Tuesday, July 10, 2018


POST #23

An article by Donaldson et al (1) has broad implications for the concept of co-evolutionary arms races between parasites and their hosts. It reports that Bacteroides fragilis determines what other bacteria can or cannot colonize a mammalian gut.

Having one organism in a host act as a gatekeeper, determining what other organisms can or cannot infect that host, means that the major species interactions are not only between parasites and their hosts, but are also between parasites and gatekeepers as well as between gatekeepers and hosts.

The substantial literature on parasite-host arms races now needs to be reconsidered in terms of three species, not two.

Parasite and host species not only have to interact with each other, they both also have to interact with gatekeeper species. This makes the gatekeeper species an integral, if not the main, participant in the co-evolutionary arms race.

Not all parasite-host interrelationships have gatekeepers, but the presence of gatekeepers was probably not considered by authors of arms race articles. From now on it should be.

Reference cited:

1. G. P. Donaldson et al., Science 360, 795 (2018).


Wednesday, June 13, 2018

Post #22
Donald A. Windsor

The Strepsiptera is an order of parasitic insects containing about 600 species in 9 families, 3 extinct and 6 extant (1). Bizarre is a good way to describe them because they do not seem to fit in prevailing phylogenetic schemes.

Caenocholax fenyesi is a species in the order Strepsiptera, family Myrmecolacidae. Its males parasitize ants and its females parasitize crickets (2).

Three ant species host male C. fenyesi: Dolichoderus bispinosus, Red Fire Ant Solenopsis invicta, and Camponotus planatus (Order Hymenoptera, Family Formicidae). Two other possible host species were not named.

The cricket species hosting female C. fenyesi is Macroanaxipha mecilenta (Order Orthoptera, Family Gryllidae).

The first-instar larvae are not sexually dimorphic and, apparently, sex is determined by the host species. If a larva enters an ant it becomes a male; if it enters a cricket, it becomes a female. Males undergo a complete metamorphosis from larvae to flying adults. Females go from larvae to a neotenic adulthood (no wings). Males leave their host ants after pupation and live for only a few hours; they do not eat. Females spend their entire lives in their cricket hosts, only poking out their genitalia to receive sperm from the male, who copulates on the abdomen of the hosting cricket. Males find female genitalia by following pheromones exuded by the females. The resulting larvae feed on their mother until they emerge and manage to find and enter a host.

This life cycle is so fraught with disaster that it is a wonder it works. The research described by Kathirithamby in several articles is daunting and frustrating but will probably turn up even more amazing situations.

Strepsipteran parasites seem to have plenty of opportunities to acquire multiple species of hosts and more should be discovered as interest in this order increases. Meanwhile, I wonder if this separation of host species for males and females occurs anywhere else besides in the Myrmecolacidae.

References cited:

1. Strepsiptera. Wikipedia. https://en.wikipedia.org/w/index.php?title=Strepsiptera&oldid=844329295

2. Kathirithamby, Jeyaraney ; Johnston, J. Spencer. The discovery after 94 years of the elusive female of a myrmecolacid (Strepsiptera), and the cryptic species of Caenocholax fenyesi Pierce sunsu lato. Proceedings of the Royal Society of London B (Supplement) 2004; 271: S5-S8.


Saturday, June 9, 2018


Post # 21
Donald A. Windsor

When a parasite uses another parasite as a tool, what do you call it? A “biotool”? A “biohenchman”? A “bioenforcer”? A “bioally”? I prefer “bioally”.

Consider the amazing case of a parasitic wasp laying its eggs in a lady beetle; then using a virus to convert the beetle to a robotic, zombie-like protector of the resulting wasp pupae.

The parasitic wasp is Dinocampus coccinellae. The host is the lady beetle Coleomegilla maculata. The bioally is a Dinocampus coccinellae paralysis virus DcPV. The life cycle is described by Dhailly et al (1).

Wasp lays an egg in the beetle. Egg hatches and larva develops within the beetle.
Larva emerges 3-weeks later and pupates, spins its cocoon between the beetle’s legs.
The beetle remains static and trembles, protecting the cocoon from predators.
Adult wasp emerges. Sometimes the beetle host recovers.

The guarding behavior of the host beetle is attributed to the DcPV in the beetle’s brain. This virus infects the oviduct cells of the wasp and is transmitted with the wasp egg into the host beetle.

Lacewing fly larvae (Neuroptera) are among the natural predators of this wasp’s pupae (2-3).

This complexity can be depicted as: H + Pw + Pv ====> HPwPv ====> HPv + Pw

I do not know what happens to the virus in the beetle’s brain.

This parasitic team of wasp and virus shows how a biological interaction between a host and a parasite has not just 2 participants, but 3. Four, if the causative predator driving its evolution is included.

