Cycad Literature Database

A majority of cycad species face multiple challenges to their long-term survival, including habitat loss and illegal collecting. Confronting these threats is made more difficult by a lack of understanding of species genetic diversity and an unstable taxonomy. A comprehensive and uniform assessment of species boundaries and population genetic structure is necessary to ensure that both ex-situ and in-situ conservation programs successfully maintain genetic diversity in threatened species. The genus Dioon (Zamiaceae) is nearly endemic to Mexico (one Honduran species), and most species are designated Vulnerable to Critically Endangered. As part of our program to understand the evolution and conservation status of Dioon species, we measured levels of genetic diversity, estimated population genetic structure, and demographic history of D. tomasellii populations in western Mexico. We also compare morphological traits among populations in both univariate and multivariate analyses and compare these to patterns of genetic differentiation. Our results indicate that these populations are isolated, with relatively high genetic diversity, and show no evidence of inbreeding. Surprisingly high levels of private alleles along with significant allelic and morphological differentiation and local adaptation suggest that D. tomasellii, as currently circumscribed, may comprise multiple species. We compare our results to previous studies in Dioon and suggest future work aimed at revising the taxonomy of the species and informing conservation efforts.