Disposable-soma senescence mediated by sexual selection in an ungulate

Abstract

Senescence may result from an optimal balance between current reproductive investment and bodily repair processes required for future reproduction, a theoretical prediction difficult to prove especially in large, long-lived animals. Here we propose that teeth that have fixed dimensions early in life, but that wear during chewing, can be taken as a measure of total lifetime 'repair', and their wear rate as a measure of current expenditure in performance. Our approach also considers the sexual selection process to investigate the advance of senescence in males compared with females, when selection favouring competition over mates reduces the reproductive lifespan of males. We studied carcasses of 2,141 male and 739 female red deer (Cervus elaphus) of different ages, finding that male molariform teeth emerged at a far smaller size than expected from body size dimorphism. This led to higher workload, steeper wear rate and earlier depletion of male teeth than in females, in concordance with sex-specific patterns of lifetime performance and reproduction. These findings provide the empirical support for the disposable-soma hypothesis of senescence, which predicts that investment in bodily repair will decrease when the return from this investment may not be realized as a result of other causes that limit survival or reproduction.

Evaluation of sex differences on mitochondrial bioenergetics and apoptosis in mice

“…In Europe, the average life span is 73.7 years for men and 83.8 years for women (Fernandez-Ballesteros et al, 1999). Similar differences have been described in several animal species (Smith, 1989), such as rats (Rollo et al, 2002), ungulates like the red deer (Carranza et al, 2004), marsupials like the northern quolls (Dasyurus hallucatus; Humphries and Stevens, 2001) and primates like the chimpanzee (Herndon et al, 1999). However, in most mouse strains there are no differences between genders, and the same occurs in some primates like Sumatran orangutan (Wich and et al, 2004).…”

Evidence of correlated evolution of hypsodonty and exceptional longevity in endemic insular mammals

“…Because of the very good fits (r 2 . 0.9), we used a linear model, although this relationship has been reported to be nonlinear in other ungulates [20,25,29]. The slopes of the linear regressions give an estimate of the wear rate.…”

“…The life-history hypothesis on hypsodonty, which predicts a correlated evolution of tooth height and longevity [25,26], relies on the deleterious effects of tooth wear (dental senescence) on life-history parameters and the animal's performance, specifically on reproductive success and survival [27 -29]. According to this hypothesis, an increase in crown height allows an increase in tooth durability independent of wear rate variation.…”

“…The two hypotheses, not mutually exclusive, attempt to explain the increase in relative molar crown height (hypsodonty) in mammalian herbivores as follows: (i) the food habits hypothesis suggests increase in molar height to be an adaptation to resist high rates of tooth wear during food processing, whatever the reason for the abrasive nature [19,20,23]; and (ii) the life-history hypothesis predicts molar height to be related to expected longevity and to be independent of dental wear rate variation [25][26][27].…”

Age-related changes in the activity and expression of manganese superoxide dismutase, and mitochondrial oxidant generation in female and male rats

“…Aging studies are mainly focused on gender-related differences in life span [10,[17][18][19][20]. Numerous studies have reported that females live significantly longer than males both in mammals and other vertebrates, as well as in some invertebrate species [18,[20][21][22].…”