African Slope Research Articles

Selection of p53 pathway in adaptive evolution and reproductive isolation in incipient sympatric speciation ofDrosophilaat Evolution Canyon

AbstractSympatric speciation (SS) refers to the origin of new species within a freely breeding population. The ‘Evolution Canyon’ (EC) in Israel is a natural microsite model for SS of species across phylogenies from viruses and bacteria to mammals, adapting to, and speciating in, interslope microclimates. The cosmopolitan Drosophila melanogaster at EC I, Mount Carmel, is undergoing incipient SS in response to sharply divergent interslope microclimate stresses, including solar radiation, temperature, humidity and pathogenicity. We demonstrated here a selective interslope divergence of single nucleotide polymorphism (SNP) distribution in the Drosophila p53 pathway. This involves a total of 71 genes, which are associated with DNA repair, heat response, and fungal and bacterial resistant pathways. This distribution pattern links the previously observed thermotolerance and ageing divergence of D. melanogaster between the opposite canyon slopes: the south-facing slope (SFS, or African slope: tropical, savannoid and dry) and the abutting north-facing slope (NFS, or European slope; temperate, forested, cool and humid). The genes with interslope-significant differential SNPs link the p53 pathway with pathways related to the responses to microclimates through protein-protein interaction. Moreover, for the first time we provide evidence that the p53 pathway is linked to reproductive isolation, and is thus actively participating in incipient SS of D. melanogaster. This is the first demonstration of a link between the p53 pathway and reproductive isolation, thereby contributing to adaptive incipient sympatric speciation.

Molecular evidence for adaptive evolution of drought tolerance in wild cereals.

The considerable drought tolerance of wild cereal crop progenitors has diminished during domestication in the pursuit of higher productivity. Regaining this trait in cereal crops is essential for global food security but requires novel genetic insight. Here, we assessed the molecular evidence for natural variation of drought tolerance in wild barley (Hordeum spontaneum), wild emmer wheat (Triticum dicoccoides), and Brachypodium species collected from dry and moist habitats at Evolution Canyon, Israel (ECI). We report that prevailing moist vs dry conditions have differentially shaped the stomatal and photosynthetic traits of these wild cereals in their respective habitats. We present the genomic and transcriptomic evidence accounting for differences, including co-expression gene modules, correlated with physiological traits, and selective sweeps, driven by the xeric site conditions on the African Slope (AS) at ECI. Co-expression gene module 'circadian rhythm' was linked to significant drought-induced delay in flowering time in Brachypodium stacei genotypes. African Slope-specific differentially expressed genes are important in barley drought tolerance, verified by silencing Disease-Related Nonspecific Lipid Transfer 1 (DRN1), Nonphotochemical Quenching 4 (NPQ4), and Brassinosteroid-Responsive Ring-H1 (BRH1). Our results provide new genetic information for the breeding of resilient wheat and barley in a changing global climate with increasingly frequent drought events.

Frequency-dependent Amplitude Versus Offset analysis of a Cenozoic mass-transport deposit on the Namibian slope

Abstract A partially tuned, ‘soft’ seismic reflection, overlying a regional limestone marker on the west African slope, is shown to represent a sequence, up to 30 m thick, within which various individual stratigraphic units are identified, some of which display characteristics of a mass-transport deposit (MTD). The seismic reflection is described in terms of its two-way time structure, reflection amplitude pattern, complex seismic attributes and AVO response. Frequency-dependent aspects of the AVO response, resulting from velocity attenuation and dispersion of seismic signals, are shown to indicate variations in pore-fluid gas concentration. These are exploited to assess lithological, petrophysical and pore-fluid characteristics of the various sub-units within the sequence. A relative acoustic impedance inversion of the seismic data is combined with a low-frequency model, constructed from acoustic velocity data, to approximate absolute acoustic impedance characteristics of the sequence and to model behaviour of the various sub-units across the area. These pseudo-absolute impedance data are combined with evidence from AVO analysis, to construct a 2D model of the MTD unit and to generate a synthetic seismic record, which confirms the interpretation of stratigraphic, petrophysical and lithological properties of the MTD complex.

