Floral visitation and reproductive traits of Stamenoid petals, a naturally occurring floral homeotic variant of Capsella bursa-pastoris (Brassicaceae)

Abstract

Homeotic changes played a considerable role during the evolution of flowers, but how floral homeotic mutants initially survive in nature has remained enigmatic. To better understand the evolutionary potential of floral homeotic mutants, we established as a model system Stamenoid petals (Spe), a natural variant of Capsella bursa-pastoris (Brassicaceae). In the flowers of Spe plants, petals are transformed into stamens, whereas all other floral organs are unaffected. In contrast with most other homeotic mutants, the Spe variant occurs in relatively stable populations in the wild. In order to determine how the profound change in floral architecture influences plant performance in the wild, we performed common garden experiments running over 3 years. Here, we show that Spe and wild-type plants attract the same assemblage of floral visitors: mainly hoverflies, wild bees and thrips. However, floral visitation is about twice as frequent in wild-type plants as in Spe plants. Nevertheless, the numbers of seeds per fruit were about the same in both variants. Wild-type plants produced more flowers, fruits and seeds per plant than Spe plants, whereas the germination capacity of Spe seeds was higher than that of the wild-type. Determination of volatile composition revealed monoterpenes and 3,4-dimethylbenzaldehyde, which were detected only in wild-type flowers, presumably because they are produced only by petals. Our data indicate that the similar fitness of Spe and wild-type C. bursa-pastoris in the field results from complex compensation between plant architecture and germination capacity. In contrast, flower structure and floral visitation are only of minor importance, possibly because C. bursa-pastoris is mainly self-pollinating.

Growth habit of the late Paleozoic rhizomorphic tree‐lycopsid family Diaphorodendraceae: Phylogenetic, evolutionary, and paleoecological significance

“…Finally, our previous analyses of architectural transitions among the rhizomorphic lycopsids were a major impetus to our development of a modern theory of saltational evolution, defined as “a genetic modification that is expressed as a profound phenotypic change across a single generation and results in a potentially independent evolutionary lineage” (Bateman, 1994; Bateman and DiMichele, 1994, 2002). The idea of a nongradualistic framework for macroevolution has since progressively accumulated adherents (e.g., Rutishauser, 1995; Carrión and Cabezudo, 2003; Vergara‐Silva, 2003; Theißen, 2006, 2009; Ziermann et al, 2009; Zander 2010; Reuveni and Giuliani, 2012; Rosenblum et al, 2012), and we remain committed to its basic principles. In the case of the multiple transitions from dominant lateral branching to exclusive crown‐branching that are the focus of this paper, it is extremely difficult to envisage a mechanism that would allow a transition from one architecture to the other that was gradual.…”

Physiological and anatomical differentiation of two sympatric weed populations

“…The occurrence of a specific flower morphology of C. bursa-pastoris individuals in the vineyards south of Mainz in southwestern Germany is known for quite some time (Reichert, 1998). At first sight, this natural mutant is predominantly important for studies of plant geneticists (Nutt et al, 2006;Ziermann et al, 2009;Hintz et al, 2006;Hameister et al, 2013). With a more detailed analysis, several traits became apparent, and population studies led to the insight that the wild type of C. bursa-pastoris and its variant C. apetala even form two different ecotypes, sympatrically occurring at one place over many years (Hameister & Neuffer, 2017; Hameister, Neuffer & Bleeker, 2009).…”

“…Recent field surveys in vineyards revealed that the wild type is the predominant taxon with tens of thousands of individuals, and the Spe occurs with a stable frequency of about 10% (Hameister, Neuffer & Bleeker, 2009). Intriguingly, potential pollinators, especially wild bees, and hoverflies, tend to prefer one over the other type, probably due to differing volatile emissions of the two flower types (Ziermann et al, 2009;Hameister & Neuffer, 2017, Fig. 1).…”

Ranunculacean flower terata: Records, a classification, and some clues about floral developmental genetics and evolution

“…Thus, the overall fitness is similar in both types of plants but with compensatory performances in plant architecture and germination. Insect visitation and floral architecture seem to have a low incidence on global fitness, possibly because the species is mainly self-pollinating (Ziermann et al, 2009).…”