Disentangling the effects of geographic peripherality and habitat suitability on neutral and adaptive genetic variation in Swiss stone pine

It is generally accepted that the spatial distribution of neutral genetic diversity within a species’ native range mostly depends on effective population size, demographic history, and geographic position. However, it is unclear how genetic diversity at adaptive loci correlates with geographic peripherality or with habitat suitability within the ecological niche. Using exome‐wide genomic data and distribution maps of the Alpine range, we first tested whether geographic peripherality correlates with four measures of population genetic diversity at > 17,000 SNP loci in 24 Alpine populations (480 individuals) of Swiss stone pine (Pinus cembra) from Switzerland. To distinguish between neutral and adaptive SNP sets, we used four approaches (two gene diversity estimates, F_ST outlier test, and environmental association analysis) that search for signatures of selection. Second, we established ecological niche models for P. cembra in the study range and investigated how habitat suitability correlates with genetic diversity at neutral and adaptive loci. All estimates of neutral genetic diversity decreased with geographic peripherality, but were uncorrelated with habitat suitability. However, heterozygosity (H_e) at adaptive loci based on Tajima's D declined significantly with increasingly suitable conditions. No other diversity estimates at adaptive loci were correlated with habitat suitability. Our findings suggest that populations at the edge of a species' geographic distribution harbour limited neutral genetic diversity due to demographic properties. Moreover, we argue that populations from suitable habitats went through strong selection processes, are thus well adapted to local conditions, and therefore exhibit reduced genetic diversity at adaptive loci compared to populations at niche margins.     

High levels of fluctuating asymmetry in isolated stickleback populations

ABSTRACT: BACKGROUND: Fluctuating asymmetry (FA), defined as small random deviations from the ideal bilateral symmetry, has been hypothesized to increase in response to both genetic and environmental stress experienced by a population. We compared levels of FA in 12 bilateral meristic traits (viz. lateral-line system neuromasts and lateral plates), and heterozygosity in 23 microsatellite loci, among four marine (high piscine predation risk) and four pond (zero piscine predation risk) populations of nine-spined sticklebacks (Pungitius pungitius). RESULTS: Pond sticklebacks had on average three times higher levels of FA than marine fish and this difference was highly significant. Heterozygosity in microsatellite markers was on average two times lower in pond (HE [almost equal to] 0.3) than in marine (HE [almost equal to] 0.6) populations, and levels of FA and heterozygosity were negatively correlated across populations. However, after controlling for habitat effect on heterozygosity, levels of FA and heterozygosity were uncorrelated. CONCLUSIONS: The fact that levels of FA in traits likely to be important in the context of predator evasion were elevated in ponds compared to marine populations suggests that relaxed selection for homeostasis in ponds lacking predatory fish may be responsible for the observed habitat difference in levels of FA. This inference also aligns with the observation that the levels of genetic variability across the populations did not explain population differences in levels of FA after correcting for habitat effect. Hence, while differences in strength of selection, rather than in the degree of genetic stress could be argued to explain habitat differences in levels of FA, the hypothesis that increased FA in ponds is caused by genetic stress cannot be rejected.     

Genetic diversity and climatic determinants of tree frogs in Israel

Summary Allozymic variation in proteins encoded by 27 loci was analyzed electrophoretically in 218 adult specimens, mostly males, representing 8 populations, 5 central and 3 marginal, of lemon yellow treefrogs, Hyla arborea savignyi, in Israel along two transects of increasing aridity: (a) north to south and (b) west to east. The results indicate that (a) Of the 27 loci examined, 5 are monomorphic in all 8 populations; 9 are locally and weakly polymorphic; 6 are regionally and weakly polymorphic; and 7 are regionally and strongly polymorphic; (b) In the populations studied, no alternative fixations were found in any of the 27 loci, except in the Wasit population. The commonest allele predominates across all populations, except Wasit, central as well as marginal; (c) Clinal patterns associated with increasing aridity southwards and eastwards occur in polymorphism, P, heterozygosity, H, and in allele frequencies of Ldh-1, Fum, Got-1, and Sdh; (d) For habitat generalists, treefrogs have above average number of alleles per locus, A, and polymorphism, P, while the heterozygosity, H, is average. All three estimates A, P, and H exhibit wide geographic variation decreasing progressively southwards and eastwards; (e) Central populations harbor more genic variation then marginal populations; (f) Genic similarity between populations is high; (g) Significant gametic phase disequilibria were found in several tests in 2 populations; (h) P, H, and allozymic variation in several gene loci are significantly correlated and predictable by environmental variables, primarily those related to water; (i) Morphological and allozymic variations are uncorrelated.The spatial patterns and environmental correlates and predictors of genic variation in Hyla arborea savignyi in Israel suggest that (i) protein polymorphisms are largely adaptive and are molded primarily by climatic selection rather than by stochastic processes or neutrality, and (ii) the environmental variation model seems to be the best predictor of genic variation in treefrogs.     