Genome-wide analysis revisits incipient sympatric and allopatric speciation in a beetle

Abstract The grain beetle, Oryzaephilus surinamensis, is a widespread species distributed in the wild and in granaries. Our earlier extensive biological studies indicated that the beetle shows incipient sympatric speciation (SS) in the wild at Evolution Canyon I (EC-I), Israel, and allopatric speciation, in a granary. Here we provide genome-wide evidence supporting our adaptive evolution scenario involving two models of speciation, SS in the wild, and allopatric in the granary. The EC-I microsite is a hot spot of SS across life from bacteria to mammals caused by the sharp opposite microclimates. The tropical hot, dry and savannoid biome dubbed the “African” slope (AS), sharply contrasts with the opposite temperate, cool, humid, and forested biome on the European” slope (ES), separated by only ~250 meters. The third allopatric granary population is 26 km north of EC-I. The granary population showed larger genomic, morphological, and behavioral distances, smaller genome size, more unique transposable elements, and reproductive isolation, displaying faster genomic divergence than between the wild populations at EC-I. The incipient SS of the wild populations, and the speciation of the granary population are reinforced by the substantial genomic divergence among the three beetle populations, supporting again the evolutionary scenario of incipient SS with gene flow at EC-I, and allopatric speciation in the granary population. We propose additional studies in Israel, the Mediterranean basin, and worldwide, to negate alternative explanations, based on a broader sampling and analysis.

Variability of the Canary Current Diagnosed by Inverse Box Models

AbstractFour hydrographic cruises carried out between ~26.5 and 31°N in the eastern North Atlantic Subtropical Gyre in fall (2016 and 2017) and spring (2017 and 2018) are used to identify water masses and infer oceanic circulation. Geostrophic velocities are initially adjusted by referencing them to data from a Lower Acoustic Doppler Current Profiler (LADCP) and later to velocities estimated with an inverse box model. The distribution of the intermediate water masses (700 to 1,400 m depth) varies seasonally. Antarctic Intermediate Water (AAIW) comprises the largest contributor to the seasonal cycle in the intermediate water masses. Circulation of the Canary Current (CC) differs in fall and spring. In fall, the CC flows southward through the western islands and recirculates south of the archipelago, subsequently flowing northward through the passage between the eastern islands and Africa. North of Lanzarote, the recirculated CC intensified as it is joined by a southeasterly branch of the CC north of Lanzarote. In spring, the net transport of the CC is southward. High interannual variability in mass transport is evident in both spring and fall as a result of the position of the current, with its easternmost (westernmost) position found in spring (fall) 2018 (2016). At intermediate levels, highly variable northward/southward transport is apparent in fall over the African slope, with the Intermediate Poleward Under Current (IPUC) only present in 2017.

Soil translocation at “Evolution Canyon” I (Mount Carmel, Israel) reveals the importance of microclimatic variation for structuring soil microfungal communities

An experimental study involving the translocation of soil from the south-facing, tropical, savannoid, “African” slope (AS) to the north-facing, temperate, forested “European” slope (ES), 250 m apart, and vice versa, was performed at “Evolution Canyon”, Mount Carmel, Israel. The purpose of the study was to explore whether the new microclimatic conditions would affect community structure of culturable fungi. The translocation of soil from the AS to the ES significantly decreased the abundance of xeric and thermotolerant components of microfungal communities – melanin-containing fungi and Aspergillus spp. Simultaneously, the mesic component – Penicillium spp, increased in the abundance. The translocation also caused substantial increases in abundance of fast-growing mycoparasitic Clonostachys rosea and Trichoderma koningii, which are known to produce toxic secondary metabolites and grow over other fungi in culture. High abundance of these species apparently caused the significant decrease in species richness in the AS-to-ES translocated communities and made these communities more similar to the native ES communities as the cluster analysis revealed. Notably, the translocation from the xeric south-facing AS to the temperate north-facing ES caused more substantial changes in the microfungal communities as compared to the opposite soil translocation. The results of the study clearly indicated that translocation of the soil to the opposite slopes of “Evolution Canyon” had changed the community structure of microfungal communities, and these changes were apparently driven by variation in environmental conditions.

