ROLE OF PARASITES IN EARTH'S BIOSPHERE

ROLE OF PARASITES IN EARTH’S BIOSPHERE

Post #13

Donald A. Windsor

Restriction of monocultures is the basic mechanism operating Earth’s biosphere.

When competition and predation do not control monocultures, parasitic diseases step in. The result is biodiversity and multiple ecosystems.

This simple explanation is based on observation. Monocultures, such as those planted by farmers, are quickly invaded by other species and attacked by numerous pests. Farmers have to be very diligent to protect their crops by using pesticides. Even then, other species manage to invade.

Our biosphere here on Earth is characterized by biodiversity, huge numbers of different species and interactions among all those species. Monocultures are rare and short-lived, found on newly formed islands and on disturbances leading to bare earth.

But what about life on other worlds? Does extraterrestrial life express itself as biodiversity or as monocultures? Do other worldly species interact in ecosystems? Or just dwell in monocultures?

Life on Earth is analogous to human economic forces. Without governmental regulation, unbridled capitalism results in a few very rich winners and vast hordes of poor losers. Our era of the robber barons in the late 1800s and early 1900s is a prime example. Parasites are similar to governmental regulations; they stifle exuberance.

Perhaps a world without parasites would be similar to unregulated capitalism, with a few very successful species and no or very few other species. Perhaps a middle class of species would have developed.

In the near future we may get an opportunity to discover extraterrestrial life. Will it be biodiverse? Or monoculturalistic? If parasites are present, so too will be biodiversity.

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PARASITE BENEFITS HOST: COPEPOD ON SHARK EYES

PARASITE BENEFITS HOST: COPEPOD ON SHARK EYES

Post # 12

Donald A. Windsor

The copepod parasite that attaches to the eyes of Greenland and Pacific sleeper sharks seems to be too harmful to persist through evolution. Surely animals with their vision impaired by this parasite would be at such a competitive disadvantage that they would not live long enough to reproduce. Yet they do. In fact, Greenland sharks (Somniosus microcephalus) are the longest lived animals (1).

The standard story is that Somniosus sharks do not depend upon their eyesight to feed and reproduce (2). But, what if they did depend on their parasitic copepod?

Perhaps the copepod parasite (Ommatokoita elongata) confers some benefit to its shark hosts. I have long wondered about parasites conferring benefits to hosts but see it at the species level (3). Maybe this grotesque case of the shark and the copepod provides an example at the individual level. In fact, also at the species level because almost all individual Greenland sharks, 99%, are parasitized by this copepod (4).

Such a high level of infestation makes me wonder if this copepod is functioning as an organ. If so, then it is benefiting its host. Berland calls it a mutualism (4). Of course, all mutualisms benefit their hosts, by definition.

Perhaps the copepod acts as a vision enhancer that enables its shark to see better. Perhaps the copepod is very sensitive to vibrations and transmits the changes in vibrations into the eye and directly to the brain.

Many aquatic animals that dwell in murky water have appendages (catfish) or whiskers (seals) that do the same thing. Some aquatic animals send out electric pulses (eels, platypus) to assist their vision. Perhaps these copepods are involved in a similar process.

Perhaps in the distant past, the Greenland sharks were losing their eyesight and only those individuals that had this copepod parasite were the ones who survived.

The best explanation (so far) seems to be the one offered by the anonymous Norwegian fishermen who told Berland (4). They claimed that the parasitic copepods lure prey to the sharks. These fishermen contended that the copepods were luminous, but Berland could find no evidence for this claim.

Greenland sharks are very sluggish and Berland wondered how they managed to catch anything to eat. So luring prey, rather than chasing it, may indeed be the answer. The chief meal in Berland’s 1961 investigation was Char. However, Neilsen in 2017 reports that seals were a common food (1).

My conclusion to this bizarre case is that perhaps what we often call parasitism is really mutualism.