I am now investigating how high the number of participants in a basic host-parasite interaction can go. What is the maximum level of complexity that has ever evolved?

References cited:

1. Dheilly, NM ; Maure, F ; Ravallec, M ; Galinier, R ; Doyon, J ; Duval D ; et al. Who is the puppet master? Replication of a parasitic wasp-associated virus correlates with host behaviour manipulation. Proceedings of the Royal Society of London B Biological Sciences 2015; 282: 20142773: 1-10.

2. Libersat, Frederic ; Kaiser, Maayan ; Emanuel, Stav. Mind control: how parasites manipulate cognitive functions in their insect hosts. Frontiers in Psychology 2018 May; 9: article 572: 1-6.

3. Maure, Fanny ; Brodeur, Jacques ; Droit, Anais ; Doyon, Josee ; Thomas, Frederic. Bodyguard manipulation in a multipredator context: Different processes, same effect. Behavioural Processes. 2013 October; 99: 81-86.


Wednesday, June 6, 2018


Post # 20
Donald A. Windsor

An interaction between a parasite and a host is like a chemical reaction.

Parasite + Host ==> ParasiteHost complex P + H ==> PH

A biobroker acts as a catalyst. P + H == biobroker ==> PH

This analogy helps me to understand my basic amazement at the complexities of biology. Nature seems to be a giant nexus of multiple species so tightly bound together that it resembles sticky cotton candy on a hot humid day.

Consequently, I visualize interactions between two species as involving multiple species. Species interactions are not between species, but among species. Many of these interactions have participants that operate behind the scenes.

Some of the behind the scenes mechanisms of biobrokers are especially interesting. A recent article reports that Bacteroides fragilis attaches itself to the gut epithelium of mice by adhering to the mouse’s immunoglobulin A. The bacterium then rules by excluding invasive pathogenic microbes (1). It acts as a gatekeeper, or in my view, a biobroker. The presence or absence of this bacterial species determines whether or not a pathogenic bacterial species (a parasite) can or cannot infect this mouse and use it as a host. The host species has retained Bacteroides fragilis to exclude parasites and to allow commensals.

                                       / ==> P + H Interaction prohibited; parasite excluded.
C + P + H == biobroker
                                       \ ==> CH Interaction accepted; commensal allowed.

To infect this host a parasite would have to overcome the biobroker.

P + H === biobroker ===> PH Interaction overcame biobroker.

In metazoan parasites and hosts this biobroker role could be played by competitive parasites.

References cited:

1. Donaldson, G.P. ; et al Gut microbiota utilize immunoglobulin A for mucosal colonization. Science 2018 May 18; 360(6390): 795-800.


Monday, May 28, 2018


Post # 19
Donald A. Windsor

Having intermediate hosts in a parasite’s life cycle must confer some survival advantage. But what? Some parasites have them; some do not, and some have two. Having or not having intermediate hosts seems to depend on particular situations. This subject has been well covered. It was even modeled (1). A recent review was published in 2015 (2).

My interest is in the participation of other species in the parasite-host interactions, the biobrokers (3). Life is more complicated than we realize and species interactions seem to involve more than merely two species. The other species are not readily seen.

A good example is the deer brainworm Parelaphostrongylus tenuis. This nematode has the white-tailed deer (Odocoileus virginianus) as its definitive host and several species of snails and slugs as its intermediate hosts. Worm eggs hatch in the deer’s bloodstream and the larvae travel to the lungs, get coughed out, swallowed, and defecated onto the ground vegetation. Snails and slugs (gastropods) eat the mucus coating on the scat pellets which contain the larvae. When the deer graze they inadvertently ingest the gastropods. The larvae from the gastropods travel from the deer’s gut to the central nervous system, where they mature, breed, and lay eggs in the blood stream (4).

The biobrokers in this interaction between the deer and the gastropods are the many species of ground vegetation. These plants have to be palatable, or at least not repulsive, both to the deer and to the gastropods. The point is that other species are involved in the interaction between the deer and the gastropods. The biobrokers would not be needed in a lab setting, but my concern is what happens in nature. The participation of the gastropod intermediate hosts offers an additional conjecture.

The brainworm is further involved in a complex network of other host species besides the white-tailed deer. In moose (Alces alces) it is usually fatal, unlike in deer where it usually is not. Consequently, overlap of these species is inhibited.

It could be argued that a biobroker is no different from a non-biological thing. Indeed. I frequently confront that thought. Inert, synthetic Astroturf could be substituted for plants, and gastropods would probably eat deer scat placed on it. But deer would probably not eat snail/slugs on Astroturf or on anything else.

