How Did Insect Metamorphosis Evolve?

22

The evolution of metamorphosis remains somewhat mysterious, but biologists have gathered enough evidence to plausibly explain its origins


In the 1830s a German naturalist named Renous was arrested in San Fernando, Chile for heresy. His claim? He could turn caterpillars into butterflies. A few years later, Renous recounted his tale to Charles Darwin, who noted it in The Voyage of the Beagle.
Imprisoning someone for asserting what today qualifies as common knowledge might seem extreme, but metamorphosis—the process through which some animals abruptly transform their bodies after birth—has long inspired misunderstanding and mysticism. People have known since at least the time of ancient Egypt that worms and grubs develop into adult insects, but the evolution of insect metamorphosis remains a genuine biological mystery even today. Some scientists have proposed outlandish origin tales, such as Donald Williamson’s idea that butterfly metamorphosis resulted from an ancient and accidental mating between two different species—one that wriggled along ground and one that flitted through the air.

Metamorphosis is a truly bizarre process, but an explanation of its evolution does not require such unsubstantiated theories (for a critique of Williamson’s hypothesis, see this study). By combining evidence from the fossil record with studies on insect anatomy and development, biologists have established a plausible narrative about the origin of insect metamorphosis, which they continue to revise as new information surfaces. The earliest insects in Earth’s history did not metamorphose; they hatched from eggs, essentially as miniature adults. Between 280 million and 300 million years ago, however, some insects began to mature a little differently—they hatched in forms that neither looked nor behaved like their adult versions. This shift proved remarkably beneficial: young and old insects were no longer competing for the same resources. Metamorphosis was so successful that, today, as many as 65 percent of all animal species on the planet are metamorphosing insects.

Written By: Ferris Jabr
continue to source article at scientificamerican.com

22 COMMENTS

  1. What an outstanding article.
    The vision of Charles Darwin was mind blowing.
    A Christian brother ,who taught me at my grammar school;referred to Darwin as not especially talented.
    I burst ot laughing and was sent to the headmaster.

  2. Yes, that’s correct, but those bodily changes are a growth and development of existing body parts. We do not change into a seemingly different creature. Human beings show accelerated growth at two stages of life – in the first two years after birth, and during puberty; and this growth gradually tapers off. All body parts are already there after birth.

    The difference with metamorphising insects is that the imaginal disks present in a caterpillar develop further body parts within the crystalis – the building blocks are there already, they “merely” require hormonal triggers to set off, and continue, growth; and simultaneously breaking down existing cells for energy. Nothing new is added, but dormant parts are activated. Fascinating really.

    EDIT: Correct me if I’m wrong btw.

  3. djs56 spoke for me as well. While I appreciate the fascinating puzzle of metamorphosis, I also wonder if it is not similar to some of the changes that occur in developing mammals. I am thinking of the changes in the human foetus, which in its early stages is indistinguishable from that of a pig. Of course, Crimbly is right, that metamorphosis involves the change in already existing body parts, which does seem like a very wasteful way for the genes to ‘make’ an adult. Perhaps it has to do with the increased survival rate of the entity if it spends some of its lifetime as a caterpillar — and subject to a different (less lethal?) set of predators.

    On the other hand, I have no idea, but love being made to realize that the puzzle exists in the first place. Another reason I love this site.

  4. I think the article had it spot-on, that the two stages of insect eat different food but live in the same habitats. A lot more to go round and no inter-species competition. :)

    A good book to read on this kind of subject is Sean B. Carroll’s “Endless Forms Most Beautiful”.

  5. The evolution of metamorphosis remains somewhat mysterious, but
    biologists have gathered enough evidence to plausibly explain its
    origins

    In insects there is a stage where the animal needs to be dormant as a pupa during the transition. – Presumably because it would be vulnerable in this state.

    There is also the question of insects evolving from simpler organisms in their distant past, as they gradually developed additional features, and this being reflected in their embryonic development.

    The stages of metamorphosis are much clearer in amphibians where this pupal stage does not happen.

