Demographic history and species delimitation of three Zamia species (Zamiaceae) in south-eastern Mexico: Z. katzeriana is not a product of hybridization

Speculations on hybridization among wild cycads are abundant, but empirical evidence of hybridization in cycad evolution is almost non-existent and the evolutionary consequences of hybridization in cycads have not been discussed. Previously, Zamia katzeriana was hypothesized to have a hybrid origin between two sympatric species: Z. splendens and Z. loddigesii. In this study, we aimed to reveal whether such a hypothesis is confirmed. Variation in 12 microsatellite loci, 12 morphological traits and environmental niche of ten populations representing the three species was examined. Gene flow and scenarios of demographic history were tested. Ecological niche models were reconstructed to examine present and past niche availability of the two putative parental species. Correlations between genetic, morphological, environmental and geographical distances were tested. We found that Z. katzeriana diverged from Z. splendens without experiencing admixture with its sympatric congeners. However, gene flow between Z. splendens and Z. loddigesii has occurred in one locality. The niches of the two latter species have overlapped since the Last Glacial Maximum, when admixture probably occurred. However, the admixed populations do not resemble Z. katzeriana. These results confirm that Z. katzeriana did not originate from hybridization between Z. splendens and Z. loddigesii.