Does stress mess with rodents’ heads? Influence of habitat amount and genetic factors in mandible fluctuating asymmetry in South American water rats (Nectomys squamipes,Sigmodontinae) from Brazilian Atlantic rainforest remnants

Loss of developmental stability can lead to deviations from bilateral symmetry (i.e. Fluctuating Asymmetry ‐ FA), and is thought to be caused by environmental and genetic factors associated with habitat loss and stress. Therefore, levels of FA might be a valuable tool to monitor wild populations if FA serves as an indicator of exposure to stress due to impacts of habitat loss and fragmentation. In studies examining FA and habitat fragmentation, FA levels are often explained by loss of genetic variation, though few studies have addressed FA’s use as indicator of environmental impact. Here, we investigated whether habitat loss, genetic variation, and/or inbreeding affect the developmental instability in Brazilian Atlantic forest populations of a Neotropical water rat (Nectomys squamipes). We sampled individuals from eight sites within Atlantic forest remnants with different amounts of available forest habitat and assessed FA levels with geometric morphometric techniques using adult mandibles. We used observed heterozygosity (H_o) and inbreeding coefficient (F_is), from seven microsatellite markers, as a proxy of genetic variation at individual and population levels. Populations were not significantly different for shape or size FA levels. Furthermore, interindividual variation in both shape and size FA levels and interpopulational differences in size FA levels were best explained by chance. However, habitat amount was negatively associated with both interpopulational variance and average shape FA levels. This association was stronger in populations living in areas with <28% of forest cover, which presented higher variance and higher average FA, suggesting that Nectomys squamipes might have a tolerance threshold to small availability of habitat. Our work is one of the first to use FA to address environmental stress caused by habitat loss in small mammal populations from a Neotropical biome. We suggest that shape FA might serve as a conservation tool to monitor human impact on natural animal populations.     

Is phenotypic canalization involved in the decline of the endemic Aquilegia thalictrifolia? Rethinking relationships between fluctuating asymmetry and species conservation status

Fluctuating asymmetry (FA), the deviation from the normal symmetrical condition of a morphological trait having specific morphological symmetry, increases in response to environmental and genetic stress, is related to phenotypic plasticity and is considered a tool for monitoring a species conservation status. However, FA–stress relations are dependent on measured traits or species‐specific characteristics such as mating system and habitat. This study investigates the relationships between FA, genetic diversity, population size, density and individual fitness traits (plant height, fruit and seed set), in the endemic Aquilegia thalictrifolia, a mixed breeder that is declining, but maintaining high levels of heterozygosity. Leaf and flower FA and other traits were investigated in 10 populations of A. thalictrifolia, the whole species range. As a result, we found similar patterns of FA in leaves and flowers between populations, indicating a homogenous level of stress between populations that differed for other traits. FA and the other traits were not related, including heterozygosity. Heterozygosity was not related to individual fitness traits with the exception of plant height. In accordance with other studies, we found that the role of FA as a tool for assessing the conservation status of a species or population should be reconsidered. However, we conclude that a low level of FA should not automatically be considered an indicator of good conservation status or low level of stress, because in species that evolved in highly stable environments it may indicate a scarce ability to plastically respond to environmental changes, as a consequence of environmental and genetic canalization. Further investigation of this point is needed.     

