Water Strider Species Research Articles

Analysis of antioxidants in water striders (Hemiptera: Gerridae) as bioindicator of water pollution.

The antioxidant enzyme system is an important defense mechanism to cope with Reactive Oxygen Species (ROS) produced due to exposure to heavy metals. In the present study lead (Pb), chromium (Cr), arsenic (As), cadmium (Cd) and nickel (Ni) in water and the antioxidant activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was investigated in three species (Metrocoris communis, Limnogonus fossarum fossarum, and Aquarius adelaidis) of water striders collected from the industrial triangle of Punjab, Pakistan. The results of present study revealed that Pb, Cr, As, Cd and Ni were according to the permissible amount of WHO. The antioxidant activity of SOD, CAT and POD was found significantly different among species against oxidative stress, but found the highest activity of determining parameters in A. adelaidis. This is one of the pioneer studies in Pakistan reporting the role of water striders as a bioindicator of heavy metals present in the water through antioxidants enzyme variations. The current results supported that variant level of antioxidant enzyme activities in different species of water strider were reflective of heavy metal pollution in the Industrial triangle of Punjab, Pakistan and will be a useful ecotoxicological tools to evaluate the detrimental effects of heavy metal pollutants in aquatic organisms.

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.

Climate Warming Since the Holocene Accelerates West-East Communication for the Eurasian Temperate Water Strider Species Aquarius paludum.

Holocene climate warming has dramatically altered biological diversity and distributions. Recent human-induced emissions of greenhouse gases will exacerbate global warming and thus induce threats to cold-adapted taxa. However, the impacts of this major climate change on transcontinental temperate species are still poorly understood. Here, we generated extensive genomic datasets for a water strider, Aquarius paludum, which was sampled across its entire distribution in Eurasia and used these datasets in combination with ecological niche modeling (ENM) to elucidate the influence of the Holocene and future climate warming on its population structure and demographic history. We found that A. paludum consisted of two phylogeographic lineages that diverged in the middle Pleistocene, which resulted in a “west–east component” genetic pattern that was probably triggered by Central Asia-Mongoxin aridification and Pleistocene glaciations. The diverged western and eastern lineages had a second contact in the Holocene, which shaped a temporary hybrid zone located at the boundary of the arid–semiarid regions of China. Future predictions detected a potentially novel northern corridor to connect the western and eastern populations, indicating west–east gene flow would possibly continue to intensify under future warming climate conditions. Further integrating phylogeographic and ENM analyses of multiple Eurasian temperate taxa based on published studies reinforced our findings on the “west–east component” genetic pattern and the predicted future northern corridor for A. paludum. Our study provided a detailed paradigm from a phylogeographic perspective of how transcontinental temperate species differ from cold-adapted taxa in their response to climate warming.

Leg length and bristle density, both necessary for water surface locomotion, are genetically correlated in water striders

Access to hitherto unexploited ecological opportunities is associated with phenotypic evolution and often results in significant lineage diversification. Yet our understanding of the mechanisms underlying such adaptive traits remains limited. Water striders have been able to exploit the water-air interface, primarily facilitated by changes in the density of hydrophobic bristles and a significant increase in leg length. These two traits are functionally correlated and are both necessary for generating efficient locomotion on the water surface. Whether bristle density and leg length have any cellular or developmental genetic mechanisms in common is unknown. Here, we combine comparative genomics and transcriptomics with functional RNA interference assays to examine the developmental genetic and cellular mechanisms underlying the patterning of the bristles and the legs in Gerris buenoi and Mesovelia mulsanti, two species of water striders. We found that two duplication events in the genes beadex and taxi led to a functional expansion of the paralogs, which affected bristle density and leg length. We also identified genes for which no function in bristle development has been previously described in other insects. Interestingly, most of these genes play a dual role in regulating bristle development and leg length. In addition, these genes play a role in regulating cell division. This result suggests that cell division may be a common mechanism through which these genes can simultaneously regulate leg length and bristle density. We propose that pleiotropy, through which gene function affects the development of multiple traits, may play a prominent role in facilitating access to unexploited ecological opportunities and species diversification.

