Island Biodiversity Race

Category: Biodiversity, Gulf of Guinea, Island endemics, Sao Tome, biogeography, gigantism, invertebrates, lizards, principe | Date: Jan 26 2009 | By: islandbiodiversityrace

Our race to discover and describe the unique fauna and flora of São Tomé and Príncipe continues, and the six members of Gulf of Guinea Expedition III (B) are diving in the ancient waters of Príncipe as I write; they return to the Academy next week.  As I wrote earlier, Marta is sampling the sea slug fauna (nudibranchs), Gary, Bob and Dana are looking at coral and barnacles, having found a new species of the latter in waters off São Tomé during GG II, and John and David are looking at small marine fish, with emphasis on eels.  The group has an added goal, and that is to bring back some freshwater prawns (Macrobrachium) that abound in the São Tomé rivers. These specimens are for a young high school student named Alex Kim.

 A freshwater Macrobrachium prawn from Guinea (www.)

Alex is a senior at Thomas Jefferson High School of Science and Technology in Virginia.  He is doing an ambitious biogeography project on these prawns, relatives of which are found on both sides of the Atlantic.  Alex contacted me through this blog—you can read his comments at the end the November posting.  During a brief visit to DC over the holidays, I brought some preserved specimens we collected in GG I and GG II which I handed over to one of his advisors, Dr. Patrick Gillevet of George Mason University, and now the GG III (B) group plans to bring him some fresh material for DNA studies.  This is really fun academic stuff, and we are delighted to have the involvement of a young colleague.

 A Macrobrachium prawn from Cameroon. (www) 

Except for documenting our exciting hunt for Príncipe Jita, (see first May posting), I have not written that much about the endemic reptiles of these islands; in fact, there are quite a few of them, some rather spectacular.  While reptiles, especially geckos and skinks, are much better dispersers over saltwater than amphibians, snakes are not particularly good at it; moreover, like the amphibian caecilian, cobra bobo, a number of these endemics are legless species.  There are also some island species that may be endemic, but we are not sure…. we just haven’t studied them closely enough yet. In this posting I will show you the unique lizard species.  One readily identifiable endemic species is Greeff’s gecko, or the Giant gecko, Hemidactylus greeffii.  

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Greeff’s Gecko, Hemidactylus greeffii . A Sao Tome specimen. RCD phot. GG I   

Greeff’s gecko is an island giant; it is evidently much larger than other African member of the genus (and there are over 55 African taxa of Hemidactylus with likely many more to be discovered). Our longest specimen is over 200 mm in total length (including original tail); but longer specimens are known.  This gecko is not only very large it also differs from all of its African relatives in lacking a claw on the first (inner) finger and first toe. Somehow, this feature has been lost during the thousands, perhaps millions of years of isolation on the Gulf of Guinea Islands. Greeff’s gecko also has greenish eyes, which also distinguishes it from other nocturnal geckos on the island which, so far as we know, are not endemics.

 H. greeffii.  Note absence of claw on first thumb. ST specimen. RCD phot. GGI

H. greeffii with  greenish eyes.  ST specimen. D. Lin phot. GG II.

Greeff’s gecko occurs on both São Tomé and Príncipe; at least we think it does. Here’s what I mean: specimens from both islands look very much the same but a couple of years ago, a group of researchers from the University of Madeira and Portugal looked at the DNA of specimens from both islands and found that data from mitochondrial DNA suggested the two populations were very different, and that they may well be two distinct species in spite of their apparent anatomical similarity. These results were not confirmed by study of nuclear DNA however, so scientifically the “jury” is still out, and we call both island forms, Greeff’s gecko. This critter is quite common in rock walls, culverts, rock crevices on both islands and is strictly nocturnal. 

Principe specimen of Greeff’s gecko. D. Lin phot. GG II.  

A similar situation exists with a small terrestrial skink called Panaspis africana, or Gulf Leaf-litter skink. A daytime forager, this small uniform-brown skink is very common in the lowlands; it can be easily heard and seen scuttling through dried cacao leaves and it is almost always found on the ground on both islands; one of our largest gravid (with eggs) female specimens from São Tomé is about 100 mm in total length, but most of our examples are smaller.  

Gulf Leaf-litter skink. Panaspis africana; D. Lin phot. GG II. 

The same group of researchers from the University of Madeira studied the DNA of leaf litter skinks of both islands, and also Annobón, the last island in the chain and part of Equatorial Guinea.  They used, in part, tissues and specimens collected by us during GG I in 2001.  In this case they found clear evidence for three separate species, one on each island (the one on Annobón is already called P. annobonensis); this was supported by both mitochondrial and nuclear DNA sequence.  However, in one of those tragic, fortunately rare, occurrences in science, the specimens from which the tissue samples were taken were either lost in transit or misplaced.  Without voucher samples the results cannot be duplicated or tested nor can we demonstrate the results.  So for now, although there was evidence that Panaspis is two different species on São Tomé and Príncipe we cannot confidently describe the populations of the different islands nor give them scientific names.  Until the study can be redone with new material, the Gulf leaf-litter skinks remain known as simply Panaspis africana. 

