02/11/2004
Youthful Oldtimers
Our moon and Mars have received a lot of attention recently. President Bush wants us to revisit the former and to start the process of visiting the latter sometime in this century. We’re talking live people visits, not the robotic visits now in progress. Longtime readers will know that one of the things I enjoy most here on Marco Island in Florida is to walk early in the morning on the beach and witness the setting of the full moon as the sun is about to rise. One morning last week, I not only saw my moonset but also spent a couple of hours on Mars.
Both experiences were awesome. OK, I wasn’t actually on Mars but, thanks to the JPL/NASA Web site, I can enjoy the next best thing. If you haven’t already done so, I strongly recommend logging on to the NASA Web site. (Just search the terms “NASA Mars images” and you’ll be led to the appropriate site.) You’ve seen pictures in the papers and on TV of the landscapes surrounding the Spirit and Opportunity rovers but these don’t begin to give you the feeling that you’ll get browsing the actual photos. I latched onto two 360-degree composite images and took the half hour or so that my dial-up Internet connection required to download each of the highest resolution images. Once downloaded, you can pan lowly up and down and across the landscapes and, if you aren’t enthralled by the experience, why are you reading this column?
At one landing site, the rocks are chunky and many resemble pyramids in shape, while in the other landing area the rocks are mostly slabs. You can clearly see that many of the slabs are layered, one of the things that has excited the scientists. Could the layering be a remnant of watery times in Mars’ past? There’s obviously a lot of history in these layers. One could let one’s imagination run away with itself and imagine finding fossils in the layers, as we have in layers of rock here on Earth.
Coming back to earth, in addition to witnessing a moonset, I’ve also begun to accomplish another goal – getting my fill of grouper, an alternative to the farmed salmon we discussed last week. The grouper sandwiches have been delicious! We’ve heard or read a lot about the health benefits of eating fish and the evidence that fish consumption helps protect against heart attacks and other life-shortening maladies. Could it be that some fish may themselves have the secret to a truly long lifespan? I found this to be a real possibility after reading two articles by Linda Marsa in the February 2 edition of the Naples Daily News.
We’ve discussed how limiting food intake or altering certain genes can lead to fantastic increases in the lifespans of certain creatures such as the worm C. elegans or the fruit fly. Marsa points out that when Ponce de Leon sailed the Atlantic in search of the fountain of youth, the answer may have been swimming in the water underneath his ship. Certain species of fish, and perhaps turtles, may have found the secret of agelessness. Take the rockfish, a perch that lives in the Pacific Ocean. It has been established that certain rockfish have lived as long as 140 years or more. Admittedly, a few of us humans have lived to 120, so what’s the big deal? Well, you have to admit that those who have lived or did live that long show(ed) obvious signs of aging.
The female of our species has a certain number of eggs in her ovaries at birth and makes no more during the course of her life. The female rockfish, on the other hand, doesn’t seem to become frail as it ages and in fact produces new eggs even in its 70s or beyond. Or take the female painted turtle, which also is quite productive in her 70s. Not only is she productive, but also she may produce five times more baby turtles in her 70s than when she was young. Just as startling is the finding that the mortality rate of the oldest turtles in one study group is the same as the mortality rate of the youngest turtles in the group. In other words, the turtles do not show signs of deterioration with age. Rather they die from accidental causes or at the hands of predators, the human driving a car being one common predator.
The results Marsa cites come from studies by the likes of Caleb Finch and Justin Congdon, leading researchers in the study of fish and turtles, respectively. The turtle work began in the 1950s with earlier workers’ observations of the nesting seasons of turtles in a University of Michigan nature preserve near Ann Arbor. Congdon took up the challenge in 1975. He and his co- workers have tagged and followed some 12,000 turtles, including the Blanding’s, painted and snapping varieties.
John Guerin, director of the Centenarian and Rockfish Project, credits Caleb Finch with coining the term “negligible senescence”. While the possibility that some fish might live to quite long ages was suggested some 70 years ago, it’s only relatively recently that serious research has begun to find out the reasons. What is negligible senescence? There are three criteria: (1) no change in mortality rate after reaching maturity, (2) no decrease in reproductive capability after maturity and (3) no detectable decrease in physiological capabilities or in resistance to disease with age. Unlike studies on short-lived worms or fruit flies, the lifespans involved in studying fish or turtles make the collection of data to satisfy the above criteria a painstaking task that requires real dedication and may take several human lifetimes.
On the agelessanimals.org Web site, Guerin presents an interesting table listing over 40 species of rockfish and their maximum lifespans. By no means are all rockfish super long- lived. The vast majority live in the range from a maximum of 12 to 118 years, almost all living well under a hundred years. Only the shortraker and the rougheye are the real Methuselahs, clocking in at 154 and 205 years, respectively.
Marco has a substantial number of snowbirds or residents who love to go out into the Gulf of Mexico to fish. What do they and virtually all fishermen do? If they hook a small fish, smaller than the legal limit for that species, they throw it back in the water. The fish they keep and take pictures of are the big ones. What’s the result? The younger fish are the survivors and it’s the older fish that end up on your dinner plates. Is this a good thing? Not necessarily.
The finding that old females in certain fish and turtle species are just as productive or even more so, compared to the younger females has an important consequence. With no loss of reproductive capability, or even increased productivity on aging, the older members of a species become more important from the standpoint of reproducing and maintaining the populations. With overfishing, the population becomes highly skewed toward the younger fish. The population of big fish declines and the fishing industry suffers.
From the research standpoint, the oldest members of a species are invaluable research subjects, providing the sources for genetic or chemical studies aimed at finding out what it is that retards or may even halt the aging process. Clearly, we all benefit if whatever it is turns out to be something that could lengthen our own lifespans.
How are the ages of the fish and turtles determined in these studies? With the turtles it’s simple, just tag them and catch them as the years go by. Zoos can be a good source of data if records have been kept; for example, some alligators have lived to 80. With fish it’s more complicated. One method is to measure bone growth in the otolith, a bone in the ear. Another is to measure the radioactive decay products in the core of bones in the fish.
One of the concerns with our own species when it comes to ageing is “quality of life”. I imagine that a rougheye enjoys its long life. It still gets around a good bit and there must be occasional excitement, avoiding bigger fish or fishermen and chowing down on a smaller fish. A turtle gets to move around a lot, albeit at a slower pace – not a bad life, it seems to me. But take the case of a certain species of tubular worm that grows to a length of about ten feet and lives on the bottom of Mexican Bay. This worm can live to the ripe old age of 170 to 250 years. However, it hardly moves and has no eyes and no mouth. It eats by adsorbing food that makes its way through its skin. I can’t help thinking what a waste – all those years and the poor creature essentially just sits there in the dark!
As I savor my grouper sandwich, I wonder, can that worm possibly enjoy “eating” through its skin? Hey, aren’t we lucky to have been born into the Homo sapiens species? We may not live as long as some creatures but I firmly believe we have more fun.
Allen F. Bortrum
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