Water Strider Research Articles

Predators induce conditions for size-dependent alternative reproductive tactics in a water strider male

Alternative reproductive tactics (ARTs) are commonly associated with differences in morphological, physiological and behavioural traits. The morphological differences can be associated with differences between ARTs in effectiveness of sexual display but the relationship has rarely been documented. We tested it using the Asian water strider Gerris gracilicornis (Heteroptera: Gerridae), in which males have two ARTs: a signalling courtship tactic and a nonsignalling tactic. Many G. gracilicornis males employ an intimidating signalling courtship tactic capitalizing on predators' behaviours and female responses to predators. The males produce courtship ripple signals on the water's surface by vibrating their middle legs after mounting the female. In this study we found that smaller males more often adopted a nonsignalling than a signalling courtship tactic. We hypothesized that smaller males with shorter middle legs and weaker muscles may not be able to produce ripples that are sufficiently strong to attract predators from a distance, and therefore sexual selection favours nonsignalling tactics in smaller but not larger males. We created a 2 x 2 experimental design to test the contribution of male body size to the intimidation effect under different levels of predation risk. We showed that only large males' ripple signals had an intimidation effect on females. We also found that females suffered a higher predation risk when large, but not small, males mounted them. The signal intensity of large males was also stronger than that of small males. Hence, we suggest that size-dependent effectiveness of the intimidation signalling maintains the size-dependent reproductive tactics in G. gracilicornis. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Life on the seafloor: adaptations and strategies in Stylophora (Echinodermata)

Stylophorans are a Palaeozoic group of non-pentamerous echinoderms, morphologically well-adapted to a benthic mode of life on soft sediment seafloors. By developing a thin and wide theca, they successively increased the surface area in contact with the substrate resulting in an even distribution of the body mass resting on the ground, and efficiently preventing the body from sinking into non-indurated sediments (snowshoe strategy). In stylophorans, the body surface is dramatically increased in result of the expansion of two integumentary areas on the lower thecal surface. While infracentral areas are reduced in primitive forms to the detriment of massive marginals; in boot-shape cornutes, infracentral areas are larger, polyplated and framed by very delicate marginals. In heart-shaped cornutes, the reduction of both infracentral areas is compensated by the development of spiny elements on the theca outline. In forms where the degree of bilateral symmetry is high, the left infracentral area is larger than the right area, resulting in an elongated thecal shape. In structural geology, changes of shape of a rock submitted to a strain can be categorized by translating the obtained deformation into a strain ellipsoid plotted on a Flinn diagram, while in biology changes of shapes of organisms are traditionally measured through morphometric analysis. By applying Flinn's principle of strain ellipsoid to biological objects, the present study aims to characterize different life adaptations across stylophorans, observing changes of shape of both infracentral areas interpreted as two ellipsoids. Once plotted on a Flinn diagram, three significantly separated clusters are observed when focusing on the left area. This concerns forms with reduced infracentral areas, highly and weakly asymmetrical forms. According to these results, three new morphological adaptations are described (water strider, flat fish and stream-lined body). These newly described adaptations enabled snowshoe strategist stylophorans to remain stable on top of the seafloor.

Low Drag Porous Ship with Superhydrophobic and Superoleophilic Surface for Oil Spills Cleanup.

To efficiently remove and recycle oil spills, we construct aligned ZnO nanorod arrays on the surface of the porous stainless steel wire mesh to fabricate a porous unmanned ship (PUS) with properties of superhydrophobicity, superoleophilicity, and low drag by imitating the structure of nonwetting leg of water strider. The superhydrophobicity of the PUS is stable, which can support 16.5 cm water column with pore size of 100 μm. Water droplet can rebound without adhesion. In the process of oil/water separation, when the PUS contacts with oil, the oil is quickly pulled toward and penetrates into the PUS automatically. The superhydrophobicity and low water adhesion force of the PUS surface endow the PUS with high oil recovery capacity (above 94%) and drag-reducing property (31% at flowing velocity of 0.38m/s). In addition, the PUS has good corrosion resistance and reusability. We further investigate the wetting behavior of water and oil, oil recovery capacity, drag-reducing property, and corrosion resistance of the PUS after oil absorbed. The PUS surface changes significantly from superhydrophobic to hydrophobic after absorbing oil. However, the oil absorbed PUS possesses better drag-reducing property and corrosion resistance due to the changes of the motion state of the water droplets.

