Many traits are phenotypically plastic, i.e. the same genotype expresses different phenotypes depending on the environment. Genotypes and individuals can vary in their response to the environment and this genetic (G × E) and individual (I × E) variation in reaction‐norm slopes can have important ecological or evolutionary consequences. Studies on I × E/G × E often fail to show slope variation, potentially due to the choice of the environmental covariate. Identifying the genuine environmental driver of phenotypic plasticity (the cue) is practically impossible and hence only proxies can be used. If the proxy is too weakly correlated with the cue, this may lead researchers to conclude there is little or no (variation in) plasticity, and hence lead to downwardly biased estimates of the potential for plastic responses (or evolutionary change in the slope) in response to environmental change. Alternatively, the environment‐specific mean phenotype (ESM) across individuals – which captures all environmental effects on the phenotype – as covariate should be less prone to such bias. We showed by simulation – after verifying the concept analytically – that using weakly correlated proxies indeed biased estimates of slope variation vis‐à‐vis the true cue downward but that ESM as a covariate held up well, even when multiple sources of I × E or an interaction between environments (I × E × E) existed in the data. Analysis of two real datasets revealed that estimated I × E and G × E, respectively, were more sizeable and precise when using ESM as opposed to reasonably informative environmental proxies. We argue that the ESM approach should be adopted by biologists as a yardstick in the study of (variation in) plasticity in the wild and that it may serve as a useful starting point for the search of better environmental proxies and unravelling complex I × E or G × E patterns.

Global warming has shifted phenological traits in many species, but whether species are able to track further increasing temperatures depends on the fitness consequences of additional shifts in phenological traits. To test this, we measured phenology and fitness of great tits (Parus major) with genotypes for extremely early and late egg lay dates, obtained from a genomic selection experiment. Females with early genotypes advanced lay dates relative to females with late genotypes, but not relative to nonselected females. Females with early and late genotypes did not differ in the number of fledglings produced, in line with the weak effect of lay date on the number of fledglings produced by nonselected females in the years of the experiment. Our study is the first application of genomic selection in the wild and led to an asymmetric phenotypic response that indicates the presence of constraints toward early, but not late, lay dates.

Im FRANZ-Projekt werden seit 2017 in ausgewählten Betrieben der intensiv genutzten Agrarlandschaft naturschutzfachlich und wirtschaftlich tragfähige Maßnahmen zur Förderung der biologischen Vielfalt erprobt. Auf den Betrieben bei Lüneburg und im Havelland wurden dazu im Jahr 2020 und 2021 Laufkäfer mit Bodenfallen auf intensiv genutzten Kulturen wie Gerste oder Roggen und auf umgesetzten Maßnahmen, wie der Anlage von Blühflächen und Insektenwällen, erfasst. Dabei gelangen die Nachweise neun faunistisch bemerkenswerter Arten für die Region Niederelbegebiet und Brandenburg.

Background Many birds species range over vast geographic regions and migrate seasonally between their breeding and overwintering sites. Deciding when to depart for migration is one of the most consequential life-history decisions an individual may make. However, it is still not fully understood which environmental cues are used to time the onset of migration and to what extent their relative importance differs across a range of migratory strategies. We focus on departure decisions of a songbird, the Eurasian blackbird Turdus merula , in which selected Russian and Polish populations are full migrants which travel relatively long-distances, whereas Finnish and German populations exhibit partial migration with shorter migration distances. Methods We used telemetry data from the four populations (610 individuals) to determine which environmental cues individuals from each population use to initiate their autumn migration. Results When departing, individuals in all populations selected nights with high atmospheric pressure and minimal cloud cover. Fully migratory populations departed earlier in autumn, at longer day length, at higher ambient temperatures, and during nights with higher relative atmospheric pressure and more supportive winds than partial migrants; however, they did not depart in higher synchrony. Thus, while all studied populations used the same environmental cues, they used population-specific and locally tuned thresholds to determine the day of departure. Conclusions Our data support the idea that migratory timing is controlled by general, species-wide mechanisms, but fine-tuned thresholds in response to local conditions.

Climate change has led to phenological shifts in many species, but with large variation in magnitude among species and trophic levels. The poster child example of the resulting phenological mismatches between the phenology of predators and their prey is the great tit ( Parus major ), where this mismatch led to directional selection for earlier seasonal breeding. Natural climate variability can obscure the impacts of climate change over certain periods, weakening phenological mismatching and selection. Here, we show that selection on seasonal timing indeed weakened significantly over the past two decades as increases in late spring temperatures have slowed down. Consequently, there has been no further advancement in the date of peak caterpillar food abundance, while great tit phenology has continued to advance, thereby weakening the phenological mismatch. We thus show that the relationships between temperature, phenologies of prey and predator, and selection on predator phenology are robust, also in times of a slowdown of warming. Using projected temperatures from a large ensemble of climate simulations that take natural climate variability into account, we show that prey phenology is again projected to advance faster than great tit phenology in the coming decades, and therefore that long-term global warming will intensify phenological mismatches.

