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Although males are generally less discriminating than females when it comes to choosing a mate, they still benefit from distinguishing between mates that are receptive to courtship and those that are not, in order to avoid wasting time and energy. It is known that males of Drosophila melanogaster are able to learn to associate olfactory and gustatory cues with female receptivity, but the role of more arbitrary, visual cues in mate choice learning has been overlooked to date in this species. We therefore carried out a series of experiments to determine: 1) whether males had a baseline preference for female eye color (red versus brown), 2) if males could learn to associate an eye color cue with female receptivity, and 3) whether this association disappeared when the males were unable to use this visual cue in the dark. We found that naïve males had no baseline preference for females of either eye color, but that males which were trained with sexually receptive females of a given eye color showed a preference for that color during a standard binary choice experiment. The learned cue was indeed likely to be truly visual, since the preference disappeared when the binary choice phase of the experiment was carried out in darkness.This is, to our knowledge 1) the first evidence that male D. melanogaster can use more arbitrary cues and 2) the first evidence that males use visual cues during mate choice learning. Our findings suggest that that D. melanogaster has untapped potential as a model system for mate choicelearning

Climate change poses a serious threat to the existence of many species. The combination of habitat fragmentation and increasing temperatures is of particular concern because it can alter demographic and population genetic processes, which may ultimately lead to extinction. Locomotion is very important in mitigating the negative impacts of these processes by upholding migration and contributing to random mating within and between populations. In the present study, a T-maze, constituting a relatively complex laboratory assay, is used to investigate whether inbreeding affects the capacity to reach a food source in male Drosophila melanogasterMeigen 1830 (Diptera: Drosophilidae) reared at 20, 25 or 30 degrees C, respectively. The effects of inbreeding and crossbreeding are highly temperature-specific. Strong heterosis for the ability to reach food in the maze is observed in flies developed and maintained at 30 degrees C, whereas inbred flies locate the food significantly faster than crossbreds when reared at 25 degrees C in four of six runs. No clear pattern is evident in flies reared at 20 degrees C. The results suggest that complex traits such as locomotor performance in a maze are highly informative in the evaluation and detection of inbreeding depression under different thermal conditions. The effect of inbreeding is most pronounced at high temperature, which is a characteristic of the conditions that many natural populations may have to face under climate change.

Behavioral traits can have great impact on an organism’s ability to cope with or avoidance of thermal stress, and are therefore of evolutionary importance for thermal adaptation. We compared the morphology, heat resistance, locomotor (walking and flying) activity and flight performance of three European populations of Musca domestica (Diptera: Muscidae) originating from different thermal conditions (Spain, Switzerland and Denmark) at benign and high temperatures. Spanish flies showed higher heat resistance compared to the Swiss and Danish populations. Similarly, at thehigh temperature (41.5°C) Spanish flies flew longest and Danish flies shortest. Swiss flies were the most active in terms of locomotor activity at the benign temperature (24°C), whereas the Spanish flies were able to stay active longer at the high temperature(43°C). Population differences in behavioral traits and heat resistance were obtained with flies held for several generations in a laboratory common garden setting, therefore we suggest that exposure to and avoidance of high temperatures under natural conditions has been an important selective agent causing the suggested adaptive differentiation between the populations.

Elucidating genes that affect life span or that can be used as biomarkers for ageing has received attention in diverse studies in recent years. Using model organisms and various approaches several genes have been linked to the longevity phenotype. For Drosophila melanogaster those studies have usually focussed on one sex and on flies originating from one genetic background, and results from different studies often do not overlap. Using D. melanogaster selected for increased longevity we aimed to find robust longevity related genes by examining gene expression in both sexes of flies originating from different genetic backgrounds. Further, we compared expression changes across three ages, when flies were young, middle aged or old, to examine how candidate gene expression changes with the onset of ageing. We selected 10 genes based on their expression differences in prior microarray studies. For about 50% of these we confirmed their potential as a candidate longevity gene. We found one robust candidate gene for longevity, CG32638. Three other genes, CG8934, mRpS10 and Spn43Ad, showed a tendency to be involved in life span determination in both backgrounds tested.

