That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information

I grew up “knowing” green iguanas to be largely arboreal lizards of thickly-forested habitats.  In time, I was able to confirm that impression by observing them high in the canopy of a Costa Rican rainforest, and in the tall trees of Tortuguero Island, Costa Rica…where, in accordance with what I had read, they dove into the river when disturbed.

So I was quite surprised, upon arriving in Venezuela’s flat, largely treeless llanos, to find these flooded grasslands well-stocked with the huge lizards.  I was there to study green anacondas (also a surprising find, given my past impressions, but we eventually tagged over 500) but found it impossible to limit my attention to them, so overwhelming was the diversity of wildlife.

The green iguanas grazed on the flat, treeless terrain like so many cows…in fact, they were often among cows, as much of our work was on a cattle ranch.  When threatened (i.e. by me trying to catch one), they took off at incredible speeds and dove into the water.

One stout brute of 5’11” in length (please see photo showing side-view) absolutely refused to enter the water when he reached its edge.  He held his ground, thrashing his tail (please see photo showing cut left on my arm by a smaller animal’s tail) and lunging at me.  Once subdued, I was able to see that he had numerous old wounds that had likely been inflicted by piranhas, and was missing several toes.  Perhaps his stretch of the river had a particularly aggressive piranha population, and he preferred a battle on land to another swim!

I’ve included a photo of typical iguana habitat in Venezuela’s central llanos country, to perhaps show you why I was so surprised to find the lizards there (the creatures in the foreground are capybaras, world’s largest rodent).  Also included is a photo of another reason that an iguana might choose to run or fight rather than swim – a huge green anaconda basking at the surface.

Today we can see ample evidence of the green iguanas’ adaptability right here in the USA – feral animals live in areas ranging from beaches to suburban gardens throughout south Florida!

Detailed information on green iguana behavior and typical habitats is posted by the Green Iguana Society at:

http://www.greenigsociety.org/inthewild.htm

Recently I wrote about some exciting information that has recently come to light concerning the effectiveness of Zoo Med UVB lamps (please see my article Product Review: The Zoo Med Reptisun 10.0 High Output UVB Lamp and 5.0 UVB Lamp, Part I and Part II for further information).

One drawback inherent in all UVB lamps (bulbs) is the fact that the lamp will continue to burn brightly long after its UVB output has declined or even ceased.  To further complicate matters, the effective life varies from model to model, and among different manufacturer’s lamps.

Zoo Med has recently introduced a service wherein customers are reminded of lamp replacement dates via email.  Lamp purchasers register the purchase date, model, terrarium type and species kept…based upon this information, the company determines the ideal time to replace the lamp and sends an email notice as that time approaches.  Advances in technology that affect lamp life will be incorporated into the system.

A tip: if you have a large collection, you may wish to invest in a small UVB meter.  UVB output and useful life can vary even among lamps manufactured by the same company.  Actually monitoring UVB production will allow you, in some cases, to leave a lamp in place after its usual expiration date.  Also, once UVB output has declined, you can move the lamp to a situation where it can be placed closer to a basking site or perhaps use it for a species that has lower UVB requirements.

You can read about Zoo Med’s new program at:

http://zoomed.com/Join/UVBSignup.php

Click here: The Natural History and Captive Care of the Mexican Axolotl, Ambystoma mexicanum: Natural History – Part 1, to read the first part of this article.

Diet
Mexican axolotls feed upon shrimp, aquatic worms, copepods, insects and other invertebrates and small fish. Adults are major predators upon small axolotls and axolotl eggs. The larvae are largely carnivorous, but may consume some algae as well.

Their main predators are herons and other wading birds, fishes and larger axolotls.

Reproduction
Males deposit spermatophores (sperm-filled capsules) on the lake bottom from March through June. After nudging the cloacal region of a gravid female – and being nudged in return – the male undulates his tail in front of her, most likely releasing pheromones (chemical attractants) in the process. He then leads the female over the spermatophore, which is taken into her cloaca. Fertilization occurs internally. The eggs, 100-300 in number, are laid after a gestation period of 2 weeks. They are attached to aquatic vegetation and hatch in 10-14 days.

The young reach sexual maturity in approximately 18 months. The Mexican axolotl is a paedormorphic (or neotenic) salamander, meaning that it retains a number of larval characteristics, including external gills (adults have lungs as well) and an aquatic lifestyle. Animals injected with the thyroid gland hormone thyroxin will transform into terrestrial adults, but do not survive for long.

Economic Importance
The Mexican axolotl is an ideal laboratory subject, and quite important in medical research. Studies of it have led to important advances many fields, including gene expression, neurobiology and limb/organ regeneration.

Axolotls possess a greater facility for regeneration than do most amphibians, and can re-grow limbs, digits, gills, tails and portions of the liver, spleen and eye. This ability may have important implications for people, and has been under investigation for some time.

Miscellaneous
Nearly all axolotls in captivity today can trace their origins to specimens collected from Lake Xochimilco and shipped to Paris in 1864. Three aquatic salamanders in the Genus Ambystoma have historically shared this species’ habitat, and it is believed that hybridization with these occurred at the time of that original collection. Current lab and pet populations may, therefore, differ genetically from wild axolotls.

The axolotl is closely related to the tiger salamander (A. tigrinum), and hybrids are fertile. Tiger salamanders also exist in neotenic form in certain populations. There is evidence that the animals forming the basis of today’s captive stock have interbred with neotenic tiger salamanders.

The name “axolotl” is taken from that of the Aztec god Xolotl, who was believed to have taken on the animal’s form, and loosely translates to terms such as “water dog”, water sprite”, “water slave” and “water monstrosity”.

