Hybridisation and genetic selection for improving desiccation tolerance of the entomopathogenic nematode Steinernema feltiae

Shelf life of biological control products based on the entomopathogenic nematode Steinernema feltiae is rather limited. In order to prolong shelf life, the metabolism of nematodes during storage must be reduced, either by low temperature or by means of desiccation of the third stage dauer juveniles (DJs). Tolerance to desiccation is limited in S. feltiae. Their tolerance can be increased by an adaptation to moderate desiccation conditions. The objective of this study was to screen for tolerant strains among wild type populations of S. feltiae, hybridise most tolerant strains and further improve desiccation tolerance by subjection of the hybrid strain to genetic selection. Dehydrating conditions, measured as water activity (a _w-values), were produced by treating DJs with different concentrations of the polymer polyethylene glycol 600. Significant variation was recorded among 24 S. feltiae strains. The mean tolerated water activity survived by 50% of the population (WA₅₀) ranged from 0.78 to 0.93 when nematodes were not adapted to desiccation stress and from 0.66 to 0.88 when preadapted to desiccation stress. The six most desiccation tolerant strains of non-adapted and adapted nematode populations were crossed. Preadapted tolerance of hybrids was superior to the tolerance of parental strains, whereas non-adapted tolerance was not increased. The most tolerant hybrid had a WA₅₀ when preadapted of 0.67 and 0.86 when not adapted. The tolerance was lost after few reproductive cycles in the insect Galleria mellonella but was recovered again after six selection cycles with exposure to increasing stress conditions. Virulence and reproduction potential was not negatively affected by the selection. Stabilisation of the selection progress will be a major challenge to enable commercial exploitation of the genetic improvement.     

Osmoregulatory traits of broad-toothed field mouse (Apodemus mystacinus) populations from different habitats

One mechanism for physiological adjustment of small mammals to different habitats and different seasons is by seasonal acclimatization of their osmoregulatory system. We examined the abilities of broad-toothed field mice (Apodemus mystacinus) from different ecosystems (‘sub-alpine’ and ‘Mediterranean’) to cope with salinity stress under short day (SD) and long day (LD) photoperiod regimes. We compared urine volume, osmolarity, urea and electrolyte (sodium, potassium and chloride) concentrations. Significant differences were noted in the abilities of mice from the two ecosystems to deal with salinity load; in particular sub-alpine mice produced less concentrated urine than Mediterranean mice with SD− sub-alpine mice seeming to produce particularly dilute urine. Urea concentration generally decreased with increasing salinity, whereas sodium and potassium levels increased, however SD− sub-alpine mice behaved differently and appeared not to be able to excrete electrolytes as effectively as the other groups of mice. Differences observed provide an insight into the kinds of variability that are present within populations inhabiting different ecosystems, thus how populations may be able to respond to potential changes in their environment. Physiological data pertaining to adaptation to increased xeric conditions, as modelled by A. mystacinus, provides valuable information as to how other species may cope with potential climatic challenges.     

Morphological variability of Carex spicata Huds. utricles among plant communities

Differentiation in the size and number of seeds among populations or particular individuals of a given species may depend on genetic features and environmental conditions. The objective of our study was to answer two questions: whether any differences exist in the size and shape of utricles among Carex spicata populations growing in several plant communities and whether the hypothesized differences remain constant in ‘common garden’ conditions (i.e. if the sedges grown in different plant communities are evolving distinctly separate ecotypes). We studied utricle morphological traits (projected area, width, length, W/L ratio and projected perimeter) and number of utricles per spike collected from plants grown in five different plant communities (natural sites) and from plants transferred to common garden conditions. C. spicata utricles showed significant variability of morphological traits that depended on the plant community of origin. Among five plant communities, the largest utricles were found in Agropyron repens–Urtica dioica and Convolvulo arvensis–Agropyretum repentis communities, while the smallest ones were in plants from the Lolio-Plantaginetum community. The similarity of the analyzed populations regarding sedge utricle traits corresponded to the similarity of plant communities where the populations had grown. Moreover, the differences in utricle traits collected from natural conditions remained stable in common garden conditions. This indicated that differences in traits among utricles had a physiological dependence on different biotope conditions or different interspecific interactions prevailing in the particular plant communities. The relationship between the similarities in the diaspores of the populations studied and the similarities in the ecological conditions of the communities may also indicate that the variability of utricles is important for evolution and adaptation.The results support the hypothesis that C. spicata populations in different communities are producing separate ecotypes, i.e. specific species forms with genetically fixed traits adapted to narrowly determined habitat conditions.     

