Winter Gnats

Winter Gnats

Fig 1 with the help of Andrew Mortley

These flies (Trichocera), look rather like chironomid midges (Fig. 1), and, also like chironomids (McLachlan & Neems, 1995), form mating swarms to acquire a mate. Chironomids are well known because of dominance of the larval stages in populations of many, perhaps most, lakes and streams (Armitage, Cranston, & Pinder, 1995). But does anyone know anything about winter gnats? They are not mentioned in Gullan and Cranston (Gullan & Cranston, 1994) but do appear in Imms (Imms, 1957), with a brief description, on p. 610. To anyone used to chironomids the proportions of wing to body are all wrong. Evidently the morphology is like that of the Tipulidae, to which they are related. What interests me about these flies is their ability to swarm on very cold December days. Indeed this is the only time mating swarms are seen. There are clear adaptive advantages to flying under these conditions because of the absence of insect predators such as bibionids and empids. Does their morphology, in contrast to the chironomids, provide an explanation? I want to suggest that the relatively large wings act as solar panels, picking up radiant heat even at very low air temperatures. Indeed the possibility of insect wings functioning as solar panels has been proposed by Reynolds (2020,) p159, as an intermediate step in the evolution  of insect flight. 

Turning to the adaptive aspects following from the possibility of wings as solar panels, some conjecture is possible. For example, the Trichoceridae share their distinctive morphology with another major family, the Tipulidae or crane flies. Both families have exceptionally long legs and exceptionally large wings (Imms, 1957), pp. 608-610). As far as I know, of these two families, it is only the trihocerids that have a swarm based mating system (McLachlan & Neems, 1995). It is within this type of mating system that the large wings may have a fitness advantage permitting conspicuous mating swam to function in the virtual absence of invertebrate predators. We need to know something of the phylogeny of these two families but it is conceivable that they share a common ancestor. In which case large wings came first and can be regarded as a pre-adaptation (Dawkins, 1996), p.95, to mating in predator free conditions.

Fig. 1. Composite drawing to illustrate the relative wing to body size of a male chironomid midge (a), and a winter gnat (b). Legs not shown.

Fig. 2. A sketch of the tether with a fly in position – a, stand; b, wire; c, drop of ‘typex’; d, midge or gnat. The attachment ‘c’ must leave the wings free of interference.   Details are from (McLachlan, 1983), p550.

An hypothesis that wings act as solar panels is, as far as I can ascertain, a novel one. Furthermore it is testable. Here is the design of a simple experiment.

Treatment: Fly winter gnats in tethered flight in a controlled temperature cabinet at various low temperatures.  A lamp provides solar radiation.

Control:  Fly chironomids under the same conditions. Choose species of approximately the same body size as the gnats in the treatment.

Treatment control: A treatment control is required with the light as a source of heat

 radiation removed.

Unknowns: Will gnats fly on a tether? I have not attempted this. I know chironomids perform well under these conditions (McLachlan, 1983).

Field work: Record air temperatures and solar radiation in mating swarms in the wild for both gnats and midges. Results should inform the treatment temperatures.

If this works it will be a neat little experiment but it may not be as straight forward as it seems. There could be other, perhaps better experiments to test the same hypothesis. 

references

 Armitage, P., Cranston, P. S., & Pinder, L. C. V. (1995). The Chironomidae. The biology and ecology of non-biting midges. . London: Chapman & Hall.

Gullan, P. J., & Cranston, P. S. (1994). The Insects: An Outline of Entomology. London: Chapman & Hall.

Imms, A. D. (1957). A General Textbook of Entomology. (9th ed.). London: Methuen.

McLachlan, A. J. (1983). Life-history tactics of rain-pool dwellers. Journal of Animal Ecology, 52, 545-561.

McLachlan, A. J., & Neems, R. M. (1995). Swarm based mating systems. In S. R. Leather & J. Hardie (Eds.), Insect Reproduction. New York: CRC Press.

Dawkins, R. (1996). Climbing Mount Improbable. London: W. W. Norton.

Imms, A. D. (1957). A General Textbook of Entomology. (9th ed.). London: Methuen.

