Genetic evidence for adaptation-driven incipient speciation of Drosophila melanogaster along a microclimatic contrast in "Evolution Canyon," Israel

Pathogen infection alters the gene expression landscape of transposable elements in Drosophila melanogaster

Transposable elements make up substantial proportions of eukaryotic genomes and many are thought to be remnants of ancient viral infections. Current research has begun to highlight the role transposable elements can play in the immune system response to infections. However, most of our knowledge about transposable element expression during infection is limited by the specific host and pathogen factors from each study, making it difficult to compare studies and develop broader patterns regarding the role of transposable elements during infection. Here, we use the tools and resources available in the model, Drosophila melanogaster, to analyze multiple gene expression datasets of flies subject to bacterial, fungal, and viral infections. We analyzed differences in pathogen species, host genotype, host tissue, and sex to understand how these factors impact transposable element expression during infection. Our results highlight both shared and unique transposable element expression patterns between pathogens and suggest a larger effect of pathogen factors over host factors for influencing transposable element expression.

The multi-omics analysis in the hepatopancreas of Eriocheir sinensis provides novel insights into the response mechanism of heat stress

Under global warming, heat stress can induce the excessive production of reactive oxygen species, causing irreversible damage to aquatic animals. It is essential to predict potentially harmful impacts on aquatic organisms under heat stress. Eriocheir sinensis, a typical crustacean crab, is widely distributed in China, American and Europe. Parent E. sinensis need migrate to the estuaries to reproduce in winter, and temperature is a key environmental factor. Herein, we performed a comprehensive transcriptomic and proteomic analysis in the hepatopancreas of E. sinensis under heat stress (20 °C and 30 °C), focusing on heat shock protein family, antioxidant system, energy metabolism and immune defense. The results revealed that parent E. sinensis generated adaptative responses to maintain physiological function under 20 °C stress via the transcriptional up-regulation of energy metabolism enzymes, mRNA synthesis and heat shock proteins. The transcriptional inhibition of key enzymes related to energy metabolism implied that 30 °C stress may lead to the dysfunction of energy metabolism in parent E. sinensis. Meanwhile, parent E. sinensis also enhanced the expression of ferritin and phospholipase D at translational level, and the glutathione s-transferase and heat shock protein 70 at both transcriptional and translational levels, speculating that parent E. sinensis can strengthen antioxidant and immune capacity to resist oxidative stress under 30 °C stress. This study elucidated the potential molecular mechanism in response to heat stress of parent E. sinensis hepatopancreas. The preliminary selection of heat tolerance genes or proteins in E. sinensis can provide a reference for the population prediction and the study of evolutionary mechanism under heat stress in crabs.

Chilo suppressalis heat shock proteins are regulated by heat shock factor 1 during heat stress

Heat shock factor 1 (HSF1) functions to maintain cellular and organismal homeostasis by regulating the expression of target genes, including those encoding heat shock proteins (HSPs). In the present study, the gene encoding HSF1 was cloned from the rice pest Chilo suppressalis, and designated Cshsf1. The deduced protein product, CsHSF1, contained conserved domains typical of the HSF1 family, including a DNA-binding domain, two hydrophobic heptad repeat domains, and a C-terminal transactivation domain. Real-time quantitative PCR showed that Cshsf1 was highly expressed in hemocytes. Expression analysis in different developmental stages of C. suppressalis revealed that Cshsf1 was most highly expressed in male adults. RNAi-mediated silencing of Cshsf1 expression reduced C. suppressalis survival at high temperatures. To investigate the regulatory interactions between Cshsf1 and Cshsps, the promoters and expression patterns of 18 identified Cshsps in C. suppressalis were analysed; four types of heat shock elements (HSEs) were identified in promoter regions including canonical, tail-tail, head-head, and step/gap. The expression of Cshsp19.0, Cshsp21.7B, Cshsp60, Cshsp70 and Cshsp90 was positively regulated by Cshsf1; however, Cshsp22.8, Cshsp702, Cshsp705 and Cshsp706 gene expression was not altered. This study provides a foundation for future studies of HSF1 in insects during thermal stress.

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

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

Does evolution of echolocation calls and morphology in Molossus result from convergence or stasis?

Although many processes of diversification have been described to explain variation of morphological traits within clades that have obvious differentiation among taxa, not much is known about these patterns in complexes of cryptic species. Molossus is a genus of bats that is mainly Neotropical, occurring from the southeastern United States to southern Argentina, including the Caribbean islands. Molossus comprises some groups of species that are morphologically similar but phylogenetically divergent, and other groups of species that are genetically similar but morphologically distinct. This contrast allows investigation of unequal trait diversification and the evolution of morphological and behavioural characters. In this study, we assessed the role of phylogenetic history in a genus of bat with three cryptic species complexes, and evaluated if morphology and behavior are evolving concertedly. The Genotype by Sequence genomic approach was used to build a species-level phylogenetic tree for Molossus and to estimate the ancestral states of morphological and echolocation call characters. We measured the correlation of phylogenetic distances to morphological and echolocation distances, and tested the relationship between morphology and behavior when the effect of phylogeny is removed. Morphology evolved via a mosaic of convergence and stasis, whereas call design was influenced exclusively through local adaptation and convergent evolution. Furthermore, the frequency of echolocation calls is negatively correlated with the size of the bat, but other characters do not seem to be evolving in concert. We hypothesize that slight variation in both morphology and behaviour among species of the genus might result from niche specialization, and that traits evolve to avoid competition for resources in similar environments.

Genomic divergence and adaptive convergence in Drosophila simulans from Evolution Canyon, Israel

Biodiversity refugia formed by unique features of the Mediterranean arid landscape, such as the dramatic ecological contrast of "Evolution Canyon," provide a natural laboratory in which local adaptations to divergent microclimate conditions can be investigated. Significant insights have been provided by studies of Drosophila melanogaster diversifying along the thermal gradient in Evolution Canyon, but a comparative framework to survey adaptive convergence across sister species at the site has been lacking. To fill this void, we present an analysis of genomic polymorphism and evolutionary divergence of Drosophila simulans, a close relative of Drosophila melanogaster with which it co-occurs on both slopes of the canyon. Our results show even deeper interslope divergence in D. simulans than in D. melanogaster, with extensive signatures of selective sweeps present in flies from both slopes but enhanced in the population from the hotter and drier south-facing slope. Interslope divergence was enriched for genes related to electrochemical balance and transmembrane transport, likely in response to increased selection for dehydration resistance on the hotter slope. Both species shared genomic regions that underwent major selective sweeps, but the overall level of adaptive convergence was low, demonstrating no shortage of alternative genomic solutions to cope with the challenges of the microclimate contrast. Mobile elements were a major source of genetic polymorphism and divergence, affecting all parts of the genome, including coding sequences of mating behavior-related genes.

