CONSERVATION, CHARACTERIZATION, AND GENETIC IMPROVEMENT OF SUBTROPICAL AND TROPICAL ORNAMENTAL GERMPLASM
Location: Subtropical Horticulture Research
Title: The coontie’s new clothes: asymmetric genetic diversification within Zamia (Cycadales: Zamiaceae) on Puerto Rico, and an hypothesis of multiple introductions
Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2012
Publication Date: November 1, 2012
Citation: Meerow, A.W., Francisco-Ortega, J., Calonje, M., Ayala Silva, T., Griffith, P., Stevenson, D., Nakamura, K. 2012. The coontie’s new clothes: asymmetric genetic diversification within Zamia (Cycadales: Zamiaceae) on Puerto Rico, and an hypothesis of multiple introductions. American Journal of Botany. 99:1828-1839.
Interpretive Summary: The Caribbean coonties are a distinctive group of American cycads (an ancient group of non-flowering seed plants) that are popular landscape plants. They are found in the West Indies and southeastern U. S. (Florida), and are considered to encompass either a single or as many as nine distinct species. We are extensively sampling populations of the group throughout its range and genotyping them with both microsatellite DNA markers and sequences of single copy genes. Here, we present our analysis of 31 microsatellite DNA markers across Puerto Rico, where three species have been recognized: Zamia erosa, Z. portoricensis, and Z. pumila. Our data support recognition of three distinct species on the island. While Z. portoriciensis and Z. pumila likely share common ancestry, we believe that Z. erosa represents an independent entry onto the island. We anticipate that an understanding of the genetic structure of the populations of this complex will help to delineate future conservation strategies, and serve as a model for population level studies of other rare Caribbean plants.
Three distinctive Zamia species occur on Puerto Rico: Z. erosa on the north coast, and Z. portoricensis and Z. pumila, both in the south. Their relationships are largely unknown. We tested an hypothesis of multiple introductions and explored whether the three species show divergent patterns of genetic variation. This study is the most intensive population genetics investigation of a cycad to date in terms of number of markers, and one of only a few microsatellite studies of plants from the Caribbean biodiversity hotspot. We used 31 microsatellite DNA loci across ten populations, and analyzed the data with genetic distance, Bayesian clustering, fine scale spatial genetic correlation, bottleneck analysis, and ABC coalescent modeling. Puerto Rican zamias exhibit an amalgam of patterns of genetic differentiation reported for cycads. Overall, the species are slightly inbred with high intra-populational variation and little evidence of recent bottlenecks; four populations show significant heterozygote deficit. Zamia erosa exhibits a more than threefold greater degree of population differentiation, with historical gene flow only evident between Z. portoricensis and Z. pumila. A selective sweep may be underway in a small population of Z. erosa in a saline environment. Fine scale spatial analysis reveals little correlation between distance and genetic differentiation at the local scale. Zamia erosa likely represents an independent introduction into Puerto Rico; Z. portoricensis and Z. pumila fit a scenario of allopatric speciation. This will be explored further in the context of genetic analysis across the entire Caribbean region.