First report of major histocompatibility complex class II loci from the Amazon pink river dolphin (genus Inia)

We report the first major histocompatibility complex (MHC) DQB1 sequences for the two species of pink river dolphins (Inia geoffrensis and Inia boliviensis) inhabiting the Amazon and Orinoco River basins. These sequences were found to be polymorphicwithin the Inia genus and showed shared homology with cetacean DQB-1 sequences, especially, those of the Monodontidae and Phocoenidae. On the other hand, these sequences were shown to be divergent from those described for other riverine dolphin species, such as Lipotes vexillifer, the Chinese river dolphin. Two main conclusions can be drawn from our results: 1) the Mhc DQB1 sequences seem to evolve more rapidly than other nuclear sequences in cetaceans, and 2) differential positive selective pressures acting on these genes cause concomitant divergent evolutionary histories that derive phylogenetic reconstructions that could be inconsistent with widely accepted intertaxa evolutionary relationships elucidated with other molecular markers subjected to a neutraldynamics.

Psorophora columbiae and Psorophora toltecum (Diptera: Culicidae) Colombian populations cannot be differentiated by isoenzymes

Two populations of the mosquito Psorophora columbiae from the central Andean area of Colombia and one population of Ps. toltecum from the Atlantic coast of Colombia were analyzed for 11 isoenzyme markers. Psorophora columbiae and Ps. toltecum are two of the main vectors of Venezuelan equine encephalitis. We found no conspicuous genetic differences between the two species. The relatively high gene flow levels among these populations indicate that these are not two different species or that there has been recent divergence between these taxa. In addition, no global differential selection among the loci was detected, although the alpha-GDH locus showed significantly less genetic heterogeneity than the remaining loci, which could mean that homogenizing natural selection acts at this locus. No isolation by distance was detected among the populations, and a spatial population analysis showed opposite spatial trends among the 31 alleles analyzed. Multiregression analyses showed that both expected heterozygosity and the average number of alleles per locus were totally determined by three variables: altitude, temperature and size of the human population at the locality. Individually, the expected heterozygosity is more related to these three variables than to the average number of alleles

Detection of stabilizing selection in favor of the Santa Cruz homokaryotype in Drosophila pseudoobscura populations from the high plateau of the Colombian Andes

Chromosome 3 rearrangements were studied in five Drosophila pseudoobscura populations from the high plateau of the Colombian Andes. As in previous studies, the Santa Cruz and Tree Line rearrangements were predominant in these populations, but for the first time other rearrangements such as the Olympic, Cuernavaca and a rearrangement similar to the endemic Mexican Amecameca rearrangement were also discovered. Researchers in the early 1960's showed that Colombian D. pseudoobscura populations were not in accordance with Carson's theory. They found a special heterotic system in this geographically isolated population. Our current results do not support these findings but instead favor Carson's theory, because in practically all the populations studied the homokaryotype excess was close to fixation. These new results indicate that some stabilizing selective pressures in favor of the homokaryotypes (especially Santa Cruz) have appeared in the Colombian plateau during the last 10-12 years. These new changes may be related to deforestation and habitat destruction by human beings and/or climatic changes motivated by the El Niño phenomenon. Genetic heterogeneity between populations was not significant and there was no isolation-by-distance between them, findings which are contrary to those observed in some North American populations and which show that the Colombian populations now have rigid genetic systems. The frequency of the Santa Cruz rearrangement was also found to have increased in some populations over the last few years