Genome size and ploidy levels in highly fragmented habitats: the case of western Mediterranean Juniperus (Cupressaceae) with special emphasis on J. thurifera L.

Mediterranean junipers are of special ecological importance as key components of resource islands in semi-arid mountain ecosystems of the Mediterranean basin. The fragmentation of their habitat, which was primarily natural and driven by climatic drought conditions, is currently being aggravated by anthropogenic pressure. In the framework of this concern, the present work aims to contribute establishing a genomic profile of Juniperus in its western Mediterranean range, with a special emphasis placed on J. thurifera. DNA contents were assessed by flow cytometry in 43 populations of nine taxa within their Mediterranean range (first reports for J. navicularis, J. thurifera subsp. africana and J. thurifera subsp. thurifera). Chromosome numbers were determined by orcein staining in eight taxa (first counts for J. oxycedrus subsp. badia, J. phoenicea subsp. phoenicea, J. phoenicea subsp. turbinata, of 2n?=?2x?=?22, and for J. thurifera subsp. thurifera, of 2n?=?4x?=?44). Tetraploid cytotypes have been the only ones found in the 19 populations of J. thurifera studied, this being the first report of a Juniperus species exclusively polyploid. In J. thurifera, C-value does not respond to habitat fragmentation, in the same way that genetic diversity within populations was previously shown to be unaltered, suggesting that this factor has not had, at least to date, a significant impact on populations at genomic and genetic levels. Habitat fragmentation leads to deeply age-biased populations with a male-biased imbalanced sex ratio (lack of females), indicating an urgent need to improve regeneration within the populations of this species.     

Reproductive isolation of two sympatric subspecies ofJuniperus phoenicea (Cupressaceae) in southern Spain

The phenology, reproductive cycle and cone crop of two sympatric subspecies ofJuniperus phoenicea (Cupressaceae) were studied during three consecutive years in southern Spain. The flowering pattern of each subspecies was constant during this period: inJ. phoenicea subsp.turbinata flowering was always in October–November, whileJ. phoenicea subsp.phoenicea flowered in February–March. There was no overlap between the flowering periods of the two taxa. The reproductive cycle of the two subspecies was similar, though there were some important differences because of their flowering times. Male cone development in both subspecies occurred in autumn, but the male cones ofJ. phoenicea subsp.phoenicea did not shed pollen until the end of February. InJ. phoenicea subsp.turbinata, the gap between pollination and fertilisation was seven months while inJ. phoenicea subsp.phoenicea it was only three months, fertilisation taking place at the same time in the two taxa. Post-fertilisation events were similar in the two subspecies, leading to a cycle of two years inJ. phoenicea subsp.turbinata and a shorter one of about 20 months inJ. phoenicea subsp.phoenicea. Alternating good and slight seed cone crops were found in both taxa during the three years studied, the good crops of one subspecies coinciding with the slight crops of the other one. Although the proximity of the two subspecies and method of pollination could make hybridisation between the taxa possible, the different flowering seasons prevent hybridisation isolating them reproductively.     

Past,present, and future geographic range of the relict Mediterranean and Macaronesian Juniperus phoenicea complex

AimThe aim of this study is to model the past, current, and future distribution of J. phoenicea s.s., J. turbinata, and J. canariensis, based on bioclimatic variables using a maximum entropy model (Maxent) in the Mediterranean and Macaronesian regions.LocationMediterranean and Macaronesian.TaxonCupressaceae, Juniperus.MethodsData on the occurrence of the J. phoenicea complex were obtained from the Global Biodiversity Information Facility (GBIF.org), the literature, herbaria, and the authors’ field notes. Bioclimatic variables were obtained from the WorldClim database and Paleoclim. The climate data related to species localities were used for predictions of niches by implementation of Maxent, and the model was evaluated with ENMeval.ResultsThe potential niches of Juniperus phoenicea during the Last Interglacial period (LIG), Last Glacial Maximum climate (LGM), and Mid‐Holocene (MH) covered 30%, 10%, and almost 100%, respectively, of the current potential niche. Climate warming may reduce potential niches by 30% in RCP2.6 and by 90% in RCP8.5. The potential niches of Juniperus turbinata had a broad circum‐Mediterranean and Canarian distribution during the LIG and the MH; its distribution extended during the LGM when it was found in more areas than at present. The predicted warming in scenarios RCP2.6 and RCP8.5 could reduce the current potential niche by 30% and 50%, respectively. The model did not find suitable niches for J. canariensis during the LIG and the LGM, but during the MH its potential niche was 30% larger than at present. The climate warming scenario RCP2.6 indicates a reduction in the potential niche by 30%, while RCP8.5 so indicates a reduction of almost 60%.Main conclusionsThis research can provide information for increasing the protection of the juniper forest and for counteracting the phenomenon of local extinctions caused by anthropic pressure and climate changes.     

