Friday, 3 December 2021

What attracts a tropical frog to deposit its transported tadpoles in a particular pond? Echos of Maxwell Savage’s big idea

Earlier this year I wrote a series of six articles on this website (see below for links) on Ronald Maxwell Savage (1900-1985), a professional scientist and amateur herpetologist who made extensive studies on the breeding of Common Frogs (Rana temporaria) in the wild. Savage’s big idea was that Common Frogs are attracted to ponds for breeding by the odour emitted by algae in the water. This phenomenon, he argued, would explain the timing in response to earlier rainfall, the preference for one pond over another, why frogs do not spawn in every pond and why frogs may spawn in a pond one year but not the next.

One cannot of course extrapolate the triggers for reproduction from one species to another or, for that matter, claim that only one trigger from the environment is necessary even with one species. However, an interesting new paper on research done in French Guiana suggests that another species of amphibian uses the odour of a compound or compounds in water during a key event in its reproductive life.

The species is Allobates femoralis, the Brilliant-Thighed Poison Frog. Clutches of approximately 20 eggs are laid in the leaf litter. After 15-20 days of development the eggs hatch and the tadpoles are carried on the back of (usually) the father in batches of 1-25 to small pools where they continue their development until metamorphosis; the tadpoles are known to be omnivorous but not predatory. Frogs are known to travel hundreds of metres to deposit their tadpoles and to spread the brood between several ponds. Deposition readily occurs in artificial pools.

Choosing the right site to breed or deposit partially developed tadpoles must have been subject to pretty strong selection. Get it wrong, a pond full of predators or likely to dry out, and the result of disastrous. But what cues do these frogs use to optimise the odds of the tadpoles’ survival? Several years earlier the same group found that tadpole-transporting frogs seemed to be attracted to distant ponds containing large numbers of tadpoles of the same species. There seemed to be two possible explanations: the odour of the conspecific tadpoles was the attractant or the odour of the water or something in the water was responsible. The new paper set out to determine which.

In field experiments three sorts artificial pool (plastic plant pot saucers) were placed on the leaf litter and filled with well water. One had nothing else added. The second had tadpoles of the same species in the water. The third had poured around it ‘stagnant’ water made by steeping leaf litter in water for two weeks. All three types of pond had fresh leaf litter placed around them so as to be visually indistinguishable. In all, 60 artificial ponds were prepared.
















The results were clear. Stagnant water was an attractant: 

Frogs showed a clear differential pool usage: 11 out of 15 occupied pools were pools from the stagnant water condition. Out of the 253 tadpoles deposited, 212 tadpoles were found in the stagnant water condition, 23 in the tadpole water condition and 18 in the control condition. Of the 18 adult frogs observed at the pools (four of which were transporting tadpoles), 15 were at the stagnant water condition. Sixteen frogs captured visiting pools with stagnant water condition had their closest known territory points between 3 and 50 m (median=12 m) from the pools where they were found. 

The questions now remaining are: Why do these frogs prefer depositing their tadpoles in the presence of rotting vegetation and what odoriferous constituent(s) of the stagnant water is attracting the frogs?

The authors suggest that ‘stagnant’ water may be an indicator of a pond’s permanence; one that has had time to remain full and therefore not just a temporary rain-filled depression. I do, however, have another suggestion. Could it be that the smell of rotting vegetation is indicative of a nutrient-rich environment ideal for growth of the tadpoles? The leaf-litter steeped water would be expected to contain all manner of algae, protozoa and small aquatic invertebrates—bottom of the food-chain stuff—ideal as tadpole food. A similar mix soon leads to the production of ‘infusoria’ from vegetation and air-born spores that aquarists use to feed their young fish. Identification of the chemical(s) involved will prove interesting: the odour of products of decay or of organisms using the products of decay to multiply? Could it be the case that algae are involved, just as envisaged for the Common Frog by Maxwell Savage?


Serrano-Rojas SJ, PaĊĦukonis A. 2021. Tadpole-transporting frogs use stagnant water odor to find pools in the rainforest. Journal of Experimental Biology 224, jeb243122. doi:10.1242/jeb.243122 

The earlier articles on Maxwell Savage can be found here, here, here, here, here, here.



Wednesday, 1 December 2021

Masai Mara Safari - 30 years ago: The widebeest who do not make it

A few more photographs from the Masai Mara in September 1991. The wildebeest were moving across Masai Mara and crossing rivers. Many had been drowned the night before. The Marabou Storks and vultures were gorging themselves while the smell of the corpses from earlier drownings was interesting. Breathing through the mouth with the tongue tucked down helps by the way.