This investigation presents results from a genetic characterization of five Danish dog breeds genotyped on the CanineHD BeadChip microarray with 170K SNPs. The breeds investigated were 1) Danish Spitz (DS, n = 8), 2) Danish-Swedish farm Dog (DSF n = 18), 3) Broholmer (B, n = 22), 4) Old Danish Pointing Dog (ODP, n = 24), and 5) Greenland Dog (GD, n = 23). The aims of the investigation were to characterize the genetic profile of the abovementioned dog breeds by quantifying the genetic differentiation among them and the degree of genetic homogeneity within breeds. The genetic profile was determined by means of principal component analysis (PCA) and through a Bayesian clustering method. Both the PCA and the Bayesian clustering method revealed a clear genetic separation of the five breeds. The level of genetic variation within the breeds varied. The expected heterozygosity (HE) as well as the degree of polymorphism (P%) ranked the dog breeds in the order: DS > DSF > B > ODP > GD. Interestingly, the breed with a tenfold higher census population size compared to the other breeds, the Greenland Dog, had the lowest within-breed genetic variation, emphasizing that census size is a poor predictor of genetic variation. The observed differences in variation among and within dog breeds may be related to factors such as genetic drift, founder effects, genetic admixture and population bottlenecks. We further examined whether the observed genetic patterns in the five dog breeds can be used to design breeding strategies for the preservation of the genetic pool of these dog breeds.

Ecological relevance and repeatability of results obtained in different laboratories are key issues when assessing thermal tolerance of ectotherms. Traditionally, assays have used acute exposures to extreme temperatures. The outcomes of ecologically more relevant ramping experiments, however, are dependent on the rate of temperature change leading to uncertainty of the causal factor for loss of function. Here, we test the physiological consequences of exposing female Drosophila melanogaster to gradually increasing temperatures in so-called ramping assays. We exposed flies to ramping at rates of 0.06 and 0.1°C min(-1), respectively. Flies were sampled from the two treatments at 28, 30, 32, 34, 36 and 38°C and tested for heat tolerance and expression levels of the heat shock genes hsp23 and hsp70, as well as Hsp70 protein. Heat shock genes were upregulated more with a slow compared with a faster ramping rate, and heat knock-down tolerance was higher in flies exposed to the faster rate. The fact that slow ramping induces a stronger stress response (Hsp expression) compared with faster ramping suggests that slow ramping induces more heat damage at the cellular level due to longer exposure time. This is supported by the observation that fast ramped flies have higher heat knock-down tolerance. Thus we observed both accumulation of thermal damage at the molecular level and heat hardening at the phenotypic level as a consequence of heat exposure. The balance between these processes is dependent on ramping rate leading to the observed variation in thermal tolerance when using different rates.

Species distributions are often constrained by climatic tolerances that are ultimately determined by evolutionary history and/or adaptive capacity, but these factors have rarely been partitioned. Here, we experimentally determined two key climatic niche traits (desiccation and cold resistance) for 92–95 Drosophila species and assessed their importance for geographic distributions, while controlling for acclimation, phylogeny, and spatial autocorrelation. Employing an array of phylogenetic analyses, we documented moderate-to-strong phylogenetic signal in both desiccation and cold resistance. Desiccation and cold resistance were clearly linked to species distributions because significant associations between traits and climatic variables persisted even after controlling for phylogeny. We used different methods to untangle whether phylogenetic signal reflected phylogenetically related species adapted to similar environments or alternatively phylogenetic inertia. For desiccation resistance, weak phylogenetic inertia was detected; ancestral trait reconstruction, however, revealed a deep divergence that could be traced back to the genus level. Despite drosophilids’ high evolutionary potential related to short generation times and high population sizes, cold resistance was found to have a moderate-to-high level of phylogenetic inertia, suggesting that evolutionary responses are likely to be slow. Together these findings suggest species distributions are governed by evolutionarily conservative climate responses, with limited scope for rapid adaptive responses to future climate change

Laboratory experiments on Drosophila have often demonstrated increased heritability for morphological and life-history traits under environmental stress. We used parent-offspring comparisons to examine the impact of humidity levels on the heritability of a physiological trait, resistance to heat, measured as knockdown time at constant temperature. Drosophila melanogaster were reared under standard nonstressful conditions and heat-shocked as adults at extreme high or low humidity. Mean knockdown time was decreased in the stressful dry environment, but there was a significant sex-by-treatment interaction: at low humidity, females were more heat resistant than males, whereas at high humidity, the situation was reversed. Phenotypic variability of knockdown time was also lower in the dry environment. The magnitude of genetic correlation between the sexes at high humidity indicated genetic variation for sexual dimorphism in heat resistance. Heritability estimates based on one-parent-offspring regressions tended to be higher under desiccation stress, and this could be explained by decreased environmental variance of heat resistance at low humidity. There was no indication that the additive genetic variance and evolvability of heat resistance differed between the environments. The pattern of heritability estimates suggests that populations of D. melanogaster may have a greater potential for evolving higher thermal tolerance under arid conditions.