Author working on Principe.  Weckerphoto. GGIII  

The way we collect these specimens is not sophisticated – we use our hands. We turn over logs, rocks and branches on the ground or sift through leaf litter with rakes; we climb trees and cliffs; we go out at night with flashlights and headlamps. After capture, the specimens are put in separate plastic bags for later processing.  

Dr. Iwamoto in Sao Tome H. greeffii habitat on Sao Tome. RCD phot. GG I 

Jens Vindum searching leaf litter on Sao Tome. D. Lin phot. GG II 

Principe day gecko in plasic bag. RDC phot. GG III.

Every specimen we collect gets a unique field number, which is the same used for photographs of it, recordings or tissues samples taken. 

My grad student, Ricka Stoelting,  processing specimens on Principe. RCD phot. GG I 

Certainly one of the oddest endemic lizards is the legless skink, unique to Príncipe Island, Feylinia polylepis.  There are about six species known in this genus, the remaining five found broadly distributed on the African mainland.   

Principe legless skink, Feylinia polylepis. brown  phase. D. Lin phot. GG I. 

 They appear in two different color morphs, a brown one and a pale gray one, regardless of size or sex.  The locals call them, Ozhgah (or at least the name  sounds like that). 

Principe legless skin - grey phase.  D. Lin  phot. GG II 

Feylinia polylepis head shot. D. Lin phot. GG II 

They can be found under almost anything on the ground provided the earth is slightly moist. Once exposed, they are very quick and can rapidly disappear into holes in the ground. They are conspicuously common in the Príncipe lowlands, and in this regard are reminiscent of the caecilians of São Tomé Island; the high density of their numbers in suitable habitats suggests predation may be low in these areas. 

Not all geckos are nocturnal.  In the Old World there are two large groups that are secondarily diurnal, although they, like all geckos, lack eyelids.  The genus Phelsuma is a group of numerous species of velvety green geckos found on Madagascar and the Indian Ocean islands; the other group, Lygodactylus are also present in Madagascar but also distributed throughout the Afrotropical region as well.  They are not brightly colored, and taxonomically rather poorly known.  The group as a whole is being studied by Dr. David Vieites (and his students) of Madrid and Dr. Adam Leache, of the University of Washington.  I have been involved as well but largely in studying the relationships of day geckos of the Gulf of Guinea Islands.  

 Lygodactylus thomensis. Sao Tome.  D. Lin  phot. GGI 

The Gulf of Guinea Day geckos are sun-lovers and strictly climbers, being fairly common on tree trunks and scuttling up walls even in São Tomé town and Santo Antonio, Príncipe.  They are very small, at about 70-80 mm total length.  The day geckos of the Gulf of Guinea islands (excluding the continental island of Bioko) have long been recognized as a distinct, endemic species, Lygodactylus thomensis, first discovered on São Tomé Island.  The day geckos on Príncipe and Annobón have been described as subspecies (or races, if you will) of the São Tomé species..  As you can see from the illustration below, one of the characteristics used to define species of day geckos is the throat pattern. 

 Day geckos of the Gulf of Guinea Islands.  RCD prep.

The throat patterns of the lizards on each of the three islands are quite consistently distinct from one another, and work by us and the University of Madeira suggest that they have been isolated from each other for a long, long time, and that each is a full species unique to its island. Work is continuing on these lizards.

 L. delicatus of Príncipe Island. RCD phot. GG III

 There are other conspicuous lizards on both islands but these are not considered endemics; i.e., they occur elsewhere and are probably just good over-water dispersers. The large speckled-lipped skink, Mabuya maculilabris, is common and widespread in the lowlands of both São Tomé and Príncipe. It is a good climber and is seen in a variety of habitats especially along the coast lines.  This species also broadly distributed on the African mainland.

 Speckle-lipped skink (Mabuya maculilabris) of the Gulf of Guinea. Sao Tome. D. Lin phot. GG II] 

M. maculilabris detail. D. Lin phot. GGII 

There are also non-endemic, nocturnal geckos on both islands. Most appear to be the widespread house gecko, Hemidactylus mabouia, also occuring nearly throughout Africa. 

House gecko, Hemidactylus mabouia.  D. Lin. phot.  GG II\] 

Note that the eyes are not greenish and that this species does not lack claws on the inner toe and finger.  There is some confusion as to how many non-endemic species are present and what to call them. 

H. mabouia foot from beneath. note claws. Weckerphoto GG III.

Snakes are coming next. 

