An unlikely example of convergent evolution at work

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WASHINGTON (Reuters) - Tiny, snail-eating caterpillars found in Hawaiian rain forests tie up their prey with sticky silk and snack on them at leisure, surprised scientists said on Thursday.

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It is the first time that caterpillars that eat snails or any other mollusk have been found, the researchers write in Friday's issue of the journal Science.

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And while caterpillars of all kinds spin silk to make cocoons, this is the first time one has been seen to use it as spiders do to capture prey.

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Read more about it on the site.We usually see examples of convergent evolution in animal that occupy similar habitats or exhibit at least some similar survival characteristics. This latest example is one of many confirmation of what the theory of evolution predicted, that two unrelated structures in unrelated organisms could evolve to perform similar functions.Why do I think this particular example is unique? Not only are these two unrelated (arachnida and limacodidae), they have evolved to become two absolutely different things. One evolved to become perfect hunters while the other remained largely non-predatory.By the way, after today I'll be in the mountains in Wyoming and will stay there for 3 weeks, so don't hold your breath waiting for me to fix this up. If this isn't biological discussion material, then I guess just put it in links and info. Thanks.LammyABEAnother link. msnbcABE again. Science magazine.

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The Hawaiian archipelago is the most isolated landmass on Earth, and this isolation appears to have allowed for feeding strategies that occur nowhere else, particularly for invertebrates. Among the novelties discovered in Hawaii are ambush predator caterpillars (1), damselflies with terrestrial nymphs (2), and spiders that impale their prey in flight (3). Web-spinning caterpillars that feed on snails are an equally unusual addition to this list of Hawaiian anomalies.

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Read more at sciencemag!This message has been edited by GAW-Snow, 07-22-2005 05:48 PM

Thread moved here from the Proposed New Topics forum.

far beit from me to argue against evolution -- but this isn't convergant evolution. it's behavior. behavior is not an inheritable trait, although one generation does tend to pass it on to the next. still, strictly speaking in terms of genetics, this has very little to do with evolution, unless they are specifically making a new kind silk.similar examples have converging hunting strategies can be seen in africa's "flying sharks:" they stalk their pray (seals) from below, and then spring upward with amazing speed and force, "flying" out of the water. no other sharks do this, even among the same species (great whites). this is, i believe an orca hunting technique. similarly, orcas have been known to beach themselves intentionally to catch prey -- something sharks do.they just happen to be after the same prey most of the time, and fill the same niche. sometimes, they'll even hunt each other, as sort of a way to eliminate competition.

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אָרַח

Behaviour is not heritable? Behaviours like making silk? Are you sure?

Question.One thing in the links was a change from plant eater to meat eater. I would think that such a change would entail major physiological changes in the design of the critter itself. Would that not be an evolutionary change?

not strictly genetically speaking, to my knowledge. well, that's not a behavior so to speak, and not unusual. it appears to be the way in which they're using the silk. however, as jar pointed below your message, there's another change...

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אָרַח

yes, i suppose that would.

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אָרַח

Certainly in human beings things like culture, our languages, etc are not genetically heritable but this would generally be considered an exception. There are plenty of genetically heritable behaviours found in humans such as shivering when cold, and the grasping reflex of newborn babies (you know, how they grab your finger automatically when you put it in their palm).In the non human world there are loads of examples of genetically inherited behaviour. There are some kind of crickets (I forget which genus) which have species specific song pitches. If you hybridize them you get an intermediate song pitch. The social behaviour of ants, wasps and bees is certainly genetically inherited. etc. etc. I guess it depends how you want to define behaviour. The activity of making silk and building a web looks like behaviour to me. Surely 'using silk" is a behaviour if anything is. But the beating of the heart doesn't look like behaviour, for some reason.I know a botanist who insists that plants do not behave. All they do is divide and differentiate their cells. What looks like a behaviour, such as growing toward light, is not a behaviour at all but a consequence of cell growth and differentiation. An exception must be the venus fly trap... speaking of which, the closing of the plant's trap is also genetically heritable, I presume!

