The evolution of senescence in fish.

Fish are over-represented among the vertebrates that are known to live over 100 years. Such trends in maximum longevity suggest that fish also experience delayed senescence relative to other vertebrates. Most applications of evolutionary theory suggest that the extrinsic mortality rate, or mortality that is attributable to external factors like disease or predation, is the major factor that shapes the evolution of senescence, so that the only way to evolve delayed senescence is to experience lower rates of extrinsic mortality. We propose instead that fish are more inclined to evolve delayed senescence because they have indeterminate growth and, as a consequence, have the capacity for a substantial increase in fecundity with age. It is thus the combined effects of the expectation of survival and fecundity that shape the evolution of senescence, as originally proposed by Williams (1957). We also argue that fish share many of the same general mechanisms that shape the evolution of senescence in other vertebrates. We support this argument with statistical analyses of life history data that show the same patterns of correlation among traits as seen in birds and mammals.