Unusual Patterns in Cephalopod Aging

You might wonder- “why is this guy talking about cephalopod aging. What relevance does this have with anything else he writes about?” As you you shall soon see, a lot!

So what are cephalopods?

A cephalopod is any member of the molluscan class Cephalopoda (Greek plural Κεφαλόποδα (kephalópoda); “head-feet”). These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink

The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea the molluscan shell has been internalized or is absent, whereas in the Nautiloidea the external shell remains.

Cephalopods are the most intelligent invertebrates, and are smarter than many mammals. Plus they have copper pigment based blood.

They also have a very peculiar life cycle. With the exception of Nautiloid cephalopods, they die after reproducing (most often after the first time). Non-nautiloid cephalopods that survive past 5 years are almost unknown.

Now you might say- so what? My counter question is- what advantage does this mode of reproduction/dying have for non-nautiloid cephalopods?

Nautiloid Cephalopods might be the most “primitive”, but they are the ultimate survivors. They have survived every single mass extinction since they first evolved over 500 million years ago. Moreover they are still fairly common, so they are doing something right.

Curiously, except for their shell- they are less tougher/smaller than other cephalopods. They cannot even dive as deep as many other cephalopods such as some species of squid and octopuses.

Nautiluses reproduce by laying eggs. Gravid females attach the fertilized eggs to rocks in shallow waters, whereupon the eggs take eight to twelve months to develop until the 30 millimetres (1.2 in) juveniles hatch. Females spawn once per year and regenerate their gonads, making nautiluses the only cephalopods to present iteroparity or polycyclic spawning. Nautiluses are sexually dimorphic, in that males have four tentacles modified into an organ, called the “spadix,” which transfers sperm into the female’s mantle during mating.

So they are not particularly fecund either.

The lifespan of nautiluses may exceed 20 years, which is exceptionally lengthy for a cephalopod.

The reality is that we do not know what their maximum life span is. It is certainly more than 20 years. So why are they different for the octopus, squid, cuttlefish group? They do share the same basic physiology, biochemistry, genes and biochemical/ signalling pathways.

What advantage does the short lifespan of the other group of cephalopods offer them? If anything, their intelligence makes longevity more useful. The answer, in my opinion, is obvious but counterintuitive to most.

Evolution does not optimize to the best configuration, merely to the nearest viable one.

Octopuses, squids and cuttlefish never regained their longevity after losing it because it offered no large or immediate advantage. But what does this have to do with what I usually write about? The answer is- a lot of HBD and other evo-psych crap is based on the unspoken assumption that every feature represents some optimization.

I am just pointing out that what might appear as an advantageous feature, could in reality be a maladaptation that is depriving the species of a much larger advantage.

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