Subobscura Populations Research Articles

Evolution and Plasticity of Gene Expression Under Progressive Warming in Drosophila subobscura.

Understanding the molecular mechanisms of thermal adaptation is crucial to predict the impacts of global warming. However, there is still a lack of research on the effects of rising temperatures over time and of studies involving different populations from the same species. The present study focuses on these two aspects, which are of great importance in understanding how organisms cope and adapt to ongoing changes in their environment. This study investigates the impact of global warming on the gene expression patterns of Drosophila subobscura populations from two different latitudinal locations after 23 generations of evolution. Our results indicate that evolutionary changes depend on the genetic background of the populations, with different starting points for thermal evolution, and that high-latitude populations show more pronounced evolutionary changes, with some evidence of convergence towards low-latitude populations. We found an interplay between plasticity and selection, with the high-latitude population showing fewer initial plastic genes and lower levels of adaptive plasticity, but a greater magnitude of change in both plastic and selective responses during evolution under warming conditions compared with its low-latitude counterpart. A substantial proportion of the transcriptome was observed to be evolving, despite the lack of observable response at higher-order phenotypic traits. The interplay between plasticity and selection may prove to be an essential component in shaping species' evolutionary responses to climate change. Furthermore, the value of conducting studies on multiple populations of the same species is emphasised, given the identification of differences between populations with different backgrounds in several contexts.

Heat-induced female biased sex ratio during development is not mitigated after prolonged thermal selection

BackgroundThe negative impacts of climate change on biodiversity are consistently increasing. Developmental stages are particularly sensitive in many ectotherms. Moreover, sex-specific differences in how organisms cope with thermal stress can produce biased sex ratios upon emergence, with potentially major impacts on population persistence. This is an issue that needs investigation, particularly testing whether thermal selection can alleviate sex ratio distortions in the long-term is a critical but neglected issue. Here, we report an experiment analyzing the sex ratio patterns at different developmental temperatures in Drosophila subobscura populations subjected to long-term experimental evolution (~ 30 generations) under a warming environment.ResultsWe show that exposure to high developmental temperatures consistently promotes sex ratio imbalance upon emergence, with a higher number of female than male offspring. Furthermore, we found that thermal selection resulting from evolution in a warming environment did not alleviate such sex ratio distortions generated by heat stress.ConclusionsWe demonstrate that heat stress during development can lead to clear sex ratio deviations upon emergence likely because of differential survival between sexes. In face of these findings, it is likely that sex ratio deviations of this sort occur in natural populations when facing environmental perturbation. The inability of many insects to avoid thermal shifts during their (more) sessile developmental stages makes this finding particularly troublesome for population subsistence in face of climate warming events.

Slow and population specific evolutionary response to a warming environment

Adaptation to increasingly warmer environments may be critical to avoid extinction. Whether and how these adaptive responses can arise is under debate. Though several studies have tackled evolutionary responses under different thermal selective regimes, very few have specifically addressed the underlying patterns of thermal adaptation under scenarios of progressive warming conditions. Also, considering how much past history affects such evolutionary response is critical. Here, we report a long-term experimental evolution study addressing the adaptive response of Drosophila subobscura populations with distinct biogeographical history to two thermal regimes. Our results showed clear differences between the historically differentiated populations, with adaptation to the warming conditions only evident in the low latitude populations. Furthermore, this adaptation was only detected after more than 30 generations of thermal evolution. Our findings show some evolutionary potential of Drosophila populations to respond to a warming environment, but the response was slow and population specific, emphasizing limitations to the ability of ectotherms to adapt to rapid thermal shifts.

Past history shapes evolution of reproductive success in a global warming scenario

Adaptive evolution is critical for animal populations to thrive in the fast-changing natural environments. Ectotherms are particularly vulnerable to global warming and, although their limited coping ability has been suggested, few real-time evolution experiments have directly accessed their evolutionary potential. Here, we report a long-term experimental evolution study addressing the evolution of Drosophila thermal reaction norms, after ∼30 generations under different dynamic thermal regimes: fluctuating (daily variation between 15 and 21 °C) or warming (daily fluctuation with increases in both thermal mean and variance across generations). We analyzed the evolutionary dynamics of Drosophila subobscura populations as a function of the thermally variable environments in which they evolved and their distinct background. Our results showed clear differences between the historically differentiated populations: high latitude D. subobscura populations responded to selection, improving their reproductive success at higher temperatures whereas their low latitude counterparts did not. This suggests population variation in the amount of genetic variation available for thermal adaptation, an aspect that needs to be considered to allow for better predictions of future climate change responses. Our results highlight the complex nature of thermal responses in face of environmental heterogeneity and emphasize the importance of considering inter-population variation in thermal evolution studies.

