Tiny amphibious insects use tripod gait for seamless transition across land, water, and duckweed.

Insects exhibit remarkable adaptability in their locomotive strategies across diverse environments, a crucial trait for foraging, survival, and predator avoidance. Microvelia, tiny 2-3 mm insects that adeptly walk on water surfaces, exemplify this adaptability by using the alternating tripod gait in both aquatic and terrestrial terrains. These insects commonly inhabit low-flow ponds and streams cluttered with natural debris like leaves, twigs, and duckweed. Using high-speed imaging and pose-estimation software, we analyze Microvelia spp.'s movement across water, sandpaper (simulating land), and varying duckweed densities (10%, 25%, and 50% coverage). Our results reveal Microvelia maintain consistent joint angles and strides of their upper and hind legs across all duckweed coverages, mirroring those seen on sandpaper. Microvelia adjust the stride length of their middle legs based on the amount of duckweed present, decreasing with increased duckweed coverage and at 50% duckweed coverage, their middle legs' strides closely mimic their strides on sandpaper. Notably, Microvelia achieve speeds up to 56 body lengths per second on water, nearly double those observed on sandpaper and duckweed (both rough, frictional surfaces), highlighting their higher speeds on low friction surfaces such as the water's surface. This study highlights Microvelia's ecological adaptability, setting the stage for advancements in amphibious robotics that emulate their unique tripod gait for navigating complex terrains.

Limb loss and specialized leg dynamics in tiny water-walking insects.

The air-water of the planet's water bodies, such as ponds, lakes and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on the Microvelia's ability to walk on water. Removal of both hind tarsi causes Microvelia spp. to rock their bodies (yaw) while running across the water surface at ±19°, compared to ±7° in non-ablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that Microvelia use their hind legs as 'rudders' to regulate yaw, originating from the contralateral middle legs' strokes on the water's surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making Microvelia turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, Microvelia lose their ability to use the alternating tripod gait to walk for water walking on the day of contralateral ablation. Remarkably, by the next day Microvelia adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of Microvelia spp., and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.

Two different jumping mechanisms of water striders are determined by body size.

Current theory for surface tension-dominant jumps on water, created for small- and medium-sized water strider species and used in bioinspired engineering, predicts that jumping individuals are able to match their downward leg movement speed to their size and morphology such that they maximize the takeoff speed and minimize the takeoff delay without breaking the water surface. Here, we use empirical observations and theoretical modeling to show that large species (heavier than ~80 mg) could theoretically perform the surface-dominated jumps according to the existing model, but they do not conform to its predictions, and switch to using surface-breaking jumps in order to achieve jumping performance sufficient for evading attacks from underwater predators. This illustrates how natural selection for avoiding predators may break the theoretical scaling relationship between prey size and its jumping performance within one physical mechanism, leading to an evolutionary shift to another mechanism that provides protection from attacking predators. Hence, the results are consistent with a general idea: Natural selection for the maintenance of adaptive function of a specific behavior performed within environmental physical constraints leads to size-specific shift to behaviors that use a new physical mechanism that secure the adaptive function.

Comprehensive Structure of the Female Marine Water-Strider Asclepios annandalei Distant, 1915 from Pranburi River Estuary, Thailand: New Information for the Genus Asclepios.

The objective of this study was to describe the structure and histochemistry of the systemic organs in the female marine water-strider Asclepios annandalei from Pranburi river estuary, Thailand. Results from this study revealed for the first time that the integumentary system of this species consisted of three layers including epicuticle, exocuticle and endocuticle. The muscular system apparently contained only skeletal muscle along the body. In the urinary system, we observed well-developed Malpighian tubules, each of which was covered with the simple cuboidal epitheliums. These epitheliums also contained the secretory granules that were reacted positively with periodic acid Schiff (PAS). The digestive system of this species was composed of three distinct parts including foregut, midgut and hindgut. The respiratory system was composed of the respiratory organ, which was rarely found near the integument system. This organ was lined with a simple squamous epithelium. Two regions of nervous system, i.e., frontal ganglion connected to the eye structure and ventral nerve cord, were found. Each ganglion basically consisted of two layers, outer cortex and inner medullae. The outer cortex contained three types of cells, including neurosecretory cells, neuroglial cells and neurons. The cytoplasmic inclusion of neurosecretory cells contained secretory granules, which reacted positively with PAS, indicating the presence the glycoprotein. The neuroglia and neuron were also observed in the inner medullae layer. The female reproductive system (the ovarian structure, the reproductive tract and the accessory organ) of this gerrid species was seen under histological sections. The well-developed integument system and Malpighian tubule as well as the abundant respiratory organ is a characteristic of this species, which might be useful for the adaption to the estuarine condition.

