Not sure how to measure cuticle thickness per se, but you could use an indirect measure: how hard you have to press to puncture the carapace. John Christy and collaborators have done a similar thing a few years back for fiddler crabs (reference below), and they showed that it is harder to puncture the claw than it is to puncture the carapace. Also, the force you needed to puncture the claw was correlated to the pinching force of the claw. These suggest that Nahuel's idea is on the right track.

I would go a bit further and say that not only diet, but how much a given species fight should also correlate to cuticle thickness.

At the individual level I would assume that there should be a good amoung of variation as well. The minerals that make up the cuticle are not easy to come by in water, thus I would guess that some individuals can capture more minerals than others.

It would also be interesting to test if crabs that consistently win fights also have thicker cuticles - that may decrease the force the opponent is able to apply on the individual. That sort of study is missing in the fighting literature...

I hope some of my rambling is helpful.

Cheers,

Alexandre

The paper I commented is this:

Article Evolutionary variation in the mechanics of fiddler crab claws

One that I know of is Artemia whose cuticle thickness is one micron, with a body size of 10 to 11 mm.

Hope it helps.

Hi Carola, exoskeletal thickness relates to the need for support and locomotion, and also, I believe, to protection against predation pressures. The adoption of a nektonic (prawns) or benthic lifestyle (crabs, lobsters, crayfish, atyid prawns) is also relevant. Freshwater crayfish and prawns may be of similar sizes, but crayfish have much thicker, more mineralised carapaces. 

Best wishes, Julian

Thanks everone, for the helpful and interesting answers!

I was actually more about the specific relationship between size and cuticle thickness within one species, e.g. juvenile vs large adult lobster. It is pretty obvious that cuticle thickness increase with size (every crustacean gourmet can tell). I have however not found a single study which looks at this relationship throughout ontogeny (maybe because it is that obvious)

I have not seen any published literature, but I think that the thickness of cuticle of crustacean will increase proportionally with its age.

Hi Carola,

We have published on this (see Leland et al., 2015) using the cuticle layers in gastric ossicles. My recently published (today) FDRC Report on the topic also contains similar information to that contained in the above -- basically the width of the cuticular layers in ossicles increases in proportion to the animals carapace length. I have attached both publications below. Hope that this is helpful.

Kind regards,

Jesse

Many thanks Jesse, I am looking forward to reading the report!

Carola

Hi Carola,

Another factor that may complicate things is that the carapace thickness is usually variable among the different parts of the body. This becomes evident if you compare the thickness of the dactyls of most durophagous crabs in relation to the rest of the body. So the thickness seems to be related also to the specific use of each part of the body. And now that I think about it, the idea sounds interesting. How plastic is this trait at the individual level? Would it vary according to different scenarios of use and/or need (e.g. crabs of the same species and molt stage, but handling soft or hard preys)?

Hi Nahuel,

thanks for your answer! Very interesting thoughts.

I tried to measure carapace thickness of different among individuals of different sizes - and it proved very difficult!

By the way, I really enjoyed your receptacle paper.

Cheers

Hi again Carola,

Thanks for your message. I also enjoyed reading your papers; great work!.

If I recall well, computerized tomography is sensitive to calcified structures, so maybe you can scan the individuals and measure the thickness directly in the image with some software? Just thinking loudly

All the best

Nahuel

Not sure how to measure cuticle thickness per se, but you could use an indirect measure: how hard you have to press to puncture the carapace. John Christy and collaborators have done a similar thing a few years back for fiddler crabs (reference below), and they showed that it is harder to puncture the claw than it is to puncture the carapace. Also, the force you needed to puncture the claw was correlated to the pinching force of the claw. These suggest that Nahuel's idea is on the right track.

I would go a bit further and say that not only diet, but how much a given species fight should also correlate to cuticle thickness.

At the individual level I would assume that there should be a good amoung of variation as well. The minerals that make up the cuticle are not easy to come by in water, thus I would guess that some individuals can capture more minerals than others.

It would also be interesting to test if crabs that consistently win fights also have thicker cuticles - that may decrease the force the opponent is able to apply on the individual. That sort of study is missing in the fighting literature...

I hope some of my rambling is helpful.

Cheers,

Alexandre

The paper I commented is this:

Article Evolutionary variation in the mechanics of fiddler crab claws

Dear Alexandre, thanks so much for your contribution to the discussion. Very interesting points made!

Cheers

Carola

hi Carola,

We recently measured cuticle thickness, but in harvestmen legs. To measure cuticle thickness, we first cut transversely the femurs at the midpoint of this leg segment. Then, we photographed the cut point of femur (close to a scale) under a stereo-microscope, and measured cuticle thickness using the software ImageJ. Maybe this approach may help you.

Cheers,

Soly

Dear Solimary, thanks very much. I tried a very different approach but the cuticle was so uneven, that I had a hard time taking measurements.

Did you find a correlation between specimen body size and cuticle thickness?

Thanks

Carola

Hi Carola, I did not do a correlation analysis between specimen body size and cuticle thickness.

Good luck,

Soly