In migratory species, the timing of arrival at the breeding grounds is a life-history trait with major fitness consequences. The optimal arrival date varies from year-to-year, and animals use cues to adjust their arrival dates to match this annual variation. However, which cues they use to time their arrival and whether these cues actually predict the annual optimal arrival date is largely unknown. Here, we integrate causal and evolutionary analysis by identifying the environmental variables used by a migratory songbird to time its arrival dates and testing whether these environmental variables also predicted the optimal time to arrive. We used 11 years of male arrival data of a pied flycatcher population. Specifically, we tested whether temperature and normalized difference vegetation index (NDVI) values from their breeding grounds in the Netherlands and from their wintering grounds in Ivory Coast explained the variation in arrival date, and whether these variables correlated with the position of the annual fitness peak at the breeding grounds. We found that temperature and NDVI, both from the wintering and the breeding grounds, explained the annual variation in arrival date, but did not correlate with the optimal arrival date. We explore three alternative explanations for this lack of correlation. Firstly, the date of the fitness peak may have been incorrectly estimated because a potentially important component of fitness (i.e., migration date dependent mortality en route or directly upon arrival) could not be measured. Secondly, we focused on male timing but the fitness landscape is also likely to be shaped by female timing. Finally, the correlation has recently disappeared because climate change disrupted the predictive value of the cues that the birds use to time their migration. In the latter case, birds may adapt by altering their sensitivity to temperature and NDVI.

The IPCC (Intergovernmental Panel on Climate Change) “Special Report on Global Warming of 1.5°C” presented the ambitious target of needing to achieve zero net emissions by 2050 in order to meet the goals of the Paris Agreement (IPCC, 2018). This report led some governments and jurisdictions to declare a climate emergency (Climate Emergency Declaration, 2019) and prompted the rise of movements of activism and civil disobedience such as the School Strike for the Climate and Extinction Rebellion. The reach of these civil actions extends beyond those directly involved, potentially increasing wider public awareness of climate change. Here, we examine trends in indicators of this wider public awareness and engagement and compare these with major global movements of civil disobedience focussed on climate, the release of substantive climate reports, and global governmental gatherings on climate change. We show that these global movements may be increasing public awareness of, and stimulating public engagement with, issues of climate change. It is not easy to accurately measure public awareness and engagement with the issue of climate change at a global scale. We use two sources of information as indicators of that engagement. First, we used data on the scaled relative frequency of pertinent terms in Google searches ("global warming," "climate change," "climate action," "climate emergency," "climate crisis," downloaded from Google Trends on October 31, 2019, https://www.google.com/trends). Second, we used data on mentions of the terms "climate change" and "global warming" by the global media, assembled by the Media and Climate Change Observatory, MeCCO (Boykoff et al., 2019, downloaded on December 4, 2019). These sources provide monthly data on the attention paid to climate change by anyone searching the internet (from the Google data), and by the newspapers, radio, and television (from the MeCCO data). We focus on 2017 onwards; a period that includes the recent rise in activism and civil disobedience associated with climate change. Although there exists substantial month-to-month variation, both data sources show an overall increase in public engagement with climate change, especially after mid-2018 (Figure 1). The Google search data also suggest an interesting evolution of the language of climate change. While the relative popularity of the search term "global warming" has shown little systematic change, public interest in “climate action” has increased greatly since 2018. In addition, "climate crisis" and "climate emergency" have become popular search terms since early 2019. Peaks in internet searches for these specific terms coincide with the first and second global school strikes, and New York Climate Week (Figure 1a). Searches for “climate emergency” and “climate crisis” were rare before 2019, but the use of these search terms increased 20-fold during that year. Furthermore, these last two terms have become four- to fivefold more common than searches for “global warming” and may be displacing the latter as a common standard for public discourse (Figure 1a). Newspaper, radio, and television reports on climate change have also increased over this time, doubling since mid-2018 (Figure 1b). Of course, with this brief analysis (Figure 1), we show only correlations. Nevertheless, the data suggest that global movements of civil disobedience focussed on climate change, as well as traditional scientific reports, may play an important role in increasing public awareness and engagement with issues of climate change. Peaks in this traditional media coverage often reflected the release of scientific reports, such as the “Global Warming of 1.5°C” from the IPCC, and social actions related to climate issues (i.e., School Strike for the Climate and Climate Week; Figure 1b). Interestingly, much of the civil action since 2018 has been led by students at school or at university. These groups have been educated about climate change, have an understanding of the science, and see a need for immediate action (BBC, 2019). A recent report by Amnesty International (2019), on a survey of 10,000 18–25 year olds across 22 countries, reported that 41% of respondents found climate change to be the most important human rights issue facing the world. A related environmental issue, regional air pollution, was this age group's second most important global concern. Of course, these activists and respondents represent the generation who will be affected most by failure to achieve net zero emissions by 2050, though there is no doubt wider interest and concern that transcends generations and educational backgrounds (Head, 2016). To address the significant challenges facing society, we need the very best science, teachers and communicators capable of translating that science to motivate and inspire wider audiences, and active engagement of the science community with the public and policy makers. While activism contributes to transformations in society, science is needed to define the nature of the problems we face and point the way to the actions that need to be taken to address them. Science must remain objective and free from preconceived notions of right and wrong; it cannot achieve societal transformations alone (Head, 2016). Science without activism is powerless to enact change, but activism without science will enact change without knowledge of the direction in which change is needed. To make constructive progress, both science and activism are needed to move society in the right direction with strength and purpose. The IPCC has made major contributions to gathering the scientific evidence to inspire and inform societal change since 1990 and, this year, Global Change Biology celebrates its 25th year of publishing the best science regarding the effects of climate change on all aspects of the biosphere. We thank Olivia Pearman for help in accessing the MeCCO data set and Paulette Burns for technical assistance.