Here’s the parting shot:  

The thrill of discovery! Bom Bom Island, Principe.  Weckerphoto. GG III  

PARTNERS We gratefully acknowledge the support of the G. Lindsay Field Research Fund,  Hagey Research Venture Fund of the California Academy of Sciences, the Société de Conservation et Développement  (SCD) for logistics, ground transportation and lodging, STePUP of Sao Tome http://www.stepup.st/, Arlindo de Ceita Carvalho, Director General, Victor Bomfim, Salvador Sousa Pontes and Danilo Bardero  of the Ministry of Environment, Republic of Sao Tome and Principe for permission to export specimens for study, and the continued support of Bastien Loloumb of Monte Pico and Faustino Oliviera, Director of the botanical garden at Bom Sucesso. Special thanks for the generosity of private individuals, George F. Breed, Gerry F. Ohrstrom, Timothy M. Muller, Mrs. W. H. V. Brooke and Mr. and Mrs. Michael Murkami for helping make these expeditions possible.  

4 responses so far

Category: Biodiversity, Gulf of Guinea, Island endemics, Sao Tome, frogs, gigantism, principe | Date: Dec 15 2008 | By: islandbiodiversityrace

 Sorry, I love titles like this… and I have more!  Actually, there are no toads (Bufonidae) on São Tomé and Príncipe; interesting in itself because seven other amphibian species of five different families have survived the ocean crossing during the many millions of years since the islands first emerged. Moreover, toads are common in almost every  conceivable terrestrial mainland habitat.  

My last two blogs have been a bit academic.  Having laid the biogeographical ground work, it is probably time to get back to the unique, endemic island critters.   The tiny, 31-million year old island of Príncipe is the only home of Africa’s largest treefrog, Leptopelis palmatus – the Príncipe Giant Treefrog.  It is one of the world’s rarest frogs, as well.

 L. palmatus – D. Lin phot. GG I 

Let me be quick to point out that the Príncipe critter is not Africa’s largest frog; that title belongs to Conraua goliath (below), which is found on the mainland in southern Cameroon and Gabon.  In fact, the goliath frog is the largest in the world but it is not related to any on São Tomé and Príncipe– no members of its family have made it across the saltwater gap to the islands, or if they ever did, they have not survived. 

Conraua goliath—J.-L. Perret phot. 

Leptopelis palmatus is the largest African treefrog (emphasis on “tree”) — frogs that are adapted for climbing with, among other features, enlarged finger and toepads.  As I have pointed out in earlier blogs, gigantism is a relative thing; the giant endemic plants, frogs, birds and lizards of São Tomé and Príncipe are bigger than all of their relatives but they are not necessarily so large you trip over them (like Galapagos or Aldabra tortoises); they are simply larger than all of their relatives.  The two images below put this frog in some perspective, and I think you will agree that this is one BIG treefrog. 

Me, with the first female. R. Stoelting phot. GG I 

The frog on Dong Lin, our photographer.  R. Stoelting phot GG I

This species was first described in 1868 on the basis of a single female specimen, housed in the Berlin Museum. At the time of GG I in 2001, the Príncipe giant treefrog was known only from this single type specimen and seven additional specimens, all females, collected by local Príncipeans for a Swiss colleague named Catherine Loumont.  The largest of Loumont’s specimens is 110 mm from snout to vent (we do not include legs when we measure frog sizes), and even after our years of work, this specimen remains the largest ever found – it is nearly 30 mm longer than the largest of its nearest mainland relative, Leptopelis macrotis, distributed from central Sierra Leone to Ghana. One of several differences between the two species is the striking deep-red eyes of our island endemic. 

The eye of the Príncipe giant treefrog. D. Lin phot. GG II 

This first specimen we found during GG I (first three treefrog images, above) was yet another female, 108 mm in length.  Our mammalogist, Doug Long, was led to the critter by some kids from the now-defunct plantation of Sundi in northwest Príncipe. Sundi may no longer function as a plantation but it is still inhabited by the descendents of former workers—lots of them, there is even a mayor. 

Doug Long and the Sundi kids. RCD phot. GG I 

The arrival of this frog was greeted with great enthusiasm by yours truly; here in my hands one of the rarest frogs in the world! And it was huge! I was not surprised to learn that it had been found on the ground, as it is hard to imagine something so bulky climbing around in bushes and trees. The male of this species was completely unknown, so far as we knew at the time,.  None had ever been collected, photographed nor described in the scientific literature.  So we also knew nothing about the species’ breeding biology, male advertisement call or tadpole.  At the time, we were unaware of a blog posted two years before our visit by Jonathan Bailey on the Gulf of Guinea Conservation Group website, entitled “One month in the Forest of  Príncipe.” Jonathan (now Dr.) Baillie described hearing the calls of male L. palmatus as “like a pop bottle being continuously opened.”  He heard them high up on Pico do Príncipe near a small stream at about 700 m and actually collected two of them which had been deposited in the Natural History Museum in London.  But during GG I, the male giant treefrog was terra incognita, so far as we were concerned.  

Second female from Rio Papagaio.  J. Ledford phot..  GG I 

During a second GG I visit to Príncipe a few weeks later, my then-graduate student,  Ricka Stoelting, collected another female along the Rio Papagaio, a large-ish river that flows through Príncipe’s only town, Santo Antonio.  It was also of a rather dull in color but with white spots. We have since learned that this is about as brightly colored as females get. 

