Posted by: chelonianresearch | April 23, 2009

Galapagos Expedition

SUMMARY REPORT OF GALAPAGOS EXPEDITION
DECEMBER 2008

Peter C. H. Pritchard
Chelonian Research Institute
Oviedo, Florida

BACKGROUND

As long ago as 1835, the youthful Charles Darwin learned from the English Vice-Governor of the Galapagos Islands that the giant tortoises were different on each of the islands of the archipelago, and that “one could with certainty tell from which island any one was brought.”  Generally speaking, the claim was true, although the hatchlings and juveniles are indistinguishable, and even the adults show significant variation within a population.  But further explorations have shown that the isolated island populations differ in adult size, in coloration (especially of the face), and in morphology, notably in the height of the anterior shell profile, the length and thickness of the neck, and the openness of the front of the carapace.  Those with the shell form known as “saddleback” generally inhabit the lower, hotter, dryer islands, where food is limited and may involve reaching for high-growing leaves and cactus pads.  By contrast, the dome-shelled tortoises are able to grow to enormous size as they graze upon the lush grasslands growing on the rich, volcanic soils of the moist uplands of the larger islands.

The tortoises were exploited on a genocidal scale throughout the archipelago by buccaneers and whalers during the 18th and 19th centuries, and the settlers and ranchers in the early 20th century continued the slaughter.  The Floreana subspecies was apparently exterminated by 1840, and the very distinctive Pinta tortoise is also extinct on its native island, as we confirmed on our 2003 expedition.  The populations of Rabida, Fernandina, and Santa Fe do not exist today, and although isolated tortoises have been found on these islands, these were probably introduced and there may never have been actual populations on any of the three. A single Pinta tortoise, found in 1972, many decades after the race had been considered totally extinct, lives to this day in a corral at the Charles Darwin Research Station on Santa Cruz Island, where, as “Lonesome George,” he has become the most famous tortoise in the world.

Tortoises exist on all of the five main volcanoes of the large island of Isabela, with some of the largest specimens ascending several thousand feet to the caldera rims of Alcedo and Cerro Azul.  Formerly, it was assumed that each mountain population was isolated from all others, and each was given a unique scientific name (species or subspecies).  However tortoises have also been found in the lowlands between each pair of volcanoes (with the exception of Perry Isthmus, between Alcedo and Sierra Negra).  The largest population, perhaps 5000-6000 animals, is thought to be that of Alcedo or Cowley Mountain, the most centrally located of the five mountains. On western Sierra Negra in southern Isabela, there is an isolated population of huge but flattened tortoises, locally known as the aplastados, currently being successfully propagated in captivity in the coastal settlement of Villamil.   Other tortoise populations occur on western Volcan Darwin and at various sites and different altitudes on Cerro Azul, with seasonal occurrence of tortoises near sea level in both cases.

Tortoises are quite widespread on Volcan Wolf, the highest and northernmost of the five volcanoes of Isabela, where the equatorial line actually passes along the southern rim of the caldera itself.  I have visited the lowlands of this 5600 foot mountain several times in the last four decades, in the later years accompanied by experienced National Park wardens, and we always found at least some tortoises, the most being 30 in three days in 2003.   An exciting recent event was the discovery, by helicopter-based goat hunters, of very large populations of tortoises in the highest parts of the volcano, rarely if ever visited by man.  It has been estimated that the tortoise population of the mountain may even be comparable to that of Alcedo.  Certainly there are a lot more than the early (1960s) estimate of just a few hundred.