The role of tides in the spreading of Mediterranean Outflow waters along the southwestern Iberian margin

The impact of tides on the spreading of the Mediterranean Outflow Waters (MOW) in the Gulf of Cadiz is investigated through a series of targeted numerical experiments using an ocean general circulation model. The full ephimeridic luni-solar tidal potential is included as forcing. The model grid is global with a strong zoom around the Iberian Peninsula. Thus, the interaction of processes of different space and time scales, which are involved in the MOW spreading, is enabled. This is of particular importance in the Strait of Gibraltar and the Gulf of Cádiz, where the width of the MOW plume is a few tens of km. The experiment with enabled tides successfully simulates the main tidal features of the North Atlantic and in the Gulf of Cádiz and the Strait of Gibraltar. The comparison of the fields from simulations with and without tidal forcing shows drastically different MOW pathways in the Gulf of Cádiz: The experiment without tides shows an excessive southwestward spreading of Mediterranean Waters along the North African slope, whereas the run with tides is closer to climatology. A detailed analysis indicates that tidal residual currents in the Gulf of Cádiz are the main cause for these differences.

Adaptive evolution of benzoxazinoids in wild emmer wheat, Triticum dicoccoides, at "Evolution Canyon", Mount Carmel, Israel.

Background"Evolution Canyon" (ECI) at Lower Nahal Oren, Mount Carmel, Israel, is an optimal natural microscale model for unraveling evolution-in-action, highlighting the evolutionary processes of biodiversity evolution, adaptation, and incipient sympatric speciation. A major model organism in ECI is the tetraploid wild emmer wheat, Triticum dicoccoides (TD), the progenitor of cultivated emmer and durum wheat. TD displays dramatic interslope adaptive evolutionary divergence on the tropical, savannoid-hot and dry south-facing, "African" slope (AS), and on the temperate, forested, cool and humid, north-facing, "European" slope (ES), separated on average by 250 m. From the perspective of chemical evolution and metabolomics, it is important to unravel interslope divergence in biologically relevant secondary metabolites between the abutting slope populations. Here, in TD we examined hydroxamic acid (Hx), which is a family of secondary cereal metabolites, and plays a major role in defending the plant against fungi, insects and weeds.ResultsOur examination revealed that higher concentrations of DIBOA and DIMBOA were found in seedlings growing in the same greenhouse from seeds collected from the cool and humid forested ES, whereas the seedlings of seeds collected from the savannoid AS (both in root and shoot tissues), showed no DIMBOA. Remarkably, only DIBOA appears in both shoots and roots of the AS seedlings. It rises to a peak and then decreases in both organs and in seedlings from both slopes. The DIMBOA, which appears only in the ES seedlings, rises to a peak and decreases in the shoot, but increased and remained in a plateau in the root, till the end of the experiment.Conculsions/SignificanceThe results suggest stronger genetic resistance of defense compounds DIBOA and DIMBOA against biotic stresses (fungi and other pathogens) by ES seedlings. However, AS seedlings responded earlier but were to the same biotic stresses. The genetic difference found in AS seedlings was caused by the main adaptive selection in AS, which was against climatic, abiotic stresses, and was weaker, or not at all, against biotic stresses. The distinct genetic interslope differences appear important and is very significant and are elaborated in the discussion.

An uncommon or just an ecologically demanding species? Finding of aggregations of the brittle-star Ophiothrix maculata on the Northwest African slope

