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The effects of Pleistocene glaciations and geographical barriers on the phylogeographic patterns of lowland plant species in Mediterranean-climate areas of Central Chile are poorly understood. We used Dioscorea humilis (Dioscoreaceae), a dioecious geophyte extending 530 km from the Valparaíso to the Bío-Bío Regions, as a case study to disentangle the spatio-temporal evolution of populations in conjunction with latitudinal environmental changes since the Last Inter-Glacial (LIG) to the present. We used nuclear microsatellite loci, chloroplast (cpDNA) sequences and environmental niche modelling (ENM) to construct current and past scenarios from bioclimatic and geographical variables and to infer the evolutionary history of the taxa. We found strong genetic differentiation at nuclear microsatellite loci between the two subspecies of D. humilis, probably predating the LIG. Bayesian analyses of population structure revealed strong genetic differentiation of the widespread D. humilis subsp. humilis into northern and southern population groups, separated by the Maipo river. ENM revealed that the ecological niche differentiation of both groups have been maintained up to present times although their respective geographical distributions apparently fluctuated in concert with the climatic oscillations of the Last Glacial Maximum (LGM) and the Holocene. Genetic data revealed signatures of eastern and western postglacial expansion of the northern populations from the central Chilean depression, whereas the southern ones experienced a rapid southward expansion after the LGM. This study describes the complex evolutionary histories of lowland Mediterranean Chilean plants mediated by the summed effects of spatial isolation caused by riverine geographical barriers and the climatic changes of the Quaternary. [ABSTRACT FROM AUTHOR]

Aim The Chilean endemic Dioscorea biloba (Dioscoreaceae) is a dioecious geophyte that shows a remarkable 600 km north-south disjunction in the peripheral arid area of the Atacama Desert. Its restricted present-day distribution and probable Neogene origin indicate that its populations have a history linked to that of the Atacama Desert, making this an ideal model species with which to investigate the biogeography of the region. Location Chile, Atacama Desert and peripheral arid area. Methods Two hundred and seventy-five individuals from nine populations were genotyped for seven nuclear microsatellite loci, and plastid trnL-F and trnT-L sequences were obtained for a representative subset of these. Analyses included the estimation of genetic diversity and population structure through clustering, Bayesian and analysis of molecular variance analyses, and statistical parsimony networks of chloroplast haplotypes. Isolation by distance was tested against alternative dispersal hypotheses. Results Microsatellite markers revealed moderate to high levels of genetic diversity within populations, with those from the southern Limarí Valley showing the highest values and northern populations showing less exclusive alleles. Bayesian analysis of microsatellite data identified three genetic groups that corresponded to geographical ranges. Chloroplast phylogeography revealed no haplotypes shared between northern and southern ranges, and little haplotype sharing between the two neighbouring southern valleys. Dispersal models suggested the presence of extinct hypothetical populations between the southern and northern ranges. Main conclusions Our results are consistent with prolonged isolation of the northern and southern groups, mediated by the life-history traits of the species. Significant isolation was revealed at both large and moderate distances as gene flow was not evident even between neighbouring valleys. Bayesian analyses of microsatellite and chloroplast haplotype diversity identified the southern area of Limarí as the probable area of origin of the species. Our data do not support recent dispersal of D. biloba from the southern range into Antofagasta, but indicate the fragmentation of an earlier wider range, concomitant with the Pliocene-Pleistocene climatic oscillations, with subsequent extinctions of the Atacama Desert populations and the divergence of the peripheral ones as a consequence of genetic drift. [ABSTRACT FROM AUTHOR]

Chromosomal analyses were conducted for the first time in all three species of the Chilean endemic Epipetrum Phil. (Dioscoreaceae; the yam family). Mitotic chromosome counts showed that all studied individuals of the rare Epipetrum bilobum and E. polyanthes, and most studied individuals of the more widespread E. humile, had 2n = 14 chromosomes. However, two populations of E. humile had 2n = 28 chromosomes. The ideograms shared a similar karyotype constitution for the three species but with a duplicated chromosome number in some populations of E. humile. Our results suggest that the Epipetrum taxa are mainly diploids, with a base number of x = 7, and the tetraploid cytotypes have arisen only in few cases. After that of Borderea (x = 6), this chromosome base number is the second lowest one found in the Dioscoreaceae. Epipetrum and Borderea are two small, relict, satellite genera of the Dioscoreaceae, endemic to Chile (South America) and the Pyrenees (Southwestern Europe), respectively. The two taxa share several morphological attributes and are adapted to rocky and mountain habitats. However, whereas Borderea is an allotetraploid genus of relatively recent hybrid origin, Epipetrum is diploid in common with the species found in the early branching clades of Dioscorea. [ABSTRACT FROM AUTHOR]