A New Species of Small Water Strider in the Genus Microvelia (Hemiptera: Heteroptera: Veliidae) from Aichi Prefecture, Honshu, Japan

A new species of small water strider (Hemiptera: Heteroptera: Veliidae), Microvelia pilosa sp. nov., is described from Aichi Prefecture, Honshu, Japan. It belongs to the subgenus Picaultia Distant, 1913 within the genus Microvelia Westwood, 1834, and is similar to Microvelia japonica Esaki and Miyamoto, 1955 and Microvelia douglasi douglasi Scott, 1874. The new species can be distinguished from these two taxa by its blackish-brown body, small punctures on the pronotum, and arcuate right paramere that is slender only in the distal part. Our molecular phylogenetic analysis using the mitochondrial COI gene revealed that M. pilosa sp. nov. is genetically separated from some of the other Japanese Microvelia and is most closely related to M. japonica.

Numerical model of the spatio-temporal dynamics in a water strider group

The water strider group demonstrates a very complex dynamics consisting of competition for the food items, territoriality and aggression to the conspecific individuals, escaping from the predators, etc. The situation is even more complex due to the presence of different instars, which in most water strider species live in the same habitat and occupy the same niche. The presented swarm model of water striders demonstrates the realistic population dynamics. For the swarm formation in the model, attraction and repulsion forces were used. Animal motion in the model takes into account inertia and kinetic energy dissipation effects. The model includes three different rates related to the growth of individuals: food appearance rate, food assimilation rate, and stored energy loss rate. The results of our modeling show that the size distribution of individuals seems to be an adequate measure for population status, and it has a characteristic shape for different model parameter combinations. Distribution of the distances between nearest neighbors is other important measure of the population density and its dynamics. Parameters of the model can be tuned in such a way, that the shape of both distributions in a steady phase coincides with that shape observed in a natural population, which helps to understand the factors leading to particular momentary distribution of both parameters (size and distance) in the population. From this point of view, the model can predict how both distributions can further develop from certain state depending on particular combination of factors.

The Microbiome of Neotropical Water Striders and Its Potential Role in Codiversification.

Simple SummaryInsects host a highly diverse bacterial community. Although we have a good understanding of the role that this microbiome plays in insects, the composition and diversity of microbiomes associated with Neotropical freshwater insects is virtually unknown. Here, we describe, for the first time, the microbiome associated with six species of Neotropical water striders in Panama. We also performed phylogenetic analyses to explore potential codiversification or coevolution between water strider species and their associated microbiome. We found a diverse microbiome associated with the six species of water striders, with the dominant bacterial taxa belonging to the phyla Proteobacteria and Tenericutes. Although some bacterial lineages were shared across species, some lineages were also uniquely associated with different water strider species. Our results suggest that both environmental variation and host phylogenetic identity are important drivers of the microbiome associated with water striders. Understanding the evolution of the host-microbiome interaction is crucial to our understanding of Neotropical freshwater ecosystems.Insects host a highly diverse microbiome, which plays a crucial role in insect life. However, the composition and diversity of microbiomes associated with Neotropical freshwater insects is virtually unknown. In addition, the extent to which diversification of this microbiome is associated with host phylogenetic divergence remains to be determined. Here, we present the first comprehensive analysis of bacterial communities associated with six closely related species of Neotropical water striders in Panama. We used comparative phylogenetic analyses to assess associations between dominant bacterial linages and phylogenetic divergence among species of water striders. We found a total of 806 16S rRNA amplicon sequence variants (ASVs), with dominant bacterial taxa belonging to the phyla Proteobacteria (76.87%) and Tenericutes (19.51%). Members of the α- (e.g., Wolbachia) and γ- (e.g., Acinetobacter, Serratia) Proteobacteria, and Mollicutes (e.g., Spiroplasma) were predominantly shared across species, suggesting the presence of a core microbiome in water striders. However, some bacterial lineages (e.g., Fructobacillus, Fluviicola and Chryseobacterium) were uniquely associated with different water strider species, likely representing a distinctive feature of each species’ microbiome. These findings indicate that both host identity and environmental context are important drivers of microbiome diversity in water striders. In addition, they suggest that diversification of the microbiome is associated with diversification in water striders. Although more research is needed to establish the evolutionary consequences of host-microbiome interaction in water striders, our findings support recent work highlighting the role of bacterial community host-microbiome codiversification.

