Semi-arid Populations Research Articles

Patterns of Genetic Diversity and Gene Flow Associated With an Aridity Gradient in Populations of Common Mole-rats, Cryptomys hottentotus hottentotus.

Genetic adaptation is the change of a population toward a phenotype that best fits the present ecological conditions of the environment it inhabits. As environmental conditions change, allele frequencies shift, resulting in different populations of the same species possessing genetic variation and divergent phenotypes. Cooperatively breeding common mole-rats (Cryptomys hottentotus hottentotus) inhabit environments along an aridity gradient in South Africa, which provides an opportunity for local genetic adaptations to occur. Using one mitochondrial gene (cytochrome b) and 3,540 SNP loci across the whole genome, we determined the phylogenetic relationship, population structure and genetic diversity of five populations of C. h. hottentotus located along an aridity gradient. Mitochondrial data identified population-specific clades that were less distinct in the two mesic populations, potentially indicating historical or recent gene flow, or the retention of ancestral haplotypes. Arid and semi-arid populations formed a distinct cluster from the non-arid populations. Genetic diversity and gene flow were higher in arid-dwelling individuals, suggesting greater connectivity and interactions between colonies in arid regions in comparison to mesic ones. Using an Aridity Index, we determined that isolation by environment, rather than isolation by geographical distance, best explains the genetic distance between the populations. Further analyses using target loci may determine if there are differing underlying genetic adaptations among populations of C. h. hottentotus. These analyses could help unravel population differences in response to environmental factors within a subspecies of bathyergid mole-rat and determine the adaptive capacity of this small nonmigratory subterranean rodent species in response to aridification in the face of climate change.

Unraveling the defensive strategies of camel thorn Alhagi maurorum medik. For thriving in arid and semi-arid environments

The study aimed to evaluate the role of morpho-physiological and anatomical attributes of Alhagi maurorum Medik. Populations from five water deficit regions in Punjab province, Pakistan, namely, Cholistan desert (KHP), Rajanpur (DGK), Thal (LYH), Patisar Lake (LAS), and Salt Range (WSM), in their adaptability to arid and semi-arid regions. The study sheds light on the adaptive components of various plant populations to cope with increasing dryness ratio. Arid populations [Khanpur-KHP (D = 44.91, P = 97.1 mm), Dera Ghazi Khan-DGK (D = 41.41, P = 105.3 mm), Layyah-LYH (D = 37.11, P = 117.5 mm) and Ladamsar-LAS (D = 34.83, P = 125.2 mm)] relied on larger roots and leaves, enhanced biomass production, ion accumulation, and photosynthetic pigments. It also encompassing larger root and stem cellular area, cortex and vascular region, thicker leaves, and numerous large stomata. Semi-arid populations display distinctive changes, such as longer shoots, higher root and shoot Na+ levels, organic osmolytes, thicker epidermis, and enlarged pith region in stems [Warcha Salt Mine-WSM (D = 8.70, P = 501 mm)]. These modifications at both structural and functional levels guarantee the survival and success of this species in challenging environmental conditionswhich will have implications for sustainable agriculture, ecosystem restoration, and adaptation to climate change adaptation in arid and semi-arid regions.

Seed germination ecology of Conyza sumatrensis populations stemming from different habitats and implications for management.