Phenotypic plasticity is an important mechanism by which an individual can adapt its seasonal timing to predictable, short-term environmental changes by using predictive cues. Identification of these cues is crucial to forecast species' response to long-term environmental change and to study their potential to adapt. Individual great tits (Parus major) start reproduction early under warmer conditions in the wild, but whether this effect is causal is not well known. We housed 36 pairs in climate-controlled aviaries and 40 pairs in outdoor aviaries, where they bred under artificial contrasting temperature treatments or in semi-natural conditions, respectively, for two consecutive years, using great tits from lines selected for early and late egg laying. We thus obtained laying dates in two different thermal environments for each female. Females bred earlier under warmer conditions in climate-controlled aviaries, but not in outdoor aviaries. The latter was inconsistent with laying dates from our wild population. Further, early selection line females initiated egg laying consistently ∼9 days earlier compared to late selection line females in outdoor aviaries, but we found no difference in the degree of plasticity (i.e. the sensitivity to temperature) in laying date between selection lines. Because we find that temperature causally affects laying date, climate change will lead to earlier laying. This advancement is however unlikely to be sufficient, thereby leading to selection for earlier laying. Our results suggest that natural selection may lead to a change in mean phenotype, but not to a change in the sensitivity of laying dates to temperature.

Assessing the genetic adaptive potential of populations and species is essential for better understanding evolutionary processes. However, the expression of genetic variation may depend on environmental conditions, which may speed up or slow down evolutionary responses. Thus, the same selection pressure may lead to different responses. Against this background, we here investigate the effects of thermal stress on genetic variation, mainly under controlled laboratory conditions. We estimated additive genetic variance ( V A ), narrow-sense heritability ( h 2 ) and the coefficient of genetic variation ( CV A ) under both benign control and stressful thermal conditions. We included six species spanning a diverse range of plant and animal taxa, and a total of 25 morphological and life-history traits. Our results show that (1) thermal stress reduced fitness components, (2) the majority of traits showed significant genetic variation and that (3) thermal stress affected the expression of genetic variation ( V A , h 2 or CV A ) in only one-third of the cases (25 of 75 analyses, mostly in one clonal species). Moreover, the effects were highly species-specific, with genetic variation increasing in 11 and decreasing in 14 cases under stress. Our results hence indicate that thermal stress does not generally affect the expression of genetic variation under laboratory conditions but, nevertheless, increases or decreases genetic variation in specific cases. Consequently, predicting the rate of genetic adaptation might not be generally complicated by environmental variation, but requires a careful case-by-case consideration.

Changing environmental conditions will inevitably alter selection pressures. Over the long term, populations have to adapt to these altered conditions by evolutionary change to avoid extinction. Quantifying the 'evolutionary potential' of populations to predict whether they will be able to adapt fast enough to forecasted changes is crucial to fully assess the threat for biodiversity posed by climate change. Technological advances in sequencing and high-throughput genotyping have now made genomic studies possible in a wide range of species. Such studies, in theory, allow an unprecedented understanding of the genomics of ecologically relevant traits and thereby a detailed assessment of the population's evolutionary potential. Aimed at a wider audience than only evolutionary geneticists, this paper gives an overview of how gene-mapping studies have contributed to our understanding and prediction of evolutionary adaptations to climate change, identifies potential reasons why their contribution to understanding adaptation to climate change may remain limited, and highlights approaches to study and predict climate change adaptation that may be more promising, at least in the medium term.

