title: Genomic coalescence in a population of laxmannia sessiliflora (Angiospermae, anthericaceae): an association of lethal polymorphism, self-pollination and chromosome number reduction
abstract: A population of Laxmannia R. Br. (Angiospermae, Anthericaceae) near Collie, Western Australia, combines the taxonomically significant sessile inflorescences of L. sessiliflora Dcne. (n = 4) and the derived breeding system of L. ramosa Lindl. (n = 4). It exhibits a polymorphism for seed-aborting lethal equivalents, significant levels of self-pollination and a chromosome polymorphism in which a haploid genome with n = 3 is most frequent. Allozyme analysis indicates that the population is either of hybrid origin or one that has uniquely diverged from a phylogenetic link between the two species. The population is considered to represent a natural demonstration of the phenomenon of genomic coalescence as modelled by James (1992, Heredity, 68, 449-456) in which devices which reduce the number of independently segregating supergenes heterozygous for recessive lethals are elevated to high frequencies by inbreeding. The population also suggests a mechanism whereby dysploid chromosome number reduction may be promoted by natural selection in natural population systems.
authors.affiliation: Department of Botany, The University of Western Australia, Nedlands, Western Australia 6907, Australia.
authors.initials: SH
authors.lastname: James
authors.initials: GK
authors.lastname: Keighery
authors.initials: A
authors.lastname: Moorrees
authors.initials: M
authors.lastname: Waycott