Can evolution explain this: parasites who use inter-species feeding dynamics

It's uncertain that the parasite really knows anything. It could just be acting out of instinct.

Studies into epigenetics have shown that certain experiences can cause hereditary behavioral changes. For example, when mice are taught to associate a specific smell with an electric shock, they will produce offspring that instinctively avoid that smell. This can explain why parasites may appear to instinctively 'know' things about their host.

Evolution theory can explain how symbiosis and parasitic relationships come about. Here's one scenario:

You have two species that don't interact with each other, but eventually they are put into an environment where they interact. Let's say there's a larva which burrows into fruit, but for some reason, it burrows into a snail that is on a piece of fruit. It turns out that living in the snail is safer and easier than burrowing into fruit, so this larva survives, produces offspring that are in proximity to other snails, and they do the same thing.

These parasites live for generations inside snails and they stop burrowing into fruit all together. Eventually, they lose their ability to live in fruit, and they become dependent on the snail.
Now, natural selection favors the parasites that are best at surviving in snails. Beneficial changes in behavior or morphology increase the parasite's chances of survival, allowing it to reproduce and pass this change onto the next generation. A negative change will decrease the parasite's chance of survival, making this change less likely to pass to the next generation.

The species adapts as these beneficial changes slowly stack up over generations, until eventually you get an extremely sophisticated, complex method of survival.

Yes, but your example explains the interaction between a parasite and one type of host.

This parasite (and others like it) needs two entirely different species to complete its complex life cycle.

Evolution theory says adapting to the environment and passing on the adapted behaviour/genes to the offspring is how it works. And it works by linking this to survival.

"Learning" how to jump from snail to bird would take countless trials and errors and many failures for those trying. Two problems here:

1) Nature doesn't work like this. Instinct is to keep it simple and ensure survival and reproduction. If the parasite got inside the snail why would it risk anything and not keep its life cycle limited to the snail.

2) The heredity aspect is questionable. If you have a large population of parasite successful in survival by infecting snails, a few who somehow manage to cross to birds too through a risky previously untested process - how would they pass that on to the whole population?

Leucochloridium infect snails, birds merely eat the snail. That doesn't require any trial and error or learning on the part of the parasite. You're assuming this larva somehow learned to get eaten by a bird.

Because birds eat the infected snails, and their droppings spread the eggs of the parasite to other snails, then their is a survival advantage for any parasite that can increase the chances of a bird eating the snail. This could be done by simply slowing the snail down, or making it more visible.

We don't know exactly how this relationship came about, but it's not a problem for evolution.

The bird is essential for their reproductive cycle.
No bird, no reproduction. It's not about survival advantage, it's about survival period.

Also, the parasite makes sure the infected snail "signals" to the bird by making its tentacles look like caterpillars.

How and why would the parasite develop such a complicated reproduction process?

It only makes sense if it was already "programmed" to do so, with the behaviour fitting perfectly in the larger picture of the biotope.

The parasite has no clue what a bird is, let alone what a bird likes to eat and is attracted by. In a normal evolutionary logic there would be no point for the parasite to use an intermediary species in a complicated and risky reproduction cycle.

Just because the bird is essential now, that doesn't mean it always was. Humans have domesticated plenty of species, and many of them are now incapable of living without human assistance. But in the past, their ancestors could survive in the wild.
It's possible the parasite's ancestors were capable of living without one or both of these hosts, but as the parasite adapted, it eventually became dependent on them. Just as domesticated animals are now dependent on us.



Again, Evolution can explain it. If getting eaten by a bird increases your chances of reproducing, then natural selection will favor the individuals that are best at attracting birds. It's like this:

First, You have a parasite that lives in the snail but does not modify the snail's behavior. Then, some parasites acquires the ability to make the snail stay in the open, where it can be spotted. Birds target the new parasites over the old ones, therefor the new parasites reproduce more often, until they outnumber the old parasites and eventually replace them.

Now all the parasites cause snails to stay in the open. Next, some acquire the ability to swell up the snails body, making it more visible. These new parasites out-compete the old ones, until they become the norm.
Next, some parasites begin to swell the snail's eye stalk, and they out-compete the old ones.
Next, some parasite's cause the eye stalk to pulsate, which makes them stand out more.
Next, some start to resemble caterpillars, and so on. Every step increases the parasite's chances of reproduction.