Photoperiod controls wing polyphenism in a water strider independently of insulin receptor signalling.

Insect wing polyphenism has evolved as an adaptation to changing environments and a growing body of research suggests that the nutrient-sensing insulin receptor signalling pathway is a hot spot for the evolution of polyphenisms, as it provides a direct link between growth and available nutrients in the environment. However, little is known about the potential role of insulin receptor signalling in polyphenisms which are controlled by seasonal variation in photoperiod. Here, we demonstrate that wing length polyphenism in the water strider Gerris buenoi is determined by photoperiod and nymphal density, but is not directly affected by nutrient availability. Exposure to a long-day photoperiod is highly inducive of the short-winged morph whereas high nymphal densities moderately promote the development of long wings. Using RNA interference we demonstrate that, unlike in several other species where wing polyphenism is controlled by nutrition, there is no detectable role of insulin receptor signalling in wing morph induction. Our results indicate that the multitude of possible cues that trigger wing polyphenism can be mediated through different genetic pathways and that there are multiple genetic origins to wing polyphenism in insects.

Breast cancer diagnosis based on guided Water Strider Algorithm.

Breast cancer is one of the main cancers that effect of the women's health. This cancer is one of the most important health issues in the world and because of that, diagnosis in the beginning and appropriate cure is very effective in the recovery and survival of patients, so image processing as a decision-making tool can assist physicians in the early diagnosis of cancer. Image processing mechanisms are simple and non-invasive methods for identifying cancer cells that accelerate early detection and ultimately increase the chances of cancer patients surviving. In this study, a pipeline methodology is proposed for optimal diagnosis of the breast cancer area in the mammography images. Based on the proposed method, after image preprocessing and filtering for noise reduction, a simple and fast tumors mass segmentation based on Otsu threshold segmentation and mathematical morphology is proposed. Afterward, for simplifying the final diagnosis, a feature extraction based on 22 structural features is utilized. To reduce and pruning the useless features, an optimized feature selection based on a new developed design of Water Strider Algorithm (WSA), called Guided WSA (GWSA). Finally, the features injected to an optimized SVM classifier based on GWSA for optimal cancer diagnosis. Simulations of the suggested method are applied to the DDSM database. A comparison of the results with several latest approaches are performed to indicate the method higher effectiveness.

Morph-specific life-history correlations in a wing-dimorphic water strider.

Life-history theory predicts a negative correlation between reproduction and survival because individuals differ in their investment in early reproduction at the expense of survival. However, life-history trade-offs can be masked when individual differences in resource allocation are smaller than those in resource acquisition. In polymorphic species, as distinct morphs exhibit differences in intrinsic physiology, the relative effects of resource acquisition and allocation on life-history traits will differ between morphs, contributing to morph-specific life-history correlations. Here, in the wing-dimorphic water strider Aquarius paludum, we found that wing morphs differed in within-morph individual-level life-history correlations. Longer-lived flight-capable long-winged females produced fewer eggs per day and matured later, whereas life-history trade-offs were not observed in short-winged flightless females. The survival-reproduction trade-off observed in long-winged females may be a result of individual differences in the timing of wing muscle histolysis. Individuals that underwent wing histolysis early would have increased reproduction at the expense of a shorter life, whereas individuals with late wing histolysis would have reduced reproduction but a longer life. Short-winged females, who never develop wings, effectively have more resources to allocate to both survival and reproduction, masking any life-history trade-offs. Thus, we suggest that morph-specific effects of resource allocation trade-offs can shape the morph-specific extent of individual variation in life-history strategies, which may contribute to the evolution and maintenance of within-species polymorphism.

Interfacial phenomena of water striders on water surfaces: a review from biology to biomechanics.

Water striders have intrigued researchers for centuries from the viewpoints of biology to biomechanics. In this review, we introduce the basic theories and techniques of physics and force measurement for biomechanical research into water striders. Morphological and behavioral traits of water striders are summarized and discussed from biomechanical perspectives, along with comparative study. This integrated review also highlights potential directions for studies on water-walking arthropods, which might inspire future biological and biomechanical research.

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.

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.

Review of Ptilomera (Ptilomera) (Hemiptera: Heteroptera: Gerridae) from India, with description of a new species.