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.

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.

Water striders adjust leg movement speed to optimize takeoff velocity for their morphology

Water striders are water-walking insects that can jump upwards from the water surface. Quick jumps allow striders to avoid sudden dangers such as predators' attacks, and therefore their jumping is expected to be shaped by natural selection for optimal performance. Related species with different morphological constraints could require different jumping mechanics to successfully avoid predation. Here we show that jumping striders tune their leg rotation speed to reach the maximum jumping speed that water surface allows. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water. These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments.

Behavioural Consistency in Female Resistance to Male Harassment in a Water Strider Species

AbstractSexual conflict over mating rate often implies that males persist at frequently harassing females to gain matings while females resist mating attempts. In water striders, females can resist by engaging in vigorous pre‐copulatory struggles to dislodge males, but alternative means of resistance have seldom been investigated. Contrary to males, female resistance has not been investigated as a repeatable behaviour. We used Gerris buenoi to investigate the capacity to abbreviate struggles and the tendency to hide off the water as two potential female resistance traits. Specifically, we asked whether these behaviours are repeatable and whether they vary according to sexual conflict intensity and past mating experience. Also, we studied the possible connections between these behaviours and traits linked to fitness, namely endured harassment and mating activity. The capacity to abbreviate struggles was poorly repeatable and decreased with sexual conflict intensity and endured harassment. It seems to be mainly determined by the social environment and by recent events related to sexual conflict. The tendency to hide off the water was significantly repeatable across sexual conflict intensities and can be considered as a repeatable behaviour. Hiding frequently off the water allowed females to decrease the harassment endured by females and may enhance female fitness. In nature, hiding is more readily and more frequently observed than pre‐copulatory struggles. Directly associating hiding off water with female fitness would confirm that this consistent phenotype contributes to sexually antagonistic female resistance.

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.

Two new species of Pleciobates (Hemiptera: Gerromorpha: Gerridae) from India, with a key to the species of Pleciobates.

Two new species of water striders in the genus Pleciobates are described from India and compared with allied species. Pleciobates bengalensis Jehamalar, Basu & Zettel sp. nov. is described from the Jalpaiguri District, West Bengal and Pleciobates expositus Jehamalar, Chandra & Zettel sp. nov. (Hemiptera: Gerridae) is described from the Dhubri District, Assam. A key to the species of Pleciobates and a distribution map of the species of Pleciobates from India are provided. For the first time the genitalia of Pleciobates females are described in detail.

Sexual conflict inGerris gillettei(Insecta: Hemiptera): influence of effective mating rate and morphology on reproductive success

In water striders, the interests of both sexes diverge over the decision to mate, leading to precopulatory sexual conflict. The influence of mating rate and key persistence and resistance traits on reproductive success has seldom been investigated in the context of multiple matings. We used amplified fragment length polymorphism (AFLP) based genetic parentage analyses to estimate mating and reproductive success in Gerris gillettei Lethierry and Severin, 1896, while allowing for free multiple matings. We tested the hypotheses that males should display stronger opportunity for sexual selection and steeper Bateman gradients. In each sex, persistence and resistance traits should also impact mating and reproductive success. Surprisingly, males and females had similarly high and variable effective mating rates (i.e., number of genetic partners), and both sexes produce more offspring when mating with more partners. As predicted, exaggerated persistence traits allowed males to mate with more partners and sire more offspring. However, we found no evidence for an impact of resistance traits for females. The mating environment may have favoured low resistance in females, but high promiscuity can be beneficial for females. This first description of the genetic mating system for a water strider species suggests that the determinants of fitness can be further deciphered using the sexual selection framework.

