Gerridae's Pollution Tolerance: An Evolutionary Advantage?

Water striders, or Gerridae, are a group of semi-aquatic insects that occupy a wide variety of habitats, from the open ocean to mountain streams. They are characterised by their ability to skim over the water surface and feed on small organisms that fall from above. With their complex three-dimensional waterproof hairy cover, they are super-hydrophobic, allowing them to navigate their environment with ease. Interestingly, some species of water striders can even jump from the water's surface to escape predators. Beyond their ecological significance, water striders have also emerged as potential bioindicators of water pollution, particularly heavy metal contamination. While they have been touted as sentinels for mercury contamination in freshwater ecosystems, there is still much to uncover about the factors influencing metal concentrations in these invertebrates.

Water striders (Gerridae) as bioindicators of heavy metal pollution

Water striders (Gerridae) are bioindicators of heavy metal pollution. They are predators that feed on terrestrial insects, planktonic crustaceans, and fish larvae. Due to their scavenging activities, water striders can accumulate heavy metals such as lead (Pb), chromium (Cr), arsenic (As), cadmium (Cd), and nickel (Ni). This accumulation of heavy metals can be used as a bioindicator of water pollution.

Water striders have a high tolerance to human impact and pollution, which has led to their wide distribution. They are particularly good bioindicators of Cd contamination. The species composition of Corixidae, for instance, is related to salinization. Water bugs, including water striders, can play an important role in water biomonitoring.

A study in Pakistan found that water striders could be used as a bioindicator of heavy metal pollution through antioxidant enzyme variations. The results showed that different species of water striders exhibited varying levels of antioxidant enzyme activities, which reflected the presence of heavy metal pollution in the water.

Additionally, water striders have been used to study the impact of specific abiotic factors in anthropogenically stressed ponds. Gerris spinolae, for example, was found to have a significant negative correlation with BOD, phosphate, free CO2, and algae dry weight, indicating that it is a pollution-sensitive and effective bioindicator for healthy, unpolluted ponds.

In summary, water striders (Gerridae) are useful bioindicators of heavy metal pollution due to their ability to accumulate heavy metals and their sensitivity to pollution levels. Their wide distribution and tolerance to human impact make them readily available for sampling, and their antioxidant enzyme variations provide valuable information about the presence and effects of heavy metal pollutants in aquatic environments.

Water striders' complex three-dimensional waterproof hairy cover

Water striders, also known as Gerridae, are a group of epineustonic insects with only 16 species inhabiting Europe. Due to their large ecological valences and high tolerance to human impact and pollution, they are widely distributed. Water striders are predators that feed on terrestrial insects, planktonic crustaceans, and fish larvae. They can accumulate heavy metals due to their scavenging activities and act as bioindicators of heavy metal contamination.

Water striders possess a complex three-dimensional waterproof hairy cover, which makes them super-hydrophobic. This unique feature allows them to have non-wetting legs, enabling them to stand and move effortlessly on water. The super-hydrophobicity of their cuticle is attributed to its complex two-level microstructure. This microstructure consists of tiny projections called microtrichia, which are 200-300 nanometers wide and 7-9 micrometers long.

The two-step moulding technique was used to replicate the microstructure, and the resulting mould exhibited similar super-hydrophobic properties to the original insect surface. The average water contact angle (CA) of the mould was 164.7 degrees, much higher than the CA of a flat polymer, which was about 92 degrees. This demonstrates that the surface topography of water striders plays a dominant role in their super-hydrophobicity.

Additionally, the grease layer on the water strider's surface also contributes to its hydrophobic properties. This grease layer is composed of a mixture of aliphatic compounds, which naturally possess hydrophobic characteristics due to their chemical structure. The combination of the microstructure and the grease layer enhances the water strider's ability to repel water and navigate aquatic environments effectively.

Water striders as sentinels for mercury contamination

Water striders (Gerridae) are predatory invertebrates that feed on aquatic and terrestrial insects, planktonic crustaceans, and fish larvae. They are abundant in many pond, lake, and river ecosystems. Due to their large ecological valences and high tolerance to human impact and pollution, they are considered good bioindicators of water pollution.

