Saturday, February 25, 2012

Only one individual of gliding frog species remains

When I was a kid, I often used to check out library books about animals, including species that have been driven to extinction in human history, usually by humans and/or the damage and foreign species they introduce into an ecosystem.

This still happens on a regular basis. Rabb's fringe-limbed tree frog, one species of frog known to be able to glide from the treetops using its enormous webbed toes, is just the most recent example that I've noticed on one of the Scientific American blogs, Extinction Countdown.
` The reason for the update is because one of the two remaining individuals has died, although, since the other one had been a male, it didn't make much of a difference anyway. In other words, the species is already doomed, assuming no more are discovered in the wild.
` As Rabb's fringe-limbed tree frog is only known from the mountain slopes above the town of El Valle de Anton, in Panama, and has actually evaded biologists's awareness until 2005, this doesn't seem very likely.

In lieu of a photo, here's a brief video PSA from Atlanta Zoo that shows the future of this species -- assuming another population is not discovered in the wild:

The pathogen the video refers to is called amphibian chytrid fungus (Batrachochytrium dendrobatidis), which has been causing the extinction of many amphibian species of South America since 2006, and seems to have been responsible for the extinction of more than a hundred species worldwide in the past several years.
` Rabb's fringe-limbed tree frog, identified only in 2005 and named after George and Mary Rabb (two amphibian conservationists of some note), has not been seen in the wild since 2007 despite much searching -- apparently, they were discovered at the last moment!

It's the kind of thing that makes me wonder about what species must have gone extinct without biologists ever having managed to find them.

The now-dead frog was euthanized at its home in Zoo Atlanta because its health was deteriorating rapidly, and because frog corpses also deteriorate rapidly, and the researchers needed to be sure they were present at its death in order to preserve its body.
` I wonder what sorts of mixed feelings must have gone through the head of the person who ended that frog's life?

According to the press release and the zoo's website, the other frog lives nearby in Atlanta Botanical Garden -- hey, what are the chances of that? I'm guessing that both frogs were transported to Atlanta in possession of Zoo Atlanta's herpetology curator Joseph Mendelson after his 2005 expedition.
` He's also the one who later named the species Ecnomiohyla rabborum, and has named 30 other amphibian and reptile species as well.

According to the Atlanta Zoo's web page on this species (which has not yet been updated), the male would guard his tadpoles in a hollow tree and actually feed them with flakes of skin from his own body. It says, "No other frog in the world is known to do this." Neat! All's we need is a female...
` Of course, even if there were a female, the offspring would have to 'commit' incest in order to keep the species going, thereby creating severe inbreeding depression. It is doubtful that could go on for long since genetic diversity is what keeps defective alleles from racking up and causing all sorts of unpleasant mutations.

According to Zoo Atlanta's press release, this zoo actually has many species of extremely rare amphibians, and that its researchers are among the hardest-working in the fight to keep the world's critically endangered amphibian species alive. Even so, they can't always win:
“This is the second time in my career that I have literally seen one of the very last of its kind die and an entire species disappear forever with it. It is a disturbing experience, and we are all poorer for it,” said Dwight Lawson, PhD, Deputy Director. “The ongoing amphibian extinction crisis has taken a rich diversity of animals from us, and more effort and resources are desperately needed to halt the losses.”
Because I am moved by Lawson's words, I am quite perplexed that some people I've talked to in my life just don't care about whether or not a species goes extinct -- not even the cute, fluffy ones like pandas!
` The way these people see it, other species have had their chance to survive, and if they look like they're going extinct, then that's the way it should be, and if that species' extinction causes yet other species to go extinct, then they 'deserved' it for being so interdependent.

Somehow I don't think they would say that if they lived during the population bottleneck which reduced human genetic diversity before we had even left Africa: Compared to most species, our gene pool is tiny, and we may have once even been an endangered species ourselves!
` If we had gone extinct then, the African animals would have appreciated not having spears flung at them, and perhaps the Neanderthals would have been the ones to survive. What would a Neanderthal paleoanthropologist have thought of us? Here's a clue:
` Having a great appreciation of the universe, a scientist of any kind would probably never look at Neanderthal remains and just say, "Oh well, they had their chance to survive!" Instead they would say, "We're a bit late to study this species and will never know if they had language like ours, what their culture was really like in detail, and what else they were mentally and/or physically capable of." This is generally regarded as a big bummer.

Tree frogs, or pandas, don't have language or culture, and so perhaps don't seem as interesting as would a species (or at least subspecies) very like us, but to someone whose passion is studying the history of the living world, the complexity of a species hardly matters. Thus, the loss of any species, since no one would ever have a chance to see (much less study) it again, would be hard to take.
` Even if an ecosystem can deal without a certain species, biologists still need them in order to understand, for example, its own unique characteristics, and how it is related to other species both biologically and ecologically: When learning about the world, there is always more.
` As Mendelson put it in the press release, “Had the frog passed away overnight when no staff members were present, we would have lost any opportunity to preserve precious genetic material. To lose that chance would have made this extinction an even greater tragedy in terms of conservation, education and biology.”

