Genomic coalescence in a population of laxmannia sessiliflora (Angiospermae, anthericaceae): an association of lethal polymorphism, self-pollination and chromosome number reduction
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.
James
SH
Department of Botany, The University of Western Australia, Nedlands, Western Australia 6907, Australia.
Keighery
GK
Moorrees
A
Waycott
M