Desert Populations Research Articles

Fine-scale spatial genetic structure in predominantly selfing plants with limited seed dispersal: A rule or exception?

Gene flow at a fine scale is still poorly understood despite its recognized importance for plant population demographic and genetic processes. We tested the hypothesis that intensity of gene flow will be lower and strength of spatial genetic structure (SGS) will be higher in more peripheral populations because of lower population density. The study was performed on the predominantly selfing Avena sterilis and included: (1) direct measurement of dispersal in a controlled environment; and (2) analyses of SGS in three natural populations, sampled in linear transects at fixed increasing inter-plant distances. We found that in A. sterilis major seed dispersal is by gravity in close (less than 2 m) vicinity of the mother plant, with a minor additional effect of wind. Analysis of SGS with six nuclear SSRs revealed a significant autocorrelation for the distance class of 1 m only in the most peripheral desert population, while in the two core populations with Mediterranean conditions, no genetic structure was found. Our results support the hypothesis that intensity of SGS increases from the species core to periphery as a result of decreased within-population gene flow related to low plant density. Our findings also show that predominant self-pollination and highly localized seed dispersal lead to SGS at a very fine scale, but only if plant density is not too high.

Strong genetic differentiation in the invasive annual grass Bromus tectorum across the Mojave–Great Basin ecological transition zone

Bromus tectorum, an inbreeding annual grass, is a dominant invader in sagebrush steppe habitat in North America. It is also common in warm and salt deserts, displaying a larger environmental tolerance than most native species. We tested the hypothesis that a suite of habitat-specific B. tectorum lineages dominates warm desert habitats. We sampled 30 B. tectorum Mojave Desert and desert fringe populations and genotyped 10–26 individuals per population using 69 single nucleotide polymorphic (SNP) markers. We compared these populations to 11 Great Basin steppe and salt desert populations. Populations from warm desert habitats were dominated by members of two haplogroups (87 % of individuals) that were distinct from haplogroups common in Great Basin habitats. We conducted common garden studies comparing adaptive traits and field performance among haplogroups typically found in different habitats. In contrast to the haplogroup abundant in sagebrush steppe, warm desert haplogroups generally lacked a vernalization requirement for flowering. The most widespread warm desert haplogroup (Warm Desert 1) also had larger seeds and a higher root:shoot ratio than other haplogroups. In the field, performance of warm desert haplogroups was dramatically lower than the sagebrush steppe haplogroup at one steppe site, but one warm desert haplogroup performed as well as the steppe haplogroup under drought conditions at the other site. Our results suggest that B. tectorum succeeds in widely disparate environments through ecotypic variation displayed by distinct lineages of plants. Accounting for this ecotypic variation is essential in modeling its future distribution in response to climate change.

Intraspecific variation in defense against a generalist lepidopteran herbivore in populations of Eruca sativa (Mill.)

Populations of Eruca sativa (Brassicaceae) from desert and Mediterranean (Med) habitats in Israel differ in their defense against larvae of the generalist Spodoptera littoralis but not the specialist Pieris brassicae. Larvae of the generalist insect feeding on plants of the Med population gained significantly less weight than those feeding on the desert plants, and exogenous application of methyl jasmonate (MJ) on leaves of the Med plants significantly reduced the level of damage created by the generalist larvae. However, MJ treatment significantly induced resistance in plants of the desert population, whereas the generalist larvae caused similar damage to MJ-induced and noninduced plants. Analyses of glucosinolates and expression of genes in their synthesis pathway indicated that defense in plants of the Med population against the generalist insect is governed by the accumulation of glucosinolates. In plants of the desert population, trypsin proteinase inhibitor activity was highly induced in response to herbivory by S. littoralis. Analysis of genes in the defense-regulating signaling pathways suggested that in response to herbivory, differences between populations in the induced levels of jasmonic acid, ethylene, and salicylic acid mediate the differential defenses against the insect. In addition, expression analysis of myrosinase-associated protein NSP2 suggested that in plants of the desert population, glucosinolates breakdown products were primarily directed to nitrile production. We suggest that proteinase inhibitors provide an effective defense in the desert plants, in which glucosinolate production is directed to the less toxic nitriles. The ecological role of nitrile production in preventing infestation by specialists is discussed.

Seasonal and geographical variation in heat tolerance and evaporative cooling capacity in a passerine bird.