Saturday, 27 November 2021

Bruce S Grant’s book ‘Observing Evolution’ and observing scientists who wrote on evolution


I have enjoyed reading Bruce Grant’s book Observing Evolution (Johns Hopkins, Baltimore, 2021) which describes his work from the early 1980s on industrial melanism in the Peppered Moth. Grant illustrates just how difficult it is to devise experiments on a natural phenomenon and how many traps for the unwary lie in the way. However, the reason for writing this article is not to go over old ground on the status of industrial melanism since despite the efforts of an American science writer to disparage the work of Henry Bernard Davis Kettlewell (1907-1979) in Oxford, the concept we first heard about at school is, thanks to the extensive work of the late Michael Majerus (1954-2009) and Bruce Grant himself, among others, even more firmly established than it was in Kettlewell’s time. Nor is to discus further one of the key rules of life: avoid reading anything by an American ‘science writer’ (the one in question being described by Grant as ‘notorious’). Instead it is to pick up a point that Grant made about E.B. ‘Henry’ Ford (1901-1988) and his book Ecological Genetics. The later editions failed to mention a paper published in Science in 1968 which threw doubt on one of Kettlewell’s untested speculations. Grant’s students were said to be ‘disappointed that world-renowned scientists could so uncritically accept and promote untested hypotheses’.

The late Bryan Clarke (1932-2014) in his Biographical Memoir on Ford for the Royal Society wrote of the approach taken in Ecological Genetics:

It is written, of course, in his [Ford’s] wonderfully lucid style. It contains accounts of the researches that have already been described above, as well as those of his friends, colleagues and students…This was a galaxy of talent indeed, and a testimony to Henry's skill in choosing students and colleagues, but there were other galaxies that did not get a mention. The book was brilliantly and annoyingly parochial. Henry did not like mathematics, despite his friendship with Ronald Fisher, so that other theoreticians got short shrift. Nor did he like molecular biology, so that even in later editions of the book there was little about variation in proteins or DNA. Workers in the U.S.A. were largely ignored. One year before the last edition of Ecological Genetics, in 1974, R.C. Lewontin produced another brilliantly and annoyingly parochial book, The Genetic Basis of Evolutionary Change. The two works, both major events in the history of evolutionary writing, hardly shared a reference in common. But still Ecological Genetics, like its American counterpart, is necessary fare for serious workers in the field, still it is the clearest and least compromising statement of the 'selectionist' view, and still it is a joy to read.

My take is that Ford’s book (and, it would appear, Lewontin’s) followed the tradition of the book—and the major scientific review—as a personal statement on the subject in question, not just as an annotated bibliography with no conclusions drawn or personal view expressed. The purchaser of the book was buying the author’s considered opinion and the evidence that the author thought should get a mention. It was probably obvious to the highly eccentric Ford that the results of the experiments published in 1968 were deeply flawed. Should Ford have spent time describing and then dismissing that work? Or should he—as he obviously did—have simply ignored it?

I end with a question I argue about with myself. What should one do when discussing the dross—and there is a lot of it about—in published science? Spend time in minutely discussing why the authors (and the increasingly poor peer reviewers) were misguided, ill-read, incompetent or just stupid? Or simply ignore it, as many British scientists did in the 20th century on the genteel grounds of, if having nothing good to say, say nothing. The first approach might though be considered akin to taking sweets from children; the second construed as intellectual arrogance.

…and a final couple of words on Grant’s book and his pursuit for research on natural selection of Biston betularia across its entire range in the northern hemisphere: highly recommended.


Wednesday, 24 November 2021

Snakes’ Teeth: New light on their structure and evolution

As the dentist’s drill vibrated my teeth last week—and before being interrupted by the nurse being stung by a wasp (in Scotland in the middle of November)—I was thinking of a paper I had been reading on the teeth of snakes and the role of a particular component, plicidentine.

Plicidentine—a folded form of dentine—was found in the teeth of the snakes examined. Potentially it is present in all species of snake. Previously in extant reptiles it had only been found with any degree of certainty in some ‘varanoid’ lizards. The authors of the paper realised that the direction of the folding could explain how tubular fangs of venomous snakes have developed independently three times during the course of evolution. Tubular fangs are viewed developmentally as fully closed grooved fangs. The orientation of the folds in the plicidentine makes it easy to envisage that any one of the folds in non-venomous ancestors could have developed as a grooved fang involved in the delivery of venom.

