The work noted here might be taken as a companion piece to a recent paper on eusociality as a driver of the evolution of exceptional longevity in a wide variety of clades, not just mammals. Here, researchers take a broad look across mammalian species that exhibit a variety of different type of social organization, and find a correlation with species longevity. While thinking about this, one might also look at the evidence for mating strategies to drive the evolution of longevity; one might think that social organization has a large impact on mating strategy. At root, one might ask how all of these various parameters and their outcomes affect the trade-off between growth and maintenance in individuals; as a rule, species that mature faster can achieve reproductive success more reliably in an uncertain environment, but at the cost of a shorter life span and less opportunities to reproduce over time.
Extrinsic mortality, largely driven by predation, imposes strong selective pressures on ageing and longevity. Body size is perhaps the most important factor: larger mammals generally face fewer predators, allowing them to allocate more resources to maintenance and repair, thereby extending their lifespans. Comparative analyses of bats and marsupials similarly support reduced environmental vulnerability as a driver of longer lifespan. Furthermore, lifespan is correlated with other traits, including age at maturity and parental investment, consistent with the trade-off between energy allocation for reproduction and cellular repair. Increasingly, behavioural factors such as sociality are recognised for their impact on lifespan dynamics, adding another dimension to our understanding of longevity evolution.
Social groups protect their members from predation and starvation. Reduced risk of death from such extrinsic causes is expected to promote the evolution of longer lifespans. Since group-living similarly aids predator avoidance, resource defence, and foraging efficiency, we might expect a positive relationship between group-living and lifespan in comparative analyses. However a broad-scale quantitative study of 253 mammalian species failed to detect this relationship. To investigate this unexpected lack of support, we present a re-analysis of the topic, expanding the sample size to include a greater diversity of mammal species.
We analysed maximum recorded lifespan, body mass, and social organisation data for 1,436 mammal species using Bayesian phylogenetic comparative methods, confirming that group-living and pair-living species exhibit longer lifespans than solitary species after controlling for body mass and phylogeny. Pair-living species showed slightly longer lifespans than group-living species (though credible intervals overlapped), while body mass slopes did not differ substantially among social categories and activity period showed weak associations with lifespan. These results provide independent corroboration of recent findings linking sociality to longevity in mammals and suggest that while group-living may reduce predation risk, pathogen transmission costs in larger groups may constrain longevity benefits. Our findings, based on the largest comparative dataset analysed to date, strengthen the evidence that social organisation is a key factor shaping mammalian life-history evolution alongside body size and ecological adaptations.
Link: https://doi.org/10.1002/ece3.73587
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