Conyza sumatrensis (Retz.) E. H. Walker is an obnoxious weed, emerging as an invasive species globally. Seed germination biology of four populations of the species stemming from arid, semi-arid, temperate, and humid regions was determined in this study. Seed germination was recorded under six different environmental cues (i.e., light/dark periods, constant and alternating day and night temperatures, pH, salinity, and osmotic potential levels) in separate experiment for each cue. Populations were main factor, whereas levels of each environmental cue were considered as sub-factor. The impact of seed burial depths on seedling emergence was inferred in a greenhouse pot experiment. Seed germination was recorded daily and four germination indices, i.e., seed germination percentage, mean germination time, time to reach 50% germination, and mean daily germination were computed. Tested populations and levels of different environmental cues had significant impact on various seed germination indices. Overall, seeds stemming from arid and semi-arid regions had higher seed germination potential under stressful and benign environmental conditions compared to temperate and humid populations. Seed of all populations required a definite light period for germination and 12 hours alternating light and dark period resulted in the highest seed germination. Seed germination of all populations occurred under 5–30°C constant and all tested alternate day and night temperatures. However, the highest seed germination was recorded under 20°C. Seeds of arid and semi-arid populations exhibited higher germination under increased temperature, salinity and osmotic potential levels indicating that maternal environment strongly affected germination traits of the tested populations. The highest seed germination of the tested populations was noted under neutral pH, while higher and lower pH than neutral had negative impact on seed germination. Arid and semi-arid populations exhibited higher seed germination under increased pH compared to temperate and humid populations. Seed burial depth had a significant effect on the seedling emergence of all tested populations. An initial increase was noted in seedling emergence percentage with increasing soil depth. However, a steep decline was recorded after 2 cm seed burial depth. These results indicate that maternal environment strongly mediates germination traits of different populations. Lower emergence from >4 cm seed burial depth warrants that deep burial of seeds and subsequent zero or minimum soil disturbance could aid the management of the species in agricultural habitats. However, management strategies should be developed for other habitats to halt the spread of the species.

Public policies on water resources for the brazilian northeastern semiarid region

ABSTRACT
 Objective: The present study has as main objective to identify the strategies taken by the municipal managers to adapt to the periods of greatest water difficulties in the northeastern semiarid, more specifically in the city of Doutor Severiano-RN, showing the importance of the development of these strategies in the region. Methodology / Approach: Research were made on the subject to identify which strategies were developed in the municipality, in addition, some field observations were made to identify the municipal public policies developed over the years. Conclusions: It is concluded with this study that it is essential to know the place and seek the best strategy to develop and apply these policies based on the characteristics of each region, considering the importance that they have for the social and economic development of the semiarid populations. Research limitations: The sample was extracted from works that addressed the topic in question, thus making the parallel of discourse between theory and practice. Originality / Value of the article: The study presents the strategies developed in the city of Doutor Severiano, to adapt to the periods of greatest water difficulties in the region, according to the climatic conditions of the place.

Population origin, maternal effects, and hydric conditions during incubation determine embryonic and offspring survival in a desert-dwelling lizard.

While the effects of incubation environment on embryonic development and offspring traits have been extensively studied in oviparous vertebrates, studies into how genetic inheritance (population origin), maternal effects, and incubation environment interact to produce varying phenotypes, are rare. To elucidate the interactive role of those three factors during incubation in shaping offspring phenotypes through hydric conditions, we conducted a fully factorial experiment [arid and semiarid populations × maternal dry and wet treatments (MDT and MWT) × embryonic dry and wet treatments (EDT and EWT)] with a desert-dwelling lacertid lizard (Eremias argus). Female lizards in dry conditions produced larger clutch sizes but smaller eggs. The incubation period and hatching success were significantly affected by embryonic but not by maternal moisture treatments. Eggs in the EDT hatched later than those in the EWT in both arid and semiarid populations. Hatching success was lower in EDT than in EWT in the semiarid population, but not in the arid population. Hatchlings from the EDT had a slower post-hatch increase in body mass than those from the EWT. EDT would decrease the survival rates of hatchlings in the semiarid population only. In addition, structural equation models revealed that population had a stronger effect on embryonic and offspring survival than maternal and embryonic moisture. Our study demonstrates locally adaptive strategies of drought resistance at multiple life-history stages in lizard populations from diverse hydric habitats and highlights the importance of genetic factors in determining embryonic drought resistance in oviparous lizards.

