Ricardo Clark-Tapia

Clonal diversity and distribution in Stenocereus eruca (Cactaceae), a narrow endemic cactus of the Sonoran Desert

Stenocereus eruca (Cactaceae), a prostrate cactus endemic to the Sonoran Desert, is thought to be highly clonal. We examined its clonal diversity and distribution: (1) at the population level, in four distinct populations along its distribution range; and (2) at a micro scale level, within a single population. Our objective was to evaluate the importance of sexual versus clonal recruitment through the use of RAPD markers. Contrary to previous field observations, clonal diversity was relatively high across the distribution range. This finding suggests that sexual recruitment is an important regeneration mechanism. The proportions of distinguishable genotypes (G/N = 0.83) and genotypic diversity (D = 0.987) were greater than in other clonal cacti, suggesting that clonal propagation is not the major regeneration mechanism. Autocorrelation analyses revealed a spatial genetic structure that may be the result of restricted gene flow (via pollen or seeds) and clonal propagation. A molecular variance analysis (AMOVA) indicated that most of the variation (66.3%) was found within and not across populations. Future studies on pollen and seed dispersal are needed to understand the role of the clonal habit in the mating system of S. eruca.

Clonal and genetic structure of two Mexican oaks: Quercus eduardii and Quercus potosina (Fagaceae)

Quercus eduardii and Q. potosina are dominant oak species in Sierra Fría, Aguascalientes, Mexico. These species have been exploited for multiple purposes since the 16th century. Both species produce clonal offspring through root suckering and acorns through sexual reproduction. To understand clonality for the implementation of the most adequate actions for the conservation of these species, we addressed the following questions: (a) what is the spatial clonal structure of both species? (b) How much clonal and genetic diversity is maintained in these species? Random Amplified Polymorphic DNAs (RAPDs) were used as molecular markers for these analyses. Genets of both species have few ramets and these grow close the parent tree. Autocorrelation analyses at the ramet level showed an aggregated distribution at short distances and a random spatial distribution at larger distances. Also, at the genet level the autocorrelation analyses showed a random distribution. Clonal diversity was high in both species (Q. eduardii: D=0.963, G/N=0.60; Q. potosina: D=0.985, G/N=0.65). Genetic diversity was high within populations (Q. eduardii: He=0.33±0.11; Q. potosina: He=0.35±0.11). Low levels of genetic differentiation among populations were observed (Q. eduardii ϕst=0.19, P < 0.002; Q. potosina ϕst=0.13, P < 0.002). Both species maintain high levels of clonal and genetic diversity, probably due to successful sexual reproduction, which allows gene flow among populations. Conservation and/or reforestation programs must include seed collections and germplasm banks. Due to the small genet size and the high clonal diversity of these species, seeds can be collected in any place in Sierra Fría, Aguascalientes.

Clonal Diversity and Allelic Relationships between Two Closely Related Species of Columnar Cacti from the Sonoran Desert: Stenocereus eruca and Stenocereus gummosus

Stenocereus eruca and Stenocereus gummosus are two closely related columnar cacti of the Sonoran Desert that are thought to be highly clonal. In addition, it has been suggested that S. eruca has recently been derived from an S. gummosus–like ancestor. We used allozymes analysis to test these hypotheses and to describe levels of genotypic diversity in populations of both taxa. Allelic composition in S. eruca was a subset of the composition found in S. gummosus, while polymorphism and expected heterozygosity were greater in S. gummosus, supporting the hypothesis that S. eruca is a recently derived species. The proportion of unique genotypes ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Demography and management of two clonal oaks: Quercus eduardii and Q. potosina (Fagaceae) in central México

G/N

Galls and host occurrences along a forest gradient in Sierra Juárez, Oaxaca, Mexico

\end{document} ) and genotype diversity (D) varied from 0.42 to 0.68 and from 0.78 to 0.98, respectively, among populations of S. eruca and from 0.64 to 0.96 and from 0.96 to 1.00, respectively, among populations of S. gummosus. The evidence on clonal diversity indicates that both species combine clonal growth and sexual recruitment as mechanisms of regeneration and that S. eruca seems to rely more on clonal propagation than does S. gummosus. We hypothesize that the procumbent growth habit of S. eruca in the plains of Magdalena may have evolved in response to aeolian dune formation during the Pleistocene.