Transgenic DNA introgressed into traditional maize landraces in Oaxaca, Mexico.

Concerns have been raised about the potential effects of transgenic introductions on the genetic diversity of crop landraces and wild relatives in areas of crop origin and diversification, as this diversity is considered essential for global food security. Direct effects on non-target species, and the possibility of unintentionally transferring traits of ecological relevance onto landraces and wild relatives have also been sources of concern. The degree of genetic connectivity between industrial crops and their progenitors in landraces and wild relatives is a principal determinant of the evolutionary history of crops and agroecosystems throughout the world. Recent introductions of transgenic DNA constructs into agricultural fields provide unique markers to measure such connectivity. For these reasons, the detection of transgenic DNA in crop landraces is of critical importance. Here we report the presence of introgressed transgenic DNA constructs in native maize landraces grown in remote mountains in Oaxaca, Mexico, part of the Mesoamerican centre of origin and diversification of this crop.     

Fish assemblage structure following impoundment of a Great Plains river

Understanding the upstream and downstream effect of impoundments on stream fish assemblages is important in managing fish populations and predicting the effects of future human activities on stream ecosystems. We used information collected over a 41-year period (1960-2001) to assess changes in fish assemblage structure resulting from impoundment of the Laramie River by Grayrocks Reservoir. Prior to impoundment (i.e., 1960-1979), fish assemblages were dominated by native catostomids and cyprinids. After impoundment several exotic species (e.g., smallmouth bass [ Micropterus dolomieu ], walleye [ Sander vitreus ; formerly Stizostedion vitreum ], yellow perch [ Perca flavescens ], brown trout [ Salmo trutta ]) were sampled from reaches upstream and downstream of the reservoir. Suckermouth minnows ( Phenacobius mirabilis ) were apparently extirpated, and hornyhead chubs ( Nocomis biguttatus ) and common shiners ( Luxilus cornutus ) became rare upstream of Grayrocks Reservoir. The lower Laramie River downstream from Grayrocks Reservoir near its mouth retains habitat characteristics similar to those prior to impoundment (e.g., shallow, braided channel morphology) and is the only downstream area where several sensitive species persist, including suckermouth minnows, hornyhead chubs, and bigmouth shiners ( Notropis dorsalis ). Grayrocks Reservoir serves as a source of exotic piscivores to both upstream and downstream reaches and has altered downstream habitat characteristics. These impacts have had a substantial influence on native fish assemblages. Our results suggest that upstream and downstream effects of impoundment on fish assemblage structure are similar and that downstream reaches which retain habitat characteristics similar to pre-impoundment conditions may serve as areas of refuge for native species.