Detecting Introgressed Populations in the Iberian Endemic Centaurea podospermifolia through Genome Size

Abstract

Based on results from previous studies, populations of the Iberian endemic Centaurea podospermifolia north of the Ebro River are considered genetically pure, while those southward are introgressed, with genetic input from C. cephalariifolia. This phenomenon is particularly relevant, especially given both the endangered and protected status for the species, which can have consequences in how to best apply conservation strategies to maintain genetic resources in the species. The main goal of this study was to evaluate whether genome size assessments using flow cytometry can help distinguishing between pure, hybrid and introgressed populations, and hence become a powerful and cost-effective tool to complement comprehensive population genetic surveys. The results indicate that there are significant genome size differences between populations of C. podospermifolia, which are coincident with previous considerations of pure and introgressed populations. Given the simplicity and reproducibility of this technique, flow cytometry could become an effective tool for monitoring pure populations of this species and, indeed, become an integral part of the management plans that are mandatory for listed taxa.

Morphological and Genome-Wide Evidence of Homoploid Hybridisation in Urospermum (Asteraceae)

“…Klotzsch and V. cruziana A.D.Orb., also displays both nuclear DNA content and chromosome number intermediate to the parental species [29]. As mentioned earlier, spontaneous hybridisation in the wild can be subjected to recurrent introgression once hybrids overcome fertility barriers and become compatible with progenitors, which would result in a more complex signature of genome sizes after generations (e.g., Centaurea [10]). Also, genomic reorganisation in homoploid hybrids could lead to deviations in genome size, such as in Helianthus, where hybrid taxa display larger genomes compared to their progenitors [30], and such increase could have been favoured by selection and adaptation to new ecological conditions.…”

“…Homoploid hybridisation (with no change of ploidy level involved) has been for long-time considered to be less common than allopolyploid hybridisation, but the actual rates and their impact on speciation continue to be a source of debate [8]. In Asteraceae, it is relatively easy to find examples of homoploid hybrids in several genera, such as for example in Argyrantheum Webb [9], Centaurea L. [10] or Helianthus L. [11], but model systems for understanding allopolyploidy in the family represent the bulk of research in this field (e.g., Tragopogon L. [12]). Among many other consequences, hybridisation impacts directly in the genome size of the resulting hybrid offspring.…”

“…Among many other consequences, hybridisation impacts directly in the genome size of the resulting hybrid offspring. Hybrids can display either a suite of sizes that fall between the nuclear DNA contents of the parental genomes, or even display more heterogeneous patterns depending on the level of polyploidy and subsequent introgression [10,13].…”

Novel Insights into the Nature of Intraspecific Genome Size Diversity in Cannabis sativa L.

“…Despite reports of intraspecific genome size variation having long been treated with caution, the advent of high-resolution techniques for genome size estimation, such as flow cytometry, has provided strong evidence of intraspecific variability in several taxonomic groups. In general, such variation has been attributed to, e.g., hybridisation and/or polyploidisation events [ 18 , 19 ], B-chromosomes [ 20 ], heteromorphic sex chromosomes [ 21 , 22 ], changes in non-coding repetitive DNA [ 23 ], presence/absence of specific DNA sequences [ 24 ], and illegitimate recombination [ 25 ]. In addition to that, intraspecific genome size variation has also been related to extrinsic and/or abiotic factors such as altitude [ 26 , 27 , 28 , 29 , 30 ], latitude [ 24 , 31 , 32 , 33 ], and temperature [ 31 ], and to different phenological and morphological characters [ 27 , 34 ].…”