Morphological and ecological comparison of populations of Juniperus turbinata Guss. and J. phoenicea L. from the Mediterranean region

The aim of the present study was the biometrical comparison and ecological analysis of six populations of Juniperus phoenicea complex from the western part of the species' geographic range, each represented by about 30 individuals. This is the first study to include the Sicilian population of J. turbinata sensu stricto. Seven features of the cones and seeds, two of the shoots and leaves and eight ratios were used to describe the individuals and populations which were then compared using statistical methods. Four of the analysed populations (representatives of J. turbinata s.s.) are closely related to each other. The two other populations representing J. phoenicea s.s. appear to be much more variable but on the whole the two taxa treated at a species level seem to be quite distinct from each other. It was also noted that there are two quite different ecologies of these species: the first is typical of the thermomediterranean belt which is only found at high altitudes in the mountains of north Africa, and the second circumscribed to the meso- or supramediterranean belt of western Spain, France and northwestern Italy. In many parts of its coastal distribution, Juniperus turbinata is endangered due to the construction of summer resorts and therefore actions to protect this species are needed.     

Taxonomic and geographic differentiation of Juniperus phoenicea agg. based on cone,seed, and needle characteristics

The aim of this study was to examine the diversity of, and differentiation between, 41 natural populations representing Juniperus phoenicea complex within their geographic range using the morphological characteristics of cones, seeds, and sprouts with leaves. Seven populations of J. phoenicea s.s., 25 J. turbinata and nine J. canariensis, each represented by ～20–30 individuals, were studied. The characteristics describing the size of cones and seeds and their proportions were different between J. phoenicea s.s., J. turbinata, and J. canariensis, and were useful in distinguishing between these three taxa. The populations of J. canariensis had a significantly higher percentage of trimerous cones, a higher number of cone scales, but a lower number of seeds, which were also larger than the seeds from other taxa. Juniperus phoenicea s.s., J. turbinata, and J. canariensis revealed a high level of multivariate differentiation, but there were no single characteristics which allowed one to distinguish between these alone. We detected significant differences between populations of J. turbinata from Europe and Africa, which supports the role of the Gibraltar Straight in the structuring of conifer species. Significant differences were also detected between European and Asiatic populations in several characters examined, indicating the important role of the Aegean Sea in the structuring of this taxon.     

Morphological differentiation supports the genetic pattern of the geographic structure of Juniperus thurifera (Cupressaceae)

Juniperus thurifera is an important component of woodland communities of dry sites within the West Mediterranean region and is characterised by a strongly disjunctive geographic range. Two subspecies were recognised, subsp. thurifera in Europe and subsp. africana in Africa. The aim of the study was the comparison of phenetic diversity to the pattern of AFLP geographic differentiation of the species described in the literature. The examination of phenetic diversity was based on the biometrical analysis of 17 populations using 12 morphological characters of cone and seed. The differences among populations were analysed using Student’s t test, analysis of discrimination, UPGMA agglomeration and hierarchical analysis of variance. The majority of morphological characters differentiated at a statistically significant level between populations and between J. thurifera subsp. thurifera and subsp. africana. Three groups of populations were detected using multivariate statistical analyses. The first, well separated, is subsp. africana, while the following two concern subsp. thurifera. The morphological differentiation of populations appeared similar to that described on the AFLP. The Gibraltar Straight appeared to be the most important barrier.     

