| dc.description.abstract | Interspecific hybridisation accompanied by multiplication of chromosome
number, or allopolyploidy, results in rapid genetic, epigenetic, chromosomal and
morphological changes. Evidence of ancient polyploidisation is found in most if not all
angiosperms, suggesting that polyploidisation may have played a role in the success of
angiosperm species. Here, I examine the fate of duplicate gene copies in the floral
development gene NICOTIANA FLO/LFY (NFL) and the evolution of floral form and
colour in Nicotiana (Solanaceae) allotetraploids of different ages.
Both NFL copies are retained in all allotetraploids examined, even those ~10
million years old (myo). There are no nonsense or frame-shift mutations, suggesting that
all copies are still functional. Both copies are expressed in all allotetraploids examined,
even those ~4.5 myo. The evolution of floral form and colour was examined using
geometric morphometrics of floral limb shape, corolla tube length and width metrics, and
spectral reflectance measurements of floral colour. In floral limb shape, younger
polyploids tend to be intermediate in shape between those of their diploid progenitors,
whereas older polyploids have more divergent forms; however, divergence in floral limb
shape can occur rapidly following polyploidisation. In corolla tube length and width, the
majority of polyploids have wider and shorter corolla tubes, suggesting more generalist
pollination after polyploidisation. In floral colour, polyploids can either be intermediate
between their progenitors, like one or other progenitor, or divergent. The floral colour of
N. tabacum is divergent and seems to have resulted from the inheritance of floral plastids
that lack chlorophyll from its maternal progenitor and the inheritance of anthocyanin
pigmentation from its paternal progenitor. Evidence for convergent evolution of floral
form in green/yellow-flowered Nicotiana seems to be linked to hummingbird pollination.
Overall, rapid molecular and morphological changes following polyploidisation may be
advantageous and may partially explain why polyploids have been so successful in
angiosperms. | |
