Chronic disturbances, such as selective logging, firewood extraction and extensive grazing, may lead to the taxonomic and phylogenetic impoverishment of remaining old-growth forest communities worldwide; however, the empirical evidence on this topic is limited. We tested this hypothesis in the Caatinga vegetation--a seasonally dry tropical forest restricted to northeast Brazil. We sampled 11,653 individuals (adults, saplings, and seedlings) from 51 species in 29 plots distributed along a gradient of chronic disturbance. The gradient was assessed using a chronic disturbance index (CDI) based on five recognized indicators of chronic disturbances: proximity to urban center, houses and roads and the density of both people and livestock. We used linear models to test if mean effective number of lineages, mean phylogenetic distance and phylogenetic dispersion decreased with CDI and if such relationships differed among ontogenetic stages. As expected, the mean effective number of lineages and the mean phylogenetic distance were negatively related to CDI, and such diversity losses occurred irrespective of ontogeny. Yet the increase in phylogenetic clustering in more disturbed plots was only evident in seedlings and saplings, mostly because clades with more descendent taxa than expected by chance (e.g., Euphorbiaceae) thrived in more disturbed plots. This novel study indicates that chronic human disturbances are promoting the phylogenetic impoverishment of the irreplaceable woody flora of the Brazilian Caatinga forest. The highest impoverishment was observed in seedlings and saplings, indicating that if current chronic disturbances remain, they will result in increasingly poorer phylogenetically forests. This loss of evolutionary history will potentially limit the capacity of this ecosystem to respond to human disturbances (i.e., lower ecological resilience) and particularly their ability to adapt to rapid climatic changes in the region.

No abstract

The 2n = 19 karyotype was probably formed by a centric fusion event occurring in N. nudicaule and later transmitted to tetraploid cytotypes of N. macrostemon. Diploids of N. nudicaule and N. macrostemon appeared as consistent recently diverged species, whereas tetraploid apomicts seem to constitute an assemblage of polyploid hybrids originating from multiple independent hybridization events between them, part of which are morphologically recognizable as N. gracile.

No abstract

No abstract

Tribe Leucocoryneae comprises the genera Beauverdia, Ipheion, Leucocoryne, Nothoscordum, Tristagma and Zoellnerallium, a more recently described genus, the validity and relationships with the other genera of the tribe of which are still unclear. The present work aims to characterize the karyotype of Zoellnerallium and to evaluate the phylogenetic relationships among the genera of Leucocoryneae. The phylogeny of the tribe was reconstructed based on trnG intron plastid and internal transcribed spacer nr(ITS) nuclear sequences. Karyotype description of the two Zoellnerallium spp. was based on chromosome morphometry, DAPI and CMA fluorochrome staining, rDNA sites and silver nitrate staining. Phylogenetic analyses indicated that all genera of Leucocoryneae, except Beauverdia (included in Nothoscordum), are monophyletic. Nothoscordum spp. appeared as sister to a major clade of Leucocoryneae (Ipheion + Tristagma and Leucocoryne + Zoellnerallium). The two Zoellnerallium spp. had 2n = 24 (8M + 16A). The occurrence of two pairs of 5S rDNA sites in Zoellnerallium and tetraploids of Nothoscordum spp. further supports the tetraploid nature of this genus. The higher diploid number of Zoellnerallium was due to centric fissions followed by the emergence of a 45S rDNA cluster on the short arm of the new acrocentric chromosomes. The data suggest that Zoellnerallium spp. are tetraploids with a basic number x = 12 (4M + 8A), whereas the ancestor diploid karyotype with n = 3M + 2A is currently present only in Nothoscordum and Leucocoryne. Different combinations of karyotypic changes may have led to the isolation of lineages and formation of most genera in Leucocoryneae.

The genus Nothoscordum Kunth comprises approximately 20 species native to South America. Karyologically, the genus is remarkable for its large chromosomes and Robertsonian translocations. Variation in chromosome number has been recorded in a few polyploid species and it is unknown among diploids. This study presents the chromosome number and morphology of 53 individuals of seven populations of N. arenarium Herter (2n = 10). In addition, karyotype analyses after C-banding, staining with CMA and DAPI, and in situ hybridization with 5S and 45S rDNA probes were performed in six individuals from one population. All individuals exhibited 2n = 10 (6M + 4A), except for one tetraploid (2n = 20, 12M + 8A) and one triploid (2n = 15, 9M + 6A) plant. C-banding revealed the presence of CMA+ /DAPI - heterochromatin in the short arm and in the proximal region of the long arm of all acrocentric chromosomes. The 45S rDNA sites co-localized with the CMA + regions of the acrocentrics short arms, while the 5S rDNA probe only hybridized with the subterminal region of a pair of metacentric chromosomes. A change in the pattern of CMA bands and rDNA sites was observed in only one individual bearing a reciprocal translocation involving the long arm of a metacentric and the long arm of an acrocentric chromosome. These data suggest that, despite isolated cases of polyploidy and translocation, the karyotype of N. arenarium is very stable and the karyotypic instability described for other species may be associated with their polyploid condition.

Representatives of the Cactaceae subfamilies Pereskioideae and Opuntioideae from northeastern Brazil were studied using banding with the fluorochromes, CMA3 and DAPI, as well as with fluorescent in situ hybridization using 45S and 5S rDNA probes to identify the distributions of their heterochromatin and rDNA sites. Pereskia aculeata, P. bahiensis, P. grandifolia (Pereskioideae), Brasilopuntia brasiliensis, Tacinga funalis, and T. palmadora showed 2n = 22, while Opuntia dillenii showed 2n = 44, and O. ficus-indica 2n = 88. The karyotypes of all of the species were symmetric, with average chromosome lengths varying from 1.94 lm in O. dillenii to 3.17 lm in P. aculeata. One pair of terminal CMA? bands corresponding to NORs occurred in all of the diploid cytotypes (except O. ficus-indica, which has two pairs of terminal CMA? bands) as well as in O. dillenii (tetraploid). CMA? bands were also observed in the interstitial region of the long arm of a chromosome pair in B. brasiliensis, while a number of variable proximal bands were observed on three chromosome pairs in O. dillenii and on most of the chromosomes of O. ficus-indica. The 45S rDNA sites corresponded to the terminal CMA? bands, while the 5S rDNA sites were located in the interstitial regions of the long arms of the chromosome pairs of P. aculeata, P. bahiensis, P. grandifolia, and B. brasiliensis. Our data, and earlier publications, suggest that the subfamily Opuntioideae can be characterized as having proximal/interstitial CMA? heterochromatin in at least one chromosome pair (except in Tacinga). The absence of proximal heterochromatic bands, however, appears to be a synapomorphy of the basal lineages of Cactaceae (subfamily Pereskioideae ? Maihuenioideae), suggesting that karyotypes with heterochromatin restricted to the terminal region of a chromosome pair (45S rDNA) represent a plesiomorphic character of the family.