Exploring the spatiotemporal dynamics of habitat suitability to improve conservation management of a vulnerable plant species

Ongoing declines in biodiversity caused by global environmental changes call for adaptive conservation management, including the assessment of habitat suitability spatiotemporal dynamics potentially affecting species persistence. Remote sensing (RS) provides a wide-range of satellite-based environmental variables that can be fed into species distribution models (SDMs) to investigate species-environment relations and forecast responses to change. We address the spatiotemporal dynamics of species’ habitat suitability at the landscape level by combining multi-temporal RS data with SDMs for analysing inter-annual habitat suitability dynamics. We implemented this framework with a vulnerable plant species (Veronica micrantha), by combining SDMs with a time-series of RS-based metrics of vegetation functioning related to primary productivity, seasonality, phenology and actual evapotranspiration. Besides RS variables, predictors related to landscape structure, soils and wildfires were ranked and combined through multi-model inference (MMI). To assess recent dynamics, a habitat suitability time-series was generated through model hindcasting. MMI highlighted the strong predictive ability of RS variables related to primary productivity and water availability for explaining the test-species distribution, along with soil, wildfire regime and landscape composition. The habitat suitability time-series revealed the effects of short-term land cover changes and inter-annual variability in climatic conditions. Multi-temporal SDMs further improved predictions, benefiting from RS time-series. Overall, results emphasize the integration of landscape attributes related to function, composition and spatial configuration for improving the explanation of ecological patterns. Moreover, coupling SDMs with RS functional metrics may provide early-warnings of future environmental changes potentially impacting habitat suitability. Applications discussed include the improvement of biodiversity monitoring and conservation strategies.     

The use of fluctuating asymmetry as a measure of farming practice effects in rodents: A species-specific response

The effects of agricultural intensification on vertebrate populations could vary depending on whether species are habitat specialists or habitat generalists. Organic farming practices are generally considered to be less intensive and more environmental friendly than conventional farming practices and, as a result, these two managements may impact on habitat specialists and habitat generalists in different ways. The effect of environmental and/or genetic stress on populations can be assessed using fluctuating asymmetry (FA) and body condition of animals. We predicted that populations of a specialist species, the Pampean grassland mouse (Akodon azarae) would have higher levels of FA and poorer body condition on conventional farms compared to populations of A. azarae on organic farms. In contrast, we predicted that populations of generalist species, the corn mouse (Calomys musculinus) and the small vesper mouse (Calomys laucha) would not show differences in FA or body condition between conventional and organic farms. We examined the expression of FA in the hind foot and used the scaled mass index as a surrogate for body condition. As predicted, we found higher FA in the habitat specialist (A. azarae) on conventional farms compared to organic farms, and found no differences in FA among the two generalist species (C. musculinus and C. laucha). However, we found no differences in body condition for the three studied species between the two managements. Our results suggest that the effect of farming practices on small mammals varies between habitat specialists and habitat generalists. The results of this study provide important insights for the study of asymmetries, both from biological and methodological perspectives. Our results support the idea that the level of FA may be used as an index to assess the effects of farming practices on vertebrate populations.     

Genetic diversity, climatic selection and speciation of Sphincterochila landsnails in Israel

Allozymic variation in proteins encoded by 29 loci was analysed electrophoretically in 364 adult specimens representing 12 populations and five species of the landsnail Sphincterochila in Israel along a north-south general transect of increasing aridity. In addition, geographic variation in three morphological body variables of these snails was also studied. The results indicate that: (i) most loci (86%) are strongly polymorphic; (ii) most loci (65%) display fixation of alternative alleles either within or between species; (iii) most of the variant alleles (51%) are not widespread, and genie differentiation is very high (66%) between populations and species, indicating sharp local and regional geographic differentiation; (iv) clinal patterns are rare or nonexistent; (v) populations of Sphincterochila display average estimates of mean alleles per locus,A=1.53; polymorphism, P (5% criterion) = 0.31; heterozygosity, H=0.07; and genie diversity, He= 0.11; (vi) wide geographic variation within and between species is displayed in A= 1.18-2.07; P=0.11–0.61; H=0.02-0.15, and He = 0.042-0.22. Wright's fixation index, F, ranges from 0.03 to 0.65. (vii) Genie diversity, He, increases southwards with aridity from 0.051 to 0.145. (viii) A differential amount of variation in different functional classes of enzymes follows the Gillespie-Kojima hypothesis, (ix) Coefficients of genetic distance, D, between populations are high, D= 0.34, range 0.09-0.58, and between species, D= 0.27, range 0.12-0.40. D's within species may be higher than between species. Likewise, D's increase clinally southwards, (x) Deviations from Hardy-Weinberg equilibria were found in several loci in some populations and species, (xi) A statistically significant (P< 0.001) amount of morphological variation of body variables exists within and between species. Size between three species increases eastwards and southwards with aridity, (xii) P, H, He, and allozymic variation in several gene loci are significantly correlated with, and predictable by, climatic variables, primarily those related to the moisture index, (xiii) Allozymic and morphological variations are partly correlated, (xiv) Significant microgeographical climatic differentiation was found in three critical tests. The pattern of genetic variation within and between species suggests that: (a) climatic selection plays a conspicuous role in allozymic morphological differentiation into ecologically adaptive patterns; (b) the environmental variation model seems to be a good predictor of genetic variation in Sphincterochila; (c) adaptive radiation of the five species of Sphincterochila in Israel occurred during Pleistocene times in accord with climatic differentiation and apparently involved few changes of structural genes.     

