Chemistry of the Amazon - American Chemical Society

Chapter 17

Future-Oriented Mapping of Biodiversity in Amazonia Otto R. Gottlieb

Downloaded by FUDAN UNIV on February 19, 2017 | http://pubs.acs.org Publication Date: March 31, 1995 | doi: 10.1021/bk-1995-0588.ch017

Departamento de Fisiologia e Farmacodinâmica, Institute Oswaldo Cruz, FIOCRUZ, Avenida Brasil 4365, 21045-900 Rio de Janerio, RJ, Brazil

The study of Amazonian plants leads to a comprehensive morpho-chemical concept of biodiversity. The latitudinal gradients from poles to equator for increasing richness run in the opposite direction for metabolic features. This is due to the fact that the production of both major macromolecular plant products, cellulose and lignins, is light-intensity dependent. High solar energy input around the equator conditions rapid metabolic turnover, while low energy input results in smaller rates of carbon flow through metabolic cycles with consequent micromolecular diversification potential. Crash programs for the investigation of Amazonian morpho-chemical biogeography would acquire predictive value if the usual count of species in restricted areas was replaced by surveys across broad geographic transects. Novel methodology, needed for the investigation of such mostly longitudinal trends, should help assign the regions of highest biodiversity, as well as the corridors leading up to them. Further work along these lines will clarify the fascinating question if morphological and chemical evolutionary or spacial gradients consistently point in the same direction, whatever the plant groups under scrutiny.

According to a recent book by Wilson (7), "tropical rain forests, though occupying only 6% of the land surface, are believed to contain more than half the species of organisms on Earth. An explicit example is offered by the vascular plants. Of the approximately 250,000 species known, 170,000 (68%) occur in the tropics and subtropics, especially in the rain forests. The peak of global plant diversity is the combined flora of the three Andean countries of Colombia, Ecuador and Peru. There over 40,000 species occur on just 2% of the world's land surface. [This number] is to be compared with 700 native species found in all of the United States

0097-6156/95/0588-0199$12.00/0 © 1995 American Chemical Society Seidl et al.; Chemistry of the Amazon ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


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and Canada, in every major habitat from the mangrove swamps in Florida to the coniferous forests of Labrador. To summarize the present global pattern, latitudinal diversity gradients rising [from north and south] toward the tropics are an indisputable general feature of life. And on land biodiversity is heavily concentrated in the tropical rain forests. The cause of tropical preeminence poses one of the great theoretical problems of evolutionary biology. Many [biologists] have called the problem intractable, suposing its solution to be lost somewhere in an incomprehensible web of causes or else dependent on past geological events that have faded beyond recall. Yet a light glimmers. Enough solid analyses and theory have locked together to suggest a relatively simple solution, or at least one that can be easily understood: the Energy-Stability-Area Theory of Biodiversity. In a nutshell, the more solar energy, the more stable the climate, andfinally,the larger the area, the greater the diversity (7)." "There is growing recognition of the need for a crash program to map biodiversity in order to plan its conservation and practical use. With up to afifthor more of the species of all groups likely to disappear over the next 30 years, as human population doubles in the warmer parts of the world, we are clearly faced with a dilemma. But what is the best way to proceed?". Raven and Wilson (2) provide answers to their own question. "Some systematists have urged the initiation of a global biodiversity survey, aimed at the ultimate full identification and biogeography of all species. Others, noting the shortage of personnel, funds, and above all, time, see the only realistic hope to lie in overall inventories of those groups that are relatively well known now, including flowering plants, vertebrates, butterflies, and a few others. In order to accomplish this second objective as quickly as possible, it would be necessary to survey transects across broad geographic areas and to examine a number of carefully selected sites in great detail. A reasonable number of specialists is available to begin this task, and with adequate funding it could be applied directly to problems of economic development, land use, science, and conservation. Meanwhile, adequate numbers of specialists could be trained and supported to deal with all of the remaining groups of organisms. The aim would be to gain a reasonably accurate idea of the representation of these groups on Earth while attempting complete inventories of all the global biota over the course of the next 50 years. As most of the tropical rain forests of the world are likely to be reduced to less than 10 percent of their original extent during this half-century, adequate planning is of the essence. The resultsfrominventories should be organized in such a way as to apply directly to the development of new crops, sustainable land use, conservation, and the enhancement of allied disciplines of science (2)." These overall inventories are clearly restricted to morphological and anatomical aspects, in spite of the fact that further on in the article one reads that "as networks of expertise and monographing grow, ecologists, population biologists, biochemists and others will be drawn into the enterprise. It is also inevitable that genome descriptions will feed into the data-base. Molecular biology is destined to fuse with systematics. [Furthermore,] chemical prospecting, the