Application of statistical control on water quality in cisterns in the semiarid Pernambucano

In the Brazilian semi-arid region, it is necessary to use alternatives for the better use of water, since evapotranspiration rates exceed rainfall rates, which may favor salt accumulation in cistern systems. This work aimed to investigate the water quality of cisterns from communities in the semiarid region of Pernambuco state. Thus, the following physicochemical and microbiological characteristics of cistern water were monitored: color, turbidity, total dissolved solids (T.D.S.), salinity through electrical conductivity (EC), pH and total and fecal coliforms. For monitoring, statistical quality control techniques, control charts and process capacity indices were employed. Results were found with high values for microbiological, total and fecal coliforms in most samples. Control charts showed no abnormality in the process. The probable reasons for the contamination of cistern water is the lack of cleaning of the gutters that are part of the stored water catchment system. In the northeastern semi-arid population, people are looking for ways to use natural resources to ensure survival and water quality is seen as a guarantee for quality of life.

Biogeographic venom variation in Russell's viper (Daboia russelii) and the preclinical inefficacy of antivenom therapy in snakebite hotspots.

BackgroundSnakebite in India results in over 58,000 fatalities and a vast number of morbidities annually. The majority of these clinically severe envenomings are attributed to Russell’s viper (Daboia russelii), which has a near pan-India distribution. Unfortunately, despite its medical significance, the influence of biogeography on the composition and potency of venom from disparate D. russelii populations, and the repercussions of venom variation on the neutralisation efficacy of marketed Indian antivenoms, remain elusive.MethodsHere, we employ an integrative approach comprising proteomic characterisation, biochemical analyses, pharmacological assessment, and venom toxicity profiling to elucidate the influence of varying ecology and environment on the pan-Indian populations of D. russelii. We then conducted in vitro venom recognition experiments and in vivo neutralisation assays to evaluate the efficacy of the commercial Indian antivenoms against the geographically disparate D. russelii populations.FindingsWe reveal significant intraspecific variation in the composition, biochemical and pharmacological activities and potencies of D. russelii venoms sourced from five distinct biogeographic zones across India. Contrary to our understanding of the consequences of venom variation on the effectiveness of snakebite therapy, commercial antivenom exhibited surprisingly similar neutralisation potencies against the majority of the investigated populations, with the exception of low preclinical efficacy against the semi-arid population from northern India. However, the ability of Indian antivenoms to counter the severe morbid effects of Daboia envenoming remains to be evaluated.ConclusionThe concerning lack of antivenom efficacy against the north Indian population of D. russelii, as well as against two other ‘big four’ snake species in nearby locations, underscores the pressing need to develop pan-India effective antivenoms with improved efficacy in high snakebite burden locales.

Soil predictors are crucial for modelling vegetation distribution and its responses to climate change

Bioclimatic envelope models have been extensively used to predict the vegetation dynamics in response to climate changes. However, they are prone to the uncertainties arising from General Circulation Models (GCMs), classification algorithms and predictors, with low-resolution results and little detail at the regional level. Novel research has focused on the improvement of these models through a combination of climate and soil predictors to enhance ecological consistency. In this framework, we aimed to apply a joint edaphoclimatic envelope to predict the current and future vegetation distribution in the semiarid region of Brazil, which encompasses several classes of vegetation in response to the significant environmental heterogeneity. We employed a variety of machine learning algorithms and GCMs under RCP 4.5 and 8.5 scenarios of Coupled Model Intercomparison Project Phase 5 (CMIP5), in 1 km resolution. The combination of climate and soil predictors resulted in higher detail at landscape-scale and better distinction of vegetations with overlapping climatic niches. In forecasts, soil predictors imposed a buffer effect on vegetation dynamics as they reduced shifts driven solely by climatic drift. Our results with the edaphoclimatic approach pointed to an expansion of the dry Caatinga vegetation, ranging from an average of 16% to 24% on RCP 4.5 and RCP8.5 scenarios, respectively. The shift in environmental suitability from forest to open and dry vegetation implies a major loss to biodiversity, as well as compromising the provision of ecosystem services important for maintaining the economy and livelihoods of the world's largest semiarid population. Predicting the most susceptible regions to future climate change is the first step in developing strategies to mitigate impacts in these areas.

