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Survival of polyploids in nature depends on several factors, including competition from diploid relatives and increased genetic diversity. Unlike other reported Centaurea polyploid complexes, diploid Centaurea aspera and tetraploid Centaurea seridis coexist in hybrid zones with frequent triploid individuals. The polyploid origin of C. seridis, the genetic diversity and population structure of the three cytotypes, and the degree of genetic differentiation among them were analyzed in seven mixed-ploidy zones, involving different subspecies and ecological conditions. Ploidy was determined by flow cytometry. Microsatellite data suggested an allopolyploid origin of C. seridis. In the contact zones, diploids and tetraploids were genetically differentiated. When compared with the related C. aspera, a low genetic diversity was observed in C. seridis, which is uncommon in tetraploids. Furthermore, although diploid individuals were grouped in a single widespread genetic cluster, tetraploids were grouped in two highly differentiated clusters and showed significant isolation by distance. This genetic pattern in C. seridis may be related to a minimal gene flow with diploid relatives and/or other genetic factors, such as rare polyploidization events, founder effects or an increased selfing rate. Neither taxonomic assignment at subspecies level, nor ecological conditions could explain the genetic differentiation between tetraploid clusters.

Polyploidy and hybridisation are the basis of the evolution of Centaurea (Compositae).At the El Saler dune field (eastern Spain), the diploid Centaurea aspera ssp. stenophylla and the tetraploid C. seridis ssp. maritima form a polyploid complex in which C. x subdecurrens individuals occur. This polyploid complex was analysed morphologically and genetically, using RAPD and TBP markers. Flow cytometry showed that the hybrids are triploid, which is a rare finding in Centaurea. Morphologically, in contrast to leaf characters, flowering characters clearly discriminated the three taxa. The genetic analyses confirm that C. x subdecurrens is a result of the hybridisation between Centaurea aspera ssp. stenophylla and C. seridis ssp. maritima, and suggest that backcrossing events and gene flow are very rare or absent. Although the hybrids likely represent true F1 offspring, they displayed some genetic diversity that is probably due to the combination of alleles. Genetic diversity was higher in diploid than in tetraploid individuals. This fact, and the high degree of sterility of the triploid hybrids, may reflect a cytotype minority exclusion effect. This may cause spatial segregation, which effectively takes place in the study area. Dune disturbance may lead to an overlapping of the parents' distribution areas, facilitating hybridisation. Keywords: Centaurea x subdecurrens, Polyploid complex, RAPD, TBP, Triploid hybridCon formato: Español (España, internacional) 3 Polyploidy can provide evolutionary advantages and is consequently widespread 1 in nature (Comai 2005). It is believed that the proportion of polyploid angiosperm 2 plants varies from 30% to 70% (Bennet 2004; Pellicer et al. 2010), and genomic data 3 even indicates ubiquity among them (Soltis 2009). Polyploid formation is the major 4 mode of sympatric speciation in flowering plants as it can occur by immediate 5 reproductive isolation (Coyne & Orr 2004; Seo et al. 2010). Diploid and related 6 polyploid taxa often coexist in contact zones. This coexistence may result in the 7 production of hybrid offspring, generally triploid individuals, and may influence the 8 dynamics and evolution of polyploid complexes (Petit et al. 1999). Even if in some 9 hybrid zones triploids may act as a bridge between different ploidy levels, in most, 10 triploid offspring is totally or highly sterile, acting as a major reproductive barrier 11 (Husband 2004). In these cases, the survival of the mixed-ploidy populations is 12 threatened by a frequency-dependent selection, called the minority cytotype principle 13 (Levin 1975). This model assumes that, in a hybrid zone with both a rare and a common 14 cytotype, the latter would pollinate the rarer cytotype to a greater extent. Consequently, 15 the rarer cytotype produces a higher proportion of inviable triploid offspring, leading to 16 a reduction of its proportion, and, ultimately, to its extinction. However, different 17 factors may sustain and promote the survival of the two ploidy levels in the contact 18 zone. The two cy...

Students’ approaches to learning can vary between students of different ages, genders, years, degrees, or cultural contexts. The aim of this study was to assess the approaches to learning of different students of life science degrees. The Revised Two-Factor Study Process Questionnaire (R-SPQ-2F) has been used to assess the approaches to learning of 505 students of thirteen different subjects of four different degrees at Universitat Politècnica de València in order to study the factors that influence their approaches. Results show a higher deep approach of the students. Differences were observed between subjects and gender, not related to level (bachelor or master) or year. The item reliability analysis showed a high consistency for the main scales, but not for the secondary scales of the R-SPQ-2F questionnaire. High correlation between the deep and surface scales were observed. These data can provide more information to the teachers, which may help them to develop strategies focused on promoting a deeper approach to learning for the students, more adapted to their subject, level, and year.

Hybridization between tetraploids and their related diploids is generally unsuccessful in Centaurea, hence natural formation of triploid hybrids is rare. In contrast, the diploid Centaurea aspera and the allotetraploid C. seridis coexist in several contact zones where a high frequency of triploid hybrids is found. We analyzed the floral biology of the three taxa to identify reproductive isolation mechanisms that allow their coexistence. Flowering phenology was recorded, and controlled pollinations within and between the three taxa were performed in the field. Ploidy level and germination of progeny were also assessed. There was a 50% flowering overlap which indicated a phenological shift. Diploids were strictly allogamous and did not display mentor effects, while tetraploids were found to be highly autogamous. This breakdown of self-incompatibility by polyploids is first described in Centaurea. The asymmetrical formation of the hybrid was also found: all the triploid intact cypselae came from the diploid mothers pollinated by the pollen of tetraploids. Pollen and eggs from triploids were totally sterile, acting as a strong triploid block. These prezygotic isolation mechanisms ensured higher assortative mating in tetraploids than in diploids, improving their persistence in the contact zones. However these mechanisms can also be the cause of the low genetic diversity and high genetic structure observed in C. seridis.