Testing the Relationship between Human Occupancy in the Landscape and Tadpole Developmental Stress

Amphibian population declines are widespread; the main causal factors are human related and include habitat fragmentation due to agriculture, mining, fires, and urban development. Brazil is the richest country in species of amphibians, and the Brazilian regions with the greatest amphibian diversity are experiencing relatively high rates of habitat destruction, but there are presently relatively few reports of amphibian declines. It is thus important to develop research methods that will detect deterioration in population health before severe declines occur. We tested the use of measurements of fluctuating asymmetry (FA) taken on amphibian larvae to detect anthropogenic stress. We hypothesized that greater human occupancy in the landscape might result in more stressful conditions for amphibians. We conducted this study at the Espinhaço mountain range in southeastern Brazil, using as a model an endemic species (Bokermannohyla saxicola, Hylidae). We chose two tadpole denticle rows and eye-nostril distance as traits for FA measurement. We measured percent cover of human-altered habitats in the landscape around tadpole sampling points and measured FA levels in sampled tadpoles. We found FA levels to differ among localities but found no relationship between human modification of the landscape and tadpole FA levels. Levels of FA in the traits we examined may not be strongly affected by environmental conditions, or may be affected by local variables that were not captured by our landscape-scale measures. Alternatively, populations may be genetically differentiated, affecting how FA levels respond to stress and obscuring the effects of anthropogenic disturbance.     

Developmental stability across the breeding distribution of the scissor-tailed flycatcher (Tyrannus forficatus)

A central question in ecology is how individual fitness interacts with the spatial variation in population density and habitat characteristics across species' ranges. We used fluctuating asymmetry (FA) as a measure of developmental stability (DS) in individuals of Tyrannus forficatus to estimate the suitability of sites of varying abundance and position within the species' range. FA in the inner-tail feathers of males and females is not spatially correlated across the species' range. FA in males increases towards the centre of the range and is not correlated with abundance. FA in females is not correlated with position in the range or abundance. Our results suggest that optimal sites are found throughout the range of the species, whereas suboptimal sites are mainly found towards the centre of the range. Additionally, our results suggest that abundance may not reflect the suitability of sites across species' ranges.     

Comparative seedling ecology of eight North American spruce (Picea) species in relation to their geographic ranges

BACKGROUND AND AIMS: Allowing for dispersal limitation, a species' geographic distribution should reflect its environmental requirements. Comparisons among closely related species should reveal adaptive differentiation in species characteristics that are consistent with their differences in geographic distribution. This expectation was tested by comparing characteristics of seedlings of spruce species in relation to environmental factors representative of their current natural ranges. METHODS: Seedlings were grown from a total of 34 populations representing eight North American spruce (Picea) species in a controlled environment chamber for 140 d. Traits related to the potential of seedling establishment, including tolerance to stress events (high temperature, desiccation) were evaluated. Correlations were sought between these characteristics and modal values of latitude, aridity and continentality in the geographic range of each species. KEY RESULTS: Many seedling traits changed significantly in response to stress events, but only the response of chlorophyll concentration differed significantly among species. Components of seedling growth were good correlates of species distribution. Seedling relative growth rate (RGR) and specific leaf area (SLA) were positively correlated with latitude, and leaf weight ratio (LWR) negatively correlated with aridity. Seed mass was negatively correlated with latitude. CONCLUSIONS: Relationships found between seedling traits and geographical variation in environmental conditions suggest that factors such as temperature regime, water availability and perhaps litter depth affect species range in North American spruces. Seedling characteristics appear to be elements in a reasonably distinct environmental niche for each spruce species at the continental scale.     

