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why don't octopus and other cephlapods live very long?

squidink

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#1
as the title says whats the reason biologically speaking why they don't live very long? i'm not talking about after they breed they die because even without mating they don't live very long do they, i had been informed on another forum it is because they have a high metabolic rate "Their cells turn over molecules more quickly, metabolizing sugars and fats and proteins in order to grow quickly. All of that rapid action leads to the production of free radicals and oxidative damage."
is this correct? and if so is there a way we can slow don't there metabolism?
 

neurobadger

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#2
They have a gland behind their eyes that, upon reproduction, causes them to age and rapidly die.

If you cut out that gland, they can live about twice as long.

Slowing down their metabolic rate might kill them. I don't know. Perhaps someone should experiment with feeding their octopus antioxidants.
 

skywindsurfer

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#3
Herbal extracts and green tea? lol

I read somewhere that a scientist did remove some gland or organ in the attempt to make them live longer but was unsuccessful.
 

DWhatley

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#4
Sadly, I don't know the credibility of this source (colorado.edu) and will continue to look for the study I last found but this outline contains a summary of what I found in a published study (I have read either the full or abstracts from 2)
http://www.colorado.edu/intphys/iphy4480tsai/Lecture26.html

Here is an abstract that summarizes the same thoughts and sites lab work done in 1930, 1956, 1959 and 1977.

Ahh, Here is the 1959 paper, HORMONAL CONTROL OF SEXUAL MATURITY IN OCTOPUS. The experiments were designed to force sexual maturity but they removed the optic gland from several octopuses and found that known procedures for rapid sex organ growth failed when the gland was removed. Page 21 discusses optic gland removal and the results. On rereading the article, this comment was interesting and I wonder if anyone has experimented with the light aspect:
It is concluded that maturation of the gonad is determined by secretion from
the optic glands which is normally held in check by an inhibitory nerve supply
from the subpedunculate/dorsal basal lobe area. The action of this region is in turn
dependent upon the integrity of the optic nerves and thus, presumably, upon light.
Later work found that removal of the optic gland extended the octopuses lives (Hoping Level Head will jump in here as I know he has read the later work and may have a ready reference). From what I remember, not only can the gland be removed and stop sexual maturity but a small piece can be reintroduced and will start up the reproductive cycle.
 

Level_Head

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#5
DWhatley;179173 said:
On rereading the article, this comment was interesting and I wonder if anyone has experimented with the light aspect:
Later work found that removal of the optic gland extended the octopuses lives
(Hoping Level Head will jump in here as I know he has read the later work and may have a ready reference). From what I remember, not only can the gland be removed and stop sexual maturity but a small piece can be reintroduced and will start up the reproductive cycle.
You've covered the ground well, it seems. There is a good collection of references on this thread:

http://www.tonmo.com/forums/showthread.php?6556-Senescence-and-the-Optic-Gland

On the light aspect, your first outline contained an interesting line:
# Removal of the optic gland and bright light prevent sexual maturation of these animals.
I've read suggestions that the timing of the light is likely to influence the optic gland, but this was the first time I'd see this idea: that bright light keeps it from maturing.

Is that "all the time"? 24 hours? What effect does that have on the animal's lifespan?

I'm still jamming on a project, but that's worth some studies.

You and I have discussed the possibility that tank lighting may be responsible for the shorter-than-natural lifespans of some octopuses in captivity.

The antigen aspect was interesting, too; the idea that the optic gland is tied in to the immune system in some manner, such that the optic gland starts secreting in reaction to foreign proteins in the animal's blood.

That work was done decades ago, and our molecular capability has dramatically improved since then, but I haven't seen an update.

To address SquidInk's original question, I note that some researchers suggested that it was rapid metabolism that caused the short lifespan -- and we now know that this isn't completely true, since we can shorten or extend that lifespan without changing the metabolic rates.

It is apparently a literal case of planned obsolescence. Or, in this case, programmed senescence.

I hold out hope that evolution can make changes here. After all, a fairly close relative of the octopus (the geoduck clam) is known to live for nearly two centuries.

While we don't think of clams and cephalopods as close, the metabolism at the cellular level is in some ways more alike than different. And their body plans have surprising similarities.
 

DWhatley

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#7
After all, a fairly close relative of the octopus (the geoduck clam) is known to live for nearly two centuries.
With that kind of lifespan one assumes low birth rate and it is a wonder they have not become extinct from predation by humans since they are eaten in China (and likely other asian countries but oddly not in the US).