The subgenus Ptilomera (Ptilomera) Amyot Serville, 1843 of India is reviewed and Ptilomera (P.) nagalanda Jehamalar Chandra, sp. nov. is described from Peren District, Nagaland, India. The new species can clearly be distinguished from its congeners in India by the presence of silvery white setae on the sub-lateral region of the meso- and metanota and the presence of a fringe of fine short setae of different lengths on the flexor region of the mid femur reaching beyond the middle in the male. Detailed illustrations of the apterous male of the new species and male and female of other species of Ptilomera, except P. occidentalis Zettel, are given. Distribution maps and a key to all known species of Ptilomera (Ptilomera) in India are given.

Self-removal of condensed water on the legs of water striders.

The ability to control drops and their movements on phobic surfaces is important in printing or patterning, microfluidic devices, and water-repellent materials. These materials are always micro-/nanotextured, and a natural limitation of repellency occurs when drops are small enough (as in a dew) to get trapped in the texture. This leads to sticky Wenzel states and destroys the superhydrophobicity of the material. Here, we show that droplets of volume ranging from femtoliter (fL) to microliter (µL) can be self-removed from the legs of water striders. These legs consist of arrays of inclined tapered setae decorated by quasi-helical nanogrooves. The different characteristics of this unique texture are successively exploited as water condenses, starting from self-penetration and sweeping effect along individual cones, to elastic expulsion between flexible setae, followed by removal at the anisotropic leg surface. We envision that this antifogging effect at a very small scale could inspire the design of novel applicable robust water-repellent materials for many practical applications.

Characterization of plasma membrane associated type II α-D-mannosidase and ß-N-acetylglucosaminidase of Aquarius remigis sperm.

For successful fertilization to occur, molecules on the surface of male and female gametes must recognize each other in a complementary manner. In some organisms, sperm possess a glycosidase on the plasma membrane overlying the head while eggs have glycoproteins that are recognized by those glycosidases resulting in sperm-egg recognition. In this study, two glycosidases, mannosidase and ß-N-acetylglucosaminidase, were identified and biochemically characterized in Aquarius remigis sperm. The mannosidase had a Km of 2.36 ± 0.19 mM, a Vmax of 27.49 ± 0.88 pmol/min and a Hill coefficient of 0.94 ± 0.18 at its optimal pH of 7.0. The mannosidase was extracted most efficiently with CHAPSO but was also efficiently extracted with sodium chloride. Mannosidase activity was effectively inhibited by swainsonine, but not by kifunesine, and was significantly reduced in the presence of Mn(2+) and Mg(2+), but not Zn(2+). N-acetylglucosaminidase had a Km of 0.093 ± 0.01 mM, a Vmax of 153.80 ± 2.97 pmol/min and a Hill coefficient of 0.96 ± 0.63 at its optimal pH of 7.0. N-acetylglucosaminidase was extracted most efficiently with potassium iodide but was also efficiently extracted with Triton X-100 and Zn(2+), but not Ca(2+), Co(2+), Mn(2+) or Mg(2+), significantly inhibited its activity. Taken together, these results indicate that the A. remigis sperm surface contains at least two glycosidases that may recognize complementary glycoconjugates on the surface of water strider eggs.

Biomimetic "water strider leg" with highly refined nanogroove structure and remarkable water-repellent performance.

The water strider is a wonderful case that we can learn from nature to understand how to stride on the water surface. Inspired by the unique hierarchical micro/nanostructure of the water strider leg, in this article, we designed and fabricated an artificial strider leg with refined nanogroove structure by using an electrospinning and sacrificial template method. A model water strider that was equipped with four artificial legs showed remarkable water-repellent performance; namely, it could carry a load that was about 7 times heavier than its own weight. Characterization demonstrated that, even though the artificial leg did not possess a superhydrophobic surface, the numerous nanogrooves could still provide a huge supporting force for the man-made model strider. This work enlightens the development of artificial water-walking devices for exploring and monitoring the surface of water. Because of the advances of the applied materials, the devices may fulfill tasks in a harsh aquatic environment.

Developmental changes in biophysical properties of photoreceptors in the common water strider (Gerris lacustris): better performance at higher cost.