McLachlan, A. J., & Neems, R. M. (1995). Swarm based mating systems. In S. R. Leather & J. Hardie (Eds.), Insect Reproduction. New York: CRC Press.

Renolds, S. (2020). Success! When, Why and How insects got their wings. Bull. Ent. Soc. Antenna, 44, 155-160.

Adaptation to habitat unpredictability and some consequences

The subject of this essay is rain pools – specifically those on rock surfaces in tropical Africa. Rain pools are at the extreme of short duration among fresh waters, some lasting just hours after rain. Yet they are inhabited by immense populations of midge larvae – strictly a single species to each pool. Over the past thirty five years, on and off, I have been interested in adaptations enabling these extraordinary animals to survive and flourish in what would appear an unpromising place. In the end this work has hinged on a comparison of the adaptations of two principal inhabitants, larvae of Chironomus species on the one hand and larvae of Polypedilum vanderplanki, on the other. What has not previously received attention are the consequences following from adaptation to habitat desiccation. I refer to exposure to parasites and predators.

For the first time I consider costs as well as benefits to adaptive strategies to habitat unpredictability. To develop my arguments I adopt the comparative method practised by John Crook and by Peter Jarman, among others (Krebs & Davies, 1993), pp. 25-29. In other words, I compare strategies and in so doing attempt to bring out the relationships between ecology and accompanying adaptation. As pointed out by John Krebs and Nick Davies 1993, p. 25, this is rather like looking at the results of an experiment done over evolutionary time with species acting as controls for each other.

To begin, some background.  The rain pool faunas include three species of midge, Chironomus imicola, Chironomus pulcher and Polypedilum vanderplanki. I focus on the two Chironomus species taken together in contrast to P. vanderplanki. For my present purposes we need to know only that Chironomus inhabit pools with an average duration close to the average duration of the aquatic larval and pupal stages. P vanderplanki, on the other hand, inhabits pools with an average duration many times shorter than the average duration of the aquatic stages. Chironomus spp have behavioural adaptations enabling them to use cues to imminent pool desiccation and are triggered by these cues to metamorphose and leave the pool as adults. These cues allow, in effect, predictions of what is likely to happen in the future. In this sense adaptation can hinge on future events, a much misunderstood matter (Dawkins, 1986), p71. P. vanderplanki by contrast, survive in the dry home pool as desiccated larvae. As would be expected the choice between stay and leave is universal wherever habitat duration is unpredictable. Maynard Smith, pp262-263, cites the case of fish in transient habitats, for example, lung fish (stay), vs. osteolepid fish (leave) (Maynard Smith, 1975).

I turn now to the costs of the parasites and predators associated with the stay or leave strategies. Both parasites and predators infect aquatic stages of the midges but costs occur in the adult stage. The predicted costs and benefits of the stay or leave strategies are shown in Table 1.

Table 1. Costs and Benefits in terms of changes in fitness due to interactions with predators and parasites. The predators considered are ants and parasites, worms and mites.  

           Taxon                                         cost                                        benefit

Chironomus	Parasites	?
P. vanderplanki	Predators	No parasites

Entries in Table 1 take the form of testable hypotheses. My reasoning is as follows: costs to Chironomus accrue to adults harbouring either mites or worms (McLachlan, 2006). For P. vanderplanki, costs are due to predation by ants mining for larvae in suspended animation (Fig. 1). Benefits accrue because P. vanderplanki individuals escape parasites which are unable to infect desiccated larvae. (Fig. 2) shown a mite (Unionicola ypsilophora) and a worm probably Gastromermis rosea. To a first approximation, I regard both as parasites.

Fig. 1. Top. Spoil tips from ant mining activity in the bed of a dry P. vanderplanki rain pool.

Below left. An ant with a larva in its mandibles. Below right. Two ants fighting over a larva in cryptobiosis. From (McLachlan & Cantrell, 1980).

Fig. 2.  Parasitic mites and worms. a,  a female midge baring several mites. b,  a females midge with a large worm (g), emerging.