Hunting and Use of Wildlife Species in the Semi-Arid Region of Brazil

This article investigates the socio-cultural and ecological aspects associated with the hunting of wild animals by the inhabitants of the Cruz village, State of Alagoas. The data was obtained through semi-structured interviews and informal conversations. A total of 23 species was indicated as a game, with mammals being preferred by the population. Among the techniques of capture, the hunting of persecution with dog and hunting with a shotgun stands out, in addition to the shuttlecock, used to reach the birds with small stones. Four forms of animal use were recorded: food, medicine, pets, and control. Despite being indicated as one of the main causes of the reduction of wildlife, hunting is strongly related to the socio-cultural aspects of the Brazilian semi-arid populations. Thus, proposals for the management of wildlife resources in traditional communities must take into account the needs of these populations.

An analysis of subspecific variation of the honeybee, Apis mellifera L., in parts of West and Central Africa using microsatellite polymorphism

The variation of two (humid and semiarid) populations of the honeybee, Apis mellifera L., from western Africa, was analysed, using microsatellite polymorphism of nuclear DNA. One worker was sampled from each of 133 colonies collected from 38 localities in Nigeria, Niger, Cameroon and Chad and analysed for 15 loci. A total of 292 different alleles were recorded for the 15 microsatellite loci. All loci were polymorphic and the number of different alleles per locus ranged between 10, in locus At163, and 31, in locus A029, while allelic frequencies ranged from 0.007 to 0.569. The mean number of different alleles per locus was 19.5 ± S.E 1.1. The unbiased expected heterozygosity was 0.861 ± S.E. 0.017 for the combined populations and 0.859 ± S.E. 0.023 and 0.864 ± S.E. 0.026 for the humid and semiarid populations, respectively. The overall FST value, which is a good estimate of genetic differentiation of populations, was very low: 0.007 ± S.E. 0.001 (0.001 - 0.014) and AMOVA revealed that the two populations were not significantly different from each other (p > 0.05). Similarly, Raymond and Rousset’s exact test of population differentiation revealed that the two populations were not significantly differentiated at p = 0.05. Furthermore a Bayesian assignment test did not produce clear grouping of the populations. In a nutshell, according to microsatellite analysis, the honeybees of the area of study belonged to a genetically undifferentiated population.

Intraspecific leaf shape at local scale determines offspring characteristics

Identifying the degree of adaptation to particular environmental constraints at small geographical scales (e.g., intra-population variability) is particularly valuable to select plant reproductive material in restoration projects. We analyzed possible differences among progeny characteristics of Quercus coccifera L. a species of interest in forest restoration under Mediterranean climates. The differences were tested among seeds and seedlings from two phenotypic groupings (small and large leaves) within one provenance under semi-arid climate. In addition, these seeds and seedlings were compared with those from a near population under contrasted climate (i.e., subhumid climate). We analyzed differences in germination, growth and seedling morphological traits (height, number of leaves and canopy area). We considered the different characteristics of the progeny across different parent individuals, intra- and inter-population levels. We found seed provenance effects on germination and seedling morphology at different scales. Progenies from semi-arid populations and from parent plants with a smaller leaf size showed lower germination rates and lower development of above-ground structures (shoots and leaves). Our results suggest that intrapopulation variability for phenotypic traits, such as leaf size, could influence offspring fitness. In addition, these morphological traits are easily identifiable by stakeholders and could be a useful tool to ensure early plant establishment in reforestation programs.

