Macaronesia covers four Atlantic archipelagos: the Azores, Madeira, the Canary Islands, and the Cape Verde islands. When discovered by Europeans in the 15th century, only the Canaries were inhabited. Historical reports highlight the impact of Iberians on settlement in Macaronesia. Although important differences in their settlement are documented, its influence on their genetic structures and relationships has yet to be ascertained. In this study, the hypervariable region I (HVRI) sequence and coding region polymorphisms of mitochondrial DNA (mtDNA) in 623 individuals from the Azores (120) and Canary Islands (503) were analyzed. Combined with published data, these give a total of 1,542 haplotypes from Macaronesia and 1,067 from the Iberian Peninsula. The results obtained indicate that Cape Verde is the most distinctive archipelago, with an mtDNA pool composed almost exclusively of African lineages. However, the other archipelagos present an mtDNA profile dominated by the presence of West-Eurasian mtDNA haplogroups with African lineages present in varying proportions. Moreover, no signs of integration of typical Canarian U6 lineages in the other archipelagos were detected. The four Macaronesia archipelagos currently have differentiated genetic profiles, and the Azores present the highest intra-archipelago differentiation and the lowest values of diversity. The analyses performed show that the present-day genetic profile of the Macaronesian archipelagos was mainly determined by the initial process of settlement and further microdifferentiation probably as a consequence of the small population size of some islands. Moreover, contacts between archipelagos seem to have had a low impact on the mtDNA genetic pool of each archipelago.

The genetic structure in Atlantic Islands and continental populations of Drosophila subobscura has been studied using autosomal and sex-linked allozymes and mitochondrial DNA (mtDNA) haplotypes. From the data it is deduced that whereas the Canary islands have long been isolated, the neighboring island of Madeira has been subjected to continuous migration from the mainland. In addition, sex-linked allozymes and mtDNA data show a large divergence between the geologically younger western islands of the Canarian Archipelago and the older central ones, finding strong founder effects in the former. Divergence rates of sex-linked and mitochondrial genes relative to autosomic loci several times higher than expected under neutrality have been explained by differential migration between sexes. The Canarian Archipelago colonization fits in well with a stepping-stone model of a directional east-west migration that parallels the geological origin of these Islands.

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Within the melanogaster subgroup the species Drosophila melanogaster, D. simulans and D. mauritiana are the most intimately related and laboratory studies have demonstrated that reproductive isolation among them is incomplete . This great similarity is also reflected at the cytological and molecular MATERIAL AND METHODS levels. Thus, Lemeunier and Ashburner Data on D. melanogaster were obtained (1976) in a study of phylogenetic relation-from samples of two natural populations, ships in the melanogaster subgroup, based one captured in the locality of Giiimar (on on sequences of polytene chromosomes, the island of Tenerife in the Canarian Arconsider them to be closely related chro-chipelago) and the other in the locality of mosomally, the simulans-mauritiana pair Fernan Nunez, in the South of the Iberian being homosequential. In a study of seven Peninsula. Those of D. simulans were obspecies of the melanogaster group, whose tained from samples of two natural popmembers were compared by the differ-ulations, one also collected in Giiimar, ences in the electrophoretic mobility of 18 and the other in Villares, very close to enzymaticloci, Eissesetal. (1979) found the Fermin Nunez. The males captured were three possible pairs of these three species immediately used for electrophoretic analto be identical since they do not point out yses. Each female was placed in an india closer relationship between any two of vidual culture for five days and was then them.transferred' into fresh vials three consec-Likewise, Cseko et al. (1979) in a com-utive times in order to obtain abundant parative study of a highly repetitive DNA offspring. One F1 larva, pupa or adult sequence containing long tracts of poly-from each was later assayed. For each 10pyrimidine/polypurine DNA, in which 101 cus a minimum of 120 genomes was anaspecies of Drosophila were compared, lyzed. The study of D. mauritiana was found that within the melanogaster done on individuals of two laboratory subgroup the only species possessing the strains sent to us in 1978 by Dr. J. melanogaster sequence are simulans and McDonald of the Department of Genetics mauritiana, although the amount of this of the University of Melbourne (Austrasequence varies between them. lia), and by Dr. L. Tsacas, of the Depart-It is generally accepted that estimations ment of Genetics of the C.N.R.S. at Gifof genetic differences between populations sur-Yvette (France), and kept since then of the same or different species should be in large population cages. For each locus based on the comparison of allelic fre-a minimum of 40 genomes were analyzed. quencies of the largest possible number of Preparation of samples, electrophoretic loci. The present work attempts to estab-techniques and the preparation of the lish the genetic distance (Nei, 1971(Nei, , 1972 starch gel have been done according to between the sibling species of the melo-Ayala et al. (1972). For the preparation of 517

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