All hypotheses are readily tested, for example by capturing adults emerging from pools in the wild to count parasites. Negative fitness effects to ant predation can be determined by counting larvae removed by ants against the number recovering after artificially flooding the home pool.

In conclusion I wish to broaden the scope of this essay and in so doing promote a better understanding of the adaptive landscapes to which the insects are exposed.

I start with Chironomus and the question over the benefits shown for Chironomus (Table 1). Pools do not invariable dry before the full growth of Chironomus larvae is complete (McLachlan & Ladle, 2001). The benefits to Chironomus larvae when the home pool is full include access to super-abundant food with virtually no inter-specific competition. But whenever larvae succeed in metamorphosing there is a considerable cost, i. e. the burden of parasites in the adult stage of the life cycle (McLachlan, 1999). So, for Chironomus, the frequency of early desiccation must be brought into the equation (McLachlan, 2006).

Turning to P. vanderplanki, these larvae enjoy the same benefits as Chironomus when pools contain  water. There is a cost in the larval stage to predication, the extent of which remains to be measured but it can be predicted that there is a very considerable fitness benefit to the absence of parasites. There is more to anhydrobiosis. Referring to my (2013) Blog, it has been suggested that anhydrobiosis is the reason for some desiccation resistant rotifers dispensing with both sex and parasites. As far as can be determined they never have sex! Perhaps, as suggested by Hamilton and Zuk (1982), they don't need sex in the absence of parasites. 

References

Dawkins, R. (1906). The Extended Selfish Gene. Oxford University Press. 

Krebs, J. R., & Davies, N. B. (1993). An Introduction to Behavioural Ecology. Oxford: Blackwell Scientific Publications.

Maynard Smith, J. (1975). The Theory of Evolution. (third ed.). New York: C. Nicholls 

McLachlan, A. J. (1999). Parasites promote mating success: the case of a midge and a mite. Animal Behaviour, 57, 1199-1205.

McLachlan, A. J. (2006). You are looking mitey fine: parasites as direct indicators of fitness in the mating system of a host species. . Ethology Ecology & Evolution 18, 233-239.

McLachlan, A. J., & Cantrell, M. A. (1980). Survival Strategies in Tropical Rain Pools. Oecologia, 47, 344 - 351.

McLachlan, A. J., & Ladle, R. (2001). Life in the puddle: behavioural and life-cycle adaptations in the Diptera of tropical rain pools. Biological Reviews 76, 377-388.

McLachlan, A. J. (2013). Anhydrobiosis, parasites and sex. http://www. atholmclachlan.blogspot,com/

Hamilton, W. D. and Zuk, M. (1982). Heritable true fitness and bright birds: a role for parasites? Science. 218. 384-387.

The Ecological Theatre and the Evolutionary Play

The Ecological Theatre and the Evolutionary Play

The above title is from Hutchinson’s influential book (Hutchinson, 1965), and encapsulates nicely my topic for this essay – that is, the nature of the ‘ecosystem’ in an evolutionary context. Here I have used the term ‘ecosystem’ as an approximation for Hutchinson’s ‘Ecological Theatre’. The level of understanding of the astonishingly popular term ‘ecosystem’, both by the public and among many professional biologists, is imperfect. Indeed, it has been suggested that the ecosystem concept should be abandoned altogether (McLachlan & Ladle, 2011). To define what we are dealing with - an ecosystem is the complex of living organisms and their physical environment and all interactions among them, in a particular place (Tansley, 1934). Here I wish to address the following questions. First, is an ecosystem, such as a warm little pond or tangled bank, an adaptation, as many people appear to think, or is it something quite different i.e. an economy of cohabiting species (Dawkins, 2004), p 266. This question leads, in turn, to the nature of adaptation itself. I give special attention to the testing context of invasions i.e. the arrival of species in a novel habitat (Elton, 1958). These are largely unresolved and indeed largely unrecognised questions. Let’s take Charles Darwin’s Tangled Bank to set the scene (Darwin, 1859).

