Allozyme Variation in the Three Extant Populations of the Narrowly Endemic Cycad Dioon angustifolium Miq. (Zamiaceae) from North-eastern Mexico

Abstract

Dioon angustifolium presents high levels of genetic diversity compared with other cycad species, in spite of small population sizes. The recent bottleneck effect did not effectively reduce the genetic variation to the extent of eliminating these populations. The distribution of D. angustifolium appears to be the result of historical biogeographical effects related to the Pleistocene glaciations. It is recommended that this species be catalogued in the IUCN Red List of Threatened Species and conservation efforts be made to preserve it.

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

“…10,000 years), this being sufficient time to generate differentiation between Dioon angustifolium and D. edule, as suggested by González-Astorga et al (2005). We estimate that population differentiation between MO and EF may have occurred in less than 10,000 years, taking into account the possibility that they may have shared genes through descent from more long-lived plants established in once much larger populations.…”

Variación genética en especies de cícadas estrechamente relacionadas en Ceratozamia (Zamiaceae: Cycadales) mediante el uso de RAPDs

“…It appears that species of the C. norstogii complex probably emerged from an allopatric speciation process resulting from recent and ongoing divergence processes due to drift stemming from founder effects, resulting in alleles from the original populations becoming fixed in most of the surviving populations. This has been reported in several species of cycads, for example Cycas debaoensis (Qing-Qing, Wang, Gong, & Peng, 2011); C. taitungensis (Huang, Chiang, Schaal, Chou, & Chiang, 2001); Dioon angustifolium (González-Astorga et al, 2005); D. edule (Octavio-Aguilar, González-Astorga and Vovides (2009); D. sonorense . A possible contribution to inbreeding could be that the cycad beetle pollinators do not fly great distances (Norstog, 1987;Norstog & Fawcett, 1989).…”

“…Isoenzymes may have different allelic forms (allozymes), mostly selective neutrals and co-dominants, which could be used to quantify allelic frequencies and different measures of genetic variation. Some analyses have been done on a wide range of cycad species, for instance; Zamia pumila (Walters & Deckers-Walters, 1991), Macrozamia pauli-guilielmi complex (Sharma, Jones, Forster, & Young, 1998), the M. heteromera complex (Sharma, Jones, Forster, & Young, 1999), the M. plurinervia complex (Sharma, Jones, & Forster, 2004), nine Encephalartos species (Van Der Bank et al, 2001), Cycas seemannii (Keppel, Lee, & Hodgskiss, 2002) and five species of Dioon have been analyzed (González-Astorga, Vovides, Ferrer, & Iglesias, 2003;González-Astorga, Vovides, Cruz-Angón, Octavio-Aguilar, & Iglesias 2005; Cabrera-Toledo, González-Astorga et al, 2008;Cabrera-Toledo et al, 2010). Genetic variation and species relationships have been studied to a lesser extent with RAPD markers, which are dominants and highly polymorphic, examples are Encephalartos (Chaiprasongsuk et al, 2004), with AFLP, RFLP and RAPDs in Cycas (Mekanawakul & Juntawong, 2004;Sangin, Thongpan, Lindstrom, Sangduan, & Mingmuang, 2004).…”

Reevaluación del riesgo de extinción de cinco especies del género Polianthes l. (Agavaceae)

“…Los análisis de la variación y estructura hereditaria, flujo de genes y efectos de botella, indican que poblaciones endémicas pequeñas, genéticamente poco diversas, son especialmente vulnerables a la extinción como consecuencia del cambio de uso del suelo, destrucción del hábitat y remoción de individuos (González-Astorga et al, 2005). Los estudios que permitan conocer la estructura alélica de las poblaciones son altamente recomendados, ya que con ellos se puede predecir si éstas podrán adaptarse a los cambios ambientales (González-Astorga et al, 2003).…”