Rio Papagaio in town, downstream. RCD phot. GG III

Ricka Stoelting, my graduate student on Sao Tome.  RCD phot. GG I.  

During this second visit, Ricka and Dr. Sarah Spaulding ascended Pico do Príncipe to the top and camped at nearly the same spot where Jonathan Baillie had been two years before.  There she found the males, lots of them, calling from bushes and branches at night near a very small creek.  

Tiny creek on the Pico.  J. Uyeda phot. GG II

 Ricka brought the series of males back down the mountain, and they were astounding.  Unlike the females they were very brightly colored and highly variable, in pattern, as well; this variability is rather unusual in frogs, although there are some species that are sexually dimorphic for color. And they were much, much smaller than the females, though we knew they were full-sized breeding adults. During later analysis we learned that the largest breeding males are only about 41% of the size of the largest females, a size disparity that is striking.

First series of live males (far right is a juvenile).  J. Ledford phot. GG I

  Ricka never heard them calling and anyway she had no way of recording them if they had.  One of the parameters we use in establishing relationships among frog species is analysis of the voice (or advertisement call.). Males call to attract females, and at the same time to advertise their presence and territory to other males.  The advertisement call is species- specific and obviously adaptive when there are other species utilizing the same water for breeding.   To really define Leptopelis palmatus, I needed a recording of the voice, and this was to become a priority in the future. Below is a preliminary analysis of the call of another Gulf of Guinea frog species which we think is present on both islands.  Here, we are comparing the advertisement calls of males from two different localities on both islands, and we can see that they are basically the same.

 Preliminary sonograms of Oceanic treefrog. Marshall/Drewes construct.  

 Back at the Academy, Ricka and I prepared the first formal description of male Príncipe giant treefrogs.  Now aware of Baillie’s blog, we read his word description of the advertisement call.  Although the Principeans insisted the frogs did call, it remained an open question, especially when I learned from anatomical study that the male frogs  lack vocal sacs and vocal sac openings, features that most calling frogs possess (including other members of the genus Leptopelis).   GG II in 2006 included Josef Uyeda as my student (now a PhD candidate at Oregon State University).  Josef was working on a different group of island endemics called puddlefrogs (see earlier blog: “We Find Jita”) but when we were on Príncipe, I sent him up the Pico with his friend Mac and the same guide, Manona, who had led Jonathan Baillie and Ricka years before. They were armed with my old Sony cassette recorder (my iPod had failed).  Bear in mind that the only known localities for males were at nearly 700 m, high on the Pico and while this made no biological sense, that’s where my stalwarts had to go. This is no small matter given the topography of the island, but graduate students are good at this sort of thing and anyway, they tend to be younger and more vigorous than their advisors!

Principe terrain. Pico do Príncipe is in the clouds to the left of the large Pico Papagaio. R. Wenk phot. GG III

 Josef Uyeda hunting for caecilians on São Tomé. D. Lin phot. GG II  

While in the same general area as earlier workers at about 700 m, Josef got a lot done but the party was caught in heavy rains.  He heard males and saw them calling but only managed some rather distant, poor-quality recordings (the conditions were miserable), but now at least we knew that the frogs did, indeed, call.  GG III, last spring, provided some answers, thanks in part to our friend Ramos of Bom Bom Island.  Ramos is assistant manager of the resort, a native Principean and a keen, observant naturalist.  See the photo of Ramos in the “We Find Jita” blog.  I described our past difficulties in trying to record the voice of the Príncipe giant treefrog to him, and he grinned and said, We will go to my roça (farm) on Pico Papagaio and at 5:30, we will get them!  I was highly skeptical…

Roça Papagaio, Ramos’s farm at 250 m. R. Wenk phot. GG III 

Ramos’s farm is in the forested area on the northern flanks of Pico Papagaio at about 250 m.  Just before you reach it on a dirt steep uphill road, you cross a tiny creek; this is where Ramos took us –  about 30 m up that small creek, thick with dense undergrowth, and there we sat, waiting for the forest cacophony of grey parrots, mona monkeys to subside.  Nothing much happened.  I had my iPod with recording head at the ready.  We waited in the gathering gloom for about 20, maybe 30 minutes, Ramos grinning throughout and occasionally exclaiming,  Just wait. We will get them! 

Me waiting, iPod in hand, for the giants to call.  T. Daniel phot GG III 

And sure enough, we began to hear frogs calling. I looked at my watch. It was 5:30. The call is certainly a strange one; it lacks resonance (remember males don’t have a vocal sac) and thus it is rather flat and unmelodius. Rather than my trying to describe it or arguing with earlier descriptions, you can listen to it yourself by clicking this link: 

Click here to listen

And here are a couple of photos of the male that was calling, taken by Wes. These are un-posed and taken before we collected it as a voucher specimen for the voice:

 Weckerphoto GG III

 Weckerphoto - GG III 

There are still great gaps in our knowledge of this most unique frog.  Obviously, the males are well-distributed in the lower elevations; we just have not been in right place at the right time.  We still cannot explain why females are dull and rather cryptic in coloration and usually found on the ground, while there appears to be no selection for color in males.  The dull color of females seems consistent, as a couple of months ago I found six additional females (no males) collected in 1988 at the Doñana Institute in Seville and they were clearly drab in life; my colleagues at Donana tell me they were collected on the ground in lowland localities at Rio Papagaio and Bela Vista.

