Abstract
BackgroundEssentially all ferns can perform both sexual and asexual reproduction. Their populations represent suitable study objects to test the population genetic effects of different reproductive systems. Using the diploid homosporous fern Alsophila spinulosa as an example species, the main purpose of this study was to assess the relative impact of sexual and asexual reproduction on the level and structure of population genetic variation.Methodology/Principal FindingsInter-simple sequence repeats analysis was conducted on 140 individuals collected from seven populations (HSG, LCH, BPC, MPG, GX, LD, and ZHG) in China. Seventy-four polymorphic bands discriminated a total of 127 multilocus genotypes. Character compatibility analysis revealed that 50.0 to 70.0% of the genotypes had to be deleted in order to obtain a tree-like structure in the data set from populations HSG, LCH, MPG, BPC, GX, and LD; and there was a gradual decrease of conflict in the data set when genotypes with the highest incompatibility counts were successively deleted. In contrast, in population ZHG, only 33.3% of genotypes had to be removed to achieve complete compatibility in the data set, which showed a sharp decline in incompatibility upon the deletion of those genotypes. All populations examined possessed similar levels of genetic variation. Population ZHG was not found to be more differentiated than the other populations.Conclusions/SignificanceSexual recombination is the predominant source of genetic variation in most of the examined populations of A. spinulosa. However, somatic mutation contributes most to the genetic variation in population ZHG. This change of the primary mode of reproduction does not cause a significant difference in the population genetic composition. Character compatibility analysis represents an effective approach to separate the role of sexual and asexual components in shaping the genetic pattern of fern populations.
Highlights
Almost all ferns are homosporous, producing only one type of spore that germinates to form a bisexual gametophyte [1]
Molecular markers have been increasingly used to infer the influence of reproductive systems on patterns of population genetic variation in plants [36,38,39]
A more recently developed genetic approach, character compatibility analysis [35], was applied to evaluate the relative contribution of sexual recombination and somatic mutation to inter-simple sequence repeat (ISSR) variations observed in the populations of A. spinulosa
Summary
Almost all ferns are homosporous, producing only one type of spore that germinates to form a bisexual gametophyte [1]. There are three possible modes of sexual reproduction [2,3,4]: (i) intragametophytic selfing - the union of sperm and egg from the same gametophyte resulting in a completely homozygous sporophyte; (ii) intergametophytic selfing - the union of sperm and egg from different gametophytes arising from spores from the same parental sporophyte (analogous to selfing in seed plants); and (iii) intergametophytic crossing - the union of sperm and egg from gametophytes arising from spores of different sporophytes (analogous to outcrossing in seed plants). Using the diploid homosporous fern Alsophila spinulosa as an example species, the main purpose of this study was to assess the relative impact of sexual and asexual reproduction on the level and structure of population genetic variation
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