Lack of ovarian skew in an allodapine bee and the evolution of casteless social behaviour

Facultatively social species exhibit varying degrees of reproductive skew that provide valuable insights into the possible evolutionary forces shaping the origins of obligate eusocial colony organisation, wherein the majority of individuals (workers) forgo direct reproduction. Here we report aspects of the nesting biology of a semi-arid population of the allodapine bee Exoneurella setosa, which forms social colonies that lack reproductive hierarchies and are therefore ‘casteless’; an intriguing discovery given that a congeneric eusocial species exhibits the greatest morphological distinction between queen and worker castes in the entire subfamily Xylocopinae (Apidae). Exoneurella setosa exhibited a modal colony size of two females per nest and we analysed nest-mate differentiation in ovarian development, body size and wing wear (a proxy for foraging activity). We then contrasted empirical results with Monte Carlo-simulated colonies to ascertain that multifemale nests lack evidence for reproductive skew. Our results suggest that nest-site limitation is a key driver for eusocial organisation within the Xylocopinae and that the absence of such environmental limitations, combined with minor benefits for group nesting, can select for casteless social organisation.

Variability in <i>Ziziphora clinopodioides </i>subsp. <i>bungeana</i> (Juz.) Based on Morphological Traits and Essential Oils Profile

Variability among populations of Ziziphora clinopodioides Lam. subsp. bungeana (Juz.) was analyzed, to evaluate the level and distribution of differentiation among four distant populations from sub-humid, upper semi-arid and semi-arid bioclimates of Khorasan provinces, Iran. Analyses of variances and cluster analysis have been carried out to define the variability and significance of morphological differentiation. Morphological differentiation was correlated with ecological situations at the location of origination and a high variation among populations based on morphological traits was observed between the plants belonging to semi-arid populations vs. the sub-humid ones. Essential oil composition varied among populations. In all of the populations pulegone was the main component, followed by isomentone and thymol. The clustering, based on oil analysis generated two distinct clusters. Essential oils of the upper semi-arid and sub-humid populations were rich in Iso-menthone, while populations from the semi-arid bioclimate were characterized by high amounts of pulegone. The relatively low morpho-chemical diversity in the populations of Z. clinopodioides indicates that the maintenance of their evolutionary potential is at risk if population sizes are not maintained and if there is no protection of the habitats.

Individual and demographic consequences of reduced body condition following repeated exposure to high temperatures

Although the lethal consequences of extreme heat are increasingly reported in the literature, the fitness costs of exposure to sublethal high air temperatures, typically identified in the 30-40 degrees C range, are poorly understood. We examine the effect of high (> or = 35 degrees C) daily maxima on body condition of a semiarid population of White-plumed Honeyeaters, Ptilotula penicillatus, monitored between 1986 and 2012. During this 26-yr period, temperature has risen, on average, by 0.06 degrees C each year at the site, the frequency of days with thermal maxima > or = 35 degrees C has increased and rainfall has declined. Exposure to high temperatures affected body condition of White-plumed Honeyeaters, but only in low-rainfall conditions. There was no effect of a single day of exposure to temperatures > or = 35 degrees C but repeated exposure was associated with reduced body condition: 3.0% reduction in body mass per day of exposure. Rainfall in the previous 30 d ameliorated these effects, with reduced condition evident only in dry conditions. Heat-exposed males with reduced body condition were less likely to be recaptured at the start of the following spring; they presumably died. Heat-exposed females, regardless of body condition, showed lower survival than exposed males, possibly due to their smaller body mass. The higher mortality of females and smaller males exposed to temperatures > or = 35 degrees C may have contributed to the increase in mean body size of this population over 23 years. Annual survival declined across time concomitant with increasing frequency of days > or = 35 degrees C and decreasing rainfall. Our study is one of few to identify a proximate cause of climate change related mortality, and associated long-term demographic consequence. Our results have broad implications for avian communities living in arid and semiarid regions of Australia, and other mid-latitudes regions where daily maximum temperatures already approach physiological limits in regions affected by both decreased precipitation and warming.