Osmotic Survival of the Entomopathogenic Nematode Steinernema carpocapsae

The effect of different osmolytes on the viability and the effect of osmotic pressure on the induction of a dormant state similar to that caused by a slow desiccation rate were evaluated in the entomopathogenic nematode Steinernema carpocapsae ‘All’. For both experiments, a high-temperature (45°C) assay (HTA) was employed. Exposing fresh infective juveniles to the HTA resulted in a drastic reduction in viability. Using the same assay, the mortality of desiccated nematodes was gradual, showing an enhanced ability to withstand high-temperature conditions. The patterns of decline in viability in the evaporatively dehydrated and the osmotically desiccated nematodes were similar. Most of the salts tested in the screening assay caused high mortality levels among the nematodes within the first 24 h of exposure. In contrast, the nonionic solutes tested did not hamper the viability of the infective juveniles. In these nonionic solutions, all nematodes were completely shrunk after 48 h. Furthermore, 72-h exposure to these solutions resulted in an increase in heat tolerance similar to that of the evaporatively dehydrated nematodes. A substantial increase in heat tolerance was recorded in the treatments with glycerol solutions at concentrations from 2.2 to 3.8 M. A similar effect was obtained by polyethylene glycol (PEG) 300 MW at concentrations ranging from 1.2 to 1.6 M. PEG 600 MW induced enhancement of heat tolerance at a concentration of 0.8 M. A high level of viability was attained among nematodes that were stored for 72 days following a gradual increase in glycerol concentrations. Exposure of these nematodes to 45°C in the HTA resulted in 87.3 ± 4.7 and 49.2 ± 3.9% survival after 4 and 8 h, respectively. Reduction in viability was observed among nematodes that were directly exposed to the glycerol solution over a 19-day storage period. With this treatment, survival levels of 72.7 ± 3.9 and 26.5 ± 4.7% after 4 and 8 h, respectively, were recorded in the HTA. Reduction in viability among nematodes stored in distilled water was noted after 36 days of storage. Evaluation of nematode infectivity by two criteria (insect mortality and invasion rate) indicated that infectivity of nematodes desiccated by gradual osmotic pressure induced by glycerol was similar to that of fresh nematodes after 54 days in storage at 25°C. In comparison, infectivity of nematodes stored in distilled water declined significantly compared to that of fresh nematodes.     

Effects of cleistogamy and pollen source on seed production and offspring performance in three endangered violets

In rare plants that often occur in small or isolated populations the probability of selfing between close relatives is increased as a consequence of demographic stochasticity. The mode of pollination (selfing, outcrossing) may have considerable effects on seed traits and offspring performance and hence potential viability. Since current efforts aiming at the restoration of floodplain grasslands through the transfer of plant material from species-rich source stands may lead to the establishment of initially small populations consisting of founders from different populations, the present paper experimentally investigated the effects of pollen source and floral types (i.e. chasmogamous (CH) and cleistogamous (CL) flowers) on seed traits and offspring performance in three highly endangered violet species (Viola elatior, V. pumila, V. stagnina) of these grasslands. We estimated inbreeding depression and tested the performance of selfed and outcrossed offspring in two microbial environments, i.e. in soil inoculated with (i) non-sterile substrate from the same species (‘home’-conditions) and (ii) sterilised substrate.Plants produced more CL capsules than CH flowers. Pollinator exclusion had only small effects on CH seed production. CL seeds had a significantly lower mass per seed than CH seeds. This may be related to constraints in allocation or environmental conditions. Seedling growth was reduced in plants grown under ‘home’-conditions as compared to control soils. Under ‘home’-conditions, relative fitness of selfed seedlings of V. stagnina was significantly higher than that of crossed progeny. Our results suggest that high genetic differentiation among populations as a consequence of isolation may result in outbreeding depression, e.g., through biochemical or physiological incompatibilities between genes or the breaking of coadapted gene complexes. In V. stagnina, offspring fitness differed considerably between environments, but in general we found no indications for inbreeding depression in these rare species.     