Subsequently, there was even more dramatic news.  A team of scientists headed by Gisella Caccone at Yale University was able to extract DNA from some of the series of 15 tortoise skeletons (all males) that I had collected from deep ravines on Pinta in 2003.  Making comparisons between DNA from these animals and that of a series of a few dozen live Volcan Wolf tortoises, it was determined that there were tortoises on Volcan Wolf that had 50% Pinta parentage.  Even more dramatic, there was genetic evidence that other tortoises on Wolf carried genes from the long-extinct Floreana tortoise, whose genetics had been investigated by the Yale team using bones of animals that had been trapped in caves on Floreana two centuries ago or more.  With modern and ever-advancing genetic techniques, it is possible to dream that the Pinta tortoise and perhaps even the Floreana tortoise might once again walk the ancient trails of their native lands.

Where does one start?

THE 2008 EXPEDITION

More blood samples were needed to document the genetic status quo of tortoises on Volcan Wolf.  The Park Service agreed to put together a large team, totaling over 40 participants, who would be divided into small groups to undertake transects throughout nine areas of western and northern Volcan Wolf.  A partial funding commitment for the expedition was made by National Geographic Society. The search territories were mostly contiguous and were not extensively covered by lava floes, where tortoises would be unlikely.  The search occupied nearly two weeks in December 2008, and the search for tortoises was thus on a scale never before tried on this mountain.  The personnel consisted mainly of National Park field staff headed by Washington “Wacho” Tapia, with two American geneticists (Kevin Shoemaker and Michael Rossello), and the Italian tortoise geneticist Claudio Ciofi  included, as well as James Gibbs, an academic Galapagos tortoise expert;  Joe Flanagan, the chief veterinarian at the Houston Zoo; a professional photographer named Peter Oxford; and myself.  Famed Galapagos photographer Tui de Roy was the only woman in the party. Dr. Caccone arrived a week before the expedition departed, supervising all the planning details, but returned toYale once plans were complete, giving up her place on the field team in favor of an experienced Ecuadorian Park warden.

Joe Flanagan’s role was to teach us blood extraction techniques as well as insertion of subdermal PIT tags by which each tortoise found could be permanently identified.  (On my previous visit in 2003, the much more primitive technique of red-hot branding of the rear of the shell was used.).  The most vital members of the team were those with the humble but demanding task of being professional water carriers.  Each day, each of them would strap a five gallon plastic water tank on to his back, hike up the mountain, and deliver it to one of the camps.  If he got lost or did not arrive, there would be danger of serious thirst, or worse.

My role was, in part, to provide continuity with Pinta tortoise conservation efforts dating from the discovery of Lonesome George in 1972 to the present, and to evaluate the morphology of any tortoises found.  I was also part of Search Team A, with responsibilities to photograph every tortoise found from standard angles, make various measurements of the shells, and keep notes.  Each tortoise encountered had to submit to our battery of tests and manipulations – blood sample, PIT tag, external painted number, precise GPS location, measurements over curve and straight line, sex, etc., as well as to record any peculiarities of shape that might indicate exotic ancestry. The DNA analysis would take place back at Yale, and the hope was that the genetically “interesting” tortoises could be identified by the PIT tags and painted numbers, and by their GPS locations.  Actually finding them on a later expedition was the weakest link in the plan; some tortoises might have minuscule home ranges that they never left; but others might migrate thousands of feet up or down the mountain.  Radio transmitters on the tortoises would have been useful for locating the animals later, but with a target of 2000 tortoises this was beyond the reach of the budget.

FINDINGS

The group broke down into nine sub-teams, each operating in a designated, GPS-defined area on the western or northern part of Volcan Wolf.  Team A consisted of two co-veterans of the 2003 Pinta expedition (“Pajaro” and “Simon Bolivar”), as well as Peter Oxford and myself.  The other eight camps and search areas were located progressively higher and further inland.  Our group was the last to be dropped off by the mother ship Sierra Negra, our landing point being a tiny bay, with a black sand beach fringed with lava and mangroves, known as Puerto Bravo.  Ours was the only one of the designated search areas that included shoreline – a disadvantage in that the lowlands became extremely hot, here at latitude 00.0 degrees, during the middle hours of the day, but there were compensating advantages, including access to lowland tortoise breeding areas, and the convenience of the seashore for bathing and washing.  More importantly, we were spared the task of hauling camping gear, food, and equipment up the mountain.