References cited:

1. Nielsen, Julius. Dating a Greenland shark. Natural History 2017 February; 125(2): 10-13.

2. Benz, George W. ; Borucinska, Joanna D. ; Lowry, Lloyd F. ; Whiteley, Herbert E. Ocular lesions associated with attachment of the copepod Ommatokoita elongata (Lernaeopodidae: Siphonostomatoida) to corneas of Pacific sleeper sharks Somniosus pacificus captured off Alaska in Prince William Sound. Journal of Parasitology 2002 June; 88(3): 474-481.

3. Windsor, Donald A. Parasites benefit their hosts – at the species level. parasitesdominate.blogspot.com Post #7 on 16 March 2014.

4. Berland, Bjørn. Copepod Ommatokoita elongata (Grant) in the eyes of the Greenland shark – a possible cause of mutual dependence. Nature 1961 August 19; 191(4790): 829-830.

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PARASITES BENEFIT HOSTS WITH SURVIVAL INSURANCE

PARASITES BENEFIT HOSTS WITH SURVIVAL INSURANCE

Post #11

Donald A. Windsor

Parasites benefit their hosts at the species level by insuring that they survive, thus ensuring their own survival. Parasites also help ecosystems survive by preventing monocultures.

Insurance provides benefits, but paying the premiums is a burden. Parasites act as insurance agents for their hosts and indeed, these agents certainly burden their hosts with payments. Parasites enable their host species to survive catastrophes that otherwise could have rendered them extinct. The result of this insurance is the enormous array of biodiversity that our biosphere exhibits.

Catastrophes are not common, but when they do occur, they can be fatal. Insurance is not used to compensate for the routine day-to-day hassles, just for serious calamities. Parasites have to confer benefits only when their hosts are at risk of extinction.

Individual organisms do not receive benefits from parasites. Species receive the benefits. The reason is that individuals do not evolve. Species evolve. Individuals die, but their species lives on, until it goes extinct. Individual parasites harm their individual hosts, by definition. By sharp contrast, at the species level, parasites benefit their hosts.

Insurance agents dole out money, but they also make money. Parasites insure hosts, but the parasites also get benefits. When a host species goes extinct, the species parasitizing that host also risk extinction. Parasitic species persist over long time periods by either keeping their host species extant or by switching to other host species. Parasitic species that do both increase their chances for survival.

Hosts and their parasites do not dwell in isolation. They live in ecosystems and they interact with other organisms. When their resident ecosystems collapse, they risk dying out. Consequently, species within ecosystems must cooperate to insure the survival of their ecosystems. Each species must fit in with the other species.

They fit in by not forming monocultures. Parasites prevent monocultures. When competition and predation are not able to retard rampant population growth, disease breaks out and monocultures are prevented. Our biosphere is biodiverse because of this process. Diseases are caused by pathogenic parasites attacking hosts already weakened by their normal parasites.

A good conceptual model is provided by financial systems. Unregulated capitalism results in wealth accumulation by a few people while most people wallow in poverty. Government regulation, taxes, black markets, and illegal schemes act as parasites on the capitalists, redistributing the wealth. Parasites fulfill this role in ecosystems.

The end result is that parasites insure that biodiversity prospers in our biosphere.

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PARASITISM ON MARS

Post #10

PARASITISM ON MARS

Donald A. Windsor

Parasitism is a property of life on Earth, because most of our species are parasites (1). However, what about life on other worlds? We are on the verge of discovering life on Mars. Will Martian life have parasites?

If parasitism is a universal property of life, then it should occur in Martian life.

If Martian life does not have any parasites, then parasitism is unique to Earth. It would have to be decided on how many potential host species would have to be examined before it could reasonably concluded that no parasites occur.

Meanwhile, we should avoid contaminating the Martian biosphere, in case it has one.

1.  Windsor, Donald A.  Most of the species on Earth are parasites. 

 International Journal for Parasitology 1998 December; 28(12): 1939-1941.

QUANTITATING ROLE OF PARASITES IN ECOSYSTEMS USING ENERGY FLOW

Quantitating Role of Parasites in Ecosystems Using Energy Flow

Post #9

Donald A. Windsor

The work of Hatton et al. may have far broader implications than perhaps the authors and even their reviewer, Cebrian, realize. I suspect that their power law might reflect the important role that parasites play in ecosystems.

