Plants show a wide variety of sexual systems. Part of this variation can be explained with the colonisation history and population dynamics. During colonization, the need for reproductive assurance selects for self-compatible monoecy (system with only herm aphroditic plants present in a population).
When population size increases, factors like tradeoffs between investment in male and female function start to play a role, a level of inbreeding is decreasing and males can invade the population. In large, stable populations dioecy (system with separate female and male plants) is considered to be an evolutionary stable strategy.
Such changes in sexual system will have also consequences for the genetic diversity, because with the lowering level of inbreeding the genetic diversity is increasing and the genetic differentiation among the populations is decreasing. Although, these predictions are implicit from the many theoretical studies, empirical evidence for them is still very poor.
This project aims at testing the predicted association between the sexual system and genetic diversity. As a study species, Mercurialis annua will be used because it shows a unique variety of sexual systems from monoecy to androdioecy (where males coexist with hermaphroditic plants) and finally to dioecy. Androdioecious populations differ widely with the percentage of male individuals.
We hypothesise that such fine-scale patterns of sex-ratio variation in M. annua are due to colonisation and patch dynamics at a small scale within sampling localities, and that these processes will be evident as signatures in the patterns of neutral genetic diversity.
The percentage of males in a population will be correlated with the genetic diversity measured by means of microsatellite loci. Then a hierarchical population genetic model will be constructed to consider the effects of both patch dynamics and metapopulation processes on the maintenance of neutral genetic diversity.
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