When it comes to things that freak me out maggots, the
compost bin and moths round my ears are the only things that give me shivers.
But when I came across this hideous insect on animal planet I nearly chucked. Ticks
are what I’m talking about. Ticks are RANK!!! It’s bad enough to think they can
get me on land but in the water?! The report Underwater survival
in the dog tick Dermacentor variabilis (Acari:Ixodidae) helps to make my life a little bit more creepier. That’s why I thought I’d face my fear of
ticks by sharing with you how they can survive living underwater. I won’t put
pictures up as they are pretty disgusting but if you want to have a look at
what
they look like and what they can do just click here.
Ticks feed on the blood of terrestrial
animals and are known as ecto-parasites (parasites that feed on the outside of
the animal). The American Dog tick, Dermacentor variabilis, can cause
great harm to the animal as a direct pest and as a vector for diseases.
Though the name indicates its preferred
host is the dog, it also doesn’t mind feeding on live stock and humans. If this
tick bites a human it can cause Rocky Mountain spotted fever as it is a vector of the Rickettsia
rickettsii bacterium. In
the process of feeding the tick can burrow its head to become imbedded in
the animals’ skin giving difficulty to removing the parasite. At each stage of
its life cycle it has a blood meal lasting several days, after which they molt
and grow.
Check out this video on paralysis caused by the tick its very interesting!!
http://www.youtube.com/watch?v=nCio6UIkTh8
Ticks can survive off-host periods for
several months and years between these meals. This is possible by mechanisms
that help the tick tolerate prolonged off-host periods. These mechanisms include
an outer waterproof protective layer which inhibits water loss, active water
sorption to replenish water reserves, lower rates of energy turnover (approx
10% of that of spiders and insects), and tolerances to extremely cold
temperatures. As heavy rainfall and flooding events are common the ability to
survive underwater is another survival mechanism for off-host periods.
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Figure 1:- (a) Spiracle plate. (b) Spiracle
plate cross-section through ostium, showing atrium opening into the tracheal
trunks. (c) Spiracle plate cross-section showing aeropyles with air chambers underneath.
(d) Spiracle plate slice through cuticle labyrinth with pedicles, view from underneath
spiracle plate.
|
Ticks have plastrons respiration which
consists of water –repellent hairs/ projections which hold thin films of air. They
also have spiracles behind the hind legs that have a protective cover that prevent debris/ water from entering. They contain internal air chambers
and cuticle pedicles. While immersed in water the tick uses these spiracle plates
as a plastron by preventing water to enter the air chamber. The
film of air that is captured is a physical gill that can extract oxygen from
the water. An air- water interface forms where oxygen from the water diffuses
through into a film in the air chambers then via
the atrial chambers into the tracheal system as a result of an oxygen gradient.
With low metabolic rates the tick can conserve this oxygen in order to survive
for long periods at a time underwater.
Obviously as the time immersed under water increase there
was a reduced rate of survival as the oxygen within the water may be depleting,
such as in stagnant water. The rate of survival was looked at in this report.
The results showed that an adult ticks can survive up to 15 days immersed in
water that has a normal oxygen concentration. But where oxygen concentrations
were depleted the survival rate decreased down to 10-12 days.
 |
Figure 2:- Survivorship
for female Demacentor variabiis
submerged in normoxic water- normal
oxygen concentrated water (•) and
hypoxic water- oxygen depleted water (○).
|
With all this said I still find ticks disgusting but after
reading this article it’s given me respect for these we suckers. As gross as
they are they can do some amazing things such as breathing underwater and being
able to survive up to 15 days. Good on em, just stay away from me!!
Want to read this report get it on:- http://www.sciencedirect.com.ezproxy.lincoln.ac.nz/science/article/pii/S0022191010002544?np=y
Want to read this report get it on:- http://www.sciencedirect.com.ezproxy.lincoln.ac.nz/science/article/pii/S0022191010002544?np=y
Check out this video on paralysis caused by the tick its very interesting!!
http://www.youtube.com/watch?v=nCio6UIkTh8
Cheers for reading my
blog!!
