Polyploidy, hybridization and evolution inPratia(Campanulaceae)

Abstract

Evolution in the genus Pratia (Campanulaceae) has been studied using a variety of techniques. The distribution of chromosome races in P. angulata has been plotted and results suggest that although they generally occupy different geographic areas there are large areas of overlap. No consistent morphological differences were found between these chromosome races. The existence of hybrids between P. angulata and P. perpusilla with 1 1x and 13x chromosome numbers has been established using genomic in situ hybridization (GISH), and random amplified polymorphic DNA (RAPD) analysis suggests several independent origins for these hybrids. Artificial hybridization studies showed a high degree of compatibility in almost all the combinations that were attempted. DNA sequences derived from both the nuclear genome (internal transcribed spacer of the rDNA locus, ITS) and chloroplast genomes (trnL intron and trnL-trnF spacer) were used to construct phylogenies. Colensoaphysaloides has been shown to be distinct from the New Zealand species of Pratia and was used as an outgroup to root the phylogenetic trees. A significant finding is that P. macrodon is sister to the other New Zealand species. DNA B04008; Online publication date 9 December 2004 Received 18 March 2004; accepted 14 June 2004sequence data also confirm the hybrid origin of the 1 1x and 13x plants and show that P. perpusilla is the maternal parent of the 1 1x plants and P. angulata is the maternal parent of the 13x ones. The origin of the putative hybrid plants with the12x chromosome number remains to be elucidated.

A review of genetic analyses of hybridisation in New Zealand

“…Chromosome doubling in animals can also have a dire effect on sex determination, and animals may be generally more susceptible to changes in gene dosage. Pratia discussed earlier is an example of new lineages arising from human induced range changes (Murray et al 2004). In this case, hybrid lineages are recognised as distinct chromosome races (not new species), but are the result of interspecific crosses.…”

“…For example, the native ground covering plant Pratia angulata has hybridised with another native P. perpusilla where they grow together at the Rotorua Golf Course forming plants with 91 chromosomes (13x) and 77 chromosomes (llx; Murray et al 2004). The hybrid nature of these plants has been established using molecular cytogenetics.…”

“…2A Pratia angulata and P. perpusilla (Murray et al 2004); 2 'Anaphalioides hookeri (inferred parentage A bellidioides andA trinervis; Smissen et al 2003;Smissen unpubl. ;Breitwieser et al 1999); 2& Ranunculus nivicola (Carter 2006);27 Six species oîAsplenium are of hybrid origin (e.g.,A.…”

Phylogenetic position and relationships ofLobelia glaberrima(Lobeliaceae), a new alpine species from southern South Island (New Zealand)

“…Druce (1992) regarded this southern entity as a distinct species affiliated with L. macrodon but with "lvs not-so-deeply toothed, fls not scented, and corolla tube much shorter, only 3-4 mm long and <2× calyx lobes" and later (Druce 1993) introduced the provisional geographic name Pratia "Garvie". Murray et al (2004) provided additional evidence that two distinct species were involved, noting that L. macrodon is a diploid with 2n = 14 chromosomes and this previously unnamed species is a tetraploid with 2n = 28 chromosomes.…”

“…The three remaining dispersal events are part of the main Australasian radiation, and each of these lineages diversified after reaching New Zealand. one closely related group of three species (L. perpusilla, L. angulata, and L. arenaria), treated in Pratia by Allan (1961), clearly have fleshy fruit and show interesting patterns of ecological and morphological variation, polyploidy, and hybridisation (Murray et al 1992(Murray et al , 2004. A second closely related group comprises plants previously treated as Isotoma fluviatilis and Hypsela rivalis (Allan 1961) plus two newly described species endemic to North-West Nelson and North Island that all have dry, thin-walled, capsule-like fruits that do not develop valves, the walls simply rupturing to release the seeds (Heenan et al 2008).…”