Aquatic and terrestrial organic matter in the diet of stream consumers: implications for mercury bioaccumulation

The relative contribution of aquatic vs. terrestrial organic matter to the diet of consumers in fluvial environments and its effects on bioaccumulation of contaminants such as mercury (Hg) remain poorly understood. We used stable isotopes of carbon and nitrogen in a gradient approach (consumer isotope ratio vs. periphyton isotope ratio) across temperate streams that range in their pH to assess consumer reliance on aquatic (periphyton) vs. terrestrial (riparian vegetation) organic matter, and whether Hg concentrations in fish and their prey were related to these energy sources. Taxa varied in their use of the two sources, with grazing mayflies (Heptageniidae), predatory stoneflies (Perlidae), one species of water strider (Metrobates hesperius), and the fish blacknose dace (Rhinichthys atratulus) showing strong connections to aquatic sources, while Aquarius remigis water striders and brook trout (Salvelinus fontinalis) showed a weak link to in-stream production. The aquatic food source for consumers, periphyton, had higher Hg concentrations in low-pH waters, and pH was a much better predictor of Hg in predatory invertebrates that relied mainly on this food source vs. those that used terrestrial C. These findings suggest that stream biota relying mainly on dietary inputs from the riparian zone will be partially insulated from the effects of water chemistry on Hg availability. This has implications for the development of a whole-system understanding of nutrient and material cycling in streams, the choice of taxa in contaminant monitoring studies, and in understanding the fate of Hg in stream food webs.

SEXUAL SELECTION AND THE EVOLUTION OF GENITAL SHAPE AND COMPLEXITY IN WATER STRIDERS

Animal genitalia show two striking but incompletely understood evolutionary trends: a great evolutionary divergence in the shape of genitalic structures, and characteristic structural complexity. Both features are thought to result from sexual selection, but explicit comparative tests are hampered by the fact that it is difficult to quantify both morphological complexity and divergence in shape. We undertake a comparative study of multiple nongenitalic and male genital traits in a clade of 15 water strider species to quantify complexity and shape divergence. We show that genital structures are more complex and their shape more divergent among species than nongenital traits. Further, intromittent genital traits are more complex and have evolved more divergently than nonintromittent genital traits. More importantly, shape and complexity of nonintromittent genital traits show correlated evolution with indices of premating sexual selection and intromittent genital traits with postmating sexual selection, suggesting that the evolution of different components of genital morphology are shaped independently by distinct forms of sexual selection. Our quantitative results provide direct comparative support for the hypothesis that sexual selection is associated with morphological complexity in genitalic traits and highlight the importance of quantifying morphological shape and complexity, rather than size in studies of genital evolution.

Spermatogenesis and karyotypes of three species of water striders (Gerridae, Heteroptera)

Although they are of economic importance, there have been few cytogenetic studies of the Gerridae (Heteroptera) in Brazil. We examined spermatogenesis (meiosis and spermiogenesis) and nucleolar behavior in three species of the family Gerridae. Brachymetra albinerva and Halobatopsis platensis were found to have a chromosome complement of 2n = 25 (24A + X0) and Cylindrostethus palmaris 2n = 29 (28A + X0) chromosomes. Fifteen individuals of these species were collected from the reservoir of São José do Rio Preto, SP, using screens and were transported in pots containing water to the laboratory, where cytogenetic preparations were made. The polyploidy nuclei are formed by several heteropyknotic regions; cells in meiotic prophase have a heteropyknotic region that is probably the sex chromosome, and the chromosomes from chiasmata. The spermatids are rounded and have a heteropyknotic region at the periphery of the nucleus; the sperm head is small, with a long tail. Silver impregnation of meiotic cells showed one or more disorganized bodies around the perichromosomal sheath. The round spermatids had two bodies next to each other, but these were elongated; one of the bodies remained in the head and the other migrated to the initial part of the tail at the end of spermagenesis, when the staining was no longer evident. The meiotic cells appear during spermatogenesis and have very similar silver-impregnation patterns in different species of Heteroptera.