Comparative Field Summer Stress of Three Tree Species Co-occurring in Mediterranean Coastal Dunes

Chlorophyll a fluorescence, water potential (_s), and root system of Juniperus oxycedrus ssp. macrocarpa, Juniperus phoenicea ssp. turbinata, and Pinus pinea were studied in Mediterranean coastal dunes of SW Spain during summer drought and after fall rains in 1999, the driest year in the 90's. A strong and reversible depression in the photochemical efficiency of photosystem 2 of the three species was recorded, which happened concomitantly with the diurnal increase and decrease in radiation. J. phoenicea, with superficial root system, was the most affected species by summer drought. It showed high rates of down-regulation of photosynthesis by photoinhibition and positive correlation between _s and F_v/F_p, with _s lower than -7 MPa. However, it tolerated this high stress, showing a fast recovery of its physiological state after fall rains. On the other hand, J. oxycedrus and P. pinea, both with deep root systems, kept their _s values up to -3 MPa, showing lower stress during summer drought. On the other hand, J. oxycedrus and J. phoenicea were more sensible to changes in edaphic water content than P. pinea. These specific responses to summer drought would be determined by their root distributions and stomatal control of transpiration, conditioning the efficiency in getting and using the available water resources. Ecophysiological responses indicate that these species are well-adapted to long periods of drought in Mediterranean climate areas, developing different strategies: J. phoenicea tolerates high stress with a fast recovery after fall rains, while J. oxycedrus and P. pinea are less affected by summer drought since their deep root systems would allow them to reach deep water resources.     

Tracking the impact of drought on functionally different woody plants in a Mediterranean scrubland ecosystem

Climate warming is predicted to amplify drought stress. Thus, it is important to understand how coexisting plant species respond to severe droughts. Here we study how seven Mediterranean woody plant species with different evolutionary history and functional characteristics (Pinus halepensis Mill., Juniperus phoenicea L., Pistacia lentiscus L., Rhamnus lycioides L., Rosmarinus officinalis L., Genista scorpius (L.) DC., and Globularia alypum L.) responded to a severe winter drought during 2011–2012 in Spain. The study site is located in the Valcuerna valley, Monegros desert, northeastern Spain. We evaluated how the drought affected the annual growth-ring formation of the species by using dendrochronology and quantified the intensity of drought-induced defoliation and mortality and compared it between species and groups of species with different evolutionary history. Radial growth of all species was strongly reduced by the 2012 drought. The pre-Mediterranean species (P. halepensis, J. phoenicea, P. lentiscus and R. lycioides) reduced growth more than the Mediterranean species (R. officinalis, G. scorpius and G. alypum). Defoliation was significantly higher in pre-Mediterranean than in Mediterranean species. When species were analyzed separately we found that P. halepensis was the species with the highest growth reduction but J. phoenicea was defoliated more severely and showed higher mortality rates as a consequence of drought. In the case of the Mediterranean shrubs, drought-induced mortality was only noticeable in R. officinalis. Drought impacted growth of all species but this did not induce mortality in all of them. Growth reduction was dependent on evolutionary history. However, functional characteristics of the species such as leaf stomatal regulation and root architecture may be more important than evolutionary history on explaining drought-induced mortality. Indeed, species with shallow root systems such as J. phoenicea and R. officinalis were the most adversely affected by the drought.     

Agricultural development vs biodiversity conservation: the Mediterranean semiarid vegetation in El Ejido (Almería, southeastern Spain)

The development of a greenhouse agriculture in the traditionally impoverished region of Poniente de Almería, on the Mediterranean coast of Spain, has caused an enormous rise in living standards. However, the environmental impact of this badly-planned growth threatens the every dynamics of the exploitation system. A special examination must be made of the use of the three major resources responsible for the functioning of greenhouse production and its impact on the ecosystems and particularly on the vegetation. These resources are: clayey soils, sand from fossil dunes and ground water. While the use of the clayey soils and sand have negative effects on the conservation of ecologically valuable communities found nowhere else in Europe, ground water overexploitation has produced an increase in salinity in most of the aquifers. Of these, sand has been by far the best monitored resource and restoration programmes have been implemented in the extraction zones. This survey deals with the recent evolution of areas where the arto (Maytenus senegalensis subsp. europaeus) and the sabina (Juniperus phoenicea subsp. turbinata) have long been the dominant species, although the presence of the former is nowadays notoriously diminished. The study is based on aerial photographs taken in 1957, 1977 and 1985, together with our own field work. Curiously enough, all this man-made process of degradation has stimulated ornithological diversity. Finally, we propose here some measures which aim to preserve the most important enclaves of these Mediterranean shrub formations, specially those of the arto, since sabina-dominated communities already belong to existing conservation areas.     