LAS CHINCHES SEMI-ACUÁTICAS DE LA RESERVA NATURAL RÍO ÑAMBÍ (NARIÑO), COLOMBIA

<p class="p1"><strong>RESUMEN</strong></p><p class="p2">En la Reserva Natural Río Ñambi, ubicada en la vertiente del pacífico de los Andes de Colombia, región del Chocó biogeográfico, se estudió la composición de las chinches semiacuáticas. Dos familias Gerridae y Veliidae, cuatro géneros Potamobates, Charmatometra, Rhagovelia y Microvelia y doce especies fueron registradas. Rhagovelia fue el más diverso con cuatro grupos y nueve especies; se incluye una clave ilustrada para las especies de éste género, proporcionando notas sobre la distribución geográfica.</p><p class="p2"><strong>ABSTRACT</strong></p><p class="p2">In the Ñambi River Natural Reserve, located in the Pacific slope of the Colombian Andes in the Chocó biogeographical region was studied the composition of semi-aquatic bugs. Two families Gerridae and Veliidae, four genera Potamobates, Charmatometra, Rhagovelia and Microvelia, and twelve species were recorded. Rhagovelia was the most diverse with four groups and nine species, also a key illustrated to species of this genus was included. Additionally notes about geographical distribution were provided.</p><p class="p2"><span class="s1">Keywords: </span></p>

The combined effects of pre‐ and post‐copulatory processes are masking sexual conflict over mating rate in Gerris buenoi

In polygynandrous animals, post-copulatory processes likely interfere with precopulatory sexual selection. In water striders, sexual conflict over mating rate and post-copulatory processes are well documented, but their combined effect on reproductive success has seldom been investigated. We combine genetic parentage analyses and behavioural observations conducted in a competitive reproductive environment to investigate how pre- and post-copulatory processes influence reproductive success in Gerris buenoi Kirkaldy. Precopulatory struggles had antagonistic effects on male and female reproductive success: efficiently gaining copulations was beneficial for males, whereas efficiently avoiding copulations was profitable for females. Also, high mating rates and an intermediate optimal resistance level of females supported the hypothesis of convenience polyandry. Contrary to formal predictions, high mating rates (i.e. the number of copulations) did not increase reproductive success in males or decrease reproductive success in females. Instead, the reproductive success of both sexes was higher when offspring were produced with several partners and when there were few unnecessary matings. Thus, male and female G.buenoi displayed different interests in reproduction, but post-copulatory processes were masking the effects of copulatory mating success on reproductive success. Given the high mating rates observed, sperm competition could easily counter the effect of mating rates, perhaps in interaction with cryptic female choice and/or fecundity selection. Our study presents a complex but realistic overview of sexual selection forces at work in a model organism for the study of sexual conflict, confirming that insights are gained from investigating all episodes in the reproduction cycle of polygynandrous animals.

Multiple mating reveals complex patterns of assortative mating by personality and body size.

Understanding patterns of non-random mating is central to predicting the consequences of sexual selection. Most studies quantifying assortative mating focus on testing for correlations among partners' phenotypes in mated pairs. Few studies have distinguished between assortative mating arising from preferences for similar partners (expressed by all or a subset of the population) vs. from phenotypic segregation in the environment. Also, few studies have assessed the robustness of assortative mating against temporal changes in social conditions. We tracked multiple matings by stream water striders (Aquarius remigis) across variable social conditions to investigate mating patterns by both body size and behavioural type (personality). We documented temporal changes in partner availability and used a mixed model approach to analyse individual behaviours and changes in mating status recorded on an hourly basis. We assessed whether all or only a subset of individuals in the population expressed a tendency to mate with similar phenotypes. Our analyses took into account variation in the level of competition and in the phenotypes of available partners. Males and females exhibited significant assortative mating by body size: the largest males and females, and the smallest males and females mated together more often than random. However, individuals of intermediate size were equally likely to mate with small, intermediate or large partners. Individuals also displayed two contrasting patterns of assortative mating by personality (activity level). Individuals generally mated preferentially with partners of similar activity level. However, beyond that general trend, individuals with more extreme personalities tended to exhibit disassortative mating: the most active males mated disproportionately with less active females and the least active males tended to mate with more active females. Our analyses thus revealed multiple, distinct patterns of nonrandom mating. These mating patterns did not arise from differences in partner availability among individuals and were robust to temporal changes in social conditions. Hence, mating patterns likely reflect mate preferences or arise from male-male competition coupled with sexual conflict. Our study also stresses the importance of accounting for variation in partner availability and demonstrates the influence of behavioural variation on mating patterns.

