Abstract
Chromosome numbers, mainly for Polish flora, were examined in order to investigate whether such features as chromosome numbers and polyploid frequencies are correlated with a plant’s origin (native vs. alien) and invasiveness. Polyploid frequencies were estimated using three methods: the 11 and 14 thresholds and the 3.5 x value. Comparisons of the 2n values were done on different levels: in all angiosperms and in dicots and monocots separately. Invasive and non-invasive plants were compared in the entire dataset and in alien species only. Significant differences in both chromosome numbers and polyploid frequencies between alien and native species were observed. In most cases, native plants had more chromosomes and were more abundant in polyploids than in alien species. Also, monocots had higher polyploid frequencies than dicots. Comparisons of invasive and non-invasive plants done for all of the data and only for alien species showed that invasive species generally had more chromosomes and polyploids were more frequent in them than in the latter group; however, these differences were not always statistically significant. Possible explanations for these observations are discussed.
Highlights
Polyploidy is usually defined as the occurrence of more than two genomes in a nucleus
In cases where the chromosome number was not known from Poland, it was acquired from other sources: Index to Plant Chromosome Numbers (Goldblatt and Johnson 1979), Karyological database of the ferns and flowering plants of Slovakia (Marhold et al 2012), Chromosome numbers for the Italian flora (Bedini et al 2010), the database of the Botanical Society of the British Isles (BSBI), BIOLFLOR—Eine Datenbank zu biologisch-okologischen Merkmalen der Gefaßpflanzen in Deutschland (Klotz et al 2002) and Modul Flora i Vegetacio
Because a plant invasion is preceded by the process of naturalization (Richardson and Pysek 2006; Williamson 2006; Pysek et al 2008), the features that enable plants to survive and establish a stable population in a new area are important for their ability to invade and prosper
Summary
Polyploidy is usually defined as the occurrence of more than two genomes in a nucleus. The estimated fraction of polyploids or their descendants ranges from 30 to 80 % in about 250,000 species of angiosperms (Bennett 2004) Such a wide range of approximation is the result of the different methods and criteria that have been used in assigning taxa to diploids or polyploids. Because polyploidization involves the multiplication of genomes, the easiest way to detect polyploids seems to be to set a threshold of a given number of chromosomes as the level above which a taxon is regarded as polyploid. Such a method is especially useful when it is used for large sets of data—the only criterion needed is the chromosome number. The most well-known estimations are n C 11, proposed by Goldblatt (1980) and n C 14, proposed by Grant (1981). Wood et al (2009), in their studies on the frequency of polyploid speciation, proposed a modified threshold method: species should be regarded as polyploid if the somatic chromosome number is greater than or equal to 3.5 times the lowest haploid count of the host genus
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