Ecological Niche Models and Coalescent Analysis of Gene Flow Support Recent Allopatric Isolation of Parasitoid Wasp Populations in the Mediterranean

Background

The integration of multiple complementary approaches is a powerful way to understand the processes of diversification and speciation. The parasitoid wasp Aphidius transcaspicus Telenga (Hymenoptera: Braconidae) is a parasitoid of Hyalopterus aphids across a wide geographic range. This species shows a remarkable degree of genetic structure among western, central, and eastern Mediterranean population clusters. In this paper we attempt to better characterize this genetic structure.

Methodology/Principal Findings

We use a Bayesian coalescent analysis of gene flow under the Isolation with Migration model using mitochondrial and microsatellite markers together with climate-based ecological niche models to better understand the genetic structure of A. transcaspicus in the Mediterranean. The coalescent analysis revealed low levels of migration among western and eastern Mediterranean populations (Nm<1) that were not statistically distinguishable from zero. Niche models showed that localities within population clusters each occupy areas of continuously high environmental suitability, but are separated from each other by large regions of completely unsuitable habitat that could limit dispersal. Overall, environmental characteristics were similar among the population clusters, though significant differences did emerge.

Conclusions/Significance

These results support contemporary allopatric isolation of Mediterranean populations of A. transcaspicus, which together with previous analyses indicating partial behaviorally mediated reproductive isolation, suggest that the early stages of cryptic speciation may be in progress.     

Ecological status of the Mediterranean Juniperus phoenicea L. Relicts in the desert mountains of North Sinai,Egypt

Juniperus phoenicea L. is listed as threatened tree by IUCN Red List. In Egypt, J. phoenicea L. is the only conifer tree that is restricted to the three mountains of northern Sinai: Gabal El-Halal, Gabal El-Maghara and Gabal Yelleq. As a Mediterranean relict it has been included in a national list as target for conservation and management. To provide baseline information for the development of a conservation strategy, the present study aims at comparing the isolated populations of J. phoenicea and their associated plant composition and diversity at the three mountains. The application of TWINSPAN and DCA analysis techniques has resulted in identifying of four vegetation types associated with juniper, and each could be related to a specific geomorphologic habitat on a topographic gradient. Chiliadenus montanus and Zygophyllum dumosum characterized the slopes of smooth-faced rock outcrops in Wadi Abu Seyal (at 350–470 m altitude of Gabal El-Halal), Deverra tortuosa, Ephedra aphylla and Gymnocarpos decander inhabited together with the target species the soil pockets of north-facing slope in Neqeb Abu Hamam (at 600–700 m altitude of Gabal El-Halal), Stachys aegyptiaca and Moricandia nitens characterized the juniper occurrences in the runnels of Wadi Arar (at 450–560 m altitude of Gabal El-Maghara), and Artemisia herba-alba, Atriplex halimus and Reaumuria hirtella represent the stands on slope runnels (at 900–960 m) of Gabal Yelleq. The two vegetation types recognized at Gabal El-Halal had, on average, the highest species diversity, juniper density and cover. Juniper shows generally poor conditions of vitality at higher elevation (600–960 m) with a higher proportions of old and recent dead trees, and with the predominance of male individuals, as compared with the populations of Gabal El-Maghara and Gabal Yelleq. In contrast, the juniper populations at lower elevation (350–470 m) of Gabal El-Halal proved to be in best condition with mostly living foliage and reproductive branches. The differences in rock types and elevation among the three mountains reflect serious limitation on recruitment of J. phoenicea due to moisture availability. The results of this study showed that J. phoenicea is an endangered species and its conservation in northern Sinai mountains is a priority. For a successful conservation of this community it is highly recommended to preserve in particular the suitable habitats at Gabal El-Halal, but also the other stands merit conservation measures.     

