title: A cryptic species produced by autopolyploidy and subsequent introgression involving Medicago prostrata (Fabaceae).
abstract: Although hybridisation through genome duplication is well known, hybridisation without genome duplication (homoploid hybrid speciation, HHS) is not. Few well-documented cases have been reported. A possible instance of HHS in Medicago prostrata Jacq. was suggested previously, based on only two genes and one individual. We tested whether this species was formed through HHS by sampling eight nuclear loci and 22 individuals, with additional individuals from related species, using gene capture and Illumina sequencing. Phylogenetic inference and coalescent simulations were performed to infer the causes of gene tree incongruence. We found no evidence that phylogenetic differences among M. prostrata individuals were the result of HHS. Instead, an autopolyploid origin of tetraploids with introgression from tetraploids of the M. sativa complex is likely. We argue that tetraploid M. prostrata individuals constitute a new species, characterised by a partially non-overlapping distribution and distinctive alleles (from the M. sativa complex). No gene flow from tetraploid to diploid M. prostrata is apparent, suggesting partial reproductive isolation. Thus, speciation via autopolyploidy appears to have been reinforced by introgression. This raises the intriguing possibility that introgressed alleles may be responsible for the increased range exploited by tetraploid M. prostrata with respect to that of the diploids.
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, 40530 Gothenburg, Sweden. Electronic address: jonna.eriksson@bioenv.gu.se.
authors.forename: J S
authors.initials: JS
authors.lastname: Eriksson
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, 40530 Gothenburg, Sweden.
authors.forename: J L
authors.initials: JL
authors.lastname: Blanco-Pastor
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, 40530 Gothenburg, Sweden.
authors.forename: F
authors.initials: F
authors.lastname: Sousa
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, 40530 Gothenburg, Sweden.
authors.forename: Y J K
authors.initials: YJK
authors.lastname: Bertrand
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Box 461, 40530 Gothenburg, Sweden.
authors.forename: B E
authors.initials: BE
authors.lastname: Pfeil
mesh_terms: D000483:Alleles; D001483:Base Sequence; D032461:Chromosomes, Plant / Q000235:genetics; D003198:Computer Simulation; D017343:Genes, Plant; D006824:Hybridization, Genetic; D007178:Inbreeding; D029902:Medicago / Q000033:anatomy & histology / Q000235:genetics*; D010802:Phylogeny; D011123:Polyploidy; D011995:Recombination, Genetic / Q000235:genetics; D013045:Species Specificity
keywords: Coalescent simulations; Gene capture; Homoploid hybrid speciation; Hybridisation; Next-generation sequencing; Polyploid speciation