Seidl et al.; Chemistry of the Amazon ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


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Future-Oriented Mapping of Biodiversity in Amazonia

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search for new natural products, is readily added to the collection of inventories. So is screening for species and gene complexes of special merit in agriculture, forestry, and land reclamation (2)." Although it is probably true that macromolecular data are destined to shortly join morphological and anatomical ones in systematics, if indeed this has not yet already happened, it is to be doubted if this fusion will be of substantial relevance for the purpose of the present program, the mapping of biodiversity. This is due to the paradigm of unit and diversity in evolution formulated by Eigen and Schuster (3). "Why do millions of species, plants and animals, exist, while there is only one basic machinery of the cell; one universal genetic code and unique chiralities of the macromolecules?" Hence, a glimpse into biodiversity preferentially requires analysis of the phenotype, and this consists in form and physiology in intimate association. That we do not yet perceive the mechanistic details of this association is of little importance in connection with the present task. The point remains that we must report both characteristics together if we really want to understand development, radiation and relevance of biodiversity. Hence, chemical prospecting must be promoted to one of the most important aims of the survey, although, even in Raven and Wilson's definition (2), it should already please the funding agencies in view of its possible direct returns in benefits to mankind. Morpho-Chemical Biodiversity Why should morphology and metabolism be linked into an inseparable fabric, or even more fundamentally, before we takle this question, are these features indeed interdependent? A simple, even if circumstantial evidence for the connection of form and chemistry refers to the fact that great numbers of species (defined morphologically) and micromolecular constituents characterize plants and invertebrates, small numbers of species and constituents characterize vertebrates. This does of course not mean that morphological and metabolic biodiversity must necessarily co-occur in plant taxa. Indeed, while in one group many species may possess a rather uniform chemical composition, in another few species may show a quite heterogeneous one. Morpho-Chemical Biogeography Latitudinal Radiation of Angiosperms. This caveat does not concern the validity of the visual observation. Travel from both poles to the equator quite obviously demonstrates a prodigious increase in plant diversity. The doubts concern the comprehensiveness of the latitudinal gradient. The concept, as defined so far, involves only the macroscopic features of the phenotype. The chemical aspects, which do not contribute less to plant diversity, and hence to adaptation potential, are usually neglected. Do such cryptic attributes occur invariably according to analogous latitudinal gradients? A generally valid answer to this question has yet to be found.



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Nevertheless, all data obtained so far (next chapter) indicate chemical diversity of floras to increase upon travelling from the equatorial forests into regions of lower latitude. On the other hand, qualitative micromolecular gradients seem to be closer related with habit, rather than with habitat. The alternate expression of morphological and metabolic biodiversity, controlled conceivably by an on/off mechanism, suggests the integration of both phenotypic features, only the operation of the switch leading to the alternatives remaining to be discussed. Both, form and chemistry, are manifestations of metabolism (4). Metabolic differentiation involves initially so called primary (ubiquous) and secondary (special) micromolecules. Biosynthesis and biodégradation of these metabolites occur from and to carbon dioxide along cyclic reaction pathways (Figure 1) with two major outlets towards polymeric (macromolecular) material. In other words, part of the oxygen produced by photosynthesis in green plants is recycled through the atmosphere and used up in the other fundamental activity of life, respiration. The remaining part of the oxygen is retained in the atmosphere (at least during most of the plant's lifetime) in view of the relative stability of the polymers, in plants chiefly cellulose and lignins. Now, it so happens that sunlight intervenes in the formation of both these materials. Energy is required in the reductive process leading to glucose, dehydration of which gives cellulose; and light activation of phenylalanine ammonia-lyase (PAL) is implicated in the deaminative process leading to the phenylpropanoid-precursors of lignins. Thus, also in theory, one would expect that in equatorial regions, characterized by the highest solar energy input, production of ligno-cellulosic biomass should attain the highest rate. In consequence, internally, micromolecular turnover, responsible for the molecular continuity between the two biomass yielding processes, must display a correspondingly high rate. This speedy carbon flow through the cycles would be expected to lessen the opportunities for stabilization of special micromolecules and shorten their half-lives. Externally, however, the faster the production of biomass, the vaster the area covered per unit time and the greater the chances of morphological adaptation (cf. the ESA theory, above). Accordingly, lowering of energy input must lead to gradual decrease in biomass deposition. The consequent diminishing rate of carbon flow through the cycles would induce scavenging of intermediates by condensation into more difficultly degradable, more complex (often considered bizarre) "natural products". The rationale behind this concept lies in the positive evolutionary relationship of increasing oxidation level of special metabolites and versatility in the elaboration of molecular protection devices, such as Schiff bases, methyl ethers and hydrogenated derivatives during the biosynthesis of alkaloids, polyphenols and terpenoids, respectively (5). Raven and Wilson's advice that inventories should be limited to groups that are relatively well known now (2) is extremely relevant. Crash programs are incompatible with the slowness inherent in experimental verifications. I doubt that in the next say 5 years the presently available mass of data can be increased significantly in the sense that the new data added to the existing ones will relevantly alter trends which are not already perceptible through the evaluation of



