A last stand in the Po valley: genetic structure and gene flow patterns in Ulmus minor and U. pumila.
OBJECTIVE
Ulmus minor has been severely affected by Dutch elm disease (DED). The introduction into Europe of the exotic Ulmus pumila, highly tolerant to DED, has resulted in it widely replacing native U. minor populations. Morphological and genetic evidence of hybridization has been reported, and thus there is a need for assessment of interspecific gene flow patterns in natural populations. This work therefore aimed at studying pollen gene flow in a remnant U. minor stand surrounded by trees of both species scattered across an agricultural landscape.


METHODS
All trees from a small natural stand (350 in number) and the surrounding agricultural area within a 5-km radius (89) were genotyped at six microsatellite loci. Trees were morphologically characterized as U. minor, U. pumila or intermediate phenotypes, and morphological identification was compared with Bayesian clustering of genotypes. For paternity analysis, seeds were collected in two consecutive years from 20 and 28 mother trees. Maximum likelihood paternity assignment was used to elucidate intra- and interspecific gene flow patterns.


RESULTS
Genetic structure analyses indicated the presence of two genetic clusters only partially matching the morphological identification. The paternity analysis results were consistent between the two consecutive years of sampling and showed high pollen immigration rates (∼0·80) and mean pollination distances (∼3 km), and a skewed distribution of reproductive success. Few intercluster pollinations and putative hybrid individuals were found.


CONCLUSIONS
Pollen gene flow is not impeded in the fragmented agricultural landscape investigated. High pollen immigration and extensive pollen dispersal distances are probably counteracting the potential loss of genetic variation caused by isolation. Some evidence was also found that U. minor and U. pumila can hybridize when in sympatry. Although hybridization might have beneficial effects on both species, remnant U. minor populations represent a valuable source of genetic diversity that needs to be preserved.
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
B
B
Bertolasi
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
C
C
Leonarduzzi
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy andrea.piotti@gmail.com.
A
A
Piotti
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
S
S
Leonardi
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
L
L
Zago
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
L
L
Gui
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
F
F
Gorian
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
I
I
Vanetti
Centro Nazionale per lo Studio e la Conservazione della Biodiversità Forestale, Corpo Forestale dello Stato, Via del Ponte 256, 37059 Peri (VR), Italy, Dipartimento di Bioscienze, Università di Parma, Viale Usberti 11/A, Parma, Italy, Institute of Biosciences and BioResources, National Research Council, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy and Department of Theoretical and Applied Sciences, University of Insubria, Via J.H. Dunant 3, 21100 Varese (VA), Italy.
G
G
Binelli
D017753:Ecosystem; D051456:Gene Flow; D014644:Genetic Variation; D006824:Hybridization, Genetic; D007558:Italy; D034403:Ulmus / Q000235:genetics*
Ulmus minor; Ulmus pumila; biological invasion; conservation genetics; elm; forest remnant; fragmentation; genetic diversity; habitat degradation; hybridization; long distance dispersal; paternity analysis; plain forest.