Counties not countries: Variation in host specificity among populations of an aphid parasitoid

Parasitic wasps are among the most species-rich groups on Earth. A major cause of this diversity may be local adaptation to host species. However, little is known about variation in host specificity among populations within parasitoid species. Not only is such knowledge important for understanding host-driven speciation, but because parasitoids often control pest insects and narrow host ranges are critical for the safety of biological control introductions, understanding variation in specificity and how it arises are crucial applications in evolutionary biology. Here, we report experiments on variation in host specificity among 16 populations of an aphid parasitoid, Aphelinus certus. We addressed several questions about local adaptation: Do parasitoid populations differ in host ranges or in levels of parasitism of aphid species within their host range? Are differences in parasitism among parasitoid populations related to geographical distance, suggesting clinal variation in abundances of aphid species? Or do nearby parasitoid populations differ in host use, as would be expected if differences in aphid abundances, and thus selection, were mosaic? Are differences in parasitism among parasitoid populations related to genetic distances among them? To answer these questions, we measured parasitism of a taxonomically diverse group of aphid species in laboratory experiments. Host range was the same for all the parasitoid populations, but levels of parasitism varied among aphid species, suggesting adaptation to locally abundant aphids. Differences in host specificity did not correlate with geographical distances among parasitoid populations, suggesting that local adaption is mosaic rather than clinal, with a spatial scale of less than 50 kilometers. We sequenced and assembled the genome of A. certus, made reduced-representation libraries for each population, analyzed for single nucleotide polymorphisms, and used these polymorphisms to estimate genetic differentiation among populations. Differences in host specificity correlated with genetic distances among the parasitoid populations.

Aggression and courtship differences found in Drosophila melanogaster from two different microclimates at Evolution Canyon, Israel

Aggression and courtship behavior were examined of wild Drosophila melanogaster flies isolated from two contrasting microclimates found at Evolution Canyon in Mt. Carmel, Israel: an African-like dry tropical Slope (AS) and a European-like humid temperate Slope (ES), separated by 250 meters. Studies were carried out to ask whether behavioral differences existed between the two populations obtained from opposite slopes with divergent microclimates in Israel. First, we measured and compared intraslope aggression between same sex fly pairings collected from the same slope. Both male and female flies displayed similar fighting abilities from both slopes. ES males, however, from the humid biome, showed a tendency to lunge more per aggressive encounter, compared with AS males from the dry biome. Next, we tested interslope aggression by pairing flies from opposite slopes. ES males displayed higher numbers of lunges, and won more fights against their AS opponents. We also observed enhanced courtship performances in ES compared to AS males. The fighting and courtship superiority seen in ES males could reinforce fitness and pre-mating reproductive isolation mechanisms that underlie incipient sympatric speciation. This may support an evolutionary advantage of adaptively divergent fruit fly aggression phenotypes from different environments.

Hawaiian picture-winged Drosophila exhibit adaptive population divergence along a narrow climatic gradient on Hawaii Island

Anthropogenic influences on global processes and climatic conditions are increasingly affecting ecosystems throughout the world.Hawaii Island's native ecosystems are well studied and local long-term climatic trends well documented, making these ecosystems ideal for evaluating how native taxa may respond to a warming environment.This study documents adaptive divergence of populations of a Hawaiian picture-winged Drosophila, D. sproati, that are separated by only 7 km and 365 m in elevation.Representative laboratory populations show divergent behavioral and physiological responses to an experimental low-intensity increase in ambient temperature during maturation. The significant interaction of source population by temperature treatment for behavioral and physiological measurements indicates differential adaptation to temperature for the two populations.Significant differences in gene expression among males were mostly explained by the source population, with eleven genes in males also showing a significant interaction of source population by temperature treatment.The combined behavior, physiology, and gene expression differences between populations illustrate the potential for local adaptation to occur over a fine spatial scale and exemplify nuanced response to climate change.

The behavior of adult Drosophila in the wild

Little is known about how Drosophila adults behave in the wild, including mating, allocation of food and space, and escape from predators. This lack of information has negative implications for our ability to understand the capabilities of the nervous system to integrate sensory cues necessary for the adaptation of organisms in natural conditions. We characterized a set of behavioral routines of D. melanogaster and D. simulans adults in three ecologically different orchards: grape, apple and prickly pear. We also investigated how the flies identify conspecifics and aliens in the wild to better understand relationships between group formation and adaptation of Drosophila to breeding sites. We characterized the locations by recording in each orchard humidity, temperature, illumination conditions, pH of fruits, the presence/absence of other Drosophila species and the predator ant Linepithema humile. Our findings suggest that the home range of these species of Drosophila includes decaying fruits and, principally, a variety of microhabitats that surround the fruits. The ecological heterogeneity of the orchards and odors emitted by adult D. melanogaster and D. simulans influence perch preferences, cluster formation, court and mating, egg-laying site selection, and use of space. This is one of the first large examinations of the association between changing, complex environments and a set of adult behaviors of Drosophila. Therefore, our results have implications for understanding the genetic differentiation and evolution of populations of species in the genus Drosophila.

Evolution of heat-shock protein expression underlying adaptive responses to environmental stress

Heat-shock proteins (Hsps) and their cognates are primary mitigators of cell stress. With increasingly severe impacts of climate change and other human modifications of the biosphere, the ability of the heat-shock system to affect evolutionary fitness in environments outside the laboratory and to evolve in response is topic of growing importance. Since the last major reviews, several advances have occurred. First, demonstrations of the heat-shock response outside the laboratory now include many additional taxa and environments. Many of these demonstrations are only correlative, however. More importantly, technical advances in "omic" quantification of nucleic acids and proteins, genomewide association analysis, and manipulation of genes and their expression have enabled the field to move beyond correlation. Several consequent advances are already evident: The pathway from heat-shock gene expression to stress tolerance in nature can be extremely complex, mediated through multiple biological processes and systems, and even multiple species. The underlying genes are more numerous, diverse and variable than previously appreciated, especially with respect to their regulatory variation and epigenetic changes. The impacts and limitations (e.g., due to trade-offs) of natural selection on these genes have become more obvious and better established. At last, as evolutionary capacitors, Hsps may have distinctive impacts on the evolution of other genes and ecological consequences.

