Storable life
The ability of organisms to survive in a form that is less metabolically active than normal could be employed in interstellar directed panspermia, as a component of human hibernation ships or as back up or buffer capacity on otherwise active interstellar arks or space colonies, allowing replenishment after environmental disasters or greater diversity than could be supported if all parts were active at the same time. As well as reduced resource demands, the resting forms may, in some cases, be more resistant to a variety of hazards. The following table shows a few of the known resting mechanisms for a sample of life forms.
Two general observation are that life forms that have to live in a changing environment have mechanisms for doing so (obvious really, but presents a problem for, e.g., rain forest types) and that such mechanisms may often be (although by no means always are) associated with sexual reproduction.
| Type of organism | sub category | Resting or spreading form(s) | Comments |
| Virus | 'complete' form, i.e. nucleic acid plus protein capsid plus envelope etc. if there is one. | when a virus isn't replicating within a host cell it is in a resting stage in which it can survive freezing or drying - not very heat resistant - generally pathogenic, although can be useful when pathogens of pathogens, and may have evolutionary role in gene transfer | |
| Prokaryote (cells without a separate nucleus - bacteria) | the normal vegetative cells | the cells of many prokaryotes (but not all, e.g. Leptospires die when they dry) can survive frozen or dry or both - while some are pathogens, most are free living, many mineral cycles depend on them (e.g. C, N, S) and only prokaryotes can fix nitrogen and break down aromatic compounds - some used in food | |
| Myxococcus | microcysts | these are a bit more heat and radiation resistant and can survive dry for >10 years | |
| Polyangium, Podangium, Chondromyces | cysts containing resting rods | " | |
| Sorangium | cysts containing cysts containing resting rods | " | |
| Azotobacter | microcyst | these aren't very heat resistant | |
| Clostridia | endospore | very long lived, heat, chemical and radiation resistant | |
| Bacilli | " | " There have been reports in respectable scientific journals of viable Bacillus spp. spores tens of millions of years old being being recovered from inclusions in amber and examples hundreds of millions of years old being recovered from inclusion in salt crystals. |
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| Sporosarcina | " | " | |
| Metabacterium | " | two or more spores formed within one cell | |
| Blue-green algae (bacteria), e.g. Nostoc | Akinete | photosynthetic oxygen producers | |
| Sporocytophaga | microcyst | ||
| Streptosporangium | spores in sporangia | ||
| Micromonospora | conidiospores | heat resistant | |
| Thermoactinomyces | " | " | |
| Streptomycetes | " | ||
| Fungus (these and all that follow are eukaryotes - with separate nuclei) | normal mycelium | many fungal mycelia survive freezing and or drying and can overwinter readily, gatherings of mycelium (rhizomorphs) can be more frost resistant as can some fruiting bodies (e.g. Polyporus) and some fruiting bodies are more resistant to drying (e.g. Tremellales) - some are pathogens, most are free living and have essential degradative functions in the carbon cycle - some used in food and some form feeding associations as in Lichens and Mycorrhizas | |
| Terrestrial phycomycetes, e.g. Rhizopus | zygospores and asexual sporangiospores | sexual spores usually more resistant to damage | |
| Ascomycetes, e.g. Neurospora | Conidia and sexual ascospores | " | |
| Basidiomycetes, e.g. Coprinus lagopus | Oidia and sexual basidiospores | " | |
| Yeasts | ascospores or basidiospores or chlamydospores depending on genera involved | " | |
| Slime Mould (Mycetozoa) | Acrasieae | asexual walled spores | |
| Myxomycetes | haploid walled spores | ||
| Protozoa | generally, protozoa may be capable of encystment, particularly those living in changeable environments - cysts are usually more resistant to heat, freezing, drought etc. | ||
| Amoeboid (rhizopoda) e.g. Amoeba viridis, Heliozoans | hard walled cyst or zygotic cyst | ||
| Ciliates (ciliophora) e.g. Colpoda, Didinium | cyst | ||
| Green algae | photosynthetic oxygen producers | ||
| Vaucheria | Asexual reproductive body with cyst | resists drying | |
