Rossella Speranza Filigheddu

The Genetic Structure of the Remnant Populations of Centaurea horrida in Sardinia and Associated Islands

BACKGROUND AND AIMS The Mediterranean region is of prime importance to biodiversity at a global level, mainly due to the abundance of endemic plant species. However, information about these species is still scarce, especially at the genetic level. In this paper the first assessment is reported of the genetic structure of Centaurea horrida (Asteraceae), an endemic, sea-cliff-dwelling plant from Sardinia. METHODS The study was conducted on seven populations covering the entire natural range of the species by means of SSR (microsatellite) markers. KEY RESULTS A considerable amount of genetic variation was found (average H(e) = 0.603-0.854), together with a medium-high differentiation among populations, as estimated both by F(ST) (0.123) and R(ST) (0.158). Both Bayesian analysis and AMOVA were employed to detect genetic structuring in this species. The results suggest that the origins of the current populations of C. horrida lie in two gene pools. CONCLUSIONS Despite the restricted range, C. horrida displays high levels of genetic diversity, structured in such a way that three management units could be deemed viable for its conservation. The protected status of the species will probably suffice to prevent the impoverishment of its genetic resources.

The conservation status of an endemic species of northern Sardinia: Centaurea horrida Badarò (Asteraceae).

Abstract When assessing the conservation status of narrow endemic plants, life history traits must be taken into account, since endemics combine small population ranges and sizes, and long persistence with limited reproductive and dispersal ability. In this paper, we present the global assessment of the conservation status of a narrow endemic plant from the Sardinian‐Corsican biogeographic province, by applying IUCN criteria and categories, together with an evaluation of some reproductive traits. Centaurea horrida Badarò (Asteraceae) is an endemic species of northern Sardinia (Italy). It is protected by the Bern Convention (Appendix I) and listed as priority species by the “Habitat” Directive (92/43/EEC, Annex II). The species appears in the 1997 IUCN Red List as “Vulnerable” (VU). With the aim of evaluating the risk of extinction and of providing management tools for the network of protected areas in which this species is present, some reproductive traits have been evaluated, and the distribution, size and structure of its population have been measured according to IUCN 2006 Guidelines. Centaurea horrida is not able to self‐pollinate and its effective seed dispersal ability is limited. Its extent of occurrence is 172.43 km2 and its area of occupancy is 108 km2. Population size has been estimated at 11,719 adult individuals. Significant differences in adult densities among sites have been highlighted. The structure of the population is dominated by adult individuals (on average 68%), while the proportion of seedlings is only 7% on average. Its habitat underwent an extinction rate of 18% in 50 years. On the basis of the data gathered, the status to be assigned to C. horrida is that of “Endangered” (EN). This first attempt to evaluate the conservation status of a narrow endemic plant from the Sardinian‐Corsican biogeographic province allowed us to conclude that the management of rare species must be site‐specific and that there is urgent need to acquire detailed data on endangered species, especially within biodiversity hotspots, and to continuously update Annex II of the EU Habitat Directive and the IUCN Red List.

Effects of browsing in relation to vegetation cover on common yew (Taxus baccata L.) recruitment in Mediterranean environments

Common yew (Taxus baccata L.) stands are recognized as prioritary habitats for biodiversity conservation within the European Union. The effects of browsing on the regeneration capacity and spatial dispersal of T. baccata recruits at the European southern limit of the species in the Mediterranean Basin have been herein studied. The efficacy of T. baccata recruitment has been evaluated at six localities in the Northern Sardinia mountains, which have similar altitude, climate, soil, and vegetation but have different types of uses (three were grazed by livestock and three were not). At each site, five habitats have been identified for T. baccata seed dispersal: reproductive female T. baccata canopy, reproductive female Ilex aquifolium canopy, non-fleshy-fruited tree canopy, fleshy-fruited shrubs, and open areas. The density of seedlings was found to be greater under fleshy-fruited trees (reproductive female T. baccata and I. aquifolium) than under shrubs, whereas the sapling density was higher in shrubby habitats, especially at grazed sites due to the mechanical protection afforded by the spiny shrubs against herbivores. Land use (LU) has been found to be the most important factor in determining the spatial distribution of seedlings and saplings in relation to forest habitats. Although browsers had an ephemeral but positive effect on seed germination through their trampling and the resultant scarification, this process eventually became ineffective as was shown by the occurrence of the lowest density of saplings in those habitats where the density of seedlings was the highest. The ultimate and most important effect of browsing was the sharp decrease in the density of saplings, and their almost complete extinction, in non-shrubby habitats. This study highlights the result that, in Mediterranean ecosystems, browsing constitutes the main negative factor on T. baccata seedling-sapling transition and furthermore confirms the necessity to preserve shrubby patches in the vicinity of reproductive female T. baccata and I. aquifolium to permit the regeneration of T. baccata in the presence of livestock. Moreover, at ungrazed sites, T. baccata is able to colonize non-shrubby shady habitats. The application of different management strategies to ungrazed and grazed sites should therefore be the main direction in the management and preservation of T. baccata stands in the Mediterranean region.

