Tuber borchii (Ascomycota, order Pezizales) is highly valued truffle sold in local
markets in Italy. Despite its economic importance, knowledge on its distribution and
population variation is scarce. The objective of this work was to investigate the
evolutionary forces shaping the genetic structure of this fungus using coalescent and
phylogenetic methods to reconstruct the evolutionary history of populations in Italy. To
assess population structure, 61 specimens were collected from 11 different Provinces of
Italy. Sampling was stratified across hosts and habitats to maximize coverage in native
oak and pine stands and both mychorrizae and fruiting bodies were collected. Samples
were identified considering anatomo-morphological characters. DNA was extracted and
both multilocus (AFLP) and single-locus (18 loci from rDNA, nDNA, and mtDNA)
approaches were used to look for polymorphisms. Screening AFLP profiles, both
Jaccard and Dice coefficients of similarity were utilized to transform binary matrix into
a distance matrix and then to desume Neighbour-Joining trees. Though these are only
preliminary examinations, phylogenetic trees were totally concordant with those
deriving from single locus analyses. Phylogenetic analyses of the nuclear loci were
performed using maximum likelihood with PAUP and a combined phylogenetic
inference, using Bayesian estimation with all nuclear gene regions, was carried out. To
reconstruct the evolutionary history, we estimated recurrent migration, migration across
the history of the sample, and estimated the mutation and approximate age of mutations
in each tree using SNAP Workbench. The combined phylogenetic tree using Bayesian
estimation suggests that there are two main haplotypes that are difficult to be
differentiated on the basis of morphology, of ecological parameters and symbiontic tree.
Between these two lineages, that occur in sympatry within T. borchii populations, there
is no evidence of recurrent migration. However, migration over the history of the
sample was asymmetrical suggesting that isolation was a result of interrupted gene flow
followed by range expansion. Low levels of divergence between the haplotypes indicate
that there are likely to be two cryptic species within the T. borchii population sampled.
Our results suggest that isolation between populations of T. borchii could have led to
reproductive isolation between two lineages. This isolation is likely due to sympatric
speciation caused by a multiple colonization from different refugia or a recent isolation.
In attempting to determinate whether these haplotypes represent separate species or a
partition of the same species we applied Biological and Mechanistic species Concepts.
Notwithstanding, further analyses are necessary to evaluate if selection favoured premating
or post-mating isolation.
| Identifer | oai:union.ndltd.org:unibo.it/oai:amsdottorato.cib.unibo.it:998 |
| Date | 11 April 2008 |
| Creators | Bonuso, Enrico <1980> |
| Contributors | Zambonelli, Alessandra |
| Publisher | Alma Mater Studiorum - Università di Bologna |
| Source Sets | Università di Bologna |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, PeerReviewed |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/restrictedAccess |
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