Six female Seville specimens at Donana Institute.  RCD phot. 

We still have not observed breeding, nor have we ever seen tadpoles.  In this genus, Leptopelis, they are very distinctive, and I would predict the tadpole will look like this: 

A Leptopelis tadpole. Image courtesy of Dr. R. Altig 

Here’s the parting shot: 

Nezo, of Angolares, Sao Tome: artist, musician, restaurateur and worthy man - Weckerphoto GG III

PARTNERS We gratefully acknowledge the support of the G. Lindsay Field Research Fund,  Academy Research Venture Fund of the California Academy of Sciences, the Société de Conservation et Développement  (SCD) for logistics, ground transportation and lodging, STePUP of Sao Tome http://www.stepup.st/, Arlindo de Ceita Carvalho, Director General, and Victor Bomfim, Salvador Sousa Pontes and Danilo Bardero  of the Ministry of Environment, Republic of Sao Tome and Principe for permission to export specimens for study, and the continued support of Bastien Loloumb of Monte Pico and Faustino Oliviera, Director of the botanical garden at Bom Sucesso. Special thanks for the generosity of four private individuals, George F. Breed, Gerry F. Ohrstrom, Timothy M. Muller and Mrs. W. H. V. Brooke for making these expeditions possible.          

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Category: Biodiversity, Gulf of Guinea, Island endemics, Sao Tome, biogeography, gigantism, principe | Date: Nov 18 2008 | By: islandbiodiversityrace

First, I thought it would be useful to illustrate, in one place, how many scientists have been involved in the Gulf of Guinea expeditions since 2001 including the folks going in January 2009 (Gulf of Guinea III B). 

In Part I of this blog, I suggested that it is not just the high numbers of plants and animals that are endemic to these islands that is striking; it is also the fact that many of them are particularly poor dispersers over salt water and, according to dogma, they just shouldn’t be there! A scientist would never predict the presence critters like amphibians on oceanic islands. Don’t believe me? Even Darwin himself made the observation:

 Courtesy Dr. M. Vences, University of Braunschweig.

Amphibians and burrowing reptiles are among the most obvious of the unlikely inhabitants on the two islands but there are more subtle oddities as well.  The plant group Acanthaceae (shrimp plants), which are the specialty of Dr. Tom Daniel (GG III – see May 2, “News From the Flower People”) is another group whose presence is surprising.  

Dr. Tom Daniel. Lagoa Amelia, Sao Tome (RCD phot. GGIII) 

Heteradelphia  paulowilhelmina– an endemic genus? Weckerphoto GGIII  

The seeds of this group have no “wings” or other morphological adaptations allowing them to be blown by winds (wind dispersal is very common among plants – think of dandelions).  They do not float, they are too heavy, and anyway they are not salt-tolerant. If that were not enough, shrimp plant seeds do not have endosperm; i.e. they are not nutritious and thus are very unlikely to be routinely eaten by birds or mammals, then transported as stomach contents.  In fact, seed dispersal in this group is accomplished by the capsule that bears the seeds “exploding” and casting the seeds a matter of a few meters away from the parent plant.  Yet, there are 15 species native to the islands (non-introduced), two of which are endemic.  How did they get there across the water? 

I think the most likely answer to this question is that in the distant past these species crossed the marine barrier between Africa (the source) and the islands by floating on rafts.  My colleagues and I published this “rafting hypothesis” about a year and a half ago, largely based on the study of one group of frogs; however, the more I learn about the island endemic fauna, the more I am convinced that this is the most likely scenario.  

The first thing to remember is that two of the mightiest rivers on earth feed directly into the Gulf of Guinea - the Congo and the Niger. The Congo especially has an enormous drainage from deep within the African interior, and we know that the Niger flowed from current Lake Chad not so long ago; these might be considered amphibian freshwater highways from the interior to the coast.  It is not difficult to envision rafts of matted vegetation, tree trunks etc., floating downstream on one of these great rivers and being discharged into the Gulf of Guinea.  But we propose rafts composed of huge chunks of riverbank, chunks large and diverse enough to harbor burrowing forms and amphibians. 

Illustration by Richard E. Cook, San Francisco.

Such rafts might be many acres (hectares) in size such as in this drawing by my artist friend, Richard Cook. Rafts of this size might be expected to have rotten logs, trees, bushes rocks etc.  Does this actually happen? Yes, such huge rafts containing all manner of wildlife are fairly common breaking off and floating down the Amazon and the La Plata (they are called Camalotes); however, in the case of the Amazon, they are not often discharged into the Atlantic. Rather, they tend to accrete together at the delta, forming large masses. 

