From Dampier to DNA: the 300-year-old mystery of the identity and proposed allopolyploid origin of Conostylis stylidioides (Haemodoraceae)

Abstract

The tetraploid Conostylis stylidioides (n= 16) has been proposed to be a stabilised hybrid between the diploid (n = 8) species C. prolifera and C. candicans because of morphological and geographical intermediacy, as well as a polyploid chromosome number. To test this hybrid-origin hypothesis, we used the DNA-fingerprinting technique amplified fragment length polymorphism (AFLP) and measured genetic variation within these taxa, as well as the putative outgroups C. robusta and C. aculeata. One AFLP primer pair generated 192 dominant markers for 36 samples from these species, of which 189 were polymorphic. Polymorphism within populations was uniformly high for all species, with 66–86% of all fragments polymorphic and estimates of heterozygosity ranging from 0.36 to 0.41. Ordination, UPGMA and maximum parsimony analyses of these genetic data consistently clustered species, supporting the current species’ level taxonomy. The intermediate placement of C. stylidioides between C. proliferaand C. candicans on the maximum parsimony tree supports the hybrid-origin hypothesis, although other interpretations are possible. The phenetic results for AFLP data, in which C. stylidioides is not strictly intermediate between C. prolifera and C. candicans, are either concordant with recent research suggesting that rapid intra- and inter-genomic rearrangements occur with the origin of polyploid taxa, or indicate an ancient hybridisation event. While our results do not reject the hybrid origin hypothesis, the extremely high levels of genetic variation detected with AFLP within these populations, in combination with extensive genomic reorganisation with the origin of C. stylidioides and the possibility of independent origins for different populations, make it difficult to confidently exclude other scenarios.