Wednesday, February 13, 2019


Host Suicide Induced by Parasites Hemlock Woolly Adelgid
Post #26
Donald A. Windsor

Suicide induced in animal hosts by animal parasites has been known for decades (1).

But suicide induced in plant hosts by animal parasites is new to me. The Hemlock Woolly Adelgid (HWA) (Adelges tsugae, Hemiptera) is currently invading Chenango County in central upstate New York, where I live (2). At a training session by the NY State Department of Conservation in Sherburne on 19 January 2019, I learned that the crawler stage of the adelgid inserts its feeding tubes into the stems of Eastern Hemlock (Tsuga canadensis) trees, just proximal to a needle and then feeds on tree sap for the rest of its life. However, this parasite does not kill its host tree. The tree kills itself by shutting off the flow of sap. This defensive reaction eventually kills all of its needles and twigs, resulting in the death of the entire tree, in about 4 years. This suicidal outcome seems to be an overreaction by the host's defense mechanism (3, 4).

The Western Hemlock (Tsuga heterophylla) is also parasitized by a lineage of HWA, but its similar defense reaction is muted enough so that infestations are not lethal (5).

A comprehensive recent review of HWA is provided by Limbu et al. (6).

All of which makes me wonder. When a person has a fatal allergic reaction to a bee sting or a peanut, is that really a suicide? Not in the sense that humans have a free will and killing oneself has to be intended to qualify as suicide. However, the body, sans mind, does indeed commit suicide.

Host suicide may confer a selective advantage if it gets rid of, or retards, its parasite. Consider the interactions of the fungus causing anther-smut disease in several species of alpine carnations (7).

References cited:

1. Trail, Deborah R. Smith. Behavioral interactions between parasites and hosts: Host suicide and the evolution of complex life cycles. The American Naturalist 1980 July; 116(1): 77-91.

2. Anon. Early detection of the Hemlock Woolly Adelgid (Adelges tsugae) in small northeastern hemlock (Tsuga canadensis) woodlots. Forest Connect Fact Sheet, Cornell University Cooperative Extension. 4 pages.

3. Radville, Laura, et al. Variation in plant defense against invasive herbivores: Evidence for a hypersensitive response in Eastern Hemlocks (Tsuga canadensis). Journal of Chemical Ecology 2011 June; 37(6): 592-597.

4. Gonda-King, Liahna ; et al. Tree responses to an invasive sap-feeding insect. Plant Ecology 2014 March; 215(3): 297-304.

5. Foley, Jeremiah R. ; Salom, Scott ; Minteer, Carey.

6. Limbu, S. ; Keena, M.A. ; Whitmore, M.C. Hemlock Wooly Adelgid (Hemiptera:Adelgidae): a non-native pest of hemlocks in Eastern North America. Journal of Integrated Pest Management 2018; 9(1): 27:1-16.

7. Bruns, Emily L. ; Antonovics, Janis ; Hood, Michael. Is there a disease-free halo at species range-limits? The codistribution of anther-smut disease and its host species. Journal of Ecology 2019; 107: 1-11.

Thursday, December 6, 2018


Post #25
Donald A. Windsor

My article, with the above title, was published in SciAesthetics Essays 2018 December and distributed by ResearchGate on 3 December 2018. DOI: 10.13140/RG.2.2.23083.08480

The attitude of biologists toward parasites was shifted from contempt to appreciation by a constellation of eight articles I published during the period November 1990 through December 1998. My participation in this paradigm shift is analyzed as the flow of an idea. Citations to my articles are increasing.

The full text of this article can be obtained from Dropbox with this link.


Sunday, September 9, 2018


Post #24

Donald A. Windsor

The phylogenetic tree, recently popularized by David Quammen (1), is indeed a very practical way to illustrate phylogenetic relationships. Horizontal gene transfer is described as connecting separate branches across the tree and altering evolution.

But without parasites, the tree would be just a gnarled stump, sparsely branched, parsimoniously twigged, and starkly leafless. Even though parasites can transfer genes from a host species on one branch to a host species on another branch, without parasitism there would be few, if any, branches to transfer between. Phylogenetic branches indicate that parasitism must have emerged very early in the evolution of living organisms.
The reason is that parasites prevent monopolistic monocultures. When competition and predation do not control monocultures, parasitic diseases step in. The result is biodiversity and multiple ecosystems (2).

Host species push back against parasites by rearranging their genetic material through sex. Other factors, such as environmental changes and competition, also cause sex. All of which leads to speciation and phylogenetic divergence, resulting in branching. Sex might have evolved without parasites, but parasites are the main drivers of sex because mating involves a choice of the most fit mates and a selection against unfit.

The real test of my hypothesis, stated in the title, will come when extraterrestrial life is discovered. Parasitism may be a property of life here on Earth, but it may not be universal. This is why it is so important for Earthlings not to contaminate other planets.

References cited:

1. Quammen, David. The Tangled Tree. A Radical New History of Life. New York, NY: Simon & Schuster. 2018. 462 pages.

2. Windsor, Donald A. Role of parasites in the Earth’s biosphere. Post#13.


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.

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.