics and hydrodynamics of fluid locomotion. However, the lack of a representative water strider genome hinders our ability to more thoroughly investigate the molecular mechanisms underlying the processes of adaptation and diversification within this group.ResultsHere we report the sequencing and manual annotation of the Gerris buenoi (G. buenoi) genome; the first water strider genome to be sequenced thus far. The size of the G. buenoi genome is approximately 1,000 Mb, and this sequencing effort has recovered 20,949 predicted protein-coding genes. Manual annotation uncovered a number of local (tandem and proximal) gene duplications and expansions of gene families known for their importance in a variety of processes associated with morphological and physiological adaptations to a water surface lifestyle. These expansions may affect key processes associated with growth, vision, desiccation resistance, detoxification, olfaction and epigenetic regulation. Strikingly, the G. buenoi genome contains three insulin receptors, suggesting key changes in the rewiring and function of the insulin pathway. Other genomic changes affecting with opsin genes may be associated with wavelength sensitivity shifts in opsins, which is likely to be key in facilitating specific adaptations in vision for diverse water habitats.ConclusionsOur findings suggest that local gene duplications might have played an important role during the evolution of water striders. Along with these findings, the sequencing of the G. buenoi genome now provides us the opportunity to pursue exciting research opportunities to further understand the genomic underpinnings of traits associated with the extreme body plan and life history of water striders.

Nature-Inspired and "Water-Skating" Paper and Polyester Substrates Enabled by the Molecular Structure of Poly(γ-stearyl-α,l-glutamate) Homopolypeptide.

We demonstrate that the molecular structure of a synthetic homopolypeptide that resembles the leg architecture of water strider insects is effective to impart flexible polymeric surfaces with superhydrophobic behavior. Filter paper (FP) and polyester (PET) were modified with a coating consisting of low-molecular weight α-helical poly(γ-stearyl-α,l-glutamate) (PSLG, Mw = 4500 Da) homopolypeptide. PSLG-coated substrates displayed near to and superhydrophobic behavior (≥150°) as reflected by the contact angle values. Despite being physically adsorbed, the PSLG coating uniformly covered and was strongly adhered to the substrate surfaces. The thin coating layer displayed remarkable mechanical abrasion resistance and was insensitive to long-time exposure to ambient conditions. PLSG-coated textile fibers exhibited useful and interesting properties. Under an iron-containing load, PSLG-coated PET was able to float and "walk" on water when exposed to a magnet. The PSLG coating was able to reduce the adhesion of Escherichia coli, model Gram-negative bacteria. The results indicated that the molecular geometry of PSLG homopolypeptide, which possesses a α-helical backbone sprouting out of highly hydrophobic stearyl side chains, was the key feature responsible for the observed behaviors. This study is relevant for a broad range of potential applications: from crop and drinking water management in arid geographic areas to biomedical devices and implants.

Identifying Differential Gene Expression in Wing Polymorphism of Adult Males of the Largest Water Strider: De novo Transcriptome Assembly for Gigantometra gigas (Hemiptera: Gerridae).

Wing polymorphism is common in a wide variety of insect species. However, few studies have reported on adaptations in the wing polymorphism of insects at molecular level, in particular for males. Thus, the adaptive mechanisms need to be explored. The remarkable variability in wing morphs of insects is well represented in the water striders (Hemiptera: Gerridae). Within this family, Gigantometra gigas (China, 1925), the largest water strider known worldwide, displays macropterous and apterous males. In the present study, we used de novo transcriptome assembly to obtain gene expression information and compared body and leg-component lengths of adult males in different wing morphs. The analyses in both gene expression and phenotype levels were used for exploring the adaptive mechanism in wing polymorphism of G. gigas. After checking, a series of highly expressed structural genes were found in macropterous morphs, which were related to the maintenance of flight muscles and the enhancement of flight capacity, whereas in the apterous morphs, the imaginal morphogenesis protein-Late 2 (Imp-L2), which might inhibit wing development and increase the body size of insects, was still highly expressed in the adult stage. Moreover, body and leg-component lengths were significantly larger in apterous than in macropterous morphs. The larger size of the apterous morphs and the differences in highly expressed genes between the two wing morphs consistently demonstrate the adaptive significance of wing polymorphism in G. gigas. These results shed light on the future loss-of-function research of wing polymorphism in G. gigas.

Surface swimmers, harnessing the interface to self-propel.