Phylogeny of the Centaurea group (Centaurea, Compositae) - geography is a better predictor than morphology.

The Centaurea group is part of the Circum-Mediterranean Clade (CMC) of genus Centaurea subgenus Centaurea, a mainly Mediterranean plant group with more than 200 described species. The group is traditionally split on morphological basis into three sections: Centaurea, Phalolepis and Willkommia. This division, however, is doubtful, especially in light of molecular approaches. In this study we try to resolve this phylogenetic problem and to consolidate the circumscription and delimitation of the entire group against other closely related groups. We analyzed nuclear (internal transcribed spacer of the ribosomal genes) and chloroplast (rpl32-trnL intergenic spacer) DNA regions for most of the described species of the Centaurea group using phylogenetic and network approaches, and we checked the data for recombination. Phylogeny was used to reconstruct the evolution of the lacerate-membranaceous bract appendages using parsimony. The magnitude of incomplete lineage sorting was tested estimating the effective population sizes. Molecular dating was performed using a Bayesian approach, and the ancestral area reconstruction was conducted using the Dispersal-Extinction-Cladogenesis method. Monophyly of the Centaurea group is confirmed if a few species are removed. Our results do not support the traditional sectional division. There is a high incongruence between the two markers and between genetic data and morphology. However, there is a clear relation between geography and the structure of the molecular data. Diversification in the Centaurea group mainly took place during the Pliocene and Pleistocene. The ancestral area infered for the Circum-Mediterranean Clade of Centaurea is the Eastern Mediterranean, whereas for the Centaurea group it is most likely NW-Africa. The large incongruencies, which hamper phylogenetic reconstruction, are probably the result of introgression, even though the presence of incomplete lineage sorting as an additional factor cannot be ruled out. Convergent evolution of morphological traits may have led to incongruence between morphology-based, traditional systematics and molecular results. Our results also cast major doubts about current species delimitation.

Spatial‐time variability and conservation relevance of plant communities in Mediterranean temporary wet habitats: A case study in Sardinia (Italy)

This research was undertaken with the aim of improving our knowledge of the floristic composition and spatial‐temporal dynamics of plant communities in Mediterranean temporary wet habitats, and to evaluate the diversity and conservation relevance of their plant assemblages. Three different types of temporary wet habitats were monitored throughout the growing season: large temporary ponds (lTPs), small temporary ponds (sTPs), and rock pools (RPs). lTPs presented a small‐scale zonation arranged in an inner, an intermediate, and a peripheral belt. A total of 98 species were recorded, of which 40 were classified as temporary wet habitat (TWH) specialists and 24 as rare. Eight different groups of plant assemblages were identified presenting space–time dynamics related to water‐depth variations and flooding period. In terms of diversity, the most relevant assemblages were located in the outer belt of the lTPs and in the sTPs. The mosaic of different assemblages and their time‐variability determined the presence of several types of habitats of community interest according to the Habitat Directive. This wide heterogeneity should be taken into account to ensure that all types of TWHs are considered in conservation programmes.

Bioclimate map of Sardinia (Italy)

Bioclimatology deals with the interrelation between climate and living organisms, in particular, plants and plant communities, considering the main climate variables that are relevant for species distribution. In this context spatial interpolation of monthly temperature and precipitation data using 203 rain gauges and 68 temperature gauges for Sardinia (Italy) was undertaken. As interpolation technique, we used regression kriging which combines multiple linear regression (MLR) with ordinary kriging of the residuals. MLR procedures include as independent variables: altitude, latitude, longitude, coast distance and a topographic factor of relative elevation. Elevation data were obtained from digital elevation model at 40 m resolution. Following the approach of the Worldwide Bioclimatic Classification System, a bioclimatic diagnosis of the entire territory was derived using map algebra calculations of the bioclimatic indices proposed by Rivas-Martínez et al. [(2011). Worldwide Bioclimatic classification system. Global Geobotany, 1, 1–638]. Two macrobioclimates (Mediterranean pluviseasonal oceanic and Temperate oceanic), one macrobioclimatic variant (Submediterranean), and four classes of continentality (from weak semihyperoceanic to weak semicontinental), eight thermotypic horizons (from lower thermomediterranean to upper supratemperate) and seven ombrotypic horizons (from lower dry to lower hyperhumid) were identified, resulting in a combination of 43 isobioclimates. The resulting map represents a useful environmental stratum, for regional planning, ecological modeling and biodiversity conservation.

Gap analysis revealed a low efficiency of Natura 2000 network for the conservation of endemic species in Mediterranean temporary freshwater habitats

Listed and rare species are abundant in temporary freshwater habitats. Among them, the endemic contingent represents a crucial conservation target particularly in the areas characterized by abundant endemic flora for which the local administrations have a high level of responsibility. The aim of this research was to test how the endemic plants found in Mediterranean temporary ponds were represented in Natura 2000 network in a biodiversity hotspot of the Mediterranean region. The results of our research at regional scale pointed out that the existing Nature 2000 sites provide a limited degree of protection and that the gap analysis should be taken into account when conservation priorities are set.