The linked article mentions aquaculture so I am a little surprised we don't see them in the aquarium hobby.
 

Level_Head

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#8
DWhatley;179238 said:
With that kind of lifespan one assumes low birth rate and it is a wonder they have not become extinct from predation by humans since they are eaten in China (and likely other asian countries but oddly not in the US).

The linked article mentions aquaculture so I am a little surprised we don't see them in the aquarium hobby.
Oh, they are definitely eaten in the US. You can buy them at seafood counters in the Pacific Northwest, where they're farmed:
http://www.geoduckrecipes.com/
 

DWhatley

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#9
I will have to look for them at the international market seafood counter (they are not in local grocery seafood counters and I have noticed some US food at the interantional marked). I think I would have seen them there though since I am always looking for new foods for the octopuses or live things to try in the aquarium. A an inch a year I would need to find a smaller than eating size one at the market if I wanted to try one in a tank and they are too expensive to feed the octopuses.

Birth rate must not be too low though since they are a 4 year investment and make money for the growers.
 

Level_Head

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#10
squidink;179136 said:
as the title says whats the reason biologically speaking why they don't live very long? i'm not talking about after they breed they die because even without mating they don't live very long do they, i had been informed on another forum it is because they have a high metabolic rate "Their cells turn over molecules more quickly, metabolizing sugars and fats and proteins in order to grow quickly. All of that rapid action leads to the production of free radicals and oxidative damage."
is this correct? and if so is there a way we can slow don't there metabolism?
It occurs to me that we have not addressed your original questions, and got sidetracked into the very interesting discussion of optic glands, which don't have an equivalent in mammals as discrete glands. The secreting neurons involved in vertebrates are apparently more broadly distributed.

Let's break your questions out a bit, and see if any experts here want to take a shot at them. I'm going to separate out the hidden assumptions as separate questions for clarity.

And throughout all of this, let's agree to use "cephalopods" as a shorthand for "cephalopods in general" -- while recognizing that this encompasses a pretty broad range of animals, lifestyles, and adaptations. Few laypersons would suggest that the half-inch male blanket octopus has much in common with the ten-meter colossal squid, the shell-bound nautilus, or the flap-winged little dumbo.

But the differences may help answer some of the questions:
  1. Do cephalopods have a high foodmass conversion rate?
  2. Does a high food conversion rate shorten cephalopod lifespans?
  3. Is foodmass conversion rate the same thing as the metabolic rate?
  4. Do cephalopods have a high metabolic rate?
  5. Is the cephalopod's high metabolic rate the cause of their short lifespan?
  6. How do cephalopod metabolic rates compare with other animals?
  7. Do cephlopods have a high production rate of free radicals?
  8. Do cephalopods show evidence of high oxidative damage?
  9. Do cephalopods show the effects of aging in a way we relate to oxidative damage?

===|==============/ Level Head
 

Level_Head

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#11
Level_Head;179323 said:
1. Do cephalopods have a high foodmass conversion rate?
This question, at least, has a clear answer: Yes.

Many studies such as this one have documented that cephalopods in general, and octopuses even more than squid, have among the highest known foodmass conversion efficiencies:
http://www.jstor.org/pss/56297

And this study, downloadable as a PDF, looks at how different individual octopuses can be, even siblings from the same clutch of eggs. In some cases, their food conversion efficiency exceeded 100%:
http://eprints.utas.edu.au/9741/3/03chapter2.pdf

Octopuses are considered to have the highest conversion percentage among invertebrates — which begs the question, "What about vertebrates?"
 

DWhatley

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#12
Tomorrow I will see if our state University provides any kind of subscription access to jstor for either state residence or alumni as I would like to read the rest of the first publication and my uni was in the list of GA subscribers (as well as one high school. It is interesting and encouraging that a high school subscribes to this kind of publication outlet).

The second seems only to show one thing, octopuses grow as differently in an aquarium environment as they do in the wild. For hobbyists, this is actually sort of a reassuring concept that suggests tank life does not alter their natural growth. One other hobbyist interests observation that was officially noted was the change in food intake over different periods. It would have been nice if they could have documented something going on at these fasting periods but the fact that they are noted in a species we do not commonly keep in the hobby suggests it is common with this sized animal (medium sized octo with 2' arm span).
 

devi

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#13
Can't remember where I read this, but isn't it also known for them to live longer if you feed very little? As in near starvation levels?
 

neurobadger

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#14
Level_Head;179329 said:
This question, at least, has a clear answer: Yes.