How phenotypic convergence arises in experimental evolution.

Evolutionary convergence is a core issue in the study of adaptive evolution, as well as a highly debated topic at present. Few studies have analyzed this issue using a "real-time" or evolutionary trajectory approach. Do populations that are initially differentiated converge to a similar adaptive state when experiencing a common novel environment? Drosophila subobscura populations founded from different locations and years showed initial differences and variation in evolutionary rates in several traits during short-term (∼20 generations) laboratory adaptation. Here, we extend that analysis to 40 more generations to analyze (1) how differences in evolutionary dynamics among populations change between shorter and longer time spans, and (2) whether evolutionary convergence occurs after 60 generations of evolution in a common environment. We found substantial variation in longer term evolutionary trajectories and differences between short- and longer term evolutionary dynamics. Although we observed pervasive patterns of convergence toward the character values of long-established populations, populations still remain differentiated for several traits at the final generations analyzed. This pattern might involve transient divergence, as we report in some cases, indicating that more generations should lead to final convergence. These findings highlight the importance of longer term studies for understanding convergent evolution.

Associations between environmental variability and inversion polymorphism of Drosophila subobscura: meta-analysis of populations from the Central Balkans

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 77:205-217 (2019) - DOI: https://doi.org/10.3354/cr01551 Associations between environmental variability and inversion polymorphism of Drosophila subobscura: meta-analysis of populations from the Central Balkans M. Stamenkovic-Radak1,*, B. Kenig2, M. Djurakic3, M. Jelic1, K. Eric1, M. Andjelkovic4 1Faculty of Biology, University of Belgrade, 11000 Belgrade, Republic of Serbia 2Institute of Biological Research ‘S. Stankovic’, University of Belgrade, 11000 Belgrade, Republic of Serbia 3Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad, 21000 Novi Sad, Republic of Serbia 4Serbian Academy of Sciences and Arts, 11000 Belgrade, Republic of Serbia *Corresponding author: marina@bio.bg.ac.rs ABSTRACT: Ecological and evolutionary factors, together with abiotic conditions, affect biogeographic patterns of genetic entities. The spatial and temporal variability of chromosomal inversions of Drosophila subobscura suggests that this species can serve as a good model for studying the effects of environmental change on the genetic structure of natural populations. A comprehensive meta-analysis of the association of environmental and climatic variables with inversion diversity patterns was performed on 20 D. subobscura populations from the central part of the Balkan Peninsula. Environmental data consisted of 3 sets of variables related to temperature and precipitation, extracted from 2 climatic databases, averaged over a 3 month period, and using biological instead of calendar dates of sampling. Arrangement frequency patterns are likely driven by a synergistic effect of factors related to temperature and precipitation. The frequencies of standard chromosomal arrangements tend to co-vary positively with precipitation, whereas parameters related to temperature appear to favor higher frequencies of the inverted and more complex chromosomal arrangements. A complex relationship among local environmental variables is evident from the results and reflects the probable effect of an altitudinal shift; the altitudinal gradient of inversions is different from their latitudinal gradient. The pattern of inversions is generally not associated with environmental variables, and a particular inversion cannot be a predictive genetic marker of global climate change. Populations in different habitats are subjected to habitat-specific selection regimes, while demographic factors and population history also affect the genetic variability pattern observed. KEY WORDS: Adaptation · Climate · Chromosomal polymorphism · Thermal response Full text in pdf format Supplement 1Supplement 2 PreviousNextCite this article as: Stamenkovic-Radak M, Kenig B, Djurakic M, Jelic M, Eric K, Andjelkovic M (2019) Associations between environmental variability and inversion polymorphism of Drosophila subobscura: meta-analysis of populations from the Central Balkans. Clim Res 77:205-217. https://doi.org/10.3354/cr01551 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 77, No. 3. Online publication date: March 28, 2019 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2019 Inter-Research.

