Status of the Nile crocodile in the Sahara desert

Middle Holocene remains and rock paintings show that the Nile crocodile (Crocodylus niloticus Laurenti) used to occur across the whole Sahara. It also occurred at the South Mediterranean shores, in swamps and rivers and it may even have been circum-mediterranean. Until the beginning of this century, many permanent waters in the Sahara still housed relict populations. Nowadays, only few specimens survive in pools in few river canyons of the Ennedi plateau (N. Chad), where they are threatened with extinction. Another relict population, in the Tagant hills of Mauretania, was found to be probably extinct in 1996.     

Processes structuring amphibian assemblages along a subtropical arid gradient

Biotic assemblages are organized according to multiple factors, including environmental filtering and species interactions. However, the roles of abiotic and biotic factors in the organization of amphibian assemblages in arid regions are still not completely understood. Here, I examined the distribution patterns of seven species of amphibians that occur in Tunisia (north-western Sahara Desert) and the composition of 328 amphibian assemblages, including their meta-structural organization. The species showed different responses to environmental gradients, predominantly the aridity and vegetation gradients. The assemblages in xeric regions were composed of nested subsets of the species present in mesic regions. Most of the significant species associations were explained by shared environmental responses, indicating that they can be largely attributed to environmental filtering. The only exception was between two species of generalist bufonids, Bufotes boulengeri and Sclerophrys mauritanica, which showed a residual correlation greater than their shared association with the gradient. In this case, phylogenetic and morphological similarities could favour patterns of mutual exclusion in habitats such as desert oases, where the resources are limited.     

Distribution of endemic relict groups of Saharan scorpions, with the description of new genus and species from Mauritania

A new genus and species of Saharan buthid scorpion is described on the basis of a single specimen collected in the desert of Mauritania. This new scorpion taxon represents yet another endemic relict in the Saharan fauna. Comments are also included on the evolution of the Sahara desert and the possible consequences of this on the distribution of the extant scorpion fauna.     

The origin of two cryptic species of African desert jerboas (Dipodidae: Jaculus)

The desert biota is exposed to extreme and variable conditions that shape its evolution and diversification processes. In this respect, the Jaculus jerboas have gained the attention of researchers as a result of their broad Saharan–Arabian distribution and their high and unexplained, morphological, anatomical, and molecular variation. In the present study, mitochondrial and nuclear genealogies where used to confirm monophyly of two cryptic species: Jaculus jaculus and Jaculus deserti. The reconstructed demography showed that the evolutionary histories of the species are markedly different and that the expansion into North‐West Africa by J. deserti was more recent than that of J. jaculus. The weak ecological separation between species and the signs of recent population growth and expansion of J. deserti suggest that its sympatric occurrence with J. jaculus is recent and that these species evolved in isolated populations, after diverging around the Pliocene–Pleistocene boundary. The importance of climate changes on the Sahara Desert biota is discussed in the context of genetic diversification. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 435–445.     

Impact of Climate Change on the Relict Tropical Fish Fauna of Central Sahara: Threat for the Survival of Adrar Mountains Fishes,Mauritania

Background

Four central Sahara mountainous massifs provide habitats for relict populations of fish. In the Adrar of Mauritania all available data on the presence and distribution of fish come from pre-1960 surveys where five fish species were reported: Barbus pobeguini, Barbus macrops, Barbus mirei, Sarotherodon galilaeus, and Clarias anguillaris. Since 1970, drought has had a severe impact in the Adrar where rainfall decreased by 35%. To investigate whether the relict populations of fish have survived the continuing drought, a study was carried out from 2004 to 2008.

