Hybridization studies in Bostrychia:: 2.: Correlation of crossing data and plastid DNA sequence data within B-radicans and B-moritziana (Ceramiales, Rhodophyta)

Hybridization of isolates of Bostrychia radicans (Montagne) Montagne and B. moritziana (Sonder ex Kutzing) J. Agardh from various geographical locations was performed in laboratory culture. Positive crosses (successful formation of carposporophytes and release of carpospores) were observed between single isolates of B. moritziana from Australia and South Africa. but this species did not hybridize with B. radicans isolates. Hybridization occurred between isolates of B. radicans from Venezuela and Pacific Mexico and between Peruvian and some Brazilian isolates. Not all Brazilian isolates were able to hybridize with each other. DNA sequences of the intergenic spacer of the plastid-encoded large- and small-subunit genes of ribulose bisphosphate carboxylase/oxygenase (RUBISCO) were used to determine relationships between and within these two species. Bostrychia radicans formed a clade distinct from B. moritziana. All phylogenetic analyses resulted in two major clades within B. radicans that did not completely correspond to geographical proximity of the isolates. The phylogenetic relationships generally correlated with the hybridization data, although isolates that were not able to hybridize were sometimes closely related, based on DNA comparisons. Incongruence between DNA sequence phylogeny and proposed relationships based on crossing results with one B. radicans isolate can be interpreted as a case of plastid introgression. Tests of alternative hypotheses, grouping isolates based on geographic proximity, ocean basin distribution, northern and southern hemisphere distribution, or parasite susceptibility/resistance were tested and were not supported by the DNA sequence data. A biogeographical history for the present distribution of the species must consider both vicariant and dispersal events.