Predictable phenotypic, but not karyotypic, evolution of populations with contrasting initial history

The relative impact of selection, chance and history will determine the predictability of evolution. There is a lack of empirical research on this subject, particularly in sexual organisms. Here we use experimental evolution to test the predictability of evolution. We analyse the real-time evolution of Drosophila subobscura populations derived from contrasting European latitudes placed in a novel laboratory environment. Each natural population was sampled twice within a three-year interval. We study evolutionary responses at both phenotypic (life-history, morphological and physiological traits) and karyotypic levels for around 30 generations of laboratory culture. Our results show (1) repeatable historical effects between years in the initial state, at both phenotypic and karyotypic levels; (2) predictable phenotypic evolution with general convergence except for body size; and (3) unpredictable karyotypic evolution. We conclude that the predictability of evolution is contingent on the trait and level of organization, highlighting the importance of studying multiple biological levels with respect to evolutionary patterns.

The ability to gain matings, not sperm competition, reduces the success of males carrying a selfish genetic element in a fly

Females are expected to avoid low-quality males fathering their offspring. X chromosome meiotic drive (XCMD) makes males very low-quality mates. XCMDs are X chromosomes that, in males, cause the failure of all Y chromosome sperm, so all functional sperm carry the driving X and produce daughters. This transmission advantage can allow the XCMD to spread through populations. However, XCMD males typically have low fertility, are very poor at sperm competition, only produce daughters, and bear low fitness alleles associated with XCMD. This imposes significant costs on females that mate with these males. Recently, several studies have shown that females can reduce the risk of their offspring inheriting XCMDs by mating with multiple males (polyandry), as XCMD males typically lose out to normal males in sperm competition. Hence it has been suggested that increased polyandry may be likely to evolve whenever a costly XCMD is common in a population, and that polyandry may be a key factor in preventing XCMDs spreading through populations. We tested this by examining the fruit fly Drosophila subobscura, in which females are known to mate only once in European populations where XCMDs are absent. However, in North African populations an XCMD, referred to as ‘SRs’, occurs. If the association between XCMDs and polyandry is true, then these North African populations should have evolved polyandry. However, we found no evidence of polyandry in North African D. subobscura populations. Instead, we found some evidence that males that carry SRs are slightly less successful at gaining matings in noncompetitive situations. These results show that polyandry does not necessarily evolve in response to the presence of harmful X chromosome drive. With both sperm competition and female choice both being unlikely to substantially reduce the success of XCMD in D. subobscura, the factors that prevent SRs spreading through these populations remain mysterious.

Keeping your options open: Maintenance of thermal plasticity during adaptation to a stable environment.

Phenotypic plasticity may allow species to cope with environmental variation. The study of thermal plasticity and its evolution helps understanding how populations respond to variation in temperature. In the context of climate change, it is essential to realize the impact of historical differences in the ability of populations to exhibit a plastic response to thermal variation and how it evolves during colonization of new environments. We have analyzed the real-time evolution of thermal reaction norms of adult and juvenile traits in Drosophila subobscura populations from three locations of Europe in the laboratory. These populations were kept at a constant temperature of 18ºC, and were periodically assayed at three experimental temperatures (13ºC, 18ºC, and 23ºC). We found initial differentiation between populations in thermal plasticity as well as evolutionary convergence in the shape of reaction norms for some adult traits, but not for any of the juvenile traits. Contrary to theoretical expectations, an overall better performance of high latitude populations across temperatures in early generations was observed. Our study shows that the evolution of thermal plasticity is trait specific, and that a new stable environment did not limit the ability of populations to cope with environmental challenges.

Effect of lead pollution on fitness and its dependence on heterozygosity in Drosophila subobscura.