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

Background

The current analysis of transposon elements (TE) in Drosophila melanogaster at Evolution Canyon, (EC), Israel, is based on data and analysis done by our collaborators (Drs. J. Gonzalez, J. Martinez and W. Makalowski, this issue). They estimated the frequencies of 28 TEs (transposon elements) in fruit flies (D. melanogaster) from the ecologically tropic, hot, and dry south-facing slope (SFS) or “African” slope (AS) of EC and compared it with the TE frequencies on the temperate-cool and humid north-facing slope (NFS) or “European” slope (ES), separated, on average, by 250 m. The flies were sampled from two stations on each slope. We received their results, including the frequencies of each TE on each slope, and the probabilities of the statistical analyses (G-tests) of each TE separately. We continued the analysis of the inter-slope differences of the frequencies of the TEs, and based our different conclusions on that analysis and on the difference between micro (=EC) and macro (2000 km.) comparisons [Gonzalez et al. 2015 doi:10.1186/s13062-015-0075-4].

Results

Our collaborators based all their conclusions on the non-significant results of each of the individual tests of the 28 TEs. We analysed also the distribution of the TE differences between the slopes, based on their results. Thirteen TEs were more frequent on the SFS, 11 were more frequent on the NFS, and four had equal frequencies. Because of the equalizing effect of the ongoing migration, only small and temporary differences between the slopes (0 – 0.06) were regarded by us as random fluctuations (drift). Three TEs were intermediate (0.08-0.09) and await additional research. The 11 TEs with large frequency differences (0.12 – 0.22) were regarded by us as putative adaptive TEs, because the equalizing power of ongoing migration will eliminate random large differences. Five of them were higher on the SFS and six were higher on the NFS. Gaps in the distribution of the differences distinguished between the large and small differences. The large gap among the 11 TEs favored on the NFS was significant and supports our rejection of drift as the only explanation of the distribution of the slope differences. The gaps in the distribution of the differences separated the putative TEs with strong enough selection from those TEs that couldn't overrule the migration.

The results are compared and contrasted with the directional effect of the frequencies of the same TEs in the study of global climatic comparisons across thousands of kilometers. From the 11 putative adaptive TEs in the local “Evolution Canyon,” six differentiate in the same direction as in the continental comparisons and four in the opposite direction. One TE, FBti0019144, differentiated in EC in the same direction as in Australia and in the opposite direction to that of North America.

Conclusions

We presume that the major divergent evolutionary driving force at the local EC microsite is natural selection overruling gene flow. Therefore, after we rejected drift as an explanation of all the large slope differences, we regarded them as putatively adaptive. In order to substantiate the individual TE adaptation, we need to increase the sample sizes and reveal the significant adaptive TEs.

The comparison of local and global studies show only partial similarity in the adaptation of the TEs, because of the dryness of the ecologically tropical climate in EC, in contrast to the wet tropical climate in the global compared climates. Moreover, adaptation of a TE may be expressed only in part of the time and specific localities.

Reviewers

Reviewed by Eugene Koonin, Limsoon Wong and Fyodor Kondrashov. For the full reviews, please go to the Reviewers’ comments section.

Electronic supplementary material

The online version of this article (doi:10.1186/s13062-015-0074-5) contains supplementary material, which is available to authorized users.

Assessing the Risk of Invasion by Tephritid Fruit Flies: Intraspecific Divergence Matters

Widely distributed species often show strong phylogeographic structure, with lineages potentially adapted to different biotic and abiotic conditions. The success of an invasion process may thus depend on the intraspecific identity of the introduced propagules. However, pest risk analyses are usually performed without accounting for intraspecific diversity. In this study, we developed bioclimatic models using MaxEnt and boosted regression trees approaches, to predict the potential distribution in Europe of six economically important Tephritid pests (Ceratitis fasciventris (Bezzi), Bactrocera oleae (Rossi), Anastrepha obliqua (Macquart), Anastrepha fraterculus (Wiedemann), Rhagoletis pomonella (Walsh) and Bactrocera cucurbitae (Coquillet)). We considered intraspecific diversity in our risk analyses by independently modeling the distributions of conspecific lineages. The six species displayed different potential distributions in Europe. A strong signal of intraspecific climate envelope divergence was observed in most species. In some cases, conspecific lineages differed strongly in potential distributions suggesting that taxonomic resolution should be accounted for in pest risk analyses. No models (lineage- and species-based approaches) predicted high climatic suitability in the entire invaded range of B. oleae—the only species whose intraspecific identity of invading populations has been elucidated—in California. Host availability appears to play the most important role in shaping the geographic range of this specialist pest. However, climatic suitability values predicted by species-based models are correlated with population densities of B. oleae globally reported in California. Our study highlights how classical taxonomic boundaries may lead to under- or overestimation of the potential pest distributions and encourages accounting for intraspecific diversity when assessing the risk of biological invasion.

Divergence of Drosophila melanogaster repeatomes in response to a sharp microclimate contrast in Evolution Canyon, Israel

Repeat sequences, especially mobile elements, make up large portions of most eukaryotic genomes and provide enormous, albeit commonly underappreciated, evolutionary potential. We analyzed repeatomes of Drosophila melanogaster that have been diverging in response to a microclimate contrast in Evolution Canyon (Mount Carmel, Israel), a natural evolutionary laboratory with two abutting slopes at an average distance of only 200 m, which pose a constant ecological challenge to their local biotas. Flies inhabiting the colder and more humid north-facing slope carried about 6% more transposable elements than those from the hot and dry south-facing slope, in parallel to a suite of other genetic and phenotypic differences between the two populations. Nearly 50% of all mobile element insertions were slope unique, with many of them disrupting coding sequences of genes critical for cognition, olfaction, and thermotolerance, consistent with the observed patterns of thermotolerance differences and assortative mating.