The physiological mechanisms underlying avian seasonal timing of reproduction, a life-history trait with major fitness consequences, are not well understood. Comparing individuals that have been selected to differ in their timing of breeding may prove to be a promising in studying these mechanisms, making selection lines a valuable tool. We created selection lines for early and late timing of breeding in great tits (Parus major) using genomic selection, that is selection based on multi-marker genotypes rather than on the phenotype. We took in nestlings (F(1 )generation) from wild broods of which the mother was either an extremely early ("early line") or extremely late ("late line") breeder. These chicks were then genotyped and, based on their "genomic breeding values" (GEBVs), we selected individuals for early and late line breeding pairs to produce the F(2 )generation in captivity. The F(2 )offspring was hand-reared, genotyped and selected to produce an F(3 )generation, which were then again genotyped and selected. This way we obtained laying dates in aviaries for F-1, F-2 and F(3 )birds. We studied the genetic response to the artificial selection and found increased genetic differentiation between the early and late reproducing selection lines over generations (F-1-F-3), indicated by both diverging GEBVs and increased fixation indices (F-ST). We studied the phenotypic response to selection for birds breeding in outdoor breeding aviaries. We found that early line birds laid earlier than late line birds, and this difference increased over the generations (F-1-F-3), with non-significant line effects for the F-1 and F-2, but highly significant line differences for the F-3. We also assessed whether there was correlated selection on two traits that are potentially part of the mechanisms underlying seasonal timing: the endogenous free-running period of the day/night clock (tau) and basal metabolic rate, but found no correlated selection. We have successfully created selection lines on seasonal timing in a wild bird species and obtained an instrument for future studies to investigate the physiological mechanisms underlying timing of breeding, and the genetic variation in these mechanisms, an essential component for evolutionary change in timing of reproduction. A free Plain Language Summary can be found within the Supporting Information of this article.

Climate change has often led to unequal shifts in the seasonal timing (phenology) of interacting species, such as consumers and their resource, leading to phenological 'mismatches'. Mismatches occur when the time at which a consumer species's demands for a resource are high does not match with the period when this resource is abundant. Here, we review the evolutionary and population-level consequences of such mismatches and how these depend on other ecological factors, such as additional drivers of selection and density-dependent recruitment. This review puts the research on phenological mismatches into a conceptual framework, applies this framework beyond consumer-resource interactions and illustrates this framework using examples drawn from the vast body of literature on mismatches. Finally, we point out priority questions for research on this key impact of climate change.

The timing of breeding is under selection in wild populations as a result of climate change, and understanding the underlying physiological processes mediating this timing provides insight into the potential rate of adaptation. Current knowledge on this variation in physiology is, however, mostly limited to males. We assessed whether individual differences in the timing of breeding in females are reflected in differences in candidate gene expression and, if so, whether these differences occur in the upstream (hypothalamus) or downstream (ovary and liver) parts of the neuroendocrine system. We used 72 female great tits from two generations of lines artificially selected for early and late egg laying, which were housed in climate-controlled aviaries and went through two breeding cycles within 1 year. In the first breeding season we obtained individual egg-laying dates, while in the second breeding season, using the same individuals, we sampled several tissues at three time points based on the timing of the first breeding attempt. For each tissue, mRNA expression levels were measured using qPCR for a set of candidate genes associated with the timing of reproduction and subsequently analysed for differences between generations, time points and individual timing of breeding. We found differences in gene expression between generations in all tissues, with the most pronounced differences in the hypothalamus. Differences between time points, and early- and late-laying females, were found exclusively in the ovary and liver. Altogether, we show that fine-tuning of the seasonal timing of breeding, and thereby the opportunity for adaptation in the neuroendocrine system, is regulated mostly downstream in the neuro-endocrine system.

