Thanks very much for your question! I am assuming ‘frog substrate’ here refers to the material properties of the frogs skin. I am going to paraphrase some of my answer from Dr. Ludwick below in that case, considering she asked a very similar question. If you meant to ask something else, please let me know!

Though I have not investigated it yet, my guess is that the frog’s skin plays a very small role (if one at all) in its propulsion. This is because from what I am aware (from literature searches, etc) both cricket frogs and E. cyanophlyctis do not have skin with material properties drastically different from other true frogs (family Ranidae). However, very few frogs can jump on the surface of the water like this. It is my thought that the specialization that allows this behaviour is morphological – Nauwelaerts 2004 for example found that of the frogs studied jumping from floating statically in water, it was only those with the cambered feet during propulsion that were able to jump greater than 1 body length high.

If these frog’s feet happen to be more hydrophobic than other frogs, however, it may be a way for the frogs to have a larger ‘effective’ foot in the water, which could help create more force in propelling the frogs both in and on the surface of the water. However, nothing of the sort has been reported in the literature thus far.

Thanks very much for your question! Unfortunately, as this project is still fairly new, we have yet to take any video of the frogs jumping. We plan to start collecting cricket frogs in early June, and hope to be able to record cricket frogs skipping in the wild as well.
For in lab experiments, data will be taken with multiple Photron APX RS cameras, so depending on what the particle movements look like the data will be recorded anywhere between 500 – 3000 fps. As a reference, the BBC clip in my video was taken at 1000 fps, but the force data calculated for the Basilisk lizards in Hsieh 2006 was taken at 250 fps.
The spatial resolution will depend entirely on the field of view and magnification of the cameras. Depending on how consistent we can get the frogs to jump, and how cooperative the frogs are, we can focus on a smaller area of interest resulting in more (real world) spatial resolution.

I assume by the “frog’s surface” you mean the material properties of the frog’s skin? This is actually a really interesting question and one that, as far as I can tell, was not really considered in the basilisk lizard as of yet.

While I don’t know for sure whether the frog’s skin properties plays any role in the ability for it to move on the water’s surface, I very much doubt it plays a significant role at all.

Amphibians different from lizards in that their skin is permeable to water and various gases. While some frogs excrete mucus that they spread over their body in order prevent water loss in dry environments, (so hydrophobic in a way), frog skin in general would probably be categorized as hydrophilic. Of course, different frog species have different surface chemistry depending on what mucus they may or may not secrete, whether they secrete toxins, etc. but cricket frogs are not known to have any special skin properties in particular.

Therefore these frog species (both Acris spp. and E. cyanophlyctis) as far as current literature is aware, have skin with very similar material properties to other species in their family (Ranidae), yet very few true frogs have every been reported having this skipping behaviour. This is a small indication that material properties are not the driving factor allowing these frogs to skip on the water’s surface. It is much more likely that it is morphological differences in the feet (which was examined briefly in Nauwelaerts 2004) and the kinematics of the feet moving through the water that allow this behaviour.

If these frog’s feet happen to be more hydrophobic than other frogs, however, it may be a way for the frogs to have a larger ‘effective’ foot in the water, which could help create more force in propelling the frogs both in and on the surface of the water. However, nothing of the sort has been reported in the literature thus far, at least in my searches.

I hope this answers your question! Its definitely something I should think about.

Sure, sorry if I was unclear in my video. Basically, E. cyanophlyctis (which is best known for its skipping behavior) can jump up to 3 body lengths vertically in the air from floating statically in water. This was examined in the Nauwelaerts 2004 paper “A functional analysis of how frogs jump out of water.”

Basically, in order for the frog to do this, all of the force required to propel the frog up into the air needs to be generated from drag-related forces: the frogs feet when floating are always under water when it is propelling the frog up into the air (so there is no impact force component here). Therefore, because E. cyanophlcytis can jump ~3 body lengths high only due to drag related propulsion, it is entirely possible that the frog uses these drag related forces to skitter as well.

Obviously, this is just a hypothesis based on the fact that these frogs can jump standstill from water, while basilisk lizards cannot. There is no really clear footage as of yet of what the frogs legs are doing under the water while skittering. For example, it may be the case that when the frog jumps on water the air cavity around the foot closes (while this air cavity is thought to be key to allowing the basilisk lizard to run on water). This would lend even more evidence that the frog is taking advantage of different forces in order to skitter on the water.