Intraspecific variation in avian thermoregulatory responses to heat stress has received little attention, despite increasing evidence that endothermic animals show considerable physiological variation among populations. We investigated seasonal (summer versus winter) variation in heat tolerance and evaporative cooling in an Afrotropical ploceid passerine, the white-browed sparrow-weaver (Plocepasser mahali; ∼ 47 g) at three sites along a climatic gradient with more than 10 °C variation in mid-summer maximum air temperature (Ta). We measured resting metabolic rate (RMR) and total evaporative water loss (TEWL) using open flow-through respirometry, and core body temperature (Tb) using passive integrated transponder tags. Sparrow-weavers were exposed to a ramped profile of progressively higher Ta between 30 and 52 °C to elicit maximum evaporative cooling capacity (N=10 per site per season); the maximum Ta birds tolerated before the onset of severe hyperthermia (Tb ≈ 44 °C) was considered to be their hyperthermia threshold Ta (Ta,HT). Our data reveal significant seasonal acclimatisation of heat tolerance, with a desert population of sparrow-weavers reaching significantly higher Ta in summer (49.5 ± 1.4 °C, i.e. higher Ta,HT) than in winter (46.8 ± 0.9 °C), reflecting enhanced evaporative cooling during summer. Moreover, desert sparrow-weavers had significantly higher heat tolerance and evaporative cooling capacity during summer compared with populations from more mesic sites (Ta,HT=47.3 ± 1.5 and 47.6 ± 1.3 °C). A better understanding of the contributions of local adaptation versus phenotypic plasticity to intraspecific variation in avian heat tolerance and evaporative cooling capacity is needed for modelling species' responses to changing climates.

Mechanisms for maintenance of dominance in a nonclonal desert shrub

Blackbrush (Coleogyne ramosissima: Rosaceae) is a slow‐growing, non‐clonal shrub that is regionally dominant on xeric, shallow soils in the North American Mojave Desert‐Great Basin transition zone and southern Colorado Plateau. Blackbrush seed production is concentrated in mast years, and most seeds are cached and later consumed by heteromyid rodents. Vegetation histories show that blackbrush stands can persist apparently unchanged for over a century. We used dendrochronological techniques to examine plant age distributions, recruitment patterns and growth rates, to ascertain how blackbrush achieves this long‐term population stability. Our study addressed the following questions: (1) What is the role of within‐clump recruitment in long‐term patterns of clump persistence? Do blackbrush clumps accrue new cohorts through time? (2) How does recruitment vary temporally, specifically in relation to years of mast seed production and climate variability? (3) What impact does intra‐specific competition have on plant growth rates? To address these questions, we aged stems from 208 clumps in five Mojave Desert and four Colorado Plateau populations. Individual plant age estimates ranged from 3 to 122 years. Clumps comprised of multiple‐aged cohorts were ubiquitous. Within clumps, plant and cohort number increased with clump age, suggesting a steady accumulation of new cohorts over time. Clumps in Colorado Plateau populations accumulated cohorts at a significantly faster rate than clumps in Mojave Desert populations. Recruitment occurred in relatively frequent pulses. It was only partially synchronized with mast years, with some seedling establishment following years of low seed production. Individuals that recruited into established clumps averaged half the radial growth rate of individuals that recruited into openings. Blackbrush recruitment is bimodal, with initial colonization of open spaces from rodent caches but with long‐term clump persistence a product of periodic, within‐clump recruitment of new plants. This dual recruitment strategy provides a mechanism for continued community dominance in an abiotically stressful environment under low levels of disturbance.

Decoupling of Sexual Reproduction and Genetic Diversity in the Female-Biased Mojave Desert MossSyntrichia caninervis(Pottiaceae)