Lead is one of the most present contaminants in the environment, and different species respond differently to this type of polution. If combined with genomic stress, lead may act synergistically, causing significant decrease of fitness components. We used two genetically diverse Drosophila subobscura populations (regarding both putatively adaptive inversion and microsatellite loci polymorphisms) originating from two ecologically distinct habitats. To establish different levels of genome heterozygosity, series of intraline, intrapopulation and interpopulation crosses were made. The progeny were reared on a standard medium and a medium with 200 μg/mL of lead acetate. Development time was significantly extended to all groups reared on lead. The progeny of intraline crosses showed significantly extended development time compared to all other groups. The obtained results suggest that genome heterozygosity reduces the effect of lead pollution.

Wing trait-inversion associations in Drosophila subobscura can be generalized within continents, but may change through time.

Clinal variation is one of the most emblematic examples of the action of natural selection at a wide geographical range. In Drosophila subobscura, parallel clines in body size and inversions, but not in wing shape, were found in Europe and South and North America. Previous work has shown that a bottleneck effect might be largely responsible for differences in wing trait-inversion association between one European and one South American population. One question still unaddressed is whether the associations found before are present across other populations of the European and South American clines. Another open question is whether evolutionary dynamics in a new environment can lead to relevant changes in wing traits-inversion association. To analyse geographical variation in these associations, we characterized three recently laboratory founded D. subobscura populations from both the European and South American latitudinal clines. To address temporal variation, we also characterized the association at a later generation in the European populations. We found that wing size and shape associations can be generalized across populations of the same continent, but may change through time for wing size. The observed temporal changes are probably due to changes in the genetic content of inversions, derived from adaptation to the new, laboratory environment. Finally, we show that it is not possible to predict clinal variation from intrapopulation associations. All in all this suggests that, at least in the present, wing traits-inversion associations are not responsible for the maintenance of the latitudinal clines in wing shape and size.

No trade-off between high and low temperature tolerance in a winter acclimatized Danish Drosophila subobscura population

Coping with cold winter conditions is a major challenge for many insects.In early spring we observed newly emerged Drosophila subobscura, which had overwintered as larvae and pupae. As temperatures increase during spring these flies are faced with higher minimum and maximum temperatures in their natural microhabitat. Thus, there is a potential costly mismatch between winter and early spring acclimatization and the increased ambient temperatures later in adult life.We obtained individuals from a natural Danish population of D. subobscura and acclimated them in the laboratory to 20°C for one generation, and compared critical thermal maximum (CTmax) and minimum (CTmin) to that of individuals collected directly from their natural microhabitat. The two populations (laboratory and field) were subsequently both held in the laboratory at 20°C and tested for their CTmax and CTmin every third day for 28days.At the first day of testing, field acclimatized D. subobscura had both higher heat and cold resistance compared to laboratory flies, and thereby a considerable larger thermal scope. Following transfer to the laboratory, cold and heat resistance of the field flies decreased over time relative to the laboratory flies. Despite the substantial decrease in thermal tolerances the thermal scope remained larger for field acclimatized individuals for the duration of the experiment.We conclude that flies acclimatized to their natural microhabitat had increased cold resistance, without a loss in heat tolerance. Thus while a negative correlation between cold and heat tolerance is typically observed in laboratory studies in Drosophila sp., this was not observed for field acclimatized D. subobscura in this study. We suggest that this is an adaptation to juvenile overwintering in temperate cold environments, where developmental (winter) temperatures can be much lower than temperatures experienced by reproducing adults after emergence (spring). The ability to gain cold tolerance through acclimatization without a parallel loss of heat tolerance affects thermal scope and suggests that high and low thermal tolerance act through mechanisms with different dynamics and reversibility.

Inbreeding and thermal adaptation inDrosophila subobscura

Using a well-adapted Drosophila subobscura population (Avala, Serbia), a drastic experiment of inbreeding was carried out to assess whether the expected level of homozygosity could be reached or if other evolutionary forces affected the process. In general, no significant changes of inversion (or arrangement) frequencies were detected after 12 brother-sister mating generations. Furthermore, no significant differences were obtained between observed and expected (under the inbreeding model) karyotypic frequencies. Thus, these results seemed to indicate that the main evolutionary factor in the experiment was inbreeding. However, in the G12 generation, complete chromosomal fixation was reached only in two out of the eight final inbred lines. In these lines, the chromosomal compositions were difficult to interpret, but they could be likely a consequence of adaptation to particular laboratory conditions (constant 18 °C, food, light period, etc.). Finally, in a second experiment, the inbred lines presented higher fertility at 18 °C than at 13 °C. Also, there was a significant line effect on fertility: inbred line number 6 (A1, J1, U1+2; U1+2+6, E8, and O3+4+7) presented the highest values, which maybe the result of an adaptation to laboratory conditions. Thus, the results obtained in our experiments reflect the adaptive potential of D. subobscura inversions.