“It is interesting to contemplate a tangled bank. Clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us…… “

Thus organisms and their physical environment interact in complex ways. I start with the vexing matter of ecosystem, adaptation or economy. One line of reasoning is that, applying natural selection to an ecosystem as a self sustaining entity leads to the conclusion that the best balanced ecosystem is most likely to persist. This idea is neatly expressed in what has been called the BBC Theorem (Dawkins, 1982), pp 236-238 with natural selection operating at the level of the ecosystem. But, and it is a very big ‘but’, there is no evidence in support of higher level selection of this kind (Williams, 1966). Thus seeing an ecosystem as a quasi-organism is not permissible and may, among other things, have encouraged Lovelock Ellis’ flawed Gaia hypothesis, with earth itself as the adaptive ecosystem to reason about (Lovelock, 1995).True, some of the organisms living in a particular place are closely interlocked and evolve adaptations to local conditions but with natural selection operating in the conventional neo-Darwinian fashion – i.e. on the reproductive success of individuals (Dawkins, 2004), pp 265-266. For these reasons an ecosystem as an adaptation can be dismissed. We are therefore left with the ecosystem as an economy of organisms living together, essentially temporarily, and exploiting the place (habitat), to their best advantage. An organism living within an economy is not locked into a particular ecosystem by rigid co-adaptations but is free to go wherever it can find an amenable habitat.

We now come to invasion of novel habitats. Invasion seems to carry with it conceptual difficulties which, I believe, have not attracted sufficient attention. I refer to the fact that organisms would seem maladapted to invasion. Any novel habitat must necessarily carry with it a suite of novel selective pressures and invaders are unlikely to have encountered all these in their home habitat. To understand how invasion is achieved in the face of this difficulty, r-K selection theory comes to our aid (McNaughton, 1975). r – K selection theory makes an important distinction between two kinds of organism. One of these, the r-selected species, is composed of individuals that are specifically adapted to the invasion of new habitats. They have good dispersal ability, get to novel habitats first and breed rapidly. To take an example from my own interest, the chironomid midges of the genus Chironomus. Ovipositing Chironomus females are typically the first to arrive at any new body of water. They immediately lay eggs from which larvae emerge (McLachlan, 1970, 1974). But Chironomus is soon replaced by other midge species that are slow to invade but push Chironomus out through superior competitive ability. These are the K selected species.

So we can easily understand how r-selected species are able to act as invaders but we are left with the difficulty of understanding how K-selected species manage the trick. And K– selected species are indeed common invaders (Elton 1958). This is the nub of my second question. The evidence supports the idea that invasion by K-selected species is permitted by two effects. Initially they undergo rapid adaptive phenotypic change through essentially non-heritable phenotypic plasticity (West-Eberhard, 2003). The well known phenomenon of character displacement (Schulter, 1994), would seem to be a component of phenotypic plasticity. Phenotypic plasticity is followed by slower, evolutionary adaptation involving heritable changes in gene frequency in the conventional Darwinian fashion. Population numbers are necessarily low for invaders and E. B. Ford shows that selection, and therefore adaptation to new conditions are strongest when at low population densities (Ford, 1964).

To summarise: I have attempted to raise questions about the value of the ecosystem concept. Perhaps it could be replaced by the better understood terms ‘habitat’ and ‘environment’. At the same time, taking an evolutionary stance, I have attempted to show how invasion can be understood in an evolutionary context.  

Thanks to Clive Howard-Williams for interesting discussion.

References

Darwin, C. D. (1859). The origin of species by means of natural selection, or the preservation of favoured races in the struggle of life. (Fascimile 1901 ed.). London: John Murray.

Dawkins, R. (1982). The Extended Phenotype. (1999 edition ed.). Oxford: Oxford University Press

Dawkins, R. (2004). A devil's chaplain. London: Phoenix.

Elton, C. S. (1958). The Ecology of Invasions by Animals and Plants. New York: John Wiley.

Ford, E. B. (1964). Ecological Genetics. London: Methuen.

Hutchinson, G. E. (1965). The Ecological Theatre and the Evolutionary Play. London: Yale University Press.

Lovelock, J. E. (1995). The Ages of Gaia. Oxford: Oxford University Press.