Premise of research. If sexual reproduction is necessary for maintaining genotypic diversity, then plant populations lacking sex might be expected to exhibit less genotypic diversity than sexually reproducing populations. This pattern could be particularly pronounced in mosses of harsh environments, where haploid gametophytes persist in the apparent absence of sex, presumably through vegetative cloning. Here we compare genetic diversity in four Mojave Desert populations of the moss Syntrichia caninervis to assess the degree to which sexual reproduction is associated with genotypic diversity. This study helps define the role of reproductive modes in producing and maintaining genetic diversity.Methodology. Eight microsatellite loci were used to genotype four Mojave Desert populations of S. caninervis, which consisted of two sites with lower environmental stress and sexual reproduction and two sites with higher stress and no apparent sexual reproduction.Pivotal results. Of 341 ramets that amplified successfully across at least seven of the eight loci, 191 unique genotypes were identified; of these, 87 and 131 differed by one and two stepwise mutations, respectively. Genetic diversity was high and did not differ significantly between sexual and asexual populations. Estimates of mutation-scaled migration rates between sites ranged from four to 48 individuals per generation.Conclusions. Despite different levels of sex expression and sporophyte production, genetic and clonal diversity did not differ significantly between higher- and lower-stress populations. The relatively low population structure among sites, high number of clonal lineages, and predominance of genotypes differing by only one or two mutation steps suggests that migration and somatic mutation are responsible for the observed genotypic diversity. These results support the idea that established populations can persist through cloning and that migration can occur over large physical distances. However, retention of genotypic diversity from a time when the environment was more permissive to sexual reproduction cannot be ruled out as an influence on population structure.

Landscape genomics of Sphaeralcea ambigua in the Mojave Desert: a multivariate, spatially-explicit approach to guide ecological restoration

Local adaptation influences plant species’ responses to climate change and their performance in ecological restoration. Fine-scale physiological or phenological adaptations that direct demographic processes may drive intraspecific variability when baseline environmental conditions change. Landscape genomics characterize adaptive differentiation by identifying environmental drivers of adaptive genetic variability and mapping the associated landscape patterns. We applied such an approach to Sphaeralcea ambigua, an important restoration plant in the arid southwestern United States, by analyzing variation at 153 amplified fragment length polymorphism loci in the context of environmental gradients separating 47 Mojave Desert populations. We identified 37 potentially adaptive loci through a combination of genome scan approaches. We then used a generalized dissimilarity model (GDM) to relate variability in potentially adaptive loci with spatial gradients in temperature, precipitation, and topography. We identified non-linear thresholds in loci frequencies driven by summer maximum temperature and water stress, along with continuous variation corresponding to temperature seasonality. Two GDM-based approaches for mapping predicted patterns of local adaptation are compared. Additionally, we assess uncertainty in spatial interpolations through a novel spatial bootstrapping approach. Our study presents robust, accessible methods for deriving spatially-explicit models of adaptive genetic variability in non-model species that will inform climate change modelling and ecological restoration.

Impact of Consumption of Certain Electrolyte Rich Natural Products on the Serum Na+ and K+ Profile, Anemia and Iodine Nutriture in Desert Population of Rajasthan

To observe the impact of supplementation of some electrolyte rich natural products on the Serum Na+ and K+ profile, anemia and iodine nutriture in desert population. Double blind randomized...

Environmental metabolomics reveal geographic variation in aerobic metabolism and metabolic substrates in Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils (Meriones unguiculatus) have a large-scale distribution in northern China. Geographic physiological variations which related to energy and water metabolism are critical to animals' local adaptation and distribution. However, the underlying biochemical mechanism of such variation and its role in adaptation remains largely unknown. We used GC–MS metabolomics approach to investigate the biochemical adaptation of Mongolian gerbils from xeric (desert), transition (desert steppe) and mesic (typical steppe) environments. Gerbils in desert population had lower resting metabolic rate (RMR) and total evaporative water loss (TEWL) than mesic population. Serum metabolomics revealed that concentrations of five tricarboxylic acid cycle intermediates (citrate, cis-aconitate, α-ketoglutarate, fumarate and malate) were lower in desert population than mesic population. Gastrocnemius metabolomics and citrate synthase activity analysis showed a lower concentration of citrate and lower citrate synthase activity in desert population. These findings suggest that desert dwelling gerbils decrease RMR and TEWL via down-regulation of aerobic respiration. Gastrocnemius metabolomics also revealed that there were higher concentrations of glucose and glycolytic intermediates, but lower concentrations of lipids, amino acids and urea in desert population than mesic population. This geographic variation in metabolic substrates may enhance metabolic water production per oxygen molecule for desert population while constraining aerobic respiration to reduce RMR and TEWL.