| Diatoms | Auxospore | seasonal resting stage | |
| Euglenoids (flagellate) | zygotic cyst | resists drying | |
| Volvox (flagellate) | zygotic cyst | colonial - cyst is resistant to freezing and drying | |
| Sponge | gemmule | food-filled mesenchyme surrounded by heavy protective coat with spicules - survives drying and freezing - typical of freshwater forms | |
| Coelenterate | e.g. Hydra | gastrula | heavy shelled - can overwinter, lying dormant until favourable conditions return - freshwater coelenterate |
| Rotifer | sexual 'egg' stage | thick wall resists drying and freezing - also, whole organism can withstand just about anything if it is first dried (cryptobiotic state - sugars e.g trehalose replace water as molecular structural stabilant) including very low temperatures, vacuum etc. | |
| Bryozoan | statoblast | overwintering stage of fresh water forms, with protective covering | |
| Platyhelminthe (flatworm) | eggs | hard shelled, sexually produced - overwintering form released as adult body decays | |
| Nematode (roundworm) | encysted forms | survive in soil for long periods - also adult form can survive unencysted if dried, as for rotifers | |
| Annelid (segmented worm) | e.g. oligochaete, earthworm | eggs produced in cocoon | some resistance to drying |
| Arthropod | Crustacea, e.g Brine shrimps, Fairy shrimps, Daphnia . | sexually produced eggs | overwintering or other adverse condition stage - resistant to freezing, drying |
| Tardigrade (Water bears) | adult, when dry | in cryptobiotic state can resist very adverse conditions (see rotifers) | |
| Arachnid, e.g. scorpions, spiders | adult, eggs | adult scorpions can survive freezing, spiders can overwinter as eggs | |
| Insects | adults, larvae, pupae, eggs | can be frost resistant, by supercooling, frost tolerant, by allowing lymph etc. to freeze - wasp larvae can e.g. supercool to -47C, adult Himalayan midges are frost tolerant and even maintain activity to -16C - eggs and pupae can be very resistant to or tolerant of drying | |
| Mollusc | e.g. gastropods (snails) | adults, eggs | adult snails hibernate in soil or under leaves, some can survive freezing in ice |
| Lichen | dry normal form | associations of fungi and algae or blue green algae (bacteria) - can survive freezing very well if dry - radiation resistant | |
| Bryophyte (mosses and liverworts) | e.g. mosses | normal form and spores | normal form can survive freezing, usually better so if dry, but some happy when wet - spores also are fairly resistant |
| Pteridophyte | e.g. ferns | spores | in some forms can resist drought and cold |
| Gymnosperm | e.g. conifers | seeds in cones | adult plants can be very frost and drought resistant, although sensitive to radiation - seeds can be similarly resistant, and also have fire survival mechanisms |
| Angiosperm (flowering plants) | seeds | adult plants can be very long lived, and may have storage organs and/or survival strategies for winters or droughts or fires - seeds of temperate plants can be very frost and or drought resistant - tropical forms much less so, although desert plant seeds can, again, be particularly long lived - desert plant seeds can survive for many decades, arctic plant seeds have been reported as surviving frozen for hundreds (maybe thousands*) of years - angiosperms include the major food species for humans - *recent work has suggested that hundreds of years is more likely than thousands | |
| Vertebrate | Fish e.g. Cynolebias (a tooth carp genus) | hard shelled eggs | these and a few other fish survive seasonal loss of water by burying eggs in mud, to hatch when water returns - adult lungfish (e.g. Lepidosiren) do this to themselves, in cocoons to avoid overdrying |
| Amphibia e.g. frogs | adult forms | some, e.g. wood frogs, can survive being completely frozen - others hibernate deep in the ground or survive drought buried in dried mud | |
| Reptiles | adults | many temperate types (e.g. turtles, snakes) hibernate in holes in the ground | |
| Mammals | adults | some can hibernate, involving lowering of temperature and/or other physiological changes such as urea recycling - humans have no natural resting stage (with the possible brief exception of the diving reflex), but sperm, ova and fertilised early embryos can be artificially frozen and recovered (as they can for the major food mammals) |