I have written articles about axolotl relatives as well. Please see:
The Spotted Salamander, Ambystoma maculatum – Part I and Part II
Algae and Salamander Eggs – an odd partnership

The abstract of an International Zoo Yearbook article detailing the use of the axolotl as a “flagship species” for the conservation of its habitat is posted at:
http://www.ingentaconnect.com/content/bpl/izy/2008/00000042/00000001/art00014;jsessionid=1hpc0rtn02l2l.alexandra?format=print

Relatively scarce in the pet trade when I first began in the field (admittedly quite awhile ago!), interest in the Mexican axolotl has exploded in recent years, and today it is arguably the most commonly-kept salamander in the USA. Its popularity has soared in other countries as well, and oddly enough, it has become somewhat of a pop culture figure in Japan.

The Mexican axolotl has the rare distinction of being simultaneously one of the world’s most highly endangered amphibians (in the wild) and a common pet and laboratory subject.

Please note: the aquatic larvae of all species of salamanders are termed “axolotls” in some references, i.e. as in “tiger salamander axolotls”. The name as used here refers to young and adult Ambystoma mexicanum only.

Classification
Class: Amphibia
Order: Caudata
Family: Ambystomatidae

A complex of a dozen or more related aquatic salamanders dwell in mountainous lakes in the vicinity of this species’ range. The waters inhabited by one of these, the Lake Patzucuaro salamander (A. dumrelii), are high in dissolved salts. Perhaps as an adaptation to its brackish environment, this salamander sheds its outer skin layer continuously throughout its life.

The family Ambystomatidae, limited to North America, contains approximately 40 terrestrial and aquatic members, including such well known species as the tiger salamander (A. tigrinum), marbled salamander (A. opacum), spotted salamander (A. maculatum) and Pacific giant salamander (Dicamptodon ensatus).

Physical Description
The Mexican axolotl is stoutly built and reaches 9-12 inches in length. The head bears large, bushy red gills and the laterally compressed tail is equipped with a swimming fin. Wild specimens are dark brown in color; albino, leucistic, black and piebald strains are common in laboratories and the pet trade.

Range
This species’ entire natural range is limited to an area of 6.2 square miles in size. It is native only to Lakes Chalco and Xochimilco, adjacent to the southern edge of Mexico City, in central Mexico.

It appears now to survive only in a small fragment of that tiny habitat – the southern remnants of Lake Xochimilco, and perhaps within associated canals and private garden ponds.

Habitat
The Mexican axolotl is entirely aquatic. The high-altitude lakes it inhabits are deep, heavily-vegetated, mud-bottomed and cool in temperature. Axolotls can extract oxygen from air or water, utilizing gills, lungs and skin.

Status in the Wild
This salamander is extremely rare in the wild, and is considered to be among the world’s most endangered amphibians. Recent surveys in its tiny natural range have turned up only 0-42 specimens, despite 1,800 net casts.

Lake Chalco has been largely drained, and no axolotls survive there. Lake Xochimilco has been severely polluted and impacted by flood control measures, and is extensively channelized to accommodate “floating gardens” of flowers and vegetables.

Protected by the Mexican government and listed on Appendix 2 of CITES, Mexican axolotls are none-the-less still collected for the food and medicinal trade, and are also threatened by large populations of introduced fish (Tilapia and carp).

Click: The Natural History and Captive Care of the Mexican Axolotl: Part 2, To read the 2nd half of this article.

Recently I posted an article about native treefrogs in my own collection: My Animal Collection: How a Herpetologist Keeps Barking Treefrogs (Hyla gratiosa) and Gray Treefrogs (Hyla versicolor). Today I’d like to add some thoughts on another US native, the very attractive green treefrog. Please see my earlier article for detailed information on treefrog care.The green treefrog is so often collected for the pet trade, and so inexpensive, that many here take it for granted. It is, however, one of the most beautifully colored of the word’s Hylids, and much favored by hobbyists in other countries.

Feeding Tips
Green treefrogs top out at 2 ½ inches in length, and are slender in build. I’ve found that they do best when given only small insects, the size of a ¼ to ½ inch cricket, despite their willingness to tackle larger prey. I suggest that you avoid adult crickets, large waxworms and the like, as they may be too much for this species’ digestive system to handle on a regular basis.

Perhaps due to their arboreal nature, these frogs react very strongly to flying insects. The feeding response is quite dramatic when I offer them moths and small flies, and noticeably different than their reaction to crickets and waxworms. Small wild-caught insects (Zoo Med’s Bug Napper is an excellent trap) should be given regularly. Most green treefrogs feed readily from plastic tongs….canned silkworms are an excellent addition to the diet. These frogs are persistently arboreal, so burrowing insects such as small butterworms and waxworms should be placed in cups suspended from tree branches, or hand-fed.

Green treefrogs are accomplished jumpers, and adept at snatching insects on the wing. At feeding time, a group I housed in the Bronx Zoo regularly stole the show from their somewhat sedentary exhibit mates – a pair of water moccasins!

Captive Breeding
Unfortunately, little attention is given to breeding this spectacular frog in captivity. Males in the zoo group I mentioned began calling in response to increased showers, but the females did not respond with eggs. As most green treefrogs in the trade hail from Florida and Louisiana, a dry period followed by frequent misting and a rise in temperature of 5-10 F might do the trick.

You can learn more about the natural history of the green treefrog at:
http://www.natureserve.org/explorer/servlet/NatureServe?searchName=Hyla+cinerea