Abstract
Fine-scale spatial genetic structure (SGS) has profound ecological and genetic consequences for plant populations, and some studies indicate that clonal reproduction may significantly enhance SGS. Clonality is widespread among dioecious species, but little is known about the relationship between clonal reproduction and SGS in the frame of sexual dimorphism. We asked the following questions: (1) Is there a sexually dependent pattern of SGS in white poplar population? (2) What is the relationship between clonal reproduction and SGS? and (3) Does this relationship have a sex-specific component? Using 16 microsatellite markers, genetic structure including fine-scale SGS and clonality of females and males of white poplar were investigated. Significant SGS was noted for both sexes at the ramet and genet levels. At the genet level, males had 2.7-fold higher SGS than that of females. Clonality significantly contributed to SGS only in females. A sibship structure revealed with pedigree analysis and clustering-based methods among males was likely the major factor of the observed SGS. The sexes differed in their clonal growth strategies. Spatial positioning of ramets in female clones suggested foraging behavior and/or avoidance of competition, while for male clones it indicated more expansion and space colonization. The obtained results led us to conclude that sexual dimorphism in life history traits may affect the course and rate of demo-genetic processes acting in natural populations of dioecious species. To our knowledge, this is the first study demonstrating a sex-specific pattern of SGS in natural populations of dioecious species.
Highlights
The majority of plants display hermaphroditic sex expression while separation of male and female functions on different individuals, dioecy, is a low frequency sexual system in plants (Renner and Ricklefs 1995)
We feel that high spatial genetic structure (SGS) and relatedness noted in females and males in studied population represents a rather abnormal course of population processes
Considering overall reproductive biology of the species, limitations in gene dispersal should lie in external factors such as fragmentation of the species occurrence and lack of sites for recruitment
Summary
The majority of plants display hermaphroditic sex expression while separation of male and female functions on different individuals, dioecy, is a low frequency sexual system in plants (ca. 6 % of land plants) (Renner and Ricklefs 1995). Dioecy provides an excellent opportunity to investigate functional differentiation among sexes, i.e., sex dimorphism (Delph 1999; Dorken and Barrett 2004; Montesinos et al 2012). This is based on the fact that sexes differ with respect to their roles and constrains, and the physical release of sexes from unity has made them possible to be under divergent evolutionary trajectories. It is widely assumed that females incur higher costs of reproduction owing to flowering and fruiting processes (Lloyd and Webb 1977; Obeso 2002; Vessella et al 2015). This may lead to resource allocation trade-offs affecting female survival rates (Obeso 2002), growth (Iszkuło and Boratyński 2011; Iszkuło et al 2011), clonal growth (Allen and Antos 1993) or other fitness-related traits, which in turn may give rise to sexrelated demographic patterns
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