Satellite image, from World Wide Web.  

In the satellite image above, the red star indicates a large accretion island in the Amazon Delta called Marajó – it is about the size of Belgium! I can think of two possible explanations for why islands formed in the Amazon accumulate at the delta rather than float out to sea. 

RCD phot. 

First, notice above that the water remains relatively shallow for a great distance seaward from the Amazon Delta; this is because the continental shelf is about 200 miles wide before dropping off into great depths.  By contrast, the continental shelf off the Niger and Congo Rivers is much narrower (arrows on the right); moreover, just offshore from the Congo Delta is a deep abyss called the Congo Canyon.   Second, I think the water velocity in the Amazon is significantly lower in the Amazon than it is in the Congo, at least.  In fact the Congo is only navigable for about 80 miles inland.  The yellow star in the image below is the town of Matadi, which is as far inland as one can get by boat.

 Matadi, D.R.C., as far as you can go.  (RCD phot. 1984 

Upstream from Matadi are a series of rapids or cataracts formed as the river cuts though the African coastal uplift. 

Congo cataract. Google Earth image.

Rapids below Stanley Pool, D.R.C. -  Souljah phot.  WWW.

 These rapids increase the water velocity so that I suspect the river is much swifter overall than the Amazon, and it is far more likely that floating objects would be ejected out over deep water from the mouth.  How such floating objects would survive the cataracts themselves is an open question.  Given a large chunk of riverbank being ejected out into the Atlantic Ocean from the mouth of the Congo, what happens next?

Google Earth, RCD composite.

 The image above shows the mouths of the Congo and Niger (yellow stars) and the directions of the dominant ocean currents in the region.  Note that any floating object ejected from the Congo River will immediately encounter the Benquela Current and be carried north; such an object from the mouth of the Niger will be carried East by the Guinea Current.  It so happens that these two major currents converge to form the South Equatorial Current which flows due west, right through the central Gulf of Guinea Islands!  Conditions being perfect, we estimate that a floating object would take less than two weeks to reach São Tomé or Príncipe from the mouth of the Congo.     But, given our knowledge of the physiology of amphibians, what about the effects of the saltwater during the voyage.  Well, it seems that at predictable times of the year, the surface water of the Gulf of Guinea is not all that salty. 

From Measey, et. al. (2007). Journal of Biogeography

Notice that during the rainy season (around February) the surface salinity around the islands drops to around 31 parts per thousand of salt (technically it is brackish). Recall that because of differences in density, freshwater floats upon salt water. This sharp decrease in surface salinity is due to massive freshwater discharges of both the Congo and the Niger into the Gulf, plus the extremely high precipitation in the area as a whole.  And of course, with high flow rates and the two mighty rivers in spate, this would be the time of year when pieces of riverbank would be most likely to break off and flow downstream.  So a combination of factors, the locations of the rivers, the directions of the dominant ocean currents and periodic surface salinity changes, all point to rafting as the most likely way the amphibian ancestors of the current endemics actually arrived on the islands. We cannot prove this happened; we simply claim it is possible and likely.  Moreover, , one must bear in mind  that there has been a 13 million year period during which it might have in the case of São Tomé; as for Principe, it has been sitting out there “available for colonization for over 30 million years! 

Here is the parting shot: 

Angle of Repose on Principe. Weckerphoto, GG III.

PARTNERS We gratefully acknowledge the support of the G. Lindsay Field Research Fund,  Academy Research Venture Fund of the California Academy of Sciences, the Société de Conservation et Développement  (SCD) for logistics, ground transportation and lodging, STePUP of Sao Tome http://www.stepup.st/, Arlindo de Ceita Carvalho, Director General, and Victor Bomfim, Salvador Sousa Pontes and Danilo Bardero  of the Ministry of Environment, Republic of Sao Tome and Principe for permission to export specimens for study, and the continued support of Bastien Loloumb of Monte Pico and Faustino Oliviera, Director of the botanical garden at Bom Sucesso. Special thanks for the generosity of four private individuals, George F. Breed, Gerry F. Ohrstrom, Timothy M. Muller and Mrs. W. H. V. Brooke for making these expeditions possible.             

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Category: Biodiversity, Gulf of Guinea, Island endemics, Sao Tome, frogs, gigantism, principe, snakes | Date: May 27 2008 | By: islandbiodiversityrace

Scientists love islands because the processes of evolution on islands are simpler than they are on more complex, much larger continents and thus more easily studied. I have made the point that the islands of Sao Tome and Principe are very poorly known, but what we do know is very exciting. One evolutionary pattern that seems to consistently appear on islands is the phenomenon of gigantism; for some reason certain successful colonizers become very large on islands: for instance, think of the tortoises on the Galapagos Ids. or on Aladabra. There are a number of hypotheses that attempt to explain this phenomenon, but none is particularly compelling; nevertheless, the pattern exists and is very evident on the oceanic Gulf of Guinea Islands. The composite image below illustrates just a few of the giants on Sao Tome and Principe.