Genetics of the Nematode Heterorhabditis bacteriophora Strain HP88: The Diversity of Beneficial Traits

Genotypic variation among infective juveniles of Heterorhabditis bacteriophora (strain HP88) in heat, desiccation, ultraviolet tolerance, and host-finding ability was assessed by comparing the performance of inbred lines of this entomopathogenic nematode in laboratory assays. Each line consisted of highly homozygous offspring originating from one individual obtained from a natural population. Considerable variation in all four traits was detected among the different inbred lines. The heritability values for heat or ultraviolet tolerance and for host-finding ability were high, indicating that selection should be an efficient way for improving these traits in the population. The results for desiccation tolerance varied considerably within each line. Heritability value was low, indicating that the results were influenced mainly by environmental variation and suggesting that selective breeding for higher desiccation tolerance would be inefficient. Improvement through induction of mutations may be a better alternative in this population.     

Desiccation tolerance and starvation resistance exhibit opposite latitudinal clines in Indian geographical populations of Drosophila kikkawai

Abstract. 1. Desiccation tolerance and starvation resistance demonstrated significant differentiation among seven Indian geographical populations of Drosophila kikkawai, collected along a latitudinal range of 12.6–32.7 °N. Lack of significant differences in two successive generations suggested that these physiological traits were genetically controlled. 2. North Indian populations of D. kikkawai displayed significantly higher desiccation tolerance than southern populations, whereas there was a reverse trend for starvation tolerance (r > 0.90). Regression slope values indicated an increase of 0.61 h for desiccation and a decrease of 1.71 h per degree latitude for starvation tolerance at 17 °C. The traits evidenced opposite latitudinal clines, and such data also matched thermal climatic conditions on the Indian subcontinent. The survival duration for such traits was significantly higher at 17 than at 25 °C. 3. Significantly higher starvation tolerance in south Indian populations might be due to large population size, species interactions, and higher metabolic rates in the humid tropical environments. In contrast, prolonged unfavourable colder climatic conditions are known to favour starvation tolerance in temperate regions. Thus, the causes of desiccation and starvation tolerance seem quite different under tropical and temperate conditions. 4. Starvation tolerance was correlated negatively with body weight and ovariole number, which might be due to a trade-off in favour of greater allocation to non-lipidic reserves for sustaining starvation tolerance in the tropics. Reduction in metabolic rate may not be applicable for observed higher starvation tolerance in the tropical populations. 5. Multiple regression analysis demonstrated a major effect of coefficient of variation of mean monthly temperature for both the traits of ecological significance. Thus, Indian geographical populations of D. kikkawai provided evidence of independent genetic divergence for starvation and desiccation tolerance under natural conditions.     

Effect of insect cadaver desiccation and soil water potential during rehydration on entomopathogenic nematode (Rhabditida: Steinernematidae and Heterorhabditidae) production and virulence

We examined the influence of insect cadaver desiccation on the virulence and production of entomopathogenic nematodes (EPNs), common natural enemies of many soil-dwelling insects. EPNs are often used in biological control, and we investigated the feasibility of applying EPNs within desiccated insect cadavers. Desiccation studies were conducted using the factitious host, Galleria mellonella (Lepidoptera: Pyralidae, wax moth larvae) and three EPN species (Heterorhabditis bacteriophora ‘HB1’, Steinernema carpocapsae ‘All’, and Steinernema riobrave). Weights of individual insect cadavers were tracked daily during the desiccation process, and cohorts were placed into emergence traps when average mass losses reached 50%, 60%, and 70% levels. We tracked the proportion of insect cadavers producing infective juveniles (IJs), the number and virulence of IJs produced from desiccated insect cadavers, and the influence of soil water potentials on IJ production of desiccated insect cadavers. We observed apparent differences in the desiccation rate of the insect cadavers among the three species, as well as apparent differences among the three species in both the proportion of insect cadavers producing IJs and IJ production per insect cadaver. Exposure of desiccated insect cadavers to water potentials greater than −2.75 kPa stimulated IJ emergence. Among the nematode species examined, H. bacteriophora exhibited lower proportions of desiccated insect cadavers producing IJs than the other two species. Desiccation significantly reduced the number of IJs produced from insect cadavers. At the 60% mass loss level, however, desiccated insect cadavers from each of the three species successfully produced IJs when exposed to moist sand, suggesting that insect cadaver desiccation may be a useful approach for biological control of soil insect pests.     

Meta-analysis of geographical clines in desiccation tolerance of Indian drosophilids

Tropical fruit flies (Drosophilidae) differ from temperate drosophilids in several ecophysiological traits, such as desiccation tolerance. Moreover, many species show significant differences in desiccation tolerance across geographical populations. Fruit flies from the tropical and subtropical Indian subcontinent show a clinal pattern for desiccation tolerance which is similar for more than a dozen species studied so far, suggesting adaptation to climatic differences. We performed a meta-analysis to investigate which particular climatic patterns modulate desiccation tolerance in natural populations of drosophilids. Latitude of the sampling site explained most of the variability. Seasonal thermal amplitude (fluctuations in temperature expressed as coefficient of variation) was the strongest climatic factor shaping desiccation tolerance of flies, while factors measuring humidity directly were not important. Implications for survival of flies after future climate change are suggested.     