Ophiuroidea constitutes the largest class of the phylum Echinodermata. It includes families with suspension-feeder behaviour that can be found in dense aggregations in all oceans worldwide. Ophiothrix maculata was known as a rare suspension-feeder brittle star, with only four records in the Eastern Central Atlantic dating from almost 100 years ago.During the ten multidisciplinary Spanish and Norwegian surveys carried out from 2004 to 2012 off Northwest Africa, between the Gibraltar Strait and the Sierra Leone border from 19 to 1888m depth, we sampled 1298 stations. We gathered about one million individuals and 124kg of brittle stars at 501 of the stations. Eight hundred and thirty-two specimens of Ophiothrix maculata were collected at six localities on the continental slope off Mauritania, Western Sahara and Guinea Bissau, at depths between 155 and 594m. The Guinea Bissau samples represent the southernmost current record for the species. Even though Ophiothrix maculata has been previously recorded only in isolation, we discovered dense concentrations on the Mauritanian slope on the Wolof's Seamount (580 individuals) and off the Western Sahara, in a Lophelia pertusa reef (202 individuals).In this paper, we describe these findings and discuss the association of this species to hard-bottom habitats and high primary production areas, outside of the oxygen minimum zone (OMZ). We also analyse what other factors may explain the patchy distribution of O. maculata on the Northwest African slope.

On the seasonal variability of the Canary Current and the Atlantic Meridional Overturning Circulation

AbstractThe Atlantic Meridional Overturning Circulation (AMOC) is continually monitored along 26°N by the RAPID‐MOCHA array. Measurements from this array show a 6.7 Sv seasonal cycle for the AMOC, with a 5.9 Sv contribution from the upper mid‐ocean. Recent studies argue that the dynamics of the eastern Atlantic is the main driver for this seasonal cycle; specifically, Rossby waves excited south of the Canary Islands. Using inverse modeling, hydrographic, mooring, and altimetry data, we describe the seasonal cycle of the ocean mass transport around the Canary Islands and at the eastern boundary, under the influence of the African slope, where eastern component of the RAPID‐MOCHA array is situated. We find a seasonal cycle of −4.1 ± 0.5 Sv for the oceanic region of the Canary Current, and +3.7 ± 0.4 Sv at the eastern boundary. This seasonal cycle along the eastern boundary is in agreement with the seasonal cycle of the AMOC that requires the lowest contribution to the transport in the upper mid‐ocean to occur in fall. However, we demonstrate that the linear Rossby wave model used previously to explain the seasonal cycle of the AMOC is not robust, since it is extremely sensitive to the choice of the zonal range of the wind stress curl and produces the same results with a Rossby wave speed of zero. We demonstrate that the seasonal cycle of the eastern boundary is due to the recirculation of the Canary Current and to the seasonal cycle of the poleward flow that characterizes the eastern boundaries of the oceans.

Recirculation of the Canary Current in fall 2014

Hydrographic measurements together with Ship mounted Acoustic Doppler Current Profilers and Lowered Acoustic Doppler Current Profilers (LADCP) obtained in October 2014 are used to describe water masses, geostrophic circulation and mass transport of the Canary Current System, as the Eastern Boundary of the North Atlantic Subtropical Gyre. Geostrophic velocities are adjusted to velocities from LADCP data to estimate an initial velocity at the reference layer. The adjustment results in a northward circulation at the thermocline layers over the African slope from an initial convergent flow. Final reference velocities and consequently absolute circulation are estimated from an inverse box model applied to an ocean divided into 13 neutral density layers. This allows us to evaluate mass fluxes consistent with the thermal wind equation and mass conservation. Ekman transport is estimated from the wind data derived from the Weather Research and Forecasting model. Ekman transport is added to the first layer and adjusted with the inverse model. The Canary Current located west of Lanzarote Island transports to the south a mass of − 1.5 ± 0.7 Sv (1 Sv = 106 m3 s− 1 ≈ 109 kg s− 1) of North Atlantic Central Water at the surface and thermocline layers (~ 0–700 m). In fall 2014, hydrographic data shows that the Canary Current in the thermocline (below at about 80 m depth to ~ 700 m) recirculates to the north over the African slope and flows through the Lanzarote Passage. At intermediate layers (~ 700–1400 m), the Intermediate Poleward Undercurrent transports northward a relatively fresh Antarctic Intermediate Water in the range of 0.8 ± 0.4 Sv through the Lanzarote Passage and west of Lanzarote Island beneath the recirculation of the Canary Current.