In the study of microscopic flows, self-propulsion has been particularly topical in recent years, with the rise of miniature artificial swimmers as a new tool for flow control, low Reynolds number mixing, micromanipulation or even drug delivery. It is possible to take advantage of interfacial physics to propel these microrobots, as demonstrated by recent experiments using the proximity of an interface, or the interface itself, to generate propulsion at low Reynolds number. This paper discusses how a nearby interface can provide the symmetry breaking necessary for propulsion. An overview of recent experiments illustrates how forces at the interface can be used to generate locomotion. Surface swimmers ranging from the microscopic scale to typically the capillary length are covered. Two systems are then discussed in greater detail. The first is composed of floating ferromagnetic spheres that assemble through capillarity into swimming structures. Two previously studied configurations, triangular and collinear, are discussed and contrasted. A new interpretation for the triangular swimmer is presented. Then, the non-monotonic influence of surface tension and viscosity is evidenced in the collinear case. Finally, a new system is introduced. It is a magnetically powered, centimeter-sized piece that swims similarly to water striders.

Electrospinning: A versatile strategy for mimicking natural creatures

Abstract Natural creatures have developed fascinating structures and properties through billions of years of evolution, which provide valuable sources of inspiration for the human being to prepare specific structural materials. The unique properties of creatures resulting from their special hierarchical structures have attracted increasing attention for the fabrication of biomimetic materials to realize various technological applications. As a simple and versatile strategy, the electrospinning technique holds great potential for fabricating biomimetic nanofibrous materials with large surface area, high porosity, and ease of surface functionalization. In this review, we summarized the recent progress in the design and fabrication of electrospun biomimetic nanofibrous materials inspired by natural creatures including lotus leaf, silver ragwort leaf, water strider leg, polar bear hair, spider web and honeycomb. In addition, the potential applications of the as-prepared electrospun biomimetic materials in self-cleaning, oil/water separation, air filtration, thermal insulation were systematically analyzed. Finally, we discussed the current challenges and future developments in the fabrication of electrospun biomimetic materials.

Water strider-inspired design of a water walking robot using superhydrophobic Al surface

Aquatic microrobots, which can walk freely on water mimicking water striders, have attracted considerable interest among scientists in biomimetic area. Most of previous water strider robots adopted gear pairs as their driving mechanism, which called for high assembly precision and thereby increased the processing difficulty. Here, a novel and simple method using servos as the driving module to prepare water walking robot was proposed. We fabricated this robot by using supporting and actuating legs with excellent superhydrophobicity. Our robot weighted 27.9 g, but could float and run quickly driven by mini-type servos under remote Bluetooth control in mobile terminal. The legs were obtained on Al substrates by chemical etching, boiling-water immersion and low surface energy modification. Then, surface morphology and chemical compositions were subsequently investigated by SEM, EDS and XRD. In order to better illustrate the floating and rowing mechanism of this robot on the water surface, mechanics analysis models were proposed to analyze the lifting force and resistance force, respectively. Due to its excellent floating capacity and rowing ability, the biomimetic robot has promising application potential in water quality monitoring, aquatic exploration, and other surveillance missions.

Sexual conflict in its ecological setting.

Sexual conflict can lead to rapid and continuous coevolution between females and males, without any inputs from varying ecology. Yet both the degree of conflict and selection on antagonistic traits are known to be sensitive to local ecological conditions. This leads to the longstanding question: to what extent does variation in ecological context drive sexually antagonistic coevolution? In water striders, there is much information about the impacts of ecological factors on conflict, and about patterns of antagonistic coevolution. However, the connection between the two is poorly understood. Here, we first review the multiple ways in which ecological context might affect the coevolutionary trajectory of the sexes. We then review ecological and coevolutionary patterns in water striders, and connections between them, in light of theory and new data. Our analysis suggests that ecological variation does impact observed patterns of antagonistic coevolution, but highlights significant uncertainty due to the multiple pathways by which ecological factors can influence conflict and its evolutionary outcome. To the extent that water striders are a reasonable reflection of other systems, this observation serves as both an opportunity and a warning: there is much to learn, but gaining insight may be a daunting process in many systems.This article is part of the theme issue 'Linking local adaptation with the evolution of sex differences'.

Measurement of Dynamic Force Acted on Water Strider Leg Jumping Upward by the PVDF Film Sensor.

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, with its peak locomotion speed reaching 150 cm/s. First of all, we observed the microstructure and hierarchy of water strider legs using the scanning electron microscope. On the basis of the observed morphology of the legs, a theoretical model of the detachment from water surface was established, which explained water striders' capability to slide on water surface effortlessly in terms of energy reduction. Secondly, a dynamic force measurement system was devised using the PVDF film sensor with excellent sensitivity, which could detect the whole interaction process. Subsequently, a single leg in contact with water was pulled upward at different speeds, and the adhesion force was measured at the same time. The results of the departing experiment suggested a deep understanding of the fast jumping of water striders.