Summary of symposium "Evolution in the Galapagos" held December 8, 1982 in London

Boag, Peter T.

English

Aquatic Commons

GALAPAGOS EVOLUTION CONTINUES 
by 
Peter T. Boag 
With the Darwin centenary year now drawn to a close, it is already clear that it has produced a rich harvest 
of new information on the man and his work. Of the many papers, books and symposia produced in his 
honour, Darwin himself might have liked most to attend the last public event - a symposium on 
'Evolution in the Galapagos', organized by R. Berry and hosted by the Linnean Society on 8 December in 
London l . 
Before Darwin, there was little appreciation of the biological uniqueness of islands, as A. Cain pointed out 
in his historical introduction. Cain ascribed this failure to the 'naive taxonomy' of the time. The lack of 
explanations for disjunct distributions of taxa or for the difference between convergence and affinity 
hindered 'amateur naturalists' such as Darwin when he set sail on the Beagle in 1831. 
This theme was pursued further by F. Sulloway in discussing his own historical detective work on Darwin 
and the Galapagos2 3. Sulloway dismissed as a myth the idea that Darwin had been converted to the theory 
of evolution by a 'Eureka!'-like experience in the Galapagos; instead his fuzzy grasp of systematics blinded 
him to the evolutionary significance of inter-island variation in the tortoises, mockingbirds and the now 
famous Darwin's finches. Darwin not only failed to separate correctly his finch specimens by island in the 
Galapagos, but also helped his shipmates eat their way through tortoise variants that were not collected 
again until years later. 
What did happen was that in the second week of March in 1837, after his return to England, Darwin had a 
meeting with John Gould to discuss the Beagle bird specimens. Darwin was stunned by Gould's findings, 
and has tily scribbled the main points on the back ofa scrap of museum paper. It seemed that , among other 
things, the motley group of birds Darwin had identified as a mixture offinches, wrens and blackbirds was 
in fact a closely related subfamily of passerines, new to science. Realizing the importance of knowing 
which forms had come from where, Darwin began the frustrating task of quizzing Captain Fitzroy and 
other shipmates, who had fully labelled specimens. Darwin was never entirely happy with the result , and 
perhaps for this reason omitted any mention of the finches from his Origin of Species. Sulloway suggested 
that this group of birds became closely identified with Darwin and evolutionary theory largely because of 
David Lack's book Darwin 's Finches. 
The " Warbler" Finch (Certhidea olivacea): one of the unfinchlik e fi nches that puzzled Darwin 
Photo by Alan Root 
6 
Noticias de Galapagos, no. 37 1983
Large Ground Finch (G. magnirostris) on Daphne Major, beside Bursera berries 
Photo by Dr. Peter T. Boag 
Recent geological work in the Galapagos and an improved understanding of the plate tectonics of the 
region (B. Rosen and T. Simkin) show that the islands are younger than previously thought - no older 
than 3-5 million years. They have never been connected to the mainland, and remain among the 12 most 
active areas of vulcanism on Earth. The likely evolutionary age of several Galapagos vertebrates was 
reduced further still in J. Patton's discussion of genetic processes in Galapagos organisms. His 
electrophoretic studies of the finches, tortoises, lizards and rats suggest that with the possible exception of 
the land and marine iguanas , the small genetic distances among most taxa indicate evolutionary histories 
of under one million years4 5. Biochemical characters produce phylogenetic trees very similar to those 
suggested by traditional taxonomic approaches but show a small and constant rate of change relative to 
changes in some morphological characters. This supports recent suggestions that evolutionary changes in 
structural genes occur in a clock-like fashion, while morphological changes can occur at different rates as 
selection acts on 'regulatory genes'. 
Recent research on Galapagos land birds, and on Darwin's ground finches in particular (P. Grant), shows 
interesting developments in at least four areas, including the origin of Darwin's finches, the discovery of 
the first fossil finches , the study of contemporary evolution in the Geospiza and the confirmation of David 
Lack's model of adaptive radiation6 7. A widely distributed South American emberizid , the blue-black 
