Vampire bats, The infrared vision is adapted via a rare gene splicing event.
The Vampire bats, Desmodus rotundus, are one of the few obligated blood feeders known to men and they also got a very special tool for sustaining this odd lifestyle. It is The Infrared vision, just like The predators in Alien vs predator. They pick up infrared radiation, which lies just out of the spectra of human vision, on the red nominal edge, at wavelengths over 700 nm. This is an adaptation made by multiple species and doesn't come with one evolutionary ancestor, it´s only for the truly genetically adapted hunters, making it even cooler.
Warm creatures with blood pumping in their veins is always radiating infrared radiation into space. Even if a certain animal would hide under leaf and such, radiation would be very likely to leak, so this truly is an amazing tool for adapted hunters like the vampire bat. Vampire bats have a close range heat sensing capacity for finding veins on cows, which also is one of their closest relatives, wierd! Snakes that have adapted this mechanism can sense heat at a longer range, and find the hiding small animals.
To have infrared vision, the sensing mechanism must be placed external on an antenna, facial pocket or perhaps the tongue,which could be placed outside the mouth otherwise the ones own body radiation would simply blind the sensors. This is probably one reason why the human vision cuts of att 700 nm, just under the infrared vision, otherwise the heat from our head would radiate into the eyes.
The fruit bat cannot detect infrared radiation, and a study comparing the fruit bat and vampire bat, on a genetic level have singled out the mechanism responsible for enabling this feature. They found that gene splicing of TRPV1, resulting in an isoform of TRPV1, called, TRPV1-Short, gives the bats this ability, or at least the right thermal threshold to make it useful.¨
This ability has also been adapted by some snakes, and bed bugs, who has their thermal sensors on antennas but via another mechanism, making this mechanism the first of its kind and with it comes insight into gene splicing, which is an elusive field to say the least.
With this genetic information in the bag, the vampire bat was moved from being closest related with rodents, to now having dogs,cows and moles as closest relatives.
Vampire bat = Small cow with wings
But how was this elusive gene splicing event found?
The article: Ganglion-specific splicing of TRPV1 underlies infrared sensation in vampire bats
In this article, the genetic mechanism behind the adaption of the heat sensing function in
vampire bats is examined. It was previously suspected to be an adaptation, since it seem to lack a common evolutionary ancestor. Instead it has been adopted in various species like, bugs,snakes and the vampire bat.
The adaption was already suspected to affect the TG, the trigeminal ganglia, mainly, since it is known that they have a special formation on the nose, responsible for thermal sensing at a threshold of 29 degrees. It was also known that a TG specific adaptation was responsible for the heat sensing capacity of some snakes.
A good starting point is comparing both the DRG, dorsal root ganglia and TG from vampire bats, but also DRG
vs TG in fruit bats, which was done.
The whole TG and DRG genome was expressed from the vampire bats, they compared it to the genome of close ancestors and the fruit bat, the closest or relatives. The team used PRC via reverse transcriptase from a cDNA library to obtain the expressed DNA in both vampire and fruit bats. The transcriptome, at first glance, looked identical, but during examination of cDNAs that just code for candidate thermosensors another unknown short isoform of
the TRPV1 gene where found. The gene is responsible for forming the capsaicin receptor, an Ion channel activated by heat under 43 degrees. Having an iso form expressed side by side with the full length expression seen it fruit bats, surely affects the heat sensing threshold.
They found the isoform expressed exclusively in vampire bat TG, at a ratio of approximately 40:60 in favor of the full length splice variant. The expression location was also verified in sensory ganglia from vampire bats by in situ hybridization, a procedure similar to IHC, but uses e.g directly labeled DNA instead of antibodies.
To investigate the effect the isomer have on the thermal sensing threshold,it was expressed in two different cell strains, HEK293 cells & Xenopus oocytes. They used calcium imaging or electrophysiological to trace the ion channel response to different temperatures The cells were stimulated at an interval between, 26-40 degrees Celsius and the fluorescence response from changing internal calcium concentrations, will relate to the opening of the said ion channel.
The results clearly shows different thermal thresholds for the short and long splice variants, approximately 30 degrees for pure short variant and approximately 40 degrees for pure TRPV1 non isomere. This is an excellent method for tracing Ion channel response in live cells in real time.
Lastley the splicing was mapped and compared to known closely related species and the gene splicing expression of isomere 14a, in the short form only, is the first of its kind. It also somewhat affects the phylogeny, by changing the vampire bats closest relatives to cows and moles from the earlier proposed links to the rodent tree.
It seems that the CAGCAG promoter for exon 14 along with a weak exone 15 tandem slice promoter, gives the possibility for 14a expression. The exon is hardly expressed in cell culture and the exact interactions and chemical environment required is not known.
But still this happens in the vampire bat, pointing to the severe effect being in the right womb, the same spicies, have on feudal growth. Would a fruit bat evolve in the womb of a vampire bat, maybe the heat sensing adaptation would be instantaneously, meaning generation one. I am pretty sure it is hard to try this experiment, but it would be interesting to see the results for sure!
Article source:
https://www.nature.com/articles/nature10245
Image sources:
1.https://www.pestwiki.com/vampire-bats-facts/
2.http://annesastronomynews.com/photo-gallery-ii/miscellaneous/wavelengths-of-light/
3.https://io9.gizmodo.com/under-the-right-conditions-humans-can-see-infrared-1665448040
4-7.https://www.nature.com/articles/nature10245