poison berries (fwd)
Janice M. Glime
jmglime at MTU.EDU
Thu Nov 9 10:20:37 EST 1995
> Dear BL101'ers, Plant Edders, and Biolabbers,
> I promised to send you the responses from students and professionals on
> poison berries. I submitted the questions to three lists and as a bonus
> question to my first term freshman biology majors. I apologize that these are
> not in any particular order, but I don't know of any way to move things
> around in this editor. The original question is a few screens down and was
> asked by Stacy Ciufo.
> Janice M. Glime
> Department of Biological Sciences
> Michigan Technological University
> Houghton, MI 49931-1295
> jmglime at mtu.edu
> FAX 906-487-3167
> From Adrienne Chopp BL 101- Lab 02:
> In response to the bonus question about why certain plants make poisonous
> fruit, I have a couple of hypotheses.
> 1) Plants make poisonous fruit because the fruit will keep away
> predators from the plant. Seeing the fruit is most obvious to be seen,
> animals and humans will want to pick and eat the fruit; henceforth, much
> energy will be lost to the plant in the picking of the fruit. Once
> predators realize this fruit is poisonous, they will then leave the plant
> the alone allowing for the plant to carry on it's lifestyle in a normal
> 2) Plants make poisonous fruit for it is a way in which the plant
> reproduces. In the making of the poisonous fruit, the plant puts forth a
> great deal of energy; however it is beneficial to the reproduction of
> the plant once the fruit is completed. For when the fruit is picked by
> predators at harvest time, it is carried away from the plant to be eaten. So
> once the fruit is bitten into, the predator realizes it is poisonous and
> drops the fruit containing seeds. In turn these seeds will implant
> themselves in the ground and begin the life of another poisonous plant.
> From a professional:
> >Why then, do some plants go through the biochemical trouble to
> >produce POISON fruit (such as berries)?
> I am going to speculate, because I know of no details for specific examples
> to assist me.
> 1. Poison fruits might not stay poisonous forever.
> There are fruits rejected by birds all fall, but
> over winter biochemical changes occur that render
> the fruits palatable by spring. This could be a
> strategy to ensure sufficient ripening of fruits
> and maturity of seeds before dispersal. Some Viburnums,
> Berberis, Parthenocissus, and Cornus could be some
> possible examples (but again, this is speculation).
> 2. Poisons are not always generic. It is possible that
> a poison for one frugivore, might not be poisonous
> to the seed disperser. I am speculating that evolution
> might result in a mammal-toxin that prevents humans
> from eating and digesting both fruit and seed, but
> which is not a bird-toxin, permitting birds to digest
> fruit but pass seeds. The mammal-toxin thus improves
> the chances for seed dispersal via birds. Possible
> examples here might be Toxicodendron and Rhus vernix.
> 3. "Toxins" might just be adaptive too! The reason
> you don't want to eat Rhamnus cathartica fruits is
> a cathartic drug. The discomfort causes us to list
> the fruits as "toxic" but in fact, by including the
> cathartic, evolution provides the plant with a way
> to ensure that seeds are carried away, but *not* digested
> by a mammal.
> There may be someone out there who can give details
> on specific examples and the toxins used, but maybe
> these ideas will get students to think on their own
> about other strategies that evolution might have
> provided. Sounds like a thought provoking topic for
> cooperative group activities!
> Here is a parallel topic:
> Try sprouting some lettuce seeds in fruit juices...
> interestingly, though moist and warm and provided with
> light, the seeds do not sprout! The germination toxin
> is to prevent premature germination in a warm, moist
> fruit. Abscisic acid may be the active agent in these
> juices. Thus tomato seeds in the rotten fruits in your
> autumn garden do not sprout until the snow-melt and
> cold wash away and degrade the Abscisic acid. Then the
> seeds are germinable in the spring. Thus toxins can
> be adaptive and their content can be reduced by a winter
> of weathering and biochemistry.
> From Andrea Peterman, BL101:
> > I think that I might have a hypothesis about the poison berries. I think
> > that maybe the plants take the time and energy to produce poisonous
> > berries because it could ensure the continuation of the plant species.
> > If animals don't eat the berries, they will fall off of the plant and
> > onto the ground. This would be beneficial because then the seeds would
> > be dropped in a location where the plant already grows and the
> > environment is best for that plant. If the berries or seeds get taken
> > elsewhere, there is no guarantee that they will end up in a place that
> > has a good environment for the plant.
> Your theory is a good one, but why should they spend the energy to
> produce a fleshy berry instead of just a dry, simple fruit?