Hopefully, once I am able to take clearer video of what the frogs legs are doing under water while skittering, and whether there are air cavities/etc, and am able to analyze them even just qualitatively, I will be able to formulate a more concrete hypothesis.

I hope this clarifies my thinking for you!

Thanks for the question! I was on a plane/in airports all of today so I hope this response is not too late.

This is actually an interesting problem, because the shape of the frog’s feet during propulsion is going to be different (most likely) than during rest. At least in terms of non-functional web area, we can simply take pictures and use calipers to measure the flat foot surface area of both alcohol preserved specimens and any live frogs they have. However, the functional web area of the frog’s feet – AKA the projected surface area of the feet (as the feet are most likely cambered during propulsion) will probably be more difficult to discern.

The best way to estimate the camber of the foot will probably be to measure the projected surface area of the foot during the frog’s jump. This could be done by filming the frogs directly beneath the tank in which they will be skipping. From there we can calculate the area of the image the foot takes up. By comparing this projected flat foot surface to the real web area, we can then roughly estimate how curled up the feet are during propulsion. If the ratio between projected area and actual area of the foot end up being consistent for the live specimens, we can then estimate the camber of museum specimens as well.

Thanks for the question! I was on a plane/in airports all of today so I hope this response is not too late.

This is actually an interesting problem, because the shape of the frog’s feet during propulsion is going to be different (most likely) than during rest. At least in terms of non-functional web area, we can simply take pictures and use calipers to measure the flat foot surface area of both alcohol preserved specimens and any live frogs they have. However, the functional web area of the frog’s feet – AKA the projected surface area of the feet (as the feet are most likely cambered during propulsion) will probably be more difficult to discern.

The best way to estimate the camber of the foot will probably be to measure the projected surface area of the foot during the frog’s jump. This could be done by filming the frogs directly beneath the tank in which they will be skipping. From there we can calculate the area of the image the foot takes up. By comparing this projected flat foot surface to the real web area, we can then roughly estimate how curled up the feet are during propulsion. If the ratio between projected area and actual area of the foot end up being consistent for the live specimens, we can then estimate the camber of museum specimens as well.

Thank you very much! I worked hard on it, so I am glad you liked it.

Thanks AJ!

Thank you very much! I will probably need all the luck I can get – this project’s success very much depends on how well I can get the frogs to behave. Hopefully it will all work out!

Thanks very much for your comment! Hopefully it will be a good project!

Thanks very much!

Thanks for your input! I am actually not yet sure that surface tension plays a major role in the frog’s skittering behavior. In basilisk lizards, the surface tension is important in allowing a larger impact force to support the weight of the lizard. However, these frogs can propel themselves up to 3 body lengths high from statically floating in water simply do to drag – based propulsion – their feet in this case never interact with the surface of the water. Therefore, there is certainly the possibility that the frogs do not need to rely on the water’s surface tension to support their body weight.

In terms of body mass dependence, there is only one paper (from 1919 – Some Frogs in the Streams of the Bombay Presidency) that mentions that all E. cyanophlyctis frogs observed, regardless of size, were able to skip on the water. This is in contrast to the basilisk lizards, of which only juveniles can run on the water surface. Granted, basilisk lizards have a much larger possible size range than these frogs. Overall, there is really not enough real data on how these frogs jump in general, never mind size dependence on jumping, to even know if larger frogs are worse at this skipping behavior than smaller frogs (or vice versa).

Thanks very much! Hopefully any results I get will be interesting!

Thanks very much! Hopefully any results I get will be interesting!

Thanks. This is actually a very interesting question. E. cyanophlyctis, from what I have been able to find in my research, is a primarily aquatic frog so how it jumps on land may not be really something to consider.

Cricket frogs (Acris spp.) however, are only semi aquatic and do jump on land as well as water. I suspect that the mechanics of jumping on these two different substrate will be quite different. However, whether the differences can be accounted for by having water be a more compliant substrate….I don’t know! We will see.

Thanks!

Thanks Dr. Socha!

Thanks for the question! It’s entirely possible that the muscles of these frogs may be partially specialized for these skittering behavior. However, my intuition is its mostly due to the morphology and kinematics, simply because I am not sure how key for survival it is for these frogs to skitter on the water. For example, it may be very key for E. cyanophlyctis, which is really known for this skipping behavior (and is thus named for it). For cricket frogs however…how important it was for them to evolve this escape behavior is unclear simply because of how undocumented this behavior really is. Thus, the probability that muscles have been specifically evolved to perform this one out of many behaviors the frogs legs must perform….its unlikely, but anything is possible!

Thank you very much!