The end result is a parasite that is perfectly adapted to attracting birds.



How do you know that this life cycle couldn't come about through gradual changes? Just because you can't imagine how this could evolve, that doesn't mean it didn't.

Leucochloridium is a flat worm. Evidence suggests that flatworms existed before birds, and different flat worm species share a common ancestor. Your spontaneous creation hypothesis is not supported by the data.

Here's the complete list of things that I have experienced which I have now come to realize is what I was conditioned to think were 'negative' things.

1. Being treated as an 'outsider'.

I was constantly being told that I was a 'stupid foreigner'. If I came off as non-Japanese I would almost always receive responses such as "how dare you think of yourselves as foreigners instead of Japanese" or "what the hell kind of language are you spewing out there? You're going to annoy me". I'd also get comments like "Do you have a sense of respect for the Japanese people?" or "I bet you're not Japanese enough and you should learn to act a little better on your trips outside the country." On various occasions I've been told to "get back to the right country" or "be thankful you're not even Japanese".

2. Being seen as weak.

On a trip a couple months ago I was walking from one hotel to another when I bumped into a group of about 4 or 5 Japanese men. They were talking and laughing all the way through and I thought it was funny until a couple of other men in the group began taking selfies.

One of the men stopped and started yelling at me in Korean saying "Why are you taking photos in Japan? Why would we want to have your photos taken like that? How dare you take a picture of your legs!?"

A fellow Japanese woman also came along and began asking me the same thing, "What kind of language are you spewing out there? Do you have a sense of respect for our people? Do you have a sense of respect for other people's cultures? Come on man, that's a little rude."

I honestly wasn't really paying attention to these three people. They were just talking amongst themselves, but the words coming from their mouths were being translated into English like my own brain. I could sense that they were pissed off and that one of them was pretty angry that I was walking down the street without any kind of ID. When I'd turn to look around to see who was mad at me I'd see all three people talking amongst themselves and it wasn't long between me and another Japanese man who decided to come up to me and ask me if I was okay, which I felt weird about. Finally one of the other men who was yelling at me began to walk away and he made a comment about something and I thought, "Well, if I hear that kind of talk from anybody again I'm leaving this person alone."

It never occurred to me, until I saw the photo I took the first time. It was in the middle of the city – in a crowded area – and I was walking by myself.

I took those photo, I thought to myself. I don't want to be talking in my own language and having somebody hear me in my own language. I really don't need to be doing that anymore. I'm going to be more careful.

In spite of this I continue to come across people who are very close to me and I wonder sometimes if the people I really want to see really know me. Sometimes, even though I've been with them for several years at this point, I feel like I'm just being used as a human ATM to exchange money.

3. Being treated as a parasite.

Evolutionary Parasitology: The Integrated Study of Infections, Immunology, Ecology, and Genetics

[link to www.amazon.com (secure)]

Yeah, "acquiring the ability to make the snail stay in the open" is the questionable part.

How would the parasite even know how a snail behaves, what it is, where it hides (what "hide" even is), and how its predators behave and like?

Even if a few parasites got eaten by accident first, and they survived, there is no way for them to process what happened.

The rest of the logic you use is correct, but pure hindsight. You see present overall dynamic, how the snail and its reproductive cycle fits in the biotope, you deduce the benefit for it to be this way, then you use hindsight to make this fit a theory.

Once again, you're assuming the parasite must 'know' things and have advanced problem solving intelligence. The parasite could cause a host to stay in the open by reducing its mobility, or ability to sense light. It doesn't have to actually process what it's doing.

Hindsight? I'm using a demonstrated, natural mechanism (evolution by natural selection) to create a hypothetical account for my observation.

We can directly observe evolution and natural selection in effect. A simple experiment performed by amateur biologists is to take a colony of bacteria, and gradually change its environment, making it less habitable, until a new strain of bacteria evolves that is adapted to the new environment. However, there is no observable mechanism that has been shown to spontaneously create fully adapted, multi cellular animals from nothing, with no ancestors.