Many studies such as this one have documented that cephalopods in general, and octopuses even more than squid, have among the highest known foodmass conversion efficiencies:
http://www.jstor.org/pss/56297

And this study, downloadable as a PDF, looks at how different individual octopuses can be, even siblings from the same clutch of eggs. In some cases, their food conversion efficiency exceeded 100%:
http://eprints.utas.edu.au/9741/3/03chapter2.pdf

Octopuses are considered to have the highest conversion percentage among invertebrates — which begs the question, "What about vertebrates?"
Raises the question! RAISES THE QUESTION!

Probably rodents.
 

Level_Head

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#15
This is actually a common (now) observation in mammals, and has been supported in a number of studies in animal models ranging from rats to human. I am not at all certain that it applies to cephalopods, though.

Moreover, the hunting of live food has been shown to increase the animal's lifespan, by keeping them actively interested in their surroundings. A bored octopus tends to live a short time, and will become neurotic and self-destructive.

I suspect that an active hunter needs such stimulation, which many keepers address in part by providing interesting toys to play with. These seem to help, too.
 

Level_Head

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#16
In answer to the raised question — "how about vertebrates?" — there are a couple of interesting answers.

In one case, insects are compared to mammals, by a group that is seriously devoted to insects as food. I imagine that they were somewhat disappointed at this Q&A bit:
Doesn't it seem that, even with ECIs at the relatively low range of 10-15%, if the forest was properly managed for caterpillar (and termite) preservation (as has been recommended in several instances by researchers in Africa), it would be about as productive for animal agriculture as grassland? Is there a short answer for this complex question, or is the question not as complex as it seems?

Dr. Lindroth: On the surface the reasoning seems sound. But a number of complicating factors come to mind; the answer really is complex. For example, because grasslands have coevolved with large grazing mammals grasses can recover remarkably well from extensive grazing. Remove the same percentage of green foliage from a forest habitat and you'll not have the forest for long. And then there are the practical matters of harvest, etc. It is probably much easier to harvest 1000 lbs of large animal biomass from a grassland than an equivalent amount of insect biomass from a forest! This is not to say that management of forests for insect production should not be considered, just that the comparison with grassland systems is fraught with problems.
In short: "Why not raise and eat insects instead of beef?" and the answer is "Cattle conversion of grasslands are more efficient than you'd think, because the grasslands themselves are very productive and have evolved to deal with grazing."

Here's the article, with the Q&A toward the bottom. By the way, "the FIN" is the Food Insect Network. Yum!
http://www.hollowtop.com/finl_html/conversion.htm

None of these references, by the way, come close to octopuses. And there's the additional complication of dry mass (grain) becoming wet mass (flesh, mostly water). Octopus growth is also sometimes measured the same way -- a paper up this thread calculated the dried mass of crabs involved.

I'm not getting any good comparable numbers for small mammals. I've learned that cavies generally break the rodent model by having a small number of very large babies (up to 18% of the parent's mass each!) and other interesting tidbits, but not closely relevant to our pursuits.

But it does seem that even on land, invertebrates (insects) are the champion individual converters of food to body mass.

A related term, assimilation efficiency, does not take into account the use of some of the assimilated material as energy. Here's one quote:
http://www.flatheadwatershed.org/natural_history/flow.shtml
Some approximate percentages of assimilation efficiency are shown in various diets below:

* 15% of the energy from decomposing material
* 30-40% of the energy from grasses
* 60-70% of the energy in young plant materials
* up to 80% from seeds.

***
As with primary producers and herbivores, energy is also lost by secondary consumers through respiration and organism death. The assimilation efficiencies of animal food by carnivores vary between 60% and 90%. And within those foods, vertebrate (species with spinal columns or backbones) prey are more efficiently digested than insect prey, as the indigestible insect exoskeletons make up a larger portion of the prey body than do scales, feathers, or hairs on vertebrates. Assimilation efficiencies of insectivores are between 70% and 80% and carnivores is 90%.
Omnivores are part of both the second and third trophic levels. Humans are omnivores because we are physiologically capable of eating animal flesh and vegetation. Some humans, however, choose not to eat animal protein.
Octopuses are capable of not only getting a lot out of their food, they're also quite efficient at conserving the energy of the result.

