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Research Project: Subtropical and Tropical Ornamental Genetic Resource Management, Characterization, and Genetic Improvement

Location: Subtropical Horticulture Research

Title: A time-calibrated species tree phylogeny of the New World cycad genus Zamia L.(Zamiaceae, Cycadales)

Author
item Griffith, Patrick - Montgomery Botanical Center
item Calonie, Michael - Montgomery Botanical Center
item Meerow, Alan
item Salas-leiva, Dayana - Dalhousie University
item Vovides, Andrew - Institute De Ecologia - Mexico
item Coiro, Mario - University Of Zurich
item Ortega, Francisco - Florida International University

Submitted to: International Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: The genus Zamia is the largest genus of cycads in the New World, and has contributed many important species to the cultivated flora of subtropical and tropical areas. This paper presents a dated tree-of-life for almost all species of the genus using DNA sequences from 9 single copy nuclear genes and one chloroplast gene. Most of the extant species evolved between 9 and 16 million years ago, although their ancestors appeared nearly 70 million years in the past. The genus originated either in the Caribbean region or in Mexico, and subsequently dispersed to Central and South America. There has been a great deal of parallel evolution of morphological characters in Zamia, including characters that have been used to describe species groups in the past. This study presents the comprehensive, well resolved tree-of-life for Zamia and will provide a strong framework for further studies

Technical Abstract: The genus Zamia L. (Zamiaceae), consisting of 77 species, is the most species-rich and widely distributed cycad genus in the Neotropics and is arguably the most morphologically and ecologically diverse genus in the Cycadales. However, a strong phylogenetic framework for this genus is still lacking. We utilized a multilocus sequence dataset of 10 independent loci (9 single copy nuclear genes + 1 plastid) and extensive taxon sampling (over 90% of species) to infer phylogenetic relationships within Zamia. We implemented concatenated matrix analyses with maximum parsimony and maximum likelihood methods as well as a time calibrated Bayesian species tree-estimation approach. Diversification, historical biogeography, and ancestral character state reconstruction analyses were conducted utilizing the species tree topology which was the most morphologically and geographically congruent. We infer a robust phylogenetic tree for the genus with a strong geographic delimitation of clades and find that four morphological characters typically used for diagnostic purposes in the genus exhibit a high degree of homoplasy. The stem group of Zamia was estimated to have originated at 68.28 Ma (95% HPD 51.0–84.5), and the crown group at 9.54 Ma (95% HPD 9.0–10.62). The majority of species richness in the genus appeared during the Pliocene and Pleistocene, with the highest diversification rates occurring in clades comprised of Caribbean and South American species. Biogeographic analysis suggests a Caribbean or Mesoamerican origin for Zamia with 3 subsequent dispersal to the Central American Isthmus and South America, where the genus reaches its maximum species and morphological diversity. The high degree of convergence found in multiple morphological characters has historically confounded efforts to elucidate species relationships utilizing nonphylogenetic methods. This study presents the most species-comprehensive, well resolved hypothesis of phylogenetic relationships within Zamia and should provide a strong phylogenetic framework for further studies.