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LIGNINS

CELLULOSE Figure 1. Schematic representation of carbon flow through metabolic pools in plants. Major reaction types: r...reduction, c...condensation, d...dehydration, o...oxidation (broken lines... post mortem events).


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data accumulated in the past 50 years with respect to micromolecular botany and in the last 250 years with respect to morphological botany. Clearly the statement stands on less firm grounds concerning chemical features. However, we ourselves have repeatedly verified its validity. To give only one example: a Master thesis listed the reported distribution of complex steroids (6). Later, in order to publish this work in the primary scientific literature (7), the data were updated by an increase of about 20% in the number of entries. Nevertheless, it was hardly necessary to introduce alterations in the text. The interpretations of the results based on distributional trends had remained valid. The survey of plant transects across broad geographic areas has in the past referred nearly always to the macroscopic, morphological part of the phenome. Unless the submicroscopic, chemical characteristics are considered additionally, we will never learn the lesson biogeography is able to teach on the subject of biodiversity. So far examples of integration of morpho-chemical biogeography were elaborated through two different types of approaches. In thefirstone we selected a botanical group, circumscribed its subgroups on a map, characterized each of these regionalized subgroups by their chemical composition and tried to interpret these compositions by mechanistically or biogenetically acceptable chemical gradients. In the second approach not the plant group, but the class of micromolecular components was selected and its variance, properties and frequencies in ecogeographically characterized plant groups was gauged. The following items summarize some of the results. Icacinaceae. Chemical evolution in the Icacinaceae, postulated to involve oxidative sequences within monoterpenoids, sesquiterpenoids and diterpenoids, is accompanied by spacial radiation of genera from Melanesia in a western direction along the tropical belt to Amazonia (8). Simaroubaceae. Specialization of quassinoid skeletons is accompanied by a West-East spacial radiation of the simaroubaceous lineage. Indeed the transition from American and West African genera to East African and Asian genera is accompanied by diversification of oxygenation and unsaturation patterns, as well as by increase in oxidation level of the quassinoids (9). Fabaceae. Quinolizidine alkaloidal evolution proceeded by skeletal specialization in tropical regions and by variation of oxidation level in temperate regions (JO). Pyrones in Lauraceae, xanthones in Gentianaceae. The variation of secondary plant constituents in major plant taxa takes place in small steps which allow to trace plant evolution and at the same time also reflect the dispersion of these taxa (77). Derris-Lonchocarpus complex (Fabaceae). Gradual modification of oxidation/methylation values of flavonoid profiles suggest dispersal of original


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stock to have taken place from Asia to America and from forest to savanna. Similar trends are observed for other genera of Tephrosieae (72). Aniba (Lauraceae). A comparison between geographical distribution and secondary metabolites of 18 species of the genus Aniba leads to a coherent picture of spatial and chemical evolution of these species. In chemical evolution, general mechanisms, as blocking of reaction steps leading to primary metabolites within biogenetic groups, are found to be operative. Sympatric distribution of closely related species seems to imply chemical diversity (73).


