Identification: This waterflea has a short and prominent antennae mound. Its helmet is narrow, pointed at the top, and somewhat undulating along the margins. The rostrum is blunt and obtuse. The ventral side of the head is convex above the optic vesicle and concave behind it. These features are important to note in order to avoid confusing D. g. galeata with the native North American subspecies, D. g. mendotae (Brooks 1957; Glagolev 1986; Taylor and Hebert 1993).
The North American and European subspecies have hybridized in the Great Lakes basin. Morphologies and genetics of hybrid D. g. galeata x D. g. mendotae tend more toward the European D. g. galeata form in Lake Erie and more towards the North American D. g. mendotae form in the Lake Ontario drainage (Taylor and Hebert 1993).
Mature parthenogenetic females of European D. galeata can reach a maximum of 2.8 mm in length, although most females range from 1.3–2 mm. Males grow up to 1.4 mm but most are around 1.2 mm. The hybrid D. g. galeata x D. g. mendotae is slightly larger than native D. g. mendotae, which can grow up to a maximum of around 1.75–2.5 mm, depending on conditions, but is usually around 0.6–1.6 mm long (Heisey and Porter 1977; Flobner and Kraus 1986; Glagolev 1986; Lynch et al. 1986; Dodson 1988; Leibold and Tessier 1991; Taylor and Hebert 1993; Boersma 1995).
Impact of Introduction:
A) Realized: After D. g. galeata was introduced to Lake Erie it rapidly hybridized with native D. g. mendotae. Hybrid clones are now very common, especially during the summer months in Lake Erie (Taylor and Hebert 1993).
B) Potential: It is possible that hybrid clones of D. g. mendotae x D. g. galeata are more vigorous and fit than parent clones, especially in times of environmental stress. This could have led to rapid expansion of the hybrid population, especially in parts of Lake Erie (Taylor and Hebert 1993).
References: (click for full references)
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Brooks, J.L. 1957. The systematics of North American Daphnia. Memoirs of the Connecticut Academy of Arts and Sciences 13: 1-180.
Dodson, S.I. 1988. Cyclomorphosis in Daphnia galeata mendotae Birge and D. retrocurva Forbes as a predator-induced response. Freshwater Biology 19: 109-114.
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Flobner, D., and K. Kraus. 1986. On the taxonomy of the Daphnia hyalina-galeata complex (Crustacea: Cladocera). Hydrobiologia 137: 97-115.
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GLMRIS. 2012. Appendix C: Inventory of Available Controls for Aquatic Nuisance Species of Concern, Chicago Area Waterway System. U.S. Army Corps of Engineers.
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This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.