Temperate Mountain Forest Biodiversity under Climate Change: Compensating Negative Effects by Increasing Structural Complexity

Species adapted to cold-climatic mountain environments are expected to face a high risk of range contractions, if not local extinctions under climate change. Yet, the populations of many endothermic species may not be primarily affected by physiological constraints, but indirectly by climate-induced changes of habitat characteristics. In mountain forests, where vertebrate species largely depend on vegetation composition and structure, deteriorating habitat suitability may thus be mitigated or even compensated by habitat management aiming at compositional and structural enhancement. We tested this possibility using four cold-adapted bird species with complementary habitat requirements as model organisms. Based on species data and environmental information collected in 300 1-km² grid cells distributed across four mountain ranges in central Europe, we investigated (1) how species’ occurrence is explained by climate, landscape, and vegetation, (2) to what extent climate change and climate-induced vegetation changes will affect habitat suitability, and (3) whether these changes could be compensated by adaptive habitat management. Species presence was modelled as a function of climate, landscape and vegetation variables under current climate; moreover, vegetation-climate relationships were assessed. The models were extrapolated to the climatic conditions of 2050, assuming the moderate IPCC-scenario A1B, and changes in species’ occurrence probability were quantified. Finally, we assessed the maximum increase in occurrence probability that could be achieved by modifying one or multiple vegetation variables under altered climate conditions. Climate variables contributed significantly to explaining species occurrence, and expected climatic changes, as well as climate-induced vegetation trends, decreased the occurrence probability of all four species, particularly at the low-altitudinal margins of their distribution. These effects could be partly compensated by modifying single vegetation factors, but full compensation would only be achieved if several factors were changed in concert. The results illustrate the possibilities and limitations of adaptive species conservation management under climate change.     

Fluctuating asymmetry and allozymic heterozygosity among natural populations of pocket gophers (Thomomys bottae)

Fluctuating asymmetry, or random deviations from bilateral symmetry, has been widely used as a measure of developmental stability. The relationship between fluctuating asymmetry (FA) and allozymic heterozygosity was evaluated using 18 natural populations of pocket gophers ( Thomomys bottae ). Heterozygosity in local populations of pocket gophers ranges over more than an order of magnitude (1.5—18.4%), making this burrowing rodent particularly apt for such studies. Two measures of FA in mensural skull characters were examined: absolute deviations between left and right sides and the variance of signed differences. After log transformations, levels of FA among individuals and populations were not related to size. Repeated-measures analyses of variance showed that FA was significant relative to measurement error, both across populations and within them. Asymmetries of different characters were uncorrelated, despite positive significant correlations among the characters themselves. FA levels varied only slightly among populations of gophers, and this variation was not significant for most characters. FA levels of populations were not correlated with allozymic heterozygosity, and analyses of variance in FA employing heterozygosity were not significant. Heterozygosity levels in these rodents appear more strongly related to aspects of population history (especially effective size and gene flow) than to developmental stability. Because so many genomic and environmental factors can affect morphological variation, caution is needed in interpreting correlations between genetic and phenetic variation.     

Environmental aridity is associated with cytotype segregation and polyploidy occurrence in Brachypodium distachyon (Poaceae)

? The ecological and adaptive significance of plant polyploidization is not well understood and no clear pattern of association between polyploid frequency and environment has emerged. Climatic factors are expected to predict cytotype distribution. However, the relationship among climate, cytotype distribution and variation of abiotic stress tolerance traits has rarely been examined. ? Here, we use flow cytometry and root-tip squashes to examine the cytotype distribution in the temperate annual grass Brachypodium distachyon in 57 natural populations distributed across an aridity gradient in the Iberian Peninsula. We further investigate the link between environmental aridity, ploidy, and variation of drought tolerance and drought avoidance (flowering time) traits. ? Distribution of diploids (2n = 10) and allotetraploids (2n = 30) in this species is geographically structured throughout its range in the Iberian Peninsula, and is associated with aridity gradients. Importantly, after controlling for geographic and altitudinal effects, the link between aridity and polyploidization occurrence persisted. Water-use efficiency varied between ploidy levels, with tetraploids being more efficient in the use of water than diploids under water-restricted growing conditions. ? Our results indicate that aridity is an important predictor of polyploid occurrence in B. distachyon, suggesting a possible adaptive origin of the cytotype segregation.     