Conclusion Brazilian Amazonia, populated by 18 million inhabitants, is facing with increasing frequency agonizing choices concerning what native areas can be sacrificed for social benefit, maintaining at the same time the dreaded extinctions within reasonable limits. The present chapter aimed to show thatfloristicinventories will continue in the realm of academic exercises until they consider morpho-chemical data within an integrated system. Methods are quoted that, for thefirsttime, allow the attainment of this objetive. Results obtained so far seem to indicate opposed latitudinal gradients to characterize morphological and metabolic biodiversity, and seem to suggest spatial radiation of angiosperms to have followed morphological and chemical gradients. This conclusion is consistent with results obtained through the application of a quantitative measurement of angiosperm biodiversity (14) and dispells any doubt that plant classification must consider the different levels of manifestation of the genotype as criteria by an integrated procedure to qualify as a "natural" system (75). Hence much of our effort these past years centered around the development of such a system. This can be gauged by the title of the most recent contribution "Plant systematics via integration of morphology and chemistry" (Gottlieb, O.R.; Borin, M.R. de M.B.; Kaplan, M.A.C., Oswaldo Cruz Foundation and Federal University of Rio de Janeiro, unpublished paper). Further investigation along these lines of problems concerning biodiversity and biogeography in Amazonia should comprise the following stages: 1. Selection of plant families possessing a relatively well known and reasonably well diversified micromolecular composition. 2. Organization of the chemical data referring to genera of these families (genera are here selected as basic taxonomic units since their circumscription is relatively stabilized in taxonomy). 3. Indication of habitats and habits of these genera. 4. Interpretation of eventual morphological and chemical gradients (by correlation of reaction sequences based on chemical mechanisms along the geographic routes of radiation of the genera). Acknowledgment The autor is grateful to Conselho National de Desenvolvimento Cientifico e Tecnologico, Brazil, forfinancialsupport.


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206 Literature Cited 1.


2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14.

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Wilson, Ε. Ο . The Diversity of Life, Allan Lane, Ed.; The Penguin Press: London, 1992, pp. 197-199. Raven, P.H.; Wilson, E.O. Science 1992, 258, 1099-1100. Eigen, M.; Schuster, P. Naturwiss. 1977, 64, 541-565. Gottlieb, O.R. Phytochemistry 1989, 28, 2545-2558. Gottlieb, O.R. Phytochemistry 1990, 29, 1715-1724. Borin, M . R. de Μ. Β. Ο valor dos Esteróides como Marcadores em Quimiossistemática; M.Sc.-Dissertation; Universidade de São Paulo, São Paulo, SP, 1988. Borin, M.R. de M.B.; Gottlieb, O.R. Pl. Syst.Evol.1993, 184, 41-76. Kaplan, M.A.C.; Ribeiro, J.; Gottlieb, O.R. Phytochemistry 1991, 30, 2671-2676. Simão, S.M.; Barreiros, E.L.; Silva, M.F. das G.F. da; Gottlieb, O.R. Phytochemistry 1991, 30, 853-856. Salatino, Α.; Gottlieb, O.R. Pl. Syst.Evol. 1983, 143, 167-174. Gottlieb, O.R.; Kubitzki, K. Naturwiss. 1983, 70, 119-126. Gomes, C.M.R.; Gottlieb, O.R.; Marini-Bettolo, G.-B.; Delle Monache, F.; Polhill, R. Biochem. Syst. Ecol. 1981, 9, 129-147. Gottlieb, O.R.; Kubitzki, K. Pl. Syst. Evol. 1981, 137, 281-289. Gottlieb, O.R.; Borin, M.R. de M.B. In The Use of Biodiversity for Sustainable Development: Investigation of Bioactive Products and their Commercial Applications; Seidl, P. R., Ed.; Associação Brasileira de Química: Rio de Janeiro, RJ, 1994, pp 23-36. Gottlieb, O.R. Micromolecular Evolution, Systematics and Ecology - An Assay into a Novel Botanical Discipline; Springer Verlag: Berlin, 1982, pp 170.

RECEIVED September 28,

1994


Chemistry of the Amazon - American Chemical Society

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