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University of Michigan Biological Station

The University of Michigan Biological Station (UMBS) was founded in 1909.

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Effects of Stacked GM Corn on the Growth and Chemically Mediated Behaviors of Juvenile Rusty Crayfish, Orconectes rusticus

Project Abstract: 
As of 2014, 93% of corn crops grown in the United States are genetically modified (GM), with almost three-quarters of GM corn now containing multiple gene insertions. These transgenes confer beneficial traits such as herbicide-tolerance (HT) or insect-resistance (Bt). The mechanisms behind Bt genes are meant to be selective toward target organisms, such as multiple varieties of lepidopteran and coleopteran orders of insects. There are, however, many factors that play a role in the selectivity and efficacy of the toxins produced by Bt transgenes. Many of these interactions have been shown to result in higher than expected overall toxicity, which could have serious implications for non-target organisms such as Daphnia magna and land snails. Negative impacts of Bt toxins on non-target species, both terrestrial and aquatic, have been found. Although HT genes are only meant to confer resistance to glyphosate and glufosinate herbicides for the crops that contain them, Atlantic salmon fed HT crops have exhibited negative histological effects. In Corn Belt states such as Ohio and Michigan, possible ecological effects of the shift to GMO’s and the trend in increasing transgenes are important to assess in both terrestrial and aquatic ecosystems. Maize components enter streams through multiple pathways, but the greatest quantity comes from decomposed byproducts left on the field after harvest. These byproducts travel to streams via wind and surface runoff. Isotope analysis indicates that 17-22% of terrestrial organic carbon in Midwestern streams originates from corn. Although accumulation of maize detritus within streams shows no clear spatial pattern, there is potential for exposure to a variety of organisms within these ecosystems given the flowing nature of streams. Despite feeding on a wide variety of items, crayfish act as shredders, ultimately impacting energy flow and nutrient cycling at many trophic levels. Therefore, they are a species of interest in assessing non-target effects of GM corn in Midwestern streams. Previous research by Linn & Moore assessed growth and survivorship effects on adult rusty crayfish fed GM corn containing one Bt toxin (Cry1Ab), and they found that crayfish fed this Bt corn diet had a 31% lower survivorship than those fed non-GM corn. Follow up studies are necessary to establish these effects. Since stacked and pyramided strains of corn are much more abundant now than those with single modified traits, assessing their impact on non-target species such as crayfish is important for establishing the environmental safety of GM corn containing multiple transgenes.
Investigator(s): 
Molly West
Paul Moore
Years Active: 
2015
Methods: 
Three GM strains of maize were obtained from Rupp Seeds (Wauseon, Ohio): SmartStax , VT Triple Pro, and Roundup Ready 2. Two of these strains contain refuge, which is a non-GM variant of corn seed that was separated out to be used as a control. All maize was grown in the BGSU greenhouse in Metromix 852 topsoil using a 10-10-10 fertilizer and 16-hour photoperiod. After maturation, the maize was given time to dry (generally until the silks on the plant start to brown, around 120 days). Then the cobs, stalks and leaves were removed and dried further in an 80°C oven for 12-24 hours. For ten days prior to growth experiments, the dried plant tissue will be preconditioned in mesh bags in the Maple River to simulate breakdown in the natural environment and allow for microbial growth. Before experimental use, stalks from each strain of maize will be cut and sent to Dairy One Forage Testing Laboratory in Ithaca, New York to assess which parts of each plant strain have similar carbon, nitrogen and lignin content. This will allow us to determine which part of the plant (e.g. leaves or stalks) to use in feeding to control for digestibility and nutritional value among the four plants types. Juvenile crayfish (Orconectes rusticus) will be caught in the Portage River in Bowling Green, Ohio in late May and early June by kick-seining. Juveniles will be identified by carapace length and only animals with a carapace length between 5 and 10 millimeters will be used. Juveniles will be stored in community aquaria in separate mesh containers and fed rabbit pellets twice a week until experimental use. One week before use, all crayfish will be moved to separate mesh compartments in the artificial stream. Once in these compartments, crayfish will be deprived of food for the week prior to experimental treatments. Four flow-through stream treatments, one for each variety of corn, will be constructed and used for the growth treatments. Incoming detritus from the river will be filtered out with pantyhose covering the inflow pipes, which will be switched out on a daily basis. The treatments will be in separate streams constructed of cinder blocks and plastic sheeting that will receive water from the Maple River at the UMBS Stream Lab in Pellston, Michigan. Environmental impacts of this project on the Maple River will be negligible. The streams will measure 114 cm x 38 cm x 19 cm (82.3 L) with a low flow speed between 0.14 and 0.22 L/s. Each treatment will contain 40 juveniles (male or female but without injuries), and the treatments will last eight weeks. At the start of each week, the crayfish will be weighed on a milligram/gram scale and their carapace length measured intraorbital by placing each juvenile on a Plexiglas sheet with a millimeter scale, taking a picture and measuring based off of that picture. Also, a fresh gram of maize detritus will be added to their Tupperware at the beginning of each week. Growth will be assessed at the end of the experiment using specific growth rate of both body weight and carapace length, and survivorship will be assessed also.