Saharan Mountains Research Articles

Contrasting Genetic Footprints among Saharan Olive Populations: Potential Causes and Conservation Implications.

The Laperrine’s olive is endemic to the Saharan Mountains. Adapted to arid environments, it may constitute a valuable genetic resource to improve water-stress tolerance in the cultivated olive. However, limited natural regeneration coupled with human pressures make it locally endangered in Central Sahara. Understanding past population dynamics is thus crucial to define management strategies. Nucleotide sequence diversity was first investigated on five nuclear genes and compared to the Mediterranean and African olives. These data confirm that the Laperrine’s olive has a strong affinity with the Mediterranean olive, but it shows lower nucleotide diversity than other continental taxa. To investigate gene flows mediated by seeds and pollen, polymorphisms from nuclear and plastid microsatellites from 383 individuals from four Saharan massifs were analyzed. A higher genetic diversity in Ahaggar (Hoggar, Algeria) suggests that this population has maintained over the long term a larger number of individuals than other massifs. High-to-moderate genetic differentiation between massifs confirms the role of desert barriers in limiting gene flow. Yet contrasting patterns of isolation by distance were observed within massifs, and also between plastid and nuclear markers, stressing the role of local factors (e.g., habitat fragmentation, historical range shift) in seed and pollen dispersal. Implications of these results in the management of the Laperrine’s olive genetic resources are discussed.

Dark Side Archaeology: Climate Change and Mid-Holocene Saharan Pastoral Adaptation.

High-resolution paleoenvironmental research allows us to pinpoint the tempo and amplitude of past climate changes. Abrupt climate events have axiomatically triggered cascades of adjustments, in vegetation, fauna, humans, and pathogens. This essay focuses on the abrupt end of the African Humid Episode (9000–6000 cal BP), ca. 5000 cal BP in the Sahara. Neolithic pastoralists, practicing transhumance between sandy lowlands and Saharan mountains, adopted new cultural practices: cattle burials and livestock bone deposits in built installations. Their ritual nature is indisputable. But ritual for what? If considered from the perspective of livestock zoonoses, such practices may point to the “dark side” of cultural adjustments—strategies to counter human and livestock diseases. Livestock zoonoses are constant sources of emerging infectious diseases (EID) in the present, as they were in the past. Sustained research on livestock and human health are of paramount importance given the accelerating rate of world urbanization.

Antioxidant Activity of Myrtus communis L. and Myrtus nivellei Batt. & Trab. Extracts: A Brief Review.

Myrtus communis L. (myrtle) and Myrtus nivellei Batt. & Trab. (Saharan myrtle) have been used in folk medicine for alleviating some ailments. M. communis is largely distributed in the Mediterranean Basin, whereas M. nivellei is confined in specific zones of the central Saharan mountains. The chemical composition and antioxidant activity of berry and leaf extracts isolated from myrtle are deeply documented, whereas those isolated from Saharan myrtle extracts are less studied. In both species, the major groups of constituents include gallic acid derivatives, flavonols, flavonol derivatives, and hydroxybenzoic acids. In coloured berries, anthocyanins are also present. In M. nivellei extracts are reported for some compounds not described in M. communis so far: 2-hydroxy-1,8-cineole-β-d-glucopyranoside, 2-hydroxy-1,8-cineole 2-O-α-l-arabinofuranosyl (1→6)-β-d-glucopyranoside, rugosin A, and rugosin B. Berries and leaves extracts of both species had antioxidant activity. Comparative studies of the antioxidant activity between leaf and berry myrtle extracts revealed that leaf extracts are best antioxidants, which can be assigned to the galloyl derivatives, flavonols, and flavonols derivatives, although the ratio of these groups of compounds might also have an important role in the antioxidant activity. The anthocyanins present in myrtle berries seem to possess weak antioxidant activity. The antioxidant activity of sample extracts depended on various factors: harvesting time, storage, extraction solvent, extraction type, and plant part used, among other factors. Leaf extracts of myrtle revealed to possess anti-inflammatory activity in several models used. This property has been attributed either to the flavonoids and/or hydrolysable tannins, nevertheless nonprenylated acylphloroglucinols (e.g., myrtucommulone and semimyrtucommulone) have also revealed a remarkable role in that activity. The biological activities of myrtle extracts found so far may direct its use towards for stabilizing complex lipid systems, as prebiotic in food formulations, and as novel therapeutic for the management of inflammation.

