Evaluation of the Impact of Genetically Modified Cotton After 20 Years of Cultivation in Mexico

For more than 20 years cotton has been the most widely sown genetically modified (GM) crop in Mexico. Its cultivation has fulfilled all requirements and has gone through the different regulatory stages. During the last 20 years, both research-institutions and biotech-companies have generated scientific and technical information regarding GM cotton cultivation in Mexico. In this work, we collected data in order to analyze the environmental and agronomic effects of the use of GM cotton in Mexico. In 1996, the introduction of Bt cotton made it possible to reactivate this crop, which in previous years was greatly reduced due to pest problems, production costs and environmental concerns. Bt cotton is a widely accepted tool for cotton producers and has proven to be efficient for the control of lepidopteran pests. The economic benefits of its use are variable, and depend on factors such as the international cotton-prices and other costs associated with its inputs. So far, the management strategies used to prevent development of insect resistance to GM cotton has been successful, and there are no reports of insect resistance development to Bt cotton in Mexico. In addition, no effects have been observed on non-target organisms. For herbicide tolerant cotton, the prevention of herbicide resistance has also been successful since unlike other countries, the onset of resistance weeds is still slow, apparently due to cultural practices and rotation of different herbicides. Environmental benefits have been achieved with a reduction in chemical insecticide applications and the subsequent decrease in primary pest populations, so that the inclusion of other technologies—e.g., use of non-Bt cotton- can be explored. Nevertheless, control measures need to be implemented during transport of the bolls and fiber to prevent dispersal of volunteer plants and subsequent gene flow to wild relatives distributed outside the GM cotton growing areas. It is still necessary to implement national research programs, so that biotechnology and plant breeding advances can be used in the development of cotton varieties adapted to the Mexican particular environmental conditions and to control insect pests of regional importance

Population Genetic Structure of a Widespread Bat-Pollinated Columnar Cactus

<div><p>Bats are the main pollinators and seed dispersers of <i>Stenocereus thurberi</i>, a xenogamous columnar cactus of northwestern Mexico and a good model to illustrate spatial dynamics of gene flow in long-lived species. Previous studies in this cactus showed differences among populations in the type and abundance of pollinators, and in the timing of flowering and fruiting. In this study we analyzed genetic variability and population differentiation among populations. We used three primers of ISSR to analyze within and among populations genetic variation from eight widely separated populations of <i>S</i>. <i>thurberi</i> in Sonora, Mexico. Sixty-six out of 99 of the ISSR bands (<i>P</i> = 66.7%) were polymorphic. Total heterozygosity for all populations sampled revealed high genetic diversity (<i>H</i>_<i>sp</i> = 0.207, <i>H</i>_<i>BT</i> = 0.224). The AMOVA showed that most of the genetic variation was within populations (80.5%). At the species level, estimates of population differentiation, θ = 0.175 and θ^B = 0.194, indicated moderate gene flow among populations. The absence of a significant correlation between genetic and geographic distances indicated little isolation by geographic distance. The large genetic variation and diversity found in <i>S</i>. <i>thurberi</i> is consistent with its open reproductive system and the high mobility of bats, a major pollinator. However, small changes in number or kind of pollinators and seed dispersal agents, in the directionality of migratory routes, and/or in the timing of flowering and fruiting among populations, can critically affect gene flow dynamics.</p></div

Geographical distribution of <i>Stenocereus thurberi</i> (diagonal lines; modified from Turner <i>et al</i>., 1995), and location of the eight studied populations (stars).

<p>Sonoran Desert extent (gray).</p

Relationship between average population heterozygosity (<i>H</i>_<i>pop</i>) and latitude for eight populations of <i>Stenocereus thurberi</i>.

<p>Relationship between average population heterozygosity (<i>H</i>_<i>pop</i>) and latitude for eight populations of <i>Stenocereus thurberi</i>.</p

Geographic location, elevation and vegetation type of <i>Stenocereus thurberi</i> populations used for genetic analysis in this study.

