Studies concentrating on a small number of model organisms have figured strongly in recent biogerontological
Figure 20.5. A hypothetical scheme for the mechanism of lifespan regulation and evolution. (A) Evolved intraspecific differences in lifespan between parasitic and free-living adults are generated by differences in gene expression, regulated by endocrine and cellular signalling systems via regulated transcription factors. We propose that, as in C. elegans (Murphy et al., 2003), parasitic adult longevity in S. ratti results from up-regulation of longevity assurance genes and down-regulation of genes which promote aging. A arrows = stimulation, and T bars = inhibition. (B) Potentially, differences in aging rate between species may evolve via similar mechanisms. Here, the environment of an ancestral species changes, such that the extrinsic mortality rate is lowered, and selection against deleterious late-life effects is increased. This leads to the evolution of slower aging and increased longevity, which might occur via alterations in regulation of longevity assurance and aging genes. This predicts that several types of gene are likely to be altered during lifespan evolution: those encoding endocrine, signalling proteins and transcription factors. In (B), asterisks represent alterations in the trait resulting from random mutation, and selection.
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