Every piece of the puzzle counts for something.

And what caused the B. dendrobatidis fungus outbreak, anyway? Did humans have anything to do with it? First, I looked at a couple of primary research articles about Bd epidemiology -- the study of how the epidemic spreads -- and didn't find any clues as to how it started.
` Then, I found this website called Bd-Maps, which tracks the spread and prevalence of the disease all over the world. Wow -- this disease must be huge!
` That website led me to the Bd-Maps blog, and then to the Thoughtnomics blog post Frog-killing fungus is a skin-loving hybrid, by Lucas Brouwers, who has combed through a lot of the primary literature himself.
` It shows, he says, that this fungus' closest relatives are known for decaying dead plant matter and other organic substances. Somehow, this species has adapted to the skin of frogs quite recently.
"Bd only became a problem somewhere in the second half of the twentieth century. Analyses of museum skins show that Bd was absent from most affected localities prior to the 1970s. It has spread over the world at an alarming rate since then, killing frogs, salamanders and newts wherever it goes."
Holy cats! The article goes on about Bd's unusual genes, before getting to exactly why it's killing amphibians at such an alarming rate. Apparently, there are some strains that seem to have been around for a long time, yet aren't so deadly.
` Since fungi have two sets of chromosomes, as we do, and since there is such wide variability that it could have gotten each chromosome from a different species, it may be that Bd is a hybrid:
“The simplest explanation for this pattern is that the hypervirulent lineage of Bd is the product of two undiscovered parents”, says Matthew Fisher a geneticist from Imperial College London and co-author of the PNAS paper. In other words, the killer lineage of Bd is a hybrid fungus. It has received two different sets of chromosomes from its parents, which explains the high degree of heterozygosity in its genome. “Sex is rare for this species. But when it happens, a new strain with new properties might emerge”, says Fisher. “We think this is how hypervirulent Bd originated, somewhere in the 20th century.”
But, did humans have something to do with the outbreak? Perhaps:
Fisher thinks the international trade in amphibians is directly responsible for the emergence of Bd. “From the 1950s onwards the African clawed frog (Xenopus laevis) was shipped all over the world, first as a pregnancy test and later as a laboratory animal. This global trade in amphibian increased the possibility that two divergent lineages of Bd come into contact with each other. I’m pretty sure that hypervirulent Bd wouldn’t have evolved without the amphibian trade. We can clearly see the ongoing effects of this trade as it spreads the killer lineage ever more widely.”
Wait... pregnancy test? According to the Slate article in the above link, before we had home pregnancy tests, one of this frog's uses was to inject the lymph sac on its back with a woman's pee and wait to see if the frog produced gametes (that is, sperm or eggs).
` That may seem like an insane way to test for embryos, but considering that earlier tests involved injecting and then killing mice and rabbits and looking at their ovaries, it was much more humane.

Anyway, it does seem that us meddling humans had something to do with the spread of this disease, although to be fair, they probably didn't know this was happening.
` To think that this is unimportant, or that the frogs had their chance to survive and failed, is a very unfortunate mindset, considering how easy it can be for us to contribute to any species' decline.

Going back to those books on recent extinctions I had read as a kid, I don't remember what any of the extinct amphibians were, but plenty of birds and mammals come to mind, especially the ones most unusual in size or some other trait.
` For example, although we're familiar with large mammals of Africa, the savannah used to include the quagga, a partly-tan species of zebra, and a blue antelope called the bluebuck. On the prowl used to be varieties of lions, including the Cape lion, with its impressively large black mane.
` In the Atlas mountains there also used to be a distinctive subspecies of brown bear called the Atlas bear, which was relatively common until the Romans took them to kill criminals in the coliseums. This was Africa's only bear.

Ancient times saw the extinction of the largest bird in the world, the elephant bird, who was a native of Madagascar along with giant lemurs, some the size of a gorilla. And of course, on the nearby Mascarene islands were giant pigeons known as solitaires, and more famously, the dodo.
` In the North Pacific used to live a mammal larger than an elephant, though not a whale, known as Steller's sea cow, which was hunted to extinction only 27 years after its discovery by Georg Steller in 1741.
` About a hundred years after that, in the North Atlantic, the sea mink of Nova Scotia was hunted to extinction in the European fur trade. This semi-aquatic mink probably hunted the Labrador duck, which went extinct at around the same time, and whose males had distinctive black and white plumage.

Down the coast used to live the only U.S. parrot species, the Carolina parakeet, which was green with an orange and yellow head. Considered to be crop pests, these squawking, yet very intelligent birds were exterminated.
` Of course, I can't forget the dazzlingly-numerous Passenger pigeon, which used to darken the skies for hours in dense flocks, which meant free food to anyone lucky enough to be underneath. The fact that there were literally billions of these pigeons, even in a single flock, was also their downfall because so many people believed that hunting them to extinction was impossible -- but it wasn't.
` Interestingly enough, the last known Carolina parakeet, Incas, died in the same Cincinnati Zoo cage that Martha, the last known passenger pigeon, had died in only four years before in 1914. Both bird species will be missed, as long as people are kept informed of them -- which I've noticed most people do not seem to be.

