Multiple-infection and recombination in HIV-1 within a longitudinal cohort of women.

BACKGROUND: Recombination between strains of HIV-1 only occurs in individuals with multiple infections, and the incidence of recombinant forms implies that multiple infection is common. Most direct studies indicate that multiple infection is rare. We determined the rate of multiple infection in a longitudinal study of 58 HIV-1 positive participants from The Women's Interagency HIV Study with a richer sampling design than previous direct studies, and we investigated the role of recombination and sampling design on estimating the multiple infection rate. RESULTS: 40% of our sample had multiple HIV-1 infections. This rate of multiple infection is statistically consistent with previous studies once differences in sampling design are taken into account. Injection drug use significantly increased the incidence of multiple infections. In general there was rapid elimination of secondary strains to undetectable levels, but in 3 cases a superinfecting strain displaced the initial infecting strain and in two cases the strains coexisted throughout the study. All but one secondary strain was detected as an inter- and/or intra-genic recombinant. Injection drug use significantly increased the rate of observed recombinants. CONCLUSION: Our multiple infection rate is consistent with rates estimated from the frequency of recombinant forms of HIV-1. The fact that our results are also consistent with previous direct studies that had reported a much lower rate illustrates the critical role of sampling design in estimating this rate. Multiple infection and recombination significantly add to the genetic diversity of HIV-1 and its evolutionary potential, and injection drug use significantly increases both.

Evolutionary implications of developmental instability in parthenogenetic Drosophila mercatorum. II. Comparison of two strains with identical genotypes, but different modes of reproduction.

Developmental instability is particularly pronounced in parthenogenetic strains of Drosophila mercatorum. All parthenogenetically produced eggs in a given strain have the same genotype, but even when reared in the same environment, only approximately 5% of the eggs initiating development ever reach adulthood. A sexual analogue of a parthenogenetic strain was created to investigate the basis of this developmental instability. The two strains have identical genotypes (except for the Y chromosome in males of the sexual strain) and differ only in mode of reproduction. The sexual strain had a much lower rate of developmental instability than the parthenogenetic strain, suggesting that the instability is caused by the mode of reproduction per se and is not due to homozygosity, disruption of coadapted gene complexes, or any other feature of the parthenogenetic genome. The increased rate of abortion with parthenogenetic reproduction is caused by a proportional increase in the normal panoply of errors that occur in sexual reproduction but at a much lower rate. Attempts to establish other sexual analogues of laboratory parthenogenetic strains revealed different male sterility factors within several parthenogenetic genomes that could potentially act to prevent hybridization with sexually reproducing ancestors during the incipient stages in the evolution of an entirely parthenogenetic lineage.

Evolutionary implications of developmental instability in parthenogenetic drosophila mercatorum. I. Comparison of several strains with different genotypes.

Natural populations of sexually reproducing Drosophila mercatorum are capable of a very low rate of parthenogenesis, but this mode of reproduction has apparently never characterized an entirely asexual population in this species. The high abortion rate observed in laboratory parthenogenetic lines suggests that developmental constraints may cause the failure of this trait to spread in nature. To investigate the basis of this developmental instability and how it may affect the evolution of parthenogenesis in natural populations, early embryonic development was compared between one sexual and four parthenogenetic laboratory strains of D. mercatorum. There is a large amount of variation within a given parthenogenetic strain, suggesting that parthenogenesis is associated with a general breakdown of developmental stability. There is relatively little variation among different parthenogenetic strains, suggesting that most abortions are due to a feature inherent to parthenogenetic reproduction rather than a feature of a particular genome. Likewise, there is little variation between parthenogenetic and sexual strains in the causes of abortions, suggesting that the developmental problems encountered by parthenogenetic lineages are not unique to parthenogens. Thus, the failure of parthenogenesis to spread within D. mercatorum can be attributed to no particular developmental constraint per se operating after the initiation of embryogenesis. However, the overall increase in all developmental problems that occurs with the transition from sexual to parthenogenetic development suggests that the high degree of developmental instability associated with parthenogenesis may be considered a developmental constraint in its own right.