The mangrove fringe was not extensive, and behind it was rough lava terrain, but we found just enough tree-shaded terrain to erect a tarpaulin-roofed kitchen and four small tents, although the resident sea lion family did not yield an inch.  High tide came within a foot or two of my tent, but each night, from sheer exhaustion, I slept soundly for about ten hours.

Every day, we woke with the sun, breakfasted, and embarked upon a day-long patrol.  My water supply for each excursion was carried in two 2-liter plastic coca-cola bottles; I tried to restrain myself from drinking the whole four liters before getting back to camp, but the pathetic remainder in the bottom of the bottle was hot as blood by the end of the day’s trek, and hardly refreshing.  I reflected that I was probably thirty years older than the average for the expedition (although a few were close to fifty), and did not do this kind of exertion on a regular basis.  But I kept up, although my initial pair of shoes lasted only four days.

The northern flank of our area was a flow of frightful black lava, originating way up the mountain and not stopping until it reached the sea.  There were other smaller lava outcrops, and a fair amount of scrubby vegetation, the most abundant tree species being the silver-barked palo santo, totally leafless, and awaiting the rains (due several months later), that would cause the trees to generate a flush of green leaves overnight.  But right now, they were useless for shade.  Better were the huge Scutia bushes, the live ones a mass of long green spines with some short green leaves; and the dead growth equally spiny but black in color.  Much machete work was necessary to get through these thickets, but they were useful on two counts:  one could wriggle under them, improvise a mattress from the thick leaf litter, and spend an hour in the shade during the midday heat; and we also found quite frequently that we were sharing our shade with tortoises.

They were mostly small ones.  Between the lava and the trees and the clumps of vegetation, there was actual soil, in some areas so riddled with land iguana burrows that we recalled Darwin’s experience on Santiago Island in 1835, where he found so many iguana burrows that he could not find a clear spot to camp.   We were struck by the apparent grouping of the young tortoises – we might find three, or four, or five, of virtually identical size under one spreading Scutia tree.  They were never active; in fact I got the impression that no tortoise that we encountered had moved for weeks, yet they were all healthy and of good weight.  This extremely sedentary lifestyle may explain the curious grouping of tortoises of similar size:  perhaps there had been a successful nest nearby several years ago, and the emerging hatchlings had walked to the nearest shade tree, and just stayed there ever since, finding safety and enough low-growing food to eat to keep them alive, and all growing at the same rate.  We found one fresh hatchling tortoise, and saw a number of nests, some intact and others with the hole made by the emerging hatchlings clearly visible.   On the other hand, although we saw lots of half-grown animals, we saw almost no fully grown adults, although during my visit to the area in 2003 we had found several adult males behind the mangroves and within a few yards of the sea.

We found chopped-off plastrons (belly shells) of five adult tortoises, illegally slaughtered by fishermen in this remote, rarely visited area.  Perhaps these were the same tortoises we had seen five years earlier.  Were there any adults left alive in the area?

The answer to this question was evident when we started to walk further inland.  Everywhere, there were huge head-sized boluses of compressed, dried vegetation, that were clearly the droppings of tortoises – and not small ones!  It seemed that a herd of giants had moved in for the season, grazed heavily on the seasonal grass and other plants, digested this vegan diet, and defecated copiously during the humid months, and then decamped and migrated to the uplands, along trails worn smooth by thousands of generations of their ancestors, in the dry season.  The goat hunters in the helicopter had seen these tortoises on their lofty feeding grounds three years earlier, and even as we patrolled the lowlands on foot, three dozen of our colleagues were evaluating the numbers and dimensions of the adult turtles a thousand or more feet higher up the mountain.