Intimidating courtship and sex differences in predation risk lead to sex-specific behavioural syndromes

Behavioural correlations between mating behaviour and antipredator behaviour are expected when sexual behaviour increases predation risk. However, the correlation would be different between males and females, particularly when the sexes experience different levels of predation risk. Here, we tested this idea using a water strider species, Gerris gracilicornis (Heteroptera: Gerridae). G. gracilicornis males employ an unusual intimidating courtship strategy capitalizing on predator behaviours and female response to predators. Since mounted females are more vulnerable than males to predatory attacks from below, we predicted that changes in female mating behaviours across predation contexts (boldness in a mating context) should be associated with female antipredator behaviours (boldness in a nonmating context), but that the correlation would be weaker for male mating behaviours. In a series of behavioural assays, we measured water striders' (1) mating behaviour in the absence of predators, (2) mating behaviour in the presence of predation risk, (3) boldness in the mating context (changes in female mating behaviour after predator attacks) and (4) boldness in the nonmating context. We found that females behaved more cautiously around predators in both the mating and nonmating contexts. We also found that females' boldness in the mating context was significantly correlated with their boldness in the nonmating context. In contrast to females, antipredator behaviour of males in the nonmating context did not correlate with their boldness in the mating context. Thus we suggest that sex differences in boldness across predation contexts appear to cause sex-specific behavioural syndromes.

Predator strike shapes antipredator phenotype through new genetic interactions in water striders.

How novel genetic interactions evolve, under what selective pressures, and how they shape adaptive traits is often unknown. Here we uncover behavioural and developmental genetic mechanisms that enable water striders to survive attacks by bottom-striking predators. Long midlegs, critical for antipredator strategy, are shaped through a lineage-specific interaction between the Hox protein Ultrabithorax (Ubx) and a new target gene called gilt. The differences in leg morphologies are established through modulation of gilt differential expression between mid and hindlegs under Ubx control. Furthermore, short-legged water striders, generated through gilt RNAi knockdown, exhibit reduced performance in predation tests. Therefore, the evolution of the new Ubx–gilt interaction contributes to shaping the legs that enable water striders to dodge predator strikes. These data show how divergent selection, associated with novel prey–predator interactions, can favour the evolution of new genetic interactions and drive adaptive evolution.

Same-sex sexual behaviour as a by-product of reproductive strategy under male–male scramble competition

A variety of hypotheses have been suggested to explain the evolution of same-sex sexual behaviour (SSB) in male insects. Males may be poor at discriminating other males from females, inexperienced, or may need to learn how to distinguish females. Alternatively SSB could be a by-product of a plastic reproductive strategy to succeed in scramble competition. Such a strategy could be adaptive if the cost of missing the chance to mate with available females exceeds the cost of mounting single males instead (i.e. SSB). We tested predictions derived from these hypotheses by experimentally varying the sex ratio and thus the intensity of scramble competition in the water strider Tenagogerris euphrosyne. We allowed males to experience female-biased or male-biased sex ratio treatments for a week, and then compared their expression of SSB under standard conditions. We also measured daily mating success of males during the treatment and related this to SSB frequency under assay conditions. Males kept in male-biased sex ratio conditions exhibited more SSB, mounting males and females equally often under assay conditions. Males kept under female-biased conditions only mounted males one-quarter as often as they mounted females in the assay. Male mating experience under treatment conditions did not influence the expression of SSB in the assay. In a second experiment we found that males that were more likely to exhibit SSB enjoyed higher initial mating success in a subsequent mating assay in a male-biased sex ratio. Our results indicate that plasticity in reproductive strategy not only increases mating opportunity but also confers a reproductive benefit. Taken together, SSB in T. euphrosyne is a highly labile trait responsive to sex ratio that delivers increased mating success under intense scramble competition.

