The Red Queen hypothesis and geographical parthenogenesis in the alpine hawkweed Hieracium alpinum (Asteraceae)
Abstract
The Red Queen hypothesis (RQH) suggests that sexuals have an evolutionary advantage in habitats with many biotic interactions (typically in southern latitudes) while asexuals are more frequent in habitats with harsher climate and consequently lowered biotic pressure (typically in northern latitudes/higher altitudes). The biotic interactions are thus considered to be a possible driver of differential geographical distributions often observed between closely related sexuals and asexuals: a pattern referred to as geographical parthenogenesis (GP).
We tested the RQH in Hieracium alpinum L., a vascular plant species exhibiting a striking pattern of GP, by assessing the frequency and intensity with which seed predator specialists occur and the level of interspecific plant-plant competition expressed through both the surrounding vegetation density and the species richness across its distributional range. Furthermore, we tested whether there were negative associations between intra-population genetic diversity, as assessed by amplified fragment length polymorphism markers, and incidences of seed predation.
Our results indicate no significant differences in frequency and intensity of seed predation nor in the level of interspecific plant-plant interactions between diploid sexual and triploid asexual populations. Furthermore, there were no consistent latitudinal and/or altitudinal patterns for the assessed parameters.
Contrary to our expectations, there were either positive or non-significant associations between genetic diversity and the level of seed predation. To conclude, the RQH cannot thoroughly explain the GP in H. alpinum, and other alternative scenarios should be considered and tested.