Hatton et al. report a predator-prey power law that applies across all ecosystems. Cebrian asks the critical question, “Where does this sublinear pattern stem from?”

I respond that it stems from the underlying actions of parasites. When predator-prey interactions depart too far from equilibrium, diseases take over, which is why our biosphere is so biodiverse. Monocultures are prevented by parasites. Parasites apparently maintain the predator-prey equilibrium at k = 0.75 by accounting for the other 0.25, which would make it linear.

Parasites have been considered as predators since at least 1927 (Elton). The difficulty is that parasite biomass is probably not comparable with free-living predator biomass. Besides, how to measure it would be another problem. It was unintentionally included in the biomasses measured by Hatton et al., which might also be an unrecognized problem. Effects of parasites per unit of their biomass would depend on their potency.

Parasites cannot be ignored in ecosystems, because they outnumber the free-living species that host them. Most of the species on Earth are parasites (Windsor). Why have parasites been so successful throughout evolution? Why have host species not been able to win the host-parasite arms race? My answer is because they are such an integral component of ecosystems that without them ecosystems would not have survived. It is as if hosts and ecosystems are addicted to parasites, at the species level.

The insidious, pervasive ubiquity of parasites renders it difficult to test my hypothesis because it is impractical to make field observations in parasite-free situations. Consequently, I am glad to see approaches, such as that of Hatton et al., which might be used indirectly.

References cited:

Cebrian, Just. Energy flows in ecosystems. Relationships between predator and prey biomass are remarkably similar indifferent ecosystems. Science 2015 September 4; 349(6252): 1053-1054.

Elton, Charles. Parasites. In: Animal Ecology. New York, NY: Macmillan. 1927. Pages 71-82.

Hatton, Ian A. ; McCann, Kevin S. ; Fryxell, John M. ; Davies, T. Jonathan ; Smerlak, Matteo ; Sinclair, Anthony R.E. ; Loreau, Michel. Thepredator-prey power law: biomass scaling across terrestrial and aquatic biomes. Science 2015 September 4; 349(6252): 1070.

Windsor, Donald A. Most of the species on Earth are parasites. International Journal for Parasitology 1998 December; 28(12): 1939-1941.

This article was posted as a comment to the Cebrian article on 7 October 2015. Link is: http://comments.sciencemag.org/content/10.1126/science.aad0684  

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MY EPIPHANY MOMENT

Post #8

Donald A. Windsor

My working life as a scientist in a pharmaceutical research and development facility was satisfactory. It provided steady employment from graduate school to retirement. The work was interesting, exciting, personally fulfilling, and it paid well. Moreover, I was contributing to curing a great many patients.

But my greatest thrill as a scientist occurred in my life after working, during retirement.

For my doctorate I studied parasites and was fascinated by their insidious involvement in ecosystems. However, to land a job, I had to abandon parasites and adapt my biological and chemical education to medical applications. Upon retirement, I wondered what was going on in parasitology during the three decades I was absent. So I undertook a massive reading of thirty years of parasitology literature. It took me a year and a half. Toward the end I was struck with a eureka moment when it became obvious to me that parasites were not just pesky bit-players. On the contrary, parasites were the prime controllers of ecosystems.

Our biosphere is not free-living organisms parasitized by a few nasty villains. It was the other way around. Our biosphere is composed of parasites that cultivate their hosts, with the parasite species outnumbering the host species. Parasites form an intricate network within the host species that most biologists study. This discovery is even more astounding when considering that most biologists have never even taken a single course in parasitology!

Moreover, parasitism is just one type of symbiosis. Include all symbiosis and the model of our biosphere becomes a mind boggling nexus of different species interacting and evolving together.

However thrilling my discovery was to me, it had no discernible impact on the field of biology. I could not get my ideas published. My greatest discovery, the biocartel, remains only self published. A biocartel is a duel aspect assemblage of all the parasite species hosted by one free-living species or all the free-living species burdened by one parasite species. Disappointed but undaunted, I tried to communicate the basic concepts in very terse letters to editors. I did get one opportunity to express my ideas in the article cited below. It languished for over a decade before it started to get cited. It is now being cited almost monthly.

