Báo cáo khoa học: "Morphological variability of oaks (Quercus robur L, Quercus petraea (Matt) Liebl, Quercus pubescens Willd) in northeastern France: preliminary results"

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Nội dung Text: Báo cáo khoa học: "Morphological variability of oaks (Quercus robur L, Quercus petraea (Matt) Liebl, Quercus pubescens Willd) in northeastern France: preliminary results"

article Original Morphological variability of oaks (Quercus robur L, Quercus petraea (Matt) Liebl, Quercus pubescens Willd) in northeastern France: preliminary results V Badeau JL Dupouey Laboratoire de phytoécologie forestière, Centre de recherches forestières, INRA Nancy, 54280 Champenoux, France Summary — Morphological variability of oaks in Lorraine (northeastern France), was studied. Eight hundred oaks were sampled in 80 stands covering a broad range of ecological variability; 10 leaves, fruits and current-year shoots were collected per tree. Thirty-four morphological variables were measured and analyzed by factorial correspondance analysis. It is concluded that Q robur and Q pe- traea are clearly separated with a few morphologically intermediate individuals (3.5%). Q petraea is more variable than Q robur. Q pubescens and Q robur are totally isolated from each other, while Q petraea and Q pubescens form a continuum. Many variables discriminate between these 3 species; some of them have been little known prior to now (pilosity, presence of intercalary ribs). These re- sults are compared with those from other parts of Europe. taxonomy/ morphometrics / hybridization/ introgression / Quercus robur / Quercus petraea / Quercus pubescens Résumé — Variabilité morphologique des chênes dans le Nord-Est de la France; résultats préliminaires. Nous avons étudié la différenciation morphologique des chênes pédonculé, sessile et pubescent dans le Nord-Est de la France. L’échantillonnage a porté sur 80 populations provenant de stations représentant toute la gamme de variation des milieux de chênaies en Lorraine. Sur 10 arbres par population, 10 feuilles, infruiescences et rameaux de l’année ont été prélevés. Trente- quatre variables morphologiques ont été mesurées et analysées par analyse factorielle des corres- pondances. On observe une très nette séparation des chênes sessile et pédonculé, avec seulement 3,5% d’individus morphologiquement intermédiaires, ainsi qu’un isolement total du chêne pubescent et du chêne pédonculé. Par contre, les chênes sessile et pubescent forment un continuum. Le chêne pédonculé est moins variable que le chêne sessile. De nombreuses variables discriminent ces 3 espèces, dont certaines peu connues jusqu’alors (pilosité, présence de nervures intercalaires). Ces résultats sont comparés à ceux obtenus par ailleurs en Europe. taxonomie / morphométrie / hybridation / introgression / Quercus robur / Quercus petraea / Quercus pubescens
total of 761 trees were sampled during summer INTRODUCTION 1989, 655 of them had produced fruit during this year. Twenty leaves, fruits (including peduncles, The distinction of species in the Quercus cupules and acorns) and twigs of the current growth year were collected. To minimize posi- complex is still a matter of debate. In west- tional variability within the tree (Blue and Jen- ern Europe, several species have been re- sen, 1988), leaves were collected from the ex- ported as potentially interbreeding, the ternal part of the canopy usually on the aspect most widespread being Quercus robur and facing south, and always in the middle part of Quercus petraea. Until now, the prevalent the first flush shoot. Ten of these 20 samples opinion was in favor of the common occur- were chosen at random for measurements, after the elimination of broken, incomplete or dam- rence of hybrids between the different spe- aged units. Eighty variables were measured or cies, producing many morphologically in- calculated. These variables concern many as- termediate forms between pure parental pects of foliar and fruit morphology: size, overall species due to hybridization and introgres- shape, color, pilosity on various parts of leaves sion. A huge body of literature has been or fruits (measured as in Grandjean and Sigaud, published with this thinking in mind, (see 1987), shape of some details (lobes, auricles at eg, Kissling, 1983; Minihan and Rushton, the lamina base). These data were acquired with a digitizing tablet hooked up to a microcom- 1984, for the most recent papers). Only a puter. Several features were obtained from dis- few recent studies (Dupouey, 1983; Du- tances and angles between different landmarks pouey et Le Bouler, 1989; Dupouey et al, along the outline of the leaf. 1990; Grandjean and Sigaud, 1987; Aas, Data were analyzed mainly by factorial corre- 1990) have come to different conclusions. spondence analysis using the SPAD.N statisti- The aim of this study was to describe cal package (Lebart et al, 1988). In the first the actual morphological status of Q robur stage of the analysis, the study of correlation co- efficients between all pairs of the 80 initial vari- and Q petraea at a regional scale (Lor- ables allowed the elimination of 46 redundant raine Plain), including Q pubescens. We variables. The comparison between results with studied inter- and intraspecific variations, or without fruit morphological characters showed and their link with