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Species Page - Gyrinus
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scientific name    Gyrinus    

habitat
Most freshwater habitats, prefer the edges of lentic and lotic habitats (Oygur and Wolfe 1991).

seasonality
Some species collected all year round, most abundant late in the summer (Oygur and Wolfe 1991).

identification
Gyrinus can be separated from other Neartic gyrinids by the following combination of characters: meso- and metatibia as long as broad; dorsal and ventral compound eyes distinctly separated; body length greater than 3 mm; last abdominal segment rounded; elytra lacking pubescents on sides; triangualar sclerite between elytra and pronotum (scutellum) visible; and elytra with 11 distinct rows (striae) (Oygur and Wolfe 1991). Males can be differentiated from females by dilated (squamose) front foot pads (tarsi) (Fall 1922).

life history
Copulation occurs on waters surface, lasts 1 to 2 minutes, males may stay attached for up to a day (Oygur and Wolfe 1991). White, ovate eggs are laid in clusters or irregular rows beneath water surface on submergent vegetation (Oygur and Wolfe 1991). Eggs gestate for approximately 12 days (Oygur and Wolfe 1991). Larvae are aquatic, passing through three instars in 30 to 40 days (Oygur and Wolfe 1991). The larvae have abdominal tracheal gills, resembling a lacey fringe (Beutel and Roughley 1988). Larvae are most susceptible to predation by fish (Oygur and Wolfe 1991). Mature larvae leave water to build a cocoon from bits of sand and plant material glued together by oral secretions (Oygur and Wolfe 1991). Pupation occurs on vertical surfaces of emergent vegetation (Oygur and Wolfe 1991). Height of cocoons above water variable with species (Oygur and Wolfe 1991). The pupal stage has been observed being parasitized by Gausocentrus gyrini Ashmead and Hemiteles hungerfordi Cushman (both Ichneumonidae) (Oygur and Wolfe 1991).

conservation
Not apparently threatened

diet info
Adults eat live and dead animal matter caught in surface film (Oygur and Wolfe 1991). Phytophagy may occur if no suitable food is available (Oygur and Wolfe 1991). Larvae are carnivorous, method of ingestion not known. Larval mandibles are grooved (Oygur and Wolfe 1991).

range
Worldwide distribution, most diverse in Nearctic (Oygur and Wolfe 1991).

notes
130 species worldwide, 46 Nearctic, 21 in Alberta (Roughly 1991). Gyrinus parcus is the type species for the genus (Oygur and Wolfe 1991). Were the first beetles to colonize aquatic habitats and did so independently of the rest of Hydradephaga (Beutel and Roughley 1988). Adults secrete defensive compounds from pygidial glands in the prothorax (Miller and Mumma 1975). Adults are rarely eaten by fish and are often quickly regurgitated if taken (Miller and Mumma 1975). These secretions also have antimicrobial properties (Kovac and Maschwitz 1990). When exposed to increased temperature and light intensity, gyrinids and other hydradepha, crawl from the water and spread these secretions over their body (Kovac and Maschwitz 1990). This behavior is known as secretion-grooming. Waves generated through swimming are used in a form of echolocation (Tucker 1969). Pressure waves on the water's surface are generated by the beetles turning and swimming (Tucker 1969). The reflections of these waves are perceived by an enlarged earlike antennal segment (Tucker 1969). This information is used to locate prey and avoid collision (Tucker 1969). Gyrinid's flattened mid and hind legs make them the most efficient swimmers of all the aquatic invertebrates (Oygur and Wolfe 1991). Species of Gyrinus are known to swim at speeds up to 1m/sec (Oygur and Wolfe 1991). Gyrinids are effective swimmers in the surface film and below the water's surface (Valinec 1987). Surfactants secreted from pygidial glands may aid in propulsion (Valinec 1987). However, the majority of propulsion comes from synchronized strokes of the swimming legs (Valinec 1987). Gyrinus sp. have been collected in multi-species (up to 7) schools (Fall 1922). Gyrinid aggregations vary in size from 1 to 1000 individuals (Watt and Chapman 1998). When exposed to a predators gyrinids swim rapidly and dive (Watt and Chapman 1998). Aggregations allow for increased foraging success and reduced risk of predation (Watt and Chapman 1998).

quick link
http://entomology.museums.ualberta.ca/searching_species_details.php?s=20407



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