McLachlan, A. J. (1970). Some Effects of Annual Fluctuations in Water Level on the Larval Chironomid communities of Lake Kariba.  . Journal of Animal Ecology, 39, 79-90.

McLachlan, A. J. (1974). Recovery of the Mud Substrate and its Associated Fauna Following a Dry Phase in a Tropical Lake. . Limnology and Oceanography, 10, 74 - 83.

McLachlan, A. J., & Ladle, R. (2011). Barriers to Adaptive Reasoning in Community Ecology. Biological Reviews, 86, 543-548.

McNaughton, S. J. (1975). r- and k-selection in Typha. . American Naturalist, 109, 251-261.

Schulter, D. (1994). Experimental Evidence that Competition Promotes Divergence in Adaptive Radiation. Science, 266, 998-801.

Tansley, A. G. (1934). The Use and Abuse of Vegetation Terms and Concepts. Ecology, 16, 284-307.

West-Eberhard, M. J. (2003). Developmental Plasticity and Evolution. Oxford: Oxford University  Press.

Williams, G. C. (1966). Adaptation and Natural Selection. Princeton: Princeton University Press.

The sleeping chironomid and the theory of panspermia

An enduring interest of mine for nearly 40 years, has been comparative studies of larvae of three endemic species of flies inhabiting transient rain pools in tropical Africa (H. E.  Hinton, 1968).  In some ways, the most extraordinary of these is the larva of the chironomid midge with the cumbersome name Polypedilum vanderplanki, originally brought to our attention by H. E. Hinton  (Hinton, 1951, 1968). What chiefly captured his imagination was the ability of this complex metazoan life form to lose virtually all tissue water and survive in a desiccated state, seemingly indefinitely. Called cryptobiosis, this condition is so clearly an adaptation to the transient nature of its habitat that it has lead to much bold conjecture. Especially relevant is the possibility of  us humans  exploiting suspended animation for the exploration of space (Oleg et al., 2010), including the use of larvae to seed life to alien worlds. A fertile imagination might go further and suggest that the process of natural selection and evolution, starting with any ancestor of man, would eventually lead to Homo sapiens, and hence to the colonisation of space by man. This, essentially, is the theory of Directed Panspermia championed by Francis Crick (Crick, 1982).

In a staff seminar I gave to the zoology department at my university many years ago, I recall mentioning the Hinton/Crick hypothesis. During the discussion that followed my paper, a senior colleague, Alec Panchen, questioned the use of P. vanderplanki as colonist for man on the ground that it could never have worked because P. vanderplanki is not an ancestor of H. sapiens. This seems a reasonable objection but is it correct? I will here attempt to show that it may not be because it ignores decomposition, among other things. The purpose of this essay is to return to Ale's comment. What I wish to examine here is whether metazoa like P. vanderplanki larvae, under novel selective pressures encountered on a strange world, could ever lead to the emergence of Homo sapiens. Because P.vanderplanki is not an ancestor of man, this, at first sight will seem a nutty, even silly idea. To discuss the point, I return to the concept of Directed Panspermia.

At the outset, to confine conjecture to manageable limits, I greatly simplify the whole matter of seeding life elsewhere. In particular I adopt Conway Morris’s simplifying assumption that the course of evolution is not composed of infinite possibilities but instead, if rerun, will follow a similar path ending every time at the same place. He confined his discussion to earth but I am going to adopt the same reasoning for any planet suitable for life. With these assumptions in place and limits in place we are ready to question the purpose of any attempt to seed life elsewhere. There would seem to be two possible aims. First, purely for reasons of intellectual curiosity – to spread that amazing phenomenon ‘life’ where it is not yet present and where it might never originate on it own. Such an intellectual basis finds strong appeal to man and might lead to the seeding of life being attempted some day fairly soon. The possibility of seeding life elsewhere is not a trivial undertaking. Just because we can do it, should it be done? In fact I read today in Nature that it has already been done by seeding live tardigrades to the moon (Nature 2019). The purpose of this act is not given. 