    Frog metamorphosis – http://en.wikipedia.org/wiki/F

  6. I found this to be rather disapointing.

    Perhaps this pro-nymphal stage, Riddiford and Truman suggest, evolved into the larval stage of complete metamorphosis. Perhaps 280 million years ago, through a chance mutation, some pro-nymphs failed to absorb all the yolk in their eggs, leaving a precious resource unused. In response to this unfavorable situation, some pro-nymphs gained a new talent: the ability to actively feed, to slurp up the extra yolk, while still inside the egg. If such pro-nymphs emerged from their eggs before they reached the nymphal stage, they would have been able to continue feeding themselves in the outside world.

    A lot of “if” with no evidence. Suggesting that not all yolk was used and that this was unfavourable and that would lead to the evolution of larvae that would eat things has its own problems – why were such “non absorbing” larvae not just selected against.
    This type of poor quality journalism just provides fuel for the creationist strawman machine

  7. This has puzzled me ever since I read Darwin back in the 1960s.  It seems the sequence is, adult and juvenile forms gradually diverge, then a quiescent period for change gradually extends. With a period for drastic revision in the middle, the juvenile and adult forms can evolve pretty well independently.
     
    The article did not make this explicit. 

    I remember Mr. Watson our 7th grade science teacher proposing, “What if humans metamorphosed?  Your new baby brother looked like a large worm.  When he got to be about 5 years  old, you put him away in a drawer of a year.”

  8. I know this is off topic, but I am traumatised by accidentally going out on a date with a creationist. I am seriously upset. You might think it’s easy to argue with someone who knows nothing, but it’s not. He didn’t even know why he thought what he thought, or why he disagreed with me. He just said ‘did you know there’s as much evidence for creation as there is for evolution’ and that was it. I thought i was going to die! I just didn’t know where to start. I found myself talking about sahelanthropis Tchadensis! I just needed to say this on RDF, because there are so many clever, wonderful, well read men who post on this site. Where are you? Why can’t I go to dinner with people like you? :( I need to put my photo of me with Richard Dawkins at the atheist con in Melbourne to show my bona fides…. What a disaster for

  9. On reflection, I think Locusts provide a better comparison, although they do not have the transition of some insects from the aquatic life to air-breathing adult forms shared by frogs.

    Locusts undergo incomplete or direct metamorphosis. Unlike in insects such butterflies or moths, there is no pupal stage.

    There are three main stages of development - egg, nymph and adult.
    The nymph or hopper stage can be further divided into growth stages
    called instars, with a moult between each. The following diagram shows
    the life cycle of the Australian plague locust
    which has five instar stages. The times given for development are under
    optimum conditions during summer and are only approximate. – http://www.daff.gov.au/animal-

    It would seem to me that the evolution of a semi-dormant pupal stage would be the result of selection against the uncompetitive state of the animal during transition, combined with the ability of the pupa to hibernate during adverse conditions in some examples.

    Metamorphosis in locusts comes in stages as illustrated by the linked diagram, with no need for a pupal stage.

    Evolution would shorten any stage which was uncompetitive, wasteful of resources, or too radical a change to survive while active (such as going from breathing with gills to breathing air), and reducing development of that stage to that of a pupa. The different body-forms could evolve independently from then on.

  10. interesting article but i’m puzzled… metamorphosis isn’t limited to insects but happens in marine invertebrates (e.g. read Richard’s chapter on Sea-squirts changing from a free-swimming larva to a rooted filter-feeder as adult in TGSOE)

    I made the assumption from that the ancestors of insects had already used metamorphosis before they crawled onto land, indeed (going a bit off topic) I wanted to ask if all insects (like land vertebrates) evolved from ancestors that crawled out of fresh water or from the sea?

    the metamorphosis of many flying insects has always made me wonder this, as they have a (freshwater) aquatic nymph stage before emerging as adults. I used to wonder if this had some reflection on their evolution from water to land but now am still confused by it all…

  11.  