Water striders have been identified as potential sentinel species for monitoring mercury contamination in small freshwater ecosystems. Sentinel species are useful for expanding contaminant-monitoring programs. Water striders are relatively long-lived, have a large body size, a long life span, are easy to identify, and have a relatively sedentary lifestyle.

In a study conducted in New Brunswick, Canada, researchers compared mercury concentrations in water striders and brook trout (Salvelinus fontinalis) from various stream sites. The results showed a strong association between mercury levels in the two species, especially in systems with both atmospheric deposition and a point source of mercury contamination, such as an abandoned gold mine. Water striders had significantly higher mercury concentrations in streams draining the gold mine tailings. This suggests that water strider mercury levels can accurately quantify the entry of mercury into the food chain.

However, it is important to note that water striders may have limited utility as sentinels for aquatic mercury contamination. This is because the majority of their biomass is derived from the terrestrial environment, and they have no secondary route of exposure to waterborne mercury. Nevertheless, their strong connection to the terrestrial environment can help link measured mercury concentrations with predicted atmospheric mercury deposition, providing insights into spatial and temporal trends in mercury contamination. Additionally, their ability to undergo rapid changes in mercury concentrations may make them useful as short-term indicators of mercury availability.

Water striders' feeding habits

Water striders, also known as pond skaters, water skippers, Jesus bugs, or water skeeters, are small insects that live on top of still water. They belong to the Gerridae family, which includes over 1,700 species, many of which are found in freshwater. Water striders have a unique ability to "walk on water" due to the tiny hairs on their legs that repel water and capture air, allowing them to float and move easily on the water's surface.

Water striders are predatory insects and play an essential role in controlling the populations of certain aquatic insects. They feed on live and dead insects that they encounter on the water's surface, such as mosquitoes, mosquito larvae, and fallen dragonflies. Additionally, they help control water aphid populations, benefiting plants like water lilies that are susceptible to aphid attacks.

The diet of water striders consists primarily of small invertebrates and planktonic crustaceans that fall on the water surface. They have also been observed consuming Diptera, Homoptera, and Hymenoptera in larger proportions than those found in sweep samples from the same habitat. This suggests that water striders do not have a preference for prey size and will feed on a variety of insects.

In a rice field near Seoul, Korea, the diet of Gerris lacustris was studied, and it was found that their diet included small invertebrates that fell on the water surface. This habitat comprised rice fields, canals, and irrigation ponds, providing an ample food source for the water striders.

Water striders have also been identified as good bioindicators of water pollution, especially heavy metal contamination. They can accumulate heavy metals through their scavenging activities, and their antioxidant enzyme systems help them cope with exposure to these toxins. Thus, studying water striders can provide valuable information about the presence and impact of water pollution in a given area.

Water striders' distribution and habitat

Water striders, also known as Gerridae, are small insects that are adapted for life on top of still water. They use the high surface tension of water and their long, hydrophobic legs with tiny hairs to stay above the water and move easily. Water striders are widely distributed due to their large ecological valence and high tolerance to human impact and pollution. They are found in a variety of habitats, including freshwater areas such as ponds, vernal pools, and marshes, as well as marine waters along coastal regions.

The majority of water striders inhabit freshwater areas, with a preference for calm or slow-moving waters. They are known to inhabit ponds, pools, marshes, and even mud puddles. Water striders are also found in the continental United States, Europe, the former USSR, Canada, South Africa, South America, Australia, China, and Malaysia. They are particularly attracted to waters with temperatures around 25 °C (77 °F) and tend to avoid temperatures below 22 °C (72 °F) as it negatively impacts the development of their young.

Some species of water striders have wings, while others do not. Wing length and presence can vary within the same species, with summer populations having different wing lengths than winter populations. Habitats with rougher waters are likely to hold gerrids with shorter wings, while habitats with calm waters are likely to hold long-winged gerrids. The presence or absence of wings allows water striders to adapt to changing environments and disperse to new habitats.

Water striders prefer environments with an abundance of insects, zooplankton, and rocks or plants to oviposit their eggs. They feed on terrestrial insects that fall into the water, such as mosquitoes and dragonflies, as well as planktonic crustaceans and fish larvae. Water striders can accumulate heavy metals due to their scavenging activities and act as bioindicators of water pollution.

Overall, water striders are widely distributed and adaptable insects that can be found in a variety of habitats, making use of their unique abilities to walk on water and sense changing environments.

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