ecological constraints. In no significant differences so only a subset of 29 this preliminary paper, only results on mor- parameters describing leaves and shoots was phological differentiation at the interspecif- used for subsequent analysis. This allowed the ic level are presented. We have tried to use of the whole set of trees instead of only those which had fruited during the sampling answer the following questions: what is the year. Fruit variables were used as supplemen- organization of morphological variability tary characters. among the 3 species? What is the degree Variables were ranked by decreasing power of isolation of each species? What are the of discrimination according to their F value in an best discriminant morphological charac- unbalanced analysis of variance between the 3 ters? species. Bonferroni t-tests of difference between means for each species were performed. Dis- criminant analysis was used to calculate a func- MATERIALS AND METHODS tion for species recognition. Stands were selected from 8 forests in the Lor- RESULTS raine Plain, and a total of 80 populations were sampled in order to cover the whole ecological variability of oakwoods in this area. Coppices Figure 1 shows the projection of trees into with standards were discarded, as were sup- the space of axes, 1, 2 and 3 of the factori- posed plantations. In each of these populations, al analysis. One can observe 3 poles of 10 dominant trees were marked at random. A
At the left end of the first axis, and at distribution for these individuals. Table I the upper part of axis 2, leaves have a gives the mean values of the most discrim- long petiole. The maximum width is at the inant variables for each pole. middle of the lamina. Fruits are shortly pe- At the right-hand side of the first axis, dunculate and pilosity is medium to dense. the leaves are shortly petiolated, with well- this pole is composed of Q petraea trees. developed auricles at the base of the The last pole is also located on the left- lamina. The maximum width of leaves is hand side of the first axis, in the lower part located in the upper part of the lamina. of axis 2. It is composed of trees with Lobe sinuses are irrigated by numerous in- leaves rather similar to those of the previ- tercalary veins. Fruits have a long and thin ous one. Lobes are sharper, often accom- peduncle. Pilosity is absent, very short on panied by lobules (lobes irrigated by all parts. This group of individuals repre- nerves of the third order). The pilosity is sents the typical Q robur.
than Q specific morphological variabililty more highly developed, both in terms of to be more homoge- robur, which appears density and length. This group can be identified as Q pubescens. neous. TableI gives the variables by decreas- Thus we find, with this analysis, that the ing power of discrimination between the 3 species have different morphological species. The best discriminant parameters poles, and also that these 3 species differ are pilosity (density and length of pilosity widely in their degree of separation from on nerves, petiole and lamina), number another. The Q robur cluster is com- one and length of intercalary veins, length of pletely separated from that of Q pubes- the petiole and of the peduncle. Some cens, and only a few morphologically inter- classical features only appear after these mediate individuals are found between Q variables, such as the development of an robur and Q petraea (3.5% of the total auricle at the lamina base. number of trees). Length of the petiole and number of in- On the other hand, Q petraea and Q pu- ercalary veins are sufficient to separate the bescens form a continuum without any 2 species Q robur an Q petraea with 99% clear distinction between the 2 species. A rate. The discriminant function for number of morphologically intermediate in- success recognition is: dividuals occurs. Consequently, Q petraea tree and Q pubescens exhibit much more intra-
where, nint. number of intercalary veins analysis. The main methods used in these (mean of 10 leaves per tree); lpet: length cases were hybridity indices for which you had to choose subjectively the range of of petiole in mm (mean of 10 leaves per each species for all the variables before tree); I species index; positive for Q robur and negative for Q petraea. Values be- calculation, principal components analysis (PCA) using ’pure’ stands as references tween -1000 and +1000 indicate an inter- and discriminant function analysis. On the mediate tree. other hand, purely descriptive methods, such as factorial correspondence analysis (or principal components without reference DISCUSSION AND CONCLUSION populations) do not require the definition of the species before the analysis. They can These results are different from those re- be regarded just as a means of looking at ported in a number of previous publica- the raw data from a particular point of view tions: Carlisle and Brown (1965), Wigston (the one with maximum variance ex- (1974), Olsson in Sweden (1975 a,b) plained). Rushton (1978, 1979, 1983), Minihan and Factorial correspondence analysis is Rushton (1984) in the United Kingdom and preferable to PCA (even when a ’reference Kissling (1980a,b, 1983) in Switzerland, all population’ is not used) because it is able concluded that there was extensive hybrid- to deal with non-linear relationships be- ization between