jimmenegay{at}sbcglobal.net (Jim Menegay) wrote in
news:ccd7e9$96i$1{at}darwin.ediacara.org: 

> William Morse  wrote in message
> news:... 
>> Guy Hoelzer  wrote in
>> news:cbdlb2$2mpm$1{at}darwin.ediacara.org: 
>> 
>> > in article cbc9qk$276c$1{at}darwin.ediacara.org, Perplexed in Peoria
>> > at jimmenegay{at}sbcglobal.net wrote on 6/23/04 9:06 AM:
>> >> I fully agree that most altruism-like behaviors in nature
>> >> (excluding parental care, and perhaps the social insects) are
>> >> based on reciprocity rather than on the unilateral altruism
>> >> covered by the Rule. 
>>  
>> > It's good to know that our estimates of reality are close.
>> 
>> 
>> I disagree with both of your estimates of reality. I thought Hamilton
>> originally suggested his rule to answer the question of how a feature
>> like the toxicity of monarch butterflies could evolve. 
> 
> What this thread lacks is some good, old fashioned, unpronounceable
> scientific terminology:
> 
> Aposematism (adj.: aposematic): "warning coloration" of an inedible 
> insect, like the monarch, to "advertise" this fact to potential 
> predators; after the first unpleasant experience (see "Emetic Unit") 
> the predator learns to avoid this and other similar appearing prey 
> (see "mimicry").
> 
> Asclepias: One of the genera of milkweeds, with about 108 species 
> in North America; 15 species are described for California; foodplant 
> of the monarch caterpillar.
> 
> Cardenolides: bitter, distasteful heart-poison compounds (cardiac 
> glycosides) found in many but not all species of milkweed; causes 
> predators, such as birds, that eat insects containing cardenolides 
> to retch and vomit, otherwise capable of causing death. See 
> "Sequestration" and "Emetic Units." 
> 
> Sequestration: the internal process whereby a caterpillar feeding 
> on a toxic plant is able to shunt the poisons out of the normal 
> metabolic pathways, and "sequester," or store them in the body (as 
> opposed to excreting the poisons or converting the poisons to 
> non-toxic forms). Monarch larvae sequester cardenolides, which 
> are subsequently incorporated into the body of an adult monarch. 
> 
> Emetic Unit: an amount of Cardenolide (q.v.) sufficient to cause 
> one Bluejay to vomit. 
> 
> Source:
> http://homepage.smc.edu/sakai_walter/Monarch%20Butterfly/lexicon.htm
> 
> As an armchair theorist, I must admit that I am in awe of the people
> who actually go out into the field and measure things.  While I 
> respect the theorist who saw the need for the concept of the emetic
> unit, I want to shake the hand of the poor graduate student who
> was assigned the project of measuring it.
> 

Thank you for the information. Follows on sbe are sometimes  long on 
long-windedness and short on facts (and I am guilty as charged). 

An interesting thing about aposematism (and I am assuming the term is not 
limited to insects) is its recurrence throughout terrestrial taxa  - e.g. 
skunks, gila monsters, poison frogs, coral snakes. It obviously pays to 
advertise! The fact that this has occurred frequently indicates that 
there is some form of selection that can produce this effect. Is there a 
form of individual selection that can lead to this? It would seem there 
would have to be an initial benefit to the individual of being toxic, but 
the first few toxic individuals are simply going to get eaten. Now 
apparently the monarch butterflies achieve their toxicity by ingesting 
toxic compounds. Are the compounds toxic to ordinary butterflies as well? 
If so the individual advantage for monarch butterflies may be in being 
able to make use of a food source unavailable to other butterflies, with 
the aposematism being a secondary benefit. I don't think this possibility 
works for skunks. I simply don't know enough about the other examples I 
mentioned to hazard a guess. An NPR program did discuss the escalating 
toxicity arms race between poison newts and their chief predator, garter 
snakes. In this case the snakes have evolved to tolerate poison doses 
that would kill other vertebrates 40 times over. The garter snakes 
themselves are toxic after eating the newts, but while the newts have 
evolved bright coloration the garter snakes have not - yet.


A second interesting thing is that I can't think of any examples of 
aposematism among aquatic species - in fact bright coloration among 
aquatic taxa appears often but is unrelated to toxicity (the same is true 
of birds). Is this simply contingency? Perhaps colors in both these 
groups became an object of sexual selection before it could become 
associated with aposematism. Being the staunch adaptationist that I am, I 
would prefer to think otherwise. It may be that most aquatic predators 
use other sensory modes than vision (e.g the lateral line in fish) as 
their primary method of catching prey, so aposematism and $1 will get you 
a cup of coffee if you are an aquatic species. Of course birds are 
primarily visual hunters - but then again bright plumage is I think 
restricted to species that live in thick vegetation. 

This leads to the question of why there are no toxic birds. Again 
contingency is one answer. Anybody have any others?


Yours,

Bill Morse
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