Inferences on the origins of polyploid Turnera species (Passifloraceae) based on molecular data

Abstract

We explore the evolution of polyploids in subseries Turnera, testing hypotheses on their origins using DNA sequences (partial ndhF and trnT-L) from the plastid genome, as well as sequences of the nuclear ribosomal internal transcribed spacer (ITS). We construct phylogenies (with both Bayesian and maximum parsimony methods) using both the plastid and ITS sequences. We test hypotheses concerning the genome contributors to polyploids where previous cytogenetic studies had designated various diploid species as possessing A or C genomes and had proposed various genomic constitutions for the polyploids. Our analyses support the occurrence of a C genome clade of species and the origin of autooctoploid T. fernandezii Arbo from T. grandiflora (Urb.) Arbo (a C genome diploid). Nuclear ITS data support the hypothesis that T. concinna Arbo (an A genome species) contributed a genome to the segmental allotetraploid T. grandidentata (Urb.) Arbo, whereas analyses of ndhF and trnT-L sequences did not lead to identification of the plastid (or additional nuclear genome) donor. Our analyses support the origins of allooctoploids T. aurelii Arbo and T. cuneiformis Poir. from hexaploid T. orientalis (Urb.) Arbo. We found no evidence that hexaploid T. velutina Presl. possesses a C genome. We provide evidence, using Bayes factors, supporting the hypothesis that the segmental allohexaploids have had independent origins.