Water Strider Research Articles

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

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

Increased female resistance to mating promotes the effect of mechanical constraints on latency to pair.

Size‐assortative mating, defined as a positive linear association of body size between members of mating pairs, can arise from mechanical constraints on pairing efficiency, particularly when mating success is affected by males’ mate‐grasping force. In this context, female resistance is predicted to have an important role in changing the threshold force necessary for males to hold females, thereby contributing to the effect of mechanical constraints. Thus, increased female resistance is expected to increase the paring success of an optimally sized male relative to the female body size (sexual size ratio = male body size/female body size = 0.86), which leads to positive size‐assortative mating. However, very little is known about the extent to which female resistance affects mechanical constraints on mate grasping. Here, using the water strider Gerris gracilicornis (Hemiptera: Gerridae), we tested whether the level of female resistance affected the relationship between the sexual size ratio and latency to pair. We found that optimally sized males mated sooner than other males when females resisted a male's mating attempts. When females did not resist, an effect of sexual size ratio on latency to pair was not found. Our results thus imply that increased female resistance to male mating attempts may strengthen the pattern of size‐assortative mating. We provide clear empirical evidence that female resistance to mating influences the effect of mechanical constraints on size‐assortative mating under sexual conflict. This result further suggests that patterns of size‐assortative mating can be altered by a variety of ecological circumstances that change female resistance to mating in many other animal species under sexual conflict.

Walking of spider on water surface studied from its leg shadows**Project supported by the National Natural Science Foundation of China (Grant Nos. 51323006 and 51425502) and the Tribology Science Fund of State Key Laboratory of Tribology (Grant No. SKLTKF17B18).

Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases: slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.

Does sexual conflict increase juvenile survival by reducing cannibalism?

To test the hypothesis that male harassment of females reduces adult female time spent on the water foraging (water use), and thus cannibalism by adult females on juveniles, we manipulated heterospecific prey availability, and social context in adult water striders and measured their effects on: 1) cannibalism of juveniles, 2) activity of adults and 3) habitat use of adults and juveniles. Cannibalism rarely occurred with alternative prey present, but was common without alternative prey. Without alternative prey, females cannibalized much more than males, but contrary to predictions, male presence did not reduce cannibalism rates. Male presence decreased female water use; however, this was counteracted by the fact that the lack of alternative prey increased female water use and activity while on the water. Furthermore, in groups of 4 males with 4 females, lack of alternative prey reduced male activity while on the water. Thus the predicted negative effect of sexual conflict on cannibalism was reduced by female and male responses to low food availability. Juveniles increased time off the water when more females or males were more on the water and active. Overall, cannibalism rates depended on alternative prey, male-female social dynamics, female foraging and juvenile refuge use.

Simple RAM Control for Water Strider Robot

In this paper, we propose a RAM (Rotate and Move) controller by considering the WSR (Water Strider Robot) with two wheels. The proposed controller commands to move straight after rotating to track the desired trajectory by applying the two wheel WSR characteristics. In this paper, a proportional controller is applied to make the error zero and there is a room to apply many other nonlinear controllers. For a given target point, the rotation angle is computed at first and the shorter rotating angle is chosen between CW (clockwise) and CCW (counterclockwise). After accomplishing rotation, the WSR moves straight toward the target point. The proposed controller is noble and simple and easily track the target point and the simulation results proves the good performance and this controller will be applied to the developing prototype WSR.

Water striders (Heteroptera: Gerromorpha: Gerridae) of Romania with an update on the distribution of Gerris gibbifer and G. maculatus in southeastern Europe

The Romanian fauna comprises two species of Aquarius Schellenberg, 1800, eight species of Gerris Fabricius, 1794 and one species of Limnoporus Stål, 1868, and we hereby update the distribution and provide insights on the phenology and ecology of all eleven species in this country. We furthermore update the distribution of the two closely related species Gerris gibbifer Schummel, 1832 and G. maculatus Tamanini, 1946 in southeastern Europe. Gerris maculatus is recorded for the first time from Hungary, Montenegro and Slovenia, and the first detailed localities from Romania and Serbia are given. All bibliographic records of G. gibbifer from Romania, Macedonia and Serbia are based on misidentification and this species is thus excluded from the faunal lists of these countries. Both G. gibbifer and G. maculatus occur in Croatia, Hungary, Ukraine, and probably Slovenia.