Variability of the Root Essential Oils of Seseli rigidumWaldst. & Kit. (Apiaceae) from Different Populations in Serbia

The chemical compositions of the essential oils of seven natural populations of Seseli rigidum were analyzed. The essential-oil yield ranged from 0.16 to 2.09%. Analysis of variance (ANOVA) revealed that there were no statistically significant differences in the mean essential-oil yields between the populations, and no significant influence of the climate or soil type on the oil yield was observed. In all 67 analyzed samples, the polyacetylene falcarinol was the main compound, followed by octanal, methyl linoleate, α-muurolene, 3-butylphthalide, falcarinone, muurola-4,10(14)-dien-1β-ol, β-sesquiphellandrene, salvial-4(14)-en-1-one, δ-amorphene, spathulenol, and isospathulenol. The principal component analysis (PCA), the canonical discriminant analysis (CDA), and the cluster analysis (CA) revealed differentiation between the populations based on the climate. Three groups of populations were formed; the first group was composed of samples growing in regions with a humid climate, with oils having high falcarinol and low sesquiterpene contents, and the second and third groups comprised samples exposed to semi-arid climate, with oils characterized by a lower falcarinol and higher α-muurolene, δ-amorphene, β-sesquiphellandrene, and salvial-4(14)-en-1-one contents. The semi-arid populations were divided into two groups, which were distinguished based on the oil contents of sesquiterpenes, falcarinone, and 3-butylphthalide. On the other hand, no clear separation between populations based on the different soil types could be observed.

Branching the risks: architectural plasticity and bet‐hedging in Mediterranean annuals

It has been suggested that architectural plasticity in shoot size and number allows plants to manage environmental risks. Simpler structures require shorter development times and fewer resources, which secure minimal fitness even under risky and unfavourable conditions. Here we tested the hypothesis that the magnitude of such architectural plasticity depends on the species' developmental strategy. Specifically, species with late reproduction were expected to express the highest levels of architectural plasticity in response to environmental cues predicting high probability of abrupt deterioration in growth conditions. This hypothesis was tested by comparing Mediterranean and semi-arid populations of three species, which differed in growth strategy: Trifolium purpureum, a determinate and late flowerer, and Emex spinosa and Hippocrepis unisiliquosa that flower indeterminately throughout the season. All plants were exposed to varying levels of water availability and competition, but only T.purpureum displayed plastic architectural responsiveness to the experimental manipulations. In contrast, the early and extended step-by-step flowering of both E.spinosa and H.unisiliquosa reflected a relatively deterministic bet-hedging reproductive schedule, whereby minimum fitness is secured even under adverse conditions. These two opposing strategies gave contrasting results, with E.spinosa and H.unisiliquosa displaying reduced efficiency under favourable conditions under which T.purpureum had the highest reproductive efficiency. The evolutionary interplay between deterministic risk-averse and plastic risk-prone growth strategies might reflect contrasts in the probability and severity of environmental risks, and the costs of missed opportunities.

Genetic variability of Tunisian wild strawberry tree (Arbutus unedo L.) populations interfered from isozyme markers

In Tunisia, Arbutus unedo populations are severely destroyed due to deforestation and over-collecting. The species occurs in small scattered populations decreasing progressively in size. Yet, there is a lack of information's regarding the amount of genetic diversity and its repartition for this resource. In this work, we analyzed the polymorphism of six isozymes in order to assess genetic variability and structuring of 15 natural populations prospected in three geographical areas. The analysis of the level and the distribution of the genetic diversity in this species might help in its conservation. Out of the 13 loci detected for all populations and isozymes analyzed, 4 loci were polymorphic. Allelic frequencies differed according to populations and particular alleles characterized ecological groups. A high genetic diversity within populations (Ap=2.2; P=63.33%) was observed. A relatively low level of differentiation (FST=0.031) coupled with a high gene flow among populations (Nm=6.81) were revealed. The differentiation of populations within the same bioclimate group was substantial and the upper semi-arid populations showed the highest differentiation (FST=0.093). The relationship between FST and geographic distance matrices was not significant, indicating that the genetic structure among populations is not affected by geographic barriers but it is rather related to ecological factors such as altitudes and rainfall. Nei's (1978) genetic distances among pairs of populations were low (0.001–0.030). The UPGMA cluster based on these distances showed three sub-clusters. Population groupings occur without evident relationship to bioclimates or geographic regions indicating that differentiation occurs at a local space scale. The species conservation strategies (in situ or ex situ) and the selection of genotypes should take into account the genetic diversity level within populations.

