The genetic diversity and spatial genetic structure of the Corso-Sardinian endemic Ferula arrigonii Bocchieri (Apiaceae)

Gone with the waves: the role of sea currents as key dispersal mechanism for Mediterranean coastal and inland plant species

Thalassochory, the dispersal of propagules through marine currents, is a key long-distance dispersal (LDD) mechanism with implications for global biogeography and particularly for island colonization. The propagules of coastal plant species are generally assumed to be better adapted for sea dispersal than those of inland plants, but this hypothesis remains largely untested. We conducted experiments on four genera (Juniperus, Daucus, Ferula, and Pancratium) and compared traits among nine species with different habitats and distributions. Our results showed that Juniperus spp. and P. maritimum have strong thalassochorous potential within the Mediterranean Basin. Interestingly, we did not find a clear association on the thalassochorous potential of coastal versus inland species within all the tested genera, apart from P. maritimum compared with the endemic inland P. illyricum. These findings suggest that thalassochory may be a more common dispersal mechanism than previously assumed. The apparently weak link of dispersal syndrome with species ecology broadens the possibility of dispersal by the sea also for inland plants, although considered to be poorly salt-tolerant. Moreover, our results reveal significant differences in sea dispersal between endemic and widespread species, but do not rule out an important role of thalassochory in shaping the distribution patterns of archipelago endemic flora. The presented method is largely replicable and could be used for further studies with a larger set of species to better delineate trends of sea dispersal syndrome among species with different ecology or dispersal traits.

An Integrated Taxonomic Approach Points towards a Single-Species Hypothesis for Santolina (Asteraceae) in Corsica and Sardinia

Santolina is a plant genus of dwarf aromatic shrubs that includes about 26 species native to the western Mediterranean Basin. In Corsica and Sardinia, two of the main islands of the Mediterranean, Santolina corsica (tetraploid) and S. insularis (hexaploid) are reported. Along with the cultivated pentaploid S. chamaecyparissus, these species form a group of taxa that is hard to distinguish only by morphology. Molecular (using ITS, trnH-psbA, trnL-trnF, trnQ-rps16, rps15-ycf1, psbM-trnD, and trnS-trnG), cypsela morpho-colorimetric, morphometric, and niche similarity analyses were conducted to investigate the diversity of plants belonging to this species group. Our results confute the current taxonomic hypothesis and suggest considering S. corsica and S. insularis as a single species. Moreover, molecular and morphometric results highlight the strong affinity between S. chamaecyparissus and the Santolina populations endemic to Corsica and Sardinia. Finally, the populations from south-western Sardinia, due to their high differentiation in the studied plastid markers and the different climatic niche with respect to all the other populations, could be considered as an evolutionary significant unit.

Genetic differentiation between bitter and sweet asafetida plants using ISSR markers

Bitter (Ferula pseudalliacea) and sweet (Ferula assa-foetida) asafetida (Apiaceae family) are well-known economic and medicinal herbs owing to their gum. This study investigates genetic differentiation of F. pseudalliacea and F. assa-foetida using ISSR markers, to determine the effective primer and to assess the possibility of separating sweet and bitter plant populations from each other. Results showed that among 22 primers, eight markers reproduced obvious DNA patterns and revealed 234 scorable DNA bands. ISSR-16 and ISSR-55 primers had better performance than other primers according to the number of bands, PIC and Marker Index. Bitter population showed polymorphic loci (224), percentage of polymorphic loci (95.73%) and observed number of alleles (1.96 ± 0.2), while sweet populations showed the amount of these parameters as 218, 93.16% and 1.93 ± 0.25, respectively. Estimated G_st of sweet population was 0.09 and G_st of bitter population was 0.06. Comparing gene flow in bitter and sweet populations showed a lower level of gene flow between sweet populations (N_m = 4.93) compared to bitter ones (N_m = 7.89). Within group genetic similarity of sweet asafetida population was higher than between group variation of bitter and sweet populations. The highest similarity was observed between bitter populations (0.95). The highest genetic dissimilarity was also estimated between bitter and sweet populations (0.08). Cluster analysis grouped four studied populations into 13 clusters using Jaccard^'s similarity coefficient and UPGMA method. Principal coordinate analysis showed that 61.02% of total variance was explained using three components and it could completely separate populations as well as cluster analysis. These grouping correspond nearly with geographical distribution. Analysis of molecular variance showed that genetic variation within populations (87%) was more than among populations (13%). The results indicated that ISSR marker is suitable to investigate genetic diversity of asafetida populations and could separate populations of the same genera with similar germplasm.