Genome differentiation of Drosophila melanogaster from a microclimate contrast in Evolution Canyon, Israel

The opposite slopes of "Evolution Canyon" in Israel have served as a natural model system of adaptation to a microclimate contrast. Long-term studies of Drosophila melanogaster populations inhabiting the canyon have exhibited significant interslope divergence in thermal and drought stress resistance, candidate genes, mobile elements, habitat choice, mating discrimination, and wing-shape variation, all despite close physical proximity of the contrasting habitats, as well as substantial interslope migration. To examine patterns of genetic differentiation at the genome-wide level, we used high coverage sequencing of the flies' genomes. A total of 572 genes were significantly different in allele frequency between the slopes, 106 out of which were associated with 74 significantly overrepresented gene ontology (GO) terms, particularly so with response to stimulus and developmental and reproductive processes, thus corroborating previous observations of interslope divergence in stress response, life history, and mating functions. There were at least 37 chromosomal "islands" of interslope divergence and low sequence polymorphism, plausible signatures of selective sweeps, more abundant in flies derived from one (north-facing) of the slopes. Positive correlation between local recombination rate and the level of nucleotide polymorphism was also found.

Local adaptation of sex induction in a facultative sexual crustacean: insights from QTL mapping and natural populations of Daphnia magna

Dormancy is a common adaptation in invertebrates to survive harsh conditions. Triggered by environmental cues, populations produce resting eggs that allow them to survive temporally unsuitable conditions. Daphnia magna is a crustacean that reproduces by cyclical parthenogenesis, alternating between the production of asexual offspring and the sexual reproduction of diapausing eggs (ephippia). Prior to ephippia production, males (necessary to ensure ephippia fertilization) are produced parthenogenetically. Both the production of ephippia and the parthenogenetic production of males are induced by environmental factors. Here, we test the hypothesis that the induction of D. magna resting egg production shows a signature of local adaptation. We postulated that Daphnia from permanent ponds would produce fewer ephippia and males than Daphnia from intermittent ponds and that the frequency and season of habitat deterioration would correlate with the timing and amount of male and ephippia production. To test this, we quantified the production of males and ephippia in clonal D. magna populations in several different controlled environments. We found that the production of both ephippia and males varies strongly among populations in a way that suggests local adaptation. By performing quantitative trait locus mapping with parent clones from contrasting pond environments, we identified nonoverlapping genomic regions associated with male and ephippia production. As the traits are influenced by two different genomic regions, and both are necessary for successful resting egg production, we suggest that the genes for their induction co-evolve.

Effects of temperature variation on male behavior and mating success in a montane beetle

Locomotion and mating ability are crucial for male reproductive success yet are energetically costly and susceptible to physiological stress. In the Sierra willow beetle Chrysomela aeneicollis, male mating success depends on locating and mating with as many females as possible. Variation at the glycolytic enzyme locus phosphoglucose isomerase (Pgi) is concordant with a latitudinal temperature gradient in these populations, with Pgi-1 frequent in the cooler north, Pgi-4 in the warmer south, and alleles 1 and 4 in relatively equal frequency in areas intermediate in geography and climate. Beetles experience elevated air temperatures during a mating season that causes differential physiological stress among Pgi genotypes, and running speeds of individuals homozygous for Pgi-4 are more tolerant of repeated thermal stress than individuals possessing Pgi-1. Here the importance of running behavior for male mating activity was examined, and differential effects of thermal stress among Pgi genotypes on male mating activity were measured. In nature, males run more than females, and nearly half of males mate or fight for a mate after running. In the laboratory, mating activity was positively correlated with running speed, and repeated mating did not reduce running speed or subsequent mating activity. Males homozygous for Pgi-4 mated longer and more frequently after heat treatment than 1-1 and 1-4 males. All heat-treated males had lower mating frequencies and higher heat shock protein expression than control males; however, mating frequency of recovering 4-4 males increased throughout mating trials, while treated 1-1 and 1-4 males remained low. These results suggest that effects of stress on mating activity differ between Pgi genotypes, implying a critical role for energy metabolism in organisms' response to stressful temperatures.

Diversity in the origins of proteostasis networks--a driver for protein function in evolution

Although the sequence of a protein largely determines its function, proteins can adopt different folding states in response to changes in the environment, some of which may be deleterious to the organism. All organisms--Bacteria, Archaea and Eukarya--have evolved a protein homeostasis, or proteostasis, network comprising chaperones and folding factors, degradation components, signalling pathways and specialized compartmentalized modules that manage protein folding in response to environmental stimuli and variation. Surveying the origins of proteostasis networks reveals that they have co-evolved with the proteome to regulate the physiological state of the cell, reflecting the unique stresses that different cells or organisms experience, and that they have a key role in driving evolution by closely managing the link between the phenotype and the genotype.

Hsp90 is important for fecundity, longevity, and buffering of cryptic deleterious variation in wild fly populations

BACKGROUND

In the laboratory, the Drosophila melanogaster heat shock protein Hsp90 can buffer the phenotypic effects of genetic variation. Laboratory experiments either manipulate Hsp90 activity pharmacologically, or they induce mutations with strong effects in the gene Hsp83, the single-copy fly gene encoding Hsp90. It is unknown whether observations from such laboratory experiments are relevant in the wild.

RESULTS

We here study naturally occurring mutations in Hsp83, and their effects on fitness and phenotypic buffering in flies derived from wild populations. We examined more than 4500 flies from 42 Drosophila populations distributed world-wide for insertions or deletions of mobile DNA in or near the Hsp83 gene. The insertions we observed occur at low population frequencies, and reduce Hsp83 gene expression. In competition experiments, mutant flies performed much more poorly than wild-type flies. Mutant flies were also significantly less fecund and shorter-lived than wild-type flies, as well as less well buffered against cryptic deleterious variation, as we show through inbreeding experiments. Specifically, in Hsp83 mutant flies female fecundity dropped to much lower levels after inbreeding than in wild-type flies. At even slightly elevated temperatures, inbred mutant Hsp83 populations went extinct, whereas inbred wild-type populations persisted.

CONCLUSIONS

Our work shows that Hsp90, a regulator of the stress response and of signaling, helps buffer deleterious variation in fruit flies derived from wild population, and that its buffering role becomes even more important under heat stress.