But not, alas, for a very long time. I still don't see an obvious relationship between lifespan and conversion efficiency.
 

DWhatley

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#17
Watching Tank go through the not eating part of senescence has me wondering about stored energy. He is the first octopus I have kept that continued much of his routine after eating stopped so I could observe the body changes (all others, male and female, have conserved energy and wasted away in their dens only to come out in the last day or two). Most notable was the loss of muscle in the arms followed by shrinkage of both the mantle length and arm girth. We know they go a long time without eating in the end and I wonder if the high rate of conversion is related to storage rather than usage.
 

Level_Head

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#18
It does seem that they are efficient both ways: converting sustenance to body mass, and body mass back to sustenance toward the end.

And this is for an animal with a metabolic rate higher than most invertebrates, as well as an energy-expensive brain. A single octopus's oxygen usage is as much as a tank-full of other marine creatures. At least, until he hunts them down and eats them.
 

ceph

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#19
Why don't cephalopods live long?

This is a tough question. Lets take a different approach and instead look at life history and game theory. Why don't all animals have long life spans? Or, to put it another way, what are the advantages of having a short semelparious (reproducing once and dying) life history? What are the disadvantages?

Game theory:
Lets say that it is a really bad year for copepods - the food for a model larval fish population and a model (para)larval squid population. This years offspring of both populations have few survivors due to lack of food. . .

Lets say the opposite happens, copepods are plentiful and finding food is easy. Larval fish and larval squid do well.

Now lets look at the reproductive output of our model fish and model squid. The fish could be best described as "slow and steady"; they divide their money between CDs, blue chip income stocks, real estate, precious metals and T-bills (from counties whose politicians can work together). Model fish take five years to mature. Once mature, they only put 5% of their body mass into reproduction. The squid, on the other hand, mature in a year and dump 50% of their body mass into reproduction. . . They put all their money in a single stock - the latest internet IPO. Squid ride their motorcycles in the rain.

In tough times, when there are few copepods, the fish have a huge competitive advantage. Sure most of their larva gets wiped out, just like the squids, but the adult fish continue to live and thrive and will be there next year to reproduce. The fishes population size may slightly decline but most likely this decline won't even be detectable.

The squid are decimated. They put all their eggs in one basked and things went very badly for them. The squid population crashes hard; they are economically extinct (meaning that fishermen can't catch enough to pay for gas).

In good times, when there is a lot of food for hatchlings, the squid do really well. As they put 50% of their body weight into reproduction and have a 10:1 advantage over the fish. Their advantage is even greater considering that it only takes one year for the squid to mature and reproduce, while the fish take many years to mature. A couple good years in a row and the larva fish still are not mature but all the squid are. . . In good times the squid population explodes. Squid's life history is dynamic and they can quickly take advantage of environmental change.

Both the fish and squid strategies are successful at times. Both work. Neither works all the time. What I just described was an Evolutionary stable strategy.

That explains why there are different strategies. Why do cephalopods have the "live fast, die young" strategy instead of the slow and steady strategy? This gets a bit speculative but the lifespans of other mollusks offers some clues. Those with large thick shells, like Tridacna clams and Queen conchs, tend to have longer life spans. Interestingly, another group of mollusks that lacks shells, the nudibranchs, tend to have shorter life spans. Within the cephalopods, the externally shelled Nautilus has one of the longest lifespans. By giving up the heavy protective armor of the shell, cephalopods gain faster growth rates, which gives them the potential to switch strategies from the fish model (I could have used tridacna clam or queen conchs) slow and steady model to the life fast and die young model.

Two additional points to ponder:

1) Intelligence has nothing to do with this explanation. We humans value it because it is the one trait that we happen to have. We tend to associate it with other animals like us, other mammals, most of which have long lifespans, parental care, etc. Evolution doesn't care.
2) What happens when we change the playing field, say by removing the large fish and mammals (predators of squid) and altering the environment (say by ocean acidification). Which group will benefit? Squid or fish?
 

Cuddlycuttlefsh

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#20
Oh yeah, do forget that the climate and size of a specimen effects how long it can live, if you take a look at pygmy squid they don't even live for a full year. Then take a look at GPO, they live for 3 to 5 years and live in colder conditions than the squid I just mentioned earlier don't they?:neutral:

I love what Dr. Wood mentioned, the fast rate of sexual maturity and reproducing is a massive pro for cephalopods. Good thinking:grin:!
 

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