The blog of Xeno, a slightly mad scientist
For several species mortality increases with age — as expected by evolutionary scientists. This pattern is seen in most mammal species including humans and killer whales, but also in invertebrates like water fleas. However, other species experience a decrease in mortality as they age, and in some cases mortality drops all the way up to death. This applies to species like the desert tortoise (Gopherus agassizii) which experiences the highest mortality early on in life and a steadily declining mortality as it ages. Many plant species, e.g. the white mangrove tree (Avicennia marina) follow the same pattern.
Amazingly, there are also species that have constant mortality and remain unaffected by the aging process. This is most striking in the freshwater polyp Hydra magnipapillata which has constant low mortality. In fact, in lab conditions, it has such a low risk of dying at any time in its life that it is effectively immortal.
\”Extrapolation from laboratory data show that even after 1400 years five per cent of a hydra population kept in these conditions would still be alive,\” says Owen Jones.
Several animal and plant species show remarkably little change in mortality throughout their life course. For example, these include rhododendron (Rhododendron maximum), great tit (Parus major), hermit crab (Pagurus longicarpus), common lizard (Lacerta vivapara), collared flycatcher (Ficedula albicollis), viburnum plants (Viburnum furcatum ), oarweed (Laminaria digitata), red abalone (Haliotis rufescens), the plant armed saltbush (Atriplex acanthocarpa), red-legged frog (Rana aurora) and the coral red gorgonian (Paramuricea clavata).
When you look at the fertility patterns of the 46 surveyed species, there is also a great diversity and some large departures from the common beliefs about aging. Human fertility is characterized by being concentrated in a relatively short period of life, and by the fact that humans live for a rather long time both before and after the fertile period.
A similar pattern of a concentrated fertile period is also seen in other mammals like killer whales, chimpanzees, and chamois (Rupicapra rupicapra), and also in birds like sparrow hawks (Accipiter nisus).
However, there are also species that become more and more fertile with age, and this pattern is especially common in plants such as the agave (Agave marmorata) and the rare mountain plants hypericum (Hypericum cumulicola) and borderea (Borderea pyrenaica).
On the contrary fertility occurs very early in the nematode worm Caenorhabditis elegans. Actually this species starts its life with being fertile, then it quite quickly and quite suddenly loses the ability to produce offspring.
To sum up there is no strong correlation between the patterns of aging and the typical life spans of the species. Species can have increasing mortality and still live a long time, or have declining mortality and still live a short time.
“It makes no sense to consider aging to be based on how old a species can become. Instead, it is more interesting to define aging as being based on the shape of mortality trajectories: whether rates increase, decrease or remain constant with age,” says Owen Jones.
If scientists are correct, jellyfish may hold the key to immortality.
That’s the premise of a New York Times Magazine article that examines a species of jellyfish (appropriately) nicknamed the “immortal jellyfish.”
Known officially as Turritopsis nutricula (and sometimes as Turritopsis dohrnii), the minute creature has the ability to transform its cells back into a youthful state. As National Geographic puts it, the jellyfish transforms “into a blob-like cyst” that grows into a polyp colony — the first stage of life.
From there, the jellyfish continues a conventional lifecycle, maturing and mating. Instead of dying, however, the immortal jelly reverts, time and again, back into the polyp colony. That ability “allows the jellyfish to bypass death, rendering [it] biologically immortal,” notes Hongbao Ma, a researcher at Brookdale University Hospital and Medical Center in Brooklyn, N.Y.
According to a study published in “Nature and Science,”the jellyfish accomplishes this unique feat via “transdifferentiation.” Essentially, the creature absorbs its cells, then transforms them into cells of any other type.
With life skills this advanced, it’s no surprise the jellyfish has populated the globe in what’s been termed “a worldwide silent invasion,” the Telegraph notes. ..