> From a Katie Whyte, BL101:
> > I DO NOT KNOW THE CORRECT ANSWER BUT I CAN TELL YOU WHAT I THINK.
> > I AGREE WITH THE FACT THAT PLANTS PRODUCE BERRIES TO ENSURE THEIR
> > SEEDS ARE SCATTERED AROUND SO MORE PLANTS CAN GROW WHERE THEY FALL. I
> > THINK THAT IT IS FOR THAT VERY REASON, TO HELP SPREAD MORE PLANTS AROUND
> > WHEN FALLEN ON THE GROUND, THAT THEY PRODUCE POISON BERRIES. IF THE
> > PLANTS HAVE BERRIES THAT ARE POISONESS (poisonous), THEY ARE LESS LIKELY
> TO BE EATEN,
> > THEREFORE CAN FALL AND SUCCESSFULLY GROW A NEW PLANT WITHOUT BEING EATEN
> > FIRST. BERRIES THAT ARE NOT POISONESS (poisonous) WILL BE EATEN AND
> DISTRUBUTED, BUT
> > THEY MAY BE DISTRIBUTED IN AN ENVIRONMENT THAT IS UNSUITABLE FOR THEM. IF
> > THAT WAS (were) TO HAPPEN, THE REPRODUCTION RATE OF THE PLANT WOULD
> DECREASE AS > APPOSED (opposed) TO THE PLANTS WITH POISONESS
> (poisonous) BERRIES.
> > I HOPE THAT HELPED. SORRY IF IT IS REALLY CONFUSING. I'M NOT
> > SURE IF IS RIGHT, BUT IT SOUNDS LOGICAL TO ME.
> > KATIE WHYTE (kawhyte at mtu.edu)
> Why become a nice fleshy berry if you don't want to be eaten? Why not
> just be an inconspicuous dry fruit?
> From Sandy Saari, BL101:
> > Hi. I have thought about the question you sent about why a plant might
> > poison its fruit, and here are the hypotheses I have:
> > 1. The poison may be a by-product of a process the plant has, and the
> > fruit is a place that the poison can be stored so it doesn't harm the rest
> > of the plant. When the fruit is removed from the tree/plant, or falls off
> > for some reason, the plant no longer has the poison.
> INTERESTING IDEA!
> > 2. The plant may not have been surviving very well because animals were
> > eating the fruits and the seeds, so no new plants could form. A new fruit
> > was then produced, including the poison so that the animals would no
> > longer eat it.
> AHH! EVOLUTION AT WORK, DERIVED FROM NICE, FLESHY, GOOD-TASTING FRUITS!
> > 3. The poison is really not a poison at all, at least from the point of
> > view of the plant. It is just another part of the plant, but for some
> > reason animals may be allergic to it. (Think of food allergies people
> > have. Not everyone is allergic to nuts, but they could kill some people.)
> > The poison could also be poisonous to some animals, but others may
> > tolerate it.
> > I'm not sure if I am on the right track for any of them, but they were the
> > only ideas that I got.
> These are excellent ideas, and all of them satisfy the criteria, that it
> is an attractive, fleshy fruit that is wasting its energy being attractive
> if it is poisonous. Good job! (The Ph. D. answering this question only
> gave three possibilities, some the same as yours.)
> From Bob Biddle, BL101:
> > I believe I have a couple of ideas pertaining to the poison
> > berries theory. I also am in dire need for a couple of extra credit points.
> > IDEA 1) Berries to human and nonhuman species are usually the first thing
> > that are noticed in viewing any such plant. If a predator would see a
> > berry first and eat them IT instead of a possibly more needed leaf,
> bud, or
> > stem they IT would be poisoned without disturbing important factors. In
> > other words the berries are a detourent DETERRENT and a very wise one at
> that. AN INTERESTING, NEW IDEA.
> > IDEA 2) It is also quite possible that the pray PREY of this berry giving
> plant > would need mass amouts of poison to discourage its feeding
> on the
> > plant. This in turn would require that the plant contain these THIS
> > quantity of poison to do such a thing, but poison is poison, and large
> > amounts might also be harmful to the plant. So it is possible that it
> > makes smaller amounts only to be concentated and stored away from
> > the main plant body in these berries, serving as a super strong
> > poison container not effecting AFFECTING the plant in any negative
> manner. >
> > That's all I could logically think of at this time if I conjure up
> > any more foolish thought I'll be sure to let you know.
> Not bad, Bob. Sort of a decoy system - be the apparent fruit to protect
> the plant. I have given you 2 points for this.