A second possibility is much more problematic, that is the seeding undertaken in order to lead to the emergence of our species elsewhere. Crick calls this Directed Panspermia. There seems a tacit assumption in both the writing of Hinton on P. vanderplanki and Crick that the desired result would be achieved whatever the details of natural selection encountered.  Let’s examine this aim in more detail; it exposes some interesting difficulties.

First is the vexing question of the type of seed that should be chosen for this bold venture. Despite science fiction stories, it is very difficult, actually nearly impossible, for complex species like us to make the journey, even within our own solar system. It would be much better to send some simple organism capable of cryptobiosis, like P. vanderplanki, rotifers, tradigrades, resurrection plants or bacteria. In cryptobiosis they can travel vast distances in space and quickly take up active life and adaptive radiation when suitable conditions return.

Whatever the seed chosen, whether bacteria as favoured by Francis Crick or the metazoa and metaphyta listed above, whether ancestor of man or not, there is something important that appears to have been overlooked. I refer to decomposition, even if only by autolysis. What might decomposition following inevitable death of seeds lead to? This is where things get interesting because decomposition must lead to the release of DNA and RNA and possibly also to the release of the bases; adenine, guanine, cytosine and thymine which comprise the alphabet of DNA and RNA, the common ancestors of all life on earth. These nucleic acids free in the oceans of an empty world, in a ‘warm little pond’ or in volcanic fumaroles and so on, open up the possibility of multiple lines of evolution and adaptive radiation parallel to that of the original seed. Crick considers that any such free stating blocks of life will be immediately destroyed by competition but this conclusion applies to earth where conditions suitable for the origin of life no longer exist. Such considerations do not apply on lifeless worlds wherever there are conditions suitable for life. So we begin to see the possibility of a complex ecosystem eventually emerging, with the parent seed evolving along with lines of evolution starting with DNA/RNA. Therefore adding decomposition introduces a greatly inflated range of evolutionary possibilities reducing the strength of Alec’s reasoning. So P. vanderplanki might serve perfectly well as a seed after all. Indeed, following this line of reasoning, do we need a living seed at all. Would not a simple package of DNA do? 

One final point I wish to make is that, baring extinction, evolution does not end with H. sapiens as we know it but is a stage in an ongoing evolutionary process. So, wherever man evolves, on earth or on an alien world, might it lead to something that, from our present perspective, we would not recognise or even like, such as the creature in the painting below by the polish artist Zdzislaw Beksinski. This would certainly put a fly in the ointment of the aims of Directed Panspermia.

references

Crick, F. (1982). Life Itself. Its Origin and Nature. London: Macdonald and Co.

Hinton, H. E. (1951). A new chironomid from Africa. Proceedings of the Zoological Society of London., 121, 371-380.

Hinton, H. E. (1968). Reversible suspension of metabolism and the origin of life. Proceedings of the Royal Society, London (B). 171, 43-47.

Oleg, G., Tetsuya, S., Valdimir, S., Nataliya, N., Manabu, S., Ludmila, M., et al. (2010). The sleeping chironomid: an insect survived 18 months of exposure to outer space. Paper presented at the 38th COSPAR Scientific Assembly., Bremen, Germany.
Nature (2019). Moon bears. Seven Days. 572, 289.

The Origin of Multicellularity

What I offer in this essay departs from my usual rule of confining myself to subjects in with I have personal research experience. It is a zoologist’s view of a complex matter.

The transition from single cell organism to multicellular ones like ourselves involves  the emergence of an entirely novel kind of life (Maynard Smith and Szathmary, 2010). This is Richard Dawkins' Threshold 4 (Dawkins, 1995). Such a major evolutionary transition brings with it interesting conceptual and evolutionary difficulties. A single cell that produces daughters by the usual method of splitting can readily be understood to lead to a colony if daughter cells stay together. Three evolutionary challenges emerge from the transition to such a colony. First, if they are to stay together, the selfish single cell parent is required to produce cooperative daughters.   Second, how is such a colony to reproduce?  Third, how is a colony to maintain integrity in the face of inevitable emergence of cheats which represent a return to the single cell selfish mode.

