Abstract
Previous studies demonstrated the effects of polyploidy on various aspects of plant life. It is, however, difficult to determine which plant characteristics are responsible for fitness differences between cytotypes. We assessed the relationship between polyploidy and seed production. To separate the effects of flowering phenology, flower head size and herbivores from other possible causes, we collected data on these characteristics in single flower heads of diploid and tetraploid Centaurea phrygia in an experimental garden. We used structural equation modelling to identify the main pathways determining seed production. The results showed that the relationship between polyploidy and seed production is mediated by most of the studied factors. The different factors acted in opposing directions. Wider flower heads displayed higher above the ground suggested higher seed production in diploids. In contrast, earlier flowering and a lower abundance of herbivores suggested higher seed production in tetraploids. However, because phenology was the strongest driver of seed production in this system, the sum of all the pathways suggested greater seed production in tetraploids than in diploids. The pathway linking ploidy level directly to seed production, representing unstudied factors, was not significant. This suggests that the factors studied likely are drivers of the between-cytotype differences. Overall, this study demonstrated that tetraploids possess overall higher fitness estimated as seed production. Regardless of the patterns observed here, strong between year fluctuations in the composition and diversity of insect communities have been observed. The direction of the selection may thus vary between years. Consequently, understanding the structure of the interactions is more important for understanding the system than the overall effects of cytotype on a fitness trait in a specific year. Such knowledge can be used to model the evolution of species traits and plant-herbivore and plant-pollinator interactions in diploid-polyploid systems.
Highlights
Determining the consequences of polyploidy is a key prerequisite for assessing the importance of this mechanism of speciation
An increasing number of studies address the consequences of polyploidy in various aspects of plant life ranging from plant morphology and physiology to individual plant performance, population dynamics and habitat requirements, most studies focused on established polyploids and struggle to decouple effects of polyploidization from subsequent evolutionary change
Based on our previous knowledge of the system, we proposed that the association between ploidy level and the number of developed undamaged seeds is mediated by a wide range of factors including flowering phenology, flower head width and flower head height above the ground, the number of species and individuals of seed herbivores and other unstudied factors
Summary
Determining the consequences of polyploidy is a key prerequisite for assessing the importance of this mechanism of speciation. It has been recognized that polyploidy affect the interactions of plants with other trophic levels such as herbivores, pollinators and mycorrhizal fungi (recently reviewed in Segraves and Anneberg 2016). Based on the previous studies dealing with the effects of polyploidy on plant-herbivore and plant-pollinator interactions, we already know that polyploidy may have substantial effects. The mechanisms behind these effects are, still only poorly understood. Plant-herbivore and plant-pollinator interactions may be affected by a wide range of factors ranging from individual plant characteristics such as plant height, floral rewards, flower size, flower duration, flower position, phenology and the chemical composition of plant tissues Plant-herbivore and plant-pollinator interactions may be affected by a wide range of factors ranging from individual plant characteristics such as plant height, floral rewards, flower size, flower duration, flower position, phenology and the chemical composition of plant tissues (e.g. Loranger et al 2012; Munzbergova and Skuhrovec 2013; Gross and Schiestl 2015; Schlinkert et al 2015; Smith et al 2015) to characteristics of plant surroundings, such as vegetation height or conspecific and heterospecific density and diversity (e.g. Weber and Kolb 2013; Burt et al 2014; Cervenkova and Munzbergova 2014; Hulber et al 2015; Kim and Underwood 2015) and to population characteristics, such as population size or density (e.g. Munzbergova 2006a; Sober et al 2009)
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