Methodology/Principal Findings

An inventory of perennial bodies of water was drawn up using a literature review and analysis of topographical and hydrological maps. Field surveys were carried out in order to locate the bodies of water described in the literature, identify the presence of fish, determine which species were present and estimate their abundance. The thirteen sites where the presence of fish was observed in the 1950s -Ksar Torchane, Ilij, Molomhar, Agueni, Tachot, Hamdoun, Terjit, Toungad, El Berbera, Timagazine, Dâyet el Mbârek, Dâyet et-Tefla, Nkedeï- were located and surveyed. The Ksar Torchane spring -type locality and the only known locality of B. mirei- has dried up at the height of the drought in 1984, and any fish populations have since become extinct there. The Timagazine, Dâyet el Mbârek and Dâyet et-Tefla pools have become ephemeral. The Hamdoun guelta appears to be highly endangered. The fish populations at the other sites remain unchanged. Four perennial pools which are home to populations of B. pobeguini are newly recorded.

Conclusion/Significance

The tropical relict fish populations of the Adrar mountains of Mauritania appear to be highly endangered. Of thirteen previously recorded populations, four have become extinct since the beginning of the drought period. New fish population extinctions may occur should low levels of annual rainfall be repeated.     

Effects of an invasive plant on a desert sand dune landscape

Given the abundance of non-native species invading wildland habitats, managers need to employ informed triage to focus control efforts on weeds with the greatest potential for negative impacts. Our objective here was to determine the level of threat Sahara mustard, Brassica tournefortii, represents to meeting regional goals for protecting biodiversity. Sahara mustard has spread throughout much of the Mojave and lower Sonoran Deserts. It has occurred in southern California’s Coachella Valley for nearly 80 years, punctuated by years of extremely high abundance following high rainfall. In those years the mustard has clear negative impacts on the native flora. Using mustard removal experiments we identified reductions in native plant reproduction, shifting composition increasingly toward Sahara mustard while decreasing the fraction of native species. High between-year variance in precipitation may be a key to maintaining biodiversity as the mustard is less abundant in drier years. Sahara mustard impacts to the native fauna were much less evident. Of the animal species evaluated, only the Coachella Valley fringe-toed lizard, Uma inornata, demonstrated a negative response to mustard abundance; however the impacts were short-lived, lasting no more than a year after the mustard’s dominance waned. Without control measures the long-term impacts to desert biodiversity may rest on the changing climate. Wetter conditions or increased periodicity of high rainfall years will favor Sahara mustard and result in reduced biodiversity, especially of native annual plants. Drier conditions will keep the mustard from becoming dominant but may have other negative consequences on the native flora and fauna.     

Origin and taxonomic status of the Palearctic population of the stem borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae)

The major pest of maize in Mediterranean Europe, the stem borer Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae), has a fragmented distribution, north and south of the Sahara. The present study aimed: (1) to clarify the uncertain taxonomic status of the Palearctic and sub‐Saharan populations which were first considered as different species and later on as subspecies (Sesamia nonagrioides nonagrioides and Sesamia nonagrioides botanephaga) and (2) to investigate the origin of the Palearctic population which extends from Spain to Iran, outside what is considered typical for this mainly tropical genus. We reconstructed the evolutionary history of both populations using one nuclear and two mitochondrial genes. The sub‐Saharan taxon was fragmented in two isolated populations (West and East) whose mitochondrial genes were distant by 2.3%. The Palearctic population was included in the East African clade and its genes were close or identical to those of a population from Central Ethiopia, where the species was discovered for the first time. Similarly, in Africa, the alleles of the nuclear gene were distributed mainly in two West and East clades, whereas some Palearctic alleles belonged to the West clade. The Palearctic population originated therefore from East and West Africa and is the progeny of the cross between these two African populations. The main species concepts were in agreement, leading to the conclusion that the three populations are still conspecific. In the surveyed regions, the species therefore does not include two subspecies but three isolated populations. The Palearctic population suffered from severe bottlenecks that resulted in the fixation of one East African mitochondrial genome and the large reduction in its genetic diversity compared to the African populations. The data suggest that natural colonization of the Palearctic region was more plausible than human introduction. The allelic distribution of the Palearctic population was similar to that of species that survived the last glaciation. It is concluded that the African populations expanded during the last interglacial, crossed the Sahara and mixed in North Africa where fixation of the East mitochondrial genome occurred. The species then colonized Europe westward through only one eastern entrance. The coalescent‐based estimate of the time to the ancestor of the Palearctic population was 108 000 years, which is consistent with this scenario. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 904–922.     