Water masses and mesoscale control on latitudinal and cross-shelf variations in larval fish assemblages off NW Africa

We explore the associations between larval fish assemblages and oceanographic conditions in the upper ocean (top 200m) along the African slope, from tropical (15°N) to subtropical (35°N) latitudes, during a period of intense upwelling. In this extensive region, the northward Mauritanian Current and Poleward Undercurrent carry South Atlantic Central Waters (SACW) while the southward Canary Upwelling Current transports North Atlantic Central Waters (NACW). South of Cape Blanc we only find SACW, and north of Cape Blanc there is NACW far offshore and a combination of NACW and SACW nearshore, separated by the Canary Upwelling Front (CUF). The larvae of different myctophid species serve as indicators of the water masses, e.g. S. veranyi and M. punctatum were found in some coastal stations that were dominated by NACW, while the tropical mesopelagic B. argyrogaster, H. macrochir, M. affine and S. kreffti were associated to the SACW. The along-slope offshore convergence of NACW and SACW takes place at the Cape Verde Frontal Zone (CVFZ), representing a region of extensive offshore export for larvae of coastal species, S. pilchardus and E. encrasicolus, far from their nearshore spawning area. The large-scale frontal systems (CVFZ and CUF) and mesoscale eddies contribute to retain larvae within productive waters, influencing both coastal and oceanic species.

Sympatric speciation of spiny mice, Acomys, unfolded transcriptomically at Evolution Canyon, Israel

Spiny mice, Acomys cahirinus, colonized Israel 30,000 y ago from dry tropical Africa and inhabited rocky habitats across Israel. Earlier, we had shown by mtDNA that A. cahirinus incipiently sympatrically speciates at Evolution Canyon I (EC I) in Mount Carmel, Israel because of microclimatic interslope divergence. The EC I microsite consists of a dry and hot savannoid "African" slope (AS) and an abutting humid and cool-forested "European" slope (ES). Here, we substantiate incipient SS in A. cahirinus at EC I based on the entire transcriptome, showing that multiple slope-specific adaptive complexes across the transcriptome result in two divergent clusters. Tajima's D distribution of the abutting Acomys interslope populations shows that the ES population is under stronger positive selection, whereas the AS population is under balancing selection, harboring higher genetic polymorphisms. Considerable sites of the two populations were differentiated with a coefficient of FST = 0.25-0.75. Remarkably, 24 and 37 putatively adaptively selected genes were detected in the AS and ES populations, respectively. The AS genes involved DNA repair, growth arrest, neural cell differentiation, and heat-shock proteins adapting to the local AS stresses of high solar radiation, drought, and high temperature. In contrast, the ES genes involved high ATP associated with energetics stress. The sharp ecological interslope divergence led to strong slope-specific selection overruling the interslope gene flow. Earlier tests suggested slope-specific mate choice. Habitat interslope-adaptive selection across the transcriptome and mate choice substantiate sympatric speciation (SS), suggesting its prevalence at EC I and commonality in nature.

Putative adaptive inter-slope divergence of transposon frequency in fruit flies (Drosophila melanogaster) at "Evolution Canyon", Mount Carmel, Israel.