Altogether, the nine teams were able to log over 1650 tortoises.  All were tagged, recorded, and processed, including the extraction of about 1 cc of blood from each for later genetic testing.  Our team’s score was numerically below average – about 91 tortoises. We were not embarrassed by this total, since the adult tortoises had almost all moved higher and we were the only ones to document the smaller tortoises on the nesting grounds and developmental habitat, still living where they had hatched during the preceding years, but not yet ready to migrate.

And we found the saddlebacks! The anterior height of the shells of Galapagos tortoises is somewhat variable, but nine of our lowland Volcan Wolf tortoises – 10 percent of our total – had shells like no Isabela tortoise is supposed to have.  We won’t have the full genetic analysis for some months to come, but my own background leans more towards morphology than genetics, and I have seen all of the surviving races of Galapagos tortoise in the wild.  These Volcan Wolf saddlebacks were the real McCoy.

Saddlebacks are found on Duncan (Pinzon), Hood (Española), and formerly Abingdon (Pinta) islands.  The tortoises of Santiago are semi-saddlebacked, and are as large as the giant domed tortoises of Santa Cruz and Alcedo.  Smaller semi-saddled animals occur on San Cristobal, and used to exist on Floreana.

The Pinzon, Española, and Pinta tortoises can be distinguished by eye, at least once they reach maturity.  The adult males are the easiest to identify; the adult females tend towards the same shapes as the males but, being smaller, the allometric growth is less advanced.  Males from Pinzon and Española are both about 30 inches long (straight shell length). The adult females are only 22-24 inches long – hardly giants, but not bad by continental standards. The Pinzon animals have a relatively wide, hoop-shaped arch at the anterior of the carapace, which rises well above the retracted head, and is indeed the highest point of the shell.  It reaches about the same height in the Española specimens, but has the form of a relatively narrow, angular, parallel-sided notch rather than a wide hoop.  Both have very long, skinny necks, and yellowish faces in old adults.  The Pinta form is known, apart from Lonesome George, from a handful of mounted specimens and complete shells in the California Academy of Sciences, the British Museum, and Lord Rothschild’s Museum in Tring, England, and there are some shells at the Darwin Station, recently supplemented by the 15 incomplete skeletons that I found on the 2003 expedition.  The Pinta tortoise is also saddlebacked, but is larger in size than the other two –  George is exactly one meter (39.4 inches) long, has a thicker neck, and the shell reaches its greatest height in the shoulder region (vertebral scute no. 2) rather than at the very front.  The anterior shell margin follows smooth curves and the edge is not flared or reverted.  Genetic studies have revealed that the Española tortoise is ancestral to that on Pinta. Even though the islands are hundreds of miles apart, the sea current patterns suggest that such a colonization is possible.  This ancestry may also explain why a strongly saddlebacked tortoise form occurs on Pinta, even though it is a relatively high island, with some good grasslands at intermediate altitudes, and thus by no means typical saddleback habitat.   It may thus have arrived as a relatively small saddleback, and the larger size today (or recently!) may be a response to this more productive feeding environment.

By the criteria above, the first saddleback we found on Volcan Wolf was a Pinta female!  Pinta females are a life form unknown in modern times, in that all of the specimens found on Pinta, alive or dead, since the mid-19th century have been male, and huge rewards have been offered for the discovery of a live female..  The remainder of the nine live strongly saddlebacked animals we found included both males and females, morphologically identifiable as from Pinzon and Española.  But this is, of course, all subject to genetic confirmation by the Yale lab.

