Jorge González-Astorga

A character-based approach in the Mexican cycads supports diverse multigene combinations for DNA barcoding

A DNA barcoding study was conducted to determine the optimal combination of loci needed for successful species‐level molecular identification in three extant cycad genera—Ceratozamia, Dioon, and Zamia—that occur in Mexico. Based on conclusions of a previous multigene study in representative species of all genera in the Cycadales, we tested the DNA barcoding performance of seven chloroplast coding (matK, rpoB, rpoC1, and rbcL) and non‐coding (atpF/H, psbK/I, and trnH‐psbA) regions, plus sequences of the nuclear internal transcribed spacer. We analysed data under the assumptions of the “character attributes organization system” (CAOS), a character‐based approach in which species are identified through the presence of ‘DNA diagnostics’. In Ceratozamia, four chloroplast regions and one nuclear region were needed to achieve > 70% unique species identification. In contrast, the two‐gene combination atpF/H + psbK/I and the four‐gene combination atpF/H + psbK/I + rpoC1 + ITS2 were needed to reach 79% and 75% unique species identification in Dioon and Zamia, respectively. The combinations atpF/H + psbK/I and atpF/H + psbK/I + rpoC1 + ITS2 include loci previously considered by the international DNA barcoding community. However, none of the three combinations of potential DNA barcoding loci found to be optimal with a character‐based approach in the Mexican cycads coincides with the ‘core barcode’ of chloroplast markers (matK + rbcL) recently proposed for universal use in the plant kingdom.

Genetic diversity through life history of Dioon edule Lindley (Zamiaceae, Cycadales)

The distribution of genetic diversity and structure for three populations of Dioon edule Lindley (Zamiaceae) at Monte Oscuro (MO), El Farallón (EF) and Rancho del Niño (RN) in Veracruz, Mexico was studied using 20 allozyme loci, considering four life history classes: seeds, seedlings, juveniles and adults. The MO population is genetically less diverse than the EF and RN populations. Total and local inbreeding differ significantly between life history classes. An increment of inbreeding among all classes was observed, and genetic differentiation among populations was higher in seeds and seedlings than in juveniles and adults. In terms of percentage of polymorphic loci, the MO seeds showed least (80%), followed by RN (95%) and EF had the highest values (100%), probably because of a reduction in effective population size and habitat fragmentation processes. In this context, the mean effective population size was 23.2 +/- 11.3 for all populations. We conclude that seed cohorts in EF and RN represent a reservoir of genetic diversity within these two populations. Also, preservation of adult plants is an essential aspect to consider in management and conservation efforts for populations of Dioon edule in natural conditions.

Character-based, population-level DNA barcoding in Mexican species of Zamia L. (Zamiaceae: Cycadales)

Background and aims: With the recent proposal of matK and rbcL as core plant DNA barcoding regions by the Consortium for the Barcoding of Life Plant Working Group, the construction of reference libraries in the botanical DNA barcoding initiative has entered a new phase. However, in a recent DNA barcoding study in the three Mexican genera of the gymnosperm order Cycadales, we found that neither matK nor rbcL allow high levels of molecular identification of previously established species. Materials and methods: Our data analysis in that study rested on the “Characteristic Attributes Organization System” (CAOS), a character-based algorithm for the definition of “DNA diagnostics.” Here, we use CAOS to analyze a population-level molecular data set in Zamia, one of the three cycad genera occurring in Mexico, whose populations display contrasting biogeographic patterns. Our population-level study, which includes all species in the region formally known as Megamexico, is restricted to the genome region, which showed the best single-locus molecular identification performance in our previous study—namely, the noncoding intergenic chloroplast spacer psbK-I. Results: Our comparison of single-individual vs. population-level psbK-I datasets in Zamia indicates that CAOS analyses are sensitive to slight alignment changes, which in turn derive from the different amounts of molecular variation present in each matrix type. Conclusion: We, therefore, suggest that character-based studies that involve population-level data should contemplate this type of comparison between data matrices, before a set of DNA diagnostics in a given DNA barcoding reference library is considered definitive.