A Natural Homoploid Hybrid between Centaurea horrida and Centaurea filiformis (Asteraceae) as Revealed by Morphological and Genetic Traits

Studies over the last two decades demonstrate that hybridization has played an integral role in the evolution of several sections of the genus Centaurea. Nevertheless, natural hybridization between narrow Mediterranean endemic Centaurea species has not been documented as yet. A population of fertile Centaurea individuals exhibiting intermediate morphological traits between two Sardinian narrow endemics, C. horrida and C. filiformis, was identified at the Tavolara Islet (Sardinia, Italy). Intermediate leaf length and head width characterized this population, suggesting its hybrid origin. The putative hybrid population was structured (i.e., composed of seedlings, saplings and adult individuals) and had a relatively high levels of seed production. The number of chromosomes was identical to that of the proposed progenitors (2n = 18). Genotyping at five microsatellite loci showed that the putative hybrid possessed several alleles in common with the proposed parental species and intermediate values of genetic differentiation, as indicated by both FST and RST, between C. horrida and C. filiformis. We therefore conclude that the studied intermediate population is of hybrid origin, and discuss possible mechanisms of its reproductive isolation from the parental species, potential re-introgression, and evolutionary implications of this hybridization.

New insights in Salicornia L. and allied genera (Chenopodiaceae) inferred from nrDNA sequence data

A phylogenetic analysis was performed based on ITS DNA sequences of fourteen samples from different sources of six species of Salicornia, the three allied genera Arthrocnemum, Sarcocornia and Halocnemum of the same tribe Salicornieae, and other genera of the subfamily Salicornioideae used in previous studies. Bassia hirsuta, Camphorosma monspeliaca (subfamily Chenopodioideae) and four species of Suaeda (subf. Suaedoideae) were chosen as outgroups. Results show that the annual genus Salicornia is a sister group to the perennial genera Sarcocornia, Arthrocnemum and Halocnemum. Moreover, the phylogenetic analysis based on ITS results distinguished two groups of Salicornia species which fitted with ploidy level: one group consisted of diploid species, and the second of tetraploid ones. Sarcocornia and Arthrocnemum are shown to be closely related, even though the species investigated here exhibited an evident distance between their ITS sequences. On the basis of our results, these two genera should be united. Bienertia (already separated as Bienertieae) was confirmed as probable outgroup to the subf. Salicornioideae, while Kalidium (subf. Salicornioideae, tribe Halopeplideae) was an outgroup to the rest of the Salicornioideae (tribe Salicornieae). The group Allenrolfea plus Halocnemum was the most basal of the tribe Salicornieae amongst those investigated in this study. The two samples of Halocnemum strobilaceum used in this work displayed numerous changes (transitions and transversions) in their respective sequences, probably related to their morphological and chorological differentiation. On the basis of our analysis, the most probable basal chromosome number for Salicornieae appears to be 2n = 18. The same number would also be the base number for the annual genus Salicornia and the perennial Arthrocnemum ( + Sarcocornia), with polyploidy arising independently in the two groups.

Human trampling effects on Mediterranean coastal dune plants

Coastal habitats are particularly vulnerable to recreational impacts because these environments are highly dynamic and continually change in response to biotic and abiotic factors. Sand dune communities are worldwide characterized by high levels of biodiversity, but are often affected by human-induced impacts as those caused by tourist trampling. To understand the effects of human frequentation, trampling, and other human-induced impacts, fencing experiments have been traditionally carried out on coastal dunes. Since in touristic areas dune systems are subjected to different intensities of human frequentations rather than to opening or fencing, in this study we explore the effects of accessibility on vascular plants cover. This study tests the hypothesis that human frequentation on beaches affects spatio-temporal variability of vascular plant abundance on dunes by comparing the plant assemblages of high and low accessible sites in North-East Sardinia (Italy). Our results show that accessibility plays a crucial role in conditioning the percentage of vegetation cover in Mediterranean dunes. In fact, not only we found a perennial vegetation cover that was significantly higher in the sites with low accessibility (and consequently low frequentation), but we also showed that at the sites with high accessibility there were significant differences in vegetation cover between times of sampling (cover was higher before than after summer): on the contrary, differences in perennial vegetation cover among times were not significant at the low frequentation sites. After summer, the difference among low and high frequentation sites in species composition and cover was >90%. Multivariate analysis identified those species that play a pivotal role in differentiating the low and the high frequentation sites. Among them, Crucianella maritima and Sporobolus virginicus can be considered as differential species. Overall, our data show vegetation and plant species responses to human-induced impacts, and are therefore important to support conservation actions in Mediterranean coastal areas interested by mass tourism.