Genetics of the early stages of invasion of the Lessepsian rabbitfish Siganus luridus

Information on the initial stages of dispersal and settlement are of great interest in understanding the dynamics of biological invasions and in designing management responses. A newly settled population of the Lessepsian rabbitfish migrant Siganus luridus, that arrived in Linosa Island (Sicily Strait) in 2000, offered a unique opportunity to examine the genetic variability of the early phase of invasion and the starting point to test genetic variation within and between colonist and source populations.Demographics and dynamic aspects of S. luridus in the Mediterranean were evaluated by using phylogeographic and demographic (coalescent) methods based on DNA sequences of the mitochondrial control region. Sequences from 95 S. luridus, 25 Siganus rivulatus, and one of Siganus (Lo) vulpinus and S. doliatus were used. Samples were collected in one locality in the Red Sea (Eilat) and three localities in the Mediterranean (Israel, Greece and Linosa, Italy). Data showed (for the first time in a Lessepsian migrant) a lowering of the genetic diversity of the invading population (Mediterranean) (haplotype diversity 0.879, nucleotide diversity 0.592) compared to the parental one (Red Sea) (haplotype diversity 0.978, nucleotide diversity 0.958).Within the Mediterranean populations, there was no pattern of regional separation and mitochondrial diversity appeared to be preserved during the Linosa colonization, with no traces of founder events. Such evidence agrees with the idea that Lessepsian migration involves many individuals from its earliest stages.     

Geographically Related Variation in Epicuticular Wax Traits of Pinus nigra Populations from Southern Carpathians and Central Balkans – Taxonomic Considerations

The chemical composition of epicuticular waxes of nine populations from three Pinus nigra J. F. Arnold subspecies (namely subsp. nigra, subsp. banatica (Borbás ) Novák , and subsp. pallasiana (Lamb .) Holmboe ) from Southern Carpathians and central Balkan Peninsula were analyzed using GC/MS and GC/FID chromatography, and multivariate statistical techniques with respect to biogeography and taxonomy. In the needle waxes, four primary alcohols and 14 n‐alkanes ranging from C₂₁ to C₃₃ were identified, and the most abundant compounds were the four odd‐numbered n‐alkanes C₂₇, C₂₅, C₂₃, and C_29. Multivariate statistical analyses (CDA and CA) have shown existence of three P. nigra groups and suggested clinal differentiation as a mechanism of genetic variation across a geographic area: the first group consisted of the southernmost populations of subsp. pallasiana from Macedonia, the second consisted of the northernmost subsp. banatica populations from Romania, while all populations in Serbia described as three different subspecies (nigra, banatica, and pallasiana) formed the third group together with subsp. nigra population from Bosnia and Herzegovina. According to simple linear regression, geographic latitude and four bioclimatic parameters were moderately correlated with the contents of epicuticular wax compounds that are important in population discrimination, while stepwise multiple regression showed that latitude participated in most of the regression models for predicting the composition of the epicuticular waxes. These results agree with CDA and CA analysis, and confirmed the possibility of recognition of fine geographic differentiation of the analyzed P. nigra populations.     

A comparative analysis between SNPs and SSRs to investigate genetic variation in a juniper species (<Emphasis Type="Italic">Juniperus phoenicea</Emphasis> ssp. <Emphasis Type="Italic">turbinata</Emphasis>)

Genomic resources are a valuable research tool for understanding and forecasting the response of forest trees to global change and for developing science-based management strategies. Yet, many ecologically relevant tree species still lack such resources. The conifer genus Juniperus contains >?70 species that are widely distributed through the Northern Hemisphere, including several keystone species that form extensive forests in arid landscapes. To date, single-nucleotide polymorphism (SNP) markers have not been described for this ecologically important tree genus and the few described simple sequence repeat (SSR) markers result insufficient for performing reliable population demographic inference. Here, we report on the successful development of 19 new SSR and 147 SNP markers for Phoenician juniper (Juniperus phoenicea ssp. turbinata), a species widely distributed along the coasts of the Mediterranean Basin. We calculate a series of population genetic diversity estimates for each set of markers independently and for both sets combined. Our comparison shows that the higher per-locus information content of SSRs makes them the marker of choice for parentage and assignment studies, whereas SNPs provide more reliable demographic inferences (N_e and detection of a recent bottleneck). We also test and confirm the transferability of the new set of SNP markers to the closely related tetraploid species J. thurifera. Finally, we perform an orthology analysis with two gymnosperm model species to search for SNPs linked with functional genes.     

Genetic variation in Mediterranean Helichrysum italicum (Asteraceae; Gnaphalieae): do disjunct populations of subsp. microphyllum have a common origin?