Disjunct distributions in Gerris species (Insecta: Hemiptera: Gerridae): an analysis based on spatial and taxonomic patterns of genetic diversity

AbstractAim To perform a comparative analysis of distribution and genetic diversity in three closely related water strider species (Gerris) in order to shed light on a putative disjunct distribution in Gerris gillettei.Location Canada and the western United States.Methods Entomological collections from Canada and the United States were surveyed for records of Gerris pingreensis, G. gillettei and Gerris incognitus in order to establish the distribution range of each species. Using samples from present populations, mitochondrial and nuclear DNA sequence variation were used to construct minimum‐spanning networks. Distribution patterns and genetic diversity were then compared among species.Results Our results showed that G. incognitus is a genetically distinct species with an unsuspected disjunct distribution. Gerris pingreensis and G. gillettei were found to share genetic polymorphism and they displayed spatial differences only in terms of haplotype distribution, suggesting that they form a single species.Main conclusions Distributional and molecular information uncover unusual distribution patterns and underline taxonomic uncertainty in a group of three closely related Gerris species. Vicariance and failure to recolonize following the last glaciation could explain the G. incognitus disjunction. Morphological and DNA‐based species identifications suggest different post‐glacial recolonization processes for G. pingreensis and G. gillettei. The putative discontinuous range of G. gillettei may be explained as disjunct phenotypes of a single species.

Male Mating Strategies through Manipulation of Female-perceived Predation Risk: A Minireview and a Hypothesis

In this minireview we focus on how males may exploit female`s sensitivity to predation risk in the context of mating. It has been shown in studies on guppies and jumping spiders that in response to altered female behaviors, which are adaptations to the unfavorable environment and a consequence of females` higher sensitivity to predator`s presence as well as females` higher predation risk, males can adopt condition-dependent mating tactics. It appears that in such cases males do not modify their reproductive behavior directly in response to their own perception of predation risk, but indirectly in response to changes in female behavior induced by predator presence. It has also been recently shown in crabs that males can exploit female behavior by creating safer habitat spots, which increases the male mating success. Hence all the evidence suggests that males not only respond to female sensitivity to the natural variation in predation risk, but that males can also exploit female behavior by altering the environment. As a logical extension of these findings, we present a hypothesis that in certain conditions males can manipulate the environment in order to increase the predation risk and to induce female behaviors that enhance the male`s mating success with the increased predation risk. We propose that such a manipulation to increase predation risk is expected to evolve in males of species with a strong sexual conflict and female-biased predation risk. Although empirical evidence has not been yet shown, initial observations in a water strider species in Korea, Gerris gracilicornis, seem to support this hypothesis.

Sexual conflicts, loss of flight, and fitness gains in locomotion of polymorphic water striders

AbstractIn insect wing polymorphism, morphs with fully developed, intermediate, and without wings are recognized. The morphs are interpreted as a trade‐off between flight and flightlessness; the benefits of flight are counterbalanced by the costs of development and the maintenance of wings and flight muscles. Such a trade‐off has been widely shown for reproductive and developmental parameters, and wing reduction is associated with species of stable habitats. However, in this context, the role of water locomotion performance has not been well explored. We chose seven water striders (Heteroptera: Gerridae) as a model to study this trade‐off and its relation to sexual conflicts, namely, Aquarius elongatus (Uhler), Aquarius paludum (Fabr.), Gerris insularis (Motschulsky), Gerris nepalensis Distant, Gerris latiabdominis Miyamoto, Metrocoris histrio (White), and Rhagadotarsus kraepelini Breddin. We estimated the locomotion performance as the legs’ stroke force, measured on tethered specimens placed on water with a force transducer attached to their backs. By dividing force by body weight, we made performance comparisons. We found a positive relationship between weight and force, and a negative one between weight and the force‐to‐weight ratio among species. The trade‐off between water and flight locomotion was manifested as differences in performance in terms of the force/weight ratio. However, the bias toward winged or wing‐reduced morphs was species dependent, and presumably related to habitat preference. Water strider species favouring a permanent habitat (G. nepalensis) showed higher performance in the apterous morph, but in those favouring temporary habitats (A. paludum and R. kraepelini) morphs’ performance did not differ significantly. Males had higher performance than females in all but three species studied (namely, A. elongatus, G. nepalensis, and R. kraepelini); these three have a type II mating strategy with minimized mating struggle. We hypothesized that in type I mating system, in which males must struggle strongly to subdue the female, males should outperform females to copulate successfully. This was not necessarily true among males of species with type II mating.