Chloroplast DNA variation in dactylis glomerata L. taxa endemic to the macaronesian islands
In the Dactylis glomerata infraspecific polyploid grass complex, restriction fragment length polymorphisms (RFLPs) of chloroplast DNA (cpDNA) were studied in diploid and tetraploid populations of several taxa endemic to Macaronesia (Madeira and the Canary islands) and in populations from the African and European continental areas closest to Macaronesia. Two chlorotypes, which differed by a single 290-bp length mutation, were observed in the Macaronesian and the continental populations. Chlorotype I, which is predominant in the whole D. glomerata complex, was found in the majority of continental populations. It was also observed in the most western Macaronesian islands, in the two diploid taxa endemic to the lowland scrub and the high elevation heath of Tenerife, respectively, and in tetraploids endemic to Madeira and La Palma. These island populations were growing under the influence of humid trade winds. Chlorotype II was found in the eastern part of the Archipelago (closer to Africa), which experienced subarid Mediterranean climate conditions, and in very few diploid and tetraploid Mediterranean populations growing at high elevation on the continent. This geographical and climatic distribution of chlorotype variation in Macaronesia is consistent with that reported previously for morphological, allozyme and phenolic variation in the same plant material. Chlorotype II was, however, also observed in tetraploid populations from La Gomera island and in one of the seven tetraploid populations analysed from Madeira, which all showed clearly subtropical characters for morphology, allozymes and phenolic compounds. This result suggests that cpDNA introgression has occurred more than once from the Mediterranean material into the subtropical one and may indicate that colonization between the mainland and islands, or among the islands, probably played a major role in the geographical pattern observed for that marker.
Sahuquillo
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