Q robur and Q petraea. tween characters, whereas PCA only Conversely, the authors of some more re- linear correlation coefficients. measures cent studies reached the same conclu- The frequency of hybrids between Q pu- sions we did: Grandjean and Sigaud bescens and Q petraea has been under- (1987) in France (including Q pubescens), lined by other authors. Semerikov et al, letswaart and Feij (1989) in The Nether- (1988), studying populations from Dage- lands; Aas (1990) in Germany. stan (Russia), even conclude that such hy- It is difficult to compare these results be- brids represent a unique species complex. they are based on different sample cause This lack of isolation could explain the sizes, sampling regimes, characters and greater variability observed in Q petraea with different companion species. But sev- versus Q robur. eral hypotheses could be advanced to ex- Variables used in previous taxonomic plain the discrepancies. One possible ex- studies were not always the most highly planation is that the extent of hybridization discriminating ones, and sometimes not differs in the different parts of the distribu- discriminant at all. The best features, in tion range of the species. Peripheral situa- our sample, are intercalary veins and pilos- tions would be more favorable to hybridiza- ity development. tion than in the inner part. This could account for results from Sweden or the Further studies in progress are explor- United Kingdom, but not those from Swit- ing the persistence of these discriminant zerland. More probably, one must look to characters under homogeneous growing the differences in the statistical approach- conditions (nursery) for the populations un- es used for data analysis. All previous der consideration. Also, the structure of the studies concluding that numerous hybrids intraspecific variability along ecological clines is of major importance. Finally, there which were present were based on statisti- cal methods according to which the limits is a need for standardization of the statisti- of each species are defined before the cal methods used for the analysis of mor-
and Quercus petraea in The Netherlands. phological variability in the different parts Acta Bot Neerl 38, 313-325 of the range of distribution of these spe- P (1980a) Un réseau de corrélations en- Kissling cies. les chênes (Quercus) du Jura. Ber tre Schweiz Bot Ges 90, 1-28 P (1980b) Clef de détermination des Kissling ACKNOWLEDGMENTS chênes médioeuropéens (Quercus L). Ber Schweiz Bot Ges 90, 29-44 We gratefully acknowledge the technical assis- Kissling P (1983) Les chênaies du Jura central tance of Gilles Doucet during the collection of Thesis, Université de Lausanne, Swit- suisse. leaves. We also thank Patrick Behr for meas- zerland, 400 p urements of fruits and Hervé Cochard for 3D Lebart L, Morineau A, Lambert T (1988) graphics. Support for this project was provided SPAD.N: Système Portable Pour l’Analyse by the EEC (Research action Programme des Données. Version 1.2: Manuel de Référ- MA1B: Genetics and Breeding of Oaks). CISIA, Paris, 306 pp ence. Minihan VB, Rushton BS (1984) The taxonomic status of oaks (Quercus ssp) in Breen Wood, REFERENCES Co Antrim, Northern Ireland. Watsonia 15, 27-32 Aas G Kreuzbarkeit und (1975a) A morphological analysis of Olsson U Unterscheidung (1990) phenotypes in populations of Quercus (Faga- Allg Forstztg 9- Stiel-und Traubeneiche. von ceae) in Sweden. Bot Not 128, 55-68 10, 219-221 Blue MP, Jensen RJ (1988) Positional and sea- Olsson U (1975b) On the size and microstruc- sonal variation in oak (Quercus, Fagaceae) ture of pollen grains of Quercus robur and leaf morphology. Am J Bot 75, 939-947 Quercus petraea. Bot Not 128, 256-264 Carlisle A, Brown HF (1965) The assessment of Rushton BS (1978) Quercus robur L and Quer- the taxonomic status of mixed oak popula- cus petraea (Matt) Liebl: a multivariate ap- tions (Quercus sp). Watsonia 6, 120-127 proach to the hybrid problem. 1. Data acqui- sition, analysis and interpretation. Watsonia Dupouey JL (1983) Analyse multivariable de 12, 81-101 quelques caractères morphologiques de pop- ulations de chênes (Quercus petraea (Matt) robur L and Quer- Rushton BS (1979) Quercus Liebl et Quercus robur L) du Hurepoix. Ann petraea (Matt) Liebl: a multivariate ap- cus Sci For 40, 265-282 proach to the hybrid problem. 2. The geo- graphical distribution of population types. Dupouey JL, Le Bouler H (1989) Discrimination Watsonia 12, 209-224 morphologique des glands de chênes ses- sile (Quercus petraea (Matt) Liebl) et pe- Rushton BS (1983) An analysis of variation of donculé (Quercus robur L). Ann Sci For 46, leaf characters in Quercus robur L and Quer- 187-194 cus petraea (Matt) Liebl population samples from Northern Ireland. Ir For 40, 52-77 Dupouey JL, Fougère V, Kremer A (1990) Vari- abilité génétique des chênes sessile et pé- LF, Glotov NV, Zhivotovskii LA Semerikov donculé. Rev For Fr42, 198-203 (1988) Example of effectiveness of analysis of the generalized variance of traits in trees. Grandjean G, Sigaud P (1987) Contribution à la Sov J Ecol 18, 140-143 taxonomie et à l’écologie des chênes du Ber- ry. Ann Sci For 44, 35-66 DL (1974) Cytology and genetics of Wigston oaks. In: The British Oak (Morris MG, Perring letswaart JH, Feij AE (1989) A multivariate anal- FH, eds). Bot Soc Br Isles, London, 27-50 ysis of introgression between Quercus robur