Earlier and more rapid ageing: Does nutrition contribute?

This paper estimated three parameters related to demographic ageing, i.e., the acce-leration in mortality rates as people get older. These parameters are: (i) the age when the process begins (onset), (ii) the rate of ageing in a (simple) Gompertz model and (iii) the rate of ageing in a (more elaborate) Gamma-Gompertz model. These three indicators were estimated on the basis of female cohorts born in seven European countries between 1890 and 1919. Our results indicated a progressively earlier onset and a steeper rise in the rate of ageing in recent cohorts, i.e., ageing seems to have accelerated over time. The reasons for these shifts are still unknown, but due to their similarity with the results of a vast body of experiments of calorie restriction on lab animals, we suggested here that the changed dietary regime of humans since the end of the 19th century may have played a part in the evolution of their mortality schedule.

The relationship between longevity and healthy life expectancy

What is the relationship between longevity and health? Health expectancies were developed more than 30 years ago specifically to answer this question. It may therefore be the time to try to answer this question, though it is worth noting that the question implies a unidirectional relationship. Almost no one questions the positive association between health and longevity. It is expected that healthy, robust people will live, on average, longer than frail people. This heterogeneity in terms of robustness/frailty may explain the shape of the mortality trajectory with age, ie. the oldest old seem to follow a lower mortality schedule (Vaupel et al, 1979). On the other hand, many people wonder about the relationship between longevity and health. Are we living longer because we are in better health? Are we living longer in good health? Or are we merely surviving longer whatever our health status? In other words, can we live in good health as long as we can survive? And this is exactly the purpose of health expectancies: monitoring how long people live in various health statuses (Sanders, 1964; Sullivan, 1971; Robine et al, 2003a).

The population age structure and reproductive biology of Gyrodactylus salaris Malmberg (Monogenea)

SUMMARYGyrodactylus salaris has recently become a major pathogen of Atlantic Salmon (Salmo salar) in Norway. The survivorship, population age structure and pattern of insemination of G. salaris were studied to determine the extent to which this species reproduces sexually. The age-specific mortality schedule of G. salaris could be described by an exponential model but day to day variations were large, with an increase in mortality after each birth. Modelling population growth using the best fit mortality schedule indicated that, at stable age structure, 35% of the population would consist of newborn and pre-1st birth flukes. Using testis, penis and embryo development, pre-1st birth and immediately post-1st birth flukes could be unambiguously identified, and established infections were found to contain 35% pre-1st birth flukes, as predicted. The proportion of pre-1st birth flukes in newly established infections was significantly smaller, probably because of differences in the rate of transmission between newborn and older flukes. Gyrodactylus salaris is relatively long-lived, and more than 40% of the population may survive to give birth for the third time. As gyrodactylids are protogynous, and the first daughter is probably produced asexually, this long-lived strategy ensures that a large part of the G. salaris population possesses a functional male system, and that the asexually derived flukes are a smaller component of the total population in this species. Flukes with whorls of inseminated spermatozoa within the seminal receptacle were found in all age groups possessing a functional male system, and were interpreted as having been cross-inseminated. G. salaris on susceptible Norwegian salmon appears to regularly reproduce sexually, possibly accounting for its morphological variability and wide range of potential salmonid hosts.