The scientific consensus at the moment is that all -if not most- species share a common ancestor. The closer they are taxonomically, the more closely related they are. I.e. mammals are more related to each other than they are to reptiles. Leucochloridium is a flatworm, and therefor most closely related to other flatworms.

There's evidence for flatworms going back about 550 million years, to the Cambrian period. Gastropods (like snails and slugs) are thought to have appeared around the same time. The oldest bird fossils are only about 70 million years old. They appear after Theropods (two legged, carnivorous dinosaurs) in the Cretaceous period.

This would suggest that Leucochloridium appeared hundreds of millions of years after the first flatworms, and that it likely evolved from them after the appearance of the first birds.

Toxplomis parasite - that thing is like space aliens.

You ignore the fact that the parasite causes the snail's tentacles to look like a caterpillar that birds like to eat.



The complexity of what we were discussing is far greater than the dish of bacteria example. Unless the new strain of bacteria in your example formed a mass resembling a piece of bread so that the biologist's parrot would eat it and the new bacteria could escape its less habitable environment...

Last Edited by RomanianGuy on 02/24/2019 03:01 PM

It's all quite very simple. Most life forms were made by intelligent design, actually all were. Life forms cannot exist without consciousness (of various degrees) and intelligence giving them life. That includes us.

And it does not need to be God, but a manifestation of God, meaning, other intelligent beings just like us, just more advanced. Unless you think we are the only ones in this Universe...

Humans are just now learning how to edit DNA and create the perfect "human"... see CRISPR.

All life is intelligent. The theory of evolution tries to explains something we have not yet understood. That we are also creators. In its most basic form, see animal breeders.

I do not know who created this parasite, but be sure this is not the result of random accidents, but careful, intelligent planning where a new species is created in harmony with others so they co-exist in balance...

I'm not ignoring anything. Not only did I acknowledge the caterpillar resemblance, I explained why natural selection would bring it about. There is selection pressure placed on the parasites that are best at attracting birds. Do you get what I mean by that?

Obviously, multicellular animals are more complex than bacteria. That's not the point. I was giving you a simple example of evolution by natural selection. This process also affects multicellular animals.

Your parrot scenario is not an example of natural selection, which makes me think you still don't understand how it works.

In order to qualify as evolution by natural selection, You need to have multiple colonies of bacteria, and the parrot would have to select the most attractive ones for multiple generations.

Evolution is junk science that depends on those special magic words...'over millions of years'. Yeah like that is proof.

Yes, and you can't explain how the parasites became "best at attracting birds".

Your explanation is hindsight: "some attracted birds, while others attracted frogs; today we only see in existence those attracting birds, hence it's clear they were the successful ones and this is how they came to be: they were successful, the others weren't. Evolution!"

Last Edited by RomanianGuy on 02/25/2019 06:17 AM

I explained it in depth.

Every generation, you have variation as a result of mutation, sexual reproduction and epigenetic inheritance. You get small variations in size, colour, shape, behaviour, scent etc.

If you have an environment where -every generation- the parasites that are better at attracting birds reproduce more than the rest, then the inevitable result is that the population will gradually become more attractive to birds. Get it?

I never said anything about frogs and I don't think you know what hindsight means.

One of the best conversations on evolution I have ever seen. Thank you guys.

You're still telling me why the population of parasites is now very good at attracting birds (reproduced more than rest).

The problem is how did it become that way.

The part with the frog is very simple. The parasite's behaviour influenced the snail to become vulnerable to predators, but there were many predators out there.

Unless you claim they got into the bird from the first try, they must have gotten into other types of animals too.

The problem is that a lot of those tries must have been failures... so the "mutated" parasites' behaviour was nothing but suicide. While those whose reproductive cycle remained inside the snail were the successful ones.

Another problem is how did the parasites' failures get "analysed" and the behaviour of new parasites who wanted to go this way adjust accordingly?

So, if parasites got eaten by frogs and died, how did a new generation of parasites know that that behaviour attracting frogs failed and they had to adjust it?

No way of knowing that. No way for information to get passed on. Because inter-species reproductive cycle means failure to adapt is not passed on herediterally, so new generation cannot adapt in reaction to the new "info".

Last Edited by RomanianGuy on 02/25/2019 04:37 PM

oh no, yet another Alexandria Ocasio thread.