Although the dependence of invertebrate photoreceptor biophysical properties on visual ecology has already been investigated in some cases, developmental aspects have largely been ignored due to the general research emphasis on holometabolous insects. Here, using the patch-clamp method, we examined changes in biophysical properties and performance of photoreceptors in the common water strider Gerris lacustris during postembryonic development. We identified two types of peripheral photoreceptors, green and blue sensitive. Whole cell capacitance (a measure of cell size) of blue photoreceptors was significantly higher than the capacitance of green photoreceptors (69 ± 20 vs. 43 ± 12 pF, respectively). Most of the measured morphological and biophysical parameters changed with development. Photoreceptor capacitance increased progressively and was positively correlated with sensitivity to light, magnitudes and densities of light-induced (LIC) and delayed rectifier K(+) (IDR) currents, membrane corner frequency, and maximal information rate [Spearman rank correlation coefficients: 0.70 (sensitivity), 0.79 (LIC magnitude), 0.79 (IDR magnitude), 0.48 (corner frequency), and 0.57 (information rate)]. Transient K(+) current increased to a smaller extent, while its density decreased. We found no significant changes in the properties of single photon responses or levels of light-induced depolarization, the latter indicating a balanced channelome expansion associated with IDR expression. However, the dramatic ∼7.6-fold increase in IDR from first instars to adults indicated a development-related rise in the metabolic cost of information. In conclusion, this study provides novel insights into functional photoreceptor adaptations with development and illustrates remarkable variability in patterns of postembryonic retinal development in hemimetabolous insects with dissimilar visual ecologies and behaviors.

Comparing salinity tolerance in embryonic and larval development of two species of water strider, Aquarius paludum and Gerris latiabdominis (Hemiptera: Gerridae).

Water strider Aquarius paludum (Fabricius) is a cosmopolitan species colonizes mainly freshwater but occasionally brackish habitats throughout the Palearctic and Oriental regions. Water strider Gerris latiabdominis (Miyamoto) is a common species in Japan lives in temporary habitats as freshwater paddy fields. These two species often occur syntopically. We investigated differences in the developmental response to brackish water during embryonic and larval stages between the two species. Eggs were exposed to 0-1.8% NaCl solutions within 24 h of oviposition. Larvae of G. latiabdominis were exposed to salinities of 0, 0.5%, and 0.9% from the first instar until adult emergence. Limits of NaCl concentration for hatching were 1.3% and 1.0% for A. paludum and G. latiabdominis, respectively. The hatching rate of G. latiabdominis was lower than that of A. paludum at salinities ≥ 0.9%. The period of embryonic development of G. latiabdominis was more prolonged than that of A. paludum at a given salinity. Although the salinity tolerance of G. latiabdominis was lower than that of A. paludum, our results suggest G. latiabdominis has the physiological capacity to expand into brackish waters. High and low salinity tolerances of A. paludum and G. latiabdominis, respectively, reflect the relatively wide range of habitat salinities utilized by A. paludum and the relatively restricted habitats preferred by G. latiabdominis. The high salinity tolerance of A. paludum could be an important factor contributing to their cosmopolitan distribution because high tolerance to salinity means the possibility of them to be dispersed via ocean or sea to other continents and islands.

Population structure influences sexual conflict in wild populations of water striders.

In sexual conflict, aggressive males frequently diminish the long-term reproductive success of females in efforts to gain a short-term advantage over rival males. This short-term advantage can selectively favour high-exploitation males. However, just as the over-exploitation of resources can lead to local extinction, the over-exploitation of females in the form of harassment by aggressive males can yield similar consequences resulting in reduced female fecundity, increased female mortality and overall decline in mating activity. This outcome may often be prevented by selection acting at multiple levels of biological organization. Directional selection favouring aggressive exploitation within groups can be balanced by directional selection amongst groups opposing exploitation. Such between-group selection has recently been demonstrated in laboratory studies of water striders, where the conditional dispersal of individuals increased variation amongst groups and influenced the balance of selection toward reduced male aggression. This multilevel selection (MLS) framework also provides predictive value when investigating natural populations differing in their relative strength of selection within versus among groups. For water striders, the consequences of local exploitation cause fitness differences between groups, favouring less aggressive males. Inconsistently flowing ephemeral streams consist of isolated pools that prevent aggressive male water striders from escaping the consequences of local exploitation. We, therefore, predicted that inconsistently flowing ephemeral streams would favour the evolution of less aggressive males than would perennial streams, which allow aggressive males to move more freely and to escape the group-level costs of their aggression. Comparing two neighbouring streams during the mating season, we found that males dispersed naturally between pools at much higher rates in the perennial stream than in the ephemeral stream. As predicted, we found that males from the perennial stream were significantly more aggressive than those from the ephemeral stream. We also found that dispersers were significantly more aggressive than non-dispersers within each stream. These field results illustrate the relevance of the MLS framework in our understanding of the evolution of sexual conflict.