Simulating Male Selfish Strategy in Reproduction Dispute

We introduce into the Penna Model for biological ageing one of the possible male mechanisms used to maximize the ability of their sperm to compete with sperm from other males. Such a selfish mechanism increases the male reproduction success but may decrease the survival probability of the whole female population, depending on how it acts. We also find a dynamic phase transition induced by the existence of an absorbing state where no selfish males survive.Comment: 7 pages, latex including 2 eps figure

The new biology of ageing

Human life expectancy in developed countries has increased steadily for over 150 years, through improvements in public health and lifestyle. More people are hence living long enough to suffer age-related loss of function and disease, and there is a need to improve the health of older people. Ageing is a complex process of damage accumulation, and has been viewed as experimentally and medically intractable. This view has been reinforced by the realization that ageing is a disadvantageous trait that evolves as a side effect of mutation accumulation or a benefit to the young, because of the decline in the force of natural selection at later ages. However, important recent discoveries are that mutations in single genes can extend lifespan of laboratory model organisms and that the mechanisms involved are conserved across large evolutionary distances, including to mammals. These mutations keep the animals functional and pathology-free to later ages, and they can protect against specific ageing-related diseases, including neurodegenerative disease and cancer. Preliminary indications suggest that these new findings from the laboratory may well also apply to humans. Translating these discoveries into medical treatments poses new challenges, including changing clinical thinking towards broad-spectrum, preventative medicine and finding novel routes to drug development

Individual variation in age‐dependent reproduction: Fast explorers live fast but senesce young?

Adaptive integration of life history and behaviour is expected to result in variation in the pace‐of‐life. Previous work focused on whether ‘risky’ phenotypes live fast but die young, but reported conflicting support. We posit that individuals exhibiting risky phenotypes may alternatively invest heavily in early‐life reproduction but consequently suffer greater reproductive senescence. We used a 7‐year longitudinal dataset with >1,200 breeding records of >800 female great tits assayed annually for exploratory behaviour to test whether within‐individual age dependency of reproduction varied with exploratory behaviour. We controlled for biasing effects of selective (dis)appearance and within‐individual behavioural plasticity. Slower and faster explorers produced moderate‐sized clutches when young; faster explorers subsequently showed an increase in clutch size that diminished with age (with moderate support for declines when old), whereas slower explorers produced moderate‐sized clutches throughout their lives. There was some evidence that the same pattern characterized annual fledgling success, if so, unpredictable environmental effects diluted personality‐related differences in this downstream reproductive trait. Support for age‐related selective appearance was apparent, but only when failing to appreciate within‐individual plasticity in reproduction and behaviour. Our study identifies within‐individual age‐dependent reproduction, and reproductive senescence, as key components of life‐history strategies that vary between individuals differing in risky behaviour. Future research should thus incorporate age‐dependent reproduction in pace‐of‐life studies

The co‐evolution of longevity and social life

Living in social groups could influence the evolution of senescence and longevity by affecting key life‐history parameters such as extrinsic mortality and the cost of reproduction. For example, a decrease in extrinsic mortality as a result of social life is predicted to lead to the evolution of increased longevity. We argue that benefits of social life in terms of increased survival are common only in species in which life in large groups is already the norm, most likely because these species have adapted to depend on social groups. By contrast, species with smaller social groups tend to show no clear association between survival and social group size. This lack of a consistent benefit of social life on survival casts doubt on the idea that extended longevity should follow the evolution of sociality. In line with this, most rigorous cross‐taxonomic studies failed to find an association between sociality and longevity, suggesting that a social mode of life does not systematically lead to the evolution of extended longevity. The only effect of sociality on longevity that has been convincingly demonstrated is increased longevity in high‐ranking individuals from cooperatively breeding vertebrates and social insects, who benefit from the protection and support of their non‐breeding helpers. In contrast, helpers in these species usually do not show evidence of increased longevity, with the exception of naked mole rats where both breeders and helpers live much longer than related solitary species. Where long‐lived phenotypes exist in highly social species, such as social insect queens and naked mole rats, the scale of longevity increase is often striking. The means by which increased longevity is achieved are still poorly understood, but both social and physiological mechanisms are involved in reducing the burden of disease, including cancer, thus increasing the chances of surviving to old age