Reciprocal illumination of morphological characters upon a molecular hypothesis supports the proposal of a new species of cycad from Mexico

Abstract The new species Dioon stevensonii, from the Rio Balsas basin spanning the states of Michoacan and Guerrero, Mexico, is described and illustrated. The description of this species implies a recircumscription of the populations of Dioon that constitute the previously characterised D. tomasellii, which also includes populations located in Durango, Nayarit and Jalisco. Dioon stevensonii differs from its congeners in characters of both vegetative and reproductive structures ‐ namely, leaflet contour shape, leaflet curvature and reflection of the megasporophyll tips. Despite its morphological affinities with D. tomasellii, complementary cladistic analyses of molecular matrices indicate that D. stevensonii has closer phylogenetic affinities with the D. edule and D. spinulosum species groups, which are distributed along the Gulf of Mexico and Caribbean seaboards. The proposal of D. stevensonii rests on the reevaluation of overlooked differences in morphological character states in herbarium material, corresponding to populations previously identified as D. tomasellii, which were confirmed after ex profeso field collections. The fact that such re‐evaluation was prompted by a hypothesis of relationships based on molecular data for the entire genus Dioon, establishes the proposal of D. stevensonii as an unusual case of reciprocal illumination, where the morphological evidence provided confirmation of a molecular hypothesis, and not vice versa.

Phylogeography and demographic history of Zamia paucijuga Wieland (Zamiaceae), a cycad species from the Mexican Pacific slope

We have investigated the phylogeographic structure and demographic history of Zamia paucijuga, based on 120 ITS2 and 117 psbK/I sequences from 13 populations distributed along the entire distribution range of the species. We have detected 15 ITS2 and four psbK/I haplotypes, for a total of 19. The genetic diversity estimated for psbK/I was relatively lower than the ITS2 diversity. These results imply that the average genetic diversity in Z. paucijuga is lower in comparison with other cycad species, but relatively higher than the diversity found in conifers. Non-hierarchical and hierarchical AMOVAs for ITS2 and psbK/I showed both low and high levels of genetic structure. This discrepancy likely reflects a decrease in gene flow intensity for seeds but high pollen gene flow, which correlates with the divergent inheritance processes in nuclear vis-à-vis organellar DNAs. SAMOVA tests for both loci (ITS2 and psbK/I) showed high correspondence with the regional geographic structure defined a priori, indicating that the use of both nuclear and chloroplast gene regions improves inferences concerning the evolutionary processes that affect population dynamics in Z. paucijuga. Furthermore, our results are consistent with the conclusions of other studies on the origin of the genus Zamia, which support locating the diversification times of Z. paucijuga populations in the Pleistocene.

Genetic Diversity in Six Govenia (Orchidaceae) Species with Different Pollinator Attraction Strategies

A few generalizations have been made about the amount of genetic diversity and life‐history traits in plants, and a number of studies have reported contrasting results, indicating that these generalizations are not necessarily reliable. Six Govenia species belonging to three groups characterized by different pollinator attraction strategies were studied: (a) small inflorescences with three to eight whitish or greenish flowers, (b) medium‐sized inflorescences with 15–30 white flowers, and (c) large inflorescences with 30–50 or more yellowish flowers. Genetic variation was assessed using starch gel electrophoresis to resolve 17 allozyme loci in 13 populations, to determine the level and distribution of genetic variation, and to evaluate the association between genetic diversity and pollinator attraction strategy. A high level of genetic variation and a low genetic differentiation among species were found. The mean number of alleles per locus was higher among species with strategy c than species with strategy a ( \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

Phenotypic variation of Zamia loddigesii Miq. and Z. prasina W.Bull. (Zamiaceae, Cycadales): the effect of environmental heterogeneity

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Population genetics of Dioon edule Lindl. (Zamiaceae, Cycadales): biogeographical and evolutionary implications

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