Evolution under environmental stress at macro- and microscales

Environmental stress has played a major role in the evolution of living organisms (Hoffman AA, Parsons PA. 1991. Evolutionary genetics and environmental stress. Oxford: Oxford University Press; Parsons PA. 2005. Environments and evolution: interactions between stress, resource inadequacy, and energetic efficiency. Biol Rev Camb Philos Soc. 80:589–610). This is reflected by the massive and background extinctions in evolutionary time (Nevo E. 1995a. Evolution and extinction. Encyclopedia of Environmental Biology. New York: Academic Press, Inc. 1:717–745). The interaction between organism and environment is central in evolution. Extinction ensues when organisms fail to change and adapt to the constantly altering abiotic and biotic stressful environmental changes as documented in the fossil record. Extreme environmental stress causes extinction but also leads to evolutionary change and the origination of new species adapted to new environments. I will discuss a few of these global, regional, and local stresses based primarily on my own research programs. These examples will include the 1) global regional and local experiment of subterranean mammals; 2) regional experiment of fungal life in the Dead Sea; 3) evolution of wild cereals; 4) “Evolution Canyon”; 5) human brain evolution, and 6) global warming.

Evolution of hsp70 gene expression: a role for changes in AT-richness within promoters

In disparate organisms adaptation to thermal stress has been linked to changes in the expression of genes encoding heat-shock proteins (Hsp). The underlying genetics, however, remain elusive. We show here that two AT-rich sequence elements in the promoter region of the hsp70 gene of the fly Liriomyza sativae that are absent in the congeneric species, Liriomyza huidobrensis, have marked cis-regulatory consequences. We studied the cis-regulatory consequences of these elements (called ATRS1 and ATRS2) by measuring the constitutive and heat-shock-induced luciferase luminescence that they drive in cells transfected with constructs carrying them modified, deleted, or intact, in the hsp70 promoter fused to the luciferase gene. The elements affected expression level markedly and in different ways: Deleting ATRS1 augmented both the constitutive and the heat-shock-induced luminescence, suggesting that this element represses transcription. Interestingly, replacing the element with random sequences of the same length and A+T content delivered the wild-type luminescence pattern, proving that the element's high A+T content is crucial for its effects. Deleting ATRS2 decreased luminescence dramatically and almost abolished heat-shock inducibility and so did replacing the element with random sequences matching the element's length and A+T content, suggesting that ATRS2's effects on transcription and heat-shock inducibility involve a common mechanism requiring at least in part the element's specific primary structure. Finally, constitutive and heat-shock luminescence were reduced strongly when two putative binding sites for the Zeste transcription factor identified within ATRS2 were altered through site-directed mutagenesis, and the heat-shock-induced luminescence increased when Zeste was over-expressed, indicating that Zeste participates in the effects mapped to ATRS2 at least in part. AT-rich sequences are common in promoters and our results suggest that they should play important roles in regulatory evolution since they can affect expression markedly and constrain promoter DNA in at least two different ways.

Environmental stress-dependent effects of deletions encompassing Hsp70Ba on canalization and quantitative trait asymmetry in Drosophila melanogaster

Hsp70 genes may influence the expression of wing abnormalities in Drosophila melanogaster but their effects on variability in quantitative characters and developmental instability are unclear. In this study, we focused on one of the six Hsp70 genes, Hsp70Ba, and investigated its effects on within- and among-individual variability in orbital bristle number, sternopleural bristle number, wing size and wing shape under different environmental conditions. To do this, we studied a newly constructed deletion, Df(3R)ED5579, which encompasses Hsp70Ba and nine non-Hsp genes, in the heterozygous condition and another, Hsp70Ba(304), which deletes only Hsp70Ba, in the homozygous condition. We found no significant effect of both deletions on within-individual variation quantified by fluctuating asymmetry (FA) of morphological traits. On the other hand, the Hsp70Ba(304)/Hsp70Ba(304) genotype significantly increased among-individual variation quantified by coefficient of variation (CV) of bristle number and wing size in female, while the Df(3R)ED5579 heterozygote showed no significant effect. The expression level of Hsp70Ba in the deletion heterozygote was 6 to 20 times higher than in control homozygotes, suggesting that the overexpression of Hsp70Ba did not influence developmental stability or canalization significantly. These findings suggest that the absence of expression of Hsp70Ba increases CV of some morphological traits and that HSP70Ba may buffer against environmental perturbations on some quantitative traits.

Microsatellite Diversity in Natural Populations of Ascomycetous Fungus, Emericella Nidulans, from Different Climatic-Edaphic Conditions in Israel

The genetic divergence of Israeli populations of the soil ascomycetous fungusEmericella nidulanswas studied on regional and local scales using fifteen microsatellite (SSR) markers. The study was performed in the framework of the "Evolution Canyon" research program at the Institute of Evolution, University of Haifa, in three "Evolution Canyons" (ECs): EC I (Mt. Carmel), EC II (western Upper Galilee), and EC III (the southern Negev desert). The first two canyons (EC I and EC II) are located in the northern part of Israel at a distance of 38 km apart; EC III is located southward at a distance of nearly 350 km from the northern ECs. In each canyon,E. nidulansstrains were isolated from opposite slopes and, in EC III, from the valley bottom. All three EC populations ofE. nidulanswere found to be genetically distinct. The estimated genetic divergences correspond to geographical distances and ecological differences between the three studied canyons. On a regional scale, simple sequence repeat (SSR) polymorphism tends to increase with severity of ecological conditions. In general, both environmental parameters (soil moisture and temperature) and genetic factors (predicted number of repeats in SSR markers, distance from marker to centromere, codon evolutionary chronologies, and hydrophobic vs. hydrophilic character of encoded amino acid) influenced genetic diversity ofE. nidulanspopulations.

Contrasting patterns of transposable element insertions in Drosophila heat-shock promoters

The proximal promoter regions of heat-shock genes harbor a remarkable number of P transposable element (TE) insertions relative to both positive and negative control proximal promoter regions in natural populations of Drosophila melanogaster. We have screened the sequenced genomes of 12 species of Drosophila to test whether this pattern is unique to these populations. In the 12 species' genomes, transposable element insertions are no more abundant in promoter regions of single-copy heat-shock genes than in promoters with similar or dissimilar architecture. Also, insertions appear randomly distributed across the promoter region, whereas insertions clustered near the transcription start site in promoters of single-copy heat-shock genes in D. melanogaster natural populations. Hsp70 promoters exhibit more TE insertions per promoter than all other genesets in the 12 species, similarly to in natural populations of D. melanogaster. Insertions in the Hsp70 promoter region, however, cluster away from the transcription start site in the 12 species, but near it in natural populations of D. melanogaster. These results suggest that D. melanogaster heat-shock promoters are unique in terms of their interaction with transposable elements, and confirm that Hsp70 promoters are distinctive in TE insertions across Drosophila.