One extinct U.S. bird that has made recent headlines was the largest species of woodpecker, the Ivory-bill, named so for its enormous, off-white bill. It went extinct because of deforestation, even though some people tried to stop it. For a while, it was thought to have been sighted in 2004, but alas it was a false alarm as much further study has shown.

Habitat loss and humans changing the ecosystem by introducing other species has also killed thousands of other plant and animal species, especially on islands, where there is only so much room for refuge. This is how the Polynesians could destroy a great deal of Hawaii's species, as well as all the birds and tall trees of Easter Island. (This is not to say that Europeans haven't made things worse, what with introducing things like mosquitoes!)
` On New Zealand there were once several species of dangerous, but wingless, birds that the Maoris called moas. With the Maoris' building villages, hunting the birds and taking their eggs, the moas went extinct only a few hundred years ago, also spelling the end of the moa's 40-pound predator, Haarp's eagle.

Nearby Australia is also notorious for its extinct species and introduced species wreaking havoc. Their most striking extinct species is the Thylacine, a striped, wolf-like marsupial which, by the time Europeans had reached Australia, was confined to the island of Tasmania.
` Although it could leap like a kangaroo and crush a sheep's skull in its jaws, it was blamed for killing livestock quite a bit more than it actually did, and thus was deliberately exterminated. The last-known Thylacine died in the Hobart zoo in 1936, only 59 days after the species was officially protected by the Tasmanian government.

However, thanks to conservation and breeding programs, some nearly-extinct species have scraped by, the whooping crane being a famous example, its population having been decimated to only 23 individuals in 1941, and recovered all the way to some 600 today.
` Another example is the black footed ferret, which has gone from actually being declared extinct in 1979 to a small population being discovered and bred in captivity. Today, over a thousand individuals live in the wild, happily munching on prairie dogs, who would probably hate humans if they knew we are responsible for this plague upon them.
` The most expensive North American program to save a species has been for the California condor, which humans had killed both unintentionally via their environmental impact, and intentionally, out of the false belief that condors killed lambs and calves.
` In 1987, all 22 of the known condors were captured and bred to about 400 individuals this year, half of which live in the wild.
` Although these species are not anywhere as unique as Thylacines, or many other species that people have contributed to the deaths of, it is good to know that sometimes, human beings can fix what they have almost ruined.

I also remember from those books I used to read that the Spix's macaw looked as though it was doomed to extinction, but a look at their Wikipedia entry shows that there are now dozens of individuals, so perhaps there is hope for this species. (It also mentions that the main characters in the animated movie Rio are supposed to be the last wild pair of Spix's macaws.)
` The same can also be said for the Pink Pigeon, a species of turtle dove native to the Mascarene islands: Although there were only ten individuals in 1991, there are now hundreds of them today, even living in the wild! I remember being so sick over thinking that at some point during my own lifetime, no one would again ever see these birds, but perhaps they will be around for some time after all.

I'm sure that although Zoo Atlanta has had its failures, it will have its share of success stories as well, and it probably does already, but that's enough research if I want to be done with this article in the same day that I started it -- well, not really, actually.
` And how did I even manage this? Well, not only did I have very little else to do today, but no loud music has driven me from my office at any point, which is good because currently there is much noise at the other end of the house which greatly annoys me in general.

I hope y'all have been as interested in this as I am. That's the point in me writing it. And, assuming that my office tends to stay nice and quiet-like, I shall probably have plenty of time to finish all those other posts I've started!

I have had complaints that this post is too gloomy. Well, that's because I didn't go on to explain what I've been learning about ecology because my post was taking too damn long.
` There's a very noticeable basic pattern in the geological and genetic records which shows that, when an ecosystem is disrupted in a small way, parts of the ecosystem that are still intact will tend to 'heal' the damaged section. However, when the environment changes over a large region, species regularly go extinct, although they are quickly replaced as new species evolve.
` When there is a more widespread mass extinction event and entire families of plants and animals go extinct, other families evolve to fill in the gaps left by them. When there is a global extinction event, and even higher taxa go extinct, others take their place. (A familiar example is when mammals evolved into large herbivores, carnivores, whales, etc. once the dinosaurs and sea reptiles left those positions.)

My point is, no matter how badly we damage the life on this planet, it will keep fixing itself, and new species have in fact been observed evolving because of our meddling with them, sometimes only over the course of decades.
` This does not, however, give humans an excuse to not curb the loss of species, because once one is gone, they've taken it from not only our future, but its own future as well.


  1. I agree with you. This makes me wonder what else is out there that has never been seen, and what may have once been there that we never knew about.

  2. Yeah, really gets me thinking! It must be what motivates biologists to actually trek through the steamiest, most mosquito- and fly-ridden jungles on earth -- or into the coldest arctic waters!


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