The role of climatic cycles and trans-Saharan migration corridors in species diversification: Biogeography of Psammophis schokari group in North Africa

Highlands, hydrographic systems and coastal areas have been hypothesised to form corridors across the hyperarid Sahara desert in North Africa, allowing dispersal and gene flow for non-xeric species. Here we aim to provide a genetic test for the trans-Saharan corridor model, and predict the location and stability of ecological-corridors, by combining phylogeography and palaeoclimatic modelling. The model was the Psammophis schokari (Schokari sand racer) group, fast-moving and widely distributed generalist colubrids occurring mostly in arid and semiarid scrublands. We combined dated phylogenies of mitochondrial and nuclear markers with palaeoclimatic modelling. For the phylogeographic analysis, we used 75 samples of P. schokari and P. aegyptius, and Bayesian and Maximum-Likelihood methods. For the ecological models, we used Maxent over the distribution of P. schokari and West African lineages. Models were projected to past conditions (mid Holocene, Last Glacial Maximum and Last Inter-Glacial) to infer climatic stable areas. Climatic stability was predicted to be mostly restricted to coastal areas and not spatially continuous. A putative temporary trans-Saharan corridor was identified in Eastern Sahara, with a more stable one along the Atlantic coast. Six parapatric lineages were identified within P. schokari, four occurring in North Africa. These likely diverged during the Pliocene. The Tamanraset River might have been a vicariant agent. African lineages may have experienced further subsequent diversification during the late Pleistocene. The main P. schokari refugia were probably located along the northern margins of the Sahara, allowing its North-to-South colonization. Trans-Saharan corridors seem to have played a role in P. schokari biogeography, allowing colonization of central Saharan mountains and Sahel. Some might have worked as refugia, and even the most stable corridors may have sections working as filters, depending on each climatic phase. We expect the use of trans-Saharan corridors to decrease for more mesic species or with less dispersal capabilities.

North-African paleodrainage discharges to the central Mediterranean during the last 18,000 years: A multiproxy characterization

Using elemental geochemistry, clay mineralogy, grain size end-member modeling, and planktonic foraminiferal δ18O, we characterize the provenance of central-Mediterranean sediments over the past 18 ka. The provenance is dust-dominated before and after the African Humid Period (AHP). By contrast, during the AHP (∼11–5 ka), largely concurrent with organic-rich sapropel S1 formation, it is predominantly riverine from North-African sources. Such fluvial supply is suggested to come from paleodrainage networks that were reactivated by intensified monsoon precipitation during the AHP. The supply is characterized by high Mg/Al and smectite contents, and has been accompanied by considerable freshwater influx, as indicated by the enhanced grain size and lighter foraminiferal δ18O. The clay-mineral assemblages in our core and in nearby cores correspond with a provenance from the Libyan-Tunisian margin, mainly via the paleo-river Irharhar. The inferred fluvial discharge is strongest during the late-AHP (∼8–5.5 ka), coinciding with reported enhanced fluvial dynamics and wettest conditions over western Libya and Tunisia/Algeria. This period is not only synchronous with the largest extension of open-water bodies in North Africa and lowest Saharan dust inputs, but also consistent with precipitation records of the West-African monsoon. Moreover, our records show a remarkable correspondence with that of a paleodrainage system towards the Atlantic West-African margin, inferring a common headwater region in the central Saharan mountains, and a similar climate mechanism. Taken together, we suggest a dominant control of North-African humid surfaces on the paleodrainage delivery, modulated by groundwater level, in response to the insolation-driven West-African monsoon precipitation.

Variations in bird communities of the Saharan mountains

Characteristics and variations of the bird communities in the Saharan mountains were evaluated in five massifs from West to East: the Adrar of Mauritania, the Ahaggar in Algeria, the Adrar of the Iforas in north-eastern Mali, the Aïr Mountains in northern Niger, and the Red Sea Mountains in the Eastern Desert of Egypt. Bird censuses (n = 110) were conducted during dry seasons. A total of 139 species were recorded, of which 120 remained after elimination of occasional visitors and were used for analysis. Total richness and diversity increased from the most central and high Ahaggar towards the western, eastern and especially southern massifs. Among the resident communities the number of Saharo-Sindian species was higher in the central, eastern and western massifs, whereas Afrotropical species were more abundant in the southern ones. A principal component analysis distinguished three opposite poles of species linked with Adrar of the Iforas, Aïr and Red Sea mountains and cluster analysis led to the ordination of the five massifs along a longitudinal gradient from West to East. Avifaunal variations between the different Saharan mountains sampled led to a regional pattern in relation with faunistic affinities and it fitted with the three biogeographical subregions of the Saharan biome: Sahara, Sahel and Nubian Desert.

