Loreta Brandao de Freitas

Pollen dispersal and breeding structure in a hawkmoth-pollinated Pampa grasslands species Petunia axillaris (Solanaceae)

BACKGROUND AND AIMSnThe evolution of selfing is one of the most common transitions in flowering plants, and this change in mating pattern has important systematic and ecological consequences because it often initiates reproductive isolation and speciation. Petunia axillaris (Solanaceae) includes three allopatric subspecies widely distributed in temperate South America that present different degrees of self-compatibity and incompatibility. One of these subspecies is co-distributed with P. exserta in a restricted area and presents a complex, not well-understood mating system. Artificial crossing experiments suggest a complex system of mating in this sympatric area. The main aims of this study were to estimate the pollen dispersal distance and to evaluate the breeding structure of P. axillaris subsp. axillaris, a hawkmoth-pollinated taxon from this sympatric zone.nnnMETHODSnPollen dispersal distance was compared with nearest-neighbours distance, and the differentiation in the pollen pool among mother plants was estimated. In addition, the correlation between genetic differentiation and spatial distance among plants was tested. All adult individuals (252) within a space of 2800u2009m(2) and 15 open-pollinated progeny (285 seedlings) were analysed. Genetic analyses were based on 12 polymorphic microsatellite loci.nnnKEY RESULTSnA high proportion of self-pollination was found, indicating a mixed-mating system. The maximum pollen dispersal distance was 1013u2009m, but most pollination events (96xa0%) occurred at a distance of 0u2009m, predominantly in an inbreeding system. Both parents among sampled individuals could be identifed in 60-85xa0% of the progeny.nnnCONCLUSIONSnThe results show that most pollen dispersal in the hawkmoth-pollinated P. axillaris subsp. axillaris occurs within populations and there is a high proportion of inbreeding. This mating system appears to favour species integrity in a secondary contact zone with the congener species P. exserta.

Intra- and intercontinental molecular variability of an Alu insertion in the 3' untranslated region of the LDLR gene

Abstract One-hundred three individuals from two Mongolian, two Siberian, and ten native American populations were studied in relation to a 340-bp sequence from an Alu insertion located in the 3 untranslated region of the LDLR gene. Seven haplotypes have been determined, and haplotype B1 was the most common, accounting for about half the sequences found. In general, diversity values are quite high, about 2.5 times higher than those found in other autosomal Alu sequences. Almost all (93%) of the variability occurs at the intrapopulation level, but the greatest among-group differentiation (6-8%) was found when we grouped in a single population all Native Americans plus Siberian Eskimos and Chukchi and compared them with Mongolians. This result is compatible with earlier mtDNA and Y-chromosome suggestions of a single origin for the first colonizers of the American continent. With this nuclear locus it was not possible to broadly distinguish between Central and South American natives. No evidence of selection or marked demographic changes was obtained with these data.