Mitjançant la citometria de flux (valors C i Cx), s’ha pogut estimar indirectament el nivell de ploïdia i han estat detectats 3 nivells diferents: diploides ( 57,1 %), triploides (1,2%) i tetraploides (41,7 %), amb forta variació intraespecífica i intrapoblacional. Als Pirineus predominen els diploides i els tetraploides es troben en tota l’àrea analitzada. Els nivells de DNA, constants als tetraploides, varien als diploides pirinencs i són atribuïts pels autors a hibridació introgressiva. L’article permet valorar l’ús de la mida del genoma com a alternativa a l’estudi cromosòmic directe per tal d’avaluar la variació en els nivells de ploïdia i forneix arguments sobre diversitat intra- i interpoblacional que cal tenir presents en el disseny d’estratègies de conservació de flora.
Cires, E., C. Cuesta, M.A. Revilla & J.A: Fernández Prieto (2010)
Intraspecific genome size variation and morphological differentiation of Ranunculus parnassifolius (Ranunculaceae), an Alpine–Pyrenean–Cantabrian polyploid group. Biological Journal of the Linnean Society 101, 251–271. – Enllaç a l’article
RESUM
The aim of this study was to assess genome size variation and multivariate morphometric analyses to ascertain cytotype distribution patterns and the morphological differentiation within the Ranunculus parnassifolius group in the Pyrenees and the Alps. Although divergences in nuclear DNA content among different species within a genus are widely acknowledged, intraspecific variation is still a somewhat controversial issue. Holoploid and monoploid genome sizes (C- and Cx-values) were determined using propidium iodide flow cytometry in 125 plants of R. parnassifolius s.l. distributed across four European countries. Three different DNA ploidy levels were revealed in the study area: diploid (2n ~ 2x, 57.14%), triploid (2n ~ 3x, 1.19%), and tetraploid (2n ~ 4x, 41.67%). The mean population 2C-values ranged from 8.15 pg in diploids to 14.80 pg in tetraploids, representing a ratio of 1 : 1.8.
Marked intraspecific/interpopulation differences in nuclear DNA content were found. Diploid populations prevail in the Pyrenees, although tetraploid cytotypes were reported throughout the distribution area. In general, mixed-cytotype populations were not found. The Spearman correlation coefficient did not reveal significant correlations between genome size and altitude, longitude, or latitude. Morphometric analyses and cluster analyses based on genome size variation revealed the presence of three major groups, which exhibited a particular biogeographical pattern. A new cytotype, DNA triploid, was found for the first time. Tetraploid populations showed constant nuclear DNA levels, whereas diploid populations from the Pyrenees, in which introgressive hybridization is suggested as a presumable trigger for genome size variation, did not. Scenarios for the evolution of geographical parthenogenesis in R. parnassifolius s.l. are discussed. Finally, the different levels of effectiveness between plant and animal reference standards are analysed.
