For humans and many other creatures, whose mortality increases sharply with age and begin to deteriorate the older they get, hernit crabs have seemingly found the fountain of youth, Nature.com reported.
As countless Hollywood starlets fight Father Time, animals such as the hermit crab, the red abalone and the hydra, a microscopic freshwater animal that can live centuries can enjoy near constant levels of fertility and mortality throughout their lives.
By comparing standardized demographic patterns across 46 species, researchers found the vast diversity of "aging strategies" among them challenges the notion that "evolution inevitably leads to ... deterioration of mortality and fertility, with age," Owen Jones, a biologist at the University of Southern Denmark in Odense who led the study, told Nature.com.
"By taking a grand view and doing a survey across species, we found plenty of violations of this underpinning theory," he said.
In the animals like the hermit crab, researchers found no association between the length of life and the degree of senescence, or biological aging.
In the study, researchers assembled published life-history data sets for 11 mammals, 12 other vertebrates, 10 invertebrates, 12 vascular plants and a green alga to compare fertility and mortality patterns.
According to Nature.com, researchers standardized the trajectories by dividing mortality rates at each point in the lifespan by the average mortality rate.
Of the 24 species showing the most abrupt increase in mortality with age, 11 had relatively long lifespans and 13 had relatively short lifespans. A similar split in lifespan occurred in the species that had a less abrupt increase in mortality.
Nature.com reported that "when the researchers organized the species along a senescence continuum, mammals were clustered at one end of the spectrum, among the organisms that have an abrupt shift in mortality, and plants, which boast vastly lower relative mortality, populated the other end. Birds and invertebrates were scattered throughout."
Jones said suggest the diversity of ageing strategies across the spectrum should challenge theoreticians. Although evolutionary theories are applicable in lots of situations, he said "they can't explain some cases."
"It's not about throwing out old theories; it's about modifying theories to work on all species," Jones said.
Many scientists have spoken against the relevance of this study.
"This approach is like making a fruit salad and imagining it can tell you something about evolution of the orange," said Steven Austad, an evolutionary biologist at the University of Texas Health Science Center in San Antonio. "This comparison of demographic trajectories across the tree of life is completely divorced from biology and ignores the impact of the environment."
