Malevolent Design - Another Arms Race Between A Parasitic Worm And Its Host - Or is It Just Unintelligent Design?

Cane Toad, Rhinella marina

Cane Toad, Rhinella marina

A secret war between cane toads and parasitic lungworms is raging across Australia

The subject of parasitic arms races throws creationists into a bout of cognitive dissonance from which they can only emerge with a hefty dose of double-think and self-deception, telling themselves that it's perfectly logical to hold two diametrically opposite and mutually contradictory views simultaneously, like believing that the term 'circle' describes a spere but the term 'square doesn't describe a cube.

They need to believe that, whilst it is central to their dogma and the belief on which all their god of the gaps and false dichotomy fallacies relies - that there is only one creator god capable of whatever it is they are waving as 'proof' or its existence, and at the same time believing that parasites were created by a different creator, over whom their omnipotent god has no powers and who goes toe to toe with it in parasite-host arms races.

Sadly for creationists, they were denied the argument concerning a second creator by their guru and Deception Institute flunky, Michael J Behe, who used the evolution of parasites like Escherichia coli and Plasmodium falciparum (the malaria parasite) as 'proof that their god is the intelligent designer behind the 'design' of all living things.

So, let's do what Behe unwittingly did and remove the second, evil designer from the equation, and see where it leads.

A case in point is the recently discovered arms race between the Australian cane toads and the lung worm parasite that infests their lungs:

What do you know about the origins and life cycle of the lung worm parasite that infests the lungs of Australian cane toads? The lungworm parasite infesting the lungs of Australian cane toads is known as Rhabdias pseudosphaerocephala. Originating from South America, it was likely introduced to Australia through the importation of infected cane toads. Once established, it has become a significant health concern for these invasive amphibians.

Life Cycle:

1. Egg Stage: Adult female lungworms lay eggs in the lungs of cane toads, which are later expelled with the toad's feces into the environment.
2. Development in Environment: In the external environment, the eggs hatch into larvae, which survive in soil or water until encountering a suitable host.
3. Penetration of Skin: Larvae infect new hosts, such as cane toads, by penetrating their skin directly upon contact with contaminated soil or water.
4. Migration to Lungs: Once inside the host's body, the larvae migrate to the lungs, where they mature into adult worms, completing the life cycle.

Impact on Australian Wildlife:

1. Direct Impact on Cane Toads: The parasitic infection weakens cane toads, making them more susceptible to predation and less competitive for resources.
2. Indirect Impact on Native Predators: Infected cane toads may become easier targets for predators, potentially leading to unintended ingestion of lungworm larvae by predators.
3. Ecosystem Disruption: Cane toads, along with their associated parasites, disrupt native ecosystem dynamics by preying on and competing with native wildlife, contributing to population declines.
4. Competition with Native Species: Cane toads compete with native species for resources, exacerbating existing threats such as habitat loss and fragmentation.

Overall, the presence of Rhabdias pseudosphaerocephala in cane toads is part of a complex web of interactions that contributes to the decline of Australian wildlife, directly impacting cane toads and their predators, altering ecosystem dynamics, and increasing competition with native species.

How does the parasite contribute to the decline of Australian wildlife?

The presence of the lungworm parasite, Rhabdias pseudosphaerocephala, in Australian cane toads can contribute to the decline of Australian wildlife in several ways:

1. Direct Impact on Cane Toads: The parasitic infection can weaken and debilitate cane toads, making them more vulnerable to predation and less effective at competing for resources. Weakened individuals may also be less successful at reproducing, potentially slowing the spread of the invasive cane toad population.
2. Indirect Impact on Native Predators: Cane toads are toxic to many native Australian predators due to the bufotoxins they secrete from their skin. However, when infected with lungworms, cane toads may become less mobile and more sluggish, making them easier targets for predators. Predators that consume infected cane toads may also inadvertently ingest the lungworm larvae, which can infect them as well, potentially impacting their health and reproductive success.
3. Alteration of Ecosystem Dynamics: The presence of invasive cane toads, along with their associated parasites like Rhabdias pseudosphaerocephala, can disrupt natural ecosystem dynamics. Cane toads prey on native fauna, including insects, reptiles, amphibians, and small mammals, leading to declines in native species populations. This disruption can have cascading effects throughout the ecosystem, impacting other species that depend on these native organisms for food or habitat.
4. Competition with Native Species: Cane toads compete with native wildlife for resources such as food, water, and shelter. Their presence, along with the associated health impacts of parasitic infections like lungworms, can exacerbate competition and further stress native species populations already facing other threats such as habitat loss and fragmentation.

Overall, the presence of the lungworm parasite in cane toads is part of a complex web of interactions that contribute to the decline of Australian wildlife by directly impacting cane toads and their predators, altering ecosystem dynamics, and increasing competition with native species.

Now a piece of research by Gregory P. Brown and Richard Shine of the School of Natural Sciences, Macquarie University, Sydney, with Lee A. Rollins of the Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia has shown that the cane toad has evolved as its range has spread, notably its mobility, and Rhabdias pseudosphaerocephala has evolved to keep up with this change, in a classic arms race. They have published their findings in the Proceeding of the Royal Society B: Biological Sciences and have described their work in an article in The Conversation. This article is reprinted here, reformatted for stylistic consistency, under a Creative Commons license:

Published: February 14, 2024 1.12am GMT

A secret war between cane toads and parasitic lungworms is raging across Australia

Greg Brown, Macquarie University; Lee A Rollins, UNSW Sydney, and Rick Shine, Macquarie University

When the first cane toads were brought from South America to Queensland in 1935, many of the parasites that troubled them were left behind. But deep inside the lungs of at least one of those pioneer toads lurked small nematode lungworms.