> From Laura Haas, BL101:
> > I think that plants produce poison berries to ensure that their fruits are
> > not eaten so that more of them can germinate and become adult plants. AT
> > least some of the seed eaten by animals are destroyed by the digestion
> > process and therefore are not viable. By making poisons, this ensures that
> > more seedlings may grow.
> > Another point would be that the plants can only grow in a very
> > restricted area. If they move too far from this place, they will not be
> > able to grow. THe poison ensures that animals will not eat them, and the
> > plants will have a better chance to grow.
> > Laura M. Haas
> Good ideas, Laura. Why do you suppose they waste energy making nice, big,
> fleshy fruits that attract predators instead of small dry ones, then put
> poison in them?
> From Sheahan Dissanayake, BL101:
> > Here is my hypothesis to, why plants make the fruit poisonous
> > First of all, a plant makes fruits (large fruits) so that their species
> > will be continued. This is done by the seeds inside the fruit. For
> > example, When the fruit falls from the tree, the seed inside gets
> > scattered around.
> > Now, if a bird or any other fruit lover happens to eat this fruit, the seeds
> > might not get scatterd around. They may even eat the seeds. But, if the
> > fruit were poisonous, it would not be eaten, and the reproduction of the
> > species could continue. Also, if these fruits were taken to another
> > environment by animals/birds, and the seeds weren't eaten they may not grow in
> > that environment. For this reason these plants make their fruits
> poisonous. >
> > I hope that this is good enough of a explanation of my hypothesis as to
> > why a plant makes their fruits poisonous.
> Sheahan, This is a good theory. Why, though, do they waste the energy to
> make a fleshy fruit instead of a small, dry one?
> From Josh Douglas, BL101:
> > In response to the question of why some plants produce poison berries I
> > offer this.
> > Maybe some plants don't grow well by themselves. So to keep the
> > plant going they produce poison fruits. Since the fruits don't get eaten
> > the seeds don't go far from the plant, and the parent plant provides cover
> > and protection for the new plants.
> > Just a theory.
> INTERESTING IDEA. COW WHEAT IS DISPERSED BY ANTS THAT CACHE THE SEEDS IN
> A PILE. THUS THEY GERMINATE AS A GROUP. THIS INCREASES THE PROBABILITY
> THAT THE ROOTS WILL GET MYCORRHIZAL FUNGI THAT ARE NEEDED TO HELP THEM
> GET ENOUGH NUTRIENTS.
> ORIGINAL QUESTION:
> Take into consideration the energy lost in making a large
> > > fruit and ask yourself why the plant might then make it poisonous.
> > > List all the hypotheses you can think of. I will post answers next week.
> > > Janice
> > >
> > > > Would one of you plant folks be so kind as to answer this question:
> > > >
> > > > I believe that plants produce fruits to ensure that their seeds are
> > > > scattered around - berries that are edible and tasty will be eaten
> > > > and excreted elsewhere.
> > > >
> > > > Why then, do some plants go through the biochemical trouble to
> > > > produce POISON fruit (such as berries)?
> > >
> From Joe Swetish, BL101:
> > I can think of two possibilities as to why some plants produce poison fruit.
> > 1. The plant's seeds may not be able to survive digestion and excretion
> > by an animal. Therefore it is not safe for animals to eat the berries.
> > 2. I think this is the more plausible of the two. Some berries are
> > poisonous to some animals and not to others. I think "Choke Cherries" are
> > an example. People and other animals can't eat them, but I believe some or
> > all birds can. If a plant produced fruit that was eaten only by birds, the
> > seeds would tend to be spread out over a larger area, as birds are more
> > mobile than land animals. If the seeds are spread over a larger area, the
> > plant will be more likely to survive. AND THE BIRDS DO NOT DIGEST THE
> SEEDS - THEY PASS THROUGH THE DIGESTIVE TRACT UNHARMED.
> Good ideas, Joe.
> From Todd Richards, BL101:
> > 1. here is what i came up with. the seeds in the berries that are
> > eaten and spead that way usally have some kind of protection that keeps
> > them from being digested or damaged. Maybe the the poisonous berries'
> > seeds don't have that protection.
> > 2. some plants can only grow in very narrow pH ranges, temps, soil
> > nutrients, ect. if they were to be moved to far from the parent plant
> > they may end up somewhere where they can not grow. if the berries are
> > poisonous then they are more than likely not going to be eaten, so the
> > seeds stand a better chance of ending up near the parent plant where it
> > can grow.