Surviving in mountain climate refugia: new insights from the genetic diversity and structure of the relict shrub Myrtus nivellei (Myrtaceae) in the Sahara Desert.

The identification of past glacial refugia has become a key topic for conservation under environmental change, since they contribute importantly to shaping current patterns of biodiversity. However, little attention has been paid so far to interglacial refugia despite their key role for the survival of relict species currently occurring in climate refugia. Here, we focus on the genetic consequences of range contraction on the relict populations of the evergreen shrub Myrtus nivellei, endemic in the Saharan mountains since at least the end of the last Green Sahara period, around 5.5 ka B.P. Multilocus genotypes (nuclear microsatellites and AFLP) were obtained from 215 individuals collected from 23 wadis (temporary rivers) in the three main mountain ranges in southern Algeria (the Hoggar, Tassili n’Ajjer and Tassili n’Immidir ranges). Identical genotypes were found in several plants growing far apart within the same wadis, a pattern taken as evidence of clonality. Multivariate analyses and Bayesian clustering revealed that genetic diversity was mainly structured among the mountain ranges, while low isolation by distance was observed within each mountain range. The range contraction induced by the last episode of aridification has likely increased the genetic isolation of the populations of M. nivellei, without greatly affecting the genetic diversity of the species as a whole. The pattern of genetic diversity observed here suggests that high connectivity may have prevailed during humid periods, which is consistent with recent paleoenvironmental reconstructions.

A new high‐resolution central and western Saharan summertime dust source map from automated satellite dust plume tracking

AbstractIn this paper, we outline a new objective dust source detection method for the central and western Sahara (CWS), based on the automated tracking of individual dust plumes in data from the Spinning Enhanced Visible and Infrared Imager, available every 15 mins. at ~0.03° spatial resolution. The method is used to map the origin of summertime dust storms in the CWS for June – August 2004 – 2010. It reveals the sources of these events in unprecedented detail, allowing for the identification of specific, highly active source areas. The study of collocated surface features reveals that many of the dominant sources are likely associated with paleolakes and outwash plains, many in close proximity to the Saharan mountains. Extensive nonsource areas are associated with low albedo and elevated terrain, pointing to the mountainous regions of the Sahara. Additionally, sand seas are not identified as important source areas, but their margins sometimes are. The automated tracking method also facilitates analysis of the transport direction of dust plumes from key source regions and the inference of emission mechanisms. It is found that there are two broad domains within the CWS: one in southwest Algeria and northwest Mali, characterized primarily by transport toward the southwest and very likely dominated by low‐level jets embedded in the northeasterly Harmattan winds; and a second in southern Algeria, northwest Niger, and northeast Mali where there is no preferred transport direction and a strong potential association between dust events and deep convection, pointing toward cold pool outflows as the likely deflation mechanism.

The Laperrine’s olive tree (Oleaceae): a wild genetic resource of the cultivated olive and a model-species for studying the biogeography of the Saharan Mountains

The Laperrine’s olive is an iconic subspecies of Olea europaea (Oleaceae) with a narrow distribution in the Saharan Mountains, from south Algeria to northeast Sudan. Recently, population genetic and phylogeographic studies gave insights on its reproductive strategies, its history since the Pleistocene, and its putative utility as a genetic resource of the cultivated olive. In natural habitats, multi-centennial individuals occur in very harsh environmental conditions and mainly reproduce vegetatively, but it appears that sexuality may be easily restored under favourable conditions. Crosses between the Laperrine’s olive and other olive diploid subspecies (subspp. cuspidata and europaea) have been recently reported. Plastid DNA analyses also indicate that the Laperrine’s olive has already been used during the secondary diversification of the cultivated Mediterranean olive in the Maghreb. This taxon could therefore be used as source of genes for the breeding of new olive cultivars, particularly to improve drought tolerance. In this review, we also address the potential utility of this taxon for studying the self-incompatibility genetic determinism and the polyploidy origin in O. europaea. Phylogeographic studies attested that Laperrine’s olive populations show affinities with both the Mediterranean and sub-Saharan olive taxa, but the high genetic differentiation between populations indicates that gene exchanges between massifs were limited or inexistent for a long time. Dating these events remains a challenge for determining in which environmental conditions these populations have been separated. Further comparisons of phylogeographic patterns and reproductive strategies between various plant groups are required to improve knowledge on the biogeography of Saharan mountains and may help to define appropriate conservation strategies of their threatened ecosystems.

