Hybridization leads to rapid genomic alterations, including chromosomal rearrangements and gene expression changes, some of which are mediated by transposable elements [10, 11]. These genomic changes often result in novel phenotypes, some that are intermediate between parentals, some that represent novel combinations of parental features, and, finally, others that are extreme or transgressive compared to those of the parental species. Homoploids with flowers intermediate between their parents in morphology or that produce a complex mixture of floral fragrances from both parents are likely to be ineffective in attracting the pollinator of either parent, so there is likely to be strong selection to conform to the morphology of one or the other parent. This affects both homoploids and allopolyploids equally.
In Nicotiana, for example, the four species in the allopolyploid N. section Repanda have flowers that attract long-tongued night-flying moths (three species) like N. sylvestris (the female parent) or short-tongued bees (one species) like N. obtusifolia (Figure 1). Although flowers of intermediate morphology and fragrance may not be well adapted to any existing pollinator, it is not always the case, particularly if there are highly specific interactions between plant and pollinator. Examples of this include when nectar spur length is highly correlated to tongue length of a particular pollinator [12] or sexual deception is operating as a pollinator attractant, as in the case of the orchid genus Ophrys. As shown in a recent paper in BMC Evolutionary Biology [13], pollinators of O. arachnitiformis and O. lupercalis are attracted by complex blends of fragrance compounds, and their hybrids produce a complete admixture of these, attracting a different species of bee (or other hymenopteran) than either of those pollinating the parental species. Thus, the hybrid is immediately reproductively isolated from its parents and, provided that it is fertile and has a suitable habitat, can become established as a species in its own right. This sort of circumstance is rare and would not be likely to occur in hybrids (regardless of ploidy) with less specific types of pollination syndromes because it is highly dependent on the well coordinated aspects of this relationship. Any shift in the fragrance bouquet can potentially mimic, by chance, the pheromones of another species of pollinating insect. Such a mechanism is not likely to occur in species in which nectar or pollen are attractants because then it is floral morphology alone that determines the sort of vector that can pollinate the flower.
Hybrid invasion of an alternative niche is likely to be successful if it parallels the reproductive isolation of its parents and thus subjects the hybrids to different selection pressures. Penstemon clevelandii, a homoploid hybrid of P. centranthifolius (red-flowered, hummingbird-pollinated) and P. spectabilis (lavender-flowered, wasp-pollinated) has established reproductive isolation by selection for a divergent pollination syndrome (magenta-flowered, bee- and hummingbird-pollinated) [14].
Overall, recent evidence has demonstrated the power of hybridization in creating new combinations of traits and genes responsible for niche divergence, both ecological and reproductive. As more examples of homoploid hybridization are identified, we predict that the frequency of successful niche novelties will also increase.