I am now 81 years old and doubt that I will still be alive when the full importance of parasites is eventually realized. Nevertheless, my case history illustrates two different aspects of a scientist's life, professional employment and personal discovery. Nice if you can get them combined, but to those scientists who cannot, I suggest turning your retirements into new careers by pursuing those aspirational ideas you had back in graduate school.

Windsor, Donald A. Most of the species on Earth are parasites.
International Journal for Parasitology 1998 December; 28(12): 1939-1941.

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PARASITES BENEFIT THEIR HOSTS — AT THE SPECIES LEVEL

Post #7

Donald A. Windsor

PO Box 604, Norwich NY 13815 USA

Why do hosts keep getting parasitized?

That big question bothers me because, surely, throughout all the eons of time that life has evolved on this planet, some host species would have managed to break free from the perpetual shackle of parasites. But no. Every free-living species has some other species parasitizing it. Why? It seems as if hosts are addicted to parasites.

The standard answer is the “arms race”. Whenever the host develops a better defense, the parasite develops a better offense. This arms race goes on in perpetuity. While accepting this answer, I suspect that there is more to it.

Perhaps parasites confer some benefit to their hosts. I have been trying to figure out what that benefit could possibly be. Finally, I think I have found it. Parasites help their hosts survive — but at the species level — not at the individual level.

What is good for a population may not be good for its individual members. For example, it is good for our society that each of us pay taxes. However, it is certainly not good for us as individuals. But we taxpayers do expect that our taxes will benefit us. Taxes are, in effect, the expense we pay for government.

Parasites, by definition, are symbionts that benefit themselves at the expense of their hosts. So, what are the hosts buying by paying these expenses? Survival. That is my claim based on my observations of host-parasite interrelationships. The reason is that parasites can harm their hosts, especially when their populations increase. But, it is the individual hosts that are harmed. The population, as a whole, can sometimes benefit from the loss of individuals. To be sustainable, ecosystems must have a way to regulate the populations of their members. When monocultures get too large, and competition and predation are not adequate to limit them, diseases break out.

A good example of how a deadly parasite can help its host species survive is anthrax. Caused by the bacterium, Bacillus anthracis, this disease plays an important ecological role in nature. B. anthracis spores lie dormant in the soil. When a grazer, such as a bison, uproots a tuft of grass, it disturbs the spores and contaminates itself. The spores may be touched, ingested, or inhaled. The infected animal is able to wander around symptom free for a few days before the disease disables it. Once it does, the animal dies. Meanwhile, the B. anthracis multiply rapidly, building up a high population. When the nutrients run out, the waste products build up, and the carcass condition becomes uninhabitable, the B. anthracis sporulate. As the carcass decomposes, the spores gravitate into the enriched soil. Plants move in and cover the site. From the perspective of the individual grazer, B. anthracis is indeed a deadly parasite. However, when viewed from the perspective of the grassland ecosystem, B. anthracis is the guardian of the prairie.

Grazers that nip grass blades without pulling up the roots have a much better chance of avoiding anthrax. Likewise, land that is not overgrazed will have more lush foliage for grazers to nibble and more decaying plant remains to bury the spores even deeper. That is, with B. anthracis spores in the ground, overgrazed land is deadlier to grazers. A field that is overgrazed will have patches of bare ground between the surviving tufts of grasses and forbs. During dry periods, dust containing anthrax spores and can be ingested and/or inhaled by the grazer. As the grazers die off, the field can recover. Later, when it is eventually overgrazed again, the latent anthrax spores will once more defend it. Perhaps this is a natural way in which grassland ecosystems regulate themselves. They punish overgrazers by imposing a death penalty.

There are several other ways that parasite species can benefit host species. I am currently preparing a full article, with references, on this subject, but some of the more elusive concepts still need clarification and more examples are being researched.

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