Phylogeny of North African Agama lizards (Reptilia: Agamidae) and the role of the Sahara desert in vertebrate speciation

The origin of Saharan biodiversity is poorly understood, in part because the geological and paleoclimatic events that presumably shaped species diversity are still controversial, but also because few studies have explored causal explanations for the origin of Saharan diversity using a phylogenetic framework. Here, we use mtDNA (16S and ND4 genes) and nDNA (MC1R and CMOS genes) to infer the relationships and biogeographic history of North African agamas (genus Agama). Agamas are conspicuous, diverse and abundant African lizards that also occur in the Saharan xeric and mesic environments. Our results revealed the presence of three Agama lineages in North Africa: one Afrotropical, one Sahelo-Saharan, and one broadly distributed in North Africa and mainly Saharan. Southern Mauritania contains the highest known diversity, with all three lineages present. Results suggest that agamas colonized the Sahara twice, but only one lineage was able to radiate and diversify there. Species in the Saharan lineage are mostly allopatric, and their splitting, genetic diversity and distribution are greatly explained by mountain ranges. One species in this lineage has colonized the Mediterranean climatic zone (A. impalearis), and another one the Sahel savannah (A. boueti). The other lineage to colonize the Sahara corresponds to A. boulengeri, an eminently Sahelian species that also inhabits Saharan mountain ranges in Mauritania and Mali. Phylogenetic analyses indicate that allopatric montane populations within some currently recognized species are also genetically divergent. Our study therefore concludes that vicariant speciation is a leading motor of species diversification in the area: Inside the Sahara, associated to mountain-ranges isolated by dune seas and bare plains; outside, associated to less harsh climates to the North and South. Paleoclimatic oscillations are suggested as causal explanations of the vicariant distribution and origin of species. Agamas are thought to have colonized northern Africa during wet periods, with subsequent dry periods fragmenting species distribution and leading to allopatric populations associated to milder and wetter climates in the Mediterranean, Sahel, and in Saharan mountains, in an island-model fashion. Finally, our results support the synonymization of A. castroviejoi with A. boueti, the reciprocal monophyly of all other North African agamas, and suggest one candidate species within A. boulengeri.

Systematics of north African Agama (Reptilia: Agamidae): a new species from the central Saharan mountains

Systematics of north African Agama (Reptilia: Agamidae): a new species from the central Saharan mountains

From Mediterranean shores to central Saharan mountains: key phylogeographical insights from the genus Myrtus

AbstractAim The Mediterranean region is often regarded as a crossroads where species of various origins meet. However, the biogeographical relationships between this region and contiguous Saharan, Macaronesian and Irano‐Turanian regions have not been investigated in detail. The aim of this study was to characterize the phylogeography of the circum‐Mediterranean species Myrtus communis and to investigate the origin of isolated central Saharan populations of Myrtus nivellei.Location The distribution ranges of M. communis from Macaronesia to the Irano‐Turanian region (173 sampled populations) and of M. nivellei in the mountains (Hoggar, Tassili n’Ajjer, Immidir, Tibesti) of the central Sahara (23 populations).Methods Nuclear ribosomal DNA (nrDNA) sequences of Myrtaceae were used to root the phylogeny of Myrtus, and to date its crown node, according to a detailed review of the palaeobotanical records used for multiple fossil calibration. Chloroplast DNA (cpDNA) sequences were analysed through the determination of genetic diversity indices and by statistical phylogeography.Results Both cpDNA and nrDNA markers indicated east–west genetic differentiation within M. communis. During the late Miocene, a key vicariance event affected the previous circum‐Mediterranean distribution of Myrtus, leading to the isolation of eastern populations. During the late Miocene or early Pliocene, two clades diverged: one is now scattered in the Mediterranean Basin and adjacent regions, whereas the other evolved in the western Mediterranean region. The differentiation of lineages during the Plio‐Pleistocene occurred mainly in the western part of the Mediterranean Basin, which has been at the origin of migrations towards Macaronesian islands and Saharan mountains. This is one of the first plant phylogeographical studies to report migrations from the Mediterranean to the Sahara.Main conclusions The genus Myrtus has persisted in the Mediterranean region since at least the Neogene and its biogeography reflects the cumulation of the species’ responses to successive palaeoenvironmental changes. The current distribution of the genus Myrtus in the Mediterranean Basin and in isolated areas, such as the Macaronesian islands and Saharan mountains, can be explained by the striking ability of this plant not only to persist locally in various refugia, but also to migrate.

