Mayfly

Abstract: We tested the efficacy of DNA barcodes in identifying mayfly species primarily from the northeastern United States and central Canada. We sequenced a 630-base-pair segment of the mitochondrial gene, cytochrome c oxidase 1 (COI), from 1 individual of each of 80 species to create a reference sequence profile. We used these reference sequences to identify 70 additional specimens representing 32 of the species that were in the profile. DNA barcodes correctly identified 69 of the 70 test specimens. The sole exception was an individual identified morphologically as Maccaffertium modestum that showed deep genetic divergence from other M. modestum specimens. Mean sequence divergence within species was 1%, whereas mean divergence among congeneric species was an order of magnitude greater (18%). We conclude that DNA barcoding can provide a powerful tool for mayfly species identification.

Abstract: Field experiments were conducted at two streams to determine the mechanisms by which mayfly prey detect and avoid stonefly predators, and to quantify the effect of stonefly predators upon mayfly behavior, distribution, and activity levels. Direct observations of the interactions be- tween stoneflies and mayflies were made at Otter Creek, Sauk County, Wisconsin, USA and the East River, Gunnison County, Colorado, USA using plexiglass boxes with screen ends and an artificial substrate. Ephemerella subvaria and Stenonemafuiscum, Otter Creek, avoided the stonefly predator Acroneuria lycorias given only noncontact chemical stimuli. Ephemerella infrequent and Baetis bicaudatus, East River, responded to long-range chemical stimuli from Megarcys signata and Ko- gotus modestus, East River. Baetis phoebus and Heptagenia hebe, Otter Creek. and Cinygmula sp., East River, did not respond to stonefly predators given long-range chemical cues alone. Differences among responses of different mayflies may be due to differential predation pressure or effectiveness of predator evasion tactics. None of the species of mayflies tested responded to the presence of stonefly predators given only visual stimuli. The Ephemerella species assumed a "scorpion"-like display posture upon encounter with the stoneflies. This posture may increase the apparent size of the mayflies which are then rejected by the tactile predators. The Baetis species characteristically swam or drifted in response to contact with the stonefly predators. Predator evasion could partially explain the high incidence of this genus of mayflies reported in stream drift. The remaining mayflies, of the family Heptageniidae, showed an effective crawling evasion upon contact with stonefly predators. Ephemerella infrequens and B. bicaudatus differentially responded to contact with three different stonefly predators in the East River. Both species of mayflies evaded contact with Pteronarcella badia, a large omnivorous stonefly which morphologically resembles M. signata, significantly less frequently than they evaded M. sig- nata and K. modestus upon contact. The mechanism by which this differentiation occurs could be chemotactile. Cinygmula sp. avoided all stoneflies equally regardless of size or relative threat of consumption. Tactile stimuli are probably responsible for this behavior.

Abstract: The extant global Ephemeroptera fauna is represented by over 3,000 described species in 42 families and more than 400 genera. The highest generic diversity occurs in the Neotropics, with a correspondingly high species diversity, while the Palaearctic has the lowest generic diversity, but a high species diversity. Such distribution patterns may relate to how long evolutionary processes have been carrying on in isolation in a bioregion. Over an extended period, there may be extinction of species, but evolution of more genera. Dramatic extinction events such as the K-T mass extinction have affected current mayfly diversity and distribution. Climatic history plays an important role in the rate of speciation in an area, with regions which have been climatically stable over long periods having fewer species per genus, when compared to regions subjected to climatic stresses, such as glaciation. A total of 13 families are endemic to specific bioregions, with eight among them being monospecific. Most of these have restricted distributions which may be the result of them being the relict of a previously more diverse, but presently almost completely extinct family, or may be the consequence of vicariance events, resulting from evolution due to long-term isolation.

Abstract: The present study evaluated the acute and chronic toxicity of imidacloprid to a range of freshwater arthropods. Mayfly and caddisfly species were most sensitive to short-term imidacloprid exposures (10 tests), whereas the mayflies showed by far the most sensitive response to long-term exposure of all seven arthropod species tested (28-d EC10 values of approximately 0.03?µg/L). The results indicated a high aquatic risk of chronic exposure of imidacloprid to mayflies.