Are new species formed in rare catastrophes, distinct from the normal processes of phyletic evolution? Or does reproductive isolation evolve gradually, as a by-product of the divergence of gene pools? Mayr (120-124) has argued the former, holding that speciation usually results from genetic revolutions triggered by founder effects: An isolated population, small in numbers and in geographic extent, colonizes a new area. Both changes in selection pressures and genetic drift result in the rapid shift of many genes to a new, coadapted combination, which is reproductively isolated from the ancestral population. Carson (27, 29, 3 1) and Templeton (I175-180), among others, have put forward similar models. This cluster of theories is woven from many strands; we will try to tease these apart in order to find out precisely which processes may be involved in speciation by founder effect. By placing them in the context of other models, we will argue that, although founder effects may cause speciation under sufficiently stringent conditions, they are only one extreme of a continuous range of possibilities. Complete geographic isolation is unnecessary; absolute coadaptation between "closed" systems of alleles is unlikely; and divergence may be driven in a variety of ways, without the need for drastic external changes. Reproductive isolation is most likely to be built up gradually, in a

Genetic Revolutions, Founder Effects, and Speciation

The ecological and evolutionary aspects of planned introductions of transgenic organisms into the environment are considered in this report. The authors support the timely development of environmentally sound products, such as improved agricultural varieties, fertilizers, pest control agents, and microorganisms for waste treatment, through the use of advanced biotechnology within the context of a scientifically based regulatory policy that encourages innovation without compromising sound environmental management. Economic, social, and ethical concerns also must be weighed along with strictly ecological and evolutionary considerations, but these other issues are beyond the scope of this report. Ecological oversight of planned introductions should be directed at promoting effectiveness while guarding against potential problems. The diversity of organisms that will be modified, functions that will be engineered, and environments that will receive altered organisms makes ecological risk evaluation complex. While we cannot now recommend the complete exemption of specific organisms or traits from regulatory oversight, we support and will continue to assist in the development of methods for scaling the level of oversight needed for individual cases according to objective, scientific criteria, with a goal of minimizing unnecessary regulatory burdens. In this report, we provide a preliminary set of specific criteria for the scaling of regulatory oversight. Genetically engineered organisms should be evaluated and regulated according to their biological properties (phenotypes), rather than according to the genetic techniques used to produce them. Nonetheless, because many novel combinations of properties can be achieved only by molecular and cellular techniques, products of these techniques may often be subjected to greater scrutiny than the products of traditional techniques. Although the capability to produce precise genetic alterations increases confidence that unintended changes in the genome have not occurred, precise genetic characterization does not ensure that all ecologically important aspects of the phenotype can be predicted for the environments into which an organism will be introduced. Many important scientific issues must be considered in evaluating the potential ecological consequences of the planned introduction of genetically engineered organisms into the environment. These include survival and reproduction of the introduced organism, interactions with other organisms in the environment, and effects of the introduced organism on ecosystem function. We encourage the use of small—scale field tests , when justified by previous laboratory and/or greenhouse studies, under conditions that minimize dispersal and under appropriate regulatory oversight. As the biotechnology industry develops, continuing regulatory oversight as well as long—term research and monitoring will be necessary for responsible risk management. Many engineered organisms will probably be less fit than the parent organism, although some important exceptions may arise. Even if an engineered trait reduces an organism's fitness only slightly, may generations may pass before the introduced organisms disappears completely due to decreased fitness. Such persistence is most probable when the turnover rate of populations is very slow. Natural selection will act on genetically engineered organisms, as it does on all others. Selection after the release of the transgenic organism will tend to increase fitness, not decrease it, by reducing the costs associated with the novel traits. If increases in fitness do occur, they will probably increase population growth rate and biological competitiveness, or produce other ecological effects that should be considered in assessing risks. Transfer of engineered genes from the modified organism to other organisms may occur through hybridization in higher organisms, or through conjugation, transduction, or transformation in microorganisms. If lateral transfer occurs, an engineered gene may persist in the natural environment even after the genetically engineered organism itself is no longer present. The available scientific evidence indicates that lateral transfer among microorganisms in nature is neither so rare that we can ignore its occurrence, nor so common that we can assume that barriers crossed by modern biotechnology are comparable to those constantly crossed in nature. Native species, as well as species newly introduced from distant habitats, may become pests. An organism engineered to prosper in a new habitat type, geographic area, or season is effectively an introduced organism in that it will probably enter into new biotic and abiotic interactions. Therefore, regulatory and risk assessment structures that rely on the distinction between ~`native" and ~`non—native" must be used with caution. Concern has frequently been expressed regarding the potential for genetically engineered organisms to displace resident species in the receiving community, particularly microbial species performing key functional roles such as nitrogen fixation of lignin decomposition. Because redundancy of function appears to be common in microbial communities, in many cases there would be little concern over microbial species displacement caused by an introduced transgenic organism. Ecological effects and the geographic ranges of organisms transcend political boundaries; we therefore consider it essential to promote and achieve international coordination of risk assessment and regulation of biotechnology. Special consideration must be given to the protection of rare genetic resources, such as the wild ancestors of domesticated species, and threatened gene pools of other wild species. We urge local, state, national, international cooperation in risk assessment and regulation of the ecological effects of the introduction of transgenic organisms. Evaluating the benefits and risks of biotechnology products requires expertise in many scientific disciplines including molecular biology, genetics, cell biology, evolutionary biology, physiology, population and community ecology, and ecosystem science. For society to realize the full benefits of biotechnology, interdisciplinary research and graduate training programs are needed to expand the expertise of the scientific community at large.