Systematics of north African Agama (Reptilia: Agamidae): a new species from the central Saharan mountains

We studied the taxonomic status of the north African Agama species A. impalearis, A. castroviejoi, and A. boueti. The study of recently collected specimens and museum material, as well as phylogenetic analyses of a short 16S ribosomal RNA gene fragment, revealed the presence of an undescribed species in Adrar des Ifoghas (Mali), Aïr Mountains (Niger), Ahaggar Mountains (Algeria) and Tassili n’Ajjer (Algeria, Lybia), previously mistaken either as A. impalearis or A. agama. The new species, Agama tassiliensis n. sp., clearly belongs to the impalearis – boueti – spinosa species group but differs from these species, among other characters, by its red, reddish-orange or orange vertebral stripe in males, long and angular head, long limbs and toes (with 4 th toe usually slightly longer than 3 rd toe), long but low nuchal crest made of 10 to 15 spines (rarely 8–9 spines) and large number of supralabials (10–16, usually around 12). Interspecific uncorrected p- distances based on the 16S rDNA gene fragment are high, ranging from 3.9% between A. boueti and A. impalearis to 7.9% between A. spinosa and A. impalearis. The new species is sympatric with A. boueti at least in the Aïr Mountains and exhibits average mtDNA divergences of 6.2%, 7.4%, and 7.6% with A. spinosa, A. impalearis, and A. boueti, respectively. Agama boueti is paraphyletic relative to A. castroviejoi in the mtDNA tree, and mtDNA genetic divergences between populations of both species are lower than 1.0%, suggesting that A. castroviejoi is better treated as a junior synonym of A. boueti pending more detailed analyses. Scattered mountain ranges in the Sahara seem to have promoted lineage divergence and ultimately speciation in this group. Further work should be done to study species taxonomy and evolution in those areas.

Biogeography and conservation of viperids from North-West Africa: An application of ecological niche-based models and GIS

North-West Africa is an outstanding region to study biogeographic patterns in biodiversity distribution. This study identifies biogeographic affinities and areas of probable occurrence for seven viperid snakes through the combination of high resolution presence data and environmental factors. Vipers exhibited distinct biogeographical affinities: Bitis arietans was mostly found along savannahs, Echis leucogaster along the Sahel/savannahs, Cerastes cerastes and C. vipera throughout most desertic areas, Daboia mauritanica in coastal and hilly regions and Vipera latastei and V. monticola in almost only mountains. Suitable habitats were predicted for B. arietans in southern Senegal and Mali, and coastal southern Morocco, for E. leucogaster in southern Mauritania, Senegal, Mali, and fragmented habitats in Saharan mountains and south-western Morocco, for C. cerastes from the Atlantic coast to northern Algeria, for C. vipera in the central region, for D. mauritanica in northern-western Morocco and northern Algeria, for V. latastei in the Rif, Middle Atlas and coastal Morocco, and for V. monticola in the High Atlas. In potential sympatric areas, competition is probably limiting distribution, resulting in parapatric ranges. Northern Saharan populations of B. arietans and E. leucogaster are isolated. Saharan mountains and coastal south-western Morocco constitute isolated suitable areas for sub-Saharan relicts.

Are ferns in arid environments underestimated? Contribution from the Saharan Mountains

Although ferns are able to colonize dry regions through specific adaptations, they are suggested to be rare in arid environments. By comparing recent observations in the South-Saharan Mountains with existing data from the whole Sahara, we re-evaluated the distribution of the understudied Saharan fern diversity. Observations in the Aïr Mountains (Niger) from 2003 to 2006 identified six ferns species, among which three were new records for the Aïr and for Niger. A total of 17 species are currently known from the Sahara. The desiccation tolerant Actiniopteris radiata and Cheilanthes coriacea were located in habitats with abiotic refuges providing shade, whereas the drought avoiding Ophioglossum polyphyllum was found in a sandy highland plain. All were growing in isolated populations at elevations above 1600 m. These results, combined with data from the Hoggar and the Tibesti mountains, indicate that ferns are more frequent than initially thought in arid environments thanks to efficient dispersal, elevation refuges, physiological adaptations, and the presence of local abiotic refuges. The three newly recorded species most likely radiated from the Ethiopian highlands. Their deep isolation, their rarity, and their successful adaptation to drought suggest that their conservation status might be particularly high.