Reproductive indicators in natural populations of Douglas-fir in Mexico

The reproductive capacity in nine Mexican Douglas-fir populations was determined by analyzing seed production traits from 144 trees collected in 2001. Significant variation was found for all traits among populations; they contributed between 21% and 43% of total phenotypic variation found in these traits, indicating broad differences in reproductive capacity for that particular year. Seed efficiency (filled seed/seed potential) varied from 14% to 42% among populations; all populations from Central Mexico had a seed efficiency below 25%. The proportion of developed that were empty seeds varied from 0.40 to 0.81 among populations, whereas seed size varied also from 0.88 to 1.21 g per 100 seeds among them. Average ratio of filled seed weight to cone weight (reproductive efficiency) was 29.6 mg g⁻¹, but it varied three-fold between populations with extreme values. Populations with larger cones had greater seed potential and heavier seed but not necessarily higher reproductive or seed efficiency. Most reproductive indicators were significantly correlated with latitude, with lower values in the marginal populations from Central Mexico, in the southern extreme of the species range. Given these results, the need for conservation of Douglas-fir populations in Central Mexico is discussed.     

Resistance to environmental stress in Drosophila ananassae: latitudinal variation and adaptation among populations

Geographical variation in traits related to fitness is often the result of adaptive evolution. Stress resistance traits in Drosophila often show clinal variation, suggesting that selection affects resistance traits either directly or indirectly. Multiple stress resistance traits were investigated in 45 natural populations of Drosophila ananassae collected from all over India. There was significant positive correlation between starvation resistance and lipid content. Significant negative correlations between desiccation and lipid content and between desiccation and heat resistance were also found. Flies from lower latitudes had higher starvation resistance, heat resistance and lipid content but the pattern was reversed for desiccation resistance. These results suggest that flies from different localities varied in their susceptibility to starvation because of difference in their propensity to store body lipid. Multiple regression analysis provided evidence of climatic selection driven by latitudinal variation in the seasonal amplitude of temperature and humidity changes within the Indian. Finally, our results suggest a high degree of variation in stress resistance at the population level in D. ananassae.     

Chemical Variation in a Dominant Tree Species: Population Divergence,Selection and Genetic Stability across Environments

Understanding among and within population genetic variation of ecologically important plant traits provides insight into the potential evolutionary processes affecting those traits. The strength and consistency of selection driving variability in traits would be affected by plasticity in differences among genotypes across environments (G×E). We investigated population divergence, selection and environmental plasticity of foliar plant secondary metabolites (PSMs) in a dominant tree species, Eucalyptus globulus. Using two common garden trials we examined variation in PSMs at multiple genetic scales; among 12 populations covering the full geographic range of the species and among up to 60 families within populations. Significant genetic variation in the expression of many PSMs resides both among and within populations of E. globulus with moderate (e.g., sideroxylonal A h²op = 0.24) to high (e.g., macrocarpal G h²op = 0.48) narrow sense heritabilities and high coefficients of additive genetic variation estimated for some compounds. A comparison of Qst and Fst estimates suggest that variability in some of these traits may be due to selection. Importantly, there was no genetic by environment interaction in the expression of any of the quantitative chemical traits despite often significant site effects. These results provide evidence that natural selection has contributed to population divergence in PSMs in E. globulus, and identifies the formylated phloroglucinol compounds (particularly sideroxylonal) and a dominant oil, 1,8-cineole, as candidates for traits whose genetic architecture has been shaped by divergent selection. Additionally, as the genetic differences in these PSMs that influence community phenotypes is stable across environments, the role of plant genotype in structuring communities is strengthened and these genotypic differences may be relatively stable under global environmental changes.     

