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Reference: Darren J. Obbard, (2004). Genetic variation and sexual system evolution in the annual mercuries. DPhil. University of Oxford.Citable link to this page:


Genetic variation and sexual system evolution in the annual mercuries

Abstract: The Mercurialis annua L. (Euphorbiaceae) species complex comprises a group of closely related lineages that present a wide range of sexual-systems, making it a valuable model for the study of plant sexual-system evolution. Within this polyploid complex, diploid populations are dioecious, and polyploid populations either monoecious or androdioecious (males coexist with functional hermaphrodites). The primary aim of this thesis was to use patterns of genetic diversity to elucidate the evolutionary origin and maintenance of the sexual-system diversity in M. annua. The phylogeny of the M. annua complex was reconstructed using chloroplast and ITS DNA sequence. This, in conjunction with morphometric analysis, showed that both hexaploid M. annua, and a novel species from the Canary Islands (newly described here as Mercurialis canariensis), were allopolyploid in origin. Such an origin for hexaploid M. annua suggests that androdioecy may have been able to arise in this group as a consequence of hybridisation between a monoecious lineage, tetraploid M. annua, and a dioecious lineage, M. huetii. Artificial crosses were used to show that hexaploid M. annua has disomic marker inheritance, and a statistical approach was developed to quantify genetic diversity and differentiation in polyploids with disomic inheritance. Strong gradients in genetic (allozyme) diversity at a pan-European scale were used to infer the existence of separate glacial refugia for dioecious and monoecious races of M. annua, at the eastern and western ends of the Mediterranean basin, respectively. A metapopulation model had previously been proposed to explain the ecological maintenance of androdioecy in M. annua. Here, population-level patterns of genetic diversity were used as an indirect test of this model. The discovery of lower within-population diversity, and of greater genetic differentiation between populations, for monoecious populations than for androdioecious populations was consistent with the metapopulation model, and suggests that androdioecy is maintained by the occurrence of regular local extinction.

Digital Origin:Born digital Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford


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 Bibliographic Details

Issue Date: 2004

Copyright Date: 2004 Identifiers

Urn: uuid:63dff548-8cd7-454b-951f-dd3560567322 Item Description

Type: thesis;

Language: en Keywords: Mercurialis annua phylogeny population genetics androdioecy mating-systemSubjects: Biology Genetics (life sciences) Evolution,ecology and systematics Evolution (zoology) Tiny URL: ora:2333


Author: Dr Darren J. Obbard - institutionUniversity of Oxford facultyMathematical,Physical and Life Sciences Division - Plant Sciences ox



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