Entomology of Star Wars. Episode III: Bears in Space

Right, here it is - the third and final instalment of 'The Entomology of Star Wars' (unlike George Lucas I will not be tempted to produce a shiny but unsatisfying second trilogy). Following on from Episode II (exogorths - giant asteroid-dwelling worms), this time I decided to focus on the 'mynocks', the parasitic space-dwelling organisms that attach themselves to spacecraft to feed off their energy (they can feed on electrical, electromagnetic and stellar energy, and so may attach themselves to structures such as power cables or 'ion ports'), absorbing it through the suctorial mouth located between their eye stalks. They can also feed on the material of the hull, causing damage or even destruction; in turn they are eaten by exogorths and may survive for some time, flying around inside the worm's gut until finally digested.

A mynock attached to the Millennium Falcon, showing its leech-like sucker. Nice.

A little light reading ensures me that mynocks are silicon-based and fatally allergic to helium (they swell and die); also they lack any major organs and so reproduce by binary fission once they have fed sufficiently. Apparently, there have been other species (or subspecies), including one that had a normal mouth (rather than a sucker), and another that gave birth to live young. They do however have bat-like wings which they can use when in an atmosphere. So, what parallels can be drawn between the mynock and real-world organisms?

Firstly, as I've mentioned before, I'm not going to look at ideas surrounding non carbon-based life - there are plenty of bloggers looking at this already. Similarly, although mynocks can feed on ship hulls, I covered chemosynthesis and the mineral metabolism in Episode II. So, let's start with the most obvious aspect of mynock life (to me anyway) - their ability to survive in the vacuum of space. Although there are no known vacuum-dwelling real-world organisms, there is one experimental example which a lot of regular science readers may well be aware of - the tardigrade. For those who don't already know about this, here goes:

Tardigrades (Phylum Tardigrada) are microscopic to just-visible (adults range from 0.1 to 1.5mm) aquatic segmented animals with eight legs, sometimes known as 'water bears' or 'moss piglets'. They are well known for their ability to survive exceptionally hostile conditions, often more so than any other animal. Tardigrades are able to survive in extreme environments that would kill almost any other animal. Some have survived temperatures down to near absolute zero, up to approx 150°C and about a thousand times as much radiation as other animals, not to mention almost a decade without water. How do they manage this?

Tardigrade - a (tiny) bear in space!

Well, along with some other groups of organisms which can survive essentially complete dehydration, tardigrades accumulate large amounts of disaccharides ('double sugars' i.e. those with two molecular rings), especially sucrose and trehalose (Crowe et al. 1998). It appears that these sugars stabilise membranes and proteins when dehydrated, probably by hydrogen-bonding to polar residues in the dry macromolecular assemblages. This maintains dry proteins and membranes in a state similar to that seen when wet. It has been suggested that, as sucrose and trehalose form a glassy state when dry, glass formation (vitrification) is sufficient to stabilise dry biomaterials - however, Crowe et al. (1998) showed that both direct stabilisation and vitrification are required and that trehalose has properties linked to its crystal structure than may aid the stability and longevity of dehydration-tolerant organisms that contain it

Meanwhile, Jönsson et al. (2005) exposed tardigrades to high levels of gamma radiation. Without going into the results in detail, tardigrades do eventually die and/or become sterile, but the study concluded that their radiation tolerance may be due to currently unknown, but efficient, DNA repair mechanisms (unlike the  biochemical protection seen for their dessication tolerance). Then, in September 2007, tardigrades were taken into low Earth orbit on the FOTON-M3 mission and exposed to either the vacuum of space or both vacuum and cosmic/solar radiation. Despite these hostile conditions, where vacuum causes severe dehydration, while cosmic/solar radiation (with an unfiltered UV component) would be expected to cause considerable genetic damage. However, upon their return to Earth, many had survived and even laid eggs that hatched normally - they are the first animals to survive such exposure (Jönsson et al. 2008).So, they can protect their cells membranes and either protect and/or repair their DNA well enough to not only survive in space, but reproduce afterwards - our first parallel with mynocks, up to a point at least, but are there any others?

Well, I'm fairly sure there are no direct energy feeders (discounting photosynthesis of course!), unless you include the 'mystic woo' of psychic healing etc. Which I don't. However, the binary fission of a large organism is interesting - generally this is associated with small organisms such as Protozoa and Algae. However, it is also seen in some Myxomycetes ('slime moulds', but not Fungi). These are often soil micro-organisms, but in some species a single-celled, but multinucleate, 'plasmodium' is formed which is the final feeding stage, engulfing many kinds of small food items. Although essentially a single cell, these can be large - one example of Brefeldia maxima in North Wales can cover whole stumps, be a centimetre thick over a square metre and weigh up to around 20kg - possibly the largest cell known (Ing 1999), and its certainly feasible that such a structure could divide. So, we have our 2nd real-world parallel.

So, lastly on to the helium allergy... well, helium poisoning certainly can occur (e.g. if overused for 'squeaky voice' purposes), but although there's a general feeling of 'you can be allergic to anything', I've not been able to find anything about genuine helium allergies. It is pretty unreactive, and I suspect at least some of the anecdotal reports I found are actually allergies to the material the helium was held in (balloon rubber, latex glove powder etc). S, although a major anaphylactic event might parallel the effect of helium on mynocks, this remains an unproven 'maybe', and as Meat Loaf said, 'two out of three ain't bad'.

With that, I shall end my 'Entomology of Star Wars' trilogy, but fear not fellow invertebrate-SF nerds - I am starting to form ideas about B-movies and Iain M. Banks novels...

References

Crowe, J.H., Carpenter, J.F. & Crowe, L.M. (1998). The role of vitrification in anhydrobiosis. Annual Review of Physiology 60: 73-103.

Ing, B. (1999). The Myxomycetes of Britain and Ireland. Richmond, Slough.

Jönsson, K.I., Harms-Ringdahl, M. & Torudd, J. (2005). Radiation tolerance in the eutardigrade Richtersius coronifer. International Journal of Radiation Biology 81(9): 649-56.

Jönsson, K.I., Rabbow, E., Schill, R.O., Harms-Ringdahl, M. & Rettberg, P. (2008). Tardigrades survive exposure to space in low Earth orbit. Current Biology 18(17): R729-R731.