Improvement of heat and desiccation tolerance in <Emphasis Type="Italic">Heterorhabditis bacteriophora</Emphasis> through cross-breeding of tolerant strains and successive genetic selection

Genetic selection can be a powerful tool to increase beneficial traits in biological control agents. In this study the heat and desiccation tolerance of the entomopathogenic nematode Heterorhabditis bacteriophora Poinar (Rhabditidomorpha: Strongyloidea) were significantly increased by cross breeding tolerant parental strains and successive genetic selection. These strains originated from a prior screening among 60 strains for increased stress tolerance. During genetic selection, the selection pressure was constantly increased and only the most tolerant 10% of the nematode populations were propagated for further selection steps. Assessment of tolerance and selection for both traits was performed with and without prior adaptation to the stress conditions. Eleven selection steps were performed to increase heat tolerance. A final overall increase in mean heat tolerance of 5.5°C was achieved when nematodes had been adapted to heat stress. For non-adapted tolerance an increase of 3.0°C from 40.1°C to 43.1°C was recorded. For comparison, a commercial strain had a mean tolerated temperature after adaptation of 38.2°C and of 36.5°C without adaptation. For assessment of the desiccation tolerance the mean tolerated water activity (a_w-value) of a population was measured. Cross-breeding most tolerant strains reduced the a_w-value from 0.67 to 0.65 after adaptation and from 0.9 to 0.7 without prior adaptation. The following six selection steps could not increase the tolerance whether nematodes had been adapted to stress or not. In comparison, the commercial strain tolerated a mean a_w-value of 0.985 after adaptation and 0.951 without adaptation. Further investigation will have to assess trait stability and possible trade-off effects. This study is a first important step on the road towards domestication of the entomopathogenic nematode H. bacteriophora.     

Reproductive attributes of <Emphasis Type="Italic">Campanula</Emphasis> populations from Mt Olympos,Greece

We studied five reproductive attributes (fruit production and volume, seed content and weight, and seed germination) of different populations of Campanula species occurring along the elevation gradient of Mt Olympos, the highest mountain of Greece (2917 m), in order to examine whether and how they change with elevation, and if there are trade-offs among them. We also studied flower and fruit (reproductive) losses and population features in order to estimate whether there might be a threat to the survival of Campanula species on Mt Olympos. The genus is represented by nine species, ranging from cosmopolitan to steno-endemic. All species were found non-autogamous, and hence they depend on pollinators for their sexual reproduction. At the genus level, there is a trade-off between seed content per fruit and seed weight. At the species level, this is manifested only for C. glomerata, which produces the heaviest seeds, far exceeding all other species, and for C. spatulata, represented on Mt Olympos by two elevation distinct subspecies. Changes of the reproductive attributes are not continuous all along the elevation gradient at the genus level nor are they monotonic at the species level. Nevertheless, upland Campanula populations (≥1500 m) produce fewer fruits per individual, containing fewer but heavier seeds than lowland populations. This indicates a transition from ‘r’ to ‘K’ strategies, from low to high elevations, respectively. The patterns of change of reproductive attributes indicate prevalence of phylogenetic over environmental constraints. Laboratory tests showed that for many populations germinability is high at 15 °C, but there are both inter- and intraspecific differences regarding temperature optima. Ecotypic variation among populations of the same species at different elevations was evident; populations from higher elevations had lower optima and vice versa. Reproductive losses, ranging from zero to over 90%, occurred mainly at the stage of fruit maturation; grazing by sheep and goats was the usual cause. Though such losses might affect the short-lived species (the annual C. sparsa and the biennial C. lingulata), which depend entirely on fruit maturation and seed dispersal for their reproduction, there does not seem to be a serious threat to the survival of Campanula species on the mountain.     

Temperature and photoperiod affect stress resistance traits in Drosophila melanogaster

The long‐term survival of species and populations depends on their ability to adjust phenotypic values to environmental conditions. In particular, the capability of dealing with environmental stress to buffer detrimental effects on fitness is considered to be of pivotal importance. Resistance traits are readily modulated by a wide range of environmental factors. In the present study, Drosophila melanogaster Meigen is used to investigate plastic responses to temperature and photoperiod in stress resistance traits. The results reveal that stress resistance traits (cold, heat, starvation and desiccation resistance) are affected by the factors temperature and sex predominantly. Cooler temperatures compared with warmer temperatures increase cold tolerance, desiccation and starvation resistance, whereas they reduce heat tolerance. Except for heat resistance, females are more stress‐resistant than males. Stress resistance traits are also affected by photoperiod. Shorter photoperiods decrease cold tolerance, whereas longer photoperiods enhance desiccation resistance. Overall, thermal effects are pervasive throughout all measured resistance traits, whereas photoperiodic effects are of limited importance in the directly developing (i.e. nondiapausing) flies used here, suggesting that pronounced photoperiodic effects on stress resistance traits may be largely limited to, and triggered by, diapause‐inducing effects.     