Digging up the roots of an insular hotspot of genetic diversity: decoupled mito-nuclear histories in the evolution of the Corsican-Sardinian endemic lizard Podarcis tiliguerta

BACKGROUND

Mediterranean islands host a disproportionately high level of biodiversity and endemisms. Growing phylogeographic evidence on island endemics has unveiled unexpectedly complex patterns of intra-island diversification, which originated at diverse spatial and temporal scales. We investigated multilocus genetic variation of the Corsican-Sardinian endemic lizard Podarcis tiliguerta with the aim of shedding more light on the evolutionary processes underlying the origin of Mediterranean island biodiversity.

RESULTS

We analysed DNA sequences of mitochondrial (12S and nd4) and nuclear (acm4 and mc1r) gene fragments in 174 individuals of P. tiliguerta from 81 localities across the full range of the species in a geographic and genealogical framework. We found surprisingly high genetic diversity both at mitochondrial and nuclear loci. Seventeen reciprocally monophyletic allopatric mitochondrial haplogroups were sharply divided into four main mitochondrial lineages (two in Corsica and two in Sardinia) of Miocene origin. In contrast, shallow divergence and shared diversity within and between islands was observed at the nuclear loci. We evaluated alternative biogeographic and evolutionary scenarios to explain such profound discordance in spatial and phylogenetic patterning between mitochondrial and nuclear genomes. While neutral models provided unparsimonious explanations for the observed pattern, the hypothesis of environmental selection driving mitochondrial divergence in the presence of nuclear gene flow is favoured.

CONCLUSIONS

Our study on the genetic variation of P. tiliguerta reveals surprising levels of diversity underlining a complex phylogeographic pattern with a striking example of mito-nuclear discordance. These findings have profound implications, not only for the taxonomy and conservation of P. tiliguerta. Growing evidence on deep mitochondrial breaks in absence of geographic barriers and of climatic factors associated to genetic variation of Corsican-Sardinian endemics warrants additional investigation on the potential role of environmental selection driving the evolution of diversity hotspots within Mediterranean islands.

Conservation genetics of two island endemic Ribes spp. (Grossulariaceae) of Sardinia: survival or extinction?

Measuring levels of population genetic diversity is an important step for assessing the conservation status of rare or endangered plant species and implementing appropriate conservation strategies. Populations of Ribes multiflorum subsp. sandalioticum and R. sardoum, two endangered endemic species from Sardinia, representing the whole genus on the island, were investigated using ISSR and SSR markers to determine levels and structure of genetic variability in their natural populations. Results indicated medium to low genetic diversity at the population level: Nei's gene diversity for ISSR markers ranged from 0.0840 to 0.1316; the expected heterozygosity (HE ) for SSR ranged from 0.4281 to 0.7012. In addition, only one remnant population of R. sardoum showed a high level of inbreeding, in accordance with its very small size. Regarding the structure of the six R. sandalioticum populations, both principal coordinates analysis (PCoA) and STRUCTURE analysis of ISSR and SSR data highlighted low population structure, although two populations appeared to be clearly distinct from the others. The genetic pattern of the two taxa associated with their different ecological positions indicated resilience of R. sandalioticum populations in fresh and humid habitats and uncertain future resistance for the residual R. sardoum population in xeric calcareous stands. Hence, this study highlights the importance of an integrated conservation approach (genetic plus in situ and ex situ conservation studies/measures) for activating management programmes in these endemic and threatened taxa that can be considered as crop wild relatives of cultivated Ribes species.