Verified casque use

[Kaizen]

Anecdotal though the following undoubtedly is, I can confirm at least one instance of a veiled chameleon using his casque for hydration purposes. For several minutes, I watched Karma sliding his casque along the condensation on the greenhouse walls, mouth open, drinking his fill of the runoff cascading down his head. And while this may be insufficient evidence to support the common theory that the veiled’s casque serves this purpose, it is at least a confirming datum.

Again, I don’t know how relevant this is to most of those who employ cages, but for the free rangers, it might be interesting.

 

[Chris Anderson]

If this were the primary function of the casque, why would it be advantageous for one sex to have a casque that is so much more weakly developed than the other sex, and for it to be so variable in development among species that live in similar habitats that could benefit from such a use?

Chris

 

[Kaizen]

I agree that this cannot be the casque’s primary function, but the observation shows at least one instance of it being used in this way. I just thought it was an interesting datum.

 

[alphakenc]

If this were the primary function of the casque, why would it be advantageous for one sex to have a casque that is so much more weakly developed than the other sex, and for it to be so variable in development among species that live in similar habitats that could benefit from such a use?

Chris

Hi Chris,so do you think the lower casque, with males lacking the marked sexual in casque size has disadvantaged to attract the opposite females for the mating purpose (for one of the function)???

 

[Chris Anderson]

I agree that this cannot be the casque’s primary function, but the observation shows at least one instance of it being used in this way. I just thought it was an interesting datum.

Hi Chris,so do you think the lower casque, with males lacking the marked sexual in casque size has disadvantaged to attract the opposite females for the mating purpose (for one of the function)???

I would say casque size is a tradeoff as there are undoubtably costs and benefits to increased casque size. It would be energetically costly to produce a large one, for instance. I would also say, however, that if the casque was under selective pressure as an adaptation for something like drinking, that this pressure would at least be exerted equally on both sexes of a single species and you wouldn't expect to see such a huge dimorphism in the trait between males and females. The fact that there are such strong male-female differences in C. calyptratus suggests to me that it has another form of selective pressure, such as sexual selection and/or species recognition, exerting a large amount of influence.

Some work by Rand (1961) examined the function of ornamentation in chameleons. In comparing the anatomy of sympatric species in East Africa found that 13 of 14 species examined differed from a sympatric species by only a single character, suggesting that ornamentation is used frequently for species recognition purposes through the process of character displacement. Casque size also relates closely to bite force in many species (Stuart-Fox et al. 2006; Karsten et al. 2009; Measey et al. 2009; da Silva et al. 2014; Ligon & McGraw 2018). Correlations with prey type and sex in different species show that this may be driven by both natural selection on prey hardness and on sexual selection (male-male combat), depending on the species.

Anyway, I have no doubt that the casque can be secondarily used for a variety of things, but I don't think there is strong support for drinking being the primary driver of its development and evolution.

Chris

 

[alphakenc]

I would say casque size is a tradeoff as there are undoubtably costs and benefits to increased casque size. It would be energetically costly to produce a large one, for instance. I would also say, however, that if the casque was under selective pressure as an adaptation for something like drinking, that this pressure would at least be exerted equally on both sexes of a single species and you wouldn't expect to see such a huge dimorphism in the trait between males and females. The fact that there are such strong male-female differences in C. calyptratus suggests to me that it has another form of selective pressure, such as sexual selection and/or species recognition, exerting a large amount of influence.

Some work by Rand (1961) examined the function of ornamentation in chameleons. In comparing the anatomy of sympatric species in East Africa found that 13 of 14 species examined differed from a sympatric species by only a single character, suggesting that ornamentation is used frequently for species recognition purposes through the process of character displacement. Casque size also relates closely to bite force in many species (Stuart-Fox et al. 2006; Karsten et al. 2009; Measey et al. 2009; da Silva et al. 2014; Ligon & McGraw 2018). Correlations with prey type and sex in different species show that this may be driven by both natural selection on prey hardness and on sexual selection (male-male combat), depending on the species.

Anyway, I have no doubt that the casque can be secondarily used for a variety of things, but I don't think there is strong support for drinking being the primary driver of its development and evolution.

Chris

Thank you for all the insight info ...I really appreciate you taking your valuable time and explain this to us.
Dr Chris.

 

[Kaizen]

I would say casque size is a tradeoff as there are undoubtably costs and benefits to increased casque size. It would be energetically costly to produce a large one, for instance. I would also say, however, that if the casque was under selective pressure as an adaptation for something like drinking, that this pressure would at least be exerted equally on both sexes of a single species and you wouldn't expect to see such a huge dimorphism in the trait between males and females. The fact that there are such strong male-female differences in C. calyptratus suggests to me that it has another form of selective pressure, such as sexual selection and/or species recognition, exerting a large amount of influence.

Some work by Rand (1961) examined the function of ornamentation in chameleons. In comparing the anatomy of sympatric species in East Africa found that 13 of 14 species examined differed from a sympatric species by only a single character, suggesting that ornamentation is used frequently for species recognition purposes through the process of character displacement. Casque size also relates closely to bite force in many species (Stuart-Fox et al. 2006; Karsten et al. 2009; Measey et al. 2009; da Silva et al. 2014; Ligon & McGraw 2018). Correlations with prey type and sex in different species show that this may be driven by both natural selection on prey hardness and on sexual selection (male-male combat), depending on the species.

Anyway, I have no doubt that the casque can be secondarily used for a variety of things, but I don't think there is strong support for drinking being the primary driver of its development and evolution.

Chris

I really appreciate the references here! You sound like a fellow academic.

 

[Chris Anderson]

I really appreciate the references here! You sound like a fellow academic.

Not a problem. Happy to provide the full citations for any of them if desired.

Yep, I am a biology professor at the University of South Dakota and my lab does research on chameleons in the lab and in the field. I am also (newly) the Chair of the IUCN/SSC Chameleon Specialist Group. Are you in academia as well?

Chris

 

[Kaizen]

I have a doctorate in philosophy, but after defending, I realized the world of academia wasn’t for me. Thanks again for the leg work!

 

[Syreptyon]

Not a problem. Happy to provide the full citations for any of them if desired.

Yep, I am a biology professor at the University of South Dakota and my lab does research on chameleons in the lab and in the field. I am also (newly) the Chair of the IUCN/SSC Chameleon Specialist Group. Are you in academia as well?

Chris

That is incredibly interesting. I'm in a molecular/cell/developmental biology doctoral program at the University of Minnesota and never figured chameleon research would be much of an accessible thing. Blending the worlds of academia and chameleons sounds like a dream come true!