Sex ratio unaffected by parental age gap

Nature (Impact Factor: 42.35). 12/1997; 390(6657). DOI: 10.1038/36762
Source: OAI

ABSTRACT Sex ratios based on a small sample of births tend to be very unstable.
It is therefore not surprising that Manning et al. found a relationship
between spousal age differences and the sex ratios at birth for a very
small sample from a restricted population. Their findings do not stand
up to scrutiny when tested with larger, representative samples of

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: AbstractNatural hybridization occurs rarely in mammals, but it is thought to have the potential to produce viable hybrid offspring in cetaceans more easily than in other mammals. Among cases of cetacean hybridiza-tion, hybrids between bottlenose dolphins (Tursiops truncatus) and Risso’s dolphins (Grampus griseus) have been documented in both the wild and in cap-tivity. However, until now, no molecular evidence has been reported for these cases, and little molecu-lar evidence is available for other cetacean species hybrids. Herein, we examined and documented a hybridization case between a female bottlenose dol-phin and a male Risso’s dolphin held in captivity at Fushun Royal Polar Ocean World in China. We used microsatellite DNA markers, which makes our study the first molecular evidence of hybridization between T. truncatus and G. griseus. Furthermore, we confirmed the usefulness of using microsatellite DNA markers to identify hybrids in other species of captive-born cetaceans.
    Aquatic Mammals 01/2014; 40(1):5-8. DOI:10.1578/AM.40.1.2014.5 · 0.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The regulation of the sex ratio at birth in human species remains poorly under-stood. After wars, a shift of the sex ratio in favor of men is always observed. Among the different hypothesis to explain this observation, one is to consider that Y-bearing spermato-zoids have a weight advantage following insemination and that X-bearing spermatozoids, heavier, are more time-resistant. Following these observations, frequent sex may favor the birth of boys, whether infrequent sex may favor the birth of girls. Sustaining this sperm weight hypothesis, I report here that in France, after the two world wars, there has been an increase of abandoned illegitimate children with a significant shift of the sex ratio in favor of men. These observations may reflect an increase in illegitimate birth and indirectly an increase of men paternity. The basis of human sex and sex ratio determinations are well understood and explained by the existence of two hetero-chromosomes, but the mechanism of the regulation of the human sex ratio is not yet known. Analysis of demographic data after wars has provided situations where the overall sex ratio (sex ratio of the whole population) changed significantly because of killed men. Interestingly, the sex ratio at birth after a war period shifts promptly in favor of men. At the time of the First World War (1914e1918), the sex ratio at birth changed in France from 0.957 to 0.948, when comparing years 1909e1913 and years 1919e1923. After the Second World War (1939e 1945), the sex ratio at birth changed from 0.964 to 0.948, when comparing years 1935e1939 and years 1946e1950 [1,2]. This rapid change of the sex ratio at birth reflects certainly a regulation of the overall sex ratio, which would compensate at term the deficit in men. Several mechanisms have been suggested to explain this regulation (Fisher's hypothesis provide a rationale, if not a mechanism). For humans, the influence of the age of fathers or the difference in age between the mother and
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The pH on the frustule of individual cells of the marine centric diatoms Coscinodiscus granii and Coscinodiscus wailesii (Bacillariophyceae) was measured with pH microsensors in culture media with increasing pH values of 8.04, 8.14, and 8.22, respectively. In 85-96% of the C. granii cells the pH on the frustule was up to 0.4 units higher than that of the medium, reaching a maximum pH 8.95. Only in 2-3% the surface pH exceeded that of the medium by up to 0.7 pH units. These results strongly suggest that diatoms in batch cultures differ, at least temporarily, in their individual photosynthetic activities. Infection experiments with the parasitoid nanoflagellate Pirsonia diadema (Stramenopile) showed that flagellates failed to infect when the culture pH was 8.8 and above. pH measurements on freshly infected C. granii showed that the prevalence of infection was higher in tendency on diatoms with low surface pH. Application of these results to parasitoid-diatom interactions in natural waters suggests that within phytoplankton populations a strong photosynthetic activity might prevent diatom cells temporarily from infection by pH-sensitive parasitoids.
    Marine Biology 04/2008; 154(1):109-116. DOI:10.1007/s00227-008-0904-4 · 2.39 Impact Factor