Hwt jh(w)t, The Administration of the Western Delta and the ‘Libyan Question’ in the Third Millennium BC*

Third millennium Hwt jh(w)t is a locality that stands apart from other Lower Egyptian sites. Its unique archaeological and epigraphic record provides an invaluable view of the role played by a Delta centre within the administrative and productive organisation of the kingdom in the third millennium bc. It thus appears that Hwt jh(w)t was a kind of checkpoint regulating access to grazing land and plant resources in the underpopulated Western Delta. Furthermore, this was a region where Libyan populations historically settled and exploited its pasture land. Finally, traces of exchange networks in the hands of both mobile desert populations (Libyans in the oases and the north, Nubians in the south) and autonomous Egyptians, apparently operating outside any institutional framework, are becoming increasingly evident across Egypt. The resulting picture is that of a complex interaction of partly complementary, partly competing interests involving nomad pastoral populations, Egyptian settlers, and the Pharaonic state. Occasional conflicts should therefore be interpreted in the light of such interests, as the consequence of competing strategies seeking to control local resources, exchange networks and flows of wealth. Thus, concepts such as ‘Libyan invasions’, stereotyped views of Libyans as poor wandering nomads, or the alleged contrast between sedentary Egyptians and nomad Libyans as distinct, opposed ethnic and productive entities should also be revised.

A Continuum of Behavioral Plasticity in Urban and Desert Black Widows

AbstractBehavioral plasticity marks an individual's ability to modulate behavior across functional contexts. Behavioral syndromes, on the other hand, appear as consistent individual variation in behavior that is both repeatable for individuals within a functional context (e.g., consistent voracity toward prey) and correlated across contexts (e.g., high voracity toward prey and high levels of boldness toward enemies). Thus, adaptive plasticity and syndromes represent two extremes of a behavioral plasticity continuum upon which most behavioral phenotypes fall. We tested for both adaptive plasticity and behavioral syndromes in the western black widow spider, Latrodectus hesperus. We measured behavior in three contexts: startle, startle + prey, and startle + mate, and found (1) classic behaviorally plastic responses to predation risk, (2) high repeatability of behavior within contexts, and (3) evidence of a correlation between startle + prey and startle + mate contexts, indicative of a behavioral syndrome. As relative behavioral plasticity may vary across populations, we also compared urban and desert populations to test whether spiders from these habitats exhibit different behaviors and/or behavioral syndromes. While we found that urban males used in mating trials courted urban females significantly more than desert females, we found no other differences in the behavior of urban and desert black widows. Thus, black widows, regardless of habitat, are characterized by both context‐specific behavioral plasticity and across‐context correlations, presenting a phenotypic complexity that is likely exhibited, to varying degrees, by most organisms.

Should I stay or should I go? Dispersal and population structure in small, isolated desert populations of West African crocodiles.

The maintenance of both spatial and genetic connectivity is paramount to the long-term persistence of small, isolated populations living in environments with extreme climates. We aim to identify the distribution of genetic diversity and assess population sub-structuring and dispersal across dwarfed desert populations of Crocodylus suchus, which occur in isolated groups, usually less than five individuals, along the mountains of Mauritania (West Africa). We used both invasive and non-invasive sampling methods and a combination of mitochondrial DNA (12 S and ND4) and microsatellite markers (32 loci and a subset of 12 loci). Our results showed high genetic differentiation and geographic structure in Mauritanian populations of C. suchus. We identified a metapopulation system acting within four river sub-basins (high gene flow and absence of genetic structure) and considerable genetic differentiation between sub-basins (F ST range: 0.12–0.24) with rare dispersal events. Effective population sizes tend to be low within sub-basins while genetic diversity is maintained. Our study suggests that hydrographic networks (temporal connections along seasonal rivers during rainy periods) allow C. suchus to disperse and maintain metapopulation dynamics within sub-basins, which attenuate the loss of genetic diversity and the risk of extinction. We highlight the need of hydrographic conservation to protect vulnerable crocodiles isolated in small water bodies. We propose C. suchus as an umbrella species in Mauritania based on ecological affinities shared with other water-dependent species in desert environments.

Dormancy-related seed positional effect in two populations of an annual grass from locations of contrasting aridity.

In grasses, variation in seed size and dormancy often results from a seed's position within a dispersal unit. In this paper, I asked whether seed positional effect within a spikelet contributes to ecotypic differentiation between two populations of Avena sterilis having different species range position and associated aridity. I created experimental seed banks in which germination of seeds (florets) having different positions within a spikelet was examined over three years. In addition, two germination tests were conducted under controlled conditions. The two populations were found to have a short-living soil seed bank due to sequential germination of the florets. Although positional seed dormancy effect in A. sterilis does not appear to be a specific desert adaptation against unpredictability of rainfall events, this trait does contribute to ecotypic differentiation between desert and Mediterranean populations. Consistent with bet hedging buffering against rainfall unpredictability, germination fractions in the first year were higher in the Mediterranean than in the desert population, while seeds of the desert origin had stronger dormancy and more sequential germination of florets.

