Because availability of resources often limits seed or fruit set, increased visits by pollinators may not always lead to increases in maternal reproduction. This observation has led evolutionary biologists to hypothesize that a plant's ability to attract pollinators may have its primary impact on male fitness achieved through the fertlization of ovules. This interpretation of angiosperm reproductive ecology is supported by field experiments. Pollinating insects strongly discriminated between two Mendelian petal-color morphs in Raphanus raphanistrum, a widespread, self-incompatible crucifer. In experimental populations composed of petal-color homozygotes. color discrimination by naturally occurring pollinators had no statistically significant effect on relative maternal function (fruit and seed production) in the two morphs. In contrast, yellow-flowered individuals were far more successful as fathers (pollen donors) than were the less visited whites. These results suggest that the evolution of floral signals such as petal color may be driven primarily by selection on male function.

Abstract. Gene flow from transgenic crops can introduce novel traits into related species, but the ecological importance of this process is unknown. Here, we report the first empirical evidence that wild plants can benefit from a bacterial transgene under uncaged, natural conditions. Cultivated sunflower (Helianthus annuus) is known to hybridize frequently with wild sunflower (H. annuus) in the western and midwestern United States. We studied a crop-developed Bacillus thuringiensis (Bt) transgene, cry1Ac, in backcrossed wild sunflower populations. Lepidopteran damage on transgenic plants was strongly reduced relative to control plants at our two study sites, while damage by several weevil and fly species was unaffected. Our results suggest that reduced herbivory caused transgenic plants to produce an average of 55% more seeds per plant relative to nontransgenic controls at the field site in Nebraska. A similar but nonsignificant trend was seen at the site in Colorado (14% more seeds per plant). In a greenhouse experiment the transgene had no effect on fecundity, suggesting that it was not associated with a fitness cost. If Bt sunflowers are released commercially, we expect that Bt genes will spread to wild and weedy populations, limit damage from susceptible herbivores on these plants, and increase seed production when these herbivores are common.

Crop-wild hybridization may produce offspring with lower fitness than their wild parents due to deleterious crop traits and outbreeding depression. Over time, however, selection for improved fitness could lead to greater invasiveness of hybrid taxa. To examine evolutionary change in crop-wild hybrids, we established four wild (Raphanus raphanistrum) and four hybrid radish populations (R. raphanistrum x Raphanus sativus) in Michigan (MI), USA. Hybrid and wild populations had similar growth rates over four generations, and pollen fertility of hybrids improved. We then measured hybrid and wild fitness components in two common garden sites within the geographical range of wild radish [MI and California (CA)]. Advanced generation hybrids had slightly lower lifetime fecundity than wild plants in MI but exhibited c. 270% greater lifetime fecundity and c. 22% greater survival than wild plants in CA. Our results support the hypothesis that crop-wild hybridization may create genotypes with the potential to displace parental taxa in new environments.

The evolutionary significance of introgression has been discussed for decades. Questions about potential impacts of transgene flow into wild and weedy populations brought renewed attention to the introgression of crop alleles into those populations. In the past two decades, the field has advanced with considerable descriptive, experimental, and theoretical activity on the dynamics of crop gene introgression and its consequences. As illustrated by five case studies employing an array of different approaches, introgression of crop alleles has occurred for a wide array of species, sometimes without significant consequence, but on occasion leading to the evolution of increased weediness. A new theoretical context has emerged for analyzing empirical data, identifying factors that influence introgression, and predicting introgression's progress. With emerging molecular techniques and analyses, research on crop allele introgression into wild and weedy populations is positioned to make contributions to both transgene risk assessment and reticulate evolution.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract.The rapid development of molecular techniques offers a palette of technical approaches for population biologists interested in a wide range of questions. For example, these tools can be used to determine individual reproductive success or to measure rates of genetic divergence among populations. Which technique is most appropriate for a particular question depends upon (1) the extent of genetic polymorphism required to best answer the question, (2) the analytical or statistical approaches available for the technique's application, and (3) the pragmatics of time and costs of materials. Here we evaluate the application of several major techniques (protein electrophoresis, nuclear and mitochondrial RFLPs [restriction fragment length polymorphisms], minisatellite and microsatellite VNTRs [variable number tandem repeats], RAPDs [random amplified polymorphic DNA], and DNA sequencing) to an array of questions regarding individual identification, exclusion and assignment of parentage, and various levels of population structure. In our evaluation, we briefly explain the technical components of each molecular approach and assess whether the typical outcomes expected from each approach will provide useful information as applied to each level of inquiry. For studies of population genetic structure, protein electrophoresis remains a powerful tool for most taxa, although techniques based on nucleic acids (particularly DNA sequencing and mitochondrial DNA RFLPs) are useful here as well. Recently developed nucleic acid techniques (e.g., VNTRs) can often identify enough genetic variability to address questions of self-identification or parentage. Some of the newest techniques (RAPDs and microsatellites) are potentially useful across a number of levels of inquiry, although procedures for adopting them are still developing. striction fragment length polymorphism (RFLP). SPECIAL FEATURE Vol. Ecolo7NVo.79, No. 2 consideration of the trade-offs associated with different techniques and the types of data obtained from them. Our aim is to provide this perspective. First we define the basic categories of genetic techniques available for use in population ecological studies, including explanations of fundamental procedures common to all techniques as well as features unique to particular classes of techniques. We present the basic categories of techniques in order of increasing resolution of resulting information, and we evaluate how these techniques can be applied to a standard range of questions in population ecology. Features such as cost, technical difficulty, appropriateness of result...