Unsteady wave pattern generation by water striders

We perform an experimental and theoretical study of the wave pattern generated by the leg strokes of water striders during a propulsion cycle. Using the synthetic schlieren method, we are able to measure the dynamic response of the free surface accurately. In order to match experimental conditions, we extend Bühler’s theory of impulsive forcing (J. Fluid Mech., vol. 573, 2007, pp. 211–236) to finite depth. We demonstrate the improved ability of this approach to reproduce the experimental findings, once the observed continuous forcing and hence non-zero temporal and spatial extent of the leg strokes is also taken into account.

From water striders to water bugs: the molecular diversity of aquatic Heteroptera (Gerromorpha, Nepomorpha) of Germany based on DNA barcodes.

With about 5,000 species worldwide, the Heteroptera or true bugs are the most diverse taxon among the hemimetabolous insects in aquatic and semi-aquatic ecosystems. Species may be found in almost every freshwater environment and have very specific habitat requirements, making them excellent bioindicator organisms for water quality. However, a correct determination by morphology is challenging in many species groups due to high morphological variability and polymorphisms within, but low variability between species. Furthermore, it is very difficult or even impossible to identify the immature life stages or females of some species, e.g., of the corixid genus Sigara. In this study we tested the effectiveness of a DNA barcode library to discriminate species of the Gerromorpha and Nepomorpha of Germany. We analyzed about 700 specimens of 67 species, with 63 species sampled in Germany, covering more than 90% of all recorded species. Our library included various morphological similar taxa, e.g., species within the genera Sigara and Notonecta as well as water striders of the genus Gerris. Fifty-five species (82%) were unambiguously assigned to a single Barcode Index Number (BIN) by their barcode sequences, whereas BIN sharing was observed for 10 species. Furthermore, we found monophyletic lineages for 52 analyzed species. Our data revealed interspecific K2P distances with below 2.2% for 18 species. Intraspecific distances above 2.2% were shown for 11 species. We found evidence for hybridization between various corixid species (Sigara, Callicorixa), but our molecular data also revealed exceptionally high intraspecific distances as a consequence of distinct mitochondrial lineages for Cymatia coleoptrata and the pygmy backswimmer Plea minutissima. Our study clearly demonstrates the usefulness of DNA barcodes for the identification of the aquatic Heteroptera of Germany and adjacent regions. In this context, our data set represents an essential baseline for a reference library for bioassessment studies of freshwater habitats using modern high-throughput technologies in the near future. The existing data also opens new questions regarding the causes of observed low inter- and high intraspecific genetic variation and furthermore highlight the necessity of taxonomic revisions for various taxa, combining both molecular and morphological data.

Propulsion Principles of Water Striders in Sculling Forward through Shadow Method

Semi-aquatic arthropods skate on water surfaces with synergetic actions of their legs. The sculling forward locomotion of water striders was observed and analyzed in situ to understand and reproduce the abovementioned feature. The bright–edged elliptical shadows of the six legs of a water strider were recorded to derive the supporting force distributions on legs. The propulsion principles of water striders were quantitatively disclosed. A typical sculling forward process was accomplished within approximately 0.15 s. Water striders lifted their heads slightly and supported their weight mainly by the two driving legs to increase the propulsion force and reduce the water resistance during the process. The normalized thrust–area ratio (defined as the ratio of the propulsion force to the projected area) was usually lower than 0.4 after sculling for approximately 0.08 s. The entire normal supporting force remained nearly constant during a stroke to reduce the mass center fluctuation in the normal direction. In addition, water striders could easily control the locomotion direction and speed through the light swinging of the two hind legs as rudders. These sculling principles might inspire sophisticated biomimetic water-walking robots with high propulsion efficiency in the future.

