Recent comparative studies point to the importance of mortality schedules as determinants in the evolution of life‐history characteristics. In this paper, we compare patterns of mortality from natural populations of mammals with a variety of life histories. We find that, after removing the effects of body weight, mortality is the best predictor of variation in life‐history traits. Mammals with high levels of natural mortality tend to mature early and give birth to small offspring in large litters after a short gestation, before and after body size effects are factored out. We examine the way in which life‐history traits relate to juvenile mortality versus adult mortality and find that juvenile mortality is more highly correlated with life‐history traits than is adult mortality. We discuss the necessity of distinguishing between extrinsic sources of mortality (e.g. predation) and mortality caused by intrinsic sources (e.g. costs of reproduction), and the role that ecology might play in the evolution of patterns of mortality and fecundity. We conclude that these results must be explained not simply in the light of the demographic necessity of balancing mortality and fecundity, but as a result of age‐specific costs and benefits of reproduction and parental investment. Detailed comparative studies of mortality patterns in natural populations of mammals offer a promising avenue towards understanding the evolution of life‐history strategies.

We compiled information from the literature on the taxonomic distributions in extant teleost fishes of alternative sex-determination systems: male-heterogametic (XY) gonochorism, female-heterogametic (ZW) gonochorism, hermaphroditism, unisexuality, and environmental dependency. Then, using recently published molecular phylogenies based on whole-genomic or partial mitochondrial DNA sequences, we inferred the histories and evolutionary transitions between these reproductive modes by employing maximum parsimony and maximum likelihood methods of phylogenetic character mapping. Across a broad teleost phylogeny involving 25 taxonomic orders, a highly patchy distribution of different sex-determination mechanisms was uncovered, implying numerous transitions between alternative modes, but this heterogeneity also precluded definitive statements about ancestral states for most clades. Closer inspection of family-level and genus-level phylogenies within each of four orders further bolstered the conclusion that shifts in sex-determining modes are evolutionarily frequent and involve a variety of distinct ancestraldescendant pathways. For possible reasons discussed herein, the evolutionary lability of sex-determining modes in fishes contrasts strikingly with the evolutionary conservatism of sex determination within both mammals and birds.

Many studies have found that older parents have shorter-lived offspring. However, the evolutionary significance of these findings is poorly understood. We carried out large-scale demographic experiments to examine the direct effect of maternal age and paternal age on offspring aging in inbred and outbred strains of the fruit fly Drosophila melanogaster. We found that the age of mothers and, to a lesser extent, the age of fathers can have a large influence on both offspring longevity and the shape of the age-specific mortality trajectory. In two independent experiments we found that older mothers generally produced shorter-lived offspring, although the exact effect of maternal age on offspring longevity differed among strains. These results suggest that maternal age effects on progeny aging may influence the evolution of aging.The youngest mother, on the average, had the longestlived offspring. -Alexander Graham Bell (1918)

Faced with reduced levels of food, animals must adjust to the consequences of the shortfall in energy. We explored how C57BL/6 mice withdrew energy from different body tissues during three months of food restriction at graded levels up to 40% (calorie restriction: CR). We compared this to the response to equivalent levels of protein restriction (PR) without a shortfall in calories. Under CR there was a dynamic change in body mass over 30 days and thereafter it stabilized. The time to reach stability was independent of the level of restriction. At the end of three months whole body dissections revealed differential utilization of the different tissues. Adipose tissue depots were the most significantly utilized tissue, and provided 55.8 to 60.9% of the total released energy. In comparison, reductions in the sizes of structural tissues contributed between 29.8 and 38.7% of the energy. The balance was made up by relatively small changes in the vital organs. The components of the alimentary tract grew slightly under restriction, particularly the stomach, and this was associated with a parallel increase in assimilation efficiency of the food (averaging 1.73%). None of the changes under CR were recapitulated by equivalent levels of PR.

Limiting food intake attenuates many of the deleterious effects of aging, impacting upon healthspan and leading to an increased lifespan. Whether it is the overall restriction of calories (calorie restriction: CR) or the incidental reduction in macronutrients such as protein (protein restriction: PR) that mediate these effects is unclear. The impact of 3 month CR or PR, (10 to 40%), on C57BL/6 mice was compared to controls fed ad libitum. Reductions in circulating leptin, tumor necrosis factor-α and insulin-like growth factor-1 (IGF-1) were relative to the level of CR and individually associated with morphological changes but remained unchanged following PR. Glucose tolerance and insulin sensitivity were improved following CR but not affected by PR. There was no indication that CR had an effect on oxidative damage, however CR lowered antioxidant activity. No biomarkers of oxidative stress were altered by PR. CR significantly reduced levels of major urinary proteins suggesting lowered investment in reproduction. Results here support the idea that reduced adipokine levels, improved insulin/IGF-1 signaling and reduced reproductive investment play important roles in the beneficial effects of CR while, in the short-term, attenuation of oxidative damage is not applicable. None of the positive effects were replicated with PR.