It has frequently been suggested that trait heritabilities are environmentally sensitive, and there are genetic trade-offs between tolerating different environments such as hot and cold or constant and fluctuating temperatures. Future climate predictions suggest an increase in both temperatures and their fluctuations. How species will respond to these changes is uncertain, particularly as there is a lack of studies which compare genetic performances in constant vs. fluctuating environments. In this study, we used a nested full-sib/half-sib breeding design to examine how the genetic variances and heritabilities of egg-to-adult viability differ at high and low temperatures with and without daily fluctuations in temperatures using Drosophila melanogaster as a model organism. Although egg-to-adult viability was clearly sensitive to developmental temperatures, heritabilities were not particularly sensitive to developmental temperatures. Moreover, we found that egg-to-adult viabilities at different developmental temperatures were positively correlated, suggesting a common genetic background for egg-to-adult viability at different temperatures. Finding both a uniform genetic background coupled with rather low heritabilities insensitive to temperatures, our results suggest evolutionary responses are unlikely to be limited by temperature effects on genetic parameters or negative genetic correlations, but by the direct effects of stressful temperatures on egg-to-adult viability accompanied with low heritabilities

A morphometric study was conducted on four skull traits of 37 male and 18 female adult East Greenland polar bears (Ursus maritimus) collected 1892-1968, and on 54 male and 44 female adult Barents Sea polar bears collected 1950-1969. The aim was to compare differences in size and shape of the bear skulls using a multivariate approach, characterizing the variation between the two populations using morphometric traits as an indicator of environmental and genetic differences. Mixture analysis testing for geographic differentiation within each population revealed three clusters for Barents Sea males and three clusters for Barents Sea females. East Greenland consisted of one female and one male cluster. A principal component analysis (PCA) conducted on the clusters defined by the mixture analysis, showed that East Greenland and Barents Sea polar bear populations overlapped to a large degree, especially with regards to females. Multivariate analyses of variance (MANOVA) showed no significant differences in morphometric means between the two populations, but differences were detected between clusters from each respective geographic locality. To estimate the importance of genetics and environment in the morphometric differences between the bears, a PCA was performed on the covariance matrix derived from the skull measurements. Skull trait size (PC1) explained approx. 80% of the morphometric variation, whereas shape (PC2) defined approx. 15%, indicating some genetic differentiation. Hence, both environmental and genetic factors seem to have contributed to the observed skull differences between the two populations. Overall, results indicate that many Barents Sea polar bears are morphometrically similar to the East Greenland ones, suggesting an exchange of individuals between the two populations. Furthermore, a subpopulation structure in the Barents Sea population was also indicated from the present analyses, which should be considered with regards to future management decisions.

Genetic prerequisites for the evolution of sexual dimorphism, sex-specific heritabilities and low or negative genetic correlations between homologous traits in males and females are rarely found. However, sexual dimorphism is evolving rapidly following environmental change, suggesting that sexual dimorphism and its genetic background could be environmentally sensitive. Yet few studies have explored the sensitivity of the genetic background of sexual dimorphism on environmental variation. In this study, on Drosophila melanogaster, we used a large nested full-sib–half-sib breeding design where families were split into four different developmental temperatures: two constant temperature treatments of 25 and 30oC and two cycling temperatures with means of 25 and 30oC, respectively. After emergence, we tested heat shock tolerance of adult flies. We found that sexual dimorphism was strongly affected by temperature during development. Moreover, we found that female heritability was significantly lower in flies developing at hot temperature and more so under hot and cycling temperatures. Interestingly, most of the genetic variation for heat shock tolerance was orthogonal (i.e. noncorrelated) between sexes, allowing independent evolution of heat shock tolerance in males and females. These findings give support to the hypothesis that the evolution of sexual dimorphism can be influenced by the environments experienced during development

Although locomotor activity is involved in almost all behavioral traits, there is a lack of knowledge on what factors affect it. This study examined the effects of sexratio and density on the circadian rhythm of locomotor activity of adult Musca domestica L. (Diptera: Muscidae) using an infrared light system. Sexratio significantly affected locomotor activity, increasing with the percentage of males in the vials. In accordance with other studies, males were more active than females, but the circadian rhythm of the two sexes was not constant over time and changed during the light period. There was also an effect of density on locomotor activity, where males at intermediate densities showed higher activity. Further, the predictability of the locomotor activity, estimated as the degree of autocorrelation of the activity data, increased with the number of males present in the vials both with and without the presence of females. Overall, this study demonstrates that locomotor activity in M. domestica is affected by sexratio and density. Furthermore, the predictability of locomotor activity is affected by both sexratio, density, and circadian rhythm. These results add to our understanding of the behavioral interactions between houseflies and highlight the importance of these factors when designing behavioral experiments using M. domestica.