A previous suggestion that plicidentine increases resistance to bending or compression during biting was examined in but biomechanical experiments provided no support for that view. Instead the authors suggest that plicidentine acts to improve the attachment of the long but shallowly rooted teeth to the underlying bone by providing an increased surface area. Since the teeth of ‘varanoid’ lizards are also relatively long and shallowly attached, the presence of plicidentine in these lizards as well as in snakes would fit the explanation proposed.










Palci A, LeBlanc ARH, Panagiotopoulou O, Cleuren SGC, Mehari Abraha H, Hutchinson MN, Evans AR, Caldwell MW, Lee MSY. 2021 Plicidentine and the repeated origins of snake venom fangs. Proceedings of the Royal Society B 288. 20211391. https://doi.org/10.1098/rspb.2021.1391 


Tuesday, 16 November 2021

Masai Mara Safari - 30 years ago: Cheetah with Four Cubs

 It would be difficult to imagine a better introduction to the Cheetah than this mother and four cubs we saw in the Masai Mara of Kenya in 1991. She had killed a Thomson's Gazelle and all five were eventually so full they could manage no more. And for physiologists a perfect example of gastric accommodation. Nothing looks more uncomfortable than a carnivore which has eaten so much that bursting seems the only possible outcome.







Monday, 15 November 2021

Edwin Ray Lankester: Gladly Making Fools Suffer

I have recently been reading a biography of Sir Edwin Ray Lankester (1847-1929). Most biologists never get to grips with the various mechanisms of evolution proposed or pursued in the six decades between Darwin and the Modern Synthesis. This was the era of comparative anatomy, a discipline which reigned triumphant in plotting the directions of evolutionary change and the relationships between organisms. Physiology was also making great progress but largely in isolation from comparative anatomy and evolutionary processes. Lankester, although a morphologist to the end, involved himself in both fields particularly as a young man. However, it is difficult to reconcile the enormous advances made by the comparative anatomists with the muddled thinking of how evolutionary change might occur propounded by those same individuals. Even while recognising the benefit of hindsight it is difficult not to conclude that many skilled anatomists with the ability to recognise homologous or analogous structures in other organisms simply could not get to grips with the implications of evolution or of natural selection. Some ideas propounded by well-established zoologists seem—and may have seemed at the time—nuts. It is for that reason that the era of Lankester is largely irrelevant to modern biologists. The twists and turns of evolutionary thought over the era fall firmly in the domain of the historians of science.

What many present-day biologists do not realise is that their immediate predecessors were brought up under a regimen of teaching the subject devised in the second half of the 19th century. One of the key players in that period was Lankester. The mix of lecture-style teaching with laboratory sessions in which ‘type’ specimens from major animal groups were dissected and drawn became the norm for around a century. 

Lankester was a man who did not mince his words, whether inveighing against the clerics who still ran Oxford or his nominal and clearly loathsome superior at the British Museum when the Natural History Museum, of which he was Director, was under its control. He walked away from a chair in Edinburgh after a few weeks when he found there was neither a lecture room or museum and that he would have to lecture throughout the whole year. He gave up this lucrative post (where the professor received the tuition fees) to return to his chair which had not been filled at University College, London. He gave the eugenics movement a mauling on the grounds its proponents were not distinguishing between the effects, in modern terms, of the genotype and the environment on the phenotype of the poor who they wished to stop breeding.

Lankester was a giant in British science, as practitioner, protagonist, promoter of new organisations, propagandist and populariser. He had interesting friends, Karl Marx, H.G. Wells and Anna Pavlova being notable examples, and many enemies. He had a rather sad personal life. Although there is some information on Lankester in books on other people and online (some of it inaccurate or misinterpreted) I had not read a proper biography. For such an important figure I was surprised to find that only one had been written. Few copies can have been printed because I had difficulty finding one to buy.

The biography, E. Ray Lankester and the Making of British Biology was published as a British Society for the History of Science Monograph in 1995. The history of its publication is interesting. Lankester’s papers were preserved by a niece. The author of the draft of the biography, Joseph Lester, contacted the niece in the 1950s. Eventually he was given access with the proviso that he would write an ‘approved’ biography. Initially the family had refused any access because Lankester was, in his time, a controversial figure. Lester worked on the biography in the 1950s and 1960s but could not find a publisher. He was an amateur—a reviewer of the book stated that he was a schoolteacher in Manchester and in his 90s at the time of publication—without the right contacts. Professor Peter Bowler FBA, a proper historian with interest in Lankester and his era of biological science, persuaded Lester that the only way his work would be published would be for it to be edited by a professional. Bowler, after reading the manuscript, decided to tackle the  job himself. He paid particular attention to the footnotes and to interpreting some of passages in the light of current knowledge. The title page therefore contains Lester as author and Bowler as editor.

