Mullerian Mimicry?

[Hellbender]

or the long-term consequences of Mullerian mimicry.

This was brought up in a recent thread and got me thinking: Have there been any studies attempting to figure out just what the long-term consequences are?

[Mokele]

I asked my Evo prof that one (hence why I mentioned it), and he didn't know (neither do I, hence why I asked).

 

I was interested because I figured that if you have two toxic species with the same or similar enough coloration (Mullerian mimicry), wouldn't the one that "cheats" and loses its toxic potential still benefit from the mimicry but without the cost of actually being toxic (becoming Batesian mimics)?

 

Maybe google scholar has something?

 

Mokele

[Hellbender]

wouldn't the one that "cheats" and loses its toxic potential still benefit from the mimicry but without the cost of actually being toxic (becoming Batesian mimics)?

Exactly, thats the question I stayed up all night thinking about. Hmm. Maybe they all benefit from potential predators learning to recognize their coloration better? I don't know.

[Hellbender]

I've got the grad-level evo class this fall; I'll bug that prof about this.

Cool. I'll have to ask around about this too, and maybe do some library research to see if anything has been published about it recently. Thanks for the help.

[Dak]

what exactly is the question? Im a bit lost and confused

[Mokele]

Ok, Mullerian, as you probably know, is when two noxious species converge on a similar warning system to facilitate the learning process for their predators and gain mutual protection. But, once that system is up and running, any mutant in either species who lacks toxins will still gain the benefits of the coloration (all the benefits, none of the costs, in effect). If that's so, does that mean that mullerian mimicry pairs are inherently unstable, and will become Batesian the moment one enterprising species gets the right mutation? If not, why not?

 

Mokele

[Dak]

ah. gotcha now.

 

2 things come to mind:

 

1/ whilst there is probably evolutionary pressure on the mimics to retain identical warning-patterns, there is probably less pressure to maintain identical toxins: if the pattern is different, the individual will get et; if the toxin is different but the pattern the same, then the individual will not get et.

 

this could lead to the situation where x species are marked the same but carry different toxins. one possible repercussion could be that some predators could tolerate some toxins, but not others, and so could eat some of the mimics but not others, thus redusing the effectiveness of the pattern, and possibly putting pressure on the species to produce their own, toxic-specific patterns.

 

2/ I studied Batesian mimics at uni briefly, and iirc the population size of toxics and mimes are linked.

 

basically, the more mimes there are the less effective the pattern is, and visa versa. so, if there are too many mimes then the pattern will become innafective and both mimes and toxics will get eaten; if the number of toxics increase, then the pattern becomes more effective and mimes increase aswell. If the number of mimes decreases, then the effect would be that there is a higher ratio of toxics, increasing the pattern effectiveness and stimulating an increase in both toxics and mimes etc.

 

iirc, this basically means that the ratio of mimes:toxics is held roughly steady; a change in one direction or another will have an effect that brings the ratio back to a sort of equilibrium point.

 

soo... I would assume that Mullerian mimetics are relatively stable in a dynamic kinda way as, for example, whilst there is an evolutionary advantage to cheating, if too many species cheat then the system temporarily stops working, many insects are et, and then the ratios of toxics:cheats reattains a functional level. also, i guess that, as the number of insects sharing a pattern increases, there is increasing pressure for them to develope their own pattern, and so some would break away from the mime-group, thus returning it to a smaller, more stable, size.

 

that ^ is mainly conjecture based on my hazyish reccolections of the lectures, but i remember that there was some (pretty harsh) maths describing the dynamics, and i think the system was self-maintaining.

 

so, my guess would be: dynamically stable mullerian mime-group with a relatively stable number of batesian mimes assocciated with (and probably originating from) the Mullerian mime-group.

 

possibly.

 

Ill ask 'odd american lecturer #1' when i go back to uni.

[Skye]

If that's so, does that mean that mullerian mimicry pairs are inherently unstable, and will become Batesian the moment one enterprising species gets the right mutation? If not, why not?

Snakes use their toxins to kill the things they eat, so it has a selective pressure anyway.

[Hellbender]

Snakes use their toxins to kill the things they eat, so it has a selective pressure anyway.

true, but think of the example with bees, hornets a yellowjackets; all have stingers, and all evolved similar patterns. There is obviously a selective advantage to having similar patterns and retaining venomous stingers. The question is why doesn't one or more simply display batesian mimicry?

[Skye]

Well if there's still some advantage in having the toxin, it shouldn't be surprising that they retain the toxin, as long as this is balanced against the cost of producing the the organs and toxin.

 

By the way, not all bees have stings (or are brightly coloured).

[LucidDreamer]

I can think of a few reasons why a plant might retain the poison:

 

1) To spread out: If the plant looses the poison then it is tied to locations near it's poisonous pal and can't spread out to new locations because the animals in the new location haven't been trained to avoid it.

 

2) Constant reinforcement: Animals don't have writing and only some have basic societies so their memories don't pass from generation to generation unless some kind of instinct is formed (I know their are exceptions.) So if one plant looses it's poison then animals will soon learn that some of those kinds of plants are not poisonous and begin to start eating them

 

3) Plant differences: One plant may be similar to another but there are usually differences. If one plant looses its poison then a smart animal may learn to distinguish it from its poisonious friend.

 

4) Mutual disadvantage: Since the non-poisonous plant will be tied to locations near it's poisonous pal it will only decrease the fitness of the poisonous plant and therefore decrease it's own fitness. If animals learn that it's sometimes ok to eat plants that look like it and the poisonous form, they will eat more of both the non-poisonous form and the poisonous form. The decreasing amount of poisonous plants that it is mimicing will only decrease it's own fitness. However, if it stays poisonous it will only improve the fitness of both itself and its partner.

 

5) Synergistic effect: It could be that the combined effect of having two similar looking plants with poison is greater than just adding their individual advantages together and therefore it makes loosing the poison very disadvantageous

 

6) Inappropriatly allocated resources: If a plant developes a strong self-defense mechanism against animals, such as poison, then protecting itself from animals is very important in its location and it is a judicious use of resources compared to using its resources for something else, such as growing faster. Freeing up resources may not be as useful as it seems if the plant is unable to allocate resources in the same fashion. After it looses the poison it may be unable to efficiently take advantage of the extra resources and it may not have enough time to evolve another equally useful attribute.

 

7) Resistance to poison: If you create a situation where an animal can eat the non-poisonous plant and not get sick but sometimes eat the poisonous plant and become somewhat sick you may evenually end up with a situation where the animal developes a resistance to the to the poison.

[Hellbender]

Well if there's still some advantage in having the toxin, it shouldn't be surprising that they retain the toxin, as long as this is balanced against the cost of producing the the organs and toxin.

And if it is not, then it is more profitable to be a batesian mimic. This is the conundrum.