The yellow‐flowered everlasting daisy Helichrysum italicum (Asteraceae, Gnaphalieae) is widely distributed in the Mediterranean basin, where it grows in continuous and widespread populations in diverse open habitats. Helichrysum italicum subsp. microphyllum has a disjunct distribution in the Balearic Islands (Majorca and Dragonera), Corsica, Sardinia, Crete and Cyprus. Numerous morphological intermediates between subsp. italicum and subsp. microphyllum are known from Corsica, where the two subspecies co‐occur. The aims of the study were to investigate if subsp. microphyllum has a common origin, constituting an independent gene pool from subsp. italicum, or if the morphological differences between subsp. microphyllum and subsp. italicum have arisen independently in different locations from a common wider gene pool. Our analyses of AFLP, cpDNA sequences and morphological characters show that there is geographic structure to the genetic variation within H. italicum, with eastern and western Mediterranean groups, which do not correspond with the division into subsp. microphyllum and subsp. italicum as currently circumscribed. Local selection on quantitative trait loci provides sufficient explanation for the morphological divergence observed and is consistent with genetic data. Within the western Mediterranean group of the species we found considerable polymorphism in chloroplast DNA sequences among and within some populations. Comparison with chloroplast DNA sequences from other Helichrysum species showed that some chloroplast haplotypes are shared across species.     

Latitudinal Environmental Niches and Riverine Barriers Shaped the Phylogeography of the Central Chilean Endemic Dioscorea humilis (Dioscoreaceae)

The effects of Pleistocene glaciations and geographical barriers on the phylogeographic patterns of lowland plant species in Mediterranean-climate areas of Central Chile are poorly understood. We used Dioscorea humilis (Dioscoreaceae), a dioecious geophyte extending 530 km from the Valparaíso to the Bío-Bío Regions, as a case study to disentangle the spatio-temporal evolution of populations in conjunction with latitudinal environmental changes since the Last Inter-Glacial (LIG) to the present. We used nuclear microsatellite loci, chloroplast (cpDNA) sequences and environmental niche modelling (ENM) to construct current and past scenarios from bioclimatic and geographical variables and to infer the evolutionary history of the taxa. We found strong genetic differentiation at nuclear microsatellite loci between the two subspecies of D. humilis, probably predating the LIG. Bayesian analyses of population structure revealed strong genetic differentiation of the widespread D. humilis subsp. humilis into northern and southern population groups, separated by the Maipo river. ENM revealed that the ecological niche differentiation of both groups have been maintained up to present times although their respective geographical distributions apparently fluctuated in concert with the climatic oscillations of the Last Glacial Maximum (LGM) and the Holocene. Genetic data revealed signatures of eastern and western postglacial expansion of the northern populations from the central Chilean depression, whereas the southern ones experienced a rapid southward expansion after the LGM. This study describes the complex evolutionary histories of lowland Mediterranean Chilean plants mediated by the summed effects of spatial isolation caused by riverine geographical barriers and the climatic changes of the Quaternary.     

Increase in density of genetically diverse invasive Asian shore crab (<Emphasis Type="Italic">Hemigrapsus sanguineus</Emphasis>) populations in the Gulf of Maine

Hemigrapsus sanguineus, the Asian shore crab, has rapidly replaced Carcinus maenas, the green crab, as the most abundant crab on rocky shores in the northwest Atlantic since its introduction to the United States (USA) in 1988. The northern edge of this progressing invasion is the Gulf of Maine, where Asian shore crabs are only abundant in the south. We compared H. sanguineus population densities to those from published 2005 surveys and quantified genetic variation using the cytochrome c oxidase subunit I gene. We found that the range of H. sanguineus had extended northward since 2005, that population density had increased substantially (at least 10-fold at all sites), and that Asian shore crabs had become the dominant intertidal crab species in New Hampshire and southern Maine. Despite the significant increase in population density of H. sanguineus, populations only increased by a factor of 14 in Maine compared to 70 in southern New England, possibly due to cooler temperatures in the Gulf of Maine. Genetically, populations were predominantly composed of a single haplotype of Japanese, Korean, or Taiwanese origin, although an additional seven haplotypes were found. Six of these haplotypes were of Asian origin, while two are newly described. Large increases in population sizes of genetically diverse individuals in Maine will likely have a large ecological impact, causing a reduction in populations of mussels, barnacles, snails, and other crabs, similar to what has occurred at southern sites with large populations of this invasive crab species.     