> Good ideas, Todd.
> Laura Haas, BL101 student:
> > Well, I have another answer for you! I think that plants make
> > big, fleshy fruits so that animals will eat them, and then the seeds
> > will be carried to another location where they may grow. An example may be
> > apples. Apple trees grow i a variety of places, and they're not too picky
> > about what type of soil they will grow in. When an animal eats it, the
> > seeds will be carried to a new location where a new orchard may be started.
> But then why should they be poisonous?
> Laura's response:
> I must have misread the question. I went back and reread it, but
> I can't really think of a good answer. Maybe the fleshy, juicy fruits
> serve as a nutrition source for the seeds as they grow. The same
> compounds that are poisonous to animals may be beneficial to the plants
> themselves nutritionally. This is the only reason I can come up with.
> Since the plants can't actually tell me why, this will have to do.
> From Walter Ogston, professional:
> On the question of poison fruit, I recall a long time ago hearing a
> theory, I think attributed to Dan Janzen, that the very large fruit of
> tropical trees etc serve to provide a fertile microenvironment for seed
> germination, and are not "intended" to be eaten at all. Does this
> theory survive today?
> From Wendy Wickstrom, BL101:
> Plants may create poison in their berries to protect animals and humans
> from eating them. Their seeds may be inside the berry which will fall off
> eventually and replant itself in the ground. This way predators who may
> like to eat berries will not destroy their seeds that may be replanted.
> From a professional:
> Have you fully considered what you mean by poisonous? Is the fruit
> univerally distasteful/deadly? Or does the nature of the fruit restrict
> its' consumption to unique species, or groups of species? Perhaps by
> restricting consumption to a few species, distribution is more
> successful, or the seed is scarified properly by the right digestive
> system, etc... Just because we can't consume it, doesn't mean a thing is
> bad or useless you know...:)
> From Eric Ribbens, professional:
> "Poison berries" are not necessarily poisonous to every frugivore. For
> example, many fruits contain chemicals that cause intestinal upsets in mammals,
> but do not affect avian frugivores at all. One evolutionary explanation for
> this is that avian frugivores tend to have short intestinal residence times,
> and quickly strip sugars and other easy chemicals from the fruit pulp and dump
> the remainder, thus dispersing the seeds. Mammals have much longer residence
> times, and thus are more likely to kill the seeds in the fruits they consume.
> Thus, having poison in the fruits that causes intestinal upsets in mammals
> serves only to enhance the seed dissemination capability: no matter who eats
> it, the seed is going to come out the other end!
> From Michael Loik, professional:
> Neat question! I might use it (if that's ok with you) for the bonus on my
> final. I'm answering privately because I have my students subscribe to
> ecolog while they're in my class. Three possibilities come immediately to mind:
> 1. The poison may be species-specific. If the plant has an obligate
> dispersal agent, maybe it has a resistance to the poison.
> 2. Perhaps the seeds germinate within the fruit.
> 3. Perhaps the seedlings require a nurse plant, and poison fruit ensures
> that the seeds stay near the parent plant.
> I'm interested in what you think of these ideas.
> It comes to mind that berries may be toxic or have irritant effect on some species and not others. For
> example, poison ivy produces allergic reactions in humans, yet seems to have little, if any, effect on
> deer and turkeys which relish its foliage and berries.
> An answer may lie in the efficiency of the digestive system of the species likely to eat the berries. If the
> seed contained in the berry is likely to be destroyed by the digestive system of an animal which eats it,
> it would seem logical that the eater should be repelled or have its gut purged so as to speed the
> passage of the seed. However, if the digestive system of the eater is such that the seed will pass
> relatively unharmed, then there would be no particular evolutionary pressure to produce toxins or
> I am interested in the results of your inquiry, and would appreciate your summary.
> From Bob Strauss, professional:
> I believe ALL plants are, to some extent, poisonous. To different
> animals/insects, the poisonous ones differ.
> Of more interest to me: how did primitive peoples figure out how to use things
> that were poisonous by "boiling three times" or whatever, in order to eliminate
> the poisons. Why bother? I suspect these were, however, "primitive Einsteins".
> From Michael Loik, professional:
> Thanks for forwarding the replies earlier today. I was just thinking about
> ectozoochory, and whether poisonous fruit might be related to it. We have a
> lot of castor bean growing as a weed around here. It is definitely
> poisonous, and its fruits are adapted for hitchhiking. Could poisonous
> fruits be a back up system to ensure that fruits don't get eaten, and
> instead are dispersed outside of the animal? Just wondering.
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