Some Island Giants

Think of potted plants for a moment… how large is a begonia? The central plant in this composite image is the largest species in the world, Begonia baccata. It is found only on the island of Sao Tome and reaches 10 meters in height! This particular specimen graces the southern shore of Lagoa Amelia at about 1480 m elevation - my head comes up to about flower level on this old friend (I am 6′ tall); these enormous plants are common at higher levels. The two birds figured are also giants: the yellow one on the right is the world’s largest weaver. Ploceus grandis,. and the one on the left is the world’s largest sunbird, Dreptes thomensis; both endemic to the larger island of Sao Tome. This is a good point at which to mention that island dwarfism is also an observable phenomenon  here as well, and the world’s smallest ibis, the Sao Tome Dwarf Ibis, Bostrychia bocagei is also an endemic.  The other critters in the collage, the frogs and the lizards, are all endemic giants but I will deal with them later. It is important to bear in mind that when we call a species a “giant”, we are describing its size compared to all of its other relatives only; such a species may not appear to be a giant at all, in our eyes.

The Sao Tome Giant Treefrog, Hyperolius thomensis, and I go back a long way; back to when I was writing my doctoral dissertation many years ago. This sapo (as all frogs are called on the islands) is endemic to Sao Tome only and is easily the largest member of its genus (Hyperolius)- females reach lengths of nearly 50 mm.from snout to vent!

Sao Tome Giant Treefrog, Hyperolius thomensis.GG I and GG II - D. Lin

Nearly all of the original material from which this species was described in 1886 was destroyed in the fire in Lisbon.  But I managed to find four remaining specimens, two in Vienna and two at the Natural History Museum in Vienna, allowing me to treat them in my dissertation.  In 1988 and again 1990 more specimens were reported by a Swiss worker, but her published locality data are very general, if not vague, and it turns out that most of the material she worked on was collected by locals at her request prior to her arrival.  During GG I, we visited most of her reported localities, finding nothing until we finally got lucky. Now, I can state that this most flamboyant of treefrogs is currently known for certain from only a single locality!  Our work in GG I, II and III has confirmed that this marvelous critter is known only from higher elevations (above 1000 m), inhabiting the canopy of old secondary or primary growth trees on steep slopes.  And it appears to breed only in the water-filled holes in trees with fluted bark or buttresses.  This is a rarity – in Africa, only 9 other frog species are known to breed in phytotelmata (scientific word for treehole). But it makes sense.  Most frogs lay eggs, which develop into free-swimming, gilled tadpoles, which then metamorphose.  Although there are many fast moving rivers on the steep slopes of Sao Tome, these are far to swift for breeding; still bodies of water simply do not exist. So, H. thomensis has adapted to breeding in ephemeral, rain-filled holes in the trunks of very large trees! All of the other frogs native to the islands utilize slow moving or still water for reproduction.

The tree - J. Clara, GG III

This is the only tree in which we have collected the Sao Tome Giant treefrog.  It is at about 1100 m on a high ridge, and we return each expedition to check its status. Adults are usually present but there are always eggs and tadpoles at different stages of development in the holes.  Tom and Rebecca, our botanists, could not identify this tree – it is simply too tall its see its canopy, and moreover it is festooned with epiphytes.

Frogs and eggs in treeholes -  WE, GG III

Wes Eckerman, our photographer tried to climb it, and then tried to climb an adjacent tree to see if there were more holes, but the tree is just too big in girth to handle; with our friend Jose Clara, we tried to erect a crude ladder to examine a hole farther up the trunk but to no avail.

RCD, GG III

I do not mean to imply that this species is restricted to this tree.  We have heard the species calling at night from high up in the canopy and reasonably certain that it is pretty widespread, at least in the high elevation forests we have visited – I suspect it is present on Sao Tome anywhere the trees are large enough and that. of course.  means upslope above the former Portuguese plantations.  What is different about this single documented tree is that it is the only one whose rain-filled holes are within our reach – there are undoubtedly more holes in many more trees that are too high for us to access.  I am left with the notion that given its restricted range and peculiar breeding biology, the Sao Tome Giant Treefrog is a classic indicator species; its presence means healthy mature forest.  If I were to choose an icon to symbolize the dogged persistence of pockets of nature in the face of man’s depredations and at the same time the attitude, beauty and whimsy of the citizens of Sao Tome and Principe, it would be this gorgeous island giant. Josef, my former student, informs me that he has already seen the name of this species on a price list in the pet trade in Europe.  If you  wonder why I have not described the location of this tree is in more detail, now you know. 

In the last posting, I promised you a picture of the cobra jita of Sao Tome. Here are shots of both island forms, which are currently considered to be the same species.