A craniometric investigation using univariate and principal component analysis (PCA) was performed on 91 skull traits of 472 field voles, collected on nine islands and from the Jutland peninsula in Denmark in order to reveal possible geographical differences in skull shape and size. Because of missing values in the skulls due to various damages, only 186 individuals were measured for the dorsal side of the skull, 174 individuals for the ventral side and 154 individuals for the mandible. Of these traits, from the dorsal side of the skull 28 traits were measured, from the ventral side 33 traits and from the mandible 30 traits. With few exceptions, differences in skull shape were found between samples collected from the different islands, and also between samples from islands and samples from the Jutland peninsula. It is therefore suggested that field voles have a genetic differentiation between island and island and between island and mainland at the loci determining the shape of the skull. The field voles from some islands and the eastern part of the Jutland peninsula had the largest skulls compared with field voles from other islands and other parts of the Jutland peninsula. The origin of size differences is discussed and attributed to be due to several environmental factors as geographic variation in habitat quality but also as a consequence of the island syndrome.

1. Acclimation or hardening to one stress in arthropods can lead to a plastic response, which confers increased resistance to other stresses. Such cross-resistance may indicate shared physiologicalresistance mechanisms and a possibility of joint evolution for resistance traits.2. In this study, we tested for cross-resistance using Drosophila melanogaster as a model system.Adult females were assayed for resistance to cold, heat, desiccation and starvation following coldacclimation, heat hardening, desiccation hardening and starvation acclimation, resulting in 12 pretreatment-by-test combinations for estimating potential cross-resistance effects. Theacclimation ⁄ hardening regimes were chosen so that flies enhanced their resistance to the same type of stress as that used for the particular pretreatment.3. Two cases of cross-resistance were found, with desiccation-hardened and starvation-acclimated flies being more resistant than control ones in heat and desiccation resistance tests, respectively. In four cases, no acclimation ⁄ hardening effect was observed, and for six pretreatment-by-test combinations, the effect of acclimation ⁄ hardening was negative.4. We also revealed that heat and desiccation hardening as well as acclimation to starvation had a cost under non-stressful conditions leading to reduced longevity. Cold acclimation did not affect longevity, although its effect was difficult to estimate precisely: during pretreatment at a low temperature, biological ageing of the flies might be delayed.5. The pattern of acclimation ⁄ hardening responses considered in the context of literature data on stress resistance indicates that expression of heat-shock proteins is not likely to contribute tothe observed cross-resistance, but other probable general stress resistance mechanisms such as reduction of metabolic rate and accumulation of energy reserves might be involved.6. The lack of cross-resistance induced by acclimation ⁄ hardening treatments suggests that in an environment with multiple stresses, evolution of shared protective systems associated with plasticresponses may be constrained.

Background: Natural environments fluctuate and all organisms experience some degree of environmental variance. Global climate models predict increasing environmental variance in the future. Yet we do not fully understand how environmental variation affects performance traits. Questions: Does temperature fluctuation during development affect adult size and wing shape in Drosophila melanogaster? If so, are the effects predictable? Do they depend on heterozygosity? Do fluctuations in developmental temperature affect adult physiological performance at high temperature? Methods: We tested the effect of one fluctuating (21°C/29°C) and several constant (21°C, 23°C, 25°C, 27°C, 29°C) developmental temperature regimes on three wing morphometric traits (wing length, wing width, and wing shape) in an experiment using three inbred lines of D. melanogaster and their first-generation hybrids. We also tested the effect of fluctuating and constant developmental temperature on adult locomotor performance at several high and stressful test temperatures (32°C, 34°C, 36°C, 38°C, 40°C). Results: Performance mostly declined if the flies were reared under the fluctuating temperature regime versus the constant temperature regime with the same mean (25°C). Heterozygosity level also affected the traits investigated, with crossbreds usually having higher trait values. Crossbred genotypes compared across constant temperatures also showed greater plasticity in wing aspect. Conclusion: The widespread use of constant developmental temperatures in laboratory experiments may lead to overestimation of performance.