Fruit wings accelerate germination in Anacyclus clavatus.

PREMISE: The lateral membranous expansions of fruits, commonly referred to as wings, have long been theorized to serve only dispersal functions. Alternatively, because winged fruits typically have earlier seed germination than unwinged fruits, we hypothesized that wings could increase the contact surface with water, ultimately triggering earlier germination. METHODS: We investigated this alternative hypothesis by exploring the potential role of fruit wings on germination in the heterocarpic species Anacyclus clavatus (Desf.) Pers. (Asteraceae), which produces both winged and unwinged fruits. First, we measured the speed and degree of water absorption in winged and unwinged fruits. Second, we investigated the effects of wings on germination performance, by either reducing wing size or by preventing water absorption by sealing wings with wax. Next, we tested the influence of water availability on the germination performance of winged and unwinged fruits by reducing the water potential. RESULTS: Winged fruits absorbed more water at a faster rate than unwinged fruits. The sealing of wings delayed germination, whereas germination time was not significantly altered by wing cutting. The restriction of water availability by decreasing water potential significantly delayed seed germination of unwinged fruits, whereas winged fruits remained unaffected. CONCLUSIONS: Altogether, our results support the effect of wings on germination and cast doubt on the unique role of wings in dispersal. Whether or not wings contribute to dispersal, we propose that they also improve seed germination and seedling establishment by facilitating water absorption after the release from their mother plants.

The effects of achene type and germination time on plant performance in the heterocarpic Anacyclus clavatus (Asteraceae).

UNLABELLED: • PREMISE OF THE STUDY: In heterocarpy, fruits with different morphologies have been associated with alternative strategies of dispersal, germination, dormancy, and seedling competitive ability. In heterocarpic species, it is common to find fruits with competitive or dispersal syndromes. The competitive advantage of nondispersing fruits has been frequently attributed to their larger size, but recent studies have suggested that this could also be mediated by germination time. The main objective of our study was to investigate which factor, fruit type or germination time, most affects plant performance and, consequently, competitive ability, using the heterocarpic species Anacyclus clavatus• METHODS: To explore the effects of achene type and germination time on plant performance, we followed an innovative experimental approach including two experiments: one allowing for differences in germination time, and the other evaluating the effect of achene type alone by synchronizing germination time.• KEY RESULTS: A significant effect of germination time on several postdispersal life-history traits was observed: Achenes that germinated earlier produced plants with higher biomass and reproductive effort. When germination time was controlled, no significant differences were observed in any of the traits.• CONCLUSIONS: The competitive advantage of achenes with different morphologies was mainly mediated by germination time and not by differences in size or other intrinsic traits. The consequences of these results are discussed in light of the dispersal-competition trade-off. Our experimental approach (i.e., the synchronization of germination time) revealed the importance of manipulative experiments for testing the effects of germination time on plant survival and performance.

Genome Size, Chromosome Number and Morphological Data Reveal Unexpected Infraspecific Variability in Festuca (Poaceae).

Polyploidy has played an important evolutionary role in the genus Festuca (Poaceae), and several ploidy levels (ranging from 2n = 2x = 14 to 2n = 12x = 84) have been detected to date. This study aimed to estimate the genome size and ploidy level of two subspecies belonging to the F. yvesii polyploid complex by flow cytometry and chromosome counting. The phenotypic variation of the cytotypes was also explored, based on herbarium material. The genome size of F. yvesii subsp. lagascae has been estimated for the first time. Nuclear 2C DNA content of F. yvesii subsp. summilusitana ranged from 21.44 to 31.91 pg, while that of F. yvesii subsp. lagascae was from 13.60 to 22.31 pg. We report the highest ploidy level detected for Festuca (2n = 14x = 98) and previously unknown cytotypes. A positive correlation between holoploid genome size and chromosome number counts shown herein was confirmed. The morphometric approach showed a slight trend towards an increase in the size of some organs consistent with the variation in the ploidy level. Differences in characters were usually significant only among the most extreme cytotypes of each subspecies, but, even in this case, the high overlapping ranges prevent their distinction.

The Evolution of Haploid Chromosome Numbers in the Sunflower Family.

Chromosome number changes during the evolution of angiosperms are likely to have played a major role in speciation. Their study is of utmost importance, especially now, as a probabilistic model is available to study chromosome evolution within a phylogenetic framework. In the present study, likelihood models of chromosome number evolution were fitted to the largest family of flowering plants, the Asteraceae. Specifically, a phylogenetic supertree of this family was used to reconstruct the ancestral chromosome number and infer genomic events. Our approach inferred that the ancestral chromosome number of the family is n = 9. Also, according to the model that best explained our data, the evolution of haploid chromosome numbers in Asteraceae was a very dynamic process, with genome duplications and descending dysploidy being the most frequent genomic events in the evolution of this family. This model inferred more than one hundred whole genome duplication events; however, it did not find evidence for a paleopolyploidization at the base of this family, which has previously been hypothesized on the basis of sequence data from a limited number of species. The obtained results and potential causes of these discrepancies are discussed.