<p>Geographic location, elevation and vegetation type of <i>Stenocereus thurberi</i> populations used for genetic analysis in this study.</p

Resultant groups from STRUCTURE.

<p>Note the multiple SE-NW grouping, and the marked E-W group in central Sonora.</p

Are 150 km of open sea enough? Gene flow and population differentiation in a bat-pollinated columnar cactus.

Genetic differentiations and phylogeographical patterns are controlled by the interplay between spatial isolation and gene flow. To assess the extent of gene flow across an oceanic barrier, we explored the effect of the separation of the peninsula of Baja California on the evolution of mainland and peninsular populations of the long-lived columnar cactus Stenocereus thurberi. We analyzed twelve populations throughout the OPC distribution range to assess genetic diversity and structure using chloroplast DNA sequences. Genetic diversity was higher (Hd = 0.81), and genetic structure was lower (GST = 0.143) in mainland populations vs peninsular populations (Hd = 0.71, GST = 0.358 respectively). Genetic diversity was negatively associated with elevation but positively with rainfall. Two mainland and one peninsular ancestral haplotypes were reconstructed. Peninsular populations were as isolated among them as with mainland populations. Peninsular haplotypes formed a group with one mainland coastal population, and populations across the gulf shared common haplotypes giving support to regular gene flow across the Gulf. Gene flow is likely mediated by bats, the main pollinators and seed dispersers. Niche modeling suggests that during the Last Glacial Maximum (c. 130 ka), OPC populations shrank to southern locations. Currently, Stenocereus thurberi populations are expanding, and the species is under population divergence despite ongoing gene flow. Ancestral populations are located on the mainland and although vicariant peninsular populations cannot be ruled out, they are likely the result of gene flow across the seemingly formidable barrier of the Gulf of California. Still, unique haplotypes occur in the peninsula and the mainland, and peninsular populations are more structured than those on the mainland

Population genomics of Vibrionaceae isolated from an endangered oasis reveals local adaptation after an environmental perturbation

Abstract Background In bacteria, pan-genomes are the result of an evolutionary “tug of war” between selection and horizontal gene transfer (HGT). High rates of HGT increase the genetic pool and the effective population size (Ne), resulting in open pan-genomes. In contrast, selective pressures can lead to local adaptation by purging the variation introduced by HGT and mutation, resulting in closed pan-genomes and clonal lineages. In this study, we explored both hypotheses, elucidating the pan-genome of Vibrionaceae isolates after a perturbation event in the endangered oasis of Cuatro Ciénegas Basin (CCB), Mexico, and looking for signals of adaptation to the environments in their genomes. Results We obtained 42 genomes of Vibrionaceae distributed in six lineages, two of them did not showed any close reference strain in databases. Five of the lineages showed closed pan-genomes and were associated to either water or sediment environment; their high Ne estimates suggest that these lineages are not from a recent origin. The only clade with an open pan-genome was found in both environments and was formed by ten genetic groups with low Ne, suggesting a recent origin. The recombination and mutation estimators (r/m) ranged from 0.005 to 2.725, which are similar to oceanic Vibrionaceae estimations. However, we identified 367 gene families with signals of positive selection, most of them found in the core genome; suggesting that despite recombination, natural selection moves the Vibrionaceae CCB lineages to local adaptation, purging the genomes and keeping closed pan-genome patterns. Moreover, we identify 598 SNPs associated with an unstructured environment; some of the genes associated with these SNPs were related to sodium transport. Conclusions Different lines of evidence suggest that the sampled Vibrionaceae, are part of the rare biosphere usually living under famine conditions. Two of these lineages were reported for the first time. Most Vibrionaceae lineages of CCB are adapted to their micro-habitats rather than to the sampled environments. This pattern of adaptation is concordant with the association of closed pan-genomes and local adaptation