Identifying the African Wintering Grounds of Hybrid Flycatchers Using a Multi–Isotope (δ 2H, δ 13C, δ 15N) Assignment Approach

Migratory routes and wintering grounds can have important fitness consequences, which can lead to divergent selection on populations or taxa differing in their migratory itinerary. Collared (Ficedula albicollis) and pied (F. hypoleuca) flycatchers breeding in Europe and wintering in different sub-Saharan regions have distinct migratory routes on the eastern and western sides of the Sahara desert, respectively. In an earlier paper, we showed that hybrids of the two species did not incur reduced winter survival, which would be expected if their migration strategy had been a mix of the parent species'' strategies potentially resulting in an intermediate route crossing the Sahara desert to different wintering grounds. Previously, we compared isotope ratios and found no significant difference in stable-nitrogen isotope ratios (δ ¹⁵N) in winter-grown feathers between the parental species and hybrids, but stable-carbon isotope ratios (δ ¹³C) in hybrids significantly clustered only with those of pied flycatchers. We followed up on these findings and additionally analyzed the same feathers for stable-hydrogen isotope ratios (δ ²H) and conducted spatially explicit multi-isotope assignment analyses. The assignment results overlapped with presumed wintering ranges of the two species, highlighting the efficacy of the method. In contrast to earlier findings, hybrids clustered with both parental species, though most strongly with pied flycatcher.     

A new species of the rare buthid scorpion genus Lissothus Vachon, 1948 from Central Algeria (Scorpiones,Buthidae)

Taxonomic considerations are given for the genus Lissothus Vachon, 1948 (Scorpiones, Buthidae). Two species are currently known, Lissothus bernardi Vachon, 1948 from Libya and Lissothus occidentalis Vachon, 1950 from Mauritania. In this contribution, a new species, Lissothus chaambi sp. n., is described from the desert of Central Algeria. The new species is most closely related to L. bernardi. The geographical distribution of the genus is discussed.     

The southern limit of the Mediterranean vegetation in the Sahara during the Holocene

Holocene records from the southern Sahara in Niger allow a reconstruction of the vegetation history and inform us about the former extension of the Mediterranean. Both pollen and charcoal analyses evidenced the direct contact of Sudanian and Saharan savannas during the middle Holocene at about 19°N, whereas at 20°N the transition from the Saharan savanna to the desert was found. In southwestern Libya (26°N) a combination of a Saharan desert vegetation and a semi‐desert Artemisia shrub on the plateaus demonstrated the contact with Mediterranean influenced formations. Regular ash and charcoal layers in middle‐Holocene sediments of the northern Niger prove an early interference of man with the vegetation development. One has to imagine that, in combination with the cattle‐keeping and the later metal production, man could have changed the former northern Sudanian vegetation into the present Sahelian savanna system from the middle Holocene on.     

Preservation of genetic diversity in a wild and captive population of a rapidly declining mammal,the Common hamster of the French Alsace region

The Common hamster (Cricetus cricetus) faced massive population declines throughout its western range margin. In France, relict populations remained in the Alsace region. By comparing allelic diversity using microsatellite analysis over a time span of 12 years we investigated if this population decline led to genetic erosion in a French relict population of the species. Genetic diversity was moderate but comparable to other populations from Western Europe. Interestingly, no decline of allelic variation was revealed between 1999 and 2012 in the study region (expected heterozygosity = 0.51 in 1999 and 0.5 in 2012, respectively), suggesting a sufficiently high effective population size of ∼500 (179–956 SD). While several alleles were lost in a captive breed maintained for restocking purposes in the region, expected heterozygosity was comparably high (=0.5). Our results show that genetic diversity has been effectively maintained in a relict population of French Common hamsters despite of massive range loss. We recommend the maintenance of intense in situ conservation effort, along with regular monitoring of genetic diversity and effective population size.     