Selective breeding for desiccation tolerance in liquid culture provides genetically stable inbred lines of the entomopathogenic nematode Heterorhabditis bacteriophora

The entomopathogenic nematode (EPN) Heterorhabditis bacteriophora is used in biological plant protection to control pest insects. In the past, several attempts targeted at an enhancement of the desiccation tolerance of EPN by genetic selection in order to improve their storage stability. The subsequent loss of improved beneficial traits after release of selection pressure has often been reported. In order to stabilize progress of selective breeding, selection during liquid culturing was tested against propagation in host insects. After release of the selection pressure, the tolerance was monitored over additional reproductive cycles in vivo and in vitro to compare the stability of the trait. Furthermore, it was tested whether the virulence of the selected strains would be impaired. Exposure to desiccation stress prior to propagation, in vivo or in vitro, both resulted in increasing desiccation tolerance. When selection pressure was released, the gained tolerance was lost again during in vivo production, whereas the tolerance was maintained at a high level when EPNs were cultured in liquid culture. In Heterorhabditis sp., liquid culture conditions produce highly homozygous, genetically stable inbred lines. The investigation provides easily applicable methods to improve and stabilize beneficial traits of heterorhabditid EPNs through selective breeding in liquid culture. Compared to nematodes from in vivo propagation, production in liquid media yielded EPN of higher virulence.     

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.     

Reasons for success: Rapid evolution for desiccation resistance and life‐history changes in the polyphagous fly Anastrepha ludens

Species that exhibit broad ranges of distribution may successfully navigate environmental changes by modifying some of their life‐history traits. Environmental humidity imposes a critical stress that organisms may overcome by increasing their resistance to desiccation. We used experimental evolution to investigate adaptation to desiccation in the tephritid Anastrepha ludens, a species with high fecundity, late maturation, and long lifespan. We measured morphological, physiological, developmental as well as demographic changes involved in the adaptation to desiccation. Notwithstanding a low heritability (h² = 0.237), desiccation resistance evolved extremely rapidly and few negative trade‐offs were detected. Selected flies exhibited correlated increases in longevity, body size, the amount of body lipids, and bulk water content, and in the duration of the pupal stage. Females further delayed sexual maturation, decreased daily fecundity but retained high lifetime reproductive potential. No differences in male mating competitiveness were found. Selected and control lines differed in longevity but not in total female fecundity, demonstrating that A. ludens flies have the capability for fast adaptation to desiccation without loosing their reproductive capability. Thus, it seems that a rapid evolutionary response to desiccation in this polyphagous insect works as a buffer for environmental variation and reduces the strength of selection on reproductive traits.     

Variation in life history and genetic traits of Hawaiian mosquitofish populations

Mosquitofish (Gambusia affinis) were collected from 17 reservoirs on three islands in Hawaii, USA. Genetic and life history traits for adult females from these populations were used to evaluate hypotheses concerning short-term evolutionary divergence of populations recently established from a common ancestral source. The effects of founder events and drift on genetic variability and population differentiation were also examined. Significant differences in life history characteristics, allele frequencies, and multi-locus heterozygosities (H) were found among fish populations collected from different reservoirs and between reservoirs classified as stable or fluctuating on the basis of temporal fluctuation in water level. Females from stable reservoirs exhibited greater standard length (35.1 vs 32.8 mm), lower fecundity (11.9 vs 15.2 embryos), lower reproductive allocation (18.2% vs 22.8%), but larger mean embryo size (1.95 vs 1.67 mg) than females from fluctuating reservoirs. Consistency in means among replicates of each reservoir class and concordance in direction and magnitude of differences reported here and results of sampling conducted from these same locations 10 years previously (Stearns, 1983a) suggest that ecological factors intrinsic to these two environments are important in determing population life history traits. Females from stable reservoirs exhibited lower heterozygosity than females from fluctuating reservoirs (0.134 vs 0.158, respectively). Levels and direction od differences in heterozygosity, the high proportion of polymorphic loci and lack of fixation of alternative alleles argue against a purely stochastic explanation for genetic and life history variation among reservoir populations. Levels of genetic variability and interpopulation differentiation were similar to those observed in mainland populations of this species. A high proportion of the genetic diversity was apportioned between populations and within populations due to differences between juveniles and adults. Significant genotypic differences between adult and juvenile age classes suggest that the genetic divergence of local populations may occur over short periods of time.     

Tolerance to multiple climate stressors: a case study of Douglas‐fir drought and cold hardiness

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