Geographical patterns of genetic variation in two species ofStylosanthesSw. using amplified fragment length polymorphism

Abstract

Understanding the extent and distribution of genetic diversity within a species is essential for the development of effective conservation strategies. The objective of this study was to assess genetic variation using amplified fragment length polymorphisms (AFLP) in two species of the tropical legume genus Stylosanthes Sw. Annual, S. humilis (2n = 20) and perennial, S. viscosa (2n = 20) are found throughout tropical America, and are sympatric for much of their range of distribution. One hundred and eleven accessions, covering a wide geographical range, were selected for AFLP analysis. Binary data matrices derived from DNA banding patterns were analysed using the software programs NTSYS-PC and ARLEQUIN. Several accessions were found to be misidentified. Of the S. humilis accessions, the overall average similarity value was (0.72) slightly higher than the value obtained for S. viscosa (0.67). Cluster analysis and principal coordinate analysis grouped accessions from both species by geographical origin, with a few exceptions. Analysis of molecular variance (AMOVA) in S. humilis revealed 59.4% of the variation among groups formed from the cluster analysis. This was highly significant (P < 0.001). For S. viscosa AMOVA also revealed more variation among than within groups (66.5%). This was also highly significant (P < 0.001). The majority of accessions of both species conserved ex situ are of Brazilian and Venezuelan origin. This study has identified areas in Central America and Mexico for which novel genetic variation may be found and where conservation activities should be focused.

Neighbour joining trees, dominant markers and population genetic structure

“…The multilocus dominant marker phenotypes of individuals are then used to generate a genetic distance matrix. This information is subjected to phenetic analysis to produce a visual representation (a tree-based diagram or principal coordinates plot (PCO)) of the genetic relationships among individuals in the sample (eg Winfield et al, 1998;Clausing et al, 2000;Drummond et al, 2000;van der Merwe et al, 2000;Sawkins et al, 2001;Barth et al, 2002;Nan et al, 2003).…”

“…The multilocus dominant marker phenotypes of individuals are then used to generate a genetic distance matrix. This information is subjected to phenetic analysis to produce a visual representation (a tree-based diagram or principal coordinates plot (PCO)) of the genetic relationships among individuals in the sample (eg Winfield et al, 1998;Clausing et al, 2000;Drummond et al, 2000;van der Merwe et al, 2000;Sawkins et al, 2001;Barth et al, 2002;Nan et al, 2003).The shape of the tree or PCO plot then forms the basis for making population genetic inferences about the populations from which the individuals were derived. For instance, grouping of individuals from different populations in the same cluster of a tree has been interpreted as evidence for gene flow between these populations; location of individuals from different populations in mutually exclusive clusters has been taken as evidence for genetic isolation of the populations.…”

Ecologia da interação entre as pequenas flores de quilha de Stylosanthes viscosa Sw. (Faboideae) e as grandes abelhas Xylocopa (Neoxylocopa) cearensis Ducke, 1910 (Apoidea, Hymenoptera), em duna tropical

“…Stylosanthes viscosa Sw. é uma herbácea ou sub-arbusto prostrado (definição que varia de acordo com o autor), perene com ampla distribuição nas Américas, onde ocupa grande variedade de ambientes, dos trópicos úmidos aos trópicos áridos (Sawkins et al 2001), sendo bastante abundante nas restingas e dunas costeiras do Brasil , Sacramento et al 2007). Apresenta floração ao longo do ano, com picos entre julho e janeiro .…”

“…O gênero Stylosanthes Sw. (Faboideae) reúne plantas herbáceas ou sub-arbustos com flores de quilha, nativas dos trópicos e sub-trópicos das Américas, África e Ásia (Sawkins et al 2001). Das 30 a 45 espécies reconhecidas (dependendo do tratamento; p.ex., Stappen et al 2002), cerca de 25 ocorrem no Brasil, que também se destaca como principal centro de dispersão do gênero.…”

“…Das 30 a 45 espécies reconhecidas (dependendo do tratamento; p.ex., Stappen et al 2002), cerca de 25 ocorrem no Brasil, que também se destaca como principal centro de dispersão do gênero. Stylosanthes viscosa Sw. (Faboideae) está amplamente distribuída na América tropical, desde o Brasil até o México (Sawkins et al 2001), incluindo regiões áridas e semi-áridas, restingas e dunas costeiras. O gênero, em particular S. viscosa, diferencia-se pelas flores de tamanho muito reduzido (estandarte com cerca de 4,0 mm de comprimento) e pela floração relativamente longa, porém com baixa quantidade de flores abertas por planta/dia.…”