Abstract Global climate change has sparked a vast research effort into the demographic and evolutionary consequences of mismatches between consumer and resource phenology. Many studies have used the difference in peak dates to quantify phenological synchrony (match in dates, MD), but this approach has been suggested to be inconclusive, since it does not incorporate the temporal overlap between the phenological distributions (match in overlap, MO). We used 24 years of detailed data on the phenology of a predator–prey system, the great tit (Parus major) and the main food for its nestlings, caterpillars, to estimate MD and MO at the population and brood levels. We compared the performance of both metrics on two key demographic parameters: offspring recruitment probability and selection on the timing of reproduction. Although MD and MO correlated quadratically as expected, MD was a better predictor for both offspring recruitment and selection on timing than MO. We argue—and verify through simulations—that this is because quantifying MO has to be based on nontrivial, difficult‐to‐verify assumptions that likely render MO too inaccurate as a proxy for food availability in practice. Our results have important implications for the allocation of research efforts in long‐term population studies in highly seasonal environments.

Background Seasonal timing of breeding is a life history trait with major fitness consequences but the genetic basis of the physiological mechanism underlying it, and how gene expression is affected by date and temperature, is not well known. In order to study this, we measured patterns of gene expression over different time points in three different tissues of the hypothalamic-pituitary-gonadal-liver axis, and investigated specifically how temperature affects this axis during breeding. We studied female great tits ( Parus major ) from lines artificially selected for early and late timing of breeding that were housed in two contrasting temperature environments in climate-controlled aviaries. We collected hypothalamus, liver and ovary samples at three different time points (before and after onset of egg-laying). For each tissue, we sequenced whole transcriptomes of 12 pools ( n = 3 females) to analyse gene expression. Results Birds from the selection lines differed in expression especially for one gene with clear reproductive functions, zona pellucida glycoprotein 4 ( ZP4 ), which has also been shown to be under selection in these lines. Genes were differentially expressed at different time points in all tissues and most of the differentially expressed genes between the two temperature treatments were found in the liver. We identified a set of hub genes from all the tissues which showed high association to hormonal functions, suggesting that they have a core function in timing of breeding. We also found ample differentially expressed genes with largely unknown functions in birds. Conclusions We found differentially expressed genes associated with selection line and temperature treatment. Interestingly, the latter mainly in the liver suggesting that temperature effects on egg-laying date may happen down-stream in the physiological pathway. These findings, as well as our datasets, will further the knowledge of the mechanisms of tissue-specific avian seasonality in the future.

Artificial selection experiments are a powerful tool in evolutionary biology. Selecting individuals based on multimarker genotypes (genomic selection) has several advantages over phenotype-based selection but has, so far, seen very limited use outside animal and plant breeding. Genomic selection depends on the markers tagging the causal loci that underlie the selected trait. Because the number of necessary markers depends, among other factors, on effective population size, genomic selection may be in practice not feasible in wild populations as most wild populations have much higher effective population sizes than domesticated populations. However, the current possibilities of cost-effective high-throughput genotyping could overcome this limitation and thereby make it possible to apply genomic selection also in wild populations. Using a unique dataset of about 2000 wild great tits (Parus major), a small passerine bird, genotyped on a 650 k SNP chip we calculated genomic breeding values for egg-laying date using the so-called GBLUP approach. In this approach, the pedigree-based relatedness matrix of an "animal model," a special form of the mixed model, is replaced by a marker-based relatedness matrix. Using the marker-based relatedness matrix, the model seemed better able to disentangle genetic and permanent environmental effects. We calculated the accuracy of genomic breeding values by correlating them to the phenotypes of individuals whose phenotypes were excluded from the analysis when estimating the genomic breeding values. The obtained accuracy was about 0.20, with very little effect of the used genomic relatedness estimator but a strong effect of the number of SNPs. The obtained accuracy is lower than typically seen in domesticated species but considerable for a trait with low heritability (∼0.2) as avian breeding time. Our results show that genomic selection is possible also in wild populations with potentially many applications, which we discuss here.

Long-term field studies coupled with quantitative genomics offer a powerful means to understand the genetic bases underlying quantitative traits and their evolutionary changes. However, analyzing and interpreting the time scales at which adaptive evolution occurs is challenging. First, while evolution is predictable in the short term, with strikingly rapid phenotypic changes in data series, it remains unpredictable in the long term. Second, while the temporal dynamics of some loci with large effects on phenotypic variation and fitness have been characterized, this task can be complicated in cases of highly polygenic trait architecture implicating numerous small effect size loci, or when statistical tests are sensitive to the heterogeneity of some key characteristics of the genome, like variation in recombination rate along the chromosomes. After introducing these aforementioned challenges, we discuss a recent investigation of the genomic architecture and spatio-temporal variation in great tit bill length, which was related to the recent use of bird feeders. We discuss how this case study illustrates the importance of considering different temporal scales and evolutionary mechanisms both while analyzing trait temporal trends and when searching for and interpreting the signals of putative genomic footprints of selection. More generally this commentary discusses interesting challenges for unraveling the time scale at which adaptive traits evolve and their genomic bases.