BackgroundThe current analysis of transposon elements (TE) in Drosophila melanogaster at Evolution Canyon, (EC), Israel, is based on data and analysis done by our collaborators (Drs. J. Gonzalez, J. Martinez and W. Makalowski, this issue). They estimated the frequencies of 28 TEs (transposon elements) in fruit flies (D. melanogaster) from the ecologically tropic, hot, and dry south-facing slope (SFS) or “African” slope (AS) of EC and compared it with the TE frequencies on the temperate-cool and humid north-facing slope (NFS) or “European” slope (ES), separated, on average, by 250 m. The flies were sampled from two stations on each slope. We received their results, including the frequencies of each TE on each slope, and the probabilities of the statistical analyses (G-tests) of each TE separately. We continued the analysis of the inter-slope differences of the frequencies of the TEs, and based our different conclusions on that analysis and on the difference between micro (=EC) and macro (2000 km.) comparisons [Gonzalez et al. 2015 doi:10.1186/s13062-015-0075-4].ResultsOur collaborators based all their conclusions on the non-significant results of each of the individual tests of the 28 TEs. We analysed also the distribution of the TE differences between the slopes, based on their results. Thirteen TEs were more frequent on the SFS, 11 were more frequent on the NFS, and four had equal frequencies. Because of the equalizing effect of the ongoing migration, only small and temporary differences between the slopes (0 – 0.06) were regarded by us as random fluctuations (drift). Three TEs were intermediate (0.08-0.09) and await additional research. The 11 TEs with large frequency differences (0.12 – 0.22) were regarded by us as putative adaptive TEs, because the equalizing power of ongoing migration will eliminate random large differences. Five of them were higher on the SFS and six were higher on the NFS. Gaps in the distribution of the differences distinguished between the large and small differences. The large gap among the 11 TEs favored on the NFS was significant and supports our rejection of drift as the only explanation of the distribution of the slope differences. The gaps in the distribution of the differences separated the putative TEs with strong enough selection from those TEs that couldn't overrule the migration.The results are compared and contrasted with the directional effect of the frequencies of the same TEs in the study of global climatic comparisons across thousands of kilometers. From the 11 putative adaptive TEs in the local “Evolution Canyon,” six differentiate in the same direction as in the continental comparisons and four in the opposite direction. One TE, FBti0019144, differentiated in EC in the same direction as in Australia and in the opposite direction to that of North America.ConclusionsWe presume that the major divergent evolutionary driving force at the local EC microsite is natural selection overruling gene flow. Therefore, after we rejected drift as an explanation of all the large slope differences, we regarded them as putatively adaptive. In order to substantiate the individual TE adaptation, we need to increase the sample sizes and reveal the significant adaptive TEs.The comparison of local and global studies show only partial similarity in the adaptation of the TEs, because of the dryness of the ecologically tropical climate in EC, in contrast to the wet tropical climate in the global compared climates. Moreover, adaptation of a TE may be expressed only in part of the time and specific localities.ReviewersReviewed by Eugene Koonin, Limsoon Wong and Fyodor Kondrashov. For the full reviews, please go to the Reviewers’ comments section.Electronic supplementary materialThe online version of this article (doi:10.1186/s13062-015-0074-5) contains supplementary material, which is available to authorized users.

Natural selection causes adaptive genetic resistance in wild emmer wheat against powdery mildew at "Evolution Canyon" microsite, Mt. Carmel, Israel.

Background“Evolution Canyon” (ECI) at Lower Nahal Oren, Mount Carmel, Israel, is an optimal natural microscale model for unraveling evolution in action highlighting the basic evolutionary processes of adaptation and speciation. A major model organism in ECI is wild emmer, Triticum dicoccoides, the progenitor of cultivated wheat, which displays dramatic interslope adaptive and speciational divergence on the tropical-xeric “African” slope (AS) and the temperate-mesic “European” slope (ES), separated on average by 250 m.MethodsWe examined 278 single sequence repeats (SSRs) and the phenotype diversity of the resistance to powdery mildew between the opposite slopes. Furthermore, 18 phenotypes on the AS and 20 phenotypes on the ES, were inoculated by both Bgt E09 and a mixture of powdery mildew races.ResultsIn the experiment of genetic diversity, very little polymorphism was identified intra-slope in the accessions from both the AS or ES. By contrast, 148 pairs of SSR primers (53.23%) amplified polymorphic products between the phenotypes of AS and ES. There are some differences between the two wild emmer wheat genomes and the inter-slope SSR polymorphic products between genome A and B. Interestingly, all wild emmer types growing on the south-facing slope (SFS=AS) were susceptible to a composite of Blumeria graminis, while the ones growing on the north-facing slope (NFS=ES) were highly resistant to Blumeria graminis at both seedling and adult stages.Conclusion/SignificanceRemarkable inter-slope evolutionary divergent processes occur in wild emmer wheat, T. dicoccoides at EC I, despite the shot average distance of 250 meters. The AS, a dry and hot slope, did not develop resistance to powdery mildew, whereas the ES, a cool and humid slope, did develop resistance since the disease stress was strong there. This is a remarkable demonstration in host-pathogen interaction on how resistance develops when stress causes an adaptive result at a micro-scale distance.