Genetic variation and climatic selection in the lizard Agama stellio in Israel and Sinai

Summary Allozymic variation in proteins encoded by 25 loci was analyzed electrophoretically in 242 adult specimens representing nine populations of the Levantine lizard, Agama stellio, comprising two subspecies: the Mediterranean A. stellio subsp., and the desert-inhabiting A. stellio brachydactyla from the Negev and Sinai. Likewise, four body traits were measured in the same populations. The nine populations were sampled along a general southward transect of increasing aridity. Agama stellio is above average in both polymorphism, P, and heterozygosity, H, as compared to other reptiles and vertebrates in general, displaying levels of genetic variation characterizing habitat generalist vertebrates. In the populations studied no fixation of alternative alleles was found in any of the 25 loci: rather the commonest allele was either fixed or predominated in 23 of 25 loci examined. Eleven loci (44%) were monomorphic in all nine populations. However, of the remaining 14 polymorphic loci, eight were strongly polymorphic displaying distinct genetic differentiation between populations. Genetic diversity (indexed by P and H) displayed geographic variation and was slightly higher in A.s. brachydactyla than in A. stellio subsp. Nevertheless, genic similarity between populations was high. A statistically significant amount of morphological variation between localities was found for all body characters. In general, body size increased southwards and eastwards with aridity.Selection at some loci is suggested by significant deviation from Hardy-Weinberg expectations and possibly by excess heterogeneity of effective inbreeding coefficients, F_e. Furthermore, allozymic variation at seven loci (Ldh-1, Idh-1, 6-Pgd-1, Aat-1, Pgm-2, Pept-1, and Trf) and geographic variation in body size and weight were significantly correlated with, and predictable by, climatic variables, primarily by water availability and secondarily by temperature. Finally, allozymic and morphological variations were partly correlated.The spatial patterns and ecological correlates of genic and morphological variations in Agama stellio in Israel and Sinai suggest that at least some proteins and body size differentiate geographically and appear to be adaptive, presumably with respect to factors affecting the availability of water.     

Dimorphisms and fluctuating asymmetry in the forceps of male earwigs

Male dimorphisms are particularly conspicuous examples of the alternative reproductive strategies employed within some species. Such dimorphisms are thought to exist as genetic polymorphisms under ESS conditions, or to be conditional strategies where exogenous conditions determine the adult body plan. Fluctuating asymmetry (FA) is currently considered to be a fitness correlate of significant use in interpreting the functional significance of secondary sexual characteristics. In particular, negative slopes of FA on trait size are thought to arise in traits whose expression is dependent on condition. We measured forceps lengths and asymmetries in 2 island populations of the European earwig Forficula auricularia and Museum specimens of 5 other earwig (Dermaptera, Forficulidae) species from different genera, that appeared to be dimorphic. In a detailed study of Forficula auricularia we found a significant fit to a statistical model for the identification of dimorphisms and, for all species examined, morphs differed in the slope and/or elevation of the allometric relationship between body size and forcep length. Possible determinates of male dimorphisms are suggested from the data. Contrary to expectation, FA was not found to be greater in the minor morphs. Negative relationships between FA and forceps length were absent in both morphs of species examined from museum collections. Of the two island populations of Forficula auricularia, the smaller and more isolated population had higher FA and a negative relationship between FA and forceps length in the major morph. We discuss these patterns in the light of recent theories of FA and honest signalling.     

Habitat-islands in the coastal Atacama Desert: loss of functional redundancy,but not of functional diversity,with decreased precipitation

Background and AimsAridity is increasing in many regions of the world, but microclimatic conditions may buffer plant communities from the direct effects of decreased precipitation, creating habitat islands. However, reduced precipitation can also impact these communities indirectly by decreasing the suitability of the surrounding habitat, thus limiting incoming propagules and increasing the chances of population decline and species loss. We test whether decreased precipitation results in loss of species and functional diversity within habitat islands, evaluating in particular whether declines in species diversity and abundance are less likely to result in loss of functional diversity if species/individual loss is stochastic (i.e. independent of species/individual traits) and communities/populations are functionally redundant.MethodsLomas communities are discrete plant communities embedded in the Atacama Desert, maintained by the microclimatic conditions created by fog. We recorded species and functional diversity in six Lomas communities along a 500 km long precipitation gradient in northern Chile. Functional traits were measured in 20 individuals per species, in those species that accounted for approx. 75 % of the abundance at each site. We calculated functional diversity and functional redundancy of the community, and intraspecific functional variation.Key ResultsDecreased precipitation was associated with lower species diversity and lower species abundances. However, no traits or functional strategies increased or decreased consistently with precipitation, suggesting stochastic species/individual loss. Species with stress-tolerant strategies were predominant in all sites. Although species diversity decreased with decreasing precipitation, functional diversity remained unchanged. Lower functional redundancy in the drier sites suggests that mainly functionally redundant species were lost. Likewise, intraspecific functional variation was similar among communities, despite the lower species abundance in drier sites.ConclusionsDecreased precipitation can impact habitat island communities indirectly by decreasing the suitability of the surrounding habitat. Our results support the idea that a stochastic loss of species/individuals from functionally redundant communities and populations does not result in loss of functional diversity.     