Divergence in an obligate mutualism is not explained by divergent climatic factors

Adaptation to divergent environments creates and maintains biological diversity, but we know little about the importance of different agents of ecological divergence. Coevolution in obligate mutualisms has been hypothesized to drive divergence, but this contention has rarely been tested against alternative ecological explanations. Here, we use a well-established example of coevolution in an obligate pollination mutualism, Yucca brevifolia and its two pollinating yucca moths, to test the hypothesis that divergence in this system is the result of mutualists adapting to different abiotic environments as opposed to coevolution between mutualists. We used a combination of principal component analyses and ecological niche modeling to determine whether varieties of Y. brevifolia associated with different pollinators specialize on different environments. Yucca brevifolia occupies a diverse range of climates. When the two varieties can disperse to similar environments, they occupy similar habitats. This suggests that the two varieties have not specialized on distinct habitats. In turn, this suggests that nonclimatic factors, such as the biotic interaction between Y. brevifolia and its pollinators, are responsible for evolutionary divergence in this system.

The adaptive role of transposable elements in the Drosophila genome

Transposable elements (TEs) are short DNA sequences with the capacity to move between different sites in the genome. This ability provides them with the capacity to mutate the genome in many different ways, from subtle regulatory mutations to gross genomic rearrangements. The potential adaptive significance of TEs was recognized by those involved in their initial discovery although it was hotly debated afterwards. For more than two decades, TEs were considered to be intragenomic parasites leading to almost exclusively detrimental effects to the host genome. The sequencing of the Drosophila melanogaster genome provided an unprecedented opportunity to study TEs and led to the identification of the first TE-induced adaptations in this species. These studies were followed by a systematic genome-wide search for adaptive insertions that allowed for the first time to infer that TEs contribute substantially to adaptive evolution. This study also revealed that there are at least twice as many TE-induced adaptations that remain to be identified. To gain a better understanding of the adaptive role of TEs in the genome we clearly need to (i) identify as many adaptive TEs as possible in a range of Drosophila species as well as (ii) carry out in-depth investigations of the effects of adaptive TEs on as many phenotypes as possible.

Phenotype-dependent native habitat preference facilitates divergence between parapatric lake and stream stickleback

Adaptive divergence between adjoining populations reflects a balance between the diversifying effect of divergent selection and the potentially homogenizing effect of gene flow. In most models of migration-selection balance, gene flow is assumed to reflect individuals' inherent capacity to disperse, without regard to the match between individuals' phenotypes and the available habitats. However, habitat preferences can reduce dispersal between contrasting habitats, thereby alleviating migration load and facilitating adaptive divergence. We tested whether habitat preferences contribute to adaptive divergence in a classic example of migration-selection balance: parapatric lake and stream populations of three-spine stickleback (Gasterosteus aculeatus). Using a mark-transplant-recapture experiment on morphologically divergent parapatric populations, we showed that 90% of lake and stream stickleback returned to their native habitat, reducing migration between habitats by 76%. Furthermore, we found that dispersal into a nonnative habitat was phenotype dependent. Stream fish moving into the lake were morphologically more lake-like than those returning to the stream (and the converse for lake fish entering the stream). The strong native habitat preference documented here increases the extent of adaptive divergence between populations two- to fivefold relative to expectations with random movement. These results illustrate the potential importance of adaptive habitat choice in driving parapatric divergence.

Functional and geographical differentiation of candidate balanced polymorphisms in Arabidopsis thaliana

Molecular population genetic analysis of three chromosomal regions in Arabidopsis thaliana suggested that balancing selection might operate to maintain variation at three novel candidate adaptive trait genes, including SOLUBLE STARCH SYNTHASE I (SSI), PLASTID TRANSCRIPTIONALLY ACTIVE 7(PTAC7), and BELL-LIKE HOMEODOMAIN 10 (BLH10). If balanced polymorphisms are indeed maintained at these loci, then we would expect to observe functional variation underlying the previously detected signatures of selection. We observe multiple replacement polymorphisms within and in the 32 amino acids just upstream of the protein-protein interacting BELL domain at the BLH10 locus. While no clear protein sequence differences are found between allele types in SSI and PTAC7, these two genes show evidence for allele-specific variation in expression levels. Geographical patterns of allelic differentiation seem consistent with population stratification in this species and a significant longitudinal cline was observed at all three candidate loci. These data support a hypothesis of balancing selection at all three candidate loci and provide a basis for more detailed functional work by identifying possible functional differences that might be selectively maintained.

Duplicate gene evolution toward multiple fates at the Drosophila melanogaster HIP/HIP-Replacement locus

Hsc/Hsp70-interacting protein (HIP) is a rapidly evolving Hsp70 cofactor. Analyses of multiple Drosophila species indicate that the HIP gene is duplicated only in D. melanogaster. The HIP region, in fact, contains seven distinctly evolving duplicated genes. The regional duplication occurred in two steps, fixed rapidly, and illustrates multiple modes of duplicate gene evolution. HIP and its duplicate HIP-R are adaptively evolving in a manner unique to the region: they exhibit elevated divergence from other drosophilids and low polymorphism within D. melanogaster. HIP and HIP-R are virtually identical, share polymorphisms, and are subject to gene conversion. In contrast, two other duplicate genes in the region, CG33221 and GP-CG32779, are pseudogenes, and the chimeric gene Crg1 is subject to balancing selection. HIP and HIP-R are evolving rapidly and adaptively; however, positive selection is not sufficient to explain the molecular evolution of the region as a whole.

