A comparison of sexual competitiveness and demographic traits of Anastrepha obliqua (Macquart) (Diptera: Tephritidae) among fruit-associated populations.

The control of Anastrepha obliqua includes the sterilization of mass-reared insects grown in isolation in a constantly controlled environment. Through time, laboratory mass-reared colonies may produce flies with lower field performance. To recover the genetic variation and aptitude of mass-reared populations, wild insects are introduced into mass-reared colonies. Our aim in this study was to determine whether the host species from two localities influence the life history traits of A. obliqua. We collected flies as larvae from infested fruits of Spondias purpurea, S. mombin, Mangifera indica cv. 'piña', and M. indica cv. 'coche' from two localities in Chiapas, Mexico. There were significant differences in the mating competitiveness of males collected from mango cv. 'coche' compared with mass-reared males. There were no differences in the mating propensity between flies from the two localities, even in the number of matings, when weight was considered as a covariable. The mass-reared strain showed the earliest age at first oviposition. The locality affected the longevity and oviposition period, and these influenced the birth rate, intrinsic rate of increase, finite rate of population increase, mean generation time, and doubling time. According to the demographic parameters, the population of S. mombin would allow artificial colonization in less time, considering that it has a high reproduction rate starting at an early age. Even in the propensity test, it had the highest number of matings. However, males with greater sexual competitiveness and longevity for colonization corresponded to those collected from S. purpurea.

Transgenes in Mexican maize: molecular evidence and methodological considerations for GMO detection in landrace populations.

A possible consequence of planting genetically modified organisms (GMOs) in centres of crop origin is unintended gene flow into traditional landraces. In 2001, a study reported the presence of the transgenic 35S promoter in maize landraces sampled in 2000 from the Sierra Juarez of Oaxaca, Mexico. Analysis of a large sample taken from the same region in 2003 and 2004 could not confirm the existence of transgenes, thereby casting doubt on the earlier results. These two studies were based on different sampling and analytical procedures and are thus hard to compare. Here, we present new molecular data for this region that confirm the presence of transgenes in three of 23 localities sampled in 2001. Transgene sequences were not detected in samples taken in 2002 from nine localities, while directed samples taken in 2004 from two of the positive 2001 localities were again found to contain transgenic sequences. These findings suggest the persistence or re-introduction of transgenes up until 2004 in this area. We address variability in recombinant sequence detection by analyzing the consistency of current molecular assays. We also present theoretical results on the limitations of estimating the probability of transgene detection in samples taken from landraces. The inclusion of a limited number of female gametes and, more importantly, aggregated transgene distributions may significantly lower detection probabilities. Our analytical and sampling considerations help explain discrepancies among different detection efforts, including the one presented here, and provide considerations for the establishment of monitoring protocols to detect the presence of transgenes among structured populations of landraces.

Self-exciting chaos as a dynamic model for irregular neural spiking

We introduce a nonlinear dynamical system with self-exciting chaotic dynamics. Its interspike interval return map shows a noisy Poisson-like distribution. Spike sequences from different initial conditions are unrelated but possess the same mean frequency. In the presence of noisy perturbations, sequences started from different initial conditions synchronize. The features of the model are compared with experimental results for irregular spike sequences in neurons. Self-exciting chaos offers a mechanism for temporal coding of complex input signals.