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Origins and genetic structure of Sorbus intermedia (Ehrh.) Pers. and S. hybrida L. (Rosaceae) in Fennoscandia

Leo, Jonatan (2015) BION01 20142
Degree Projects in Biology
Abstract
Within the systematically complex genus Sorbus, repeated hybridization, polyploidization and apomixis has led to a series of intermediate and evolutionary independent species. Sorbus intermedia (Ehrh.) Pers. (Swedish whitebeam) and S hybrida L. (Swedish service tree) are endemic to the Fennoscandian region and are both apomictic polyploid hybrids derived from diploid sexual species. However, their number of origins and genetic variation is unclear. By using microsatellite markers, I have studied the within species genetic structure to determine the number of independent origins, amount of gene flow, possible parental species and reproduction systems, factors that will have both taxonomical and conservational implications.
Sorbus hybrida... (More)
Within the systematically complex genus Sorbus, repeated hybridization, polyploidization and apomixis has led to a series of intermediate and evolutionary independent species. Sorbus intermedia (Ehrh.) Pers. (Swedish whitebeam) and S hybrida L. (Swedish service tree) are endemic to the Fennoscandian region and are both apomictic polyploid hybrids derived from diploid sexual species. However, their number of origins and genetic variation is unclear. By using microsatellite markers, I have studied the within species genetic structure to determine the number of independent origins, amount of gene flow, possible parental species and reproduction systems, factors that will have both taxonomical and conservational implications.
Sorbus hybrida has originated independently several times in Fennoscandia. There are at least seven independent origins in the Baltic Sea region and seven in western Scandinavia. Further morphological and genetical studies are needed to make comprehensive taxonomical conclusions. In the Baltic Sea region, S. hybrida has evolved repeatedly by hybridization between S. aucuparia and S. rupicola. A more complex pattern is seen in the western Scandinavian region. No variation was discovered in S. intermedia with the six microsatellite markers used, which indicates a single origin and dispersal by seeds formed by obligate agamospermy. I could confirm the involvement of three different parental species (S. torminalis, S. aria and S. aucuparia) in S. intermedia. (Less)
Popular Abstract
The origins of Sorbus intermedia and S. hybrida

Humans have always classified objects into groups and named these groups. Plants are no exception. In this way we can organize information and communicate with each other. The classification of living organisms has also another purpose; we want to understand how the species are related to each other and how they have evolved.

The species within the genus Sorbus (Rowans and Whitebeams) are difficult to classify. Many species originate from hybridization (reticulate evolution) and chromosome doubling (polyploidization) in combination with mainly asexual seed reproduction (agamospermy). This means that when a hybrid is formed, the offspring is identical to the mother, and that lineage may... (More)
The origins of Sorbus intermedia and S. hybrida

Humans have always classified objects into groups and named these groups. Plants are no exception. In this way we can organize information and communicate with each other. The classification of living organisms has also another purpose; we want to understand how the species are related to each other and how they have evolved.

The species within the genus Sorbus (Rowans and Whitebeams) are difficult to classify. Many species originate from hybridization (reticulate evolution) and chromosome doubling (polyploidization) in combination with mainly asexual seed reproduction (agamospermy). This means that when a hybrid is formed, the offspring is identical to the mother, and that lineage may spread over a wide area. Different lineages with the same parental species can be very similar and difficult to distinguish from one another. Until genetic markers became widely available, botanists had to rely on characters that were visible to the eye, like leaf shape, to infer the relationship between the Sorbus species. Similar populations were lumped together into single species. Today, by studying genetic variation and structure, we can get a deeper understanding of speciation within the genus and relationships both between and within species.

Sorbus intermedia (Swedish whitebeam, oxel) and S. hybrida (Swedish service tree, finnoxel) are endemic to Fennoscandia and have arisen through hybridization since the last ice age. In this study, I have collected plant material from wild populations in Norway, Sweden, Finland, Denmark and Estonia in order to find out how many times they have formed (the number of independent hybridization events). By measuring particular DNA fragments that vary in length due to frequent mutations (microsatellites), it is possible to differentiate between very close related species and even populations.

No genetic variation could be found in S. intermedia with the method used in my study. This indicates that the species has been formed only once and only reproduce by asexual seeds. Hence, all trees of S. intermedia are one clone! My results also show that S. intermedia is a hybrid between three species (S. torminalis, S. aria and S. aucuparia).

Sorbus hybrida, on the other hand, has been formed several times from independent hybridization events in Fennoscandia. Based on the number of lineages found, the species has been formed at least seven times independently in the Baltic Sea region and at least seven times in the western Scandinavian region. One lineage dominates in the Baltic Sea region, but on northwestern Gotland a higher genetic variation was found. This proves a high level of new lineage formation in that area. In a conservational aspect, it is not only important to preserve particular species and genetic variation but also evolutionary processes and areas of intense speciation.

In the Baltic Sea region, S. hybrida probably originates from S. aucuparia and S. rupicola. Its parentage is complex in Norway, since the number of potential parental species is higher.

So, should S. hybrida be divided into several different species? To answer the question we must also consider the amount of gene flow (amount of sexual reproduction) between the independent lineages and if we actually can differentiate between the lineages by means of visible characters. There seems to be a low frequency of sexual reproduction between lineages in the Baltic Sea region. A higher genetic variation could be found in western Norway, which indicates a higher amount of gene flow (sexuality). Morphological studies are needed to make a satisfying classification, but the Baltic Sea forms should at least be distinguished from the western Scandinavian ones.

Advisor: Mikael Hedrén
Master´s Degree Project 45 credits in Plant Biology 2015
Department of Biology, Lund University (Less)
Please use this url to cite or link to this publication:
author
Leo, Jonatan
supervisor
organization
course
BION01 20142
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
5471105
date added to LUP
2015-06-10 14:24:19
date last changed
2015-06-10 14:24:19
@misc{5471105,
  abstract     = {Within the systematically complex genus Sorbus, repeated hybridization, polyploidization and apomixis has led to a series of intermediate and evolutionary independent species. Sorbus intermedia (Ehrh.) Pers. (Swedish whitebeam) and S hybrida L. (Swedish service tree) are endemic to the Fennoscandian region and are both apomictic polyploid hybrids derived from diploid sexual species. However, their number of origins and genetic variation is unclear. By using microsatellite markers, I have studied the within species genetic structure to determine the number of independent origins, amount of gene flow, possible parental species and reproduction systems, factors that will have both taxonomical and conservational implications.
Sorbus hybrida has originated independently several times in Fennoscandia. There are at least seven independent origins in the Baltic Sea region and seven in western Scandinavia. Further morphological and genetical studies are needed to make comprehensive taxonomical conclusions. In the Baltic Sea region, S. hybrida has evolved repeatedly by hybridization between S. aucuparia and S. rupicola. A more complex pattern is seen in the western Scandinavian region. No variation was discovered in S. intermedia with the six microsatellite markers used, which indicates a single origin and dispersal by seeds formed by obligate agamospermy. I could confirm the involvement of three different parental species (S. torminalis, S. aria and S. aucuparia) in S. intermedia.},
  author       = {Leo, Jonatan},
  language     = {eng},
  note         = {Student Paper},
  title        = {Origins and genetic structure of Sorbus intermedia (Ehrh.) Pers. and S. hybrida L. (Rosaceae) in Fennoscandia},
  year         = {2015},
}