REVISITING ḤAḌAR AND BADŪ IN KUWAIT: CITIZENSHIP, HOUSING, AND THE CONSTRUCTION OF A DICHOTOMY

AbstractKuwait today is 99 percent urbanized. Though hosting a substantial desert population in the past, Kuwait no longer contains any Bedouin who practice a nomadic or pastoral lifestyle. And yet the term badū remains in popular use in Kuwait to designate a group considered sociologically and culturally distinct from the ḥaḍar, or settled urbanites, which in Kuwait's context refers solely to descendants of the pre-oil townspeople. This article explores why these social designations still exist in Kuwait and analyzes the origins of the conflictual relationship between the two groups. I argue that the persistence of the ḥaḍar/badū dichotomy is an outcome of state-building strategies adopted in the early oil years, mainly linked to citizenship and housing policies, that contributed to fixing ḥaḍar and badū as not only socially distinct but also geographically bounded groups. These state policies implemented between the 1950s and 1980s fostered the political integration but social exclusion of the badū. The article examines the lived realities of these incoherent policies as one way of explaining how the badū shifted from being the rulers’ main loyalty base in the early oil decades to becoming their primary opposition today.

Divergence in Olfactory Host Plant Preference in D. mojavensis in Response to Cactus Host Use

Divergence in host adaptive traits has been well studied from an ecological and evolutionary perspective, but identification of the proximate mechanisms underlying such divergence is less well understood. Behavioral preferences for host plants are often mediated by olfaction and shifts in preference may be accompanied by changes in the olfactory system. In this study, we examine the evolution of host plant preferences in cactophilic Drosophila mojavensis that feeds and breeds on different cacti throughout its range. We show divergence in electrophysiological responses and olfactory behavior among populations with host plant shifts. Specifically, significant divergence was observed in the Mojave Desert population that specializes on barrel cactus. Differences were observed in electrophysiological responses of the olfactory organs and in behavioral responses to barrel cactus volatiles. Together our results suggest that the peripheral nervous system has changed in response to different ecological environments and that these changes likely contribute to divergence among D. mojavensis populations.

Thermal adaptation and acclimation of ectotherms from differing aquatic climates

To elucidate the mechanisms of thermal adaptation and acclimation in ectothermic aquatic organisms from differing climates, we used a common-garden experiment for thermal stress to investigate the heat shock response of redband trout (Oncorhynchus mykiss gairdneri) from desert and montane populations. Evidence for adaptation was observed as expression of heat shock genes in fish from the desert population was more similar to control (unstressed) fish and significantly different (P ≤ 0.05) from those from the montane population, while F1 crosses were intermediate. High induction of heat shock proteins (Hsps) in the montane strain appeared to improve short-term survival during first exposure to high water temperatures, but high physiological costs of Hsp production may have led to lower long-term survival. In contrast, the desert strain had significantly lower heat shock response than the montane fish and F1 crosses, suggesting that these desert fish have evolved alternative mechanisms to deal with thermal stress that provide better balance of physiological costs. Genomewide tests of greater than 10 000 SNPs found multiple SNPs that were significantly associated with survival under thermal stress, including Hsp47 which consistently appeared as a strong candidate gene for adaption to desert climates. Candidate SNPs identified in this study are prime targets to screen more broadly across this species' range to predict the potential for adaptation under scenarios of climate change. These results demonstrate that aquatic species can evolve adaptive responses to thermal stress and provide insight for understanding how climate change may impact ectotherms.