The famous line about Lankester was written by his hero, Thomas Henry Huxley (under posthumous attack at present by the witchsniffers). Lankester need to work for his living and he felt his position at University College London had become precarious as student numbers and, therefore, income, fell. He wondered whether to apply for the job of Assistant Secretary at the British Association. Huxley dissuaded him:

Looking at things solely from the point of view of your interests, I should advise you against taking it—even if it were offered. My pet aphorism, ‘Suffer fools gladly’, should be the guide of the Assistant Secretary—You do not suffer fools gladly; on the contrary, you gladly make fools suffer.

….and having read about Lankester I have just remembered that in the final year at school for the Scholarship Level paper taken in addition to the ‘A’ Level papers I was asked to write about the body cavities and their origins. All that stuff about the coelom and in which phyla it is present came flooding back. It was Lankester who sorted it all out. Oh, and we were told that some examiners liked the blood to be referred to as a tissue, not just as a fluid. Lankester again.

I will though end with a quote from Lankester himself:

Science is no handmaiden, but in reality the master—the master who must be obeyed. The sooner and more thoroughly the people recognise the fact—and insist upon its acceptance in practice by tis representatives and governors—the better for them and their posterity.

Amen to that.


Ray Lankester by Leslie Ward, Vanity Fair 1905
The caption read::
”His religion is the worship of all sorts of winged and finny freaks"


Lester J. 1995. E. Ray Lankester and the Making of British Biology. Edited by PJ Bowler. British Society for the History of Science Monograph. ISBN 0-906450-11-X

This following obituary notice is rarely quoted because it is not picked up by internet searches, being buried in Proceedings of the Royal Society under a general title: Goodrich ES. 1930. Edwin Ray Lankester—1847-1929. Proceedings of the Royal Society B 106, ix-xv.


Sunday, 7 November 2021

ZOO LIFE: ZSL’s Post-War Magazine 1946-1957

Zoo Life was a magazine published by the Zoological Society of London from 1946 until 1957. It was very different from its predecessor that had ceased publication in 1941 as wartime paper shortage made it impossible to continue. The pre-war magazine was a joint venture between ZSL and Odhams Press. It crammed an enormous amount of information, factual as well as anthropomorphic animal fiction, into its pages over the three years it was published under three titles, ending its run as Animal & Zoo Magazine.

Zoo Life was a far more sober affair. It was launched with the Spring issue of 1946. The first Honorary Editor was Edward Hindle FRS. He had become Scientific Director of the Zoo in 1944, vacating the regius chair in Glasgow which he had occupied for nine years.

The first page of the first issue contains the following editorial:


The Zoological Society of London has great pleasure in presenting to its Fellows and all other friends, a new publication which will be devoted mainly to illustrated descriptions of animals likely to be seen when visiting Regent’s Park or Whipsnade. The main features of each issue will be an article on some animal of special interest, because of its rarity or novelty, with a photographic illustration; a series of photographic studies; and an illustrated report on recent additions to the collection. Besides these attempts to portray some of the beauties of animal life, which should appeal to everyone, readers will also find vivid descriptions of the ways and manners of Zoo Life. 


Anybody coming across the early issues of Zoo Life will be struck by the quality of the artwork for the front covers. Many were available to subscribers as prints and may have been included with each issue since I found a number enclosed in a batch I have bought on eBay a few years ago.




The cover of the first issue was of a Markhor (Capra falconeri), reproduced from an original painting by the famous artist Joseph Wolf (1820–1899) around 1865 and held in the Society’s collection.




The first article was written by the former superintendent of London Zoo, Reginald Innes Pocock FRS (1863-1947). It was on the Okapi and gives far more information on its discovery than finds its way into modern accounts. A regular features was on happenings at London Zoo. The first was  particularly interesting because it described how the Zoo was trying to recover from the war years. One snippet from the war years was the arrival of a Coyote, brought from the USA in a bomber as a mascot by its crew and swiftly impounded as a potential carrier of rabies.

Finally, there is a reminder of the pre-war magazine. One of the articles—on play in animals at the Zoo (i.e. ‘behavioural enrichment’ in modern jargon) was by Craven Hill. He was the Evening Standard’s Zoo Correspondent at a time when all the major newspapers had such a designated position to follow the goings-on at Regent’s Park.