Genetic diversity and stress of Ricotia lunaria in "Evolution Canyon," Israel

We examined the genetic diversity and divergence of Ricotia lunaria, a family relative species of Arabidopsis thaliana, sampled from 6 stations on 2 opposing slopes, the south-facing slope ("African" or AS) and north-facing slope ("European" or ES), separated on average by 200 m, at "Evolution Canyon," Lower Nahal Oren, Mount Carmel, Israel, along a transect presenting sharply differing microclimates. The density of R. lunaria populations was slope specific: a higher density and smaller plants were observed on the AS. In addition, the density was positively correlated with annual plant cover. The interslope and intraslope genetic diversities of R. lunaria populations were examined using the amplified fragment length polymorphism (AFLP) technique with 5 primer pairs. Ricotia lunaria populations inhabiting the ES and AS differed, and among the 468 scored loci, 304 (65%) were polymorphic (at P >or= 0.05 level). Polymorphism values obtained for AS and ES populations were similar (52% vs. 56%), but different loci were polymorphic in different populations; 40% of polymorphic loci were identical on both the ES and AS, 16% were polymorphic for the ES only, and 12% were polymorphic only for the AS. The AFLP results grouped the analyzed genotypes into 2 distinct clusters: one cluster included the plants belonging to the AS and the other included ES plants. The unbiased estimate of Nei genetic distances (D) indicated significantly higher interslope (D = 0.124 +/- 0.011) than intraslope (D = 0.076 +/- 0.015) differences (P < 0.001 in t-test). Correspondingly, mean intraslope gene flow was significantly higher than the interslope gene flow (2.9 +/- 0.6 vs. 1.9 +/- 0.2). Natural selection appears to adaptively diverge the plant ecotypes on the opposite slope, both phenotypically and genotypically. This includes significant divergence in flowering time likely to initiate incipient sympatric speciation.

Location of P element insertions in the proximal promoter region of Hsp70A is consequential for gene expression and correlated with fecundity in Drosophila melanogaster

We compared a series of Drosophila strains with P element insertions from -28 to -144 nucleotides 5' to the transcription start site of the Hsp70A genes-corresponding to the range of naturally occurring P element insertion sites-to elucidate the consequences of insertion site for Hsp70A gene expression. Although all insertions reduced Hsp70A expression below that of a control strain, the magnitude of the reduction was inversely related to the number of nucleotides between the transcription start site and the insertion site. A pre-existing hypothesis is that naturally occurring transposable element insertions in Hsp promoters may be beneficial in some circumstances, which may account for their retention in natural populations. In the present study, in a control line heat shock reduced fecundity, whereas in lines with P element insertions heat shock typically increased fecundity. Finally, according to cluster-specific quantitative RT-PCR, expression of the Hsp70A cluster genes was typically greater than that of the Hsp70B gene cluster genes, although the latter are more numerous and, in this case, free of P element insertions.

Molecular ecology of global change

Global environmental change is altering the selection regime for all biota. The key selective factors are altered mean, variance and seasonality of climatic variables and increase in CO(2) concentration itself. We review recent studies that document rapid evolution to global climate change at the phenotypic and genetic level, as a response to shifts in these factors. Among the traits that have changed are photoperiod responses, stress tolerance and traits associated with enhanced dispersal. The genetic basis of two traits with a critical role under climate change, stress tolerance and photoperiod behaviour, is beginning to be understood for model organisms, providing a starting point for candidate gene approaches in targeted nonmodel species. Most studies that have documented evolutionary change are correlative, while selection experiments that manipulate relevant variables are rare. The latter are particularly valuable for prediction because they provide insight into heritable change to simulated future conditions. An important gap is that experimental selection regimes have mostly been testing one variable at a time, while synergistic interactions are likely under global change. The expanding toolbox available to molecular ecologists holds great promise for identifying the genetic basis of many more traits relevant to fitness under global change. Such knowledge, in turn, will significantly advance predictions on global change effects because presence and polymorphism of critical genes can be directly assessed. Moreover, knowledge of the genetic architecture of trait correlations will provide the necessary framework for understanding limits to phenotypic evolution; in particular as lack of critical gene polymorphism or entire pathways, metabolic costs of tolerance and linkage or pleiotropy causing negative trait correlations. Synergism among stressor impacts on organismal function may be causally related to conflict among transcriptomic syndromes specific to stressor types. Because adaptation to changing environment is always contingent upon the spatial distribution of genetic variation, high-resolution estimates of gene flow and hybridization should be used to inform predictions of evolutionary rates.

Are traits that experience reinforcement also under sexual selection?

Where closely related species occur in sympatry, reinforcement may result in the evolution of traits involved in species recognition that are at the same time used for within-species mate choice. Drosophila serrata lives in forested habitat on the east coast of Australia, and over the northern half of its distribution it coexists with a closely related species, Drosophila birchii. Here we show that the strength of reinforcing selection in natural populations is sufficient to generate reproductive character displacement along a 36-km transect across the contact between sympatric and allopatric populations of D. serrata. The sympatric and allopatric populations display genetically based differences in male cuticular hydrocarbons (CHCs), while female CHCs changed with latitude across the contact. The directional changes observed in male CHCs between sympatric and allopatric regions were the same changes that were generated by experimental sympatry in the laboratory, providing direct evidence that the changes across the contact zone are due to the presence of D. birchii. We show that sympatric and allopatric females differ in preference for male CHCs and that females from allopatric populations prefer allopatric-like male CHCs over sympatric-like CHCs. Male attractiveness within D. serrata may therefore be compromised by reinforcing selection, preventing the spread of sympatric-like blends to the area of allopatry.

Abundant, diverse, and consequentialPelements segregate in promoters of small heat-shock genes inDrosophilapopulations

The present study extends evidence that Drosophila heat-shock genes are distinctively evolvable because of insertion of transposable elements by examining the genotypic diversity and phenotypic consequences of naturally occurring P element insertions in the proximal promoter regions of two small heat-shock genes. Detailed scrutiny of two populations revealed 16 distinctive P transposable elements collectively segregating in proximal promoters of two small heat-shock genes, Hsp26 and Hsp27. These elements vary in size, orientation and insertion site. Frequencies of P element-containing alleles varied from 5% to 100% in these populations. Two Hsp26 elements chosen for detailed study, R(s)P(26) and D(2)P(m), reduced or abolished Hsp26 expression respectively. The R(s)P(26) element increased or did not affect inducible tolerance of high temperature, increased fecundity, but decreased developmental rate. On the other hand, the D(2)P(m) element decreased thermotolerance and fecundity. In lines subjected to experimental evolution, the allelic frequency of the R(s)P(26)P element varied considerably, and was at lower frequencies in lines selected for increased longevity and for accelerated development than in controls. Transposable element insertions into small Hsp genes in Drosophila populations can have dramatic fitness consequences, and therefore create variation on which selection can act.