Leave a comment!
"The film of air that is captured is a physical gill that can extract oxygen from the water" I don't quite understand this part. Is there a membrane between the air chamber and the spiracles? Why can't they survive underwater for months to years if this acts as a physical gill (providing it's not stagnant water)?
ReplyDeleteSorry in advance :)
Sorry Ashley, but i don't quite understand the bit about the physical gill and it extracting oxygen from the water also. How does the oxygen get from the water into the air film on the tick? Cool little creatures though!
ReplyDeleteIm not 100% sure. It says that the thin film of air is a physical gill that can extract oxygen from the water which then diffuses into the air space and from there into the internal respiratory system which suggests that they can breath under water and would expect then to do so happily for a long long time.
ReplyDeleteBut in the experiment they wetted the spiracle plates, which acts as a plastron, with alcohol. This showed that as the spirical was wetted its function to obtain air was weakened. it says in the article "A plastron may be debilitated by “wetting” with alcohol as the alcohol breaks the surface tension of the air–water interface and destroys the air space maintained by the cuticular hairs or projections"
But with this said they did this experiment with alcohol not water so this too makes me slightly confused.
It also says that when a tick was placed underwater, the spiracle plate developed sheen due to trapped air. When alcohol was applied to the spiracle plate out of water, the structure darkened. When the tick was placed underwater, the plate remained discoloured, but if allowed to dry and then placed underwater, the structure returned to its glossy lighter shade. This makes me think that as they can absorb air from the surrounding water they rely on the air that is captured when they are out of the water, but it doesn't say why in the paper.
It also says as they are submerged they're metabolic rates are reduced and come into a paralyzed state in order to limit the amount of energy used. With this said along with the fact that they may rely on the original terrestrial air captured to breath under water and that as the spiracles are wettend it destroys the air space maintained by the cuticular hairs leads to why they can only survive under water for several days rather than several years.
Sorry for the novel length reply but i hope this answers your question. :) give the report a read yourself and maybe you can enlighten me too :)
Thanks for explaining. I think it is a quite indepth physical process our meager undergrad brains arn't going to understand with someone a bit more knowledgable explaining to us.
ReplyDeleteAfter reading this and clicking the Amercian dog tick link, I frantically googled ticks in New Zealand. Turns out most are native and as such are specialists of native mammals, birds and reptiles. Whewph! No cause for panic, it's still safe to swim in our glorious rivers! The only one which is known to have (but rarely has) humans as a host is the introduced cattle tick, Haemaphysalis longicornis, but so far this is mainly limited to the North Island. (Here's the link I found:
ReplyDeletehttp://www.smsl.co.nz/Services/New+Zealand+BioSecure/Ticks.html)
Yet another reason to stay in safe, tame ole New Zealand, and all the more reason to protect what we have here. Just thought I'd share to put your mind at ease :)
One of my favorite parts about New Zealand (although there are many I assure you) is that you can go tramping in shorts and not have to check yourself for ticks every so often. As a person with experience with ticks, here are my two cents. They're gross!!! Once you catch one crawling on you, you will feel like they're everywhere on you. And they don't just burrow in; you can't just pull them out. You have to use something to TWIST it out or you risk breaking the head off in your skin. One way to attempt to force them out is to put a bubble of soap over them. This way you "suffocate" them. Turkey mites are baby ticks in the midwest and they are even harder to spot on your skin. Rocky Mountain spotted fever is only a problen in the western and midwestern USA. In the east we get Lyme disease from deer ticks. I think I'll stop there but last summer I had 34 even though I wore 33% Deet bugspray when in the field!
ReplyDeleteBloody hell lyme disease is serious stuff!
ReplyDeleteYeah ticks are awful! I've luckily never had one on myself, but I remember having to remove them from my dog a time or two!
ReplyDelete