The evolution of mating systems in small populations of Lythrum salicaria

Project Description

Small populations may lack compatible mates, which can favor partial self-compatibility and the invasion of missing mating types into the population. We are using the invasive plant Lythrum salicaria to answer two questions. Our first question is: do individuals with higher levels of self-compatibility form colonies more successfully than individuals with lower levels of self-compatibility? To address this question, we are establishing small artificial colonies of L. salicaria that possess different levels of self-compatibility. We will measure the persistence of these colonies to understand the role of self-compatibility in colony formation. Our second question is: to what degree does gene flow by pollen restore lost mating types to small populations? To address this question, we will establish source and sink populations of L. salicaria various distances from each other. The sink populations will lack mating types and by observing the restoration of missing morphs to sink populations, we aim to learn how gene flow by pollen restores lost mating types to small populations.

Additional Scientific Information

We are interested in two questions pertaining to evolution in small populations of tristylous L. salicaria: 1. what is the functional significance of partial self-compatibility in the M-morph of L. salicaria and 2. What is the role of pollen flow in restoring lost morphs to small populations of L. salicaria? To address the first question, we will establish 20 small colonies of L. salicaria in artificial “wetlands” constructed from plastic pools. Each colony will consist of 6 individuals and will be either trimorphic or monomorphic with respect to mating type. We hypothesize that partial self-compatibility increases the likelihood of establishment of colonies monomorphic for the M-morph, and results in the commonly observed dimorphic L- and M-morph colonies reported in Ontario. The seed set and year-to-year persistence of these colonies will be measured, with the prediction that M-morph colonies will produce more seed and persist more often than the L- and S-morph monomorphic colonies. To address the second question, we will set out 4 populations of M- and S-morph individuals with 2 to 8 L-morph sink colonies placed around them. Seed set on plants in the L-morph sink populations will be subsequently planted in the glasshouse at Toronto, and the number of offspring possessing M- or S-morph flowers will be counted to measure the dispersal of M and S alleles into the sink populations. We predict that populations closer to the source population will regain morphs more often, but that the distribution of M and S allele movement will be leptokurtic, with occasional morph restoration occurring at long distances relative to shorter distances.

Principal Investigator: Spencer Barrett
Researcher(s): Christopher Balogh

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