How hazardous is the Sahara Desert crossing for migratory birds? Indications from satellite tracking of raptors

We investigated the risk associated with crossing the Sahara Desert for migrating birds by evaluating more than 90 journeys across this desert by four species of raptors (osprey Pandion haliaetus, honey buzzard Pernis apivorus, marsh harrier Circus aeruginosus and Eurasian hobby Falco subbuteo) recorded by satellite telemetry. Forty per cent of the crossings included events of aberrant behaviours, such as abrupt course changes, slow travel speeds, interruptions, aborted crossings followed by retreats from the desert and failed crossings due to death, indicating difficulties for the migrants. The mortality during the Sahara crossing was 31 per cent per crossing attempt for juveniles (first autumn migration), compared with only 2 per cent for adults (autumn and spring combined). Mortality associated with the Sahara passage made up a substantial fraction (up to about half for juveniles) of the total annual mortality, demonstrating that this passage has a profound influence on survival and fitness of migrants. Aberrant behaviours resulted in late arrival at the breeding grounds and an increased probability of breeding failure (carry-over effects). This study also demonstrates that satellite tracking can be a powerful method to reveal when and where birds are exposed to enhanced risk and mortality during their annual cycles.     

Crocodiles in the Sahara desert: an update of distribution, habitats and population status for conservation planning in Mauritania

Background

Relict populations of Crocodylus niloticus persist in Chad, Egypt and Mauritania. Although crocodiles were widespread throughout the Sahara until the early 20^th century, increased aridity combined with human persecution led to local extinction. Knowledge on distribution, occupied habitats, population size and prey availability is scarce in most populations. This study evaluates the status of Saharan crocodiles and provides new data for Mauritania to assist conservation planning.

Methodology/Principal Findings

A series of surveys in Mauritania detected crocodile presence in 78 localities dispersed across 10 river basins and most tended to be isolated within river basins. Permanent gueltas and seasonal tâmoûrts were the most common occupied habitats. Crocodile encounters ranged from one to more than 20 individuals, but in most localities less than five crocodiles were observed. Larger numbers were observed after the rainy season and during night sampling. Crocodiles were found dead in between water points along dry river-beds suggesting the occurrence of dispersal.

Conclusion/Significance

Research priorities in Chad and Egypt should focus on quantifying population size and pressures exerted on habitats. The present study increased in by 35% the number of known crocodile localities in Mauritania. Gueltas are crucial for the persistence of mountain populations. Oscillations in water availability throughout the year and the small dimensions of gueltas affect biological traits, including activity and body size. Studies are needed to understand adaptation traits of desert populations. Molecular analyses are needed to quantify genetic variability, population sub-structuring and effective population size, and detect the occurrence of gene flow. Monitoring is needed to detect demographical and genetical trends in completely isolated populations. Crocodiles are apparently vulnerable during dispersal events. Awareness campaigns focusing on the vulnerability and relict value of crocodiles should be implemented. Classification of Mauritanian mountains as protected areas should be prioritised.     

The root of the East African cichlid radiations

Background  

For decades cichlid fishes (Perciformes: Cichlidae) of the East African cichlid radiations (Teleostei: Cichlidae) have served as natural experimental subjects for the study of speciation processes and the search for potential speciation key factors. Despite numerous phylogenetic studies dealing with their intragroup relationships, surprisingly little is known about the phylogenetic placement and time of origin of this enigmatic group. We used multilocus DNA-sequence data from five nuclear and four mitochondrial genes and refined divergence time estimates to fill this knowledge gap.     

Distribution and morphological variation of Streptocephalus torvicornis (Waga, 1842) in Northern Africa

The known range of S. torvicornis is extended to areas of the Western and Central Sahara and Sahel. Morphological variation between populations is important, and cannot be accomodated within the known Iberian and Maghrebian subspecific taxa, which appear untenable. A grouping of populations according to drainage basins appears, however, possible. Populations of the Hoggar, Air, and Tibesti waters, draining towards the Soudanian zone, are more closely related than populations from waters draining towards the Atlantic. Tassili-n-ajjer populations from Central Algeria have individual characteristics, and deserve further study.     

