Gerridae - WikiHQ

The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, water gliders, water skimmers or puddle flies. They are true bugs of the suborder Heteroptera and have mouthparts evolved for piercing and sucking. A distinguishing feature is the ability to move on top of the water's surface, making them pleuston (surface-living) animals. They can be found on most ponds, rivers or lakes, and over 1,700 species of gerrids have been described, 10% of them being marine.

While 90% of gerrids are freshwater bugs, the oceanic Halobates makes the family quite exceptional among insects. The genus Halobates was first heavily studied between 1822 and 1883 when Francis Buchanan White collected several different species during the Challenger expedition. Around this time, Eschscholtz discovered three species of the Gerridae, bringing attention to the species, though little of their biology was known.

Hydrofuge hairpiles are small, hydrophobic microhairs. These are tiny hairs with more than one thousand microhairs per mm. Among widespread genera, the North Hemisphere Aquarius includes the largest species, generally exceeding , at least among females, and the largest species averaging about . Females are typically larger than males of their own species,

Antennae

thumb|Waterstrider in the genus [[Gerris]]

Water striders have two antennae with four segments on each. Antennal segments are numbered from closest to the head to farthest. The antennae have short, stiff bristles in segment III. Relative lengths of the antennae segments can help identify unique species within the family Gerridae, but in general, segment I is longer and stockier than the remaining three. The four segments combined are usually no longer than the length of the water strider head.

Thorax

The thorax of water striders is generally long, narrow, and small in size. It generally ranges from 1.6 mm to 3.6 mm long across the species, with some bodies more cylindrical or rounder than others. Wing dimorphism consists of summer gerrid populations evolving different length wings than winter populations within the same species. Habitats with rougher waters are likely to hold gerrids with shorter wings, while habitats with calm waters are likely to hold long-winged gerrids. This is due to potential for damage of the wings and ability for dispersal. However, it was later interpreted as an indeterminate member of Gerroidea. The Gerridae are morphologically similar to the unrelated Chresmoda, an enigmatic genus of insect known from the Late Jurassic to the Mid Cretaceous with a presumably similar lifestyle.

Molecular analysis suggest an origin of the family Gerridae about 128 Million years ago (Mya) in the Cretaceous, splitting from the sister group Veliidae, with whom they share a single origin of rowing as a locomotive mechanism. According on the transcriptome-based phylogeny, Gerridae is a monophyletic group. something that has been important for the evolution of the variety in species we see today, and dispersal of Gerridae. The existence of wing polymorphism in a given species can be explained as a particular case oogenesis-flight syndrome. Following this rationale, which is commonly applied in insects, developing short wings provides the individual with the capacity to dedicate the energy stores that would usually be used for wing and wing muscle development to increasing egg production and reproducing early, ultimately enhancing the individual's fitness. The ability for one brood to have young with wings and the next not allows water striders to adapt to changing environments. Long, medium, short, and nonexistent wing forms are all necessary depending on the environment and season. Long wings allow for flight to a neighboring water body when one gets too crowded, but they can get wet and weigh a water strider down. Short wings may allow for short travel, but limit how far a gerrid can disperse. Nonexistent wings prevent a gerrid from being weighed down, but prevent dispersal.

Wing polymorphism is common in the Gerridae despite most univoltine populations being completely apterous (wingless) or macropterous (with wings). Apterous populations of gerrids would be restricted to stable aquatic habitats that experience little change in environment, while macropterous populations can inhabit more changing, variable water supplies.

The tiny hairs on the legs provide both a hydrophobic surface as well as a larger surface area to spread their weight over the water. The middle legs used for rowing have particularly well developed fringe hairs on the tibia and tarsus to help increase movement through the ability to thrust. When the rowing stroke begins, the middle tarsi of gerrids are quickly pressed down and backwards to create a circular surface wave in which the crest can be used to propel a forward thrust.

Life cycle

Gerrids generally lay their eggs on submerged rocks or vegetation using a gelatinous substance as a glue. Gravid females carry between two and twenty eggs. The eggs are creamy white or translucent, but become bright orange. This means that individuals tend to develop at the same rate through each instar stage. Each nymphal stage lasts 7–10 days and the water strider molts, shedding its old cuticle through a Y-shaped suture dorsal to the head and thorax. The marine species are generally coastal, but a few Halobates live offshore (oceanic) and are the only insects of this habitat. Halobates, which are found on open sea, feed off floating insects, zooplankton, and occasionally resort to cannibalism of their own nymphs. << Doubtful. Are they actually able to dive when air is trapped on their legs and body hair? Would they not "disperse" over the entire water surface even without predators and migrate to different sites when the numbers are high and food is scarce? The adaption to new environments and evolution of species is not particular to gerrids. See also the paragraph "Dispersal" below .. -->

Parasites

Several endoparasites have been found in gerrids. Trypanosamatid flagellates, nematodes, and parasitic Hymenoptera all act as endoparasites. Nymphal population density also affects the dispersal of water striders. The higher density of water striders in the nymphal stage results in a higher percentage of brachypterous adults developing flight muscles. These flight muscles allow for the water striders to fly to neighboring bodies of water and mate, resulting in the spread of genes. This spread and mixing of genes can be beneficial due to a heterozygotic advantage. Generally, water striders will try to disperse in such a way to lower the density of gerrids in one area or pool of water. Most do this by flight, but those that lack wings or wing muscles will rely on the current of their water body or flooding. Eggs in Halobates are often laid on floating ocean debris and thus spread across the ocean by this drifting matter. Water striders will reproduce all year long in tropical regions where it remains warm, but only during the warm months in seasonal habitats. Gerrids that live in environments with winters will overwinter in the adult stage. This is due to the large energy cost which would need to be spent to maintain their body temperature at functional levels. These water striders have been found in leaf litter or under stationary shelters such as logs and rocks during the winter in seasonal areas. Those two species are highly prevalent in American waters. These species do not show familial tendencies, leaving their young to forage on their own. Females cannibalize more on young than males do and, in particular, on first-instar nymphs.

In the 2002 film The Tuxedo, water striders are genetically modified by bioterrorists to have bacteria that can spread from person to person, causing severe dehydration and instant death.
In the third generation of Pokémon games developed by GameFreak and published by The Pokémon Company and Nintendo, the 2002 video games Pokémon Ruby and Pokémon Sapphire introduced Surskit, the first dual Bug/Water type Pokémon, which is based on the appearance and behavior of a water strider.

References

External links

Large format pictures: winged and wingless varieties
Row, Row, Row Your Bug
Video of water strider movements
Video of Pond Skaters (Gerris lacustris) in Wales, U.K.