Fitness benefits for the cells in a colony flow from the shared protection of a soma  (body) – ‘the vehicle’ of Richard Dawkins (Dawkins, 1982). Costs include colony losses in fitness due to the emergence of cheats. It is often assumed that the emergence of cheats can be circumvented by unexplained adaptive mechanisms arising in the colony to suppress cheats. An alternative, seemingly less likely idea, is that cheats act as a germ line that facilitates colony reproduction, thus solving the second difficulty above (Hammerschmidt, Rose, Kerr, and Rainey, 2014) (Fig. 1.). Cheats as a novel germ line (gametes), open up an unprecedented adaptive world. An example that illustrates this model is Volvox (Fig. 2).

Fig. 1. A life cycle of a simple organism switching between the singe cell ancestor (a), and a colony of co-operative daughters (b). In (c), a mutant cheat has arisen which escapes (d), and reproduces a mix of cooperatives and cheats (pink).

Fig. 2.  The eukaryote cell Volvox (c. 0.25mm diameter), with cells of spherical soma enclosing germ cells. Two of these are shaded pink to show analogy to the cheats in Fig. 1c. (Modified from the internet).

The idea that cheat cells originate as specialised reproductive cells has been tested in an extraordinary series of experiments by Paul Rainey and colleagues using the bacterium Pseudomonas fluorescens as the test organism. If I understand them correctly, they view the embracing of cheats as an innovation that has lead to an adaptive radiation of organisms both large and complex.

It is instructive to note that in this essay I have adopted a cell division model for the origin of multicellularity. But this is not the only origin possible. The little known but extraordinary creatures called slime moulds achieve multicellularity, not by cell division as in  Volvox, but instead by cell aggregation. Single cell, free living amoebae aggregate to form complex, often strikingly beautiful complex organisms. To illustrate this I have added two pictures of slime moulds from the internet.  John Tyler Bonner has spent much of his professional life in the study of  slime moulds and his book entitled Life Cycles (1993), is well worth a read. 

Whatever the method of achieving multicellarity, the time has come to substitute the term ‘cancer’ for ‘cheats’. Cancer has a presence in our human consciousness as a much feared disease. It appears to involve the regression of cooperative body cells to an original selfish single cell state accompanied by uncontrolled proliferation to create a tumour (Nowell, 1976). A tumour, I suggest is the adaptive equivalent of the ancestral colony. The adaptive battle between cooperatives and cheats takes place in the tumour. In this view, cost to the organism  as a whole would seem incidental. Note there are here two somas, the phenotype and the smaller cancer tumour. 

To summarise; as we know the original emergence of cancer cells in the evolutionary transition to multicellularity does not exclude its re-emergence as a disease. Indeed the emergence of cheats of many kinds, in colonies as we have seen but also in the behaviour of metazoa (multicellular animals), such as that based on reciprocal altruism or frequency dependent selection (Davies, Krebs, and West, 2012), and indeed wherever there is co-operation. It may be said that the incorporation of a cheating strategy to our understanding of evolution underlies many of the revelations of neo-Darwinism. For a different approach to the origin of multicellularity see Bonner (1978).

references
Bonner, J. T. (1993). Life Cycles. Reflections of an evolutionary biologist. Princeton University Press. Princeton, New Jersey. 

Bonner, J. T. (1978). On Development. The Biology of Form. Harvard University Press. 

Davies, N. B., Krebs, J. R., and West, S. A. (2012). An Introduction to Behavioural Ecology. (4 ed.). Oxford: Wiley-Blackwell.

Dawkins, R. (1982). The Extended Phenotype. (1999 edition ed.). Oxford: Oxford University Press.
Dawkins, R. (1996). Climbing mount improbable. W. H. Norton & Co, London.
Dawkins, R. (1995). River Out of Eden. Phoenix, London.

Hammerschmidt, K., Rose, C. J., Kerr, B., and Rainey, P. B. (2014). Life Cycles, Fitness Decoupling and the Evolution of Multicellularity. . Nature, 515, 75 - 79.

Maynard Smith, J., and Szathmary, E. (2010). The Major Transitions in Evolution. Oxford: Oxford University Press.

Nowell, C. P. (1976). The clonal evolution of tumour cell populations. Science, 194, 23-28.