References cited:

1. Coisy, Marc ; Brown, Sam P., ; Lafferty, Kevin D. ; Thomas Frederic. Evolution of trophic transmission in parasites: why add intermediate hosts? The American Naturalist 2003 August; 162(2): 172-181.

2. Auld, S.K.J.R. ; Tinsley, M.C. Review. The evolutionary ecology of complex lifecycle parasites: linking phenomena with mechanisms. Heredity 2015; 114: 125-132.

3. Windsor, Donald A. Biobrokers in parasite-host interactions. parasitesdominate.blogspot.com 2018 May 15. Post #18.

4. Parelaphostrongylus tenuis. Wikipedia https://en.wikipedia.org/w/index.php?title= Parelaphostrongylus_tenuis&oldid=835393860


Tuesday, May 15, 2018


Post #18

Donald A. Windsor

I hypothesize that other species may be involved in parasite-host interactions.

In my previous post #17, I speculated that probiotics may be involved. But after further research revealed that the terms “probiotic” and “contrabiotic” are already in widespread use, so I will not use them.

Instead I will use the term “biobroker”. A broker facilitates transactions between sellers and buyers. A biobroker facilitates interactions between parasites and hosts. Biobrokers are probably microorganisms, but could be any other organisms, including other parasites.

Just as a financial transaction can occur without a broker, a parasite can infect/infest a host without a biobroker. However, some transactions are much smoother with a broker, because the broker may be able to work out a good deal for both participants.

Parasites must convince hosts to accept them. It seems that this convincing is usually of the “offer they cannot refuse” type of bullying. Parasites are usually host specific, showing that most other possible hosts are not convinced to accept the parasite and meet such overtures with rejection.

Evolution is all about evading extinction. Parasites may benefit their hosts, at the species level, by helping them survive. When a host species survives, its parasite species stand a better chance at surviving.

When a host species goes extinct, its parasite species will also go extinct, unless it is already in other species of hosts. A parasite species that has only one host species will survive its host species extinction only if it can find another species of host.

Here is where biobrokers can save the parasite species, by helping find new host species.

Parasites carrying the appropriate bacteria would be more successful infecting hosts compared to parasites without these bacteria. These bacteria would be probiotic for the parasites and contrabiotic for their hosts. Likewise, if the hosts were harboring bacteria that would thwart the parasites, those bacteria would be probiotic for the hosts and contrabiotic for the parasites. Biobrokers are both probiotic and contrabiotic and all gradations in between.

Right now, this hypothesis is pure speculation. I am looking for some real-world examples.


Wednesday, April 25, 2018


Post # 17

Donald A. Windsor

Probiotic bacterial coatings on seeds enable plants to endure stresses, such as drought, and produce better crop yields. Indigo Agriculture is the company that is developing these coatings (1).

Could parasites, especially those that enter hosts’ bodies, naturally carry along their own probiotic bacteria? Probiotics might be the parasites’ way of preparing their hosts for enduring the stresses of their burden. Some parasites may even be able to be probiotics themselves. I have often wondered if parasites actually help their hosts bear the afflictions they cause.

In fact, a parasite has already been reported as being a probiotic. The haemoflagellate, Leishmania mexicana, protects its phlebotomine sand fly vector, Lutzomyia longipalpis, from the pathogenic bacterium, Serratia marcescens (2).

Could probiotics partially explain why some parasite species have intermediate hosts? Perhaps larval stages pickup probiotic bacteria from their intermediate hosts and carry them to their definitive hosts.

Probiotics may even explain host specificity and could offer a way to conserve parasites by providing new hosts.

Other microbes besides bacteria, such as fungi and even viruses, could also be probiotic.

Probiotics might also be useful in the therapy of pathogenic parasites. A probiotic is being tested as a treatment of white-nose syndrome in bats, an often fatal disease caused by a fungus (3).

I suspect that there is a lot more to the involvements of probiotics in ecosystems. I am now investigating.

References cited:

1. Anon. Less pesticide, more bacteria (That’s a good thing). Bloomberg Bussinessweek 2018 April 23; (4566): 25-26.

2. Sant’Anna, Mauricio R.V. ; Diaz-Albiter, Hector ; Aguiar-Martins, Kelsilandia ; Al Salem, Waleed S. ; Cavalcante, Reginaldo R. ; Dillon, Viv M. ; Bates, Paul A. ; Genta, Fernando A. ; Dillon Rod J. Colonisation resistance in the sand fly gut: Leishmania protects Lutzoyia longipalpis from bacterial infection. Parasites & Vectors 2014 July 23; 7: 329-338.

3. Oosthoek, Sharon. Bats to the wall. New Scientist 2018 April 21; 238(3174): 42-43.