Ecological Factors Influencing Tetraploid Speciation in Snow Buttercups (Ranunculus Adoneus): Niche Differentiation and Tetraploid Establishment

Abstract

Chromosome doubling plays an important role in generating new species of flowering plants. However, reproductive incompatibilities between newly formed tetraploid plants and their diploid progenitors are expected to create a significant barrier to the persistence and establishment of neopolyploid populations. Ecological differentiation can reduce this barrier via prezygotic isolation arising from spatial separation. Alternatively, superior viability or fecundity of neotetraploid plants might compensate for the reproductive cost of incompatible pollen from diploid neighbors. The performance of plants of both cytotypes can be assessed in their respective habitats through reciprocal transplants, although such experiments have not been used previously in the study of tetraploid speciation. We used a series of seed and seedling transplant experiments to assess ecological differentiation and competitive ability during early establishment phases for tetraploid and diploid forms of the snow buttercup (Ranunculus adoneus). At two sites, seeds from diploids and tetraploids had similar germination probabilities. Tetraploid snow buttercup seedlings had a significant growth advantage in a controlled environment chamber experiment. However, in the field diploid and tetraploid buttercup seedlings did not differ consistently in survival or growth, nor did the two cytotypes show reciprocal advantages in performance, as expected if ecological differentiation has occurred. At the seed and seedling stages, neither niche differentiation nor tetraploid competitive superiority appears sufficient to explain neotetraploid success in the presence of their diploid progenitors.

Why only tetraploid Solidago gigantea (Asteraceae) became invasive: a common garden comparison of ploidy levels

“…In some cases, no effects were detected, such as for Aster amellus (Münzbergova 2007) and Ranunculus adoneus (Baack and Stanton 2005), while in others, differences between ploidy levels were considerable, as in Arrhenatherum elatius (Petit and Thompson 1997), Dactylis glomerata (Bretagnolle and Thompson 1996) and Centaurea maculosa (Müller-Schärer et al 2004).…”

Ecogeographic isolation: a reproductive barrier between species and between cytotypes in Houstonia (Rubiaceae)

“…Classical methods for measuring ecogeographic differences between species include reciprocal transplants and common garden experiments (Felber 1991;Felber-Girard et al 1996;Johnson et al 2003;Baack 2004;Stuessy et al 2004;Baack and Stanton 2005;Buggs and Pannell 2007;Raabova et al 2008). These methods are informative for estimating differences in niches, but are often not feasible because they are time-consuming and expensive, and are difficult to implement if studying endangered plant species.…”

Niche differentiation between diploid and hexaploid Aster amellus

“…Habitat diVerentiation has been inferred from comparison of habitats in Dactylis glomerata (Lumaret et al 1987) and Cardamine pratensis (Arvanitis et al 2007), from comparison of associated vegetation in Anthoxanthum alpinum (Felber-Girard et al 1996) and Galax urceolata (Johnson et al 2003) or from diVerent performances of two cytotypes in the common garden in D. glomerata (Bretagnolle and Thompson 2001). It has been argued that studies based on habitat comparisons may confound competitive displacement with niche diVerentiation and that only reciprocal transplant experiments provide a direct test of diVerences in fundamental niches (Baack and Stanton 2005).…”

“…However, only two sites were used in previous reciprocal transplant experiment with tetraploid Anthoxanthum odoratum and diploid A. alpinum (Flégrová and Krahulec 1999). To our knowledge, there are only two studies that used a larger number of populations in reciprocal transplant experiments with diploid and polyploid pairs: ten populations of Ranunculus adoneus (Baack and Stanton 2005) and 12 populations of Mercurialis annua (Buggs and Pannell 2007). However, habitats of these species are very unstable (depending on snowmelt in R. adoneus and disturbed roadsides in M. annua).…”