title: RbcL sequences indicate a single evolutionary origin of multinucleate cells in the red algal tribe Callithamnieae.
abstract: In the Ceramiaceae, one of the largest families of the red algae, there are from 1 to 4000 nuclei in each vegetative cell, but each tribe is homogeneous with respect to the uninucleate/multinucleate character state, except for the Callithamnieae. The goals of this study were to analyze rbcL gene sequences to clarify the evolution of taxa within the tribe Callithamnieae and to evaluate the potential evolutionary significance of the development of multinucleate cells in certain taxa. The genus Aglaothamnion, segregated from Callithamnion because it is uninucleate, was paraphyletic in all analyses. Callithamnion (including Aristothamnion) was monophyletic although not robustly so, apparently due to variations between taxa in rate of sequence evolution. Morphological synapomorphies were identified at different depths in the tree, supporting the molecular phylogenetic analysis. The uninucleate character state is ancestral in this tribe. The evolution of multinucleate cells has occurred once in the Callithamnieae. Multiple nuclei in each cell may combine the benefits of small C values (rapid cell cycle) with large cells (permitting morphological elaboration) while maintaining a constant ratio of nuclear volume: cytoplasmic volume.
authors.affiliation: School of Biology and Biochemistry, Queen's University Belfast, Medical Biology Centre, 97 Lisburn Road, UK. lynne.mcivor@seaweed.ie
authors.forename: Lynne
authors.initials: L
authors.lastname: McIvor
authors.forename: Christine A
authors.initials: CA
authors.lastname: Maggs
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Stanhope
mesh_terms: D005075:Biological Evolution; D002467:Cell Nucleus; D010802:Phylogeny; D018087:Plastids / Q000235:genetics; D000461:Rhodophyta / Q000166:cytology* / Q000502:physiology*; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics*
chemical_list: C101625:RbcL protein, plastid; D012273:Ribulose-Bisphosphate Carboxylase