Sympatric incipient speciation of spiny miceAcomysat “Evolution Canyon,” Israel

Does the paucity of empirical evidence of sympatric speciation in nature reflect reality, despite theoretical support? Or is it due to inappropriate searches in nature with overly restrictive assumptions and an incorrect null hypothesis? Spiny mice, Acomys, described here at Evolution Canyon (EC) incipiently and sympatrically speciate owing to microclimatic interslope divergence. The opposite slopes at EC vary dramatically, physically and biotically, representing the dry and hot south-facing slope savannoid-African continent ["African" slope (AS)], abutting with the north-facing slope forested south-European continent ["European" slope (ES)]. African-originated spiny mice, of the Acomys cahirinus complex, colonized Israel 30,000 y ago based on fossils. Genotypically, we showed significantly higher genetic diversity of mtDNA and amplified fragment length polymorphism of Acomys on the AS compared with the ES. This is also true regionally across Israel. In complete mtDNA, 25% of the haplotypes at EC were slope-biased. Phenotypically, the opposite slope's populations also showed adaptive morphology, physiology, and behavior divergence paralleling regional populations across Israel. Preliminary tests indicate slope-specific mate choices. Colonization of Acomys at the EC first occurred on the AS and then moved to the ES. Strong slope-specific natural selection (both positive and negative) overrules low interslope gene flow. Both habitat slope selection and mate choices suggest ongoing incipient sympatric speciation. We conclude that Acomys at the EC is ecologically and genetically adaptively, incipiently, sympatrically speciating on the ES owing to adaptive microclimatic natural selection.

Population-genetic analysis of HvABCG31 promoter sequence in wild barley (Hordeum vulgare ssp. spontaneum)

BackgroundThe cuticle is an important adaptive structure whose origin played a crucial role in the transition of plants from aqueous to terrestrial conditions. HvABCG31/Eibi1 is an ABCG transporter gene, involved in cuticle formation that was recently identified in wild barley (Hordeum vulgare ssp. spontaneum). To study the genetic variation of HvABCG31 in different habitats, its 2 kb promoter region was sequenced from 112 wild barley accessions collected from five natural populations from southern and northern Israel. The sites included three mesic and two xeric habitats, and differed in annual rainfall, soil type, and soil water capacity.ResultsPhylogenetic analysis of the aligned HvABCG31 promoter sequences clustered the majority of accessions (69 out of 71) from the three northern mesic populations into one cluster, while all 21 accessions from the Dead Sea area, a xeric southern population, and two isolated accessions (one from a xeric population at Mitzpe Ramon and one from the xeric ‘African Slope’ of “Evolution Canyon”) formed the second cluster. The southern arid populations included six haplotypes, but they differed from the consensus sequence at a large number of positions, while the northern mesic populations included 15 haplotypes that were, on average, more similar to the consensus sequence. Most of the haplotypes (20 of 22) were unique to a population. Interestingly, higher genetic variation occurred within populations (54.2%) than among populations (45.8%). Analysis of the promoter region detected a large number of transcription factor binding sites: 121–128 and 121–134 sites in the two southern arid populations, and 123–128,125–128, and 123–125 sites in the three northern mesic populations. Three types of TFBSs were significantly enriched: those related to GA (gibberellin), Dof (DNA binding with one finger), and light.ConclusionsDrought stress and adaptive natural selection may have been important determinants in the observed sequence variation of HvABCG31 promoter. Abiotic stresses may be involved in the HvABCG31 gene transcription regulations, generating more protective cuticles in plants under stresses.

