Genetic diversity and structure of the cycad Zamia loddigesii Miq. (Zamiaceae): implications for evolution and conservation

Abstract

The genetic diversity and structure of four populations of the cycad Zamia loddigesii were studied throughout its range in Mexico. Allozyme electrophoresis of 15 loci was conducted. The mean number of alleles per locus was 1.80 ± 0.09, the percentage of polymorphic loci was 66.6 ± 5.4, and the expected heterozygosity was 0.266 ± 0.02. The results indicated that the genetic diversity was relatively higher, with respect to tropical tree species and other cycads. The genetic variation explained by differences among populations was 18%. On average, gene flow between paired populations was similar ( Nm = 1.6) to other tropical forest trees and cycad species. Our results indicated that the geographical isolation among populations of Z. loddigesii generated allele loss, as well as a clinal variation in the frequencies of two loci ( MDH and MNR2 ), in relation to the latitudinal distribution of populations. The populations have become fragmented due to increasingly higher pressure of habitat conversion and disturbance. The importance of the establishment of sanctuaries and protected areas and a reduction in deforestation is highlighted in this research as a way of preserving the high genetic diversity of this and other endemic species. AA. 1994. Population genetic structure of Cecropia obtusifolia, a tropical pioneer tree species. Evolution 48: 437-453. Alvarez-Buylla ER, García-Barrios R, Lara-Moreno C, Martínez-Ramos M. 1996. Demographic and genetic models in conservation biology. Applications and perspectives for tropical rain forest tree species.

ORIGINAL ARTICLE: Cycads in the insular South‐west Pacific: dispersal or vicariance?

“…Although we cannot comment on the genetic diversity within the various species because of the small sample sizes, our data confirm the general trend towards low heterozygosity in populations in many cycads (Appendix 2 in González‐Astorga et al. , 2006).…”

Diversity and genetic structure of three species of Dioon Lindl. (Zamiaceae, Cycadales) from the Pacific seaboard of Mexico

“…The second line of research concerned with the characterization of cycad genetic variation is represented by population genetic studies sensu stricto . Most population genetics on cycads has consisted of analyses of the distribution of genetic diversity within and between populations of a single species (Keppel, 2002; González‐Astorga et al ., 2003a, 2005, 2006). However, a few studies have also been conducted for two or more closely‐related species within the same genus, namely, Macrozamia (Sharma, Jones & Foster, 1998, 1999, 2004) and Cycas (Xiao et al., 2005; Xiao & Gong, 2006).…”

“…short‐term) events upon the present distribution of populations. In a series of recent studies, we have already attempted this type of integration for the Mexican cycad species Dioon edule and Dioon angustifolium (González‐Astorga et al ., 2003a, b, 2005), as well as for Zamia loddigesii (González‐Astorga et al ., 2006). However, in all these studies, every cycad species was considered individually; by definition, the interesting possibility of common biogeographical processes affecting more than one species simultaneously has not been investigated.…”

Morphometric and geographical variation in theCeratozamia mexicanaBrongn. (Zamiaceae) complex: evolutionary and taxonomic implications

“…Either through the lens of 'classical' population genetics (Gonz alez-Astorga et al, 2003b, 2005, 2006 or through phylogeography (Huang et al, 2001;Chiang et al, 2009;Kyoda & Setoguchi, 2010;Zhan et al, 2011;Guti errez-Ortega, Kajita & Molinar-Freaner, 2014;Nolasco-Soto et al, 2015), the results of further work in this direction will allow the construction of ancestor-descendant hypotheses involving known populations, as well as the assessment of demographic history and genetic differentiation between these populations. In accordance with our population-genetic research programme, evolutionary inferences derived from these phylogeographical interventions will constitute the starting point in species recognition and circumscription.…”