Identity ofTetragonia pentandraand taxonomy and distribution ofPatellifolia (Chenopodiaceae)

The little-known Tetragonia pentandra, long regarded as a member of Aizoaceae in the Horn of Africa region, is included in a phylogenetic analysis using ITS sequence data of members of Betoideae (Chenopodiaceae). Patellifolia, including Tetragonia pentandra, is strongly supported as monophyletic and weakly supported as sister to a clade with Aphanisma, Oreobliton and Beta. Within Patellifolia relationships are largely unresolved and, as the characters that have been used to distinguish taxa in the group are found to be unreliable, we propose that all members of the Patellifolia clade are treated as a single variable species, P. procumbens. Synonymies of Patellifolia and of P. procumbens are provided and two names are lectotypified. The distribution of P. procumbens is mapped and shown to be widely disjunct between the W Mediterranean region/Macaronesia and the Horn of Africa region, with isolated occurrences also in the Saharan mountains.

Biogeography and conservation of taxa from remote regions: An application of ecological-niche based models and GIS to North-African canids

In North Africa, and especially in the Sahara Desert, biodiversity is poorly known. Of the five widespread canid species present, one is Data Deficient, three are considered widespread although habitat selection could limit their area of occupancy, and distribution maps available are coarse for conservation planning. This study identifies biogeographic patterns in North-African canids through the combination of high resolution presence data with 16 environmental factors. Predictive models trained in north-west Africa are projected to all North Africa. canids exhibited distinct biogeographical affinities. GIS tools and Maximum Entropy models identify a mixture of climatic and habitat factors as main predictors of species occurrence. Suitable habitats for North-African canids are mostly fragmented: probable occurrence was identified for Canis aureus in Saharan peripheral regions and mountains, for Vulpes pallida in a narrow band along the Sahel and in southern Saharan mountains, for Vulpes rueppellii throughout the Sahara, for Vulpes vulpes in northern Africa until the Sahara northern limit, and for Vulpes zerda in almost all Sahara. Areas of potential sympatry between species with similar niches and parapatric ranges are identified along relatively narrow bands. The small pixel size of projections allows the identification of suitable refuges for species otherwise absent in the driest Saharan habitats, providing framework data for the definition of the global conservation status of V. pallida, and conservation strategies for the guild. The biological value of Saharan mountains is emphasised as they constitute isolated suitable areas. Ecological-niche based models should be developed for other endangered Saharan vertebrates.

Disjunctions in the Diptera (Insecta) fauna of the Mediterranean Province and southern Africa and a discussion of biogeographical considerations

This paper explores disjunctions in the Diptera fauna of the Mediterranean Province and southern Africa, drawing from eight families of Diptera, the more ancient Psychodidae and Vermileonidae, and the more recent Acroceridae, Asilidae, Bombyliidae, Dolichopodidae, Pipunculidae and Sciomyzidae. Information from recent published revisions is geo-referenced and plotted onto maps using GIS software. These distribution patterns are interpreted and probable means and routes of dispersal between the two regions are discussed. The concept of an Afrotropical sub-Saharan boundary is outlined and it is argued that although the vast, arid and virtually abiotic Sahara acts as a barrier to dispersal today, relict floral and faunal populations of Mediterranean provincial origin still occur on the Hoggar and Tibesti Mountains of the central Sahara, indicating that the aridification of the Sahara is a very recent event. The presence of extensive palaeolakes formerly covering ca 10% of the present-day Sahara is regarded as evidence in support of this hypothesis. These lakes and their associated catchments, situated in basins between the central Saharan mountains, could clearly have acted as a humid route of dispersal as recently as 4000 BP, when these lakes began to recede, and this route is here regarded as a “central high Africa corridor”; a filter-bridge between the Mediterranean Province and southern Africa. Examples of Mediterranean provincial species of Ephydridae and the muscid genus Lispe Latreille, 1796, occurring as far south as the Aïr Massif in northern Niger are cited as examples of relict montane Diptera of Mediterranean provincial origin in the southern Hoggar Mountains; these groups being associated with the margins of standing water. Balinsky's (1962) concept of an “arid corridor” is also re-examined, using examples from the larger, less mobile Diptera, and it is concluded that such a pattern may not be the result of aridity, but represent an “eastern high Africa corridor”, broadly corresponding to the “African Superswell”. Other perceived distribution pathways between the Holarctic and Afrotropical Regions are mapped. Anemochore dispersal is considered, and the extent of the Afrotropical Region is discussed. Mediterranean tectonic evolution on both a globe of constant size and on a smaller Jurassic globe is also considered. It is concluded that if all the transitional zones between the zoogeographical regions are to be given more-or-less equivalent treatment, we must avoid setting boundaries based on earlier faunal distributions. For this reason the current boundary between the Palaearctic and Afrotropical Regions, arbitrary as it is, should be retained, despite evidence suggesting recent continuity between sub-Saharan Africa, North Africa and the Arabian Peninsula, corresponding broadly to the African and Arabian lithospheric plates.

