Tracing the colonization of Madeira and the Canary Islands by Drosophila subobscura through the study of the rp49 gene region

Abstract

Nucleotide variation at the nuclear ribosomal protein 49 (rp49) gene region has been analysed by fine restriction mapping in a sample of 47 lines from a population from Madeira. Five restriction-site (out of 37 sites scored) and 3 length polymorphisms have been detected, resulting in 14 different haplotypes. This population shows less variation than both continental and Canary Island populations. The population from Madeira shows some differentiation from mainland populations, which does not favor the idea of extensive migration between the continent and Madeira. Chromosomal and restriction-map variation of the rp49 region in D. subobscuru populations, together with data on sequence comparison of this nuclear region in D. guanche and D. mudeirensis clearly indicate that the Canary Islands underwent at least two colonization events from the nearby continent. Although the data for Madeira are compatible with a single colonization event by a continental sample polymorphic for gene arrangements 0, and 0, + 4, an alternative scenario with at least two colonization events seems more likely.

The Diversification of the Genus Nesotes (Coleoptera: Tenebrionidae) in the Canary Islands: Evidence from mtDNA

“…Some studies of colonization patterns in other organisms in the Canary Islands have shown stepping-stone models of dispersal from older to progressively younger islands, for example, the tenebrionid beetles Pimelia and Hegeter are both essentially compatible with a stepping-stone model, with a probable back colonization from Tenerife to Gran Canaria in Pimelia (Juan et al, 1995(Juan et al, , 1996. The curculionid beetle Brachyderes rugatus and Drosophila subobscura are both absent in the eastern Canary Islands, but show a pattern of sequential colonization from older to younger islands in the west (Emerson et al, 2000a;Khadem et al, 1998;Pinto et al, 1997). In addition to simple stepping-stone models, more complex patterns of island colonization have also emerged in a range of organisms.…”

DNA variation at the rp49 gene region in Drosophila madeirensis and D. subobscura from Madeira: inferences about the origin of an insular endemic species

“…O 3+4+8 in North‐western Africa and O 3+4+7 in the Atlantic coast of the Iberian peninsula) does not seem to favour the hypothesis of recent migration from the continent. Otherwise, selection against the establishment of these other arrangements in the islands should be very strong given their high frequency in those continental populations (see Khadem et al ., 1998).…”

“…Additionally, O 3+4 lines from these locations are not genetically differentiated for that region. Some differentiation had been, however, detected in a previous restriction‐map survey (Khadem et al ., 1998). The discrepancy between the results of these studies might be partly due to the relatively low number of nucleotides sampled in the previous study and therefore to the high stochastic variance associated with nucleotide variation estimates.…”

“…This study also revealed less variation in the insular than in continental populations (Rozas et al. , 1995; Khadem et al ., 1998).…”

“…Unlike in D. subobscura , only a few studies on intraspecific genetic variation have been conducted with D. madeirensis (González et al ., 1983, 1990). Other studies have shown that the ancestors both of D. madeirensis and of extant populations of D. subobscura in Madeira are probably the result of independent colonization events from the continent (Khadem et al ., 1998).…”