A study was recently done at the University of Toronto in which dragonflies were raised in tanks with fish, which are their predators. The dragonflies were hatched and raised from larva in aquariums where they could see and smell the fish, but could not be eaten by them. The study found that larva that were raised in these conditions had survival rates that were 2.5 to 4.3 times lower than those that were not.
In a different experiment, 11% of larva died during metamorphosis after being exposed to fish, compared to only 2% that died that were not exposed to fish. It is thought that the amount of stress that they were under contributed to their deaths, although it is unclear how.
The reasons behind the mechanism of stress-related death are still unknown to scientists. However, researchers feel that this new discovery could lead to understanding of how other organisms cope with stress. Studies can even be done to compare lethal stress levels in other species. What is most interesting about this topic is the evolutionary value of it. How do stress-induced death mechanisms evolve in dragonflies that have not even reached their reproductive age? Hopefully the new research will give some insight on this phenomenon, which may even further our understanding of the evolution of seemingly detrimental mechanisms.
Posted by Janelle Hayes
The increase in stress may have some hormonal affects on the dragonfly that may trigger something to be abnormal and die. Stress can increase the hormone norepinephrine which can cause hypertension to the dragonfly. This will cause and increase in the heart which may lead to a heart attack during metamorphis. This is just a theory , but it was the first thing that came to my head.
ReplyDeleteJobin
I wonder if their inability to cope with stress is a function of their particularly small size; maybe the ability to cope with stress increases directly with body size? Do you know if there are different species of dragonflies that are differ substantially in body mass? If this is the case, it would be interesting to compare the statistics of stress-induces death rates across different sized species of dragonflies.
ReplyDeletePosted by Johanna Brophy
I agree that it would be interesting to compare the statistics to those of a larger dragonfly species and look for a correlation. Are they having heart attacks? What Jobin posted about makes sense to me.
ReplyDeletePosted by Emily Nobrega
This is interesting! Lots of stress in humans have many detrimental health effects, and this may be the same thing in dragonflies. However, this doesn't seem feasible in nature. Dying is not a very good way to escape predators! It would be interesting to see the physiological mechanisms and what chemical changes occur in the dragonflies when stress is induced.
ReplyDeletePosted by Michael Shi
Jobin's comment about hormones being the cause makes a lot of sense. Heart problems and hypertension in such a delicate time as metamorphosis would probably be quite deadly. In another class of mine I learned that hormones often work in a negative feedback loop and shut off the production of other hormones. The high levels of norepinephrine could be interfering with the production of other hormones for the metamorphosis phase, which could cause the dragonfly to not develop properly and die.
ReplyDelete-Rhys Ursuliak
Neuroimmunology is the term used for the study of how stress effects humans. It actually is starting to be understood as a precursor to many diseases, such as heart disease and possibly even some links to cancer. It is starting to be a much more researched field. This article about dragonflies doesn't surprise me. I seem to always get sick when I get too stressed. Maybe understanding stress effects on dragonflies can be related to how it effects humans too, and can possibly help us understand what stress is actually causing in our body.
ReplyDeletePosted by Abbie Saranteas
I would imagine that any creature with enough stress you experience problems. For example human babies will start to decline and head towards death if they do not feel their mothers heartbeat for a certain amount of time. I am curious if there has been research into the same sort of conditions, but for different insects. Is this just too much stress for any bug to handle? I am thinking of how I might feel and I recently read "Unbroken" which was about WWII POW. For them having the constant fear of death killed some of the men. Mentally I think they just broke down. Oh and the book is really great. It is a survivor/ underdog story.
ReplyDeletePosted by Caroline Adams
This reminds me of "fainting" goats. Shepherds will add one of these goats to their flock so if a predator stalks the flock, the goat will faint from stress and the predator will target him instead of the sheep running away. How do these detrimental traits exist? Has evolution just not been able to ween them out through natural selection? If stress is affecting all of the species mentioned in the aforementioned comments, is it better for our survival to always be relaxed and carefree? To an extent, stress exists to help an animal survive, giving it cues when it should be quiet or aware, but here it seems that too much of a good thing can lead to a much worse outcome.
ReplyDeletePosted by Chelsea Van Thof
This was a really cool article. The fact that this stress response occurs in larvae indicates that this is an innate response; as these dragonflies were brought up right next to these fish, and have no real reason to fear them since they cannot be eaten. Stress hormones can have a huge number of effects on physiology including an increase in heart and respiratory rates, and can act shut down other processes such as digestion its not hard to see how something, that is constantly exposed to a stressor, would react this way; especially in such a fragile developmental state.
ReplyDeletePosted by Michael Thomas
To respond to a few of your questions: the actual causes of these dragonfly deaths are still unknown to scientists. A few theories have been thrown around, but none have been sufficiently tested to provide answers. Some ideas are that stress hinders the immune system of dragonflies, causing them to fall sick easier. Stress may also inhibit the dragonfly's ability to efficiently use energy. Also, it could cause many minor problems that as a whole are lethal. I am not sure if dragonflies can have heart attacks, I do not think very much research has been done on that. Dragonflies have open circulatory systems with very different hearts, but I would think that some version of a heart attack is possible.
ReplyDeletePosted by Janelle Hayes
http://io9.com/5855419/stress-can-literally-kill-dragonflies
http://books.google.com/books?id=N3YeAQAAMAAJ&pg=PA157&lpg=PA157&dq=circulatory+systems+in+dragonflies&source=bl&ots=G4uAvWl8X0&sig=wbd2NS1tGR-d-Apq_2n8GTfNowM&hl=en&ei=Fjq3TovgFofu0gHF7LTRBw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CGYQ6AEwBw#v=onepage&q&f=false
This was an interesting read and never knew this occurred in dragonflies, or any species for that matter. Do you think that if all hatchlings of dragonflies were exposed to this type of stress at an early age and the ones that survived and reproduced and their future generations were also exposed to this, that they would develop some sort of mechanism that could control their stress levels and have a higher survivability rate? Also, do you know any other factors, abiotic or biotic, that can cause stress to these dragonflies?
ReplyDeletePosted by Ryan Dulmaine