Microbial hitchhikers on intercontinental dust: catching a lift in Chad

Ancient mariners knew that dust whipped up from deserts by strong winds travelled long distances, including over oceans. Satellite remote sensing revealed major dust sources across the Sahara. Indeed, the Bodélé Depression in the Republic of Chad has been called the dustiest place on earth. We analysed desert sand from various locations in Chad and dust that had blown to the Cape Verde Islands. High throughput sequencing techniques combined with classical microbiological methods showed that the samples contained a large variety of microbes well adapted to the harsh desert conditions. The most abundant bacterial groupings in four different phyla included: (a) Firmicutes—Bacillaceae, (b) Actinobacteria—Geodermatophilaceae, Nocardiodaceae and Solirubrobacteraceae, (c) Proteobacteria—Oxalobacteraceae, Rhizobiales and Sphingomonadaceae, and (d) Bacteroidetes—Cytophagaceae. Ascomycota was the overwhelmingly dominant fungal group followed by Basidiomycota and traces of Chytridiomycota, Microsporidia and Glomeromycota. Two freshwater algae (Trebouxiophyceae) were isolated. Most predominant taxa are widely distributed land inhabitants that are common in soil and on the surfaces of plants. Examples include Bradyrhizobium spp. that nodulate and fix nitrogen in Acacia species, the predominant trees of the Sahara as well as Herbaspirillum (Oxalobacteraceae), a group of chemoorganotrophic free-living soil inhabitants that fix nitrogen in association with Gramineae roots. Few pathogenic strains were found, suggesting that African dust is not a large threat to public health.     

On the evolutionary pathway of parental care in mouth-brooding cichlid fishes

Evolutionary theory predicts that differences in parental care patterns among species arose from interspecific differences in the costs and benefits of care for each sex. In Galilee St Peter''s fish, Sarotherodon galilaeus (Cichlidae), male care, female care and biparental care all occur in the same population. We exploit this unusual variability to isolate conditions favouring biparental versus uniparental mouth-brooding by males or females. We first review a game-theoretic model of parental care evolution, predictions of which we test experimentally in this paper. Manipulations of the operational sex ratio show that males and females desert their offspring more frequently when the costs of care are high (in terms of lost mating opportunities). Breeding trials with males of different sizes show that small fathers desert more frequently than large fathers. We attribute this to the associated difference in the fitness benefit of biparental care relative to female-only care. Our experimental results confirm that in St Peter''s fish the probability of caring is determined facultatively according to current conditions at each spawn. The experiments and model together suggest that interspecific variation in remating opportunities and clutch size may be responsible for differences in care patterns within the sub-family Tilapiini. Our results support the hypothesis that biparental mouth-brooding was the ancestral state of both male and female uniparental mouth-brooding in cichlid fishes.     

Are captive tortoises a reservoir for conservation? An assessment of genealogical affiliation of captive Gopherus agassizii to local, wild populations

The conservation of tortoises poses a unique situation because several threatened species are commonly kept as pets within their native ranges. Thus, there is potential for captive populations to be a reservoir for repatriation efforts. We assess the utility of captive populations of the threatened Agassiz’s desert tortoise (Gopherus agassizii) for recovery efforts based on genetic affinity to local areas. We collected samples from 130 captive desert tortoises from three desert communities: two in California (Ridgecrest and Joshua Tree) and the Desert Tortoise Conservation Center (Las Vegas) in Nevada. We tested all samples for 25 short tandem repeats and sequenced 1,109 bp of the mitochondrial genome. We compared captive genotypes to a database of 1,258 Gopherus samples, including 657 wild caught G. agassizii spanning the full range of the species. We conducted population assignment tests to determine the genetic origins of the captive individuals. For our total sample set, only 44 % of captive individuals were assigned to local populations based on genetic units derived from the reference database. One individual from Joshua Tree, California, was identified as being a Morafka’s desert tortoise, G. morafkai, a cryptic species which is not native to the Mojave Desert. Our data suggest that captive desert tortoises kept within the native range of G. agassizii cannot be presumed to have a genealogical affiliation to wild tortoises in their geographic proximity. Precautions should be taken before considering the release of captive tortoises into the wild as a management tool for recovery.