Do lizards have heat?

Do reptiles have an estrus cycle? If not, how do they time reproduction? If they don’t and get away with it, why do mammals have them?

Well, as there’s a good umpity-ump thousand species of reptiles, it is difficult to make ANY blanket statement about their reproductive habits.

However, as you asked about lizards in the title, we can say that the “average” lizard (defined by me to be one of the iguanid or agamid species) has a seasonal reproductive cycle. Usually, the production of hormones is stimulated by the increasing light detected by the lizard’s pineal gland. When days are long enough, or the lizard has been exposed to enough light (after a hibernation period or not), mating displays and behaviour begin. The displays by the males seem as important to egg production as anything else for some species. Of course, some species of lizard reproduce parthenogenically, so as I said before, no blanket statement made is valid in all cases.

Temperature, food abundance, light levels, and probably a host of other environmental factors tell reptiles when it is best for them to breed. Reptiles who are not in synch with their environment or the other members of their population tend to not be genetically represented in the next generation.

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
“You cannot reason a man out of a position he did not reach through reason.”

And mäni interesting furry animals

I’m sure I could get better results by reading any zoology text, but what exactly is meant by ‘cold-blooded’?

I mean, any metabolic process is going to generate heat as a by-product. Are lizards just not well insulated? Are their digestive processes more efficient than mammals? What gives?

I’m not a zoologist, but here are the very basic basics:
Cold blooded creatures have their body temperature regulated by external heat sources (the sun etc.). Everything they metabolise is used up on running around.
Warm blooded creatures use body chemistry to regulate and generate body temperture.
I’ll leave anything more complicated to a professional.

I once lost my corkscrew and had to live on food and water for several days
(W.C. Fields)

Mammals don’t necessarily geneate heat on purpose. Heat is generated as a by-product of any chemical or nuclear reaction. It is decay, it is the death of the universe, bleah bleah. Why don’t lizards benefit from it?

Because most animals are not as wasteful of their energy as birds and mammals are. Every other type of animal uses the energy they get from their food for the purposes of motion, reproduction, and other things of immediate benefit. If they need to be warmer, they move to a warmer spot. If they need to be cooler, they move to a cooler spot.

Mammals have had to develop all sorts of complicated plumbing to dump the waste heat generated by their overactive metabolisms. That adds more overhead to their systems and makes them so much less efficient than reptiles of the same mass. Birds have an air-cooled engine whose passages are as complex as the water-cooled mammal plan.

Asking why herps have kept their system simpler isn’t a question that will give interesting answers. Asking what benefits mammals get from their over-engineered system might be the better question. Remember, reptiles outnumber mammals at least two to one in therms of species, and even higher in terms of individuals. Their more efficient metabolisms can support a higher concentration of individuals in any given environment that meets their needs.

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
“You cannot reason a man out of a position he did not reach through reason.”

And mäni interesting furry animals

A cord of well seasoned dried anoles contains about 35 BTU. I suggest oak. Many tropical reptiles do not have a seasonal reproductive cycles,ot at least not based on temperature so much as availability of food, water,etc. A lizard that eats banana bugs would have a cycle based on the banana cycle. Then there are some reptile ‘cycles’ that are just based on the general physical condition of the individual reptile. Sea turtle cycles are influenced by tide cycles. I have had a pair of king snakes breed in the winter,in an outside cage but heated with a light bulb that burned 24 hrs. It probably screwed their rythums up ( king snakes are Catholic) I have had lizards breed out of season too, but they were horney toads so it was to be expected.

“Pardon me while I have a strange interlude.”-Marx

Actually, the terms “warm blooded” and “cold blooded” are rather over-simplifications. I’ve read in Discover that contemporary vertebrates employ some 12 different forms of thermal regulation, from “classic warm bloods” (humans et al who keep a constant body temperature no matter what); “variable warm bloods” (usually desert species that maintain a body tempurature, but allow it fluctuates quite a bit over the course of the day); “mass homeotherms” (rilly, rilly BIG critters who generate plenty of heat just by moving their muscles); those that huddle together for warmth; those that shiver; various other approaches; and those who use several strategies.

There are even “warm-blooded” fish (tuna and I believe one of the billfish).

But the OP was about mating cycles (oh, THAT kind of “heat”…)

Let me clarify. I’m aware of only two types of fertility cycles in mammals: the estrus and the menstrual. Almost all mammals have an estrus.
Perhaps a better statement of the question would be: What is the reptile analog of this cycle? Does it have a name ? If there is none, that is interesting, from an evolutionary point of view. Is it connected to homeothermy?

Being warm-blooded allows A) various systems to be tuned for maximum efficiency and B) continued activity under hostile conditions. In a cold environment, a mouse is more likely than a lizard to die of hypothermia, but a lizard is more likely than a mouse to be too torpid to escape a predator. In a hot environment, the lizard must find shade, while the mouse can choose between finding shade or water.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

I know from personal observation that the reproductive cycles of Great Green Iguanas (iguana iguana) are not determined by temperature, light or food supplies. These critters become active breeders from December through March. This makes sense in their native environment, the Southern Hemisphere. However, captive green iguanas in North America maintain the same breeding cycle. During the North American winter, females lay eggs, fertilized or not, and males become more aggressive while displaying brighter colors.

One would think that iguanas kept in the north from hatching would develop a reversed breeding pattern. Apparently, their nature is too primitive to adapt to an environment different from that in which they originally evolved.


Is there a Herptologist in the house?

Actually, tymp, it may just be that we do not yet have very many iguanas that have actually been bred in the Northern Temperate zone. With the current trade bringing in several thousands of the critters each year, (the vast majority of which never live the three years necessary to reach sexual maturity), there really are not very many northern-bred iguanas and even fewer multiple generation northern-bred iguanas. I don’t claim that there are none, but I suspect that it is still a pretty small number.

(To the general readership: unless you want a 5-foot long lizard with an attititude in your house and are prepared to provide sufficient living space for it, please do not buy an iguana. Go for geckos, dragons, or anoles. The majority of iguanas that are imported die from (ignorant, not malicious) mistreatment. You cannot keep your 10 inch iguana at 10 inches without starving it or keeping it confined in a too small cage or both.)

(Iguanas, BTW, do have an estrus cycle and a few male iguanas have actually been noted responding to the hormonal cues from the human menstrual cycle.)


I would add that watching a fifteen pound lizard make advances towards my girlfriend while giving me the head-bob / push-up combination (Ig. equivalent of “the finger”) is a really fun, surreal experience.

Tom, I must concede that you are most likely correct. I’ve never actually met a confirmed second or third generation North American Ig.

Note to self: Think, THEN post.

tymp, I don’t think your question was ill-considered. Most herps are captive-bred these days (finally) and only the huge import business in iguanas (combined with ill-informed owners killing them off) actually results in the propensity of first-generation iguanas. It’s not as if we go to herp shows and see lots of breeding lines posted à la dog or horse shows–with all of them ending immediately above the animal being displayed when it’s an iguana.


I’m sorry sir, but I must question your credentials. You know entirely too much about this matter, and I therefore call you on your claim of “Charlatan.”

Cease and desist this masquerade!

Mr. Dobalina. Mr. Bob Dobalina.
“Never mind the furthermore, the plea is self defense.”

Pretty big talk for a Monkees fan…

Oh, and welcome to the board, “Bob”.

So if DrFi makes claim to the title Charlatin,but it turns out he is NOT a charlatan…
Hmm ,are there ‘above average’ lizards?

“Pardon me while I have a strange interlude.”-Marx

There are in Lake Wobegon. All of 'em.