The Planned Introduction of Genetically Engineered Organisms: Ecological Considerations and Recommendations

Resistance detection and documentation: the relative role of pesticidal and biochemical assays - Richard H. French-Constant and Richard T. Roush Investigating mechanisms of insecticide resistance: methods, strategies and pitfalls - Jeffrey G. Scott Molecular mechanisms of resistance - David M. Soderlund and Jeffrey R. Bloomquist The role of population genetics in resistance research and management - Richard T. Roush and Joanne C. Daly Modelling and evaluation of resistance management tactics - Bruce E. Tabashnik The effect of agrochemicals on vector populations - George P. Georghiou Pesticide resistance in arthropod natural enemies: variability and selection responses - Marjorie A. Hoy Management of pyrethroid-resistant tobacco budworms on cotton in the United States - Frederick W. Plapp, Jr., Clayton Campanhola, Ralph D. Bagwell and William F. McCutcheon Resistance management in multiple-pest orchard ecosystems in Eastern North America - David J. Pree Developing a philosophy and program of pesticide resistance management - Brian A. Croft.

Pesticide resistance in arthropods.

Insects are exposed to a variety of stress factors in their environment, and, in many cases for insect pests to agriculture, those factors include toxic chemical insecticides. Coping with the toxicity of insecticides can be costly and requires energy and resource allocation for adaptation and survival. Several behavioural, physiological and genetic mechanisms are used by insects to handle toxic insecticides, sometimes leading to resistance by constitutive overexpression of detoxification enzymes or inducing mutations in the target sites. Such actions are costly and may affect reproduction, impair dispersal ability and have several other effects on the insect's fitness. Fitness costs resulting from resistance to insecticides has been reported in many insects from different orders, and several examples are given in this mini-review.

Fitness costs associated with insecticide resistance.

Mutants selected for novel phenotypes frequently exhibit maladaptive pleiotropic effects. One may reasonably ask whether these effects are properties of the novel phenotypes per se, or whether these effects depend upon the particular genotypes conferring the novel phenotypes. To address this issue, I examined an array of independent mutants, derived from Escherichia coli B, that were all completely resistant to the virus T4. Each resistant mutant had maladaptive pleiotropic effects, but there was highly significant variation in competitive fitness among mutants. The degree of reduction in competitive fitness was strongly associated with cross-resistance to virus T7 and with the inferred position of the mutated gene in a complex metabolic pathway. This variation in competitive fitness permits refinement of the resistant phenotype by selection among resistant genotypes. This mechanism complements refinement of the resistant phenotype by selection for epistatic modifiers of maladaptive pleiotropic effects.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1988.tb04149.x

Experimental studies of pleiotropy and epistasis in escherichia coli. i. variation in competitive fitness among mutants resistant to virus t4.

Laboratory and field experimentation has shown that resistant and susceptible diazinon genotypes of flies collected from the field may have similar fitness in an environment free of diazinon. If the genetic background of resistant genotypes from the field is disrupted, the fitness of the resistant genotype declines. These results, in conjunction with previous data, indicate a modification of the genetic background in field populations following the spread of the resistance allele some ten years earlier. It is suggested that this outcome is dependent on the availability of genetic variability, the intensity of selection and the duration of insecticide usage after resistance develops.

/pdf/the-effect-of-genetic-background-on-the-fitness-of-diazinon-32jicpc3uv.pdf

M J Whitten

Papers

The effect of genetic background on the fitness of diazinon resistance genotypes of the Australian sheep blowfly, Lucilia cuprina