Sao Tome Jita - RCD, GG I

Principe Jita - WE, GG III

Not only do these critters look different from those on Sao Tome (stripes vs. patterned blotches), they act differently as well. On Sao Tome, cobra jita appears to be strictly nocturnal; during GG I and GG II we easily found them at night by first listening for the loud choruses of oceanic treefrogs (more about them later). So far as we know, the Sao Tome jita largely feeds on these frogs while they are breeding and is strictly nocturnal; to see at least ten of these snakes in a single night under the right conditions is not uncommon.

R. Stoelting, my grad student, with her first Jita - GG I, RCD phot. After our week on Principe, however, I am prepared to say that that jita is diurnal and although we will not know until we check stomachs, I think it feeds on lizards and small rodents. We even located a chorus of treefrogs behind Bombom but failed find a jita, nor did we ever find one during our night hunts. Only time and careful study of morphology nd DNA will tell us how closely related these two island snakes really are.Thanks to Caitlin D. for her generous donation. We are doing what we can!

PARTNERS We gratefully acknowledge the support of the Research Investment Fund of the California Academy of Sciences, the Société de Conservation et Développement  (SCD) for logistics, ground transportation and lodging, STePUP of Sao Tome http://www.stepup.st/ and especially the generosity of three private individuals, George F. Breed, Gerry F. Ohrstrom and Timothy M. Muller, for making GG III possible.

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Category: Biodiversity, Gulf of Guinea, Island endemics, Sao Tome, biogeography, gigantism, principe | Date: Apr 29 2008 | By: islandbiodiversityrace

What We Are Doing.

Surprisingly, São Tomė and Príncipe have remained largely unstudied since the early 19th Century work of Portuguese biologists Fea, Greef and Newton. In spite of the wonderful but preliminary stuff discovered by these early biologists, São Tomė and Príncipe have remained “off the scientific beaten path”. Historically, the islands were used as major slave entrepots by the Portuguese and were of world importance in the production of sugar, coffee and then cacao. Lying 200 to 250 km off the coast of West African coast, the islands have always been rather remote, and even to this day, there is but one flight per week from Europe to São Tomė (via Lisbon) and only a couple from Libreville, Gabon. In spite of several hundred years of agricultural efforts, fairly large amounts of original forest remain in higher elevations that were simply too steep to be cultivated by the colonials. While the birds have been studied and a preliminary flora has been published, huge portions of the biodiversity of these unique islands remain completely unknown.

Drs. Iwamoto and Drewes sampling fish. Principe GG I (D. Lin phot)

Periopthalmus A Principe mudskipper GG I (D. Lin phot)

So what we are doing is the most basic work in science; we are hiking into these remaining natural areas and surveying them to find out what species live there, what their evolutionary relationships are and where they came from. Depending upon our different specialties, we work both by day and by night, collecting, sampling, photographing, recording, etc. Most of our material is brought back to the California Academy of Sciences for study, but much also goes out to specialists around the world. As systematists, our job is to explore and sample all of the elements of the fauna and flora. When new species are discovered, we must analyze and describe them. Systematics is the fundamental discipline upon which all other biological work depends, especially including conservation efforts. You cannot save what you do not know.

Grad student R. Stoelting. Night work on Sao Tome GG I (RCD phot)

Giant gecko (H. greefii) Principe GG II (D. Lin phot)

WHY A “RACE”?

Exclusive Economic Zone, Rep. Sao Tome and Principe.
As the title “Island Biodiversity Race” implies, there is a significant element of urgency in our work. The islands of the are about to undergo profound change, and the reason is oil. The exclusive economic zone of the Republic includes areas in the Gulf of Guinea where oil has been discovered. This means that at the very least, there will be a huge influx of revenue into this tiny republic of less than 300,000 people, and along with this revenue will come enormous pressure to expand infrastructure and a consequent burgeoning of the human population. History repeatedly shows us that such a phenomenon almost always affects natural wild areas negatively. Thus, It is our purpose to learn as much about the flora and fauna of the islands as quickly as we can, before the changes come. We hope to demonstrate to the citizens of the Republic of São Tomė and Príncipe the unique biological nature of their islands and enable them to make informed decisions down the road. We hope to show what they, and for(and for that matter, the rest of the world) stand to lose without adequate stewardship.

Kids at Santa Catarina, Sao Tome GG II (D. Lin phot)

Sao Tome GG II (D. Lin phot)

In this blog, I will describe the Third California Academy of Sciences Gulf of Guinea Expedition (GGIII) as it unfolds. Each expedition is made up of scientists chosen because their specialties are poorly known on the islands. The following URL describes our goals, the participants in the first two expeditions, and our scientific progress since the first expedition in 2001 (GGI).

PARTNERS We gratefully acknowledge the support of the Research Investment Fund of the California Academy of Sciences, the Société de Conservation et Développement  (SCD) for logistics, ground transportation and lodging, STePUP of Sao Tome http://www.stepup.st/ and especially the generosity of three private individuals, George F. Breed, Gerry F. Ohrstrom and Timothy M. Muller, for making GG III possible. http://research.calacademy.org/research/herpetology/bdrewes/

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