grassquit (Vo/atinia jacarina), has recently been proposed by D. Steadman as the direct ancestor of all the 
Darwin's finches. Steadman has also discovered the first vertebrate fossil in the Galapagos, confirming the 
previous abundance of two finch populations rendered extinct since Darwin's time and suggesting that 
other finches as well as native rats went extinct before ever having been recorded8 9 
Specific island populations of tortoise are being identified by T. Fritts, partly to aid captive brc:eding 
programmes by including animals of unknown origin located in zoos. The small genetic distances between 
tortoise populations have hindered this task, as has the apparently high degree of morphological 
convergence seen in different tortoise populations in similar environments. H. Snell has also looked at the 
7 
Noticias de Galapagos, no. 37 1983
similarity of various iguana populations in the Galapagos, as recent assaults by feral dogs have nearly 
obliterated two land iguana populations. Prompt work by Snell and his colleagues has led to the successful 
captive breeding and reintroduction of these animals, in concert with programmes to eliminate the dogs 10. 
Snell found that on the basis of morphology, land and marine iguanas are very similar to each other and 
different from mainland species. Patton had suggested that the large genetic distances between the marine 
and land iguanas indicated that they were unrelated and colonized the Galapagos separately a long time 
ago. But in a surprising announcement Snell revealed that he had been studying what appears to be a land-
marine iguana hybrid for three years. The hybrid shares features of each genus - it has, for instance, 
unwebbed front toes but webbed rear toes. 
Y. Lubin and D. Porter discussed recent work on introduced invertebrates and plants. Lubin has been 
following the invasion of the fire ant (Wasmannia), which probably arrived in the islands in the 1930s, but 
is still dispersing at rates of up to 170m yr_l. As it enters an area, native ant species disappear, as do other 
arthropods such as scorpions and spiders. Porter pointed out that up to 26 per cent of the 738 known 
Galapagos plant taxa are now introduced, most within the past centuryll. There is no sign that the rate of 
invasion or redistribution of introduced plants is slowing and although many of the 'weeds' occur in 
disturbed habitats, several invaders threaten natural areas. 
Finally, in a discussion of the role of man in the accelerated rate of 'evolutionary' change in the Galapagos, 
P. Kramer argued that in addition to trying to understand how native Galapagos plants and animals 
evolved and attempting to control introduced species, biologists should also monitor the process of 
invasion. Understanding why particular introduced plants or animals succeed or fail and how native 
species respond to introduced species may in the long run contribute as much to our understanding of 
evolution as research on native organisms l2. This brought home a bitter-sweet message about 
evolutionary research in the Galapagos: much less is known about evolution in the Galapagos than most 
people think, but Galapagos populations and communities are probably now changing faster than ever. 
Peter T. Boag is at the Edward Grey Institute, University of Oxford, Oxford OX1 3PS. 
'. The symposium will be published in Bioi. J. Linn. Soc. in 1983. 
'. Sulloway, F.J. J.His/.Biol. 15, I (1982). 
J. Sullo way, F.J. Bull.Br.Mus.Nat.Hist. (Zool.) 43, 49 (1982). 
'. Yang, S.Y. & Patton, J.L. Auk 98, 230 (1981). 
5. Marlow, R.W. & Patton, J.L. J.Zool.Lond. 195,413 (1981). 
". Boag, P.T. & Grant, P.R. Science 214, 82 (1981). 
7. Grant, P.R. Am. Sci. 69,653 (1981). 
8. Steadman, D.W. Proc. 8th into Cot/gr. Speleo. 2,549 (1981). 
9. Steadman, D.W. Trans. San Diego Soc. Nat. Hist. 19,279 (1982). 
10. Reynolds, R.P. Not. de Ga/tipagos 36, 13 (1982). 
11. Eliasson, U. Not. de Ga/tipagos 36, 7 (1982). 
". Duffy, D.C. Not. de Galapagos 33, 21 (1981). 
Reprinted by permission from NATURE, Vol. 301, 6 January 1983, p.1l. Copyright © 1983. Macmillan Journals 
Limited. 
8 
Large Ground Finch 
Geospiza magnirostris 
Drawing by Peter Scott 
Noticias de Galapagos, no. 37 1983


Galapagos evolution continues

http://aquaticcommons.org/9993/1/NG_37_1983_Boag_Galapagos_evolution_continues.pdf

Galapagos evolution continues

Abstract

Similar works

Full text

Available Versions

Aquatic Commons