The obvious question is: what were these apparently displaced animals doing on Volcan Wolf?  In the Indian Ocean, giant tortoises were taken freely from island to island by voyagers as local populations collapsed, but there has been remarkably little of this kind of transfer in Galapagos.  Natural dispersal by flotation between islands presumably occurred very occasionally in geological times, but hardly or not at all within the span of human experience.  However, Volcan Wolf is unique in having tortoise habitat so close to the shore that it is possible both for raiding parties to grab a few tortoises and escape quickly, and also possible for tortoises that might be tossed overboard from a ship to swim or drift ashore, and to colonize the littoral and near-shore zones of the island. Such animals, if saddlebacked, might find themselves well adapted to the dry lowland areas even of a large island like Isabela, and they may simply remain in such areas and ultimately reproduce, never climbing to the high elevations as the native tortoises do.  This was probably not a recent event on Wolf; at least one saddlebacked tortoise was found there a century ago, and they have been seen sporadically ever since.

And there is one historical event that may be relevant.  In 1812, the American admiral David Porter, cruising in East Pacific waters (without the permission of his superiors), decided to attack three British whaling ships (the Montezuma, Georgiana and Policy) in Banks Bay.  As he closed in on them, the British sailors started to toss large numbers of live tortoises (collected for long-term food supplies) into the sea, to clear the decks for action and to make for greater sailing speed. Porter retrieved about fifty of the animals, and others may well have been washed ashore in the Puerto Bravo area.  Floreana tortoises still existed at that time, and the Pinta tortoise was still abundant, and we know from Porter’s Memoires that “on the 8th of June (1813), a fresh breeze sprung up and carried the Essex and her prizes northward to Abingdon,” and this incident may well have resulted in tortoise collection, and possibly been the origin of the Volcan Wolf saddlebacks. Presumably reproduction and some hybridization took place subsequently – our own observations were made almost two centuries after Porter’s adventure, but the saddlebacks we found were mostly old, judging by carapace texture and sculpturing, and may, in some cases, have been centenarians, only a couple of generations removed from Porter’s 1813 exploits.

At the time of writing, there is extremely interesting news from Gisella Caccone at Yale, who advised me that “preliminary analyses on 95 tortoises selected on the basis of morphology (saddleback, yellow faces, etc.) from all the seven field groups showed the presence of 35 individuals of mixed ancestry, including either Pinta or Floreana genes as well as those typical of the native Volcan Wolf tortoises.  Another interesting point is that most of these individuals were from the A and B (coastal and near costal areas near Puerto Bravo), not the ones up in the highlands.  There are no pure Pinta or Floreana samples among the animals we screened so far.”

Gisella concluded:  “I hope you can raise the funds for completing the genetic analyses!”

Once these analyses are done, an important policy question will remain.  What should be done with the tortoises that show significant Pinta ancestry?  Possibly, some of these tortoises will have the physical appearance of Pinta animals, yet not show the crucial marker genes for Pinta tortoises, whereas others may not show this phenotype but may test positive for the Pinta markers.  It should be noted that many genes and large sections of the DNA strands in living organisms do not “program” the animal in any physically detectable way – they are simply space fillers. In terms of adaptation to the special conditions of Pinta, in may be the tortoises that show the prescribed neck length, shell form, adult size, etc. that meet the unique ecological requirements of the island, whereas those that do not show these features but that do have Pinta marker genes may be less well adapted.  It would also be something of an anti-climax if the tortoises selected for restocking of Pinta lacked the classical proportions and shell shape of the original tortoises from this island, and would only be recognized as Pinta tortoises by the concerned public because the geneticists told them so!


Responses

  1. This is a fascinating post and I enjoy the discussion of morphological vs. genetic differences across populations. One thing that strikes me is how often turtle populations appear to have been “mixed up” by human intervention, including: green turtles (by flying eggs from Tortuguero to various places around the Caribbean for incubation and release), diamondback terrapins (from captive rearing and subsequent long-distance releases in the early part of the 20th Century), red-eared sliders (which appear to have colonized almost every continent via the pet trade). Then again, turtles seem to have a marvelous propensity for mixing up their own genetic code through hybridization – I saw today two large juvenile green x loggerhead crosses that had originally cold-stunned in Massachusetts and were released back to the ocean today following successful rehabilitation. I look forward to more posts!


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