Browsing by Author "Segarra, C."
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- DNA variation at the rp49 gene region in Drosophila madeirensis and D. subobscura from Madeira: inferences about the origin of an insular endemic speciesPublication . Khadem, M.; Rozas, J.; Segarra, C.; Aguade, M.An 1.6-kb fragment spanning the rp49 gene was sequenced in 16 lines of Drosophila subobscura from Madeira and in 22 lines of the endemic species D. madeirensis. Nucleotide diversity in D. subobscura from Madeira (p 0.0081) was similar to that in lines from Spain carrying the O3+4 chromosomal arrangement (p 0.0080). No signi®cant genetic differentiation was detected between insular and continental O3+4 lines of D. subobscura. These results are compatible both with a rather recent and massive colonization, and with multiple colonization events from the continent. Nucleotide diversity in D. madeirensis (p 0.0076) was similar to that in D. subobscura, which deviates from the expectation, under strict neutrality, of a lower level of variation in an insular species with a small population size. The observed numbers of shared polymorphisms and of ®xed differences between D. madeirensis and D. subobscura are compatible with the isolation model of speciation, where shared polymorphisms are due to common ancestry.
- Multilocus analysis of nucleotide variation in Drosophila madeirensis, an endemic species of the Laurisilva forest in MadeiraPublication . Khadem, M.; Munté, A.; Camacho, R.; Aguadé, M.; Segarra, C.Drosophila madeirensis is an endemic species of Madeira that inhabits the island Laurisilva forest. Nucleotide variation in D. madeirensis is analysed in six genomic regions and compared to that previously reported for the same regions in Drosophila subobscura, an abundant species in the Palearctic region that is closely related to D. madeirensis. The gene regions analysed are distributed along the O3 inversion. The O3 arrangement is monomorphic in D. madeirensis, and it was present in ancestral populations of D. subobscura but went extinct in this species after the origin of the derived OST and O3+4 arrangements. Levels of nucleotide polymorphism in D. madeirensis are similar to those present in the OST and O3+4 arrangements of D. subobscura, and the frequency spectrum is skewed towards rare variants. Purifying selection against deleterious nonsynonymous mutations is less effective in D. madeir ensis. Although D. madeirensis and D. subobscura coexist at present in Madeira, no clear evidence of introgression was detected in the studied regions.
- Tracing the colonization of Madeira and the Canary Islands by Drosophila subobscura through the study of the rp49 gene regionPublication . Khadem, M.; Rozas, J.; Segarra, C.; Brehm, A.; Aguade, M.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 polymor phisms 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.