Natural or Naturalized? Phylogeography Suggests That the Abundant Sea Urchin Arbacia lixula Is a Recent Colonizer of the Mediterranean

We present the global phylogeography of the black sea urchin Arbacia lixula, an amphi-Atlantic echinoid with potential to strongly impact shallow rocky ecosystems. Sequences of the mitochondrial cytochrome c oxidase gene of 604 specimens from 24 localities were obtained, covering most of the distribution area of the species, including the Mediterranean and both shores of the Atlantic. Genetic diversity measures, phylogeographic patterns, demographic parameters and population differentiation were analysed. We found high haplotype diversity but relatively low nucleotide diversity, with 176 haplotypes grouped within three haplogroups: one is shared between Eastern Atlantic (including Mediterranean) and Brazilian populations, the second is found in Eastern Atlantic and the Mediterranean and the third is exclusively from Brazil. Significant genetic differentiation was found between Brazilian, Eastern Atlantic and Mediterranean regions, but no differentiation was found among Mediterranean sub-basins or among Eastern Atlantic sub-regions. The star-shaped topology of the haplotype network and the unimodal mismatch distributions of Mediterranean and Eastern Atlantic samples suggest that these populations have suffered very recent demographic expansions. These expansions could be dated 94–205 kya in the Mediterranean, and 31–67 kya in the Eastern Atlantic. In contrast, Brazilian populations did not show any signature of population expansion. Our results indicate that all populations of A. lixula constitute a single species. The Brazilian populations probably diverged from an Eastern Atlantic stock. The present-day genetic structure of the species in Eastern Atlantic and the Mediterranean is shaped by very recent demographic processes. Our results support the view (backed by the lack of fossil record) that A. lixula is a recent thermophilous colonizer which spread throughout the Mediterranean during a warm period of the Pleistocene, probably during the last interglacial. Implications for the possible future impact of A. lixula on shallow Mediterranean ecosystems in the context of global warming trends must be considered.     

Electrophoretic study of isozyme patterns in some wild populations of Aubrieta columnae Guss. (Cruciferae)

Aubrieta columnae Guss. is currently divided into three subspecies: A. columnae subsp. columnae, A. columnae subsp. italica, both found as isolated and fragmented populations in rocky habitats of Central and Southern Apennines (Italy), and A. columnae subsp. croatica found in the Balkan region. In order to gain information about the degree of genetic variability and to clarify taxonomic relationships among these taxa, we studied the isozyme patterns at 8 marker loci of 376 individuals from 8 populations by means of starch gel electrophoresis. Data analysis by using Wright's F-statistics and UPGMA clustering method was performed. The results show: 1) a general deviation from Hardy–Weinberg equilibrium within each subspecies; 2) a lesser genetic variation in populations occurring in habitats characterized by milder climatic conditions and relatively small seasonal variations; 3) a relatively high degree of differentiation between the three subspecies; 4) the possible common transadriatic origin of A. columnae subsp. italica and A. columnae subsp. croatica; 5) the possible origin of A. columnae subsp. columnae from A. columnae subsp. italica; and 6) that the current taxonomic status of A. columnae may be substantially confirmed, even if the findings are from a limited number of loci explored.     

Chemical Variability of the Essential Oil of Juniperus phoenicea var. turbinata from Algeria

The chemical composition of 50 samples of leaf oil isolated from Algerian Juniperus phoenicea var. turbinata L. harvested in eight locations (littoral zone and highlands) was investigated by GC‐FID (in combination with retention indices), GC/MS, and ¹³C‐NMR analyses. The composition of the J. phoenicea var. turbinata leaf oils was dominated by monoterpenes. Hierarchical cluster and principal component analyses confirmed the chemical variability of the leaf oil of this species. Indeed, three clusters were distinguished on the basis of the α‐pinene, α‐terpinyl acetate, β‐phellandrene, and germacrene D contents. In most oil samples, α‐pinene (30.2–76.7%) was the major compound, associated with β‐phellandrene (up to 22.5%) and α‐terpinyl acetate (up to 13.4%). However, five out of the 50 samples exhibited an atypical composition characterized by the predominance of germacrene D (16.7–22.7%), α‐pinene (15.8–20.4%), and α‐terpinyl acetate (6.1–22.6%).