A unique new species of halophilous water strider of the genus Aquarius Schellenberg (Hemiptera: Gerridae: Gerrinae) endemic to Omura Bay, Nagasaki, Japan

AbstractA new species of halophilous water strider, Aquarius haliplous Yasunaga, Asanabe, and Nagashima new species (Hemiptera: Gerridae: Gerrinae), is diagnosed and described. This species is endemic to Omura Bay, Nagasaki, southwestern Japan, and has a unique adaptation to this mixohaline habitat. Based on unique morphology and ecology both in the adult and immature forms, this new Aquarius Schellenberg species can be separated unequivocally from a similar species inhabiting freshwater, A. paludum (Fabricius). A key is provided to facilitate identification of the Japanese species and subspecies of Aquarius.

Morphological and histological structure of the male reproductive system of the water strider Gerris lacustris (Linnaeus 1758) (Gerridae, Heteroptera).

This work presents the male reproductive system morphology and histology of the water strider Gerris lacustris (Linnaeus 1758) (Gerridae, Heteroptera) using light microscopy and scanning electron microscopy. The male reproductive system of G. lacustris comprise of a pair of testes, two vasa deferentia, two seminal vesicles, an ejaculatory duct. There is no bulbus ejaculatorius and the long vas deferantia uniting to form a simple ductus ejaculatorius which is connected to the aedeagus. The testes are white colored and this cylindiric-shaped structure lies along genital abdominal segment. The testicular follicles have three different development zones (growth zone, maturation zone, differentiation zone). Each testis has two follicles, which are not lined by a common peritoneal sheath and involving many cysts arranged in a progressive order of maturation from the distal to the proximal region; spermiogenesis occurs in mature males, finishing with the organization of sperm bundles. The testes are connected to the seminal vesicles, specialized sperm storage places, by the vas deferentia.

Notes on Water Striders (Heteroptera: Gerridae) in Southwest Iran with a Description of a New Macropterous Form of Metrocoris communis (Distant, 1910)

In a sample collection trip across Fars Province, Iran, Gerris thoracicus, G. costae, G. argentatus, and Metrocoris communis were found and macropterous form of M. communis is described for the first time.

Does Population Density Determine the Mating Strategy in Males of the Water Strider Aquarius paludum?

Mating behavior of a large Aquarius paludum paludum (Fabricius 1794) (Hemiptera: Gerridae: Gerrini) population was investigated on several field surveys during the mating season. Both types of mating behavior known for semi-aquatic true bugs were observed in the studied population: aggressive Type I mating for non-territorial males and unaggressive Type II mating for the territorial males. Some males establish individual territories at the lake shores that they defend for around one hour and switch to aggressive mating if they fail to attract a female to mate, while most males remain non-territorial. Radial 1–1.5 meter territories were aggressively defended from other males, conflicts being always won by the male already occupying the territory. The presence of Type II males is conditioned by the absence of sufficient space for all males to establish territories. Contact guarding was much longer than documented before for A. paludum paludum, lasting for at least 12–13 hours in some cases. Based on the observations and on the existing information on the group, a more comprehensive classification of mating behavior of true bugs is proposed: Type I - non-territorial, unsignaled grasping, with contact guarding; Type II - territorial, signaled mounting with noncontact guarding; Type III - non-territorial, signaled mounting with contact guarding.