Eastern boundary drainage of the North Atlantic subtropical gyre

The eastern boundary of the North Atlantic subtropical gyre (NASG) is an upwelling favorable region characterized by a mean southward flow. The Canary Upwelling Current (CUC) feeds from the interior ocean and flows south along the continental slope off NW Africa, effectively providing the eastern boundary condition for the NASG. We follow a joint approach using slope and deep-ocean data together with process-oriented modeling to investigate the characteristics and seasonal variability of the interior–coastal ocean connection, focusing on how much NASG interior water drains along the continental slope. First, the compiled sets of data show that interior central waters flow permanently between Madeira and the Iberian Peninsula at a rate of 2.5 ± 0.6 Sv (1 Sv = 106 m3 s-1 109 km s-1), with most of it reaching the slope and shelf regions north of the Canary Islands (1.5 ± 0.7 Sv). Most of the water entering the African slope and shelf regions escapes south between the easternmost Canary Islands and the African coast: In 18 out of 22 monthly realizations, the flow was southward (−0.9 ± 0.4 Sv) although an intense flow reversal occurred usually around November (1.7 ± 0.9 Sv), probably as the result of a late fall intensification of the CUC north of the Canary Islands followed by instability and offshore flow diversion. Secondly, we explore how the eastern boundary drainage may be specified in a process-oriented one-layer quasigeostrophic numerical model. Non-zero normal flow and constant potential vorticity are alternative eastern boundary conditions, consistent with the idea of anticyclonic vorticity induced at the boundary by coastal jets. These boundary conditions cause interior water to exit the domain at the boundary, as if recirculating through the coastal ocean, and induce substantial modifications to the shape of the eastern NASG. The best model estimate for the annual mean eastward flow north of Madeira is 3.9 Sv and at the boundary is 3.3 Sv. The water exiting at the boundary splits with 1 Sv flowing into the Strait of Gibraltar and the remaining 2.3 Sv continuing south along the coastal ocean until the latitude of Cape Ghir. The model also displays significant wind-induced seasonal variability, with a maximum connection between the interior and coastal oceans taking place in autumn and winter, in qualitative agreement with the observations.

Adaptive microclimatic evolution of the dehydrin 6 gene in wild barley at “Evolution Canyon”, Israel

Dehydrins are one of the major stress-induced gene families, and the expression of dehydrin 6 (Dhn6) is strictly related to drought in barley. In order to investigate how the evolution of the Dhn6 gene is associated with adaptation to environmental changes, we examined 48 genotypes of wild barley, Hordeum spontaneum, from "Evolution Canyon" at Mount Carmel, Israel. The Dhn6 sequences of the 48 genotypes were identified, and a recent insertion of 342bp at 5'UTR was found in the sequences of 11 genotypes. Both nucleotide and haplotype diversity of single nucleotide polymorphism in Dhn6 coding regions were higher on the AS ("African" slope or dry slope) than on the ES ("European" slope or humid slope), and the applied Tajima D and Fu-Li test rejected neutrality of SNP diversity. Expression analysis indicated that the 342bp insertion at 5'UTR was associated with the earlier up-regulation of Dhn6 after dehydration. The genetic divergence of amino acids sequences indicated significant positive selection of Dhn6 among the wild barley populations. The diversity of Dhn6 in microclimatic divergence slopes suggested that Dhn6 has been subjected to natural selection and adaptively associated with drought resistance of wild barley at "Evolution Canyon".

Benthic phosphorus and iron budgets for three NW African slope sediments: a balance approach

Abstract. Despite intensive research on the different domains of the marine phosphorus (P) cycle during the last decades, frequently discussed open questions still exist especially on controlling factors for the benthic behaviour of P and its general distribution in sediment-pore water systems. Steady state or the internal balance of all relevant physical and (bio)geochemical processes are amongst the key issues. In this study we present and discuss an extended data set from surface sediments recovered from three locations on the NW African continental slope. Pore water data and results from sequential sediment extractions give clear evidence to the well-known close relationship between the benthic cycles of P and iron. Accordingly, most of the dissolved phosphate must have been released by microbially catalyzed reductive dissolution of iron (oxhydr)oxides. However, rates of release and association of P and iron, respectively, are not directly represented in profiles of element specific sediment compositions. Results from steady-state based transport-reaction modelling suggest that particle mixing due to active bioturbation, or rather a physical net downward transport of P associated to iron (oxyhydr)oxides, is an essential process for the balance of the inspected benthic cycles. This study emphasizes the importance of balancing analytical data for a comprehensive understanding of all processes involved in biogeochemical cycles.