    I made the assumption from that the ancestors of insects had already
    used metamorphosis before they crawled onto land, indeed (going a bit
    off topic) I wanted to ask if all insects (like land vertebrates)
    evolved from ancestors that crawled out of fresh water or from the sea?

    Indeed their ancestors lived in the sea and some refer to insects as “flying prawns”.

    http://whyevolutionistrue.word… –
    One of my favourite questions relating to evolution is ‘Why are there
    no insects in the sea?’ Arthropods came onto the land around 380 MY
    ago, and crustaceans and insects separated soon afterwards, probably
    because of that ecological shift. More or less, you get crustaceans in
    the sea, and insects on land. So why didn’t the insects go back into the
    sea? It’s very hard to be certain of the answer to this – doing an
    experiment would be pretty tricky, after all. But we can get towards
    what might be the answer by thinking about some of the possible answers
    we might give:

    - Insects can’t live in water. Although no insect species lives its
    whole life-cycle in water without access to air, many insect species
    pass their nymphal stage in freshwater, breathing with gills. Mayflies
    (more on this in an upcoming post) and dragonflies are two obvious
    examples. Last year Daniel Rubinoff, an entomologist at the University
    of Hawaii, discovered a number of moth species that
    have caterpillars (= larvae) that are equally at home on land or in
    freshwater. You can see a great video of one of these caterpillars
    moving between water and land here.

  12. hmm, so did some return to water? or are these flies animals that evolved from a freshwater shrimp-like ancestor? also, are there any insects that have part of their life-cycle in salt water? or maybe they’re not fussy (unlike amphibians)?

    and again, did the larva/pupa/adult/egg cycle evolve on land only or did it exist in the sea first?

  13. @SaganTheCat 

    are there any insects that have part of their life-cycle in salt water? or maybe they’re not fussy (unlike amphibians)?

    Some nymphs live in brackish water, but the link I gave suggests insects would no longer be competitive in the sea. 

    – @link:disqus -  The sea is full. I think this is probably the right answer – the
    niches that insects would occupy in the sea are already full. The
    insects’ cousins, the crustaceans, are already there. This is what
    ecologists call ‘competitive exclusion’. Any insect that started going
    back into the sea would either starve or be eaten, I reckon. Proving
    this, however, is tricky.

    Freshwater gives a much greater range of specialist sheltered environments, such as isolated ponds and lakes, where competition from fish etc is limited or absent, but flying insects have access. (Hence mosquito plagues)

  14.   SaganTheCat

    and again, did the larva/pupa/adult/egg cycle evolve on land only or did it exist in the sea first?

    Clearly the Arthropod ancestors lived in the sea first.  While insects have not returned to the sea, there are some unusual crustaceans (marine relatives of insects) which illustrate the “no-going-back-as further evolved adults”.

    Land crabs (which can compete living on isolated islands) as adults, drown in the sea, but have to return to the sea to lay their eggs.  Their larvae hatch and live in the sea as juveniles, before crawling out on to a life on land.

    Embryology generally traces the steps of evolution, so perhaps caterpillars represent hatching at a progressively more premature stage, with the period of metamorphosis later compacted into the pupa in those species with a pupal stage.  This would have advantages if adult features were a liability while they were unneeded.  Suppressing the growth of adult features would be a relatively simple genetic step.  The pupal stage seems to have evolved on land.

    If you look at my link on locusts, you will see significant stepped changes in the body as it grows. (Although they do not have a more primitive “caterpillar stage” or a “pupal stage”)  I would guess that the development of a specialist pupa is related to the simpler process of moulting.

  15. the thread on organisms building tissue they don’t use is woth considering here too.

    I guess it’s easy to pigeonhole different types of metamorphosis based on our subjective view of their extremity but it’s all embryology unfolding in some sense.

    a bit like humans. they’re born looking like grubs, go through a nymph stage which includes a reproductive stage then go into a state of stasis where they get buried by the colony until they hatch out with wings and swarm to heaven to feed off their god until a new planet can be found to infect.

    i get my books muddled

Leave a Reply