That IS the explanation. Evolution by natural selection. I don't know what more you want me to say. In the same way that humans selectively breed new types of dogs, by picking desirable traits, nature can selectively breed new species.



I told you, getting eaten by a bird helps spread the eggs of the parasite to other snails. Snails eat bird droppings. Getting eaten by frogs isn't as helpful for reproduction. Because natural selection favoured the parasites that attract birds, the parasite evolved to suit that purpose.



It didn't have to make it on the first try. Only the ones that were successful passed on their genes.
It likely didn't 'try' to get eaten at all. There's no reason to think it has the intelligence for that. A bird eats the snail, the parasite survives, the bird craps out its eggs, and this increases its chances of reproduction. Its offspring share the same traits, so they are also more likely to reproduce than the other parasites. They pass it on, and so on.

Because getting eaten by the bird increases its chance of reproduction, natural selection favors any trait that increases its chance of getting eaten by a bird.
This automatically results in the breeding of a type of flatworm that is specialized for attracting birds. There are other kinds of flatworms that live in other hosts, including humans.



They don't analyse. They didn't adjust their behavior. They just live in snails, if it fails to reproduce, it doesn't pass on its genes. It it succeeds, then what ever traits that parasite has do get passed on.



They didn't. The ones that die simply don't pass on their genes. If they have a trait that makes them get eaten by frogs, and getting eaten by frogs stops them reproducing, this trait won't be passed on.



Obviously, the information is passed by the ones that survive, not the ones that die. That's the whole point. The ones that breed pass on their traits. The ones that have a trait which prevents it from reproducing don't pass that trait on. This is what natural selection is.

Every generation, natural selection is picking the parasites that are best at reproducing in their environment, which makes them get better over time. In the same way, Humans turned wolves into poodles by selecting the cutest, fluffiest, friendliest wolves every generation over thousands of years.

The question was why would the parasite who lived and reproduced inside the snail start using other species to reproduce.

If there was a problem with living and reproducing inside snails, it would have been logical for them to adapt to the new conditions INSIDE the snails.

Your only hypothesis is "mutation".

And if we add the amount of iterations the mutated parasites must have gone through to finally hit the bird jackpot and then to fully replace the rest of the population of snail parasites, then this whole theory requires just as much blind faith as any other.



"It didn't have to make it on the first try".

That's a strange statement to make. They did have. Because if they didn't make it on the first try, that meant they DIDN'T reproduce. They DIDN'T pass on their genes. Do you see in nature any behaviour like this? Trying new, risky stuff at the risk of dying or not reproducing?

Even today many populations of animals die out during droughts or other stressful environmental situations and natural selection doesn't make some of them mutate and try new reproduction techniques. A crocodile's reproductive cycle is still the same and tied to water, despite many droughts. Just an example.

Last Edited by RomanianGuy on 02/26/2019 02:56 AM

Because birds eat the snails. It wasn't the parasite's choice. If birds start eating the infected snails, only the parasites capable of surviving in the bird will spread their genes. The rest die.



What? It can't adapt to conditions if it doesn't live in those conditions. That doesn't make sense. They didn't start getting eaten by birds because there was a problem living in snails. They didn't have a choice. The parasite didn't plan. It didn't use logic. Birds just ate the snails. If some change allowed it to survive in the bird, that would be a beneficial change.



That's a load of bull. We directly observe evolution by natural selection all the time. Show me an observable instance of your supernatural creation. The evidence indicates that flatworms existed before birds, and that different species are related to each other.



Wrong. Millions of infected snails could have been eaten, and the parasites all died. Then, the next parasite to get eaten survived. The survivor passes on its 'survivor' genes, resulting in more parasites that survive in birds.

How many times do I have to repeat myself. The parasite didn't 'try' or risk anything. It lives in snails. A bird came along and ate the snail. This isn't that complicated. I think you're just trying to be disagreeable. And yes, animals take risks all the time.



Yes it does! This happens all the time. Insects become immune to pesticides. Bacteria become resistant to antibiotics. Why do you think we need new flu shots every season? Because the flu mutates and becomes immune to treatment. You don't know what you're talking about. You need to do more research on this topic.