Almost a century later, the toads are evolving and spreading across the Australian continent. In new research published in Proceedings of the Royal Society B, we show that the lungworms too are evolving: for reasons we do not yet understand, worms taken from the toad invasion front in Western Australia are better at infecting toads than their Queensland cousins.

An eternal arms race

Nematode lungworms are tiny threadlike creatures that live in the lining of a toad’s lung, suck its blood, and release their eggs through the host’s digestive tract. The larvae that hatch in the toad’s droppings lie in wait for a new host to pass by, then penetrate through its skin and migrate through the amphibian’s body to find the lungs and settle into a comfortable life, and begin the cycle anew.

Parasites and their hosts are locked into an eternal arms race. Any characteristic that makes a parasite better at finding a new host, setting up an infection, and defeating the host’s attempts to destroy it, will be favoured by natural selection.

Over generations, parasites get better and better at infecting their hosts. But at the same time, any new trick that enables a host to detect, avoid or repel the parasites is favoured as well.

So it’s a case of parasites evolving to infect, and hosts evolving to defeat that new tactic. Mostly, parasites win because they have so many offspring and each generation is very short. As a result, they can evolve new tricks faster than the host can evolve to fight them.

The march of the toads

The co-evolution between hosts and parasites is most in sync among the ones in the same location, because they encounter each other most regularly. A parasite is usually better able to infect hosts from the local population it encounters regularly than those from a distant population.

But when hosts invade new territory, it can play havoc with the evolutionary matching between local hosts and parasites.

Since cane toads were released into the fields around Cairns in 1935, the toxic amphibians have hopped some 2,500 kilometres westwards and are currently on the doorstep of Broome. And they have changed dramatically along the way.

The Queensland toads are homebodies and spend their lives in a small area, often reusing the same shelter night after night. As a result, their populations can build up to high densities.

For a lungworm larva, having lots of toads in a small area, reusing and sharing shelter sites, makes it simple to find a new host. But at the invasion front (currently in Western Australia), toads are highly mobile, moving over a kilometre per night when conditions permit, and rarely spending two nights in the same place.

At the forefront of the invasion, toads are few and far between. A lungworm larva at the invasion front, waiting in the soil for a toad to pass by, will have few opportunities to encounter and infect a new host.

Lungworms from the invasion front

When hosts are rare, we expect the parasite will evolve to get better at infecting the ones it does encounter, because it is unlikely to get a second chance.

To understand how this co-evolution is playing out between cane toads and their lungworms, we did some experiments pairing hosts and parasites from different locations in Australia. What would happen when toad and lungworm strains that had been separated by 90 years of invasion were reintroduced to each other?

Is 'Toadzilla' a sign of enormous cane toads to come? It's possible – toads grow as large as their environment allows

To study this we collected toads from different locations, bred them in captivity and reared the offspring in the lab under common conditions. We then exposed them to 50 lungworm larvae from a different area of the range, waited four months for infections to develop, then killed the toads and counted how many adult worms had successfully established in their lungs.

As expected, worms from the invasion front were best at infecting toads, not just their local ones. Behind the invasion front, in intermediate and old populations we found that hosts were able to fight their local parasites better than those from distant populations.

While we saw dramatic differences in infection outcomes, we have yet to determine what biochemical mechanisms caused the differences and how changes in genetic variation of host and parasite populations might have shaped them.

In the evolutionary arms race between cane toads and lungworms, skin secretions play a surprising role

Greg Brown, Postdoctoral researcher, Macquarie University; Lee A Rollins, Scientia Associate Professor, UNSW Sydney, and Rick Shine, Professor in Evolutionary Biology, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Published by The Conversation.
Open access. (CC BY 4.0)

In the abstract to the paper in Proceedings of the Royal Society B the scientists say:

Abstract

By imposing novel selection pressures on both participants, biological invasions can modify evolutionary ‘arms races’ between hosts and parasites. A spatially replicated cross-infection experiment reveals strong spatial divergence in the ability of lungworms (Rhabdias pseudosphaerocephala) to infect invasive cane toads (Rhinella marina) in Australia. In areas colonized for longer than 20 years, toads are more resistant to infection by local strains of parasites than by allopatric strains. The situation reverses at the invasion front, where super-infective parasites have evolved. Invasion-induced shifts in genetic diversity and selective pressures may explain why hosts gain advantage over parasites in long-colonized areas, whereas parasites gain advantage at the invasion front.

This evolutionary arms race has occurred in the relatively short period of time, in evolutionary terms, (20 years) since the cane toad was introduced to Australia. What creationists will need to ignore or wave aside is the fact that, if there were an intelligence behind this evolution of parasite and host, either their putative 'intelligent' designer doesn't know what it is doing and keeps on treating the solution to the problem it created yesterday and a problem to be solved tomorrow, or there are two competing designers over whom creationism’s favourite has no control and can only react to what it opponent does, and then never very successfully, because its opponent can always find a way around what it comes up with.

Or they can resolve these paradoxes and stop portraying their putative god as either a fool or an incompetent and accept that there is a natural process that better explains these parasite-host arms races, but that leaves their magic friend as a powerless observer which might as well not exist.

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