Hydrophobic modification of nanoscale zero-valent iron with excellent stability and floatability for efficient removal of floating oil on water

Usually, nanoscale zero-valent iron (NZVI) cannot float on water because of high density and hydrophilic surface. Herein, alkyltrimethoxysilanes with different carbon chain lengths (C1, C8 and C16) were used as “water-repellent legs” to graft onto NZVI, enduing NZVI with hydrophobic and floatable characteristics like a water strider. The hydrophobic performance of as-modified NZVI materials was found to be better when NZVI was modified by alkyltrimethoxysilane with longer carbon chain, and a large contact angle of 151.2°(>150°) was obtained in C16-NZVI, indicating the superhydrophobic characteristic of C16-NZVI. The oil-absorption experiments showed that the absorption capacity of C16-NZVI for lubricating oil reached 9.73 g/g within 30 s. After seven consecutive runs, the oil-absorption capacity of C16-NZVI still maintained at 9.26 g/g, indicating high reusability of C16-NZVI. Also, C16-NZVI exhibited excellent stability in NaCl solution without being oxidized for 32 d. Significantly, C16-NZVI possessed admirable chemical stability with high hydrophobic property in acid and alkaline solutions (pH 3–12). Considering the advantages of easy preparation, high stability and reusability, excellent oil-absorption capacity as well as magnetic recovery property, C16-NZVI is expected to have remarkable potential in the treatment of floating oil on water/seawater.

Protein Nanosheet Mechanics Controls Cell Adhesion and Expansion on Low-Viscosity Liquids

Adherent cell culture typically requires cell spreading at the surface of solid substrates to sustain the formation of stable focal adhesions and assembly of a contractile cytoskeleton. However, a few reports have demonstrated that cell culture is possible on liquid substrates such as silicone and fluorinated oils, even displaying very low viscosities (0.77 cSt). Such behavior is surprising as low viscosity liquids are thought to relax much too fast (<ms) to enable the stabilization of focal adhesions (with lifetimes on the order of minutes to hours). Here we show that cell spreading and proliferation at the surface of low viscosity liquids are enabled by the self-assembly of mechanically strong protein nanosheets at these interfaces. We propose that this phenomenon results from the denaturation of globular proteins, such as albumin, in combination with the coupling of surfactant molecules to the resulting protein nanosheets. We use interfacial rheology and atomic force microscopy indentation to characterize the mechanical properties of protein nanosheets and associated liquid-liquid interfaces. We identify a direct relationship between interfacial mechanics and the association of surfactant molecules with proteins and polymers assembled at liquid-liquid interfaces. In addition, our data indicate that cells primarily sense in-plane mechanical properties of interfaces, rather than relying on surface tension to sustain spreading, as in the spreading of water striders. These findings demonstrate that bulk and nanoscale mechanical properties may be designed independently, to provide structure and regulate cell phenotype, therefore calling for a paradigm shift for the design of biomaterials in regenerative medicine.

Mobility of free surface in different liquids and its influence on water striders locomotion

Dynamics of the surface layer in different liquids is examined by means of infrared thermography of the surface and simultaneous velocity fields measurements using surface and infrared Particle Image Velocimetry. This technique allows measurements and comparison of two velocity fields—at the surface and at small depth about 50–200 μm. In distilled water the velocity fields at the surface and at small depth exhibit significant dissimilarity. The flow field below the surface is essentially 3D, whereas the surface flow is characterized by vanishing 2D divergence of velocity, indicating predominantly planar motion. In contrast, in ethanol–butanol mixture two velocity fields are well correlated, both corresponding to 3D flow with continuous surface renewal. Thermal patterns, observed at the surface, and the flow field structure in different liquids are associated with different boundary conditions for velocity at the surface. Water surface is seldom renewed, which inhibits heat and mass exchange between the liquid and atmosphere. However, absence of vertical advection also enables organisms to live within the surface layer, to stand and walk on the free surface. This is illustrated by the difficulties a water strider faces on the surface of ultrapure water, which exhibits Marangoni convection.

