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Chemicals (pesticides, Atrazine, gonadotrophin) and Their Effects on Frog and Fish Sexuality and Reproduction

May 6, 2008 Comments Off on Chemicals (pesticides, Atrazine, gonadotrophin) and Their Effects on Frog and Fish Sexuality and Reproduction 4126 Views

download (2)Amphibians and fish are highly susceptible to even minute amounts of foreign chemicals in their habitats. As such, their current population declines should serve as an important “early warning signal”, forecasting problems that will eventually affect other animals and ourselves.

An odd twist to this sensitivity issue among frogs is that an injection of gonadotrophin, a human growth hormone, brings many species into breeding condition. This discovery was a boon to captive breeding programs, as most frogs require the duplication of certain environmental cues – dry or wet seasons, for example – if they are to breed normally. However, things can easily go wrong – while using hormones to stimulate breeding, I and others have noted that some male frogs began to develop organs resembling ovaries.

Now, male frogs in the wild are being found to have inter-sex characteristics, including immature eggs within the testes. A recent Harvard University study found such characteristics in 21% of the male green frogs, Rana clamitans, in ponds in suburban Connecticut. It seemed that the affected frogs were more common in suburban than agricultural areas, but other studies have yielded opposite results. Similar reproductive system changes have been documented among catfish in Africa, sturgeon in the Mississippi and other fishes.

Drainage_nitrates_vers_HondeghemFr_2003_04_09Pesticides, the herbicide Atrazine, and other chemicals commonly found in water and soil have been shown to affect sex hormone development, but much more research needs to be done.

There is a great deal of ongoing research in this important area – please read any related articles that you may come across and write in to share new information.

An article describing research into the effects of Atrazine on amphibians is posted at:http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1247376

The Natural History and Captive Husbandry of the Pancake Tortoise

May 5, 2008 1 Comment 6020 Views

Pancake Tortoise

Pancake tortoises are 1 of 53 tortoise species that inhabit Africa (where they reach their greatest diversity), North America (where 4 species reside), Europe, South America and Asia. Terrestrial and largely vegetarian, tortoises range in size from the Aldabra tortoise, Geochelone gigantea, whose carapace approaches 5 feet in length, to the speckled tortoise, Homopus signatus, which is fully grown at 4 inches.
Pancake tortoises, the sole member of their genus, possess a carapace (upper shell) that is flat or even sway-backed, and so flexible – a result of gaps between the rigid, bony plates – that it can easily be squeezed between thumb and forefinger. Colored yellow-tan with dark rings, the shell provides excellent camouflage. The limbs and tail are brown, tan or yellow-tan in color. Pancake tortoises reach 6-7 inches in length yet are merely 1-1 ½ inches in “height”. Their flattened profile strains our conception of what a tortoise “should look like” – one that came under my care was found wandering about Jamaica Bay Refuge in NYC (a released pet). A park visitor had rushed it to the ranger’s station – distraught over the plight of the animal, which he believed, understandably, to have survived being run over by a car!
This tortoise’s uniqueness does not end with its appearance – when threatened, it runs off in a most “un-tortoise-like” fashion and wedges itself deep within a rock crevice or below a boulder. The flatness and light weight of the shell and the highly flexible legs assist in this endeavor. Once within a crevice, the tortoise rotates its powerful forelegs outward to lock itself in place. It has recently been discovered that a flexible, diamond-shaped area on the plastron (lower shell) also rotates outward when the legs are withdrawn, rendering the animal even more immobile. Even this ingenious defense is not, however, foolproof – a species of hawk with very long legs has been observed lying on its side, snatching tortoises from within their shelters. Individuals rarely forage far from a favored retreat, and return un-erringly to specific rock fissures when displaced. Amazingly acrobatic, they can even climb vertical rock crevices by utilizing a maneuver similar to that known as the “chimney climb” among human rock-climbers – the carapace and legs are wedged against opposite sides of the crevice and, maintaining constant pressure, the tortoise inches its way upward.

Pancake tortoises are found only in southern Kenya and northern and eastern Tanzania, including within Serengeti National Park. Limited to rock outcroppings (kopjes) and rock ledges on savannas in areas of arid scrub and thorn-brush, they rarely cross open land. Therefore, the populations (which are quite dense, for a tortoise) near each kopje are more or less reproductively isolated, and local extinctions are easily caused by over-collecting. They forage for dry and growing grasses, leaves, succulents and seeds in the early morning, late afternoon and evening, and shelter in deep rock crevices during the heat of mid-day. Some populations aestivate during January and February, the hottest times of the year.
Pancake tortoises make fine pets, but extreme care should be taken to assure that you are buying captive bred animals. Over-collection for the pet trade has decimated their numbers, and their low reproductive potential and limited natural range puts the species at additional risk. They are classified as “Vulnerable” by the IUCN and listed on CITES Appendix II (under consideration for inclusion under Appendix I).
Click here: The Natural History and Captive Husbandry of the Pancake Tortoise to read the rest of the article.
The photo above is courtesy of Adam Darrenkamp of the Lancaster, PA Herpetological Society. They meet at the North Museum in Lancaster, PA.

Algae and Salamander Eggs – an odd partnership

May 2, 2008 34 Comments 9265 Views

Spring Peeper
Spring in the northeastern USA is prime time for amphibian watchers. Its arrival is most noticeably announced by frogs – first by spring peepers, Pseudacris crucifer and wood frogs, Rana (Lithobates) sylvaticus, with a succession of others following close behind. However, the season’s earliest greeters are silent. I have observed tiger salamanders Ambystoma tigrinum, move into breeding ponds during warm spells in late January (Long Island, NY).

Another amphibian that breeds in early spring is the strikingly marked spotted salamander, A. maculatum. Reaching 9 ¾ inches in length, these stout animals are jet black with yellow spots, and have been observed crossing snow during breeding migrations (I find them in ponds in southern NY in mid-March).

Amazingly, a species of green algae, Oophila amblystomatis, colonizes the spotteSpotted Salamanderd salamander’s globular egg masses. The algae most likely utilizes carbon dioxide and ammonia produced by the developing salamander embryos, and may in turn provide the embryos with oxygen (although the amount released is quite low). There is speculation that the algae may produce a growth factor that benefits the embryos, but more research is needed. In any event, experiments have shown that egg masses with this algae hatch faster, and with a higher survivorship, than do those lacking the algae. Conversely, algae growth slows markedly if the embryos are removed from the egg mass upon which it is established.

Spotted salamanders make interesting pets, and, while adapted to a burrowing lifestyle, adjust well to life above ground. Properly cared for, they can live for over 25 years. I will discuss them further in a future article.

More detailed information on this unique relationship is available at:
http://jeb.biologists.org/cgi/reprint/197/1/17.pdf

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