An interommatidial exocrine gland with a “nail-headed” structure in the water strider Aquarius remigis (Hemiptera, Gerridae)

The fine structure of the interommatidial exocrine glands, found in the compound eyes of the water strider Aquarius remigis, is described using light, scanning, and transmission electron microscopy. The glandular pores of the glands are specialized into minute “nail-headed” structures (NS), which are described for the first time in arthropod compound eyes. Each NS is composed of two components: a rod-like stalk and a cup-like depression. The TEM study shows that the glands are class 3 epidermal glands as defined by Noirot and Quennedey (1974, 1991). Each gland consists of 3 cells: a gland cell, an intermediary cell, and a duct (canal) cell. The gland cell contains abundant electron-lucent vesicles, while the intermediary cell contains a large number of osmiophilic secretory granules. These two cells might secrete different substances which mix together in the dilated sac-like portion of the conducting canal before final release. The possible functions of the secretions released from these glands are discussed.

A miniature surface tension-driven robot using spatially elliptical moving legs to mimic a water strider’s locomotion

The highly agile and efficient water-surface locomotion of the water strider has stimulated substantial interest in biomimetic research. In this paper, we propose a new miniature surface tension–driven robot inspired by the water strider. A key feature of this robot is that its actuating leg possesses an ellipse-like spatial trajectory similar to that of a water strider by using a cam-link mechanism. Simplified models are presented to discuss the leg–water interactions as well as critical conditions for a leg penetrating the water surface, and simulations are performed on the robot’s dynamic properties. The final fabricated robot weighs about 3.9 g, and can freely and stably walk on water at different gaits. The maximum forward and turning speeds of the robot are measured as 16 cm s−1 and 23°/s, respectively. Furthermore, a similarity analysis with Bond number and Weber number demonstrates that the locomotion of this robot is quite analogous to that of a real water strider: the surface tension force dominates the lifting force and plays a major role in the propulsion force. This miniature surface tension–driven robot might have potential applications in many areas such as water quality monitoring and aquatic search and rescue.

First record of Metrocoris quynhi Tran and Zettel, 2005 (Insecta: Heteroptera: Gerridae) from India

Metrocoris quynhi Tran and Zettel of the genus Metrocoris Mayr was described from Vietnam in the year 2005. During the recent surveys to explore the diversity of water striders (Gerridae) in the State of West Bengal and in Himachal Pradesh, Metrocoris quynhi Tran and Zettel, 2005, was collected from different localities of Bengal and Himachal Pradesh. This species is widespread in Himalayan region of Bengal but not previously known from India. Hence, it is a new record to India after Vietnam.

BIOMECHANICS. Jumping on water: Surface tension-dominated jumping of water striders and robotic insects.

Jumping on water is a unique locomotion mode found in semi-aquatic arthropods, such as water striders. To reproduce this feat in a surface tension-dominant jumping robot, we elucidated the hydrodynamics involved and applied them to develop a bio-inspired impulsive mechanism that maximizes momentum transfer to water. We found that water striders rotate the curved tips of their legs inward at a relatively low descending velocity with a force just below that required to break the water surface (144 millinewtons/meter). We built a 68-milligram at-scale jumping robotic insect and verified that it jumps on water with maximum momentum transfer. The results suggest an understanding of the hydrodynamic phenomena used by semi-aquatic arthropods during water jumping and prescribe a method for reproducing these capabilities in artificial systems.