Laboratory selection quickly erases historical differentiation.

The roles of history, chance and selection have long been debated in evolutionary biology. Though uniform selection is expected to lead to convergent evolution between populations, contrasting histories and chance events might prevent them from attaining the same adaptive state, rendering evolution somewhat unpredictable. The predictability of evolution has been supported by several studies documenting repeatable adaptive radiations and convergence in both nature and laboratory. However, other studies suggest divergence among populations adapting to the same environment. Despite the relevance of this issue, empirical data is lacking for real-time adaptation of sexual populations with deeply divergent histories and ample standing genetic variation across fitness-related traits. Here we analyse the real-time evolutionary dynamics of Drosophila subobscura populations, previously differentiated along the European cline, when colonizing a new common environment. By analysing several life-history, physiological and morphological traits, we show that populations quickly converge to the same adaptive state through different evolutionary paths. In contrast with other studies, all analysed traits fully converged regardless of their association with fitness. Selection was able to erase the signature of history in highly differentiated populations after just a short number of generations, leading to consistent patterns of convergent evolution.

O-chromosome lethal frequencies in Serbian and Montenegrin Drosophila subobscura populations

Lethal chromosomal frequencies were obtained from three Drosophila subobscura samples from the Mt. Avala (Serbia) population in September 2003 (0.218), June 2004 (0.204) and September 2004 (0.250). These values and those from other Balkan populations studied previously (Petnica, Kamariste, Zanjic and Djerdap) were used to analyze the possible effect of population, year, month and altitude above sea level on lethal chromosomal frequencies. According to ANOVAS no effect were observed. Furthermore, the lethal frequencies of the Balkan populations did not vary according to latitude. This is probably due to the relative proximity and high gene flow between these populations. From a joint study of all the Palearctic D. subobscura populations so far analyzed, it can be deduced that the Balkan populations are located in the central area of the species distribution. Finally, it seems that lethal chromosomal frequencies are a consequence of the genetic structure of the populations.

Does inbreeding affects developmental stability in Drosophila subobscura populations?

In the present paper, we focused on the coadaptive aspect of genetic variability at population level and its relation to genomic stress such as inbreeding. The paper evaluates the effects of an experimental reduction of average heterozygosity after fourteen generations of systematic inbreeding in laboratory conditions, on developmental stability in Drosophila subobscura populations from two ecologically and topologically distinct habitats, knowing that they possess a certain degree of genetic differences due to their different evolutionary histories. The aims were to analyze: (i) the variability change of wing size (length and width) among the inbred lines from both populations; (ii) the relations between homozigosity and level of fluctuating asymmetry as a potential measure of developmental instability, in inbred lines originating from two populations. Results for the wing size showed similar between line variability pattern across generations of systematic inbreeding in both populations. The obtained results suggest that variability of fluctuating asymmetry as a measure of developmental instability can not be related to homozygosity due to inbreeding per se, in both experimental populations.

Climate change and chromosomal inversions in Drosophila subobscura

In natural populations, the large changes in chromosomal structure occurring through chromosomal inversions show pronounced variations in frequency that often correspond to temporal and spatial climatic trends, which suggests that they may be employed to monitor the impact of global warming. Here we review and update the evidence on the association between chromosomal inversions and climate in D. subobscura, which provides one of the best studied models in this con- text. Chromosomal inversion frequencies of D. subobscura populations vary predictably with lati- tude, and this association has evolved independently in Europe and South and North America. They also exhibit clear seasonal trends that are consistent with temperature fluctuations. More importantly, latitudinal clines in chromosomal inversion frequencies seem to be responding to the global rise in mean temperatures in all continents. We analyze the relevance of these results in the light of climate change, and discuss how a better understanding of the mechanisms underlying these patterns may contribute to our knowledge on the impacts of global warming in biological systems.