Life history variation in an annual plant under two opposing environmental constraints along an aridity gradient

Environmental gradients represent an ideal framework for studying adaptive variation in the life history of plant species. However, on very steep gradients, largely contrasting conditions at the two gradient ends often limit the distribution of the same species across the whole range of environmental conditions. Here, we study phenotypic variation in a winter annual crucifer Biscutella didyma persisting along a steep gradient of increasing rainfall in Israel. In particular, we explored whether the life history at the arid end of the gradient indicates adaptations to drought and unpredictable conditions, while adaptations to the highly competitive environment prevail at the mesic Mediterranean end. We examined several morphological and reproductive traits in four natural populations and in populations cultivated in standard common environment. Plants from arid environments were faster in phenological development, more branched in architecture and tended to maximize reproduction, while the Mediterranean plants invested mainly in vertical vegetative growth. Differences between cultivation and field in diaspore production were very large for arid populations as opposed to Mediterranean ones, indicating a larger potential to increase reproduction under favorable conditions. Our overall findings indicate two strongly opposing selective forces at the two extremes of the aridity gradient, which result in contrasting strategies within the studied annual plant species.     

Environmental stress as an indicator of anthropogenic impact across the African Albertine Rift: a case study using museum specimens

We examined fluctuating asymmetry (FA) and body condition (BC) as two measures of environmental stress using museum specimens of Lophuromys aquilus, a rodent species complex wide-spread across the African Albertine Rift. We related FA and BC to a spatially-derived index of anthropogenic impact using a principal components analysis (PCA). We found no relationship between the four PCA scores and mean FA or BC, but did find that FA variance was higher in areas with lower anthropogenic impact. There was also a negative, albeit non-significant, trend for PC3, suggesting that populations with higher than average BC were in areas with higher anthropogenic impact. Overall, our case study does not support FA and BC as effective predictors of environmental stress with low to moderate habitat disturbance. In fact, L. aquilus, as a habitat generalist, may be positively affected by some aspects of anthropogenic change. Studies relating environmental stress to anthropogenic impact should examine sites with a wide range of habitat qualities and human impact and utilize multiple measures of environmental stress to characterize the health of one or more populations.     

Desiccation resistance along an aridity gradient in the cactophilic fly Drosophila buzzatii: sex-specific responses to stress

Stress resistance characters are valuable tools for the study of acclimation potential, adaptive strategies and biogeographic patterns in species exposed to environmental variability. Water stress is a challenge to terrestrial arthropods because of their small size and relatively high area: volume ratio. Fruit flies have been investigated to record adaptive morphological and physiological traits, as well as to test their responses to stressful factors. In this study, we investigate the ability to cope with water stress, by examining variation in desiccation resistance in a species that lives mainly in desert lands. Specifically, we explored the genetic and ecological basis of desiccation resistance in populations of Drosophila buzzatii from Northern Argentina. We used a common garden experiment with desiccation treatments on a number of isofemale lines from four populations along an aridity gradient. Our results revealed significant among-population differentiation and substantial amounts of genetic variation for desiccation resistance. We also detected significant genotype-by-environment and genotype-by-sex interactions indicative that desiccation resistance responses of the lines assayed were environment- and sex-specific. In addition, we observed clinal variation in female desiccation resistance along gradients of altitude, temperature and humidity; that desiccation resistance is a sexually dimorphic trait, and that sexual dimorphism increased along the aridity and altitudinal gradients. Based on current evidence, we propose that the observed sex-specific responses may reflect different life history traits, and survival and reproductive strategies in different ecological scenarios.