"Sex ratio" in Drosophila pseudoobscura: spermiogenic failure.

Contrary to earlier reports, testes of "sex ratio" Drosophila pseudoobscura males have only half as many sperm per bundle as testes of normal males do. This fact, determined from electron micrographs, indicates that the functional pole hypothesis is not applicable to the action of "sex ratio."

Revisiting the commons: local lessons, global challenges.

In a seminal paper, Garrett Hardin argued in 1968 that users of a commons are caught in an inevitable process that leads to the destruction of the resources on which they depend. This article discusses new insights about such problems and the conditions most likely to favor sustainable uses of common-pool resources. Some of the most difficult challenges concern the management of large-scale resources that depend on international cooperation, such as fresh water in international basins or large marine ecosystems. Institutional diversity may be as important as biological diversity for our long-term survival.

Gene Differences between the Sex Ratio and Standard Gene Arrangements of the X Chromosome in DROSOPHILA PERSIMILIS.

The sibling species Drosophila pseudoobscura and D. persimilis each carry two gene arrangements in the right arm of the X chromosome; Standard (ST) and Sex Ratio (SR). The SR sequence of D. persimilis and the ST sequence of D. pseudoobscura have the same banding pattern. These cytologically identical arrangements carry different alleles at the esterase-5 (Est-5) and phosphoglucomutase-1 ( Pgm-1) loci. All the alleles on the SR arrangement of D. persimilis are also present on the ST arrangement of that species, and the same allele was most common in all cases. However, the allele frequencies at the Pgm-1 locus are significantly different between the two arrangements. Within the ST arrangement of D. persimilis, the alleles at the Est-5 and Pgm-1 loci are in linkage equilibrium.

Sex choice and the size advantage model in jack-in-the-pulpit (Arisaema triphyllum).

Arisaema triphyllum is a perennial herb whose sex and size often change from one growing season to the next. The proportional gain in reproductive success (RS) with size is much greater for female (carpellate) plants than it is for male (staminate) plants. I constructed RS-size curves for males and females; the curves intersect at a point t = 398 mm. According to theory derived from the size advantage model, t is the point below which the plants should be male and above which they should be female. Plots of size-frequency distributions of males and females show that below 380 mm the proportion of males is greater than the proportion of females, whereas above that point the proportion of females is greater than the proportion of males. Thus prediction and observed results are in very close conformity.

Peer reviewed: evaluating impacts of hormonally active agents in the environment.

Information about endocrine disrupters is limited, with sparse data, few answers, great uncertainties, and a definite need for further research.