Viabilities of Drosophila subobscura homo- and heterokaryotypes at optimal and stress temperatures. I. Analysis over several years

The interactions of lethal and non-lethal genes and their contributions to the viability of Drosophila inversion karyotypes are not well understood. This is especially true under variable environmental conditions. Here we examine the viability of natural chromosomal O-inversion homo- and heterokaryotypes in a D. subobscura population from Avala Mountain, Serbia. The observations we report were performed at a range of temperatures over several years. The heterotic effect of O-lethal heterozygotes on viability was found to be independent of the effects of inversion backgrounds and temperature. Positive epistatic interactions of lethal, mildly deleterious (subvital) and quasinormal (normal) genes were found in O-inversions in heterokaryotypes but not in homokaryotypes. These interactions were independent of temperature. This finding could explain the limitation of the genetic load in D. subobscura populations. In the population analyzed, annual fluctuations in the frequencies of certain chromosomal arrangements, karyotypes and non-lethal chromosomes under cold-stress temperatures seemed to indicate a correlation between these polymorphisms and environmental conditions. Our results indicate that there is a response in tolerance to extreme temperatures that may be due to natural selection. The differences in mean viability between some O-inversion karyotypic combinations indicate that there are differences in their tolerance to variable temperatures. All our results suggest that both frequency-dependent and supergene selection are mechanisms that protect O-chromosomal inversions. Chromosomal inversions may be genetically differentiated and coadapted complexes in D. subobscura populations.

Viabilities of Drosophila subobscura homo- and heterokaryotypes at optimal and stress temperatures. I. Analysis over several years

The interactions of lethal and non-lethal genes and their contributions to the viability of Drosophila inversion karyotypes are not well understood. This is especially true under variable environmental conditions. Here we examine the viability of natural chromosomal O-inversion homo- and heterokaryotypes in a D. subobscura population from Avala Mountain, Serbia. The observations we report were performed at a range of temperatures over several years. The heterotic effect of O-lethal heterozygotes on viability was found to be independent of the effects of inversion backgrounds and temperature. Positive epistatic interactions of lethal, mildly deleterious (subvital) and quasinormal (normal) genes were found in O-inversions in heterokaryotypes but not in homokaryotypes. These interactions were independent of temperature. This finding could explain the limitation of the genetic load in D. subobscura populations. In the population analyzed, annual fluctuations in the frequencies of certain chromosomal arrangements, karyotypes and non-lethal chromosomes under cold-stress temperatures seemed to indicate a correlation between these polymorphisms and environmental conditions. Our results indicate that there is a response in tolerance to extreme temperatures that may be due to natural selection. The differences in mean viability between some O-inversion karyotypic combinations indicate that there are differences in their tolerance to variable temperatures. All our results suggest that both frequency-dependent and supergene selection are mechanisms that protect O-chromosomal inversions. Chromosomal inversions may be genetically differentiated and coadapted complexes in D. subobscura populations.

Outbreeding causes developmental instability in Drosophila subobscura

A possible effect of interpopulation hybridization is either outbreeding depression, as a consequence of breakdown of coadapted gene complexes which can increase developmental instability (DI) of the traits, or increased heterozygosity, which can reduce DI. One of the principal methods commonly used to estimate DI is the variability of fluctuating asymmetry (FA). We analysed the effect of interpopulation hybridization in Drosophila subobscura through the variability in the wing size and the FA of wing length and width for both sexes in parental, F1 and F2 generations. The results of the wing size per se in intra- and interpopulation hybrids of D. subobscura do not explicitly reveal the significance of either of the two hypotheses. However, the results of the FA of the wing traits give a different insight. The FA of wing length and width generally increases in interpopulation crosses in F1 with respect to the FA in the parental generation, which suggests the possibility that outbreeding depression occurred in the first generation after the hybridization event. We generally observed that the FA values for the wing length and width of interpopulation hybrids were higher in F1 and F2 generations, compared to intrapopulation hybrids in same generations. These results suggest that the association between coadaptive genes with the same evolutionary history are the most probable mechanism that maintains the developmental homeostasis in Drosophila subobscura populations.