Rigor Vitae: Life Unyielding

Thursday, January 17, 2008

TYRONE HAYES COMES TO TOWN

You know Tyrone Hayes, the biologist from UC Berkeley who's been studying the effects of the weed-killer Atrazine for years.
Over 60 million pounds of Atrazine are applied to the United States every year. It is the herbicide of choice among corn farmers. It's persistent in soil and water, and acts as an endocrine disrupter. Hayes has shown that very low levels of the chemical can and do feminize male Northern Leopard Frogs (Lithobates=Rana pipiens), turning them into reproductively functionless hermaphrodites, both in the lab and in the wild. He's also tied Atrazine to an increased susceptibility in frogs to limb deformities caused by the trematode Ribeiroia ondatrae. These effects occur at levels far below the EPA standard of 3ppb.

Hayes' work has been harshly criticized, and reams of dodgy literature discrediting his work exists, all of it based on the research of Ecorisk, which is funded by Syngenta, the manufacturer of Atrazine.

Dr. Hayes will speak this afternoon at 4pm at the Skaggs Biology building on the campus of the University of Utah.

UPDATE: Back now from the lecture--I give it five stars. If Dr. Hayes comes to your town, don't miss him. He's a far better speaker than any other endocrinologist I've ever met. He's quite inspiring and has a lot to say about some very important issues. If he's not coming to your town, watch his lecture on Youtube.
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illustration: SOUTHERN LEOPARD FROG & TRICOLORED HERON (2000) acrylic 13.5" x 9"

Sunday, January 13, 2008

A SERPENT'S TAIL


Those of us from certain parts of North America tend to take rattlesnakes for granted, rarely bothering to appreciate how fantastic they really are. They comprise about 50 species, in two unique American pitviper genera, all with tails that are tipped with a series of complex, interlocking, cornified scales, completely unlike anything else known to have been evolved by snakes—until very recently, anyway. These reptiles are not only specialized at their very tips; the musculature of the tail itself is dominated by three pairs of “shaker” muscles, two of which produce lateral, back-and-forth movements, while the third pair applies torsion, drawing the ventral edge of the rattle outward to either side. The fibers of these muscles are rich in mitochondria, sarcoplasmic reticula, capillaries and glycogen, and capable of sustaining the high respiratory levels necessary to vibrate the tail as rapidly as 100 Hz. for as long as an hour at a time. These speeds are comparable to the oscillations of sphingid moth wings. Among vertebrates, only the hummingbirds (family Trochilidae) can vie with the rattlesnakes in this respect.The rattling system's main function is to warn away dangerous animals like predators and large grazing animals, although in some of the small Sistrurus species, it is only audible at close range, and appears to be of little use in this area. I've never witnessed a wild ungulate or carnivore interacting with a rattlesnake, but have many times seen how effective rattling is in deterring domestic analogs like dogs and horses. Whatever the first proto-rattlers used their tails for, they probably enhanced an already existent behavior. Similar tail movements are exhibited in snakes of many species, in many unrelated taxa. Tail-thrashing of various forms can be a prelude to battle or mating, or a means of evading predators. Some fossorial boids like Calabar Pythons (Charina=Calabaria reinhardtii) and Rubber Boas (C. bottae) wave their blunt tails about while hiding their heads (see photograph here). Some elapids, like the Langsdorff's Coralsnake (Micrurus langsdorffii) pictured above, confuse the enemy by moving both ends simultaneously. Many snakes, including some vipers, vibrate the tail defensively. When doing so against dry vegetation, the resulting sound is not unlike a rattler's. Defensive tail-shaking colubrids, like the Common Racer (Coluber constrictor), lack the specialized tail musculature, and cannot sustain the motion more than several seconds, but the tail muscles of the Copperhead (Agkistrodon contortrix), a close cousin of the rattlesnake, have a significantly elevated respiratory capacity. The traditional view of rattler evolution posits that rattles evolved to enhance this behavior, and, since the earliest-known rattlesnake fossils were found in the American Great Plains, it's tempting to visualize the first rattler warding off vast bison herds like in the painting up top. Genetic mapping, though, strongly suggests that rattlesnakes first evolved in America's southeast, severely shaking this attractive theory.

A third form of tail movement is caudal luring (see video here), a not uncommon behavior in vipers and a number of another snake taxa. It is possible that the earliest rattlers drew potential prey within striking distance by writhing and twitching a simple rattling tail appendage. Caudal luring is practiced by some of the earlier mentioned Sistrurus rattlesnakes, particularly the young ones; in fact, in many of the Crotalus spp. as well, the rattle could function more as a caudal lure in hatchlings, which can't produce sounds until their first shed. Concurrent with the young snakes' diet shift from ectotherms to mammals is the rattle's increased effectiveness as a sounding device, and the fading of bold colors and patterns on the tail. Both caudal luring and defensive tail-shaking are behaviors seen in the Copperhead.


