E. Sahuquillo et R. Lumaret, Chloroplast DNA variation in Dactylis glomerata L-taxa endemic to the Macaronesian islands, MOL ECOL, 8(11), 1999, pp. 1797-1803
In the Dactylis glomerata infraspecific polyploid grass complex, restrictio
n fragment length polymorphisms (RFLPs) of chloroplast DNA (cpDNA) were stu
died in diploid and tetraploid populations of several taxa endemic to Macar
onesia (Madeira and the Canary islands) and in populations from the African
and European continental areas closest to Macaronesia. Two chlorotypes, wh
ich differed by a single 290-bp length mutation, were observed in the Macar
onesian 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 elevati
on heath of Tenerife, respectively, and in tetraploids endemic to Madeira a
nd La Palma. These island populations were growing under the influence of h
umid trade winds. Chlorotype II was found in the eastern part of the Archip
elago (closer to Africa), which experienced subarid Mediterranean climate c
onditions, 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 tha
t reported previously for morphological, allozyme and phenolic variation in
the same plant material. Chlorotype II was, however, also observed in tetr
aploid populations from La Gomera island and in one of the seven tetraploid
populations analysed from Madeira, which all showed clearly subtropical ch
aracters for morphology, allozymes and phenolic compounds. This result sugg
ests that cpDNA introgression has occurred more than once from the Mediterr
anean material into the subtropical one and may indicate that colonization
between the mainland and islands, or among the islands, probably played a m
ajor role in the geographical pattern observed for that marker.