Control of source fertility on the eruptive activity of Piton de la Fournaise volcano, La Réunion.

The eruptive activity of basaltic hotspot volcanoes displays major fluctuations on times scales of years to decades. Theses fluctuations are thought to reflect changes in the rate of mantle melt supply. However, the crustal filter generally masks the mantle processes involved. Here, we show that the cyclic and generally increasing activity of the Piton de la Fournaise volcano (La Réunion) since the mid 20th century is tightly linked to the fertility of its source, as recorded by 87Sr/86Sr and incompatible trace elements ratios of lavas. We identify a twofold control of source fertility on eruptive activity: melt extraction from fertile, incompatible element-enriched veins initiates decadal-scale eruptive sequences, so that vein distribution in the plume source directly controls the cyclic activity. Indirectly, reactive flow of enriched melts increases mantle porosity and promotes melts extraction from the peridotite matrix. This process is thought to have caused a fourfold increase in magma supply between 1998 and 2014 at Piton de la Fournaise, and could also explain magma surges at other frequently active hotspot volcanoes, such as Kilauea, Hawaii. The short-term eruptive activity of hotspot volcanoes appears to be ultimately linked to the distribution and size of lithological heterogeneities in mantle plumes.

Chromosome studies in patients with defective reproductive success.

PROBLEM: The objective of this study was to evaluate the contribution of chromosomal anomalies to decreased fertility in humans. METHOD OF STUDY: In order to investigate the aetiology of infertility in our population and to assess the karyotype in a group of infertile couples and individuals with fertility problems, 782 persons (259 couples, 158 male and 106 female) with different clinical diagnoses of sterility and infertility were analysed cytogenetically. RESULTS: The overall frequency of major chromosomal aberration was 13.1% (103/783), which suggests that fertility or sterility problems in this population are due to chromosomal aberrations. Couples experiencing repeated spontaneous abortions, having malformed children or having sterility problems had chromosomal abnormalities in 18.0% (47/259 couples) of the population studied, and constituted chromosomal disorders occured in couples seeking IVF and ICSI with prevalence of 22.2% (8/38 couples), especially minor mosaicism of sex chromosomes in the female partners. The prevalence of chromosome abnormalities in infertile men was 17.7% (28/158), and in subfertile females, it was 26.4% (28/106). CONCLUSIONS: These results could indicate an increased tendency to miotic sex chromosome non-disjuction in humans.

Quantitative analysis of constitutive heterochromatin in couples with fetal wastage.

PROBLEM: Heteromorphism of constitutive heterochromatin is a stable evolutionary feature that is thought to cause no phenotypic alterations. Nevertheless, the role of constitutive heterochromatin is still unknown. The instability of constitutive heterochromatin was generally restricted to T-lymphocytes and was associated with variable immunodeficiency. The heterochromatin regions of chromosomes 1, 9, 16, and Y have been postulated to play a role in the immune response and during early embryo development. METHOD OF STUDY: To investigate a possible influence of constitutive heterochromatin in human reproductive ability, quantitative analysis of constitutive heterochromatin in human chromosomes 1, 9, 16 and Y was done. Thirty couples were divided into two groups, owing to the clinical heterogeneity of their reproductive disorders. The first group included couples with two or more spontaneous abortions as the only pregnancy outcomes, and the second group included couples with a stillborn child with or without malformations. In the control group were couples with one or more healthy children without a history of fetal wastage. All of the persons in this study had normal karyotypes. The amount of constitutive heterochromatin was expressed by relative value using the simple transformation [q/(p + q)]. This value, obtained on GTG-banded metaphase chromosomes, represented an indirect measure of heterochromatin content. The Y/F index was used to express the relative amount of heterochromatin in chromosome Y. RESULTS: There was a significant increase in the heterochromatin content of the chromosomes 16 homologue pair in males and females with a stillborn or a stillborn malformed child (P < 0.01) and an increase in total heterochromatin cell content compared to controls (P = 0.005). The same couples had significantly increased mean maximal heterochromatin content in the potential zygotes (P < 0.02). The couples who experienced spontaneous abortions only had a minimal total heterochromatin content in the potential zygotes (P < 0.05). The Y/F index was significantly lower in the males in both groups compared to controls (P1 < 0.02; P2 < 0.02). CONCLUSION: The quantitative analysis of constitutive heterochromatin could be valuable in predicting pregnancy outcome.