Wonderful world: gastric brooding frog

Redmond O’ Hanlon recently made a number of documentaries in which he walked in the footsteps of mostly 19th century adventurers who had the bravery and zest to explore the unexplored, like Prezwalski and Fawcett. In the intro to every episode he explained that friends told him he ‘had been born in the wrong century’ and should have lived in an era when all significant explorations still had to be done. I empathize with his words, because I remember reading when I was young a book about the great explorers of all time, amongst others Orellano, Livingston and Scott, and adoring the romantic vibe that comes with going where no man has ever gone before. Even though, for example in the case of Scott, the ending wasn’t that glorious, it still seemed to me such a thrill to have been there. So i can understand this romantic feeling of wanting to be in some other time and place. I myself would love  to know what discoveries will be made in coming centuries and how far from the truth we are now with our current scientific theories, but alas I will never know… And at the same time I also regret not having been able to see dinosaurs, moa’s and other legendary creatures from the past. It’s the same feeling of regret I had when i first heard about the gastric brooding frog and its extinction. The genus of gastric brooding frogs (presumably) disappeared from the wild a couple of  years after I was brought into this world and actually the Southern gastric breeding frogRheobatrachus silus, disappeared a year before I was born and that’s definitely my loss. I’ll try to make up for it a bit by writing this post.

My first acquaintance with this special frog was through reading Tim Flannery’s ‘The Weather Makers’ (I have mentioned him before, mostly because this read is still fresh in my mind) in which he mentions the very special breeding habits of it and I figured that this blog was an excellent excuse to find out more about it.  Well, what was so special about this genus of frogs, comprising of two species? Its name says it all: this was a genus of frogs in which the females of these species incubated their offspring in their stomach. Giving birth in these species therefore meant that the fully developed froglets emerged from their mother’s mouth into the world.  If that isn’t amazing than I don’t know what is! And it is this feature that obviously set them apart from all other frogs.

The story that is told by these frogs is interesting in its own right, because it shows how evolution has given rise to the most wondrous and unimaginable creatures, and provides us with a sense of wonder of what evolution is capable of ‘creating’. But it teaches us as well a lesson about the often unrecognized value of biodiversity and sadly enough also about extinction of amphibian species in modern times and its supposed causes. Before I go into this more, I first want to point you to a video from a living Southern gastric breeding frog. It’s not a remarkable piece of footage, because it’s just a frog in a tank, but of course it’s the context that makes it more than moderately interesting; it’s footage of a species that no longer hops or swims the earth. Without philosophical thoughts about gazing in our past, this realisation befittingly gives me a weird sensation in my stomach. It’s just a pity to put it mildly.

Two species made op the genus, the before mentioned Southern gastric brooding frog and its counterpart the Northern gastric breeding frog, Rheobatrachus vitellinus. The former was discovered in Queensland, Australia in 1972 while the latter was discovered as recently as 1984. Their distribution was confined to freshwater streams over 300 m in altitude, in rainforest and wet sclerophyll forest communities of the Conondale and Blackall Ranges in south east Queensland (image).  According to the IUCN Red List both of them are listed as extinct while they are still included in management plans from the Australian government and seen as highly threatened instead of extinct. However, they haven’t been seen despite intensive survey effort in the past 25 years.

Because they had been discovered quite recently and some scientific work has been done on these species, they are not as elusive to us as for instance the dodo still is. The Southern gastric brooding frog was an aquatic species and was never located more than four metres from water.  It preferred rock pools and backwaters with leaf litter and rocks in which to shelter . They were assumed to hibernate during the colder months in spaces between rocks or in crevices  in rocks underwater. The Northern gastric brooding fro lived in a similar habitat and had a preference for  the shallow section of fast-flowing creeks and streams in rainforest. Anybody interested in the call of this species can find it here  (you have to love the internet for that though).

Distribution of the two Rheobatrachus species

The disappearance of the Northern gastric brooding frog is quite remarkable, because it happened somewhat a year after it was discovered and after a population assessment had shown that it was quite common in its habitat. Both species had a small range where they occurred and were therefore probably vulnerable to human influences on their habitat. Research on their extinction mainly  has been done many years after their disappearance, simply because nobody saw this as a priority. For the Southern gastric brooding frog it is known that timber harvesting was going on in their habitat but this hasn’t been confirmed as the main agent of decline. Because seven upland rainforest frog species had gone extinct in Queensland since the 1970s and all species were living in similar habitats, two researchers (Glen Ingram and Greg Czechura) investigated the possible causes. They concluded that the chytrid fungus probably is the main agent of decline for the Queensland frogs, together with pollution, introduced fish, the damming of rivers and also climate change.

Elaborating on the latter cause, in 1993 Dr. Ingram reported that data had shown an increase in temperature and UV-radiation in Queensland and rains tended to occur less frequently but with more vigour. When it did fall, it mainly occurred in the cooler months when frogs didn’t breed, so drought may have affected breeding success too. A change in temperature can push these montane rainforest species up the mountain, thereby restricting their distribution. A research by Laurance in 2008 focused on the interplay between rising temperatures and the chytrid fungus; by use of statistics he showed it to be likely that range and activity of the chytrid pathogen had increased by global warming.

Going back to the one feature that sets these frogs apart from the rest: their most unusual reproductive behavior. This has actually made it an iconic example of the great wealth that biodiversity presents to us humans, illustrated by it starring in an article in Time magazine on ‘nature’s gifts’.  (interestingly enough,  creationists also adopted them as a case of ‘irreducible complexity’ , probably haven’t read thoroughly one of Dawkins’ books). Their gift was that while normally anything that ends up in the stomach will be digested by stomach acids, the tadpoles of these species could sit there comfortably and develop into froglets. The discoverer of the Southern gastric brooding frog, Tyler, conducted research on this and found the tadpoles to secrete a substance, prostaglandin E2, that inhibited the secretion of gastric acids. Such a chemical that inhibits the secretion of these acids looked like a promising discovery in finding a treatment to stomach ulcers.

Unfortunately the extinction of these species so short after their discovery robbed scientist (and the human species in general) from the opportunity  to study this chemical and the pathways through which this inhibition works. So with a bit of imagination we can see the extinction of these species as a crime against humanity. And to all people that believe in the superiority of human technology it teaches a lesson that we still are very dependable on these gifts from nature for our well-being. Understandable, because these are the outcomes of millions or even billions of years of natural selection and species surviving with all the genetic resources they have in them and more. And seeing how many species are alive today and have been alive, we should expect that nature has come up with much more ingenious ways of battling diseases, reproducing and merely surviving than we can ever dream of. And it becomes clear then, that we cannot mimic these inventions so easily.  Not as easily as we can destroy them.


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