Recombinational micro-evolution of functionally different metallothionein promoter alleles from Orchesella cincta

Background

Metallothionein (mt) transcription is elevated in heavy metal tolerant field populations of Orchesella cincta (Collembola). This suggests that natural selection acts on transcriptional regulation of mt in springtails at sites where cadmium (Cd) levels in soil reach toxic values This study investigates the nature and the evolutionary origin of polymorphisms in the metallothionein promoter (pmt) and their functional significance for mt expression.

Results

We sequenced approximately 1600 bp upstream the mt coding region by genome walking. Nine pmt alleles were discovered in NW-European populations. They differ in the number of some indels, consensus transcription factor binding sites and core promoter elements. Extensive recombination events between some of the alleles can be inferred from the alignment. A deviation from neutral expectations was detected in a cadmium tolerant population, pointing towards balancing selection on some promoter stretches. Luciferase constructs were made from the most abundant alleles, and responses to Cd, paraquat (oxidative stress inducer) and moulting hormone were studied in cell lines. By using paraquat we were able to dissect the effect of oxidative stress from the Cd specific effect, and extensive differences in mt induction levels between these two stressors were observed.

Conclusion

The pmt alleles evolved by a number of recombination events, and exhibited differential inducibilities by Cd, paraquat and molting hormone. In a tolerant population from a metal contaminated site, promoter allele frequencies differed significantly from a reference site and nucleotide polymorphisms in some promoter stretches deviated from neutral expectations, revealing a signature of balancing selection. Our results suggest that the structural differences in the Orchesella cincta metallothionein promoter alleles contribute to the metallothionein -over-expresser phenotype in cadmium tolerant populations.

Character displacement and the evolution of mate choice: an artificial neural network approach

Interactions with heterospecifics can promote the evolution of divergent mating behaviours between populations that do and do not occur with heterospecifics. This process--reproductive character displacement--potentially results from selection to minimize the risk of mating with heterospecifics. We sought to determine whether heterospecific interactions lead to divergence of female preferences for aspects of conspecific male signals. We used artificial neural network models to simulate a mate recognition system in which females co-occur with different heterospecifics in different populations. Populations that evolved conspecific recognition in the presence of different heterospecifics varied in their preferences for aspects of conspecific male signals. When we tested networks for their preferences of conspecific versus heterospecific signals, however, we found that networks from allopatric populations were usually able to select against heterospecifics. We suggest that female preferences for aspects of conspecific male signals can result in a concomitant reduction in the likelihood that females will mate with heterospecifics. Consequently, even females in allopatry may discriminate against heterospecific mates depending on the nature of their preferences for conspecifics. Such a pattern could potentially explain cases where reproductive character displacement is expected, but not observed.

Patterns of thermal adaptation of Bacillus simplex to the microclimatically contrasting slopes of 'Evolution Canyons' I and II, Israel

Identification of selective forces that drive evolution and speciation of bacteria in natural habitats is a central issue in bacterial ecology and evolution. Exploring the adaptive evolution of Bacillus simplex at 'Evolution Canyons' I and II, Israel, we report here on the impact of high heat stress on the speciation progress of individual evolutionary lineages. These canyons represent similar ecological replicates, separated by 40 km, in which the orientation of the sun yields a strong sun-exposed and hot 'African' south-facing slope (SFS) versus a rather cooler and mesic-lush 'European' north-facing slope (NFS) within a distance of only 50-100 m at the bottom and 400 m at the top. Among 131 strains studied, in Luria-Bertani broth, 'African' strains grow better than 'European' strains at a stressful high temperature (43.25 degrees C). The results suggest that adaptation to the hotter and more stressful SFS is continuously ongoing. The patterns of heat adaptation override the phylogenetic history of individual lineages. A positive correlation of growth rates at 43.25 degrees C and 20 degrees C, more markedly among 'African' strains, reflects probably the broader temperature range on the SFS. Summarizing, the hot temperature stress on the 'African' slope is a major environmental force driving the twin evolutionary processes of adaptation and speciation of B. simplex at 'Evolution Canyon'. Finally, we discuss the data in light of current controversies on species concepts.

Cryptic species as a window on diversity and conservation

The taxonomic challenge posed by cryptic species (two or more distinct species classified as a single species) has been recognized for nearly 300 years, but the advent of relatively inexpensive and rapid DNA sequencing has given biologists a new tool for detecting and differentiating morphologically similar species. Here, we synthesize the literature on cryptic and sibling species and discuss trends in their discovery. However, a lack of systematic studies leaves many questions open, such as whether cryptic species are more common in particular habitats, latitudes or taxonomic groups. The discovery of cryptic species is likely to be non-random with regard to taxon and biome and, hence, could have profound implications for evolutionary theory, biogeography and conservation planning.

Selection on knockdown performance in Drosophila melanogaster impacts thermotolerance and heat-shock response differently in females and males

We studied adaptive thermotolerance in replicate populations of Drosophila melanogaster artificially selected for high and low knockdown temperature (T(KD)), the upper temperature at which flies can no longer remain upright or locomote effectively. Responses to selection have generated High T(KD) populations capable of maintaining locomotor function at approximately 40 degrees C, and Low T(KD) populations with T(KD) of approximately 35 degrees C. We examined inducible knockdown thermotolerance, as well as inducible thermal survivorship, following a pretreatment heat-shock (known to induce heat-shock proteins) for males and females from the T(KD) selected lines. Both selection for knockdown and sex influenced inducible knockdown thermotolerance, whereas inducible thermal survivorship was influenced only by sex, and not by selection. Overall, our findings suggest that the relationships between basal and inducible thermotolerance are contingent upon the methods used to gauge thermotolerance, as well as the sex of the flies. Finally, we compared temporal profiles of the combined expression of two major heat-shock proteins, HSC70 and HSP70, during heat stress among the females and males from the selected T(KD) lines. The temporal profiles of the proteins differed between High and Low T(KD) females, suggesting divergence of the heat-shock response. We discuss a possible mechanism that may lead to the heat-shock protein patterns observed in the selected females.