Photo-thermal regulation of seed germination in natural populations of Eruca sativa Miller (Brassicaceae)

Populations of the winter annual Eruca sativa in Israel are distributed along a climatic gradient, from Mediterranean mesic habitats in the north to semi-arid and arid habitats in the south. Seed cohorts of five populations sampled across the gradient were produced in a common-garden experiment, and their germination was tested under continuous light or darkness at 5–35 °C, as well as with alternating 30/20 and 25/15 °C temperatures under a 12/12 h photoperiod. Germination was enhanced by light and by increasing temperature. Under constant temperatures maximal germination of arid and semi-arid populations was lower than in the mesic populations, suggesting on higher levels of primary dormancy with increasing aridity. Seeds that did not germinate in darkness or at low temperatures in light, germinated almost fully when exposed to GA3 at 25 °C, indicating that imbibition under less favorable conditions induces secondary dormancy in E. sativa. Daily alternating temperatures did not affect or even reduced seed germination compared to constant 25 and 30 °C in continuous light. Exposure of dry seeds to 30 °C before imbibition increased germination to ≥80% in seed cohorts of all populations. These responses to light and temperature indicate that adaptation of E. sativa to the Mediterranean environment is associated with the ability to germinate under the relatively warm autumn temperatures, and is enhanced by exposure to high temperature during the dry summer.

Isozyme markers and volatiles in Tunisian Rosmarinus officinalis L. (Lamiaceae): A comparative analysis of population structure

Genetic and essential oil variations from 14 Tunisian natural populations of Rosmarinus officinalis L. were assessed using eight isozymes and 25 terpenoids. Isozymes were revealed by 13% gel electrophoresis. Volatiles were analysed by GC and GC–MS. Populations were collected from different regions belonging to sub-humid, upper semi-arid and upper arid bioclimates. A high genetic diversity within population was revealed by isozymes due to the species mating system and the large size of populations before fragmentation. Cluster constructed using Nei's genetic distances showed mainly bioclimatic related population groupings. A high differentiation among populations and ecological groups was observed. Essential oil composition varied among populations. Volatiles of the sub-humid and the upper semi-arid populations located in regions of Cap Bon and Tunisian Dorsal were rich in 1,8-cineole, while populations from the upper arid bioclimate (Matmata regions) were characterized by high amounts of camphor. Genetic and chemical data were highly correlated. Population differentiation performed on the two sets of data was similar to those shown using isozyme and terpenoids matrices separately. Conservation strategies should take into account genetic diversity and chemical variation levels in relation to bioclimatic and geographic location of populations.

The trade-off between breaking of dormancy of caryopses and revival ability of young seedlings of wild barley (Hordeum spontaneum)

The relationship between breaking of dormancy of wild barley (Hordeum spontaneum C. Koch) caryopses and revival ability of young seedlings from a long period of desiccation was studied using barley caryopses stored for 2 years at 5°C and freshly harvested caryopses from a semiarid population in Israel. The 2 years of storage at 5°C significantly enhanced the germination percentages, but dramatically decreased the revival ability of the young seedlings from drought stress. There was a negative correlation between the breaking of dormancy of caryopses and revival ability. There were no significant changes in the effects of storage at a high temperature for periods longer than 5 days. The earlier germination occurred, the higher the revival ability of young seedlings from drought. The results suggest that breaking of dormancy might be at the expense of lowering the subsequent revival ability of young seedlings. The general premise is that a trade-off is expected between dormancy release of caryopses and revival ability of seedlings from drought stress, and that a treatment that aims at breaking dormancy must reach some compromise that optimizes the balance between the two traits based on the specific circumstances.Key words: dormancy breaking, caryopses, revival ability, seedlings, Hordeum spontaneum, wild barley.