well, those are arguably physiological traits -- not "behavior" itself, but behavior causing traits. properties of the nervous system. the reason i brought up the sharks is because they are still same species -- c. charcharias -- and they only exhibit that behavior in one specific place. the very same individual sharks don't hunt that way elsewhere. just around that particular island.the beaching-orcas display the same behavior. the only do it on one beach -- and some apparently cite this as evidence that they communicate in some rudimentary way. the idea of animals teaching each other things isn't so shocking, really. we know bees tell each other how to find pollen. animals with pack/herd or hive mentalities to appear to form something kind of akin to culture on a very small scale.but anyways. these particular caterpillars seem to have changed from herbivorous to carnivorous, and that (generally) involves a little more than behavioral patterns. so it's kind of moot.

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אָרַח

The beaching technique is not limited to Orcas or shark. Right around your neck of the woods you can observe similar behaviour in dolphin.Dolphin will cooperate to herd fish into shoal waters of an estuatry and then rush in chasing the fish towards shore. After the fish jump up onto the area above the water line they will beach themselves to eat the trapped fish. I have seen as many as four dolphin at one time wriggling across the mud to snap up stranded fish. It was amazing.

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Aslan is not a Tame Lion

really? whereabouts? i've never even seen dolphins in the wild myself.(if i recall, btw, orcas are technically dolphins)

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אָרַח

You need to spend some time along the Atlantic coast.If possible, get up around Brunswick and St. Simons. We used to watch them feed about once a week in the marshes right off the GA DNR docks at Coastal Resources. Catch them near low tide. That's when the largest extent of mud flats are exposed. They hunt in packs of from three to as many as a dozen.The dolphin form a fan driving a school of fish before them. Gradually they move closer to the bank. Suddenly one or more will dart in and the spooked fish will jump into the air. Some fall onto the mud banks where they flop helplessly. The dolphin then rush up onto the flat and squirm around to grasp a fish, then wiggle back into the water.If you ever want to see more, contact Susan Shipman at the Coastal Resources Division of GADNR. Tell her jar sent you and ask if she could arrange for you to spend a day with one of the marine biologists. I promise you'll have a day to remember if only in the Dead Shed.

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Aslan is not a Tame Lion

i'm about half a mile from the atlantic coast. however, georgia is at least a day's drive.

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אָרַח

The moths in question appear closely related to the Psychidae (bagworms). Silk spinning appears to have been gained and lost a number of times in various lineages within the Hexapoda (insects) since their divergence from Aranea. Virtually all Lepidoptera have retained silk-spinning abilities as larvae, but they can use silk in different ways. Usually, it functions either in dispersal by 'ballooning', but more often in formation of a hibernacula or coccoon to protect the overwintering larvae or pupal stage, respectively.So the use of silk by Lepidoptera to secure prey represents a convergence of behavior or silk application (relative to Arachnida), since no other Lepidoptera employ silk for this purpose. Note, however, that certain bagworms are also predatory on phytophagous mites (I have observed this directly in one of my colleague's work). Predatory behavior in lepidopterous larva is not entirely unique, although it is unusual. It likely evolved several times via a shift first to omnivory. The fortuitous consumption of small arthropods on leaf surfaces by herbivorous forms could have afforded benefits in terms of increased protein consumption that then selected for more purposeful carnivory. Note also that many exclusively herbivorous lepidoptera are also cannibalistic in larval stages when this behavior is required to secure resources such as a limited food supply or a single available overwintering site within a plant. The impetus here is elimination of conspecific competitors, but the bodies of the vanquished are consumed since they are protein-rich and there is no point in wasting good protein.

I'm a bit confused. I have always been under the impression that convergent evolution refers to the use of different parts "intended" for different uses for the same goal, in this particular case the apprehension of prey.If this is not convergent evolution, then how is this different than the bat and bird example?