A population genetic transect of Panicum hallii (Poaceae)

Understanding the relationship between climate, adaptation, and population structure is of fundamental importance to botanists because these factors are crucial for the evolution of biodiversity and the response of species to future climate change. Panicum hallii is an emerging model system for perennial grass and bioenergy research, yet very little is known about the relationship between climate and population structure in this system. • We analyzed geographic population differentiation across 39 populations of P. hallii along a longitudinal transect from the savannas of central Texas through the deserts of Arizona and New Mexico. A combination of morphological and genetic (microsatellite) analysis was used to explore patterns of population structure. • We found strong differentiation between high elevation western desert populations and lower elevation eastern populations of P. hallii, with a pronounced break in structure occurring in western Texas. In addition, we confirmed that there are high levels of morphological and genetic structure between previous recognized varieties (var. hallii and var. filipes) within this species. • The results of this study suggest that patterns of population structure within P. hallii may be driven by climatic variation over space. Overall, this study lays the groundwork for future studies on the genetics of local adaptation and reproductive isolation in this system.

Soil seed bank and among-years genetic diversity in arid populations of Eruca sativa Miller (Brassicaceae)

Populations of Eruca sativa from arid environments exhibit greater physiological dormancy than those that originated in more favorable ones. We tested the possible relative contribution of the soil seed bank (SSB) to the aboveground cohorts in desert and semiarid populations. Seedlings that emerged from the SSB under controlled irrigation were distinguished from those that emerged after exposure of the remaining ungerminated SSB to gibberellic acid as constituting non-dormant and dormant SSBs, respectively. On average, the total SSB was significantly larger in the semiarid than in the desert population. In both sites, the aboveground and SSB cohorts exhibited closely similar genetic diversity, and in the aboveground cohorts similar year-to-year genetic diversity was found. These results indicate continuous recruitment from the SSB to the aboveground cohorts. Nevertheless, Ne estimates indicated that the SSB can contribute to enlarging the aboveground effective populations in both habitats. Furthermore, Nei's genetic distances suggested that the non-dormant SSB contributed more than the dormant SSB to the aboveground cohorts. These results highlight the potential of the SSB to maintain a genotype reservoir that protects annual populations in arid environments.

Nitrate Accumulation Related to the Location of Two Populations of Xero-halophyteHaloxylon ammodendronin Sandy or Saline Desert

We investigated whether there is a relationship between nitrate accumulation and geographic origin of Haloxylon ammodendron C. A. Mey, a xero-halophyte growing in both saline and sandy deserts in Central Asia. A pot culture experiment was conducted with two NaCl levels (1 and 300 mmol/L) factorially combined with three nitrate levels (0.05, 1 and 10 mmol/L) as Ca(NO3)2 and KNO3 under greenhouse conditions. The results indicated that root biomass and root relative growth rate in the plants from a saline desert population were significantly reduced at 300 mmol/L NaCl, while no significant effect was observed in the plants from a sandy desert population. Meanwhile, salinity led to a significant increase in the concentrations of NO3− in the roots of both populations, and the increase of nitrate concentration in plants from the sandy desert population was significantly greater than that of the saline desert population. The estimated contribution of NO3− to osmotic potential in roots of the sandy desert population at 300 mmol/L NaCl was about 2.9 times those of the saline desert population. It is concluded that H. ammodendron from the sandy desert population may exert superior NO3− uptake ability in the roots compared with the saline desert population. This trait was related to the variations of inherently different root growth, which was the result of selection and adaptation to different desert environments.

Demographic consequences of delayed germination in two annual grasses from two locations of contrasting aridity

Delayed seed germination is considered to be a bet-hedging strategy, but experimental evidence of its adaptive role as an inherited trait is still lacking. In each of two co-occuring annual grass species, populations of Mediterranean and desert origin were studied during three consecutive years for population demography and seed germination in the reciprocally introduced experimental soil seed banks. The two environments strikingly differed in productivity (annual rainfall) and predictability (variation in amount and timing of annual rainfall). The two species exhibited highly similar pattern of seed size and dormancy across the two environments. In both species, a higher proportion of dormant seeds was observed at the desert location and for the seeds of desert origin, consistent with bet-hedging buffering against unpredictability of rainfall and high probability of drought in this environment. In addition, in both species seed mass was significantly less in plants of desert origin than in plants of Mediterranean origin. The two environments differed in demographic consequences of temporal variation in precipitation. In the Mediterranean population, even in the year of least precipitation, adults grew to maturity and seeds were produced. These seeds served to maintain population size. In contrast, in the desert population, in the year of least rainfall no seedlings survived to maturity and the soil seed bank was the only source of population persistence. Altogether, the results concur with predicted by adaptive bet hedging importance of delayed germination under marginal precipitation. (C) 2012 Elsevier GmbH. All rights reserved.