Distribution, shape and clonal growth of the rare endemic tree Olea europaea subsp. laperrinei (Oleaceae) in the Saharan mountains of Niger

The populations of the Laperrine’s olive (Olea europaea subsp. laperrinei) are located in three main areas corresponding to the mountains of northern Niger (Aïr), southern Algeria (Hoggar), and north-western Sudan (western Darfur). The populations native of Niger were found to occur in very fragmented patches from 1550 to 1850 m in five isolated mountains with population sizes not exceeding 100 trees each, except in the Tamgak. Samples in the Tamgak and the Bagzane mountains were studied by combining field observations with identification of genets (using highly variable DNA marker analyzes). Trees were relatively small and multi-stemmed like those in the Hoggar, and were associated with some tropical species as in the western Darfur. They were found on borders of “wadis”, i.e., temporary water courses, in ravines and on hillsides. They were unable to rely on sexual reproduction, which was found to be ineffective. In contrast, 28% of the genetic profiles found (n genet = 98) were represented with two or more trees without aboveground connections. Molecular and morphological data both demonstrated that the populations used clonal growth (CG) to survive in the current unfavorable period of hyper-aridity, and thus are likely to be remnant populations. Signs of human-related disturbances, recorded on 43% of the sampled trees, should be a determining factor of distribution as well. In the Bagzane mountains especially, where human activities are more intense than in the Tamgak mountains, trees developed preferentially on hillsides and ravines with low access rather than on wadi borders with better edaphic conditions but easier access for livestock/people. CG may be therefore, a survival strategy both against aridity and human-related disturbances. Sexual reproduction may be triggered during a less arid period, following the model of multiple demographic strategies, widespread in arid environments. However, survival would be affected by browsing and cuttings. Lastly, the absence of an efficient sexual strategy coupled with the high fragmentation of very small populations and a narrow altitudinal range of distribution indicates that today the populations of O. e. laperrinei in the Aïr mountain range are more endangered than those from southern Algeria and north-western Sudan.

Spatial genetic structure in the Laperrine's olive (Olea europaea subsp. laperrinei), a long-living tree from the central Saharan mountains

The Laperrine's olive (Olea europaea subsp. laperrinei) is an emblematic species of the Sahelo-Saharan Mountains. Populations of this tree are locally threatened by extinction due to climatic vicissitudes and human activities, particularly in Niger and Algeria. In order to study the spatial genetic structure and the dynamics of O. e. laperrinei populations, we sampled trees in four isolated mountain ranges (Tassili n'Ajjer and Hoggar (Algeria), Tamgak and Bagzane (Niger)). A total of 237 genets were identified using nuclear microsatellites. Phylogenetic reconstruction based on plastid DNA data supported a maternal origin of O. e. laperrinei populations in South Algeria, where a higher allelic richness was observed. Based on nuclear microsatellite data, two levels of structure were revealed: first, individuals from Niger and Algeria were separated in two distinct groups; second, four less differentiated clusters corresponded to the four studied mountain ranges. These results give support to the fact that desert barriers have greatly limited long distance gene flow. Within populations, pairwise kinship coefficients were significantly correlated to geographical distance for Niger populations but not for Algerian mountains. Historical factors and habitat heterogeneity may explain the differences observed. We conclude that the Hoggar acts as an important genetic reservoir that has to be taken into account in future conservation programmes. Moreover, very isolated endangered populations (for example, Bagzane) displaying evident genetic particularities have to be urgently considered for their endemism.