A new species of viper sheds a bit of new light on the subject. Pseudocerastes urarachnoides was described just over a year ago, from two specimens collected in Iran (a pdf is available here). The holotype, an adult male (above, top), was collected in 1968 and deposited in Chicago's Field Museum. At the time, it was identified as a Persian Horned Viper (P. persicus), but its tail bore a strange appendage resembling a small solifugid (below). This Linkwas assumed to be a tumor or other aberration, until a second specimen, a young male (above, lower), was collected in 2003.

The tails of both specimens were carefully examined, and confirmed to be normal and uninjured. The assumption is that these structures are caudal luring devices, although so far, nothing is known of the species' behavior, and caudal luring has not to my knowledge been observed in the other two Pseudocerastes spp (--update--a video of the tail appendage can be seen here. The stomach of the paratype contains a partially digested, unidentified passerine bird. Latifi's Snakes of Iran lists P. persicus' diet as consisting of mice and lizards. Since the female P. urarachnoides is unknown, it's anybody's guess whether or not this tail appendage is a sexual characteristic. Both specimens were preserved in formalin, and their tissues were deemed to be unsuitable for molecular analysis. We can only hope that live specimens will be found and observed. If these hopes are realized, surely they will give us insight into the evolution of their distant cousins on the other side of the northern hemisphere, as well as into the nature of all life.
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upper: PRAIRIE SENTINEL--PRAIRIE RATTLESNAKE (2002) acrylic 40" x 15"
middle: LANGSDORFF'S CORALSNAKE AND BLUE-CROWNED MOTMOT (2008) acrylic 15" x 20"
lower two: Photos of P. urarachnoides taken from BOSTANCHI et al : NEW SPECIES OF PSEUDOCERASTES FROM IRAN. Proceedings of the California Academy of Sciences, ser 4, 57(14): 443-450 figs 1-4, 8-9

Monday, January 07, 2008

SO LONG, ROCKY...FOR NOW


Rocky Anderson is out of a job today, as Democrat Ralph Becker begins his term as mayor of Salt Lake City, and even though I voted rather enthusiastically for him, I hold little hope for his ability to adequately fill the shoes left by his predecessor.

The headquarters of the Church of Jesus Christ of Latter-Day Saints (Mormons) has a somewhat undeserved reputation as a bastion of right-wing thought, and indeed, Utah gave George W. Bush a greater percentage of our vote than did any other state. In the 1992 presidential election, we were the only state that lavished fewer votes upon Bill Clinton than H. Ross Perot. Still, forward thinking does have a place in Salt Lake City proper, and nowhere has that been more evident than in our election of our outgoing two-term mayor, one of the country's most liberal. When the Bush administration eschewed the international Kyoto protocols, Anderson committed Salt Lake City to abide by them, surpassing those goals last year, seven years ahead of schedule. He's been an effective cultural leader, using his bully pulpit to spread the gospel of sustainable living to a populace that, frankly, thought little of it ten years ago. In the late '70s, the city ticketed me for replacing my lawn with a garden of native plants. Today, one can see xeriscaped yards on nearly every block of street in this desert metropolis, and Rocky deserves a good share of the credit. He's worked to make the city more walkable and bikeable, and has been an ardent supporter of minority and gay rights and of the arts. Over the past two years, he's gained national notoriety as vocal critic of the current White House, organizing demonstration rallies, circulating impeachment petitions, and debating such high-profile opponents as Bill O'Reilly and Sean Hannity.

Mind you, Rocky's no saint. He's an egomaniac and a bully. He tends towards self-righteousness and snivelry. He's even made me feel slightly embarrassed, a time or two, but far more often, it's been pride he's made me feel within, and that's something I can say of far too few elected officials.

Last July, Rocky announced he would not run for a third term as mayor, and he's been a bit coy about future plans. He implies that his immediate future will be in grass-roots organizing, but a retreat from the limelight couldn't be anything but frustrating for him. He's far too liberal to win a state-wide office, and the office of junior congressman seems as far from the limelight as anything. It's hard to imagine exactly what the future holds for Rocky Anderson, but it's a safe assumption that he'll continue to be a surprising and entertaining force for positive change.

Friday, January 04, 2008

Bd IN THE YEAR OF THE FROG


It seems like only yesterday that I promised to post part two of my overview of Bd, aka Chytridiomycosis, the fungal disease that is blamed for much of the amphibian carnage that distresses so many of us today. I fully expected that post to materialize a month or so ago, but events irrelevant to this discussion prevented that. Be that as it may, a late appearance as the first post of 2008 is appropriate, since a consortium of international conservation organizations has deemed this the “year of the frog,” in an effort to raise awareness of the catastrophic situation, my first whiff of which occurred in the spring of 1973, when I witnessed seemingly healthy populations of Northern Leopard Frogs (Lithobates=Rana pipiens) failing to wake from their winter torpor.