How to walk and jump on water

Biomechanics Jumping on land requires the coordinated motion of a number of muscles and joints in order to overcome gravity. Walking on water requires specialized legs that are designed to avoid breaking the surface tension during motion. But how do insects, such as water striders and fishing

Water repellent Ag/Ag2O@bamboo cellulose fiber membrane as bioinspired cargo carriers

Water striders can walk on water. To mimic this function, a porous membrane consisted of bamboo cellulose fiber was hybridized with Ag/Ag2O nanoparticles through a facile in situ method to produce water repellent and well-ventilated materials. Herein, we report the sole surface roughness created by Ag/Ag2O nanoparticles could render the membrane a water contact angle (CA) of 140±3.0°. When floating on water, the hybrid membrane was able to support a heavy load more than 10 times the weight of the membrane itself. Additionally, this membrane demonstrated capabilities for oil sampling under water or oil/water separation and strong antibacterial activity against Escherichia coli. Thus we foresee that this novel hybrid membrane can be potentially utilized as drag-reducing, gas permeable and antibiotic substrates for constructing miniature aquatic devices.

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.

Supporting Force Test of Living Water Strides on Water Surface and Mechanical Analysis

Accuracy of designing and producing a micro-force measuring device is 0.1μN, through the device, the maximum supporting force of living water striders sample and their legs were measured. The results showed that the maximum supporting force of living water striders is 23.6 times its weight, the maximum supporting force of living water striders greater than the sum of six legs, the reason that living water strider’s chest and abdomen touched water surface on process of measuring; Established supporting force model of water strider leg, analyzed the factors associated with supporting force, the key parameters are the water strider leg length and depth of water dimple; Compared the water strider leg’s the maximum supporting force of the measurement value and the calculated value according to theoretical model, verified the correctness of the supporting force model.

Key patterning genes contribute to leg elongation in water striders.

BackgroundHow adaptive phenotypes are shaped by the action of key developmental genes during ontogeny remains poorly understood. Water striders, a group of hemipteran insects, present a unique example of adaptation to life on the fluid water surface substrate. The group has undergone a set of leg modifications allowing them to efficiently move on the water surface and hence invade a variety of niches from ponds to open oceans. The elongated legs of water striders play a key role in generating efficient movement on the fluid by acting as propelling oars.ResultsTo determine the developmental mechanisms underlying leg elongation, we examined the function of the key developmental genes decapentaplegic (dpp), wingless (wg), epidermal growth factor receptor (egfr), and hedgehog (hh) during embryonic development in the water strider Limnoporus dissortis. By analyzing expression patterns and RNAi knockdown phenotypes, we uncover the role of these genes in leg growth and patterning during embryogenesis. Our results indicate that wg and egfr contribute to the elongation of all the three segments of all thoracic legs, whereas hh specifies distal leg segments.ConclusionsTogether, our results suggest that key patterning genes contribute to the dramatic elongation of thoracic appendages in water striders.

Biophysical properties of photoreceptors in Corixa punctata facilitate diurnal life-style

Measurement of evolutionary adaptations of a visual system to its visual and operational ecology requires comparison of visual function in different species with similar morphologies and visual ecologies, occupying the same habitats but displaying differences in visually-guided behavior. The goal here was to document the biophysical properties of photoreceptors in the lesser water boatman Corixa punctata, which shares many features with the previously studied aquatic predator water boatman backswimmer Notonecta glauca. However, unlike the backswimmer, which heavily relies on vision to catch its prey, Corixa is a detritivore. Using the patch-clamp method, I found that the average whole-cell capacitance of Corixa photoreceptors was 441±206pF, higher than in any other insect studied so far, and that absolute sensitivity was positively correlated with capacitance (Spearman rank correlation coefficient, 0.73). Interestingly, both the sensitivity distribution median and variation in Corixa were similar to the corresponding values in the diurnal water strider Gerris lacustris and were substantially smaller than in the noctidial N. glauca or the nocturnal/crepuscular cockroach Periplaneta americana. Furthermore, capacitance was correlated with the amplitudes of light-induced (0.70) and delayed rectifier K+ (0.46) currents, membrane corner frequency (0.68) and maximal information rate (IRmax, 0.74). No correlation was observed between capacitance and transient K+ current. Average IRmax in Corixa was 36.0±21.3bitss−1, much higher than in G. lacustris but smaller than in N. glauca. These findings support the hypothesis that Corixa’s retinal function is adapted to its diurnal life-style, which is also consistent with field observations.

Characterization of plasma membrane associated type II α-d-mannosidase and β-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 β-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 Mn2+ and Mg2+, but not Zn2+. 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 Zn2+, but not Ca2+, Co2+, Mn2+ or Mg2+, 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.