Time evolution of the Partridge-Barton Model

The time evolution of the Partridge-Barton model in the presence of the pleiotropic constraint and deleterious somatic mutations is exactly solved for arbitrary fecundity in the context of a matricial formalism. Analytical expressions for the time dependence of the mean survival probabilities are derived. Using the fact that the asymptotic behavior for large time $t$ is controlled by the largest matrix eigenvalue, we obtain the steady state values for the mean survival probabilities and the Malthusian growth exponent. The mean age of the population exhibits a $t^{-1}$ power law decayment. Some Monte Carlo simulations were also performed and they corroborated our theoretical results.Comment: 10 pages, Latex, 1 postscript figure, published in Phys. Rev. E 61, 5664 (2000

Manipulation of feeding regime alters sexual dimorphism for lifespan and reduces sexual conflict in Drosophila melanogaster

Sexual dimorphism for lifespan (SDL) is widespread, but poorly understood. A leading hypothesis, which we test here, is that strong SDL can reduce sexual conflict, by allowing each sex to maximise its sex-specific fitness. We used replicated experimental evolution lines of the fruit fly, Drosophila melanogaster, which had been maintained for over 360 generations on either unpredictable ‘Random’ or predictable ‘Regular’ feeding regimes. This evolutionary manipulation of feeding regime led to robust, enhanced SDL in Random over control, Regular lines. Enhanced SDL was associated with a significant increase in the fitness of focal males, tested with wild type females. This was due to sex-specific changes to male life history, manifested as increased early reproductive output and reduced survival. In contrast, focal female fitness, tested with wild type males, did not differ across regimes. Hence increased SDL was associated with a reduction in sexual conflict, which increased male fitness and maintained fitness in females. Differences in SDL were not associated with developmental time or developmental survival. Overall, the results showed that the expression of enhanced SDL, resulting from experimental evolution of feeding regimes, was associated with male-specific changes in life history, leading to increased fitness and reduced sexual conflict

Exact Solution of an Evolutionary Model without Ageing

We introduce an age-structured asexual population model containing all the relevant features of evolutionary ageing theories. Beneficial as well as deleterious mutations, heredity and arbitrary fecundity are present and managed by natural selection. An exact solution without ageing is found. We show that fertility is associated with generalized forms of the Fibonacci sequence, while mutations and natural selection are merged into an integral equation which is solved by Fourier series. Average survival probabilities and Malthusian growth exponents are calculated indicating that the system may exhibit mutational meltdown. The relevance of the model in the context of fissile reproduction groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.

USE OF DIMETHYL SULPHOXIDE FOR PRESERVING CORNEAL TISSUE*t

SINCE it was discovered by We have been concerned with retaining the viability of corneal tissue after freezing and in the past Our need to maintain a supply of stored corneae for keratoplasty prompted us to set up an experiment to evaluate the usefulness of dimethyl sulphoxide in preserving the viability of cornea during freezing. Experiment.-Our purpose was to compare the preserving qualities of dimethyl sulphoxide with those of glycerol during the storage of corneal tissue at -64°C. Concentrations of 15 per cent./V glycerol and 15 per cent./V dimethyl sulphoxide, both in Hank's balanced salt solution, were used. Corneal material from rabbits, cats, and dogs was obtained from eyes removed as soon as possible after death, usually within 30 minutes. Pig and ox corneae were obtained from eyes removed approximately 4 hours after death. Method.-The eyes were soaked for 10 minutes in a balanced salt solution containing 200 units penicillin and 75 mg. streptomycin per ml. Then the corneae were removed and washed again in balanced salt solution and antibiotics. Each