The study of dynamic force acted on water strider leg departing from water surface

Water-walking insects such as water striders can skate on the water surface easily with the help of the hierarchical structure on legs. Numerous theoretical and experimental studies show that the hierarchical structure would help water strider in quasi-static case such as load-bearing capacity. However, the advantage of the hierarchical structure in the dynamic stage has not been reported yet. In this paper, the function of super hydrophobicity and the hierarchical structure was investigated by measuring the adhesion force of legs departing from the water surface at different lifting speed by a dynamic force sensor. The results show that the adhesion force decreased with the increase of lifting speed from 0.02 m/s to 0.4 m/s, whose mechanic is investigated by Energy analysis. In addition, it can be found that the needle shape setae on water strider leg can help them depart from water surface easily. Thus, it can serve as a starting point to understand how the hierarchical structure on the legs help water-walking insects to jump upward rapidly to avoid preying by other insects.

Nymph Water Strider's Water-repellency Mechanism by Tack Shape Surface Structure

Nymph Water Strider's Water-repellency Mechanism by Tack Shape Surface Structure

Tertiary water striders (Hemiptera, Gerromorpha, Gerridae) from the central Tibetan Plateau and their palaeobiogeographic implications

The semi-aquatic hemipteran family Gerridae (water striders), similar to other gerromorphan bugs, is a distinct group noted for their ability to walk on the surface of water, especially with respect to their locomotion, feeding, and behaviour. The three principal Holarctic gerrine genera, Aquarius Schellenberg, Gerris Fabricius and Limnoporus Stål, are important organisms for studies of biogeography, evolutionary trends and ecological adaptations of the Gerridae. Fossil gerrids are comparatively sparse, and direct fossil evidence elucidating the early diversification and biogeography of the extant widespread genus Aquarius remains elusive. Here we redescribe and reinterpret the extinct species Aquarius lunpolaensis (Lin, 1981) based on new well-preserved conspecific specimens from contemporaneous localities in the Lunpola and Nima basins of central Tibet, China. The new fossils confirm the placement of these fossils in Aquarius as evidenced by their large body size, first antennal segment longer than the following two segments combined, and well-developed abdominal connexival spines. The new discovery of a series of larval instars at different developmental stages confirms that “Halobates bagonensis” should be interpreted as an exuvium of the dominant species Aquarius lunpolaensis and demonstrates that the extant western Palaearctic najas-group had a much wider distribution in the late Oligocene (Chattian). The occurrence of an Aquarius water skater supports the hypothesis that the elevation of central Tibet was comparatively low, some 25 million years ago.

Female mate choice and the emergence of male coercion

When females choose mates, males may respond in several ways: by allowing an evaluation by the female and investing substantially in subsequent reproduction (here, type 1), by allowing evaluation but withholding investment following mating (type 2), or by preventing evaluation and attempting to coerce the female to mate (type 3). In this modeling analysis, we examine the conditions under which these strategies, individually or in combination, are expected to persist in the population primarily using the criterion of evolutionary stability. We also consider the roles of female resistance, social policing, and extra-pair paternity in influencing these outcomes. Using six focal systems taken from primates, fish, birds, and insects, we derived parameters for a game-theoretical model to determine the expected evolutionary stable frequencies or unstable combinations of the male strategies based on system-specific parameter magnitudes. In chimpanzees, guppies, Japanese water striders, and scorpionflies, males making the highest investment in each reproductive event were the sole persisting type; in mallard ducks, an evolutionarily stable mixture of types 1 and 3 prevailed; and in humans, a stable mixture of types 1 and 2 persisted. In accord with the infrequency of consistent coercion across taxa, our results suggest that coercion may often be evolutionarily unstable and available only opportunistically as the strategy of last resort. Our game theory model examined mate choice in six species of primates, fish birds, and insects to identify patterns predicted to persist from an evolutionary perspective. We found that differences in ecological, physiological, and behavioral characteristics resulted in the persistence of individual or multiple male mating strategies generally consistent with observations in nature. In particular, coercive males could persist in a population when fertilization rates and reproductive outcomes were similar to those of less forceful males.