Search

Vertebrates show substantial interspecific variation in brain size in relation to body mass. It has long been recognized that the evolution of large brains is associated with both costs and benefits, and it is their net benefit which should be favoured by natural selection. On one hand, the substantial energetic cost imposed by the maintenance of neural tissue is expected to compromise the energetic budget of organisms with large brains and their investment in other critical organs (expensive brain framework, EBF) or important physiological process, such as somatic maintenance and repair, thus accelerating ageing that shortens lifespan, as predicted by the disposable soma theory (DST). However, selection towards larger brain size can provide cognitive benefits (e.g., high behavioural flexibility) that may mitigate extrinsic mortality pressures, and thus may indirectly select for slower ageing that prolongs lifespan, as predicted by the cognitive buffer hypothesis (CBH). The relationship between longevity and brain size has been investigated to date only among terrestrial vertebrates, although the same selective forces acting on those species may also affect vertebrates living in aquatic habitats, such as fish. Thus, whether this evolutionary trade-off for brain size and longevity exists on a large scale among fish clades remains to be addressed. In this study, using a global dataset of 407 fish species, I undertook the first phylogenetic test of the brain size/longevity relationship in aquatic vertebrate species. The study revealed a negative relationship between brain size and longevity among cartilaginous fish confirming EBF and DST. However, no pattern emerged among bony fish species. Among sharks and rays, the high metabolic cost of producing neural tissue transcends the cognitive benefits of evolving a larger brain. Consequently, my findings suggest that the cost of maintaining brain tissue is relatively higher in ectothermic species than in endothermic ones., (© 2022 The Author. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Aim: The 'rate‐of‐living' theory predicts that life expectancy is a negative function of the rates at which organisms metabolize. According to this theory, factors that accelerate metabolic rates, such as high body temperature and active foraging, lead to organismic 'wear‐out'. This process reduces life span through an accumulation of biochemical errors and the build‐up of toxic metabolic by‐products. Although the rate‐of‐living theory is a keystone underlying our understanding of life‐history trade‐offs, its validity has been recently questioned. The rate‐of‐living theory has never been tested on a global scale in a phylogenetic framework, or across both endotherms and ectotherms. Here, we test several of its fundamental predictions across the tetrapod tree of life. Location: Global. Time period: Present. Major taxa studied: Land vertebrates. Methods: Using a dataset spanning the life span data of 4,100 land vertebrate species (2,214 endotherms, 1,886 ectotherms), we performed the most comprehensive test to date of the fundamental predictions underlying the rate‐of‐living theory. We investigated how metabolic rates, and a range of factors generally perceived to be strongly associated with them, relate to longevity. Results: Our findings did not support the predictions of the rate‐of‐living theory. Basal and field metabolic rates, seasonality, and activity times, as well as reptile body temperatures and foraging ecology, were found to be unrelated to longevity. In contrast, lower longevity across ectotherm species was associated with high environmental temperatures. Main conclusions: We conclude that the rate‐of‐living theory does not hold true for terrestrial vertebrates, and suggest that life expectancy is driven by selection arising from extrinsic mortality factors. A simple link between metabolic rates, oxidative damage and life span is not supported. Importantly, our findings highlight the potential for rapid warming, resulting from the current increase in global temperatures, to drive accelerated rates of senescence in ectotherms. [ABSTRACT FROM AUTHOR]

Animal lifespan is determined by extrinsic and intrinsic factors causing mortality. According to the evolutionary theories of senescence, when mortality pressures are low, animals delay reproduction. This enables species to grow more slowly and, consequently, natural selection can act against harmful mutations in adulthood, thereby increasing lifespans. To test predictions of these theories we assembled a dataset on the maximum longevities and relevant ecological variables of 1320 reptilian species. Correcting for phylogeny, we modelled the link between reptile longevity and factors such as body size, microhabitat, activity period, insularity, annual temperature, temperature seasonality, elevation and clutch size that we hypothesized will affect extrinsic mortality rates and hence lifespan. Body mass explained a small proportion of the variance in reptile longevity. Species living on islands, and in colder and more seasonal environments, lived longer. Observed maximum longevity was positively associated with the number of individuals used to estimate it. Our results suggest that species exposed to reduced extrinsic and intrinsic mortality pressures (lower predation, lower metabolic rates and shorter activity periods) live longer. Sampling more individuals increases the chances of finding older specimens and should be corrected for when studying maximum longevity. [ABSTRACT FROM AUTHOR]

Aim: Longevity is a critical life‐history trait of organisms. Multiple abiotic and biotic factors are thought to exert different selection pressures, resulting in a great variation in species longevity. We examined factors that, according to evolutionary theories of senescence, are thought to be related to extrinsic and intrinsic mortality rates, and thus shape the variation in longevity among amphibians. Location: World‐wide. Time period: Present. Major taxa studied: Amphibia. Methods: We collected literature data on the maximum longevities of 527 amphibian species. Correcting for phylogeny and sample size, we modelled the relationship between amphibian longevity and body size. We also examined the effects of chemical protection, activity period, microhabitat preferences and annual temperature on amphibian longevity. Results: In general, members of larger amphibian species live longer. Body size, however, explained less of the variation in amphibian longevity than it does in mammals and birds. Nocturnal amphibians, species that use poison for defence and those inhabiting cold regions live longer, but microhabitat preferences had little effect. Main conclusions: Our results supported predictions of evolutionary theories of senescence. Large amphibians living in colder environments probably experience slower growth and metabolic rates, reducing intrinsic drivers of mortality and increasing longevity. Moreover, species that reduce extrinsic mortality pressures via chemical protection and nocturnality have increased longevity. Sampling captive animals and sampling more individuals of a species increases the chances of finding older individuals and should be corrected for when studying maximum longevity. [ABSTRACT FROM AUTHOR]