Consider the octopus

Being attacked by an octopus gives the opportunity to marvel at how convergent evolution created similar organs and senses in cephalopod and man.It is a scene that would do justice to a horror movie: body clamped against the diver''s mask, one tentacle deftly turning off the oxygen supply while others tug relentlessly at the connecting hoses. Despairingly, the diver looks at the octopus and, across an immense phylogenetic gulf, camera eye meets camera eye. If the struggling diver is a biologist he might take some consolation that the glances exchanged depend on a classic example of convergent evolution.Overwhelmingly, however, the octopus is an encounter with the alien: no hands, but tentacles that can untie surgical silk and clamp with innumerable suckers. Its bulbous body houses an enormous brain, but more than half of the nervous system lies in remote ganglia. Across the body flicker the coruscating patterns of the chromatophores, sometimes freezing the animal into an almost exact replica of the sea-floor, or alternatively transforming itself into a facsimile of the banded sea-snake. Science fiction collides with scientific fact. Are the octopus and its relatives not the best thing we have for a proxy alien? Step a little closer.The octopus and related cephalopods might seem to exemplify the ‘other'', but when it comes to reinventing the evolutionary wheel they are dab hands. In addition to those camera eyes, some squid have the reverse arrangement, whereby transparent portals in the body pour bioluminescent light into the inky oceans. Other sensory convergences include a lateral line system, a good approximation of the semicircular canals and superb oculomotor reflexes. The independent evolution of giant axons and a blood–brain barrier are complemented by an impressive list of anatomical convergences. These include cartilage, a closed circulatory system with elastic arteries, a swim-bladder, respiratory proteins (haemocyanin), the famous ink and even a fair stab at a penis.So, in many ways, cephalopods are honorary fish, but as Andrew Packard (1972) made clear there are still “limits of convergence”. This point is robustly echoed by Ronald O''Dor & Dale Webber (1986) whose paper carries a corresponding subtitle “why squid aren''t fish”. Quite so, but again, step a little closer. Concealed in the body plan are convergences that point to some far more interesting evolutionary principles. Consider those writhing arms. ‘One for all, and eight for all''; in principle all are equipotent, but some are evidently employed for one task and others for another (Byrne et al, 2006). This is exemplified by octopuses that stroll bipedally across the lagoon floor. Yet more remarkable are muscular contractions that move in either direction and collide to define pseudo-joints: a rubbery tentacle is transformed into a limb, complete with ‘wrist'' and ‘elbow''. This led Germán Sumbre and colleagues (2005) not only to identify what to some is an apparently surprising functional convergence, but also to suggest that, in the context of any articulated limb, this could be “the optimal design”.Much is also made of the obvious differences in locomotion: myotomal sinuosity compared with jet propulsion in the squid. In the former, the locomotory efficiency depends crucially on the oxidative red muscle and the larger bulk of white muscle. Red muscle is used in routine swimming, whereas the white one springs into action in times of urgent need, and then repays the oxygen debt in just the same way as when the jogger collapses on the park bench and gasps “lactic acid, lactic acid”. The squid''s mantle muscle holds another surprise. The muscle types are directly analogous to the red and white muscle of fish, with corresponding mitochondrial content and glycolytic activity (Mommsen et al,1981).But if squid are honorary fish, somewhere, surely, the convergences must break down. Well, let''s consider the cephalopod kidney. They are excretory, but do not resemble that of any vertebrate. However, they show something curious: with few exceptions, the kidneys are infested with tiny symbionts, but from two entirely unrelated groups (Furuya et al, 2004). One are the dicyemid mesozoans, which earn the trophy for metazoan simplification, being composed of only about 50 cells. They have abandoned all organs including a nervous system, but intriguingly still employ Pax6. The other group are ciliates and belong to the otherwise obscure chromidinids. Consider this evolutionary conundrum: the only place on the planet where these dicyemids and chromidinids can be found is in places awash with cephalopod urine. Long dismissed as parasitic, they are probably vital to kidney function, and I suspect this is the cephalopods'' smart way of constructing a high-performance kidney.So specific, so precise, so strange is this convergence that I am forcibly reminded of Ramón y Cajal''s (1937) contemplation of the insect eye as “a machine so subtilely devised and so perfectly adapted to an end as the visual apparatus” that it provoked him to continue “I must not conceal the fact that […] I for the first time felt my faith in Darwinism […] weakened, being amazed and confounded by the supreme constructive ingenuity”. So too with the cephalopod kidney, haunted as it is by this symbiotic inevitability.But if you really want to feel the hairs pricking on your neck, consider the brain of the octopus (Young et al, 1963). Lobate and of quite different construction to the vertebrates, nevertheless once again the similarities emerge not least between its vertical lobe and our hippocampus. Within these neural recesses, consciousness has flickered into existence and, by a separate evolutionary route, the Universe is becoming self-aware.     

A purified agonist-activated G-protein coupled receptor: truncated octopus Acid Metarhodopsin

G-protein coupled receptors (GPCRs) mediate responses to many types of extracellular signals. So far, bovine rhodopsin, the inactive form of a GPCR, is the only member of the family whose three dimensional structure has been determined. It would be desirable to determine the structure of the active form of a GPCR. In this paper, we report the large scale preparation of a stable, homogenous species, truncated octopus rhodopsin (t-rhodopsin) in which proteolysis has removed the proline-rich C-terminal; this species retains the spectral properties and the ability for light-induced G-protein activation of unproteolyzed octopus rhodopsin. Moreover, starting from this species we can prepare a pure, active form of pigment, octopus t-Acid Metarhodopsin which has an all-trans-retinal as its agonist. Photoisomerization of t-Acid Metarhodopsin leads back to the inactive form, t-rhodopsin with the inverse agonist 11-cis-retinal. Octopus t-Acid Metarhodopsin can activate an endogenous octopus G-protein in the dark and this activity is reduced by irradiation with orange light which photoregenerates t-Acid Metarhodopsin back to the initial species, t-rhodopsin.     

Mapping of neurons in the gravity receptor system of the octopus statocyst by iontophoretic cobalt staining

Summary The presence of uni-, bi- and multipolar neurons beneath the hair cell epithelium of the Octopus gravity receptor system has been demonstrated by iontophoretic cobalt staining. Counts give an average number of 1,940 neurons per macula. Whether the hair cells are primary of secondary sensory cells is discussed.This work was supported by grant Wo 160/3 of the Deutsche Forschungsgemeinschaft (DFG) to H.G.W. Thanks are due to the Director and staff of the Zoological Station in Naples for their hospitality and help     

Glycogenolysis in octopus spermatozoa

During in vitro incubation at 8 °C the glycogen reserve of octopus spermatozoa undergoes glycogenolysis. For the first 48 h, during which motility remains high, the formation of D(?)lactic acid accounts for most of the metabolized glycogen. Upon longer incubation, when motility begins to decrease, the glycogen content of the octopus spermatozoa continues to fall, but the concentration of lactic acid remains static, indicating that the latter is no longer the sole metabolic end-product.     

An unusual tachycardia

The following article presents an unusual case of atrial tachycardia, initially misdiagnosed due to a lack of clear P waves. The diagnosis was eventually confirmed using the atrial electrogram from the patient's pacemaker.     

Egg development in the octopus Eledone cirrhosa

The development of egg/follieular cell complexes is described in maturing females of the octopus Eledone cirrhosa. Follicle cells proliferate to enclose the oocyte in a single epithelial layer which becomes deeply infolded. Active cell division of the follicle cells and recruitment of cells from an outer (thecal) layer generate this expansion of follicle cell epithelium. The onset of the main phase of vitellogenesis, secretion of protein yolk, occurs when eggs reach about 2 mm in length and is marked by the columnar appearance of the follicle cells and an increased number of larger and more complex nuclei. A significant proportion of the egg population fails to develop beyond 2–3 mm in length and these eggs subsequently degenerate.     

Lipid-protein interaction in the photolysis of octopus rhodopsin

Microvillar membranes of octopus photoreceptor cells were treated with phospholipase A₂, phospholipase C, hexane, or their combinations. By these means, various membrane preparations containing qualitatively and quantitatively different lipids were obtained. The lipid composition and phospholipid content of the membrane preparations obtained by the above methods were determined.Photochemical processes in the digitonin extract of the native and treated membranes have been studied by flash photometry. The results suggest that several different variations in the lipids can affect the rates of the photochemical transformations; these are: the content of phospholipid, the amount of unsaturated hydrocarbon chains and free fatty acids.     

An unusual desaturase in Aquilegia vulgaris

Aquilegia vulgaris seed oil contains high levels of the rare fatty acid columbinic acid (18:3 Delta(5,9,12)), which is unusual in having the double bond at the Delta(5) carbon in the trans configuration. Columbinic acid was found to be a seed-specific fatty acid not only present in the storage oil but also in membrane lipids. Several putative gene fragments have been isolated from plant RNA with sequences similar to previously characterized 'front-end' desaturases. Functional characterization of the Aquilegia cDNA is underway.