Niche differentiation between diploid and hexaploid Aster amellus

Abstract

The maintenance of separated diploid and polyploid populations within a contact zone is possible due to both prezygotic and postzygotic isolation mechanisms. Niche differentiation between two cytotypes may be an important prezygotic isolating mechanism and can be studied using reciprocal transplant experiments. We investigated niche differentiation between diploid and hexaploid Aster amellus in their contact zone in the Czech Republic. Diploid populations are confined to habitats with low productivity, whereas hexaploid populations occur in habitats with both low and high productivity. Thus, we chose three diploid populations and six hexaploid populations, three in each of the two different habitat types. We analyzed habitat characteristics and carried out reciprocal transplant experiments in the field using both seeds and adult plants. Sites of diploid and hexaploid populations differed significantly in vegetation and soil properties. The mean number of juveniles was higher at sites of home ploidy level than at sites of foreign ploidy level, suggesting niche differentiation between the two cytotypes. On the other hand, transplanted adult plants survived at all sites and juvenile plants were able to establish at some sites of the foreign cytotype. Furthermore, the mean number of juveniles, survival, and flowering percentages were higher at home sites than at foreign sites, indicating local adaptation. We conclude that niche differentiation between the two cytotypes and local adaptation within each cytotype may contribute to the maintenance of diploid and hexaploid populations of A. amellus in their contact zone. Moreover, further factors, such as differences in flowering phenology and exclusion of minority cytotypes, should also be considered.

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

“…Here we test two hypotheses: (1) Houstonia L. species occupy different niches, and thus are ecogeographically isolated, and (2) diploids and tetraploids within species, also occupy different niches and are ecogeographically isolated. Results from other studies show significant ecological divergence between closely related species and by the cytotype segregation hypothesis (Ramsey et al 2003;Kay 2006;Raabova et al 2008), thus we expected to find a similar pattern in Houstonia.…”

“…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.…”

Breeding barriers at a diploid–hexaploid contact zone in Aster amellus

“…This aggregate is an interesting model system because it comprises a contact zone between diploids and hexaploids, with several populations growing in close proximity, but no hybrids (i.e., tetraploids) have been detected so far (Mandáková and Münzbergová 2006). Furthermore, according to previous studies, the habitat requirements appear to be insufficient to lead to habitat segregation (Mandáková and Münzbergová 2008;Raabová et al 2008) and no morphological differentiation has been detected between diploid and hexaploid plants (Mandáková and Münzbergová 2008). To understand the dynamics of this contact zone, we investigated the breeding barriers between the cytotypes, namely, temporal segregation, assortative mating mediated by pollinators and crossing ability by asking the following questions: (1) Does any asynchrony in floral phenology exist that may lead to temporal segregation of the cytotypes?…”

Linear landscape elements in an Austrian viticultural landscape have limited effects on spatial patterns of plant genetic diversity

“…This is a rosette-forming perennial which reproduces both vegetatively and sexually and is pollinated mainly by bees and hoverflies (Raabová et al 2008). The plant is self-incompatible with a sporophytic selfincompatibility system (Richards 1986).…”