Whether Bd played a role in that dramatic crash is hard to say, but the recent extinctions of around 122 anuran species are being blamed on it. This flies in the face of conventional ecological dogma, which states that a pathogen cannot directly cause the extinction of a host species, since transmission is density-dependent: as the host population declines, so does transmissibility. The pathogen in this case, the fungus Batrachochytrium dendrobatidis, seems to persist in waters long after all frogs have died. Presumably, alternate hosts that aren't susceptible to the disease serve as reservoirs, but so far, no such hosts have been discovered. In my earlier Bd post, I discussed our current state of knowledge, which is so incomplete that designing a plan to thwart it is difficult. What we do know is that Bd does best in cool temperatures, under 27ºC. It is killed by drying or by prolonged exposure to temperatures over 30ºC. Even so, warming can have unpredictable results. Alan Pounds, who has been studying the cloud forest ecology of Monteverde, Costa Rica for decades, has chronicled a warming and drying trend there which has shrunk the available habitat for cloud forest species, crowding the population, and, he posits, increasing Bd transmission. This is the same forest where the famous Golden Toad (Bufo periglenes) mysteriously vanished 30 years ago. Crowding of frogs in breeding ponds has been shown to be important in the spread of Bd. In western North America, Male Boreal Toads (Bufo boreas) spend 2-3 weeks in breeding ponds each spring, while the females spend less than 24 hours there. The males always succumb to Bd long before their mates do. Northern populations of this species are rather tolerant of Bd, while some others are highly susceptible. Bd appears to have extirpated the species from New Mexico, and in Colorado, Wyoming and Utah it is considered endangered. Similar mysterious variation in Bd resistance appears in different populations of Columbia Spotted Frogs (Rana luteiventris) here in Utah. Perhaps the difference is behavioral. Perhaps it's a difference of antimicrobial skin peptides or microbiota. It's been suggested that the acquired resistance among individual frogs that have been cured of Bd could be attributable to evolution of probiotic skin microbes. Pseudomonas reactans, various Lysobacter spp., and other bacteria that occur naturally on the skin of some frogs have been shown to prevent Bd infection. The introduction of such microbes to infected waters has been proposed as a means of controlling Bd.

In California, the two species of Yellow-legged Frog, Rana muscosa and R. sierrae have suffered 96% and 92% declines, respectively, although agricultural toxins must bear substantial blame for this. The beautiful Neotropical stub-footed toads (Atelopus spp.) have been hit particularly hard; it's estimated that 67% of the 110 species, many of which were abundant, have been wiped out. The World Association of Zoos and Aquaria has initiated an effort, christened the “Amphibian Ark” to captively propagate frog species imperiled by Bd. A number of species extinct in the wild, including the well-known Atelopus zeteki, are currently being bred in zoos. Less hopeful is Australia's iconic Corroboree Toadlet (Pseudophryne corroboree - above). Probably extinct in the wild, nearly 5,000 of these frogs linger in captivity, as herpetoculturists vie to be the first to get the species to breed. Hopes for reintroducing them to their small former range in the Australian Alps are faint, since the entire region is rife with Common Eastern Froglets (Crinia signifera), nearly all them carriers of Bd. A few other interesting victims of the fungus include the two Australian gastric-brooding frogs (Rheobatrachus spp.), which died out in the 1980s, and Tanzania's Kihansi Toad (Nectophrynoides asperginis), whose population went from 18,000 to undetectable during the summer of 2003. Bd can threaten salamanders as well. It has been linked to die-offs of California Slender Salamanders (Batrachoseps attenuatus) and Hellbenders (Chryptobranchus alleganiensis). In the latter species, a grisly communal infection of Bd and the bacterium Citrobacter freundii destroys the digits and limbs before killing the host.
Bd cannot be eradicated, but a few things can be done, including:

1.Research. A better understanding Bd's biology is imperative; how it moves geographically and spreads, the nature of Bd resistance, and an understanding of how it kills its host, if indeed it does, and how its aetiology is affected by environmental toxins, other pathogens and parasites, etc.
2.Prevent further spread and reduce impact. Of particular interest are regions of great frog diversity and endemism, as well as habitats of the most basal frog species. So far, Bd does not appear to have reached Madagascar, an island with well over 200 endemic frog species.
3.Promote recovery of threatened species, including captive breeding, restocking of populations, and cryopreservation of gametes. It is possible to cure individuals of many species infected with Bd. Itraconazole baths have been the preferred treatment for several years, although they adversely affect tadpoles and young metamorphs, and may cause kidney disease. Malachite green and benzalkonium chloride also have an affect on the fungus as does an elevation of temperature. Recent laboratory tests in New Zealand with the antibacterial Chloramphenicol have had very exciting results. This could quickly become the drug of choice.
4.Coordinate hygiene protocols for biologists and recreationists and quarantine strategies for import and export.
5.Spread the word to agencies and the general public.

For more information, visit the Amphibian Ark site, and while you're at it, sign their online petition.
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upper: ASCENSION--STRAWBERRY DART FROG & TADPOLE (